Patent Application
20240277396
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It is estimated that one out of eight women will face breast cancer at some point during their lifetime, and for women age 40-55, breast cancer is the leading cause of death. While methods for detecting and treating breast cancer initially were crude and unsophisticated, advanced instrumentation and procedures now are available which provide more positive outcomes for patients.
In the 1800s the only treatment for breast cancer was removal of the entire breast. Given that the sole method of detection and diagnosis was palpation, treatment was only directed when the breast tumor was well advanced. Modified radical mastectomies are still performed today for patients with invasive cancer, such a procedure involving the removal of the entire breast and some or all of the axillary lymph nodes. Radical or modified radical mastectomies involve serious trauma for the patient during surgery, with the severest cosmetic results after surgery.
Another surgical option upon the discovery of malignant tumor is what is referred to as breast conserving surgery, which also is referred to as lumpectomy, tumorectomy, segmental mastectomy or local excision. Meant to address the cosmetic concerns associated with removal of the breast, only the primary tumor and a margin of surrounding normal breast tissue is removed. Determining the proper amount of tissue to be removed involves balancing the need to take sufficient tissue to prevent recurrence with the desire to take as little tissue as possible to preserve the best cosmetic appearance. A more limited nodal dissection now is performed with the primary purpose being staging rather than therapy. While an improvement over radical mastectomy, breast-conserving surgery still involves the removal of large sections of breast tissue. Risks associated with such surgery include wound infection, seroma formation, mild shoulder dysfunction, loss of sensation in the distribution of the intercostobrachial nerve, and edema of the breast and arm. For more information on invasive tumor therapy, see:
Mastectomies and breast-conserving surgeries generally are procedures utilized for invasive tumors. Advances in tumor detection, however, have radically changed the course of diagnosis and treatment for a tumor. With the advent of imaging devices, such as the mammogram, a suspect tumor may be located when it is of relatively small size. Today, tumor detection generally involves both a mammogram and a physical examination, which takes into account a number of risk factors including family history and prior occurrences. Technical improvements in mammogram imaging include better visualization of the breast parenchyma with less exposure to radiation, improvements in film quality and processing, improved techniques for imaging, better guidelines for the diagnosis of cancer and greater availability of well-trained mammographers. With these advances in imaging technology, a suspect tumor may be detected which is 5 mm or smaller. More recently substantial progress has been witnessed in the technical disciplines of magnetic resonance imaging (MRI) and ultrasound imagining. With these advances, the location of a lesion is observable as diagnostic or therapeutic procedures are carried out.
In the past, because a tumor normally was not discovered until it had reached an advanced stage, the issue of whether a tumor was malignant or benign did not need to be addressed. With the ability to locate smaller areas of suspect tumor, this issue becomes of critical importance, particularly in light of the fact that only 20% of small, non-invasive tumors are malignant. Tumors identified as being benign may be left in situ with no excision required, whereas action must be taken to excise suspect tissue confirmed to be malignant. In view of the value of classifying a tumor as malignant or benign, breast biopsy has become a much-utilized technique with over 1 million biopsies being performed annually in the United States. A biopsy procedure involves the two-step process of first locating the tumor then removing part or all of the suspect tissue for examination to establish precise diagnosis.
Improvements in the detection of suspicious lesions in the breast are described in U.S. Patent Publication No. US 2006/0036173 published Feb. 16, 2006. In this patent application ultrasonic scanning and diagnostics for cellular tissue are disclosed. An ultrasonic tissue incision and retrieval assembly is moved across cellular tissue at a rate that is synchronized with the image capture rate of the ultrasonic scanner, to achieve a contiguous and complete set of scan images of the tissue. The tissue incision and retrieval assembly can be held in a single position as it is moved across the tissue, or it can be dynamically adjusted during the scan to provide optimal contact with the scanned tissue. The image data are captured and converted to a format that is easily stored and compatible with a viewer. The viewer allows playback of the scanned images in a manner that is optimized for screening for cancers and other anomalies. A location function allows the user to select a point of interest on an individual scan image, and choose another known reference point, and the function calculates and provides the distance from the reference point to the point of interest in three dimensions. The system can be used for virtually any tissue, but can also be optimized for breast cancer screening. Clinical studies using the method and apparatus described in this patent application have revealed that suspicious and potentially malignant lesions in the human breast can be detected having maximum dimensional extents as small as 2 to 3 mm. This non-invasive diagnostic imaging capability would enable the complete excision of such small lesions surrounded by healthy margins of tissue in volumes as small as 10 to 15 mm in diameter using minimally invasive excisional methods.
One biopsy option available upon detection of a suspected tumor is an open surgical biopsy or excisional biopsy. Prior to surgery, a radiologist, using mammography, inserts a wire into the breast to locate the suspected tumor site. Later during surgery, the surgeon makes an incision in the breast and removes a large section of breast tissue, including the suspect tissue and a margin of healthy tissue surrounding the tumor. As with other similar procedures, such as those described above, open surgery may result in high levels of blood loss, scarring at the location of the incision and permanent disfigurement, due to the removal of relatively large amounts of tissue. Because of the critical prognostic significance of tumor size, the greatest advantage of the excisional biopsy is that the entire area of the suspect tumor is removed. After being removed and measured, the specimen is typically transected by a pathologist in a plane that should bisect a suspected tumor and then the margin between tumor and healthy tissue is examined. Microscopic location of carcinoma near the margin provides information for future prognosis. Thus, the pathology laboratory is oriented to the morphological aspect of analysis, i.e. the forms and structures of involved tissue. For information on pathology of breast biopsy tissue, see:
Other less invasive options are available which avoid the disadvantages associated with open surgery. One such non-invasive option is that of needle biopsy, which may be either fine needle aspiration or large core. Fine needle aspiration (FNA) is an office procedure in which a fine needle, for example of 21 to 23 gauge, having one of a number of tip configurations, such as the Chiba, Franzeen or Turner, is inserted into the breast and guided to the tumor site by mammography or stereotactic imaging. A vacuum is created and the needle moved up and down along the tumor to assure that it collects targeted cellular material. Generally, three or more passes will be made to assure the collection of a sufficient sample. The needle and the tissue sample are then withdrawn from the breast.
The resulting specimen is subject to a cytological assay, as opposed to the above-noted morphological approach. In this regard, cell structure and related aspects are studied. The resultant analysis has been used to improve or customize the selection of chemotherapeutic agents with respect to a particular patient. While a fine needle aspiration biopsy has the advantages of being a relatively simple and inexpensive office procedure, there are some drawbacks associated with its use. With fine needle aspiration, there is a risk of false-negative results, which most often occurs in cases involving extremely fibrotic tumor. In addition, after the procedure has been performed there may be insufficient specimen material for diagnosis. Finally, with fine needle aspiration alone the entire area of suspect tissue is not removed. Rather, fragmented portions of tissue are withdrawn which do not allow for the same type of pathological investigation as the tissue removed during an open surgery biopsy.
This last limitation also is observed with respect to large core needle biopsies. For a large core needle biopsy, a 14 to 18-gauge needle is inserted in the breast having an inner trocar with a sample notch at the distal end and an outer cutting cannula. Similar to a fine needle aspiration, tissue is drawn through the needle by vacuum suction. These needles have been combined with biopsy guns to provide automated insertion that makes the procedure shorter and partially eliminates location mistakes caused by human error. Once inserted, multiple contiguous tissue samples may be taken.
Samples taken during large core needle biopsies may be anywhere from friable and fragmented to large pieces 20 to 30 mm long. These samples may provide some histological data, unlike fine needle aspiration samples; however, they still do not provide the pathological information available with an open surgical biopsy specimen. Further, as with any mechanical cutting device, excessive bleeding may result during and following the procedure. Needle biopsy procedures are discussed in:
A device which is somewhere between a needle biopsy and open surgery is referred to as the Advanced Breast Biopsy Instrumentation (ABBI). With the ABBI procedure, the practitioner, guided by stereotactic imaging, removes a core tissue sample of 5 mm to 20 mm in diameter. While the ABBI has the advantage of providing a large tissue sample, similar to that obtained from an open surgical biopsy, the cylindrical tissue sample is taken from the subcutaneous tissue to an area beyond the suspect tumor. For tumors embedded more deeply within the breast, the amount of tissue removed is considerable. In addition, while less expensive than open surgical biopsy, the ABBI has proven expensive compared to other biopsy techniques, and it has been noted that the patient selection for the ABBI is limited by the size and location of the tumor, as well as by the presence of very dense parenchyma around the tumor. For discussion on the ABBI, see:
Other biopsy devices have been referred to as the Mammotome and the Minimally Invasive Breast Biopsy (MIBB). These devices carry out a vacuum-assisted core biopsy wherein fragments of suspect tissue are removed with an 11 to 14-gauge needle. While being less invasive, the Mammotome and MIBB yields only a fragmentary specimen for pathological study. These devices therefore are consistent with other breast biopsy devices in that the degree of invasiveness of the procedure necessarily is counterbalanced against the need for obtaining a tissue sample whose size and margins are commensurate with pathology requirements for diagnosis and treatment.
Another excisional biopsy device is described in U.S. Pat. No. 6,022,362, and includes a tubular member having a window near a distal tip thereof; a cutting tool, a distal end of the cutting tool being attached near the distal tip of the tubular member, at least a distal portion of the cutting tool being configured to selectively bow out of the window and to retract within the window; and a tissue collection device externally attached at least to the tubular member, the tissue collection device collecting tissue excised by the cutting tool as the biopsy device is rotated and the cutting tool is bowed. An excisional biopsy method for soft tissue includes the steps of inserting a generally tubular member into the tissue, the tubular member including a cutting tool adapted to selectively bow away from the tubular member and an external tissue collection device near a distal tip of the tubular member; rotating the tubular member; selectively varying a degree of bowing of the cutting tool; collecting tissue severed by the cutting tool in the tissue collection device; and retracting the tubular member from the soft tissue. The tubular member may include an imaging transducer and the method may include the step of displaying information received from the transducer on a display device and the step of varying the degree of bowing of the cutting tool based upon the displayed information from the imaging transducer. Alternatively, the imaging transducer may be disposed within a removable transducer core adapted to fit within the tubular member.
Yet another minimally invasive approach to accessing breast lesions wherein the lesion is partially removed or removed in its entirety for diagnostic as well as therapeutic purposes has been described in U.S. Pat. No. 6,277,083 by Eggers, et al., entitled “Minimally Invasive Intact Recovery of Tissue”, issued Aug. 21, 2001. The instrument described includes a tubular delivery cannula of minimum outer diameter, the tip of which is positioned in confronting adjacency with a tissue volume to be removed. Following such positioning, the electrosurgically excited leading edge of an electrically conducting cable supported at the distal ends of leaf members is extended forwardly from the instrument tip to enlarge while the electrosurgically cutting and surrounding or encapsulating a tissue volume, severing it from adjacent tissue. Following such electrosurgical cutting, the instrument and the captured tissue volume are removed through an incision of somewhat limited extent. The electrosurgical cutting requires current flow from the cable to and through the surrounding tissue to maintain an electrical arc between the cables that is achieved by maintaining the cable at an elevated peak-to-peak voltage of at least 1000 volts relative to tissue. In order to enable current flow through the tissue, the elevated voltage must be applied at an alternative current frequency of at least 300 kHz in order to enable current flow from the cable through the surrounding tissue to a return electrode usually attached to the skin surface of the patient in the form of a pad having a surface area of at least 20 square inches. In this prior art, the voltage is maintained at a predetermined constant level (e.g., 1000 volts peak-to-peak), which the current flow from the cable and into the surrounding tissue is variable depending on the electrical resistivity of the surrounding tissue. The current flow from the cable into the surrounding tissue is higher for the case of denser, more fibrous tissue while the current flow from the cable into the surrounding tissue is lower for the case of fatty tissue. Maintaining an adequate current flow into the surrounding tissue to sustain an arc and associated cutting effect requires a sufficiently high voltage to overcome the electrical impedance of adjacent tissue having a very high fat content (e.g., fatty breast tissue).
An improved design for the instrument described in U.S. Pat. No. 6,277,083 is described in U.S. Pat. No. 6,471,659 by Eggers, et al., entitled “Minimally Invasive Intact Recovery of Tissue”, issued Oct. 29, 2002. This instrumentation includes a tubular delivery cannula of minimum outer diameter, the tip of which is positioned in confronting adjacency with the target tissue volume to be removed. Such positioning is facilitated through the utilization of a forwardly disposed precursor electrosurgical electrode assembly. Located within the interior channel of this delivery cannula are five relatively elongate thin leaf members mutually interconnected at their base to define a pentagonal cross-sectional configuration. Each of the five leaf members terminates forwardly at a tip with a transversely bent eyelet structure. Slideably extending through each eyelet is a separate electrically conductive electrosurgical cutting and pursing cable, which extends to an attachment with the next adjacent leaf tip. The five separate cables extend rearwardly through five small guide tubes attached to each of the five separate leafs for connection with the slideable cable terminator component of a drive assembly. The drive assembly is driven forwardly by an electric motor through a translation assembly. By adjusting the location of a stop component, which engages the cable terminator component, the size of a captured specimen may be varied. For example, the device can be configured to recover tissue specimens of between 10 mm and 15 mm effective maximum diametric extent. As the cable terminator component is pulled by the cable assembly into abutting engagement with the stop component, the cables are tensioned to draw the leaf eyelet structures together in a pursing action.
Cabling involved with the instrument specified in U.S. Pat. No. 6,471,659 must be quite diminutive in size while retaining adequate tensile strength in the temperature environment of an electrosurgical cutting arc. The electrosurgical arc temperature has been reported to be at least 1000° C. Heretofore, cable having a nominal diameter of 0.006 inch has been employed. While this electrosurgical cutting arc is present, the cables further must sustain not only stresses associated with the forward movement of the leaf members but also those loads imposed by the pursing activity during which the eyelets are drawn together to complete encapsulation of the tissue sample. For discussion of temperatures associated with electrosurgical arcs, see:
The prior art methods other than excision using surgically sharp cutting blades (e.g., open surgery excision for biopsy or lumpectomy, ABBI method) utilize a cutting method known as electrosurgical tissue cutting (or often incorrectly referred to as “electrocautery” tissue cutting). For discussion of tissue cutting with electrosurgical arcs, see:
In this modality of tissue cutting also known as monopolar electrosurgical cutting of tissue, a large electrical potential difference is imposed between the cutting member or active monopolar electrode (e.g., a flexible wire or multi-wire cable) and a passive or return electrode placed on the surface of the patient's body, typically a voltage difference in the range from 500 to 2000 volts peak-to-peak at a frequency ranging from 250 KHz to 5 MHz. This large potential difference allows the formation of electrical arcs between the cutting member and the adjacent tissue. At the point of impingement of the cutting arcs with the surrounding tissue, highly concentrated Joulean heating within the electrically conductive tissue occurs due to the very high current flux in the tissue at the point of impingement of the arcs with the tissue. This highly localized heating at the point of arc impingement causes the cellular fluid within the tissue cells to vaporize thereby fracturing the cellular walls and effecting the separation of the tissue along the advancing pathway of the electrosurgically induced electrical arcs.
In addition to the very high temperatures associated with the formation of electrical arcs during the process of electrosurgical cutting, which can lead to the failure of thin cutting wire or cable members, methods and apparatus which utilize electrosurgical cutting can also result in aberrant current flow in the tissue beyond the point of impingement by the arcs. As a consequence, electrical currents flowing from the active electrode (e.g., the flexible cutting wire or cable) to the passive electrode (e.g., the return electrode) placed on the surface of the patient's skin can induce unintended thermal damage to both the surrounding, un-excised tissue as well as the circumscribed tissue being excised for the purpose of diagnostic pathological evaluation. Furthermore, the electrical currents flowing from the active or monopolar electrode (e.g., the flexible cutting wire or cable) to the passive electrode (e.g., the return electrode) placed on the surface of the patient's skin can cause unintended stimulation of nerve tissue beyond the zone of the applied localized anesthesia (e.g., by interstitial injection of agents such as Lidocaine) resulting in significant discomfort to the patient during the electrosurgical cutting procedure. For discussion of the potential for iatrogenic injury to the patient and damage to excised pathology specimens associated with the use with electrosurgery, see:
Also, in addition to the disadvantages described above related to the use of electrosurgery for the cutting and excision of breast tissue as described in U.S. Pat. Nos. 6,277,083 and 6,471,659, another limitation is related to the significant difference in the electrical resistivity of the tissue being cut. As described above, the process of electrosurgical cutting requires the flow of electrical current from the point of impingement of the electrosurgical arc to the return electrode placed on the surface of the patient's skin. However, for the case of excision of breast tissue as described in U.S. Pat. Nos. 6,277,083 and 6,471,659, the electrical resistance of the breast tissue can differ by a factor of almost ten-fold as a result of the electrical properties inherent in regions of highly adipose breast tissue in contrast to very dense breast tissue. As a consequence, electrosurgical cutting may be inadequate in some patients with highly adipose breast tissue. For a discussion of the electrical resistivity or related properties of human tissue, see:
Improvements in apparatus for minimally invasive diagnostic and therapeutic excision of tissue are described in U.S. Pat. No. 11,737,808. This apparatus incorporates the use two rigid tubes to provide a conduit for first and second tensioning portions of a cutting and pursing cable. The distal end of each rigid tube provides for electrical contact with a flexible cable that is sliding over the end of each rigid tube. The rigid tubes allow only the adjacent flexible leaf members to deploy radially outward while the rigid tubes deploy only along the longitudinal axis as seen in FIGS. 18A and 18B of U.S. Pat. No. 11,737,808 thereby disadvantageously requiring the excision of a significantly larger portion of healthy tissue in order to obtain the targeted tissue volume as seen in
Another limitation of the apparatus for minimally invasive diagnostic and therapeutic excision of tissue described in U.S. Pat. No. 11,737,808 is the problem of intermittent loss of adequate electrical contact at the sliding interface between the cutting and pursing cable and one or both distal ends of the rigid tubes. The intermittent loss of adequate electrical contact at the sliding interface between the cutting and pursing cable and one or both distal ends of the rigid tubes results in a corresponding increase in the electrical contact resistance at the sliding contact between the cutting and pursing cable and the source of constant current at the one or both distal ends of the rigid tubes. An increase in the electrical contact resistance at the sliding interface between the cutting and pursing cable and one or both distal ends of the rigid tubes has been observed to be sufficiently large during the initial phase of deployment to cause overheating and failure of the cutting and pursing cable. During the initial phase of deployment of the rigid tubes and the adjacent leaf members, the tension applied to the cutting and pursing cable must be maintained at a minimum level in order to achieve the required slope or ramp of deployment of the leaf members and avoid premature pursing down of the distal ends of the leaf members. Consequently, during the initial phase of deployment to attain the maximum opening of the leaf members, the low level of allowed cable tension increases the likelihood that the electrical contact resistance at the sliding interface between the cutting and pursing cable and one or both distal ends of the rigid tubes may occasionally and momentarily become sufficiently large to induce excessive resistance heating at the sliding contact interface leading to overheating and melting of the cutting and pursing cable.
An objective of the present disclosure is to enable minimally invasive excision of a defined volume of tissue while overcoming or greatly limiting the disadvantageous effects described above which are associated with electrosurgical tissue cutting and excision.
In addition, an objective of the present disclosure is to enable minimally invasive excision of a nearly spherical volume of tissue and minimizing the unnecessary removal of any adjacent healthy tissue. A further objective of the present disclosure is to detect one or more occurrences of a significant increase in the electrical contact resistance at the sliding interface between the source of constant current and the cutting and pursing cable during its the deployment. Upon detection of a significant increase in the electrical contact resistance at the sliding interface between the source of constant current and the cutting and pursing cable, it is a further objective of the present disclosure to interrupt the application of constant current for a brief period until an acceptable level of electrical contact at one or both sliding interfaces is re-established and the application of the constant current can be resumed, thereby avoiding overheating and failure of the cutting and pursing cable at the locus of its sliding contact with the source of constant current.
The present disclosure is addressed to apparatus, system and method for retrieving a tissue volume having an intact form utilizing minimally invasive surgical instrumentation. This instrumentation includes a tubular delivery cannula of minimum outer diameter, the tip or distal end of which is positioned in confronting adjacency with the target tumor or tissue volume to be excised. The tubular delivery cannula is disposed at the distal end of a single-use support housing that is inserted into the receiving cavity of a reusable housing or handpiece assembly. Such positioning of the delivery cannula is facilitated through the utilization of a forwardly disposed cutting blade assembly supporting a surgically sharp blade.
By way of example and without limitation, located within the interior channel of this delivery cannula are two or more, preferably five, flexible leaf members and one multi-lumen flexible polymeric extrusion member. As used herein, the term polymeric, as it refers to the multi-lumen flexible extrusion, includes flexible synthetic polymers that exhibit, by way of example, the following characteristics: [a] biocompatibility with respect to direct contact with human tissue, blood and other bodily fluids, [b] sterilizable by way of example, using radiation (e.g., gamma radiation) or ethylene oxide [c] electricaly insulative having a volume electrical resistivity of preferably greater than 1×1012 ohm-cm, [d] flexibility of the extruded member and [e] extrudable in configurations having multiple lumens, thickness as small as 0.020 inch and widths as small as 0.090 inch. Examples of polymeric materials suitable for the multi-lumen flexible polymeric extrusion disclosed herein include polyamides (e.g., Nylon 6, 11 and 12), polyethylene, fluorinated ethylene propylene and polytetrafluoroethylene.
Each leaf member is preferably formed by photochemically etching a thin metallic sheet using a known biocompatible metal having a high modulus of elasticity and yield strength such as full-hard austenitic stainless steel. The leaf member may incorporate a multiplicity of slots or perforations in order to provide the required stiffness during deployment to the maximum opening position (i.e., basket deployment phase) of the leaf members while limiting the stiffness of the leaf members during the purse down phase of the tissue capture procedure.
The multi-lumen flexible polymeric extrusion members is formed using an electrically insulative, biocompatible extrudable polymer (e.g., nylon or polytetrafluoroethylene). The multi-lumen flexible polymeric extrusion member incorporates a multiplicity of conduits, preferably four conduits. The leaf members and the multi-lumen flexible polymeric extrusion members are mutually supported and secured at their proximal ends on the perimeter surface of a leaf and multi-lumen flexible polymeric extrusion support member to define a polygonal cross-sectional configuration.
By way of example, each of the five leaf members terminate forwardly with an eyelet-containing tip. In addition, each leaf member is covered by a thin, flexible biocompatible electrically insulative coating (e.g., Parylene HT) capable of withstanding temperatures of up to at least 300° C., preferably up to 400° C. in order to prevent unwanted electrical current flow between the leaf members, between the leaf members and surrounding structures within the delivery cannula, and also to prevent unwanted electrical current flow between individual leaf members and the surrounding tissue during the conduction of a substantially constant level of electrical current through the cutting and pursing cable segments that extend between and supported within the eyelets at the distal end of each leaf member and the multi-lumen flexible polymeric extrusion member. Since the multi-lumen flexible polymeric extrusion member is formed using an electrically insulative polymer (e.g., nylon or polytetrafluoroethylene), no electrically insulative coating is required for the exterior of the multi-lumen flexible polymeric extrusion member.
The apparatus for retrieving a tissue volume of given peripheral extent includes a cutting and pursing cable that is flexible, electrically conductive and is of fixed length, the length of the flexible cutting and pursing cable having two functional regions. Throughout the present disclosure, the term “cutting and pursing cable” refers to a cable or single wire that is flexible, having sufficient flexibility to enable passage of the cutting and pursing cable (or wire) through bend radii as small as 0.030″.
A first functional region is the tensionable portion of the cutting and pursing cable and is that portion of the cutting and pursing cable in which no electrical current is conducted and that is proximal to each of first and second electrically and thermally conductive eyelets located at the distal end of the multi-lumen flexible polymeric extrusion assembly. A second functional region is the resistively heated portion of the cutting and pursing cable and is that portion of the cutting and pursing cable in which electrical current is conducted and that is distal to first and second electrically and thermally conductive eyelets located at the distal end of the multi-lumen flexible polymeric extrusion assembly. Each first and second electrically and thermally conductive eyelet is disposed at the distal end of first and second electrically and thermally conductive wires, respectively, and function as first and second electrodes, respectively, for conducting electrical current from first and second electrically and thermally conductive wires to the resistively heated portion of the cutting and pursing cable at the locus of sliding electrical contact between the cutting and pursing cable and each first and second electrically and thermally conductive eyelet as the cutting and pursing cable is advanced or retracted through the each first and second electrically and thermally conductive eyelets during the retrieval of a tissue volume.
The functional transition between the tensionable portion of cutting and pursing cable and the resistively heated portion of cutting and pursing cable is the location of sliding electrical contact between the cutting and pursing cable and each of the first and second electrically and thermally conductive eyelets. During the excision of a targeted volume of tissue, the component lengths of the first and second tensionable portions of the cutting and pursing cable decrease while the component length of the resistively heated portion of the cutting and pursing cable increase as the ensemble of leaf members and the extrusion member that form the tissue capture basket extend forwardly to a maximum peripheral extent of the tissue capture assembly. Upon the tissue capture basket having extended forwardly to a maximum peripheral extent, the component lengths of the first and second tensionable portions of the cutting and pursing cable increase while the component lengths of the resistively heated portion of the cutting and pursing cable decrease as the ensemble of leaf members and the extrusion member that form the tissue capture basket extend forwardly while an increased level of tension is applied to the cutting and pursing cable to effect the pursing down of the tissue capture assembly.
Throughout a first period when the tissue capture basket is extended forwardly to a maximum peripheral extent (i.e., capture basket opening phase) and throughout a second period when the tissue capture basket is extended forwardly and pursed down to a minimum peripheral extent, sufficient contact pressure is maintained between the cutting and pursing cable and each of the first and second electrically and thermally conductive eyelets to maintain good electrical contact at the sliding interface between the cutting and pursing cable and each of the first and second electrically and thermally conductive eyelets. Sufficient contact pressure is maintained between the cutting and pursing cable and each of the first and second electrically and thermally conductive eyelets by applying a minimum level of tension to the tensioning portions of the cutting and pursing cable, preferably an applied tension level of not less than 7 grams to each of the first and second tensioning portions of the cutting and pursing cable. The application of at least a minimum level of tension to the tensioning portions of the cutting and pursing cable allows good electrical contact to be maintained at the sliding interface between the cutting and pursing cable and each of the first and second electrically and thermally conductive eyelets disposed at the distal end of the multi-lumen flexible polymeric extrusion assembly as the multi-lumen flexible polymeric extrusion assembly is advanced through the arcuate path that defines the hemispherical shape of the proximal end of the tissue capture basket.
Extending between the multi-lumen flexible polymeric extrusion member and each adjacent leaf member is a small-diameter, resistively heated portion of a cutting and pursing cable comprising multiple wires (e.g., 7 to 19 wires) or formed from a single small-diameter wire. Hereinafter, the term “cutting and pursing cable” will commonly be used but does not exclude the possibility of the alternative use of an electrically conductive single wire in place of a cable comprising a multiplicity of wires. By way of example, the composition of the single wire may be austenitic stainless steel, nickel alloy, cobalt/nickel alloy, titanium or titanium alloy.
By way of example, the multi-lumen flexible polymeric extrusion assembly comprises an electrically insulative flexible polymeric extrusion having four lumens. A first electrically and thermally conductive lead wire (e.g., high purity silver wire) extends from a current source through a first lumen and a second electrically and thermally conductive lead wire (e.g., high purity silver wire) extends from a current source through a second lumen. A first tensionable portion of the cutting and pursing cable (e.g., a cable comprising seven wires of a cobalt/chrome/tungsten/nickel alloy such as L605) extends through a third lumen and a second tensionable portion of a cutting and pursing cable (e.g., a cable comprising seven wires of a cobalt/chrome/tungsten/nickel alloy such as L605) extends through a fourth lumen. That portion of the distal end of the first electrically and thermally conductive lead wire that extends beyond the distal end of the multi-lumen flexible polymeric extrusion member forms a first electrically and thermally conductive eyelet through which the first tensionable portion of cutting and pursing cable extends, the first tensionable portion of cutting and pursing cable making sliding electrical contact with first electrically and thermally conductive eyelet located at the distal end of the first electrically and thermally conductive lead wire. Likewise, that portion of the distal end of the second electrically and thermally conductive lead wire that extends beyond the distal end of the multi-lumen flexible polymeric extrusion member forms a second electrically and thermally conductive eyelet through which a second tensionable portion of cutting and pursing cable extends, the second tensionable portion of cutting and pursing cable making sliding electrical contact with second electrically and thermally conductive eyelet located at the distal end of the second electrically and thermally conductive lead wire. Those portions of the first and second electrically and thermally conductive lead wires located at the proximal end of the multi-lumen flexible polymeric extrusion member are connected to first and second single-use housing lead wires, respectively.
By way of example, a tissue cutting and capture assembly forms a circumferential sequence of cutting and pursing cable support members. The tissue cutting and capture assembly comprise, in sequence, the multi-lumen flexible polymeric extrusion, a first leaf member, a second leaf member, a third leaf member, a fourth leaf member and a fifth leaf member.
The first tensionable portion the cutting and pursing cable extends from the third lumen within the multi-lumen flexible polymeric extrusion and passes through the first eyelet at the distal end of the first electrically and thermally conductive lead wire that extends beyond the distal end of the multi-lumen flexible polymeric extrusion. That portion of the cutting and pursing cable that extends distally from the first eyelet at the distal end of the first electrically and thermally conductive lead wire functions as a resistively heated portion of the cutting and pursing cable and is that portion of the cutting and pursing cable in which electrical current is conducted. The portion of the cutting and pursing cable through which electrical current is conducted extends distally from the first eyelet at the distal end of the first electrically and thermally conductive lead wire continues, in sequence, through the eyelet at the distal end of the first leaf member, through the eyelet at the distal end of the second leaf member, through the eyelet at the distal end of the third leaf member, through the eyelet at the distal end of the fourth leaf member, through the eyelet at the distal end of the fifth leaf member and continues to the second eyelet at the distal end of the second electrically and thermally conductive lead wire that extends beyond the distal end of the multi-lumen flexible polymeric extrusion. In addition to electrical current flow in the cutting and pursing cable that is distal to the first and second eyelets, the total path of electrical current flow in the cutting and pursing cable also includes [a] the electrical current flow across the interface between the first eyelet at the distal end of the first electrically and thermally conductive lead wire and the portion of the cutting and pursing cable that extends distally to the first eyelet and [b] the electrical current flow across the interface between the second eyelet at the distal end of the second electrically and thermally conductive lead wire and the portion of the cutting and pursing cable that extends distally to the second eyelet. This total path of electrical current flow in the cutting and pursing cable is hereinafter referred to as the resistively heated cutting and pursing cable circuit. The second tensionable portion of the cutting and pursing cable is that portion of the cutting and pursing cable that extends through and is proximal to the second eyelet at the distal end of the second electrically and thermally conductive lead. The second tensionable portion of the cutting and pursing cable continues rearwardly through the fourth lumen in the multi-lumen flexible polymeric extrusion.
The first and second tensioning portions of the cutting and pursing cable slideably extend through a third and fourth lumen, respectively, within the multi-lumen flexible polymeric extrusion and continue to a first and second electrically and thermally conductive eyelet, respectively, disposed at the distal ends of the first and second electrically and thermally conductive lead wires, respectively, that extend through the first and second lumens, respectively, of the multi-lumen flexible polymeric extrusion as described above. Importantly, electrical current only flows in that portion of the cutting and pursing cable that extends distally to the first and second lumens of the multi-lumen flexible polymeric extrusion and beyond the point of sliding electrical contact with the first and second electrically and thermally conductive eyelets. In this manner, electrical current only flows in that portion of the cutting and pursing cable that is in contact with the tissue being incised and does not flow proximally to the first and second electrically and thermally conductive eyelets (i.e., in the first and second tensioning portions of the cutting and pursing cable that are located, respectively, within the third and fourth lumen of a multi-lumen flexible polymeric extrusion). In this manner, electrical current only flows in those portions of the cutting and pursing cable that are in thermal contact with tissue wherein the resistive heating generated within the cutting and pursing cable dissipates. The amount of heat generated within the cutting and pursing cable and transferred to the tissue in contact with the resistively heated cutting and pursing cable is sufficient to thermally sever the tissue that is in contact with the resistively heated cutting and pursing cable.
Preventing the flow of electrical current in those portions of the cutting and pursing cables that are in within the lumens of the multi-lumen flexible polymeric extrusions thereby prevents overheating the cutting and pursing cables as well as the surrounding multi-lumen flexible polymeric extrusion due to the limited ability to dissipate resistive heating within any portions of the cutting and pursing cable that is not in direct contact with the tissue being incised.
By way of example, a hexagonal shaped pattern of the resistively heated cutting and pursing cable segments is formed for the case of one multi-lumen flexible polymeric extrusion in combination with five leaf members. The hexagonal shaped pattern of the resistively heated cutting and pursing cable segments thereby form a substantially complete circumscribing cutting and pursing cable path as the segments are advanced through the tissue being incised (i.e., severed).
Each resistively heated cutting and pursing cable segment extends between either the first and second electrically and thermally conductive eyelets and the eyelets disposed at the distal ends of the nearest first and fifth adjacent leaf member, respectively, or between the eyelets disposed at the distal ends of the first and second leaf member, the eyelets disposed at the distal ends of the second and third leaf member, the eyelets disposed at the distal ends of the third and fourth leaf member and the eyelets disposed at the distal ends of the fourth and fifth leaf member.
The proximal ends of the two tensionable cutting and pursing cable portions continue rearwardly through third and fourth lumens within the multi-lumen flexible polymeric extrusions where their proximal ends are securely attached to an electrically insulative cable mounting hub.
The first electrically and thermally conductive lead wire (e.g., high purity silver wire) that extends from a current source through a first lumen within the multi-lumen flexible polymeric extrusion is electrically isolated from a second electrically and thermally conductive lead wire (e.g., high purity silver wire) that extends from a current source through a second lumen within the multi-lumen flexible polymeric extrusion. The only path for electrical current flow from the first electrically and thermally conductive lead wire to the second electrically and thermally conductive lead is through that portion of the cutting and pursing cable that is distal to the first and second eyelets at the distal ends of the first and second electrically and thermally conductive lead wires, respectively.
The first electrically and thermally conductive lead wire and the second electrically and thermally conductive lead wire serve four functions. A first function for the first and second electrically and thermally conductive lead wires is to support an electrically and thermally conductive eyelet formed at the distal end of each lead wire. Each electrically and thermally conductive eyelet provides a low-friction pathway for the passage of the cutting and pursing cable as it extends from the orifice of a third or fourth lumen within the multi-lumen flexible polymeric extrusion member to the eyelet of an adjacent leaf member.
A second function for each first and second electrically and thermally conductive lead wires is to electrically conduct a predetermined level of constant current from the electrically and thermally conductive eyelet at the distal end of each electrically and thermally conductive lead wire through a low electrical resistance sliding contact between the electrically and thermally conductive eyelet and the cutting and pursing cable as it emerges from each of the electrically and thermally conductive eyelets. Hereinafter, the term “constant current” refers to a constant electrical current. The application of a predetermined level of constant current to the resistively heated cutting and pursing cable causes the temperature of the resistively heated cutting and pursing cable to increase to a predetermined level sufficient for the controlled thermal incision of tissue by the resistively heated portion of the cutting and pursing cable without overheating and melting or fracturing the resistively heated portion of the cutting and pursing cable.
Accordingly, the predetermined level of constant current is supplied by a current source located within the handpiece assembly and operating at a frequency of at least 25 kHz, preferably at least 100 KHz. The constant current preferably operates at an elevated frequency in order to prevent unwanted electrical stimulation of tissue in contact with the resistively heated portion of the cutting and pursing cable. The constant current is delivered through a first pair of contacts on the interior of the reusable handpiece assembly and an aligned second pair of contacts on the exterior of the single-use support housing and finally through lead wires within the single-use support housing that extend from the second pair of contacts on the exterior of the single-use support housing to the proximal ends of the first and second electrically and thermally conductive lead wires. In this manner, the supply of a constant level of electric current flows through low electrical resistance leads, low electrical resistance contacts and low electrical resistance paths along the length of the first and second electrically and thermally conductive lead wires located within lumens in the multi-lumen flexible polymeric extrusion assembly. The electrical current only commences its flow through the relatively higher resistance cutting and pursing cable as it exits the first or second electrically and thermally conductive eyelets at the distal ends of each of the first and second electrically and thermally conductive lead wires, respectively, and then into to the cutting and pursing cable.
Throughout the present disclosure, the term “electrical resistance” and “electrical impedance” are used interchangeably. The more widely used designation for the “electrical resistance” of electrical circuits wherein an alternating current is flowing is “electrical impedance”. The term electrical impedance in circuits wherein alternating current is flowing includes the effects of the induction of voltages in conductors by the magnetic fields (inductance), and the electrostatic storage of charge induced by voltages between conductors (capacitance). The impedance component caused by these two effects is collectively referred to as reactance and is additive to the electrical resistance of the circuit associated with direct current or “DC” flow.
A third function for each first and second electrically and thermally conductive lead wire contained within lumens extending the length of the multi-lumen flexible polymeric extrusion assembly is to conduct heat from the first and second electrically and thermally conductive eyelets at the distal end of the first and second electrically and thermally conductive lead wires to the proximal portions of the first and second electrically and thermally conductive lead wires thereby minimizing the temperature rise of the first and second electrically and thermally conductive lead wires at the distal end of the multi-lumen flexible polymeric extrusion.
A fourth function for each first and second electrically and thermally conductive lead wire contained within lumens extending the length of the multi-lumen flexible polymeric extrusion assembly is to increase the column strength of a multi-lumen flexible polymeric extrusion formed using elastomeric materials having a low modulus of elasticity such as, by way of example, nylon or fluoropolymer materials. The increased column strength enables the multi-lumen flexible polymeric extrusion formed using elastomeric materials having a low modulus of elasticity to maintain its longitudinal configuration within the delivery cannula during the deployment of the multi-lumen flexible polymeric extrusion assembly.
A fifth function for each first and second electrically and thermally conductive lead wire contained within lumens extending the length of the multi-lumen flexible polymeric extrusion assembly is to guide the movement of the cutting and pursing cable.
The individual lumens within the multi-lumen flexible polymeric extrusion member are electrically isolated from each other since the flexible polymeric extrusion member is formed of an electrically insulative material such as nylon or polytetrafluorethylene. The electrical isolation of the first and second lumens through which the first and second electrically and thermally conductive leads extend prevents electrical current flow within the extrusion between the first and second electrically and thermally conductive leads even though the constant current applied to the first and second electrically and thermally conductive leads results in a voltage differential between the first and second electrically and thermally conductive leads of opposite polarity ranging from several volts to several tens of volts.
No significant electrical resistive heating occurs until the applied constant current flow begins within those portions of the relatively high electrical resistance cutting and pursing cable that extend into and that are in direct contact with the surrounding tissue that is positioned beyond the electrically and thermally conductive eyelets at the distal ends of the first and second electrically and thermally conductive lead wires. Importantly, the distal end of the delivery cannula of the tissue incision and retrieval assembly that abuts the targeted tissue is configured so that those portions of the cutting and pursing cable that extend beyond the electrically and thermally conductive eyelets at the distal ends of the first and second electrically and thermally conductive lead wires are always in direct thermal contact with soft tissue and/or fluids (e.g., blood). Additionally, the distal end of the tissue incision and retrieval assembly that abuts the targeted tissue may initially be advanced a short distance without any applied constant current within the resistively heated portion of the cutting and pursing cable to assure good thermal contact between the cutting and pursing cable with the targeted tissue prior to the commencement of resistive heating within the portion of the cutting and pursing cable that is distal to the first and second electrically and thermally conductive eyelets at the distal ends of the first and second electrically and thermally conductive lead wires.
According to the teachings of this disclosure, a tissue cutting and capture assembly may comprise two or more leaf members, one multi-lumen flexible polymeric extrusion assembly and a resistively heatable cutting and pursing cable that is resistively heatable along those portions of the cutting and pursing cable that are in direct contact with tissue and distal to the first and second electrically and thermally conductive eyelets at the distal ends of the first and second electrically and thermally conductive lead wires, respectively, The two or more leaf members and the multi-lumen flexible polymeric extrusion assembly are secured at their respective proximal ends to a leaf member and extrusion assembly support member.
The leaf member and extrusion assembly support member is driven forwardly by a motor-actuated drive tube drive member translation assembly that is abuttingly engaged against the leaf member and extrusion assembly support member to actuate the deployment of the tissue cutting and capture assembly. The tissue cutting action is enabled by the passage of electrical current only through those segments or sections of the resistively heated portion of cutting and pursing cable that are in direct contact with tissue or fluids within the body. Hereinafter, references to contact with tissue may include contact with tissue and other fluids within the body. The electrical current passing through only those portions of the resistively heated portion of cutting and pursing cable in direct contact with tissue is of sufficient current flux to induce resistive heating of the cutting and pursing cable to achieve an elevated temperature sufficient to establish a thermally induced cutting effect at the leading edge of the resistively heated portion of cutting and pursing cable. By way of example, the current flux and associated resistance heating is sufficient to maintain the temperature of the resistively heated portion of cutting and pursing cable at a temperature of at least 300° C., preferably at least 400° C., at a predetermined tissue cutting rate, Rcut and types of soft tissue media including, but not limited to, muscle tissue, adipose tissue, tendons, lymphatic tissue as well as transecting blood vessels and exposure to blood and other liquids within the body.
An essential attribute of the apparatus of the present disclosure is the confinement of the path of electrical conduction of constant current required to achieve tissue cutting to only those portions of the expanding and contracting resistively heated segments of the cutting and pursing cable that are distal to the electrically and thermally conductive eyelets at the distal ends of the first and second electrically and thermally conductive lead wires located at the distal end of the multi-lumen flexible polymeric extrusion assembly and that are in direct contact with tissue. The confinement of the path of electrical conduction of constant current to only those portions of the expanding and contracting resistively heated segments of the cutting and pursing cable that are in direct contact with tissue avoids overheating those portions of the tensionable cutting and pursing cable that are located proximal to the electrically and thermally conductive eyelets at the distal ends of the first and second electrically and thermally conductive lead wires and within the third and fourth lumens of the multi-lumen flexible polymeric extrusion assembly and not in contact with tissue. As a consequence, the rate of heat dissipation from the cutting and pursing cable is negligible in those proximal portions of the cutting a pursing cable that are not distal to the eyelets and that are not in contact with tissue.
The tensionable portions of the cutting and pursing cable extending through and rearwardly within the third and fourth lumens of the multi-lumen flexible polymeric extrusion assembly enable the application of a mechanical load or tension level required for the pursing down of the tissue capture basket during the process of incising and capturing a target tissue volume. The mechanical load or tension level is uniformly applied to the proximal ends of each of the tensionable portions of the cutting and pursing cable beginning after the basket has reached the pre-selected maximum opening diameter (e.g., 25 mm diameter opening size).
The tensionable portions of the cutting and pursing cable that are not in direct contact with tissue and proximal to the tip of the tissue capture basket are not intended to support the electrical conduction of the constant current required to heat the cable above temperature threshold levels required for the thermal cutting of tissue. Importantly, electrical current flows only within the resistively heated portion of cutting and pursing cable in direct contact with tissue while no electrical current flows into or through the tissue being cut. Advantageously, the prevention of electrical current flow into or through the tissue being cut minimizes necrosis of tissue beyond the immediate surface of the tissue incision thereby assuring a pathology specimen having minimal thermal and electrical current related damage or artifact. In addition, for the case of procedures performed with only local anesthesia, the prevention of electrical current flow into or through the tissue being cut can prevent the induction of pain in the patient's nerve pathways located beyond and more distant from the path of tissue incision and beyond the localized region of induced anesthesia as with the injection of analgesic agents such as Lidocaine.
By way of example, as the two or more leaf members and the multi-lumen flexible polymeric extrusion assembly engaged with the drive assembly drive member are driven forwardly by a motor-actuated drive tube drive member translation assembly incorporating a first motor and planetary gear train assembly (hereinafter referred to as the first motor-actuated drive tube drive member translation assembly), the eyelets disposed at the distal ends of the two or more leaf members and the distal end of the multi-lumen flexible polymeric extrusion assembly are correspondingly driven forwardly. Alternatively, other means for advancement of the drive tube drive member translation assembly may be employed, including, but not limited to, pneumatic or spring-loaded advancement. The eyelets at the distal ends of the leaf members and the multi-lumen flexible polymeric extrusion assembly support the resistively heated portions of the cutting and pursing cable as the cutting and pursing cable is driven forwardly at a deployment angle mutually outwardly through a guidance assembly to an extent that the cutting leading edge of the resistively heated portion of the cutting and pursing cable reaches an effective maximum diameter extending about and circumscribing the target tissue volume to be excised and captured. By way of example, a first pivotable drive finger extending from the first motor-actuated drive tube drive member translation assembly within a handpiece assembly may drivably engage the drive assembly drive member to affect its advancement and the supported leaf members and multi-lumen flexible polymeric extrusion assembly. The pivotable aspect of first pivotable drive finger enables the single-use tissue incision and retrieval assembly to be removed from the handpiece assembly in the presence of the drive block advancement ear extending from drive assembly drive member and pivoting drive ear extending from cable mounting hub.
In a preferred embodiment, the tissue incision and retrieval system includes a practitioner-actuatable capture size selection switch on the handpiece assembly that enables the practitioner to select a diameter of a substantially spherical volume of tissue in the range, for example, from 15 mm to 30 mm in diameter increments of 5 mm. Upon the selection of the desired diameter of a substantially spherical volume of tissue by the practitioner using the capture size selection switch, the second-motor actuated cable mounting hub translation assembly advances the position of the second pivotable drive finger to a predetermined position. The predetermined position of the second pivotable drive finger controls the travel distance of the cable mounting hub along a support tube between its initial position and its position abutting the pivoting drive ear extending from the cable mounting hub. The larger the preferred diameter of a substantially spherical volume of tissue the greater the travel distance between the initial position of the cable mounting hub and its position abutting the pre-positioned second pivotable drive finger.
While the deploying leaf members and the multi-lumen flexible polymeric extrusion assembly are being advanced to attain the pre-selected diameter of the substantially spherical volume of tissue, the cable mounting hub encounters and is abuttingly engaged against the second pivotable drive finger. As the cable mounting hub advances, in conjunction with the advancement of the deploying leaf members and the multi-lumen flexible polymeric extrusion assembly, tension is applied to the first and second tensioning portions of the cutting and pursing cable. The applied tension is pre-selected to be sufficiently high to maintain low electrical contact resistance between the cutting and pursing cable as it makes sliding electrical contact with each of the electrically and thermally conductive eyelets at the distal ends of the first and second electrically and thermally conductive lead wires located at the distal end of the multi-lumen flexible polymeric extrusion assembly. Also, the applied tension is pre-selected to be sufficiently low to prevent unwanted premature pursing down of the ensemble of deploying leaf members and the multi-lumen flexible polymeric extrusion assembly prior to the attainment of the practitioner selected diameter extent of the target tissue being incised ant captured.
The practitioner-selected diameter of a substantially spherical volume of the tissue being excised corresponds to the maximum diameter reached by the distal ends of the two or more (preferably five) leaf members and the distal end of the multi-lumen flexible polymeric extrusion. The maximum diameter reached by the distal ends of the two or more (preferably five) leaf members and the distal end of the multi-lumen flexible polymeric extrusion occurs when the cable mounting hub reaches and abuts a second pivotable drive finger extending from a second motor-actuated cable mounting hub translation assembly. The second pivotable drive finger that extends from a second motor-actuated cable mounting hub translation assembly serves two functions. The first function is to determine the maximum diameter reached by the distal ends of the two or more (preferably five) leaf members and the distal end of the multi-lumen flexible polymeric extrusion. The second function is to control the rate of purse down of the cutting and capture basket. The rate of purse down of the cutting and capture basket is controlled by a pre-selected rate of rearward advancement of the second pivotable drive finger that extends from a second motor-actuated cable mounting hub translation assembly. As the second pivotable drive finger is driven rearwardly along with the abutting cable mounting hub, the first and second tensioning portions of the cutting and pursing cable that are attached to the cable mounting hub are tensioned and draw together, in a pursing action, the eyelet structures that are located at the distal ends of the two or more (preferably five) leaf members and the distal end of the multi-lumen flexible polymeric extrusion. In this pursing process, the eyelets located at the distal ends of the leaf members and multi-lumen flexible polymeric extrusion assembly are drawn mutually inwardly to define a hemispherical curvilinear profile to close the leading edge about the tissue volume as the forward movement of the leaf members and the multi-lumen flexible polymeric extrusion assembly continues. The resistively heated portion of the cutting and pursing cable, now under tension and constrained by the interior surfaces of the leaf members and multi-lumen flexible polymeric extrusion assembly contributes to the structural stability of the resultant tissue capture basket.
In a preferred method, upon reaching a predetermined electrical current level in the second motor incorporated in the second motor-actuated cable mounting hub translation assembly, a pre-selected voltage is no longer applied to the first motor-actuated drive tube drive member translation assembly, a pre-selected voltage is no longer applied to the second motor-actuated cable mounting hub translation assembly and a pre-selected level of constant current is no longer supplied to the resistively heated portion of the cutting and pursing cable. The termination of the first and second voltages applied to the first motor-actuated drive tube drive member translation assembly and the second motor-actuated cable mounting hub translation assembly as well as the termination of the constant current that is no longer supplied to the resistively heated portion of the cutting and pursing cable corresponds to the end of the excision and capture of the targeted tissue volume followed by the removal of the delivery cannula of the tissue incision and retrieval system by the practitioner along with the captured volume of tissue.
The rate of translation of the first motor-actuated drive tube drive member translation assembly that forwardly advances the leaf members and the multi-lumen flexible polymeric extrusion assembly in combination with the rate of translation of the second motor-actuated cable mounting hub translation assembly that rearwardly retracts the cable mounting hub determines the degree or extent of curvature of the noted curvilinear profile.
In a preferred embodiment, first and second electrical terminals are located on the left and right interior sides of the handpiece assembly and are in slideable electrical contact with corresponding first and second terminals located on the left and right exterior sides of the single-use support housing, respectively. These slideably communicating first and second electrode pairs provide the supply of constant current to the cutting and pursing cable. As a result of the small diameter and high electrical resistivity of the cutting and pursing cable, substantially all of the electrical resistance in the resistively heated cutting and pursing cable circuit carrying the applied constant current is confined to those portions of the cutting and pursing cable that extend from and are distal to the eyelets of the two or more leaf members and the multi-lumen flexible polymeric extrusion assembly. As the leaf members and multi-lumen flexible polymeric extrusion assembly deploy during the incision and capture of the target tissue volume, the length of the resistively heated portion of the cutting and pursing cable increases from an initial starting position until the practitioner-selected diameter of a substantially spherical volume of tissue is attained.
Once the practitioner-selected diameter of a substantially spherical volume of tissue is attained, the second pivotable drive finger induces the pursing down of the distal ends of the leaf members and multi-lumen flexible polymeric extrusion assembly, thereby causing the length of the resistively heated portion of the cutting and pursing cable to decrease to a minimum length upon the completion of the drawing together or pursing down of the distal ends of the leaf members and multi-lumen flexible polymeric extrusion assembly. As the length of the of the resistively heated portion of cutting and pursing cable increases to a maximum value during the basket opening phase followed by a decrease to a minimum value during the basket pursing down phase, the electrical resistance of the resistively heated portion of the cutting and pursing cable increases or decreases. Since a predetermined constant current is supplied to the resistively heated portion of the cutting and pursing cable during the tissue incision and capture process, the corresponding applied voltage will increase or decrease proportionately as the electrical resistance of the resistively heated portion of the cutting and pursing cable increases or decreases according to the well-known Ohm's Law. As applied to the present disclosure, Ohm's Law specifies that the voltage differential across the ends of a conductor is proportional to the product of the electrical current flow through a conductor and the electrical resistance of the conductor. Hence, although the level of electrical current supplied to cutting and pursing cable is selected to be substantially constant, the applied voltage level varies throughout the course of the tissue incision and capture process. The predetermined level of constant current is selected to achieve [a] a sufficient heat generation rate within the portions of the cutting and pursing cable that are distal to the eyelets of the multi-lumen flexible polymeric extrusion assembly and extend to the adjacent leaf member eyelets to maintain a temperature sufficient to incise tissue (e.g., a temperature of at least 300° C.) while [b] maintaining the maximum temperature of the cable, throughout the tissue incision and capture process, below the threshold of mechanical failure (i.e., breaking) of the cable under the applied tensile load or the threshold of melting the cable.
In addition to measuring the current level delivered to Motor 2 as an indication of the completion of the purse down of the leaf members and the multi-lumen flexible polymeric extrusion assembly as describe above, the voltage level applied to the resistively heated cutting cable may also be used to indicate the completion of the purse down of the leaf members and the multi-lumen flexible polymeric extrusion assembly. By way of example, the voltage level applied across the first and second constant current terminals located on the left and right interior sides of the handpiece assembly, which varies according to the length of the deployed resistively heated portions of the cutting and pursing cables as discussed above, is continuously measured throughout the tissue cutting and capture process. In addition, the predetermined constant current level supplied to the varying length of the resistively heated portions of the cutting and pursing cables that extends beyond the distal ends of the two or more leaf members and the multi-lumen flexible polymeric extrusion assembly is also continuously measured and controlled throughout the tissue cutting and capture process. Circuitry within the controller located within the handpiece assembly ratiometrically combines the measured varying voltage level and the measured constant current level to continuously derive the effective electrical resistance of the resistively heated cutting and pursing cable, Rcable. When the derived value of Rcable decrease below a predetermined minimum cable resistance value, Rmin, corresponding to the minimum length of deployed cutting and pursing cable that exists upon the completion of the drawing down or pursing together of the distal ends of the multi-lumen flexible polymeric extrusion assembly and all leaf members, then the process of the incision and capture of the target tissue volume is complete.
Following the completion of the incision and capture of the target tissue volume, the substantially constant current applied to the resistively heated portion of the cutting and pursing cable is discontinued. Additionally and simultaneously, the voltage applied to the first motor-actuated drive tube drive member translation assembly is discontinued and the voltage applied to the second motor-actuated cable mounting hub translation assembly is discontinued. Additionally and simultaneously, the controller within the handpiece assembly provides a visual cue on the handpiece assembly and an audible cue or tone is discontinued (i.e., the audible cue or tone being issued from the handpiece assembly throughout the incision and capture process) to indicate that the incision and capture process for circumscribing and capturing the target tissue volume is complete. At this point, the delivery cannula is removed from the patient along with a retained volume of captured tissue containing the target tissue volume.
The tissue incision and retrieval instrument of the present disclosure enjoys the capability of providing a range of maximum effective diameters during tissue incision and capture. Accordingly, the maximum effective diameter is selected by the practitioner once the single-use tissue incision and retrieval assembly is inserted into the handpiece assembly and secured into position using the rotatable locking nut positioned at the distal end of single-use support housing. Once the single-use tissue incision and retrieval assembly is inserted into the handpiece assembly and just prior to the start of a procedure, the practitioner may select the diameter of the tissue volume to be captured by manually depressing a capture size selection switch located on the handpiece assembly. By way of example, the practitioner may select a diameter for the intended incised and captured tissue volume of 15, 20, 25 or 30 mm. Upon the practitioner's selection of the intended diameter of the incised and captured tissue volume, the motor-actuated cable mounting hub translation assembly positions the second pivotable drive finger at a precise distance from the starting position of the cable mounting hub.
The relatively straightforward structuring of the delivery cannula, leaf member assembly, multi-lumen flexible polymeric extrusion assembly and drive assembly drive member permits their incorporation within a single-use support housing that is removably insertable within a manually maneuverable handpiece assembly. The first motor-actuated drive tube drive member translation assembly within the handpiece assembly may be arranged either in-line along the same longitudinal axis of the delivery cannula, leaf member assembly, multi-lumen flexible polymeric extrusion assembly and drive assembly drive member or may be arranged side-by-side relative to the longitudinal axis of the delivery cannula, leaf member assembly, multi-lumen flexible polymeric extrusion assembly and drive assembly drive member. Likewise, the second-motor actuated cable mounting hub translation assembly within the handpiece assembly may be arranged either in-line along the same longitudinal axis of the delivery cannula, leaf member assembly, multi-lumen flexible polymeric extrusion assembly and drive assembly drive member or may be arranged side-by-side relative to the longitudinal axis of the delivery cannula, leaf member assembly, multi-lumen flexible polymeric extrusion assembly and drive assembly drive member.
User control over the tissue incision and retrieval instrument of this disclosure is provided in the form of control switches located on the hand-held handpiece assembly. All practitioner usage and cueing functions are incorporated within the handpiece assembly in combination with a rechargeable battery, thereby eliminating the need for an external control assembly and associated interconnecting cable. If the tissue incision and retrieval procedure is to be performed in a sterile field (e.g., the sterile field of an operating room), then a single-use, thin, transparent and flexible sterile sheath may first be placed over the handpiece assembly, after first inserting pre-sterilized single-use handpiece assembly, to ensure that the tissue incision and retrieval instrument is effectively sterile as a result of the handpiece assembly being enclosed within a sterile sheath. By way of example, a single-use sterile sheath suitable for enveloping the handpiece assembly is available from Protek Medical Products, Inc. located in Coralville, Iowa.
In carrying out the tissue incision and retrieval procedure, the distal end of the delivery cannula is positioned in confronting adjacency with the target tissue volume to be removed. The positioning step is achieved through the utilization of a forwardly disposed, surgically sharp cutting blade assembly and guided to confronting adjacency with the target tissue volume using stereotactic, ultrasound, MRI or other guidance methods suitable for locating the target tissue volume.
The delivery cannula being thus positioned, the practitioner depresses the start tissue incision and capture switch located on the handpiece assembly to commence the incision and capture of the target tissue volume. Upon depressing the start tissue incision and capture switch, the internal control system, comprising a circuit board assembly within the handpiece assembly, enters a capture mode. At the commencement of the capture mode, an electrical current is applied exclusively and only through the resistively heated portion of the cutting and pursing cable located at the distal ends of the multi-lumen flexible polymeric extrusion assembly and leaf members. The electrical current is preferably an electrical current applied at a constant level from a current source located within the handpiece assembly. The electrical current, when applied, may be delivered continuously or in a sequence of pulses.
A predetermined level of electrical current, preferably a substantially constant current, is applied only to the resistively heated portions of the cutting and pursing cables that are in contact with tissue and the electrical current is applied in conjunction with the activation of a first motor-actuated drive tube drive member translation assembly and the activation of a second motor-actuated cable mounting hub translation assembly such that the cutting and pursing cable is advancing through tissue while constant current is being applied to the cutting and pursing cable by a constant current source. The constant current source preferably operates at a frequency of at least 25 kHz and more preferably at a frequency of 100 kHz or greater. The current source preferably delivers a substantially constant current level as an alternating current at an elevated frequency of at least 25 kHz and preferably at a frequency of 100 KHz or greater to minimize the occurrence of electrical stimulation of tissue that is in contact with the resistively heated portion of the cutting and pursing cable. However, unlike prior art devices, minimal or no electrical current flows through surrounding tissue but essentially only flows through the resistively heated portions of the cutting and pursing cables.
With the commencement of the activation of the first motor-actuated drive tube drive member translation assembly in combination with the subsequent commencement of the activation of the second motor-actuated cable mounting hub translation assembly and the delivery of a substantially constant current to the resistively heated portions of cutting and pursing cable that is in contact with tissue, the tissue cutting and capture assembly commences to be deployed from the cannula distal end assembly.
The resistively heated portion of the cutting and pursing cable can be partitioned into six segments. The six segments of the resistively heated portion of the cutting and pursing cable include, in sequence, the length of resistively heated portion of the cutting and pursing cable located between [a] the first electrically and thermally conductive eyelet located at the distal end of the first electrically and thermally conductive lead wire and the eyelet disposed at the distal end of the first (adjacent) leaf member, [b] the eyelets disposed at the distal ends of the first and second leaf members, [c] the eyelets disposed at the distal ends of the second and third leaf members, [d] the eyelets disposed at the distal ends of the third and fourth leaf members, [e] the eyelets disposed at the distal ends of the fourth and fifth leaf members and [f] the eyelet disposed at the distal end of the fifth (adjacent) leaf member and the second electrically and thermally conductive eyelet located at the distal end of the first electrically and thermally conductive lead wire.
Once the tissue incision and capture process for circumscribing and capturing the target tissue volume has been completed, the delivery cannula with captured tissue specimen is removed from the body of the patient through the same incision site used to advance the delivery cannula to the site of the target tissue. The captured tissue specimen within the enveloping tissue cutting and capture assembly, an assembly that is formed by the leaf members and the multi-lumen flexible polymeric extrusion assembly, is released from the tissue cutting and capture assembly by severing the cutting and pursing cable located at the distal end of the captured tissue specimen. By way of example, the cutting and pursing cable may be severed using a small surgical scissors such as a tenotomy scissors.
If, during the capture mode, the practitioner wishes to halt the procedure, the start tissue incision and capture switch can be depressed to cause the control assembly to enter a pause mode. In this pause mode, the current applied to the resistively heated portion of cutting and pursing cable as well as the voltage applied to the first motor-actuated drive tube drive member translation assembly and the second motor-actuated cable mounting hub translation assembly are suspended. The practitioner carries out the return to the capture mode performance by again depressing the start tissue incision and capture switch.
The control system includes one or more circuit board assemblies that incorporate a current source, first and second motor drive power sources, one or more microcomputers and a circuit to continuously measure the electrical impedance of the resistively heated cutting and pursing cable circuit. By way of example of the control system, programming within a first microcomputer enables a response to the capture actuation switch disposed on the handpiece assembly, activate the audible tones and display indicator lights and to stop the procedure when capture complete state is attained. The control system also activates a visual que to indicate when the rechargeable battery within handpiece assembly requires recharging.
By way of another example of the control system, programming within a second microcomputer within a circuit board assembly uses the continuously measured values of the electrical impedance of the resistively heated cutting and pursing cable circuit to compare the amount of increase of the continuously measured electrical impedance of the resistively heated cutting and pursing cable circuit, ΔCR during a predetermined brief time interval, Δt with a pre-programmed maximum acceptable increase during the brief time step, Δt of the continuously measured electrical impedance of the resistively heated cutting and pursing cable circuit, Amax. In a preferred embodiment, the brief time interval, Δt is in the range from 0.001 to 0.003 second and the maximum acceptable increase of the continuously measured electrical impedance of the resistively heated cutting and pursing cable circuit, Amax is in the range from 0.3 to 0.5 ohm. If a measured increase in the electrical impedance of the resistively heated cutting and pursing cable circuit, ΔCR during a predetermined brief time interval, Δt exceeds the maximum acceptable increase, Amax, then the increase is attributable to a sudden loss of good electrical contact between the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets (i.e., a sudden increase in the electrical contact resistance between the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets). Upon the detection of a sudden loss of good electrical contact between the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets corresponding to the measured value of ΔCR exceeding Δmax during a brief time interval, Δt, programming within the microcomputer temporarily interrupts the supply of constant current for a predetermined time interval, Δpause while continuing to advance the multi-lumen flexible polymeric extrusion and leaf members to re-establish good electrical contact between the resistively heated portion of the cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets by increasing the contact pressure between the resistively heated portion of the cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets. In a preferred embodiment, the duration of the interruption, Δpause ranges from 0.10 to 0.30 second. A momentary loss of acceptable contact pressure between the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets can result in an associated unacceptably large increase in the electrical contact resistance at the interface between the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets thereby causing overheating of the resistively heated cutting and pursing cable and its failure through melting or a significant decrease in the load-bearing capability to withstand the tensile forces applied to the resistively heated cutting and pursing cable.
If the measured value of ΔCR exceeds Δmax during a brief time interval, Δt for five consecutive temporarily interruptions of the supply of constant current for the predetermined time interval, Δpause while continuing to advance the multi-lumen flexible polymeric extrusion and leaf members after each interruption, then programming within the second microcomputer in the circuit board assembly promptly interrupts the deployment of the tissue capture basket and begins flashing the “Capturing” indicator light, stops any further application of constant current to the resistively heated portions of the cutting and pursing cable, stops the application of voltage to the first motor and discontinues the audible tone generated by the speaker within the handpiece assembly to alert the practitioner that a malfunction has occurred.
As a result of the intentional interruption of the supply of constant current to the resistively heated cutting and pursing cable circuit upon the detection of an unacceptably large momentary increase in the measured electrical impedance within the resistively heated cutting and pursing cable circuit, the resulting high level of Joulean heating at the interface of the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets and an associated significant increase in the localized temperature of the resistively heated cutting and pursing cable is avoided. The amount of localized Joulean heating (in watts) associated with unacceptably large electrical contact resistance at the interface between the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets is equal to the product of the square of the applied constant current (in amps) and the unacceptably large value of the electrical contact resistance (in ohms) at the interface between the resistively heated portion of the cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets.
By way of another example of the control system, programming within a second microcomputer within a circuit board assembly uses the continuously measured values of the electrical impedance of the resistively heated cutting and pursing cable circuit to continuously compute the rate of increase of electrical impedance with respect to time, Rrate during a predetermined initial period of deployment, tcapture of the leaf members and the multi-lumen flexible polymeric extrusion to the maximum peripheral extent of the tissue cutting and capture assembly. If the rate of increase of electrical impedance with respect to time, Rrate during a predetermined initial period of deployment, tcapture is below a specified threshold, then it is indicative of an insufficient diameter of the captured specimen. The computed rate of increase of electrical impedance with respect to time, Rrate during a predetermined initial period of deployment, tcapture is compared with a predetermined minimum rate of increase of electrical impedance with respect to time, Rratemin. If the computed rate of increase of electrical impedance with respect to time, Rrate during a predetermined initial period of deployment, tcapture is less than a predetermined minimum rate of increase of electrical impedance with respect to time, Rratemin, then programming within the second microcomputer in the circuit board assembly interrupts the deployment of the tissue capture basket and begins flashing the “Capturing” indicator light, stops the application of constant current to the resistively heated portions of the cutting and pursing cable, stops the application of voltage to the first motor and discontinues the audible tone generated by the speaker within the handpiece assembly to alert the practitioner that a malfunction has occurred.
A series of bench-top tests were performed to measure the temperature of a constant-current resistively heated wire (viz., solid platinum wire) using resistance thermometry while the wire is cutting and advancing through a sample of ex vivo animal tissue. The diameters of the cutting wires used in these bench-top tests were selected to be similar to the diameters of the constant-current, resistively heated portions of the cutting and pursing cables (e.g., stainless steel 316 or cobalt/tungsten/chromium/nickel alloy L605). Unlike the preferred stainless steel or cobalt-based alloys preferred for the cutting and pursing cable employed in the present invention, platinum was used in these bench-top tests since its significantly larger and well-established temperature coefficient of resistance value enables the use of resistance thermometry to determine the temperature of a heated wire during tissue cutting tests. The results of bench-top tests confirmed that the average temperature of a cutting wire or cable having overall diameters in the range from nominally 0.003 inch to 0.005 inch ranges from about 350° C. to 400° C. while cutting ex vivo animal tissue at a cutting (i.e., advancement) rate of 2.3 to 3.0 mm/second. In addition, the results of bench-top tests confirmed that the average heat flux required to cut or advance at a rate of 2.3 to 3.0 mm/second through a sample of ex vivo animal tissue ranges from 150 to 220 watts/cm2. Based on the results of the cutting tests in samples of ex vivo animal tissue, the heat flux dissipated from the cutting and pursing wire employed in the tissue incision and retrieval assembly of the present disclosure is preferably at least 150 watts/cm2 and more preferably at least 220 watts/cm2.
Other objects of the present disclosure will be obvious and will, in part, appear hereinafter. The present disclosure, accordingly, comprises the method, system and apparatus possessing the construction, combination of elements, arrangement of parts and steps, which are exemplified in the following detailed description. For a fuller understanding of the nature and objects of the present disclosure, reference should be made to the following detailed description taken in connection with the accompanying drawings.
For a fuller understanding of the nature and advantages of the present method and process, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:
The drawings will be described in more detail below.
A predominate characteristic of the present disclosure resides in the employment of a single-use tissue incision and retrieval assembly in conjunction with a reusable, battery-powered handpiece assembly. In a preferred embodiment of the detailed description of the present disclosure that follows and by way example, the tissue cutting and capture assembly includes a multi-lumen flexible polymeric extrusion assembly and five leaf members oriented in a regular hexagon pattern wherein the multi-lumen flexible polymeric extrusion assembly and five leaf members are positioned at the vertices of the hexagon pattern. The tissue incision and retrieval assembly is configured with a forward portion that extends to a forwardly disposed delivery cannula distal end assembly which incorporates a mechanically sharp cutting blade. Targeted tumor or tissue along with adjacent healthy tissue is circumscribed and encapsulated by a leaf member and multi-lumen flexible polymeric extrusion assembly through the utilization of a resistively heated portion of cutting and pursing cable extending along the distal tip of each leaf member and multi-lumen flexible polymeric extrusion assembly. The resistively heated portion of cutting and pursing cable provides a thermal cutting effect by virtue of being resistively heated and maintained above a temperature threshold and heat flux level sufficient to effect thermal cutting of tissue. As the multi-lumen flexible polymeric extrusion assembly and five leaf members are advanced forwardly and radially outwardly into tissue, the resistively heated cutting and pursing cable effects the thermal cutting of tissue. Once the distal ends of the multi-lumen flexible polymeric extrusion assembly and five leaf members reach a practitioner-selected tissue diameter (e.g., 25 mm), then the handpiece assembly commences the application of a sufficient level of tension to the resistively heated portion of the cutting and pursing cable in combination with the continuing forward advancement of the multi-lumen flexible polymeric extrusion assembly and five leaf members to induce the pursing down of the distal ends of the multi-lumen flexible polymeric extrusion assembly and five leaf members. Upon completion of the pursing down of the distal ends of the multi-lumen flexible polymeric extrusion assembly and five leaf members, the incised tissue becomes circumscribed within a tissue capture basket. The forward portion of the tissue incision and retrieval system along with the tissue capture basket containing the excised volume of target tissue are then withdrawn from the body of the patient.
In a preferred embodiment, two of the four lumens within the multi-lumen flexible polymeric extrusion assembly serve as conduits for the first and second electrically and thermally conductive leads having eyelets at their distal ends. Also, in a preferred embodiment, the other two of the four lumens within the multi-lumen flexible polymeric extrusion assembly serve as conduits for the first and second tensionable portions of the cutting and pursing cable. By selecting a component orientation establishing where a pursing or constricting action commences, the maximum leading-edge periphery for capture may be elected and, typically, may range, for example, from about a 15 mm to about a 30 mm effective diametric extent.
Initial positioning of the delivery cannula tip in confronting adjacency with a tissue volume is facilitated through the utilization of a surgically sharp cutting blade assembly located at the tip. Following appropriate positioning of the tip, a motor-actuated drive tube drive member translation assembly is enabled to actuate the forward deployment of the multi-lumen flexible polymeric extrusion assembly and five leaf members wherein eyelets located at the distal ends of the multi-lumen flexible polymeric extrusion assembly and the leaf members support the resistively heated portion of the cutting and pursing cable as it incises and circumscribes the target tissue volume.
A desirable feature of the tissue incision and retrieval system of the present disclosure resides in the incorporation of the delivery cannula and cable-implemented leaf member and multi-lumen flexible polymeric extrusion assembly within a single-use support housing. That single-use support housing is removably mounted within a reusable handpiece assembly containing a first motor-actuated drive tube drive member translation assembly, a second motor-actuated cable mounting hub translation assembly, a control system and internal energy source. Hereinafter, the term energy source refers to a rechargeable battery and the two terms are equivalent. A practitioner-accessible capture size selection switch is located on the handpiece assembly for pre-selection of the diameter of a substantially spherical volume of tissue along with a practitioner-accessible display of the selected capture size enables the tissue excision and retrieval assembly to be used to incise and capture substantially spherical target tissue volumes (e.g., human breast tissue) having maximum diameter extents ranging from 15 to 30 mm. The term “cannula” or “delivery cannula” as used herein is intended to refer to any elongate surgical delivery structure, rigid or flexible, having a capability for deploying the resistively heated portion of the cutting and pursing cable.
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The tissue incision and retrieval system 10 also includes a handpiece assembly battery charger 9 that comprises an alternating current to direct current converter 3, first battery charger indicator light 4 used to provide a visual cue that handpiece assembly battery recharging is in progress, second battery charger indicator light 5 used to provide a visual cue that handpiece assembly battery recharging has been completed, handpiece assembly battery charging cable 6 and handpiece assembly battery charging cable connector 7 removably attachable to charging receptacle 14 on handpiece assembly 15.
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Upon illumination of the on/off and “Ready” indicator light 42 indicating sufficient energy stored in rechargeable battery within handpiece assembly 15, the practitioner next selects the maximum diameter of the intended tissue capture volume by depressing capture size selection switch 479 and observing selected capture size at selected capture size display 485. The practitioner next inserts the forward end 27 of delivery cannula 22 into tissue of patient's body aided by blade 31 and advances the forward end 27 of delivery cannula 22 into confronting adjacency to target tissue volume aided, for example, by ultrasound, stereotactic radiography or computer-based robotic guidance methods. Once in confronting adjacency with respect to the target tissue volume, the start tissue incision and capture switch 39 is momentarily depressed. Upon depressing the start tissue incision and capture switch 39, a visually accessible capturing indicator light 46, located distal to the start tissue incision and capture switch 39, on handpiece assembly 15 is singularly illuminated. By way of example, capturing indicator light 46 may be a green light emitting diode (LED). In addition to a visually accessible capturing indicator light 46, an audible cue may be generated within the handpiece assembly 15 that continues throughout the period of tissue incision and capture procedure.
Upon completion of the tissue incision and capture procedure, as determined by the controller within the handpiece assembly 15, based on the measured electrical impedance of that portion of the heatable cutting and pursing cable conducting the applied constant current, the capture complete indicator light 52 is singularly illuminated, the applied constant current and the applied voltage to the first motor-actuated drive tube drive member translation assembly is suspended, the second motor-actuated cable mounting hub translation assembly and the audible cue is suspended. At the completion of the tissue incision and capture procedure, the practitioner withdraws the distal end portion of delivery cannula 22 from the patient, which includes the captured and substantially spherical tissue volume.
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The constant current source 247 supplies constant current to the first through sixth segments of the resistively heated portion of the cutting and pursing cable 89-94, as described in greater detail in the specification that follows. Circuit board assembly 184 includes [a] circuitry and logic to respond to first, second and third sensor switches 48, 49 and 479, [b] circuitry and logic to control illumination of light emitting diodes 44, 50, 54, [c] circuitry to display selected size (diameter) of target tissue volume 354 (as seen in
Advantageously, all penetrations through the left and right housing sides 16 and 18 including waterproof switch housing 38, light emitting diodes 44, 50, 54 and charging receptacle 14 as well as the joining together of the left and right housing sides 16 and 18 are assembled with water-tight seals. In addition, as seen in
During cleaning and disinfecting operations performed between uses of the reusable handpiece assembly 15, the temporary placement of sealing cap 155 in combination with O-ring 156 (as seen in
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Likewise, the exploded view seen in
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In a preferred embodiment and referring to
Circuitry within the circuit board assembly 184 located within the handpiece assembly 15 continuously measures the voltage level applied to the resistively heated portion of cutting and pursing cable, i.e., that portion of the cutting pursing cable residing within and distal to the first and second electrically and thermally conductive eyelets 446 and 450, respectively, that supply constant current to the resistively heated portion of cutting and pursing cable as seen in
As seen in
The single-use tissue incision and retrieval assembly 12 with single-use support housing 100 and delivery cannula 22 is illustrated in detail in connection with
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First and second drive nuts 182a and 182b are seen in
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In a preferred embodiment and referring to
In order to more fully understand the apparatus structure and method of operation, the construction and functional regions of the cutting and pursing cable is now described in greater detail. Referring to
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An alternative embodiment for a multi-lumen flexible polymeric extrusion assembly is the multi-lumen flexible polymeric extrusion assembly 427 incorporating two oval lumens and two round lumens is seen in
The oval lumens 510 and 512 within multi-lumen flexible polymeric extrusion member 508 enable the use flat electrically and thermally conductive lead wires 518, 520 having a through hole of diameter D5 that functions as an eyelet 533 as seen in
In the preferred embodiment of the multi-lumen flexible polymeric extrusion assembly 427 seen in
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Hereinafter in the present disclosure, references to the multi-lumen flexible polymeric extrusion assembly may apply interchangeably to either [a] the multi-lumen flexible polymeric extrusion assembly 426 seen in
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As described in the foregoing specification and seen in
The essential requirement that constant current be confined to flow within only the resistively heated portion of the cutting and pursing cable that is in contact with and distal to the electrically and thermally conductive eyelets as well as the confinement of the flow of constant current within only the resistively heated portion of the cutting and pursing cable that is in direct thermal contact with tissue is more fully understood by examining the rate of power dissipation and corresponding temperature of the cutting cable that is required to incise tissue. In this regard and referring to
Based on the preferred range of diameters for the cutting and pursing cable, the two diameters of the substantially pure platinum wire used in the bench-top cutting of samples of ex vivo animal tissue 251 (e.g., steak tissue) using the test fixture schematic seen in
The two selected diameters of platinum wire 250 in the experimental ex vivo tissue cutting apparatus 242 seen in
The silver tubes 249a and 249b are supported in an electrically insulative silver tube holder 248 that maintains the length of the heatable platinum wire 250 during each cutting test on sample of ex vivo animal tissue 251 as seen in
The width of the sample of ex vivo animal tissue 251 during cutting with the heated platinum wire 250 is slightly less than the spacing between the inside boundary surfaces of the two silver tubes 249a and 249b so that the silver tubes 249a and 249b slide freely over the outside faces of the sample of ex vivo animal tissue 251 as seen in
Still referring to
The electrical resistance of the nominal 0.003-inch diameter platinum wire 250 and the nominal 0.005-inch diameter platinum wire 250 used in cutting tests was determined at room temperature (nominally 20° C.) with auxiliary cooling of the platinum wire during the application of a constant test current of about 0.2 to 0.3 amps. The resistance of each platinum wire 250 was calculated using Ohms Law, wherein the electrical resistance, R (in unit of ohms) is equal to the voltage difference across an electrical conductor, V (in unit of volts) divided by the electrical current flowing through the conductor, I (in units of amperes). Likewise, during a tissue cutting test, a pre-selected constant current level 261 was applied to the platinum wire while it is in direct contact with the ex vivo animal tissue 251 as seen in
The test procedure specified above was used to perform cutting tests performed on samples of ex vivo animal tissue 251 using a solid platinum wire 250 having a nominal diameter of 0.003 inch or 0.005 inch. The first step in the test protocol was to compare the voltage levels for two battery voltage sources, viz., a nominal 1.5-volt primary battery (not shown) and a nominal 9.0-volt primary battery (not shown). The measured voltage values using the second digital voltmeter 246 (used for measuring the voltage difference across the platinum wire support posts) and the first digital voltmeter 243 (used for measuring the voltage difference across the current shunt resistor) were within 0.05% and 0.07% for the nominal 1.5-volt and 9.0-volt battery sources, respectively. The confirmed close agreement between the two voltage measuring instruments, upon calibration in the voltage range to be used for the subsequent tests, assured the accuracy of the measurements of the resistance of the platinum wire 250 at 20° C. and subsequently the resistance of the platinum wire 250 at an elevated temperature during the period in which a constant current 261 is flowing in the platinum wire 250. In addition, since the electrical resistance of the platinum wire 250 under various applied constant current levels is calculated based on the ratio of the voltages measured using first digital voltmeter 243 and second digital voltmeter 246 during the cutting of each sample of ex vivo animal tissue 251, any bias in the closely agreeing voltage meters would effectively be cancelled out as a result of the ratiometric analysis.
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The rate of cutting by the heated platinum wire 250 through the sample of ex vivo animal tissue 251 was determined primarily by the pre-selected constant current level. The higher the constant current level, the greater the heating rate generated within the platinum wire 250 and the greater the heat flux dissipated at the surface of the platinum wire 250 and, correspondingly, the higher rate of cutting of the sample of ex vivo animal tissue 251. Correspondingly, the higher the constant current level, the higher the temperature of the platinum wire 250 during the thermal cutting through the sample of ex vivo animal tissue 251.
For the case of the nominal 0.005-inch diameter platinum wire, an acceptably fast cutting rate through the ex vivo animal tissue 251 was achieved at a constant current level of 4.859 amps (see Test No. 1 in Table 1). An even faster rate of cutting rate through the ex vivo animal tissue 251 was achieved at a constant current level of 5.335 amps but significantly exceeded the actual cutting rate intended for the deployment of the cutting and capture assembly 329 through in vivo tissue tests in actual incision and capture of en bloc tissue samples within the body of human patients. For the case of an actual applied constant current level of 4.859 amps, the measured cutting rate was 2.3 mm/second. The measured cutting rate of 2.3 mm/second is within the preferred range of 2.0 to 3.0 mm/second for of advancement of the cutting and capture assembly 329 being driven by the first motor actuated drive tube drive member translation assembly 180a as seen in
For the case of the nominal 0.003-inch diameter platinum wire 250, an acceptably fast cutting rate through the sample of ex vivo animal tissue 251 was achieved at a constant current level of 2.709 amps as seen in Test Nos. 5 and 6 of
Table 1. For the case of an applied constant current level of 2.709 amps, the measured cutting rate was 2.8 to 2.9 mm/sec, which is slightly greater the intended rate of advancement of the cutting and capture assembly 329 and may enable the completion of the incision and capture of an en bloc tissue specimen within a patient during a shorter period of power application.
The calculated resistances of the heatable platinum wire at 20° C. and during the period of heating using an applied constant that provides an adequate cutting rate (e.g., 2.7 amps for the nominal 0.003-inch diameter platinum wire) were used in conjunction with the known temperature coefficient of resistance of platinum (viz., 3927 ppm/C) to calculate the temperature of the heated platinum wire during the application of a known constant current level. The video recording of the voltage values displayed by the first digital voltmeter 243 and second digital voltmeter 247 during the brief period (e.g., 2 to 3 seconds) that the platinum wire 250 traverses the sample of ex vivo animal tissue 251 was used to determine the average of the voltage differences between the two silver tubes 249a and 249b measured by the second digital voltmeter 246 and, hence, across the platinum wire 250 during the application of a constant current 261.
The electrical resistance, RT of a conductor (in Ohms) at an elevated temperature, T (in degrees Celsius) is given by the relationship:
where R0 is the measured electrical resistance of the conductor at a known temperature, T0 (in degrees Celsius) and a is the known temperature coefficient of electrical resistance of the conductor (in ppm per degree Celsius). For the case of a pure platinum conductor, the term a is equal to 3927 ppm/C or 0.003927 per degree C. Rearranging the terms of Equation 1 to express the unknown temperature, T as a function of the known and measured quantities gives the relationship:
The above Equation 2 was used to calculate the temperature of the platinum heating wire 250 during the period in which a constant current 261 is applied to heat the platinum wire 250 and enable the cutting of sample of ex vivo animal tissue. The average of the calculated temperatures of the platinum wires 250 having nominal diameters of 0.003 inch and 0.005 inch for various levels of applied constant current are presented in Table 1.
As seen in Table 1 for Test No. 3, based on a heated 0.0048-inch diameter platinum wire 250 while cutting a sample of ex vivo animal tissue that is initially at room temperature (i.e., nominally 20° C.) and achieving a cutting rate that is comparable to the cutting rate using the motor-driven tissue cutting and capture assembly 329, the average calculated temperature of the platinum wire 250 is 373° C. By comparison, as seen in Table 1 for Test Nos. 5 and 6 based on a heated 0.0029-inch diameter platinum wire 250 while cutting a sample of ex vivo animal tissue 251 that is initially at room temperature (i.e., nominally 20° C.) and achieving a cutting rate that is comparable to the cutting rate using the motor-driven tissue cutting and capture assembly 329, the average calculated temperatures of the platinum wire temperature ranges from 358° C. to 363° C.
Based on the results of the cutting tests in samples of ex vivo animal tissue 251 using the ex vivo animal tissue cutting apparatus 242 seen in
The cutting tests in samples of ex vivo animal tissue 251 using the ex vivo animal tissue cutting apparatus 242, as seen in
Based on the established preferred heat flux from the multi-wire cutting cable (viz., at least 150 watts/cm2 and preferably 220 watts/cm2), the level of constant current that needs to conducted through the first through sixth segments of the resistively heated portion of the cutting and pursing cable 89-94 can be derived using the Joule-Lenz Law (also known as Joule's First Law combined with Ohm's Law). According to the Joule-Lenz Law, the power or the heating, P (also known as Joulean heating) can be expressed as the product of the square of the current, I and the resistance of the conductor, R as seen below in Equation 3:
The minimum and preferred heat fluxes (i.e., heating power, P dissipated per unit surface area, A of the cutting wire or cable) of 150 watts/cm2 and 220 watts/cm2, respectively, can be converted into the unit of heating power per unit length, L of the first through sixth segments of the resistively heated portion of the cutting and pursing cable 89-94 by dividing the preferred heat flux by the circumference, Ccable of the assumed-round first through sixth segments of the resistively heated portion of the cutting and pursing cable 89-94. Recall that the surface area, A of a length, L of a round wire or cable having a diameter, Dcable is given by the equation:
The cross-section of an individual cutting and pursing cable 33 within the tissue incision and retrieval assembly 12, is seen in
By way of example, a preferred construction for cutting and pursing cable 33 is manufactured by Fort Wayne Metals, Inc. (Fort Wayne, Indiana) and comprises seven individual cobalt/chromium/tungsten/nickel alloy L605 wires 34a-34g in full-hard temper, each wire 34 having a diameter, D15 of 0.0013 inch to produce an overall nominal diameter, D16 for cutting and pursing cable 33 of 0.0039 inch (0.00991 cm). The electrical resistance of this second preferred construction for cutting and pursing cable 33 was determined by measuring a known length of cable (e.g., 60 cm) at a room temperature of about 20° C. using a digital ohmmeter. The cable resistance per centimeter length was determined by dividing the measured resistance (in units of ohms) by the length of cable included in the resistance measurement. Using the above resistance measurement method, the resistance per unit length, R/L at 20° C. for the second preferred construction of cutting and pursing cable 33 was determined to be 1.63 ohms/cm. Based on measurements performed within the testing laboratory of the cable manufacturer, Fort Wayne Metals, the cable break strength at 20° C. for the second preferred cable construction was determined to be 3.18 pounds (force).
Referring now to Equation 4, the peripheral surface area of a unit length of cutting and pursing cable 33 of one centimeter is equal to the product of 3.1416 and the diameter, D16 of cutting and pursing cable 33. For the case of a preferred cable design having a nominal cable diameter of 0.00991 cm, the surface area of cutting and pursing cable 33 per unit (centimeter) length is 3.1416×0.00991 cm×1.0 cm or 0.0311 cm2. Based on the established minimum heat flux of 150 watts/cm2 and preferred heat flux of 220 watts/cm2 emanating from the surface of the multi-wire cutting cable, the amount of resistive heating power (i.e., Joulean heating) required per centimeter of cable length, P/L to generate the minimum heat flux of 150 watts/cm2 and preferred heat flux of 220 watts/cm2 can be derived by the product of the required minimum and preferred heat fluxes (viz., 150 and 220 watts/cm2, respectively) and the surface area of a unit cable length of one centimeter (0.0331 cm2), the products computed to be 4.97 and 7.28 watts per centimeter length, respectively.
As described above and seen in
The power dissipation rates per unit length for cutting and pursing cable 33 having a preferred diameter of 0.0039 inch were derived above based on measurements of the power, cutting wire temperature and heat fluxes required for the cutting of ex vivo animal tissue at a known cutting rates. These derived power dissipation rates per unit length for cutting and pursing cable 33 are next compared with the theoretical power dissipation rates per unit length of resistively heated portion of cutting and pursing cable derived based on the assumption of “thermal cutting” of tissue. As used herein, the term “thermal cutting” refers to a cutting mechanism wherein the incision of tissue is the result of the vaporization of liquid contained in the cells of tissue and consequent mechanical fracturing of the cell walls as a result of the volumetrically expanding vapor phase of liquid being vaporized. It is well known that cells in human or animal tissue contain about 70% water (see Cooper, G., The Cell: A Molecular Approach. 2000; Sinaeur Associates, Inc., Sunderland, Massachusetts). Assuming a preferred cutting and pursing cable diameter, Dcable of 0.0099 cm, a cutting rate of 2.3 mm/second and a cut duration, tout of 1.0 seconds during which the resistively heated portion of the cutting and pursing cable of length equal to 1.0 centimeter is advanced through tissue, the volume of tissue traversed by the resistively heated portion of cutting and pursing cable is the product of the width of the incision, Wincision×length of the cable, Lcable×length of the incision, Lcut wherein the width of the incision, Wincision 20% greater (or a factor 1.2 greater) than the resistively heated portion of cutting and pursing cable diameter, Dcable due to the combination of conduction and radiation heat transfer into the tissue on either side of the resistively heated portion of cutting and pursing cable. In this example, the volume of tissue thermally cut is 0.0099 cm×1.2×0.23 cm×1.0 cm or 0.0019 cm3. The corresponding mass of the tissue is the product of the total volume of tissue traversed by the resistively heated portion of cutting and pursing cable and the density of water (viz., 1.0 gram/cm3) or 0.0019 grams.
In adult women, the water-content represents between 50% and 70% of the mass of normal breast tissues. In this regard, see Conceicao, A. L C., et. al., The Influence of Hydration on the Architectural Rearrangement of Normal and Neoplastic Human Breast Tissues. Heliyon 2015; 5:1-13. The water-content, WC of the mass of tissue in the present example is assumed to be 70% to assure that the amount of energy transferred to the tissue during thermal cutting of tissue is sufficient to sustain the vaporization of cellular water that is required for the thermal cutting of tissue. Assuming water, having a density, dwater equal to 1.0 gram/cubic centimeter, comprises about 70% of the mass of tissue, then the mass, mwater of water vaporized for the resistively heated portion of cutting and pursing cable having length, Lcable of 1.0 cm is given by the equation:
By way of example, for the case of a preferred design for the cutting and pursing cable 33 seen in
where Cwater is the well-known specific heat of water (viz., 1 calorie/gram-C), ΔT is the temperature rise of cellular water at normal body temperature of 37° C. to the boiling point of water of 100° C. and LHwater is the well-known latent heat of vaporization of water of 540 calories/gram corresponding to the energy required to convert the liquid phase of water at 100° C. to the vapor phase of water at 100° C. Substituting these known values into Equations 6 through 8 corresponding to the assumed thermal cutting of tissue by vaporization of cellular water yields the following amounts of thermal energy per unit length of cut of 1.0 cm for the case of a cutting and pursing cable 33 having a diameter of 0.0039 inch:
Referring to
wherein the multiplying factor 1.2 refers to the increased effective width of the path of thermal cutting of tissue due to heat that is conducted and radiated into the tissue beyond the boundary diameter, Dcable of the resistively heated portion of cutting and pursing cable as it advances through tissue.
The length of the tissue being thermally cut, Lcut can be expressed as the product of the cutting rate, Rcut and the duration of cut, tcut as follows:
Substituting Equation 6B into Equation 6A yields the following equation:
wherein the density of cellular water, dwater has the value 1.0 gram/cm3, Dcable is in units of centimeters, Rcut is in units of centimeters/second, tout is in units of seconds, WC is a unitless fractional value corresponding to water content, Cwater is in units of calories/gram-° C., LHwater is in units of calories/gram, Qcut is in units of calories and the length of the resistively heated portion of cutting and pursing cable that thermally cuts through tissue is fixed value of 1.0 centimeter for the purpose of calculations.
The amount of energy, Qcut delivered to a length of tissue being cut, Lcut by the resistively heated portion of cutting and pursing cable (in units of calories) as seen in Equation 6C can be expressed as a rate of energy application per unit time, Qcut/tcut (in units of calories/second) by dividing both sides of Equation 6C by the duration of cut, tout, and assigning a value of 1.0 second to the duration of cut, tout yielding the following equation:
The amount of thermal energy, Qcut required for the thermal cutting of tissue for a duration of cut, tout having the value 1.0 second as seen in Equation 6D can next be converted into the amount of power required, Pout for the thermal cutting of tissue by converting the energy unit calories into Joules. Since 1.0 calorie is equivalent to 4.186 Joules and 1.0 Joule/second is equivalent to 1.0 watt, then Equation 6D can be expressed as follows:
By way of example, the well-known values for the density of water (viz., 1.0 gram/cm3), an length of the resistively heated portion of cutting and pursing cable of 1.0 centimeter for the purpose of calculations, the specific heat of water, Cwater (Viz., 1.0 calorie/gram-° C.), the latent heat of vaporization of water, LHwater (viz., 540 calories/gram), the amount of increase in tissue temperature, ΔT to elevate cellular water from a normal body temperature of 37° C. to the boiling point of water of 100° C. (viz., 63° C.) and the published water content of breast tissue (viz., 70%) can be substituted into Equation 6E. In addition, also substituting the values of the diameter of the resistively heated portion of cutting and pursing cable, Dcable (viz., 0.0099 centimeters) and rate of cutting, Rcut (viz., 0.23 centimeters/second) used by the applicant in laboratory testing of a prototype tissue incision and retrieval system as seen in
In the above example, the calculated amount of power or resistance heating (viz., 4.83 watts) represents the minimum amount of power that needs to applied to the six segments of the resistively heated portion of the cutting and pursing cable 89-94 (as seen in
The amount of resistance heating, also known as Joulean heating, in the resistively heated portions of the cutting and pursing cable can also be expressed in terms of the cable electrical resistance, Rcable and the minimum level of substantially constant current, Icut conducted through the resistively heated portion of the cutting and pursing cable as specified in Equation 3 above. Substituting Equation 3 into Equation 6E yields:
Expressing Equation 6G in terms of the minimum level of substantially constant current, Icut required for the thermal cutting of tissue provides an equation for the calculation of the minimum level of substantially constant current required, Icut to achieve the thermal cutting of tissue for [a] a selected cable material having a resistance per 1.0 cm length of cable, Rcable, [b] a diameter of the resistively heated portion of the cutting and pursing cable, Dcable, [c] a selected tissue cutting rate, Rcut and [d] tissue having a water content per unit mass, WC.
Equation 6H can be further generalized by expressing the electrical resistance of the cable in terms of the electrical resistivity of the cable material at a nominal temperature of 400 C, a unit length of the cutting cable, Lcable and the conduction area of the cable, Aconduction. The electrical resistance, Rcable of the resistively heated portion of the cutting and pursing cable is the product of the electrical resistivity of the cable, ρcable and the length of the cable, Lcable divided by the cross-sectional area, Aconduction Of the current conductor(s) as shown in the following equation:
The total cross-sectional area for conduction of electrical current, Aconduction in Equation 6I can be expressed as follows:
where N is the number of individual wires 34 in the cutting and pursing cable 33 (as seen, for example in
Substituting Equation 6I into Equation 6H provides the equation for the minimum level of substantially constant current required for the cutting of tissue with a cable, or alternatively a single wire, as follows:
Substituting Equation 6J into Equation 6K provides a generalized equation for the thermal cutting of tissue having [a] known water content, WC, [b] the resistively heated portion of the cutting and pursing cable having known electrical resistivity and dimensions and [c] advancing through tissue at a known cutting rate, Rcut as follows:
As seen in Equation 6L, the length of the resistively heated portion of the cutting and pursing cable, Lcable appears in both the numerator and denominator and therefore cancels from the equation. Hence, the equation for the thermal cutting of tissue having [a] known water content, WC, [b] the resistively heated portion of cutting and pursing cable having known electrical resistivity and dimensions and [c] advancing through tissue at a known cutting rate, Rcut seen in Equation 6L is independent of the length of the resistively cutting portion of the cutting and pursing cable. Also, referring to Equation 6L, for the alternative embodiment wherein the cutting and pursing cable comprises a single wire, the value of N in Equation L is 1. After canceling the term Lcable that appears in both the numerator and denominator of Equation L, the generalized equation for the thermal cutting of tissue can be expressed, as follows:
By way of example, the minimum level of substantially constant current, Icut required for the thermal cutting of tissue can be calculated for the case of the actual apparatus and test parameters utilized in laboratory testing performed by the applicant. The actual apparatus, known thermo-physical properties and test parameters utilized in laboratory testing performed by the applicant are as follows: [a] the electrical resistively ρcable for the Haynes 25 (also known as L605) cable at a nominal tissue cutting temperature of 400 C is 98.5×10−6 ohm-cm, [b] the diameter of the cable Dcable is 0.0099 cm, [c] the diameter of seven individual wires in the cable, Dwire is 0.0033 cm, [d] the rate of tissue cutting Rout is 0.23 cm/second, [e] the water content fraction of tissue WC is 70%, [f] the specific heat of water, Cwater is 1.0 cal/gram-C, [g] the temperature increase, ΔT required to raise the cellular liquid in tissue being thermally cut from body temperature of 37° C. to the boiling of water, 100° C. is 63° C. and [h] the latent heat of vaporization of water in cells being thermally cut is 540 calories/gram Since the cable length, Lcable appears in both the numerator and denominator of Equation 6L, this term cancels out and the calculated minimum level of substantially constant current required for the thermal cutting of tissue is independent of the length, Lcable of the resistively heated portion of the cutting and pursing cable. Using the above values for all of the parameters on the right side of Equation 6L yields the calculated minimum level of substantially constant current of 1.71 amps that is required for the thermal cutting of tissue. During laboratory testing using a prototype tissue incision and retrieval system 10 as illustrated in
The minimum amount of power required, Pout for the thermal cutting of tissue, as seen in Equation 6E, can also be expressed as the minimum heat flux, Pcut/Asurface required for the thermal cutting of tissue by dividing both sides of Equation 6E by the surface area, Asurface for a known length, Lcable of the resistively heated portion of cutting and pursing cable 33. The surface area, Δsurface for a known length, Lcable of the resistively heated portion of the cutting and pursing cable 33 is the product of the circumference and length of the resistively heated portion of the cutting and pursing cable and the can be defined as follows:
Dividing both sides of Equation 6E by the surface area of the cable, Asurface provides an equation for the minimum heat flux required for the thermal cutting of tissue can be expressed as follows:
As seen in Equation 60, the cable length, Lcable appears in both the numerator and denominator of Equation 60 and therefore this term cancels out and the calculated minimum heat flux, Pcut/Asurface required for the thermal cutting of tissue is independent of the length, Lcable of the resistively heated portion of the cutting and pursing cable. After canceling out the terms for the cable length, Lcable in Equation 60, the generalized equation for the minimum heat flux required for the thermal cutting of tissue can be expressed as follows:
By way of example, the minimum heat flux, Pcut/Asurface required for the thermal cutting of tissue can be calculated for the case of the actual apparatus and test parameters utilized in laboratory testing performed by the applicant. The actual apparatus, known thermo-physical properties and test parameters utilized in resistively ρcable for the Haynes 25 (also known as L605) cable at a nominal tissue cutting temperature of 400 C is 98.5×10−6 ohm-cm, [b] the diameter of the cable Dcable IS 0.0099 cm, [c] the diameter of seven individual wires in the cable, Dwire is 0.0033 cm, [d] the rate of tissue cutting Rout is 0.23 cm/second, [e] the water content fraction of tissue WC is 70%, [f] the specific heat of water, Cwater is 1.0 cal/gram-C, [g] the temperature increase, ΔT required to raise the cellular liquid in tissue being thermally cut from body temperature of 37° C. to the boiling of water, 100° C. is 63° C. and [h] the latent heat of vaporization of water in cells being thermally cut is 540 calories/gram. Using the above values for all of the parameters on the right side of Equation 6N yields the calculated minimum heat flux, Pcut/Asurface of 155 watts/cm2 that is required for the thermal cutting of tissue.
As seen above in Table 1 for Test No. 3, the laboratory testing performed to determine the minimum level of constant current required for the thermal cutting of tissue using the same cable diameter, Dcable (viz., 0.0099 cm) and rate of cutting, Rcut (viz., 0.23 cm/sec.) as used in the above calculation of the minimum heat flux required for thermal cutting, the measured heat flux during laboratory testing was 150 watts/cm2. The close agreement between actual laboratory measurement of the actual minimum heat flux required for the thermal cutting of tissue (viz., 150 watts/cm2) and the calculated minimum heat flux required for the thermal cutting of tissue (viz., 155 watts/cm2) provides validation of the generalized Equation 6N for the calculation the minimum heat flux required for the thermal cutting of tissue.
As discussed above, the mechanism of thermal cutting of tissue is the advancement of a resistively heated cable, operating at a temperature of about 400° C., through soft tissue. The confinement of electric current to flow only within the cable, the cable having an electrical resistance that is orders of magnitude lower than the surrounding soft tissue, effectively avoids the flow of any electrical current into the adjacent tissue. Hence, the thermal cutting of tissue involves only the conduction of heat into the adjacent tissue during tissue cutting. Consequently, due to the small diameter of the cutting cable (e.g., 0.0039 inch) and the rate at which the cable is advanced through the tissue, the small cable surface area in contact with tissue combined with the brief contact period results in a depth of thermal injury at the surface of the captured tissue specimen that is limited to less than about 0.001″ to 0.002″. As a consequence of the very thin layer of thermal injury on the surface of the captured tissue specimen, as defined by the circumscribing tissue capture basket seen in FIG. 25, essentially all of the captured tissue specimen is suitable for post-excision examination by a pathologist and, importantly, the assessment of the extent of malignancy-free (i.e., “clear” or healthy) margins around any identified malignant lesion.
In contrast, electrosurgical cutting of tissue with a wire or cable in prior art devices requires the flow of electrical current from a wire or cable into and through the tissue being incised wherein an electrical arc is formed in the gap between the wire or cable and the tissue as a result of application of a high voltage difference between the wire or cable and the tissue, typically at a level of greater than 1000 volts (peak-to-peak) at a frequency of at least 300 kHz. In the case of electrosurgical cutting to excise and capture a volume of tissue, as specified in U.S. Pat. No. 6,471,659 and incorporated in its entirety herein by reference, the essential flow of electrical current into and through adjacent tissue to achieve tissue cutting may cause unwanted heating of adjacent tissue well beyond the path of tissue cutting that can result in significant thermal damage to nerves and cause pain due to the effect of unwanted current flow in regions of the body beyond the region of applied local anesthesia. The thermal damage to portions of the excised volume of captured tissue is disadvantageous in that the damaged portions of the captured tissue specimen, intended for subsequent examination by a pathologist, are compromised and limit the available portions of the capture tissue specimen suitable for such examination by a pathologist (e.g., assessment of the boundary between malignant and healthy tissue).
The test procedure described above to perform cutting tests performed on samples of ex vivo animal tissue 251 using a solid platinum wire 250, having a nominal diameter of 0.003 inch or 0.005 inch, enabled the estimation of the temperature of a cutting wire or cable during the thermal cutting of tissue at a preferred rate of 2.3 to 2.7 mm/second. Based on the above-described thermal cutting tests in ex vivo animal tissue, the temperature of the cutting wire or cable was calculated to be in the range of 350° C. to 400° C. The resistance per unit length of the first through sixth segments of the resistively heated portion of the cutting and pursing cable 89-94 can next be estimated assuming a cutting cable temperature at the upper end of this range, viz., at 400° C. According to Page 8 of the technical data brochure (Catalog H-3057G available from Haynes International, Kokomo, Indiana) for the cobalt/chromium/tungsten/nickel alloy known as Haynes 25 (also known as L605), the measured electrical resistivity values for Haynes 25 at 20° C. and 400° C. are 88.6 and 98.5×10−6 ohm-cm, respectively. The electrical resistivity values indicate that the resistance of a Haynes 25 cable exhibits a temperature associated coefficient of 1.201 that results in a cable resistance that is 1.251× higher at 400° C. than at 20° C. (i.e., room temperature).
As stated above, the measured electrical resistance per unit centimeter length for the second preferred design for cutting and pursing cable 33 having a nominal diameter of 0.0039 inch is 1.63 ohm/cm at 20° C. Using the manufacturer supplied electrical resistivity values for L605 at 20° C. and 400° C., the electrical resistance per unit centimeter length measured at 20° C. can be estimated for the cable operating at a temperature of 400° C. (i.e., the expected cable temperature during thermal cutting of tissue) by the product of the electrical resistance at 20° C. (viz., 1.63 ohms/cm) and the temperature associated coefficient of 1.251 resulting in an estimated electrical resistance per unit centimeter length for the first preferred design for cutting and pursing cable 33 of 1.81 ohms/cm at an operating temperature of 400° C.
The required level of the constant current flowing in the first through sixth segments of the resistively heated portion of the cutting and pursing cable 89-94 to achieve thermal cutting of tissue at a rate of 2.3 to 2.7 mm/second can now be estimated. The estimated required constant current level is based on the above measured and derived properties of cutting and pursing cable 33 in combination with the experimentally determined level of the preferred heat flux of 220 watts/cm2 emanating from cutting and pursing cable 33 during the thermal cutting of tissue. The required level of constant current required for thermal cutting of tissue can be estimated based the Joule-Lenz Law in combination with the above derived values for the required resistive heating power per unit length, P/L and the electrical resistance per unit length, R/L of the first through sixth segments of the resistively heated portion of the cutting and pursing cable 89-94. The above Equation 3 can be revised to express the required constant current, Iconstant in terms of the required power dissipation per unit 1.0 cm length, P/L at the preferred heat flux of 220 watts/cm2 and the measured electrical resistance adjusted to an operating temperature of 400° C.
For the case of a preferred design for cutting and pursing cable 33 having a nominal diameter of 0.0039 inch and operating at the preferred heat flux of 220 watts/cm2, the resistive heater power per unit centimeter length of the first through sixth segments of the resistively heated portion of the cutting and pursing cable 89-94 was determined to be 7.28 watts/cm based on cutting tests at constant current in ex vivo animal tissue, as discussed above. Also, as discussed above, the calculated electrical resistance per unit centimeter length, R/L of the first through sixth segments of the resistively heated portion of the cutting and pursing cable 89-94 was determined to be 1.81 ohms/cm at an operating temperature of 400° C. Based on Equation 9, the required level of constant current, Icurrent to generate a preferred heat flux of 220 watts/cm2 within a cutting and pursing cable 33 having a nominal diameter of 0.0030 inch and operating at a temperature of 400° C. is 2.01 amps.
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The levels of constant current required for the thermal cutting of tissue by the first through sixth segments of the resistively heated portion of the cutting and pursing cable 89-94 in direct contact with tissue would result in very high temperatures if the constant current levels were required to flow in the first and second tensionable portions of the cutting and pursing cables 118 and 119, respectively, since these tensionable portions of the cutting and pursing cable are not in contact with tissue but are surrounded by a thermally insulative layer of air and/or a thermally insulative interior wall of a lumen of the multi-lumen flexible polymeric extrusion 420 or 508. Due to the low thermal conductivity of the air that surrounds the first and second tensionable portions of the cutting and pursing cables 118 and 119, respectively, the largest portion of the heat dissipation from the surface of the cutting and pursing cable 33 in the tensionable portions of the cutting and pursing cables would be heat dissipation by radiation heat transfer. According to the Stefan-Boltzmann Law, assuming the maximum radiation emittance of 1.0 from the surface of cutting and pursing cable 33 (i.e., also known as black body radiation), radiated heat flux, Wradiation can be expressed as the fourth power of absolute temperature, Tabsolute as seen below in Equation 10 (McAdams, W., Heat Transmission. 1954; McGraw-Hill Book Company, New York: 59-60).
where σ is the Stefan-Boltzmann constant equal to 5.67×10−12 watts/cm2-K−4 and the absolute temperature is the temperature in units of ° K or temperature in ° C. plus 273° C. Since the preferred heat flux of 220 watts/cm2 has been established based on cutting tests in ex vivo animal tissue, as described above, and the associated constant current levels required to achieve the preferred heat flux for the two preferred diameters of cutting and pursing cable 33, Equation 10 can solved for the estimated cable temperature if the same heat flux of 220 watts/cm2 is required to be dissipated for the case in which the cutting and pursing cable 33 is in air and not in contact with tissue.
Based on operation at a constant current level sufficient to generate the preferred heat flux required for thermal cutting of tissue, the calculated temperature assuming black body radiation (i.e., the maximum achievable radiation heat transfer) is 2,496° K or 2,223° C. This calculated temperature is more than 800° C. higher than the melting point of any metal alloy (L605 alloy or austenitic stainless steel alloys) that could be selected for the manufacture of cutting and pursing cable 33. In addition, such high temperatures in electrical leads would result in significant thermal damage and the melting of plastic components with the tissue incision and retrieval assembly 12. Hence, the present disclosure specifies apparatus and methods that are essential for the conduction of constant current only through low-resistance electrically conductive paths that extends from the current source within circuit board assembly 184 to the location that the cutting and pursing cable 33 is in sliding electrical contact with first and second electrically and thermally conductive eyelets 446 and 450, respectively.
By way of example, the low-resistance electrical current flow paths are seen in
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In a preferred construction of the tissue incision and retrieval assembly 12 of the present disclosure seen in
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By way of example, surgically sharp blade 31 seen in
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The mechanism of thermal cutting of tissue using a resistively heated wire or cable allows only the conduction of heat into adjacent tissue and avoids any flow of electrical current into the adjacent tissue. As a consequence, the depth of unwanted thermal injury at the surface layer of the captured tissue specimen is limited to less than about 0.001″ to 0.002″. In contrast, electrosurgical cutting of tissue with a wire or cable in prior art devices requires the flow of electrical current from the wire or cable into and through the tissue being incised wherein an electrical arc is formed in the gap between the wire or cable and the tissue as a result of application of a high voltage difference between the wire or cable and the tissue, typically at a level of greater than 1000 volts (peak-to-peak) at a frequency of at least 300 kHz. In the case of electrosurgical cutting to excise and capture a volume of tissue, as specified in U.S. Pat. No. 6,471,659 and incorporated herein by reference, the essential flow of electrical current into and through adjacent tissue to achieve tissue cutting may cause unwanted heating of adjacent tissue well beyond the path of cutting resulting in thermal damage to portions of the excised volume of captured tissue. The thermal damage to portions of the excised volume of captured tissue are disadvantageous in that the damaged portions of the captured tissue specimen, intended for subsequent examination by a pathologist, are compromised and limit the available portions of the capture tissue specimen suitable for such examination (e.g., assessment of the boundary between malignant and healthy tissue).
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The range of preferred dimensions for the various components seen in
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Once first and second tensioning portions 118 and 119 of the cutting and pursing cable 33 become constrained as the cable mounting hub 296 abuts the second pivoting drive finger 185b, secured to second transition nut 182b as part of second motor-actuated cable mounting hub translation assembly 180b, then the pursing down of the distal ends of the first through fifth leaf members 82-86 and the distal end of the multi-lumen flexible polymeric extrusion assembly 420 commences. Referring to
During the period of expansion 379 of the tissue capture basket 326, as seen in
The decrease of the total electrical resistance 373 to its minimum extent 378 corresponds to the completion of the pursing down of the tissue capture basket 326. The time at which the measured total resistance of the first through sixth segments of the resistively heated portion of the cutting and pursing cable 89-94 decreases to or less than a lower-limit total electric resistance level, RMIN as seen at 378 (e.g. a value in the range from about 1.0 to 2.0 ohms) corresponds to the time at which tissue cutting and capture ends 376 as seen in
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Once practitioner selects the desired diameter D10 of a substantially spherical volume of tissue, the practitioner inserts tissue incision and retrieval assembly 12 into handpiece assembly 15, as represented at line 1502 and block 1504 and may be enveloped within optional single-use, transparent and flexible sterile sheath 109, as represented at line 1552 and block 1504. Next, practitioner momentarily depresses on/off and initialization switch 40 on handpiece assembly 15 and visually confirms if the indicator light 42 (e.g., yellow light) adjacent to the label “Ready” on the handpiece assembly is illuminated, as represented at line 1506 and block 1508. Where the “Ready” indicator light 42 is not illuminated, the activity described at block 1512 fails and the procedure reverts as represented at line 1513 to line 1544 and block 1546, the practitioner having been pre-instructed that a non-functional handpiece assembly 15 is at hand and the procedure reverts to selecting another handpiece assembly 15 to replace the non-functional handpiece assembly 15, as represented at line 1548 and block 1550. Following the replacement of the non-functional handpiece assembly 15, practitioner inserts sterile tissue incision and retrieval assembly 12 into handpiece assembly 15 where the handpiece assembly may be enveloped within optional single-use, transparent and flexible sterile sheath 109, as represented at line 1552 and block 1504. Where the “Ready” indicator light 42 is illuminated, the activity described at block 1512 proceeds to the next step in the procedure.
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Next, practitioner makes an incision at skin site 24 using a cold scalpel to a depth of 2 mm to 4 mm and a width about 2 mm wider than the maximum width of blade 31 located at forward end 27 of delivery cannula 22 (e.g., an incision width of about 8 mm) at the location appropriate to the intended excision of target tissue volume 354, as represented at line 1518 and block 1519. Practitioner next advances surgically sharp blade 31 at the forward end 27 of delivery cannula 22 into incision at skin site 24 to a depth of 2 mm to 4 mm, as represented at line 1520 and block 1521. The positioning of the forward end of the cannula 27 commences using an ultrasound, stereotactic radiography, MRI or upright mammographic imaging modality to guide the advancement of the forward end 27 of delivery cannula 22 to a position just proximal to the target tissue volume 354, incising healthy tissue 366 using blade 31 at tip of tissue incision and retrieval assembly 12, as seen in
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Programming within microcomputer 202 of circuit board assembly 184 next starts clock within microcomputer to accumulate capture duration time, tcapture during the initial deployment of the leaf members 82-86 and multi-lumen flexible extrusion assembly 426 or 427 toward the time at which the maximum opening of the tissue capture assembly occurs 371 as seen in
Programming within microcomputer 202 of circuit board assembly 184 next begins comparing the amount of increase of the continuously measured electrical impedance of the resistively heated cutting and pursing cable circuit, ΔCR during a predetermined brief time interval, Δt with a pre-programmed maximum acceptable increase during the brief time step, Δt of the continuously measured electrical impedance of the resistively heated cutting and pursing cable circuit, Δmax. In a preferred embodiment, the brief time interval, Δt is in the range from 0.001 to 0.003 second and the maximum acceptable increase of the continuously measured electrical impedance of the resistively heated cutting and pursing cable circuit, Δmax is in the range from 0.3 to 0.5 ohm. As seen at line 704 and block 672, if a measured increase in the electrical impedance of the resistively heated cutting and pursing cable circuit, ΔCR during a predetermined brief time interval, Δt exceeds the maximum acceptable increase, Δmax, then the increase is attributable to a sudden loss of good electrical contact between first and/or sixth segments of the resistively heated portion of the cutting and pursing cable 89 and/or 94, respectively, and the first and/or second electrically and thermally conductive eyelets 446 and/or 450, respectively, (i.e., a sudden increase in the electrical contact resistance between the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets). Upon the detection of a sudden loss of good electrical contact between the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets corresponding to the measured value of ΔCR exceeding Δmax during a brief time interval, Δt, as seen at block 672, programming within microcomputer 202 in handpiece assembly 15 temporarily interrupts the supply of constant current for a predetermined time interval, Δpause while continuing to advance the multi-lumen flexible polymeric extrusion and leaf members to re-establish good electrical contact between the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets as seen at line 674 and block 675. In a preferred embodiment, the duration of the interruption, Δpause ranges from 0.10 to 0.30 second. A momentary loss of acceptable electrical contact between the first and/or sixth segments of the resistively heated portion of the cutting and pursing cable 89 and/or 94, respectively, and the first and/or second electrically and thermally conductive eyelets 446 and/or 450, respectively, can result in an associated unacceptably large increase in the electrical contact resistance at the first transition boundary 396 and/or the second transition boundary 406, respectively, thereby causing overheating of the resistively heated cutting and pursing cable and its failure through melting or a significant decrease in the load-bearing capability to withstand the tensile forces applied to the resistively heated cutting and pursing cable.
As a result of the intentional interruption of the supply of constant current to the resistively heated cutting and pursing cable circuit upon the detection of an unacceptably large increase in the measured electrical impedance within the resistively heated cutting and pursing cable circuit, the resulting high level of Joulean heating at the interface the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets and an associated significant increase in the localized temperature of the resistively heated cutting and pursing cable is avoided. The amount of localized Joulean heating (in watts) associated with unacceptably large electrical contact resistance at the interface between the first and sixth segments of the resistively heated portion of the cutting and pursing cable 89 and 94, respectively and the first and/or second electrically and thermally conductive eyelets 446 and 450, respectively, is equal to the product of the square of the applied constant current (in amps) and the unacceptably large value of the electrical contact resistance (in ohms) at the interface between the resistively heated cutting and pursing cable and the first and/or second electrically and thermally conductive eyelets. Upon the interruption of the supply of constant current for a brief period Δpause, the application of the constant current is resumed as seen in line 677 continuing to line 582 and returning to block 576 as seen in
As seen in block 672, if a measured increase in the electrical impedance of the resistively heated cutting and pursing cable circuit, ΔCR during a predetermined brief time interval, Δt does not exceed the maximum acceptable increase, Δmax, then the application of the predetermined constant current to the first through sixth segments of the resistively heated portion of the cutting and pursing cable, 89-94 as well as the predetermined constant voltage applied to first motor 170a continues to block 678 as seen at line 676.
As seen in block 678, if the accumulated capture duration time, tcapture is less than the computed maximum capture duration time limit, trampstart, then programming within microcomputer 202 of circuit board assembly 184 continues to block 682 at line 680 and compares the computed time-based electrical resistance increase rate, Rrate of the electrical impedance of the resistively heated cutting and pursing cable circuit with a predetermined minimum rate electrical resistance increase rate, Rratemin to determine if Rrate is less than Rratemin. In a preferred embodiment, the computed maximum capture duration time limit, trampstart of 5.0 seconds at an advancement speed of the first motor and planetary geartrain assembly 170a is at least 2.3 mm/second. Alternatively, if the advancement speed of the first motor and planetary geartrain assembly 170a is less than 2.3 mm/second, then the computed maximum capture duration time limit, trampstart is proportionately greater. By way of example, if the advancement speed of the first motor and planetary geartrain assembly 170a is 1.8 mm/second, then the computed maximum capture duration time limit, trampstart IS (2.3/1.8)×5.0 seconds or 6.4 seconds.
If Rrate is less than Rratemin, thereby representing a fault condition in the initial ramp of one or more leaf members 82-86 and/or the multi-lumen flexible polymeric extrusion assembly 426 or 427, the programming within microcomputer 202 of circuit board assembly 184 initiates the flashing of the “Capturing” indicator light 46 on handpiece assembly 15, stops the application of the predetermined level of constant current to the first through sixth segments of the resistively heated portion of the the cutting and capture cable 89-94, stops the application of the predetermined constant voltage applied to first motor 170a and stops the audible tone being issued by speaker 200 on circuit board assembly 184 as seen at line 686 and block 688 and represents the end of the procedure as seen at line 690 and block 700.
If Rrate is equal to or greater than Rratemin, thereby representing a normal condition in the initial ramp of one or more leaf members 82-86 and/or the multi-lumen flexible polymeric extrusion assembly 426 or 427, then programming within microcomputer 202 of circuit board assembly 184 returns to comparing the change in the total resistance, ΔCR of resistively heated portions of cutting and pursing cable circuit during brief time period Δt with Δmax as seen in line 684 and block 672.
As seen in block 678, if the accumulated capture duration time, tcapture is equal to or greater than the computed maximum capture duration time limit, trampstart, then programming within microcomputer 202 of circuit board assembly 184 continues to block 578a as seen at line 577. If the change, ΔI in the continuously measured current level delivered to first motor 170a during a brief time interval (e.g., 0.1 to 0.3 second) is less than a predetermined limit, ΔImax as seen in block 578a, then opening of tissue capture basket continues as seen at line 578b and block 576.
If the change, ΔI in the continuously measured current level delivered to first motor 170a during a brief time interval (e.g., 0.1 to 0.3 second) is equal to or greater than a predetermined limit, ΔImax as seen at line 577 and block 578a, then the purse down of tissue capture basket 326 commences as seen at line 578c and block 579. The purse down of tissue capture basket 326 commences upon the application of a predetermined voltage to second motor 170b as seen at line 578c and block 579. Beginning at the point of maximum opening 371 of tissue capture basket 326, pursing down of tissue capture basket 326 commences with the application of a predetermined level of voltage to second motor 170b causing second motor-actuated cable mounting hub translation assembly 180b to advance second pivoting drive finger 185b to be advanced in rearward direction 477 thereby increasing the rate of pursing down of the distal ends of the first through fifth leaf members 82-86 and the distal end of the multi-lumen flexible polymeric extrusion assembly 420.
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Still referring to
Referring now to
Referring 1A, 9A, 16, 28 and 30E, as represented at line 638 and block 644, the captured target tissue volume 354 (i.e., tissue specimen) containing suspicious and potentially malignant lesion 368 is next removed from tissue capture basket 326 by severing the cutting and pursing cable 33 adjacent to an eyelet 327 at the distal end of one or more first through fifth leaf members 82-86 by way of example using a small scissors (e.g., tenotomy scissors). Place extracted target tissue volume 354 in a container with immersion in a fixative solution (e.g., fixative agent such as 3.7% formaldehyde in water) in preparation for subsequent diagnostic examination by a pathologist, as represented at line 646 and block 648. Next, target tissue volume 354 submerged in fixative solution with the container is transported to pathology laboratory, as represented at line 650 and block 652.
An optional arrangement is represented at line 654 and block 656. The latter block provides for placing a radio-opaque and/or echogenic marker in the tissue at the site from which the target tissue volume 354 is removed and verifying the position thereof using radiography or ultrasonography. If a radio-opaque and/or echogenic marker in not placed in the tissue at the site from which the target tissue volume 354 is removed, then proceed at line 658 to block 660.
Then, as represented at line 658 and block 660, the incision at skin site 24 is closed using appropriate conventional closure techniques.
Referring now to
Since certain changes may be made in the above method, system and apparatus without departing from the scope of the present disclosure herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. For example, throughout the disclosure presented herein, the first through sixth segments of the resistively heated portion of the cutting and pursing cables 89-94, respectively, containing multiple wires as seen in
While the apparatus, system, and method have been described with reference to various embodiments, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope and essence of the disclosure. In addition, many modifications may be made to adapt a particular situation or material in accordance with the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed, but that the disclosure will include all embodiments falling within the scope of the appended claims. In this application all units are in the metric system and all amounts and percentages are by weight, unless otherwise expressly indicated. Also, all citations referred herein are expressly incorporated herein by reference.
This application is a continuation-in-part of U.S. Ser. No. 15/877,730 filed Jan. 23, 2018; and is cross-referenced to U.S. Pat. No. 11,737,808.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15877730 | Jan 2018 | US |
| Child | 18602076 | US |
