Patent Application
20080172037
1. Field of the Invention
The present invention relates generally to medical apparatus and methods. More particularly, the present invention relates to catheter constructions which provide for controllable rigidity and column strength over the length of the catheter.
Catheters are long tubular devices used for providing access to internal body locations in a wide variety of medical procedures. Catheters will generally include at least one lumen or passageway over their length, and may include additional lumens for particular purposes. Some catheters include interventional or diagnostic components for achieving particular purposes, such as balloons for luminal dilation, optical components for imaging, energy-directing elements for therapy, and the like.
Catheters may be used in a variety of body locations and may be introduced through both solid tissue and luminal passages, such as the vasculature, the ureter, the urethra, nasal passages, the trachea, the cervix, the uterus, the fallopian tubes, and other natural and created body passages. As catheters will be guided through such body passages, it is generally desirable that the catheter bodies be flexible both to accommodate tortuosity and to reduce trauma.
It will be appreciated, however, that medical catheters must also possess sufficient column strength or rigidity to permit them to be advanced through the body passageway. Catheters will typically be advanced by manually pushing their exposed external lengths so that the advancement force is transmitted axially along the length of the catheter to advance the distal end through the body via a sometimes tortuous path. In order to transmit this force without kinking or buckling, the body or shaft of the catheter must possess sufficient column strength to resist the compressive forces of advancement. Additionally, many catheters must also possess a rotational or torsional stiffness sufficient to allow the distal end to be rotated by turning the proximal end. Other desirable and sometimes necessary performance characteristics include hoop strength, fluid carrying capacity, material characteristics, and the like.
Many catheter designs attempt to balance flexibility and column strength by providing proximal portions which are more rigid and distal portions which are more flexible. This is particularly true in coronary and cerebral catheters where the distal regions must enter highly tortuous vasculature while the proximal regions pass through much less tortuous anatomy and therefore may be much less flexible. Micro-catheters used in the cerebral vasculature often have multiple zones of flexibility, where the distal region is highly flexible, an intermediate region has intermediate flexibility, and the proximal portion is more rigid to enhance column strength. The relative amount of flexibility and column strength may be adjusted, zone by zone, by selecting catheter materials having different hardnesses (durometers), providing catheter bodies laminated from different materials, providing different regions of reinforcement selected from coils, braids, and/or fibers, and the like.
While the use of catheters having regions of different flexibility is useful in many instances, it does not address all needs that may be encountered. For example, urinary drainage catheters introduced through the male urethra into the bladder encounter sphincters, strictures, and differing tortuosities which, in some patients, can require a catheter with relatively high axial force transmission for passage. Typical urinary drainage catheters are constructed of elastomeric tubes that rely on increased cross section or more rigid materials to provide adequate handling and efficient force transmission. While many patients might not require such rigid, and therefore uncomfortable drainage catheters, the catheters must be designed for such “worst case” scenarios. Moreover, the need to employ relative rigid catheters often results in a catheter having a large wall thickness, thus reducing the size of the available drainage lumen in that catheter.
In addition to variations in tortuosity between patients, catheters being introduced through body lumens and other passages will frequently encounter localized strictures, obstructions and the like. Each of these may require a relatively high column strength to transmit the higher force necessary for crossing, where such column strength is not required during the remainder of the catheter advancement. Again, present catheters are typically designed with sufficient column strength to address the most demanding portions of their introduction, resulting in excessively rigid and traumatic catheter being advanced during the other portions of the introduction. This compromised flexibility required for the most difficult placements, is particularly troublesome when the catheter is left in place for an extended period, and high flexibility is important for patient comfort.
For these reasons, it would be desirable to provide improved catheters and methods for their use, where the catheters are adaptable to different conditions of luminal introduction. In particular, it would be desirable to provide catheters which have adjustable column strength and flexibility over different region(s) or over their entire lengths. It would be further desirable if such column strength and flexibility could be adjusted by the physician or other user during the performance of a procedure so that differing introduction conditions could be addressed without having to remove the catheter from the patient. Finally, it would be advantageous to have a catheter having sufficient stiffness to traverse a difficult insertion path, but be adjustable to become more flexible, once in position. At least some of these objectives will be met by the inventions described below.
2. Description of the Background Art
Catheters having structures with varying flexibilities and column strengths are described in U.S. Pat. Nos. 4,350,169; 4,464,176; 4,659,328; 4,739,768; 4,861,337; 4,930,521; 5,704,926; 5,919,164; 6,319,244; 7,001,369; 7,001,420; 7,025,758; and published applications US2001/021840 and US2004/034383. Variable stiffness and adjustable guidewires are described in U.S. Pat. Nos. 5,697,380; 5,957,903; 6,113,557; 6,146,339; and 6,183,420. Medical devices having shape lock tubes are described in U.S. Pat. No. 6,790,173. A steerable support catheter having a slotted tube element is described in U.S. Pat. No. 6,746,422.
Catheters and related apparatus having everting sheaths for facilitating catheter introduction are described in copending, commonly owned application Ser. Nos. 10/794,317; 10/794,337; 10/886,886; 10/951,922; 11/233,886; 11/256,562; 11/346,600; 11/367,084; 11/436,256; and 60/821,002, the full disclosures of which are fully incorporated herein by reference.
The present invention provides medical catheters having adjustable column strength and flexibility over at least a portion or a region thereof. The medical catheters may be of a type used in any one of a wide variety of medical procedures including vascular procedures, urological procedures, gynecological procedures, pulmonary procedures, gastroenterological procedures, endotracheal procedures, and the like. The medical catheters will include a catheter body having a proximal end, a distal end, and at least one lumen therethrough for providing access from a location external to a patient to a location internal to the patient. The catheters will be intended for advancement through a body lumen, typically a natural body lumen such as a blood vessel, a ureter, a urethra, a cervix, a uterus, a fallopian tube, a nasal passage, a trachea, an esophagus, an intestine, a lung passageway, and the like. In other instances, the catheters could be intended for introduction through a created passageway, such as an incision, puncture, or the like made through solid tissue for the purpose of biopsy, therapy, or the like. In most instances, the catheter will have a proximal hub which provides for manipulation of the catheter during its introduction as well as for control of the column strength and flexibility while the catheter is resident in the body lumen. The hub will also usually provide for access to the catheter lumen(s).
As used herein, the phrase “column strength” refers to the ability of the catheter to resist bending, buckling kinking, axial compression and collapse when subjected to a compressive force over its length or any portion of its length. Such compressive forces will typically be encountered as the catheter is being pushed from its proximal end to advance it through the body lumen. The compressive force will result from friction, the presence of tortuosity, strictures, occlusions, sphincters and other natural luminal constrictions, and the like As used herein the term “flexibility” generally means the opposite of column strength and is defined as the inverse of stiffness or the ability to be easily bent. That is, when a lateral force is applied to the catheter, the amount of lateral displacement will vary directly with the degree of flexibility. Thus, a highly flexible catheter will bend easily as it is advanced through tortuous body lumens or encounters strictures or obstructions within the body lumen. Conversely, a catheter having a high column strength will not readily bend, buckle, kink, compress or collapse when advanced through a tortuous body lumen or when encountering a stricture or other obstruction.
In a first aspect of the present invention, a catheter comprises an inner column and an elastic member. The inner column is typically made of a relatively incompressible material and has a distal end, a proximal end, and a lumen therebetween. At least a portion of the column is adapted to stiffen or rigidify in response to axial tensioning in order to increase that portion's column strength. The elastic member is disposed coaxially over the inner column and has a distal end and a proximal end. The distal end of the elastic member is coupled to the column, typically at some point at or near its distal end, and the proximal end of the elastic member is adapted to be axially tensioned, typically by manually pulling or tensioning the member in a proximal direction relative to the column. Thus, applying axial tension to the elastic member will apply compression to the inner column.
The inner column may be constructed in a variety of ways. Most commonly, the inner column will be constructed to straighten and/or to stiffen in response to axial tensioning. In such instances, the inner column of the catheter will still bend when encountering obstructions or luminal tortuosity which applies a lateral bending force to the catheter, but the force required will increase with the amount of axial tensioning In other instances, the inner column will be constructed so that it will assume a predefined curve or other geometry in response to axial tensioning of the elastic member. Such designs may be desirable, for example, to provide steerable catheter configurations, where rotation of the catheter body can selectively direct the distal end of the catheter into side branches, conform to curved tracts such as a male urethra or other luminal locations as the catheter is advanced. For both the straightened and curved catheter designs, increasing the axial tensioning force applied by the elastic member will increase the stiffness or rigidity of the straight or curved geometry, thus making the catheter more pushable.
In the specific embodiments described below, the inner column will comprise a plurality of adjacent links which are able to pivot relative to each other in response to a lateral bending force. Typically, the adjacent links will engage each other or “nest” in response to the axial tensioning force applied by the elastic member. The geometry of the adjacent links will determine the geometry of the column assumed under tension, typically straight or curved as discussed above. The column links may be provided by a variety of specific column constructions, including helical coils (optionally having varying cross-sectional shapes), slit tubes, slotted tubes, hellically slit tubes, nested rings, and the like, as described more fully below. The contact surfaces between links can also affect flexibility as the tension is adjusted, e.g. flat surfaces brought into opposition under tension will resist bending/provide more column strength than will curved contact surfaces.
The elastic member may be any structure which is coaxially disposed about the inner column and which provides for application of axial tension on the column as a proximal portion of the elastic member is pulled proximally relative to the column. Typically, the elastic member will comprise a tubular member having a continuous surface which forms a fluid tight seal or constraint around the catheter structure. Alternatively, the elastic member could be a lattice, a braid, or other open or foraminous structure which could be penetrable or allow the passage of body fluids through the wall of the catheter.
Most commonly, the tubular member will comprise a continuous tubular body composed at least partly of an elastomeric polymer. In other instances, however, the tubular member could comprise a non-elastic tubular body having one or more elastic components or reinforcements to provide for elasticity along at least a portion of the length of the body.
The tubular member may extend substantially over the entire length of the inner column or in other instances may be attached at a location proximal to the distal end of the column. In still other instances, the tubular member may extend distally beyond the distal end of the inner column, in which case the tubular member may provide a distal tip or attached region of the catheter of different deflection characteristics or geometry, for example, providing an atraumatic curved tip, a region for diagnostic or interventional tools or an anchoring balloon.
A hub(s) will usually be attached to the proximal end(s) of the inner column and/or the elastic member. Usually, the hub includes a mechanism for axially tensioning the elastic member relative to the inner column. For example, the tensioning mechanism may comprise a slide member, a screw mechanism, ratchet, snap or a variety of other mechanical devices for allowing manual or automatic adjustment of the tensioning. The tensioning mechanism could alternatively be attached directly to the elastic member, for example as a ring or a collar, to permit proximal translation.
In other embodiments, the catheter may further comprise a distal tip which is attached to the distal end of the inner catheter and/or elastic member. The catheter may also further comprise a sheath positioned in the lumen of the inner catheter, where the sheath is able to evert from the distal end of the catheter as the catheter is advanced through a body lumen. In still further embodiments, the catheter could comprise a liner in the lumen of the inner catheter, where the liner could provide for isolation of a lumen from the surrounding body environment.
The ability of the elastic member to “elastically” tension the inner column is particularly advantageous since it provides for adjustment of the column strength and flexibility of the catheter over a wide range from very flexible when the elastic member is very loose or slack over the inner column to a very high stiffness or column strength when the elastic member is pulled to a maximum tension. Preferably, the elastic member will be fabricated from natural or synthetic rubber elastomers such as silicone, latex, urethane, fluorocarbon elastomers or thermoplastic elastomers with low compression set and and elongation in the range from 100% to 1400%, usually 200% to 1000%, and preferably from 300% to 800%.
It should be appreciated that even when the inner column of the catheter is under axial compression applied by the elastic member, the catheter will retain a degree of flexibility since the elastic member will be able to yield laterally when the catheter encounters vessel tortuosity or an obstruction. The degree and nature of flexibility in yielding will, of course, be first a function of the geometry of the intersection of the links, and further dependent on the degree of axial force applied by the elastic member and the degree of elasticity in the elastic member itself, and both these latter quantities may, of course, be adjusted by the user by pulling or axially translating the proximal end of the elastic member relative to the inner column.
In a second aspect of the present invention, a method for advancing a catheter through a body lumen comprises pushing the catheter from a proximal portion outside of the body lumen to advance a distal portion of the catheter through the lumen. While the distal portion of the catheter is within the body lumen, the stiffness of at least a portion of the catheter may be adjusted by axially tensioning an elastic member located coaxially over an inner column. The body lumen may be selected from a group consisting of ureters, urethras, blood vessels, an intestine, nasal passages, a lung passage, the esophagus, the trachea, the cervix, the uterus, the fallopian tubes, and the like. The catheter may be positioned over a guidewire as it is pushed through the body lumen, but will often be advanced without the use of the guidewire.
Pushing the catheter typically comprises manually advancing a hub attached to a proximal portion of the catheter. Alternatively, pushing may comprise robotically advancing a hub attached to a proximal portion of the catheter. In such instances, the robot and its attached control system could automatically control the tension applied by the elastic member to the inner column in order to control the catheter stiffness in response to the conditions encountered.
Adjusting the catheter stiffness will usually comprise stiffening the catheter when more column strength is needed to pass through an obstruction or stricture in the body lumen. Usually, stiffening will comprise straightening at least a portion of the catheter. In other instances, however, stiffening may comprise inducing a curve into at least a portion of the catheter, where the curve may often be used for steering to target regions within the body lumen.
Alternatively, adjusting could comprise reducing the stiffness of the catheter when the catheter is being pushed through a tortuous region of the body lumen to allow conformance of the catheter body to the lumen or in creating a highly flexible and comfortable device once placed into its proper position. This unique ability to reduce stiffness, and thereby increase comfort, is particularly important where a catheter requiring significant pushability to place in position, will be left in that position, within a patient, for an extended period of time.
In the preferred embodiments, the catheter will comprise the catheter structures described above. That is, the inner column will typically comprise a plurality of adjacent links which pivot relative to each other in response to laterally applied bending forces resulting from the catheter engaging a luminal wall, obstruction, or stricture if the catheter is pushed. Axial tensioning of the elastic member will cause the adjacent links to nest or otherwise to resist pivoting and increase the column strength of the inner column. Even in the absence of tension in the elastic member, axial compression of the catheter resulting from the pushing of catheter during advancement may generate forces that will cause the elements of the inner column to resist pivoting and nest in their most axially compact (straight or curved) geometry. The amount of axial compression will vary while the catheter lumen is pushed through the body lumen depending on the particular conditions encountered. In the case where the fully nested form of the inner links is a straight column, axial compression from advancement, (in addition to any tension introduced by the elastic member), will increase column strength of the catheter for improved pushability and efficient transmission of forces through the catheter.
It may be disadvantageous for portions of the catheter, particularly the distal end of the catheter, to become more stiff when compressed. In such cases, the inner nesting elements may terminated proximal to the tip, inner nesting elements may be spaced apart and bonded to the elastic sleeve to prevent solid stacking, or the geometry of the inner elements may be changed to preserve lateral pivoting under compression. Further optionally, the methods may still further comprise everting a sheath over a distal portion of the catheter as it is pushed through the body lumen. The methods may further optionally comprise performing an interventional procedure through the catheter after the catheter has been placed at the target lumen. Still further optionally, the methods may further comprise performing a diagnostic procedure through the catheter after the catheter has been placed at a target location. As in the above, the methods may further comprise reducing the amount of axial tensioning in order to provide a softer, more comfortable catheter for long-term placement within a patient.
Referring to
The links 16 shown in
The catheter structure 10 will be able to bend in response to a lateral bending force as indicated by arrow 22 in
Referring now to
The catheter structures 10 and 30 may have additional components, including a distal tip 50 as shown in
The catheter structures of the present invention may also include a liner 60 disposed within the lumen 18/38 of the catheter structures 10 and 30. As shown in
As described above, the columns may comprise a plurality of discrete links or other elements which are held together in a column structure by the outer elastic member and/or tethers or other retaining structures. In many cases, however, it would be preferable to provide an inner column which is defined by a continuous structure which is inherently flexible but which returns to a straight or other pre-defined geometry upon the application of axial tension. As shown in
An alternative inner column in the form of a slotted tube 80 is illustrated in
As shown in
As shown in
As shown in
Referring now to
Typically, as shown in
In some cases it may be desirable to be able to partially or completely remove the inner column from the catheter. In such embodiments, an abutment stop 133 (broken line,
Referring now to
An alternative hub structure 170 is shown in
Referring now to
While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used. Therefore, the above description should not be taken as limiting the scope of the invention which is defined by the appended claims.
