Patent Application
20050187525
1. Field of the Invention
The present invention relates, in general, to devices and methods for extracting bodily fluid and, in particular, to devices and methods that promote bodily fluid flow during extraction of the bodily fluid in a continuous or semi-continuous manner.
2. Description of the Related Art
In recent years, efforts in medical devices for monitoring the concentration of analytes (e.g., glucose) in bodily fluids (e.g., blood and interstitial fluid) have been directed toward developing devices and methods that allow continuous or semi-continuous monitoring.
In the context of blood glucose monitoring, continuous or semi-continuous monitoring devices and methods are advantageous in that they provide enhanced insight into blood glucose concentration trends, the effect of food and medication on blood glucose concentration and a user's overall glycemic control. In practice, however, continuous and semi-continuous monitoring devices can have drawbacks. For example, during extraction of an interstitial fluid (ISF) sample from a target site (e.g., a user's dermal tissue target site) via a sampling module of a medical device, ISF quantities and/or flow rates can be insufficient and a user may experience discomfort.
Furthermore, continuous and semi-continuous monitoring devices can suffer from a deleterious effect known as “sensor lag.” Such a sensor lag effect occurs when a significant difference exists between an analyte concentration at a sensor of the continuous monitoring device and the real-time analyte concentration at the target site.
Still needed in the field, therefore, is a device and associated method for extracting bodily fluid (such as ISF) that facilitate continuous or semi-continuous monitoring of the extracted bodily fluid while enhancing bodily fluid flow rate and/or quantity and/or reducing sensor lag effect. In addition, the device and associated method should reduce user discomfort.
Embodiments of bodily fluid extraction devices and methods according to the present invention facilitate continuous or semi-continuous monitoring of extracted bodily fluid while enhancing bodily fluid flow rate and/or quantity and/or reducing sensor lag effect. In addition, the device and associated method can reduce user discomfort.
A bodily fluid extraction device according to an exemplary embodiment of the present invention-includes a penetration member configured for penetrating a target site (such as a dermal tissue target site) and subsequently residing within the target site and extracting a bodily fluid sample. The penetration member includes a proximal end adapted for fluid communication with an analyte analysis system, a distal end, and a channel extending from the distal to the proximal end. The distal end includes a sharp portion for penetrating the target site and a flexible feature (e.g., a “leaf spring” flexible feature or an expandable flexible feature) adapted for promoting bodily fluid flow into the channel by protruding into the target site after the penetration member has penetrated the target site.
The bodily fluid extraction device optionally includes a flexible conduit for communicating an extracted sample from the channel to an analyte analysis system.
It is postulated, without being bound, that the flexible feature of embodiments of the present invention promotes bodily fluid flow by exerting a pressure on the target site, stretching the target site and/or creating a pocket within the target site. In addition, the use of a flexible conduit to communicate a bodily fluid sample from the penetration member to an analyte analysis module is expected to eliminate or reduce the discomfort that may otherwise result from the use of a completely stiff or rigid conduit.
A method according to an exemplary embodiment of the present invention includes providing a bodily fluid extraction device as described immediately above. Subsequently, a target site is penetrated with the distal end of the bodily fluid extraction device's penetration member and the flexible portion of the penetration member is caused to protrude into the target site and promote bodily fluid flow into the penetration member's channel. Bodily fluid (e.g., ISF) is then extracted from the target site (e.g., a dermal tissue target site) via the channel of the bodily fluid extraction device.
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:
For purposes of illustration throughout the following description, embodiments of the present invention will be described with reference to the extraction of interstitial fluid (ISF) for analyte (e.g., glucose) testing using a bodily fluid extraction device that penetrates into a dermal tissue target site. However, once apprised of the present disclosure one skilled in the art will recognize that embodiments of the present invention are not necessarily limited to the extraction of ISF.
Embodiments of the present invention can be included, for example, in ISF extraction devices that are adapted to provide continuous or semi-continuous flow of ISF to an analyte monitoring device. Examples of ISF extraction devices with which embodiments of the present invention may be used are described in International Patent Application PCT/GB01/05634 (published as International Publication No. WO 02/49507 A1), and U.S. patent application Ser. No. 10/653,023, both of which are fully incorporated herein by reference. Examples of combined sample collection and metering systems designed for in-situ testing as can also be used with embodiments of the present invention are described in International Patent Application Nos. PCT/US01/07169 (published as International Publication No. WO 01/64105) and PCT/GB02/03772 (published as International Publication No. WO 2003/015627), and U.S. patent application Ser. No. 10/143,399, each of which is fully incorporated herein by reference.
Referring to
Penetration member 101 includes a proximal end 102 adapted for fluid communication with an analyte analysis system (not shown), a distal end 104 and a channel 106 (such as a channel with an inner diameter in the range of 0.25 mm to 1.25 mm) extending from the distal end to the proximal end. The walls of channel 106 can have a thickness in the range, for example, of about 0.02 mm to about 0.5 mm. In addition, the length of penetration member 101 is such that it can reside in a dermal tissue target site to a maximum depth in the range of from about 1.5 mm to 3 mm below the surface of the dermal tissue target site.
Proximal end 102 is configured to be in fluid communication with an analyte analysis system (not shown), an example of which is described in the aforementioned International Patent Application PCT/GB01/05634 (published as International Publication No. WO 02/49507 A1) and U.S. patent application Ser. No. 10/653,023. Proximal end 102 can, if desired, communicate with such an analyte analysis system via a flexible conduit of appropriate inner diameter.
Distal end 104 includes a sharp portion 108 for penetrating a target site, and a flexible feature 110 adapted for promoting bodily fluid flow into channel 106 by protruding into the target site either during penetration or after the penetration member has penetrated the target site. In the embodiment of
Flexible feature 110 is configured as a “leaf spring” in a manner that provides for flexible feature 110 to be deflected and/or compressed as penetration member 101 penetrates a target site (e.g., as the distal end penetrates dermal tissue or subcutaneous tissue). Such deflection (and/or compression) causes the flexible feature to protrude into, and exert pressure on, the target site, thus promoting the flow of bodily fluid from the target site into channel 106. In this respect, flexible feature 110 serves as a target site displacement member. It is also postulated, without being bound, that the flexible nature of the flexible feature improves the ease by which the penetration member can penetrate a target site in comparison to a theoretical rigid penetration member that is capable of displacing an equivalent volume in the target site.
Flexible feature 110 includes a first end 114, an arch 116 and a second end 118. Second end 118 can be, for example, rounded or tapered to a point. Second end 118 is a “free end” in that second end 118 is not attached to any portion of the bodily fluid extraction device other than arch 116. A tangential line to arch 116 from second end 118 (in a plane of symmetry of flexible feature 110) defines angle α with a longitudinal axis A-A of channel 106 (see
Once apprised of the present disclosure, those skilled in the art will recognize that angle α will affect the manner in which flexible feature 110 and penetration member 101 interact with the target site both during and after penetration. The initial value (i.e., the value prior to penetration) for angle α is typically in the range of from about 1 to about 75 degrees. The final value (i.e., the value after the penetration member has penetrated the target site and the flexible feature caused to protrude) for angle α ranges from about 5 to about 80 degrees. The change in angle α before and after insertion of the penetration member is typically, for example, in the range of about 5 degrees to about 75 degrees. Angle α can either increase such that arch 116 protrudes into and exerts pressure on the target site or angle α can decrease such that second end 118 protrudes into and exerts pressure on the target site.
Bodily fluid extraction device 100 can be formed of, for example, a non-corroding metal (e.g., stainless steel) or other non-corroding material, such as a plastic material. Bodily fluid extraction device 100 can be formed using, for example, conventional metal stamping, sheet metal forming, micro-machining, welding and polymer molding techniques.
The bodily fluid extraction performance of bodily fluid extraction devices according to embodiments of the present invention can be enhanced by electrical, mechanical, chemical, or other methods or combinations thereof that serve to beneficially decrease surface roughness and/or by the application of coatings that inhibit bodily fluid clotting (e.g., a heparin-based coating).
Although flexible feature 110 is depicted in
When bodily fluid extraction device 100 is employed to penetrate a dermal tissue target site, penetration member 101 and flexible feature 110 penetrate the target site, as shown in
A result of the flexing of flexible feature 110 is the promotion (e.g., an increase in flow rate and/or flow quantity) of ISF flow from the dermal tissue target site. An increased ISF flow rate is desirable because it can reduce sensor lag. Yet another benefit of an increased ISF flow rate is that more analytical measurements can be taken in a given period of time. A benefit of increased flow quantity is the simplification that comes from handling and analyzing larger volumes.
Penetration member 301 includes a proximal end 302 adapted for fluid communication with an analyte analysis system (not shown), a distal end 304 and a channel 306 extending from the distal end to the proximal end.
Proximal end 302 is configured to be in fluid communication with an analyte analysis system (not shown), an example of which is described in the aforementioned International Patent Application PCT/GB01/05634 (published as International Publication No. WO 02/49507 A1) and U.S. patent application Ser. No. 10/653,023. Proximal end 302 can communicate with such an analyte analysis system via a flexible conduit of appropriate inner diameter.
Distal end 304 includes a sharp portion 308 for penetrating a target site, and a flexible feature 310 adapted for promoting bodily fluid flow into channel 306 by protruding into the target site after the penetration member has penetrated the target site. In the embodiment of
In
Pores 314 are of a suitable size such that the pores are not clogged by bodily fluid components during use. A typical range for the diameter of pores 314 is from approximately 5 micrometers to approximately 0.5 millimeters. The porosity of flexible feature 310 due to the presence of pores 314 can be, for example, in the range of from about 1% to about 95%. If the porosity percentage is too low, then an optimally high bodily fluid flow rate may not be achieved. If the percentage is too high, the physical integrity of the flexible feature may be compromised.
Depending on the type of analyte measurement to be performed, the bodily fluid extraction devices illustrated in
Those skilled in the art will recognize that bodily fluid extraction devices according to embodiments of the present invention can also be used in combination with other techniques that enhance ISF flow rate including, but not limited to, application of a low current to the target site, application of heat to the target site and/or to the penetration member, application of a vacuum to the target site or vacuum applied to channel of the penetration member.
Referring to
Subsequently, as set forth in step 520, the target site is penetrated with the distal end of the penetration member and the flexible portion is caused to protrude into the target site and promote bodily fluid flow into the channel. The flexible feature can be caused to protrude while the penetration member is penetrating the target site and/or after the penetration member has penetrated the target site. Bodily fluid (e.g., ISF) is then extracted from the target site via the channel of the bodily fluid extraction device, as set forth in step 530.
As previously described, embodiments of bodily fluid extraction devices according to the present invention can also be employed in conjunction with an extraction device containing one or more oscillatable pressure rings.
During use, bodily fluid extraction device 550 is positioned such that pressure rings 554A, 554B and 554C are facing a user's skin layer. This can be accomplished, for example, by employing bodily fluid extraction device 550 in a sampling module of a system for extracting bodily fluid (as described in the aforementioned International Application PCT/GB01/05634 and U.S. Patent Application No. 60/476,733) and placing the system against the user's skin layer.
Pressure ring 554A is then urged against the user's skin layer by first biasing element 556A, thereby creating a bulge in the user's skin layer that will subsequently be lanced (i.e., penetrated) by bodily fluid extraction member 552. While pressure ring 554A is in use (i.e., deployed), pressure ring 554B and pressure ring 554C can be maintained in a retracted position by first biasing elements 556B and 556C, respectively.
Bodily fluid (e.g., ISF) can be extracted from the bulge formed in the user's skin layer while bodily fluid extraction member 552 resides totally or partially within the user's skin layer. After about 3 seconds to 3 hours, the pressure ring 554A can be retracted to allow the user's skin layer to recover for a time period in the range of about 3 seconds to 3 hours. After retracting the pressure ring 554A, pressure ring 554B can be deployed to apply pressure on the user's skin layer. While pressure ring 554B is in use (i.e., deployed), pressure ring 554A and pressure ring 554C can be maintained in a retracted position by first biasing elements 556A and 556C, respectively. After a time period of about 3 seconds to 3 hours, pressure ring 554B can be retracted for a time period in the range of 3 seconds to 3 hours, followed by the deployment of pressure ring 554C. Pressure ring 554C maintains pressure on the user's skin layer for a time period in the range of 3 seconds to 3 hours and is then retracted for a time period in the range of 3 seconds to 3 hours. While pressure ring 554C is in use (i.e., deployed), pressure ring 554A and pressure ring 554B can be maintained in a retracted position by first biasing elements 556A and 556B, respectively. This process of cycling between deployment and retraction of pressure rings 554A, 554B and 554C (i.e., the oscillation of the pressure rings 554A, 554B and 554C) can proceeds until fluid extraction has ended. The deployment and retraction cycles in the multiple pressure ring embodiment of
Those skilled in the art will also recognize that a plurality of pressure rings in bodily fluid extraction devices according to embodiments of the present invention can be deployed in any order and that one is not limited to the deployment and retraction sequence described above. For example, a sequence can be used in which pressure ring 554B or 554C is applied before pressure ring 554A. Further, more than one pressure ring can be deployed simultaneously. For example, the embodiment shown in
For the embodiment shown in
The pressure rings 554A, 554B and 554C can have, for example, outer diameters of in the range of 0.08 to 0.560 inches, 0.1 to 0.9 inches and 0.16 to 0.96 inches, respectively. The wall thickness of each pressure ring can be, for example, in the range of 0.02 to 0.04 inches.
Inclusion of at least one pressure ring in extraction devices according to embodiments of the present invention provides a number of benefits for extraction of ISF. First, oscillating the pressure ring(s) between a deployed and retracted state serves to mitigate (i.e., reduce) ISF glucose lag. Upon retraction of the pressure ring(s), pressure on the user's skin layer is released, and the user's body reacts by increasing blood perfusion to the target site. This phenomenon is known as reactive hyperemia and is hypothesized to be a mechanism by which ISF is beneficially replenished in the target site by oscillation of the pressure ring(s). Such a replenishment of ISF helps mitigating the lag between the ISF glucose and whole blood glucose values.
Another benefit of bodily fluid extraction devices according to the present invention is that oscillation of the pressure ring(s) allows the skin under the pressure ring(s) to recover, thus reducing a user's pain, discomfort and the creation of persistent blemishes.
Moreover, extraction devices with a plurality of pressure rings (e.g., the embodiment of
Still another benefit of bodily fluid extraction devices according to embodiments of the present embodiment is that the pressure ring(s) can be used in conjunction with the bodily fluid extraction member to increase the flow rate of ISF extracted from a lance site even more than when only the bodily fluid extraction member is used to extract ISF from a lance site. Increased ISF flow rate is desirable because it reduces the lag in time between the glucose concentration measured in ISF and the actual glucose concentration obtained from whole blood. Another benefit of an increased ISF flow rate is that greater sample volumes of ISF are available for testing at any given time. Thus, a glucose detection system used in conjunction with the present invention is easier to develop and manufacture than are systems that must utilize very small volumes of ISF. Yet another benefit of an increased ISF flow rate is that more measurements can be taken in a given period of time.
While preferred embodiments of the present invention have been shown and described herein, those skilled in the art will recognize that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the invention.
It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.
