Abstract:
A variable stiffness catheter having two concentric coils. A first coil is fixed with relation to the body of the catheter and a second coil is able to rotate in the space between adjacent turns of the first coil. The second coil translates axially in response to being rotated. When the second coil is advanced to its distal position, the stiffness is maximized. When the second coil is refracted proximally, the stiffness of the coil is reduced.

Description:
RELATED APPLICATIONS 
       [0001]    The present patent document claims the benefit of the filing date under 35 U.S.C. §119(e) of Provisional U.S. Patent Application Ser. No. 61/777,447 filed Mar. 12, 2013, which is hereby incorporated by reference. 
     
    
     FIELD 
       [0002]    Embodiments of the present invention generally relate to medical devices and more particularly to wire guides and catheters for use in peripheral intervention. 
       BACKGROUND 
       [0003]    Wire guides are commonly used in vascular procedures, such as angioplasty procedures, diagnostic and interventional procedures, percutaneous access procedures, and radiological and neurological procedures. In general, wire guides may be used to introduce a wide variety of medical devices into the vascular system. 
         [0004]    Generally, during each of the foregoing procedures, a wire guide is first inserted into a patient&#39;s vascular system and is then advanced toward a target site. Various wire guides comprise flexible distal regions to facilitate navigation through the tortuous anatomy of a patient&#39;s vasculature. Where such flexible distal regions are used, it may be difficult to insert a medical component over the wire guide because of the flexibility of the distal region. However, if the distal region is too stiff, then it may be too difficult to advance the wire guide to the target site. 
         [0005]    In order to facilitate advancement of medical component to the target site, some medical procedures utilize two wire guides, a first flexible wire guide for initially traversing the vasculature, and then a stiffer wire guide is advanced over or along the side of the initial wire guide. Once the stiffer wire guide is in place, a catheter can then be advanced over the stiffer wire guide. This procedure works well, but requires three different components be advanced through the vasculature of the patient. 
         [0006]    It would be beneficial to have a single component that could function as both a wire guide and a catheter, such that a single procedure could be used to guide a catheter to a target area. Such a component would need to be flexible to navigate the tortuous anatomy of a patient, yet would also need to be stiff to facilitate pushability of the component. 
       SUMMARY 
       [0007]    In one embodiment of the invention a variable stiffness catheter comprises an outer layer, an inner layer, a first coil, and a second coil. The outer layer has a bore with an inner surface and the inner layer is disposed within the bore. The inner layer is coaxial with the outer layer and has an outer surface. The first coil has a first helical axis coaxial with the inner layer and comprises a first wire wrapped around the first helical axis in a first plurality of turns disposed between the inner surface and the outer surface. The first coil is fixed in place relative to the outer layer and the inner layer. The second coil has a second helical axis coaxial with the inner layer and comprises a second wire wrapped around the second helical axis in a second plurality of turns disposed between the first inner surface and the second inner surface. The second plurality of turns are disposed between the first plurality of turns and the second coil is rotatable about the second helical axis relative to the outer layer, the inner layer, and the first coil. 
         [0008]    In another embodiment a variable stiffness catheter comprises a wall, a first coil, a helical channel in the wall, and a second coil. The wall has an inner surface and an outer surface and the first coil is disposed in the wall between the inner surface and the outer surface. The first coil is fixed in place relative to the wall. The helical channel is disposed in the wall between the inner surface and the outer surface between adjacent turns of the first coil and the second coil is disposed in the helical channel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    To further clarify the above and other advantages and features of the one or more present inventions, reference to specific embodiments thereof are illustrated in the appended drawings. The drawings depict only typical embodiments and are therefore not to be considered limiting. One or more embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0010]      FIG. 1  is a side view of the distal end of variable stiffness catheter. 
           [0011]      FIG. 2  is a longitudinal cross section of the distal end of the variable stiffness catheter of  FIG. 1 . 
           [0012]      FIG. 3  is a side view of the distal end of a first coil. 
           [0013]      FIG. 4  is a side view of the distal end of a second coil. 
           [0014]      FIG. 5  is a longitudinal cross section of the distal end of the variable stiffness catheter of  FIG. 1  with the second coil moved axially. 
           [0015]      FIG. 6  is a longitudinal cross section of the distal end of a variable stiffness catheter having a tube proximal to the second coil. 
           [0016]      FIG. 7  is a side view of an embodiment of the first coil having a lateral bias at the distal end. 
       
    
    
       [0017]    The drawings are not necessarily to scale. 
       DETAILED DESCRIPTION 
       [0018]    As used herein, “at least one,” “one or more,” and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C,” “at least one of A, B, or C,” “one or more of A, B, and C,” “one or more of A, B, or C” and “A, B, and/or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together. 
         [0019]    Various embodiments of the present inventions are set forth in the attached figures and in the Detailed Description as provided herein and as embodied by the claims. It should be understood, however, that this Detailed Description does not contain all of the aspects and embodiments of the one or more present inventions, is not meant to be limiting or restrictive in any manner, and that the invention(s) as disclosed herein is/are and will be understood by those of ordinary skill in the art to encompass obvious improvements and modifications thereto. 
         [0020]    Additional advantages of the present invention will become readily apparent from the following discussion, particularly when taken together with the accompanying drawings. 
         [0021]    In the following discussion, the terms “distal” and “proximal” will be used to describe the opposing axial ends of the inventive balloon catheter, as well as the axial ends of various component features. The term “distal” is used in its conventional sense to refer to the end of the apparatus (or component thereof) that is furthest from the operator during use of the apparatus. The term “proximal” is used in its conventional sense to refer to the end of the apparatus (or component thereof) that is closest to the operator during use. For example, a catheter may have a distal end and a proximal end, with the proximal end designating the end closest to the operator heart during an operation, such as a handle, and the distal end designating an opposite end of the catheter, such as treatment tip. Similarly, the term “distally” refers to a direction that is generally away from the operator along the apparatus during use and the term “proximally” refers to a direction that is generally toward the operator along the apparatus. 
         [0022]      FIG. 1  illustrates a side view of a distal end  102  of a variable stiffness catheter  100 .  FIG. 2  is a cross-sectional view of the variable stiffness catheter  100  of  FIG. 1 . The variable stiffness catheter  100  is comprised of an outer layer  104 , an inner layer  106 , a first coil  108 , and a second coil  110 . 
         [0023]    The outer layer  104  has an outer surface  112  and an inner surface  114  defining a bore. The inner layer  106  is disposed within the bore of the outer layer  104  and is coaxial with the outer layer  104 . The inner layer  106  has an outer surface  116  and an inner surface  118  defining a bore of the variable stiffness catheter  100 . The outer surface  116  of the inner layer  106  faces the inner surface  114  of the outer layer  104 . 
         [0024]      FIG. 3  is a side view of the first coil  108 . The first coil  108  is comprised of a first wire  120  wound into a first helix  300  about a first helical axis  306 . The first helix  300  has a plurality of turns  302  having a gap  304  between adjacent turns  302 . Each turn  302  of the first helix  300  is separated by a pitch  308  distance. The first wire  120  has a cross section  310  defined by a plane cutting through the first wire  116  perpendicular to its axis. In the example of  FIG. 3  the cross section  310  is a circle, although other patterns are possible. In other embodiments the cross section  310  may be rectangular, square, or other shape. In some embodiments the cross section  310  may vary along the length of the wire. The first wire  120  may be comprised of stainless steel, although other materials such as nickel titanium alloys and stiff polymers are suitable for use as the wire. 
         [0025]    Returning to  FIG. 2 , the first coil  108  is disposed between the inner surface  114  of the outer layer  104  and the outer surface  116  of the inner layer  106 . The first coil  108  is fixed in place relative to the outer cylindrical layer  104  and the inner cylindrical layer  106 . In some embodiments the first coil  108  may be bonded to the inner surface  114  of the outer layer  104  and the outer surface  116  of the inner layer  106  to fix the first coil  108  in place. 
         [0026]      FIG. 4  is a side view of the second coil  110 . The second coil  110  is comprised of a second wire  122  wound into a helix  400  about a second helical axis  402 . The second coil  110  has a pitch  408  that is substantially the same as the pitch  308  of the first coil  108 , such that the second wire  122  may be disposed in the gap  304  between adjacent turns  302  of the first coil  108  without interfering with the first wire  120 . The second coil  110  is disposed between the inner surface  114  of the outer layer  104  and the outer surface  116  of the inner layer  106  with the second wire  122  lying in the gap  304  between adjacent turns  304  of the first coil  108 . The second coil  110  is not fixed relative to the outer layer  104  and the inner layer  106  and is constrained in movement by the first wire  108 , the outer layer  104 , and the inner layer  106 . 
         [0027]    The second coil  110  is rotatable about the second helical axis  402  relative to the outer layer  104 , the inner layer  106 , and the first coil  108 . Like a screw, when the second coil  110  rotates about the second helical axis  402 , the second coil  110  translates axially relative to the first coil  108 . Rotating the second coil  110  in a first direction will cause the second coil  110  to translate distally, while rotation of the second coil  110  in the opposite direction will cause the second coil  110  to translate proximally. 
         [0028]    The second wire  122  may have a second cross section  406  that is substantially the same as the first cross section  306  as shown in  FIG. 4 . In other embodiments, the cross section  406  of the second wire  122  is shorter in a radial direction than the cross section  306  of the first wire  120 . Having a shorter cross section  406  reduces the resistance to rotation of the second coil  110  relative to the inner surface  114  of the outer layer  104  and the outer surface  116  of the inner layer  106 . The second wire  122  may be comprised of stainless steel, although other materials such as nickel titanium alloys and stiff polymers. In some embodiments, the second wire  122  may comprise a different material than the first wire  120 . For example, the first wire  120  could be comprised of a nickel titanium allow and the second wire  122  could be comprised of stainless steel. 
         [0029]    The variable stiffness catheter  100  has a stiffness along its length that is equal to the combined stiffness of the inner layer  106 , the outer layer  104 , the first coil  108 , and the second coil  110 . When the second coil  110  is moved proximally through the rotation of the second coil  110 , a region of reduced stiffness is present in the region distal to the distal end  410  of the second coil  110 . Thus, when the second coil  110  is retracted proximally, the variable stiffness catheter  100  has a first region  502  proximal to the distal end  410  of the second coil  110  having a higher stiffness and a second region  500  distal to the distal end  410  of the second coil  110  having a lower stiffness, as shown in  FIG. 5 . 
         [0030]      FIG. 5  shows a longitudinal cross section of the distal end  102  of the variable stiffness catheter  100  with the second coil  110  being displaced proximally relative to the first coil  108 . The second region  500  of the variable stiffness catheter  100  can be lengthened by further moving the distal end  410  of the second coil  110  distally. Similarly, the length of the second region  500  can be increased by moving the distal end  410  of the second coil  110  distally. For example, it may be useful to have a flexible tip when traversing a tortuous vascular system, and then switch to a more rigid tip once past the tortuous vascular system. This would be accomplished by moving the distal end  410  of the second coil  110  proximally for use when traversing the tortuous vascular system and then advancing the distal end  410  of the second coil  110  once past the tortuous vascular system. 
         [0031]      FIG. 6  illustrates another embodiment of a variable stiffness catheter  600 . This embodiment is similar to the previously described embodiment of  FIG. 1  and is comprised of an outer layer  602 , an inner layer  604 , a first coil  606 , a second coil  608 , and a tube  610 . A distal end  618  of the tube  610  is coupled to a proximal end  614  of the second coil  608 . In the embodiment of  FIG. 6 , the tube  610  has an outside diameter  614  greater than an inside diameter  616  of the first coil  606 . To avoid interference between the first coil  606  and the tube  610 , first coil  606  ends prior to the distal end  618  of the tube  610 . In other embodiments, the tube  610  may have an outside diameter  614  less than the inside diameter  616  of the first coil  606  such that the tube  610  is able to pass within the first coil  606 . The tube  610  has a greater torsional stiffness than the second coil  608  and is used to transmit torque over a greater distance than the second coil  608  alone. The proximal end (not shown) of the tube  610  is disposed proximate the proximal end of the variable stiffness catheter  600  and transmits relative rotation of the tube  610  near the proximal end of the variable length catheter  600  to the second coil  608  disposed at the distal end of the variable length catheter  600 . The tube  610  may be comprised of stainless steel, although other materials such as nickel titanium alloys and stiff polymers are suitable for use as the tube. 
         [0032]      FIG. 7  illustrates a longitudinal cross section of an alternative embodiment of the first coil  700 . In this embodiment the first coil  700  is self-biased to have a lateral displacement  702  at its distal end  704 . The second coil is biased to be substantially straight. When the distal end of the second coil is proximate the distal end  704  of the first coil  700 , the variable stiffness catheter  100  is substantially straight. As the second coil is retracted proximally, the bias of the first coil  700  causes the distal end of the variable stiffness catheter  100  to deflect in the direction of the bias. This allows the variable stiffness catheter  100  to have a variable curve depending on the needs of the user. 
         [0033]    In some embodiments the inner surface of the outer catheter may extend into the gap between adjacent turns of the first coil. In such embodiments the inner surface of the outer layer may have a helical groove in the gap for receiving the second coil. In other embodiments the inner catheter may extend into the gap between adjacent coils of the first catheter. In such embodiments the inner layer may have a helical groove in the gap for receiving the second coil. 
         [0034]    In another embodiment the inner layer and the outer layer may be comprised of the same material and form an integral wall having the coils disposed within the wall. In such embodiments the first coil is fixed within the wall and the second coil is free to rotate relative to the first coil and the integral wall. The helical channel is formed in the integral wall in the gap between adjacent turns of the first coil. The second coil travels in the helical channel when rotated relative to the first coil and the integral wall. The channel may be formed by coating the second coil with a release compound allowing the integral wall to be formed with the second wire in place. Because the second coil is coated with the release compound it may be rotated within the integral wall since it is not adhered to the integral wall lie the first coil. 
         [0035]    In some embodiments a helical plug having a cross section larger than the second coil may be coated with a release compound when the integral wall is formed. The helical plug may then be removed leaving a channel having a cross section greater than the second coil. The second coil may then be threaded into the helical channel left by the helical plug. 
         [0036]    Embodiments of the invention have been primarily described in terms of a single lumen catheter. It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.