Patent Publication Number: US-10780247-B2

Title: Catheter structure with improved support and related systems, methods, and devices

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. § 119(e) to U.S. Provisional Application 62/235,751, filed Oct. 1, 2015 and entitled “Catheter Structure with Improved Support and Related Systems, Methods, and Devices,” which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The various embodiments disclosed herein relate to catheters for use as medical devices, including extension catheters (as defined herein) for use with guiding catheter systems, and more particularly to catheters having a length or section containing a discontinuous or segmented structure, including such structures that can be modified or varied to modify the torsional compliance characteristics of the device. Further embodiments relate to an improved catheter tip for incorporation into the various types of catheters, especially those having multi-layer tubes. 
     BACKGROUND OF THE INVENTION 
     The general use of catheters as medical devices is fairly well-developed at this point. U.S. Pat. No. 4,581,017 to Sahota, for example, shows the use of a guide catheter for insertion into an artery to assist with treating the artery (e.g. with a stenosis); and it further shows the use of another catheter for telescoping insertion into the first catheter to extend beyond the first catheter to treat or access portions of the artery that the first catheter cannot reach because of its larger diameter or lack of flexibility, trackability or support. Subsequent patents show further developments of such telescoping or extension catheter systems. For example, U.S. Pat. No. 5,385,562 to Adams et al., U.S. Pat. No. 5,439,445 to Kontos, and U.S. Pat. No. 5,290,247 to Crittendon all show the use of a catheter having a tubular portion that extends or telescopes beyond the guiding catheter, and an elongated manipulation/insertion wire or shaft attached to the tubular portion to manipulate the tubular portion axially—in push/pull fashion—within the guiding catheter after it has been inserted through the hemostasis valve and into the guiding catheter. The Adams &#39;562 patent suggests that the proximal manipulation/insertion wire may actually be a low-diameter tubular shaft for conducting fluid to inflate and deflate a restriction balloon that restricts movement of the tubular portion. 
     Certain known extension catheters have proximal shafts that transfer twisting motion (also referred to as “torque”) by the user from the proximal shaft to the distal tube. In addition, torsion is also generated along the proximal shaft of such devices as a result of urging the catheter distally or proximally through the guiding catheter and further through tortuous vasculature. However, this transmission of torque can induce stresses on the connection between the proximal shaft and the tube, in some cases stresses that are so great that the stresses cause failure or separation of the shaft and tube at the connection point. Thus, the torque generated at the connection point as a result of the low torsional compliance characteristics (including, for example, high torque transmission) of these devices coupled with the tensile or compressive forces generated from urging the catheter axially can cause device failures. Many of these known catheters have proximal shafts with low torsional compliance, thus making them susceptible to the problems described above. 
     Further, many of the catheters discussed above are multi-layer catheters. A multi-layer catheter is a catheter having a multi-layer tubular construction. Many known catheters can have such a multi-layer tubular construction, including guiding catheters, sheaths, guide extension catheters, and boosting catheters, for example. Typically, the multi-layer catheters have at least two layers: an inner liner layer and an outer layer. In many cases, the inner liner layer is a lubricious liner that is intended to facilitate the passage of other devices through the inner lumen of the catheter. Such an inner layer is often made of PTFE, but can also be made of Teflon, polyethylene, or any other known material that can be incorporated into a medical device. 
     One disadvantage of a multi-layer catheter is the possible delamination that can occur between layers. That is, one or more layers of the multi-layer catheter tube begin to separate from the rest of the layers. This is especially common with lubricious layers. For example, the distal end  322  of a typical known multi-layer tubular catheter  320  with exposed ends of the layers is shown in  FIG. 14A . Note that the catheter has an inner layer  324  and an outer layer  326 , and both layers are exposed at the distal end  322  of the catheter  320 . As shown in  FIG. 14B , one common problem with multi-layer catheters is delamination of the inner layer  324  from the adjacent layer (in this case, the outer layer  326 ), such as at the distal end  322  as shown. According to one exemplary scenario, the delamination can occur during use of the catheter  320  when the tube is being flexed or advanced through the vasculature. A result of such a delamination is that passage (especially withdrawal) of a device through the distal tip may be impaired. 
     Another disadvantage of a catheter having a proximal shaft coupled to a distal tube is that the typically metallic proximal or manipulation shaft may shear, delaminate, peel or disconnect from the distal tube during use. 
     Accordingly, there has been a need in the art for improved catheters and/or improved catheter tips and related methods and systems. 
     SUMMARY OF THE INVENTION 
     Discussed herein are various catheter embodiments for use with standard guiding catheters and sheaths. 
     In Example 1, a catheter comprises a distal tube comprising a tubular wall and a tube lumen defined within the tube by the tubular wall, a support membrane disposed around a portion of the distal tube, and a proximal shaft operably coupled to a proximal portion of the distal tube. The proximal shaft comprises first and second elongate members and a first sheath segment disposed around a first length of the first and second elongate members such that the first length of the first and second elongate members is disposed within the first sheath segment. The first and second elongate members are configured to extend distally into a portion of the distal tube. 
     Example 2 relates to the catheter according to Example 1, wherein the proximal shaft further comprises a second sheath segment disposed around a second length of the first and second elongate members such that the second length of the first and second elongate members is disposed within the second sheath segment, wherein a total length of the first and second sheath segments is less than a total length of the first and second elongate members. 
     Example 3 relates to the catheter according to Example 1, wherein the proximal shaft further comprises a second sheath segment disposed around a second length of the first and second elongate members such that the second length of the first and second elongate members is disposed within the second sheath segment; and at least one unsheathed segment wherein a length of the first and second elongate members is not disposed within the sheath. 
     Example 4 relates to the catheter according to Example 1, wherein the proximal shaft comprises at least one additional sheath segment, wherein each of the at least one additional sheath segments is disposed around a different length of the first and second elongate members. 
     Example 5 relates to the catheter according to Example 4, wherein the proximal shaft comprises at least one unsheathed segment wherein a length of the first and second elongate members is not disposed within the sheath. 
     Example 6 relates to the catheter according to Example 1, wherein at least one of the first and second elongate members defines a lumen within the at least one of the first and second elongate members. 
     Example 7 relates to the catheter according to Example 1, wherein at least one of the first and second elongate members has no lumen. 
     Example 8 relates to the catheter according to Example 1, wherein the first elongate member is configured to extend distally into a first portion of the tubular wall, and further wherein the second elongate member is configured to extend distally into a second portion of the tubular wall. 
     Example 9 relates to the catheter according to Example 1, wherein the proximal shaft further comprises a shaft lumen defined by the first sheath segment. 
     Example 10 relates to the catheter according to Example 9, wherein the proximal shaft further comprises a distal opening in fluid communication with the shaft lumen, whereby the shaft lumen is in fluid communication with the tube lumen. 
     Example 11 relates to the catheter according to Example 10, wherein the shaft lumen is configured to receive fluid such that fluid can be caused to flow distally through the proximal shaft and out of the distal opening. 
     Example 12 relates to the catheter according to Example 10, wherein the proximal shaft is configured to extend distally into a portion of the tubular wall such that the shaft lumen extends distally into the tubular wall and such that the distal opening is in fluid communication with the tube lumen. 
     Example 13 relates to the catheter according to Example 9, wherein the shaft lumen is not in fluid communication with the tube lumen. 
     Example 14 relates to the catheter according to Example 9, wherein the proximal shaft further comprises a distal opening in fluid communication with the shaft lumen, whereby the shaft lumen is in fluid communication with an area external to the catheter. 
     Example 15 relates to the catheter according to Example 9, wherein the proximal shaft further comprises a distal opening in fluid communication with the shaft lumen, whereby the shaft lumen is in fluid communication with an area external to the catheter and proximal to the distal tube. 
     Example 16 relates to the catheter according to Example 9, wherein the proximal shaft further comprises a distal opening in fluid communication with the shaft lumen, whereby the shaft lumen is in fluid communication with an area external to the catheter and distal to the distal tube. 
     Example 17 relates to the catheter according to Example 1, further comprising at least one support member disposed in the proximal portion of the distal tube. 
     Example 18 relates to the catheter according to Example 1, wherein a distal portion of the proximal shaft is at least one support member disposed in the proximal portion of the distal tube. 
     Example 19 relates to the catheter according to Example 1, wherein the proximal shaft comprises a third elongate member. 
     Example 20 relates to the catheter according to Example 19, wherein the proximal shaft comprises at lease one additional elongate member. 
     Example 21 relates to the catheter according to Example 1, further comprising a filler material disposed within at least a portion of the first sheath segment. 
     Example 22 relates to the catheter according to Example 1, further comprising a filler material disposed within at least a portion of the first sheath segment and at least a portion of a second sheath segment. 
     Example 23 relates to the catheter according to Example 1, wherein the first length of the first and second elongate members is an entire length of the first and second elongate members, such that the first sheath segment is disposed around the entire length of the first and second elongate members. 
     Example 24 relates to the catheter according to Example 1, wherein the first length of the first and second elongate members is a portion of an entire length of the first and second elongate members such that the first sheath segment is disposed around the portion of the entire length of the first and second elongate members. 
     Example 25 relates to the catheter according to Example 1, further comprising a second sheath segment disposed around a second length of the first and second elongate members such that the second length of the first and second elongate members is disposed within the second sheath segment, wherein the proximal shaft further comprises a first shaft lumen defined by the first sheath segment and a second shaft lumen defined by the second sheath segment. 
     In Example 26, a catheter comprises a distal tube comprising a tubular wall and a tube lumen defined within the tube by the tubular wall, a support membrane disposed around a portion of the distal tube, and a proximal shaft operably coupled to a proximal portion of the distal tube. The proximal shaft comprises first and second elongate members, at least one sheath segment disposed around a length of the first and second elongate members such that the length of the first and second elongate members is disposed within the at least one sheath segment, and at least one unsheathed segment wherein a length of the first and second elongate members is not disposed within any sheath segment. The first and second elongate members are configured to extend distally into a portion of the distal tube. 
     Example 27 relates to the catheter according to Example 26, wherein characteristics of the at least one sheath segment determine torsional compliance characteristics of the catheter. 
     Example 28 relates to the catheter according to Example 26, wherein the first and second elongate members are disposed in rolling contact with each other along the unsheathed segment. 
     Example 29 relates to the catheter according to Example 26, wherein the first and second elongate members are disposed in sliding contact with each other along the unsheathed segment. 
     Example 30 relates to the catheter according to Example 26, wherein the first and second elongate members are disposed in rolling and sliding contact with each other along the unsheathed segment. 
     Example 31 relates to the catheter according to Example 26, wherein the first and second elongate members are disposed in rolling contact with each other within the sheath segment. 
     Example 32 relates to the catheter according to Example 26, wherein the first and second elongate members are disposed in sliding contact with each other within the sheath segment. 
     Example 33 relates to the catheter according to Example 26, wherein the first and second elongate members are disposed in rolling and sliding contact with each other within the sheath segment. 
     Example 34 relates to the catheter according to Example 26, wherein characteristics of the at least one unsheathed segment determine torsional compliance characteristics of the catheter. 
     In Example 35, a method of using an extension catheter in combination with a standard guiding catheter to perform a procedure at a predetermined location within the vasculature of a patient comprises positioning the standard guiding catheter into a target vessel in the patient, selecting the extension catheter based on desired torsional compliance characteristics, inserting the extension catheter into the standard guiding catheter, urging the extension catheter distally through the standard guiding catheter such that a distal portion of the distal tube extends distally out of the distal end of the standard guiding catheter, and performing a procedure through the extension catheter and standard guiding catheter. The extension catheter comprises a distal tube comprising a tubular wall and a tube lumen defined within the tube by the tubular wall, a support membrane disposed around a portion of the distal tube, and a proximal shaft operably coupled to a proximal portion of the distal tube. The proximal shaft comprises first and second elongate members, at least one sheath segment disposed around a length of the first and second elongate members such that the length of the first and second elongate members is disposed within the at least one sheath segment, and at least one unsheathed segment wherein a length of the first and second elongate members is not disposed within any sheath segment. The torsional compliance characteristics are determined based on the at least one sheath segment and the at least one unsheathed segment. 
     Example 36 relates to the method according to Example 35, wherein an increase in size or number of the at least one sheath segment decreases the torsional compliance characteristics of the catheter. 
     Example 37 relates to the method according to Example 35, wherein an increase in size or number of the at least one unsheathed segment increases the torsional compliance characteristics of the catheter. 
     Example 38 relates to the method according to Example 35, further comprising adding a filler material to at least a portion of the sheath segment, wherein the filler material is a binding material, wherein adding the binding material decreases the torsional compliance characteristics of the catheter. 
     Example 39 relates to the method according to Example 35, further comprising adding a filler material to at least a portion of the sheath segment, wherein the filler material is a lubricant, wherein adding the lubricant increases the torsional compliance characteristics of the catheter. 
     Example 40 relates to the catheter according to Example 1, wherein the support membrane is a partial circumference membrane. 
     Example 41 relates to the catheter according to Example 1, wherein the distal tube further comprises a protective wrap disposed around a portion of a proximal opening of the distal tube. 
     Example 42 relates to the catheter according to Example 1, wherein the distal tube comprises a distal portion that has a higher stiffness than a proximal portion. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is an environmental view showing the use of one embodiment of the subject device in a conventional guiding catheter, which is used to perform various medical procedures. 
         FIG. 2A  is a closer environmental view showing the distal end of an extension catheter extending out the end of a conventional guiding catheter engaged in the coronary vasculature, according to one embodiment. 
         FIG. 2B  is another environmental view showing an extension catheter in a guiding catheter and including a proximal portion and a distal portion, according to one embodiment. 
         FIG. 3A  is a perspective view of an extension catheter having a manipulation shaft with two elongate members, according to one embodiment. 
         FIG. 3B  is a close-up perspective view of the manipulation shaft of the extension catheter of  FIG. 3A . 
         FIG. 3C  is an end view of the manipulation shaft of  FIG. 3A . 
         FIG. 4A  is a perspective view of an extension catheter, according to another embodiment. 
         FIG. 4B  is a perspective view of another extension catheter, according to a further embodiment. 
         FIG. 5A  is a cross-sectional view of a proximal shaft of an extension catheter, according to one implementation. 
         FIG. 5B  is a cross-sectional view of a proximal shaft of an extension catheter, according to another implementation. 
         FIG. 5C  is a cross-sectional view of a proximal shaft of an extension catheter, according to a further implementation. 
         FIG. 5D  is a cross-sectional view of a proximal shaft of an extension catheter, according to yet another implementation. 
         FIG. 5E  is a cross-sectional view of a proximal shaft of an extension catheter, according to another embodiment. 
         FIG. 5F  is a cross-sectional view of a proximal shaft of an extension catheter, according to a further embodiment. 
         FIG. 5G  is a cross-sectional view of a proximal shaft of an extension catheter, according to yet another embodiment. 
         FIG. 5H  is a cross-sectional view of a proximal shaft of an extension catheter, according to another implementation. 
         FIG. 5I  is a cross-sectional view of a proximal shaft of an extension catheter, according to a further implementation. 
         FIG. 5J  is a cross-sectional view of a proximal shaft of an extension catheter, according to another implementation. 
         FIG. 5K  is a cross-sectional view of a proximal shaft of an extension catheter, according to a further implementation. 
         FIG. 5L  is a cross-sectional view of a proximal shaft of an extension catheter, according to another implementation. 
         FIG. 5M  is a cross-sectional view of a proximal shaft of an extension catheter, according to a further implementation. 
         FIG. 5N  is a cross-sectional view of a proximal shaft of an extension catheter, according to another implementation. 
         FIG. 6A  is a perspective view of a proximal shaft of an extension catheter, according to one embodiment. 
         FIG. 6B  is a perspective view of a proximal shaft of an extension catheter, according to another embodiment. 
         FIG. 6C  is a perspective view of a proximal shaft of an extension catheter, according to a further embodiment. 
         FIG. 6D  is a perspective view of a proximal shaft of an extension catheter, according to yet another embodiment. 
         FIG. 6E  is a perspective view of a proximal shaft of an extension catheter, according to a further embodiment. 
         FIG. 6F  is a perspective view of a proximal shaft of an extension catheter, according to another embodiment. 
         FIG. 7A  is a top view of an extension catheter showing the junction of the proximal and distal portions, according to one implementation. 
         FIG. 7B  is a side view of the extension catheter of  FIG. 7A . 
         FIG. 7C  is an end view of the proximal shaft of the extension catheter of  FIG. 7A . 
         FIG. 8A  is a side view of an extension catheter showing the junction of the proximal and distal portions, according to one implementation. 
         FIG. 8B  is a top view of the extension catheter of  FIG. 8A . 
         FIG. 9A  is a cross-sectional side view of a proximal shaft of an extension catheter, according to one embodiment. 
         FIG. 9B  is a cross-sectional side view of a proximal shaft of another extension catheter, according to a further embodiment. 
         FIG. 10  is a cross-sectional top view of a proximal shaft of an extension catheter, according to one embodiment. 
         FIG. 11  is a cross-sectional top view of a proximal shaft of an extension catheter, according to another embodiment. 
         FIG. 12A  is a side view in partial section of an extension catheter with two marker bands, according to one embodiment. 
         FIG. 12B  is a side view in partial section of an extension catheter with three marker bands, according to another embodiment. 
         FIG. 12C  is a side view in partial section of an extension catheter with three marker bands, according to a further embodiment. 
         FIG. 13A  is a cross-sectional side view of an extension catheter showing the junction of the proximal and distal portions, according to one implementation. 
         FIG. 13B  is a cross-sectional side view of an extension catheter showing the junction of the proximal and distal portions, according to another implementation. 
         FIG. 13C  is a cross-sectional side view of an extension catheter showing the junction of the proximal and distal portions, according to a further implementation. 
         FIG. 14A  is a cross-sectional view of a distal end of a standard multi-layer catheter. 
         FIG. 14B  is another cross-sectional view of the distal end of the standard multi-layer catheter of  FIG. 14B . 
         FIG. 15  is a cross-sectional view of a distal end of a multi-layer catheter with a protective wrap, according to one embodiment. 
         FIG. 16  is a cross-sectional view of a distal end of a multi-layer catheter with a protective wrap, according to another embodiment. 
         FIG. 17  is a cross-sectional view of a distal end of a multi-layer catheter with a protective wrap, according to a further embodiment. 
         FIG. 18  is a perspective view of a portion of a catheter with a support membrane, according to one embodiment. 
         FIG. 19  is a cross-sectional view of a distal tube of a catheter with a support membrance, according to one embodiment. 
         FIG. 20  is a perspective view of a portion of another catheter with a support membrane, according to another embodiment. 
         FIG. 21  is a side view of a portion of another catheter with a support membrane, according to a further embodiment. 
         FIG. 22  is a perspective view of a portion of another catheter with a support membrane, according to yet another embodiment. 
         FIG. 23  is a perspective view of a portion of another catheter with a support membrane, according to a further embodiment. 
         FIG. 24  is a perspective view of a portion of another catheter with a support membrane, according to another embodiment. 
         FIG. 25  is a side view of a portion of a catheter with a proximal protective wrap, according to one embodiment. 
         FIG. 26  is a side view of a portion of a catheter with a proximal protective wrap, according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments disclosed and contemplated herein relate to a catheter, such as an extension guide catheter, having a length or section containing a discontinuous or segmented structure. Further embodiments relate to catheters having such discontinuous or segmented structures that can be modified or varied to modify the torsional compliance characteristics of the device. Certain of these catheter embodiments can be adapted to be positioned through and extend distally from a conventional guiding catheter or sheath, wherein the guiding catheter or sheath is adapted to extend into a patient. 
     Further embodiments disclosed and contemplated herein relate to an improved catheter tip that can be incorporated into any known multi-layer catheter, including an extension catheter, guiding catheter, sheath, delivery catheter, or any other such catheter. 
     Additional embodiments disclosed and contemplated herein relate to a support layer than can be positioned around a portion of any known catheter to provide additional strength and/or support to the catheter. 
     Further implementations disclosed and contemplated herein relate to an improved proximal portion of a catheter tube that can be incorporated into any known multi-layer catheter, including an extension catheter, guiding catheter, sheath, delivery catheter, or any other such catheter. 
     For purposes of the remainder of this application, it is understood that the term “guiding catheter” relates to any known guiding catheter, sheath, or delivery system. Additionally, for purposes of this application, “extension catheter” and “extension guide catheter” shall mean any catheter that can be used in combination with a guiding catheter to perform a procedure, including a boosting catheter. It is understood that the various embodiments disclosed herein can be incorporated into any extension catheter, but also can be incorporated into other types of catheters as well. 
       FIG. 1  depicts a conventional guiding catheter  12  being used in the general operating environment, which is partially within a human body, and usually within an artery or vein. As shown in the figure, the guiding catheter  12  may be inserted into the vasculature through a number of different access points in the body. For example, a femoral artery approach is shown at A, while a radial artery approach is shown at B. Further, other parts of the vasculature may be accessed with various guiding catheters or sheaths. For example, at C, a sheath is shown inserted through the femoral artery for a contralateral approach for procedures in the leg or other parts of the body. In another example, the sheath is inserted through the femoral artery to access the renal arteries in one of the kidneys at D or to access the coronary vasculature. 
     Regardless of the access point or the target portion of the vasculature, certain catheter implementations disclosed herein are extension catheter embodiments that can be used in combination with guiding catheters to assist with various procedures. For example, the extension catheter embodiments in combination with guiding catheters can be used to assist with the passage of other interventional, diagnostic, or therapeutic devices to various locations in the vasculature. In other instances, the various types of catheters can be used in combination with guiding catheters or sheaths to assist with the transmission of contrast, diagnostic, or therapeutic fluids/agents by injecting the fluids/agents through the catheter to various locations, or by transmitting the fluids/agents through the guiding catheter via a hemostasis valve adaptor and subsequently passing it through the distal tube of the catheter. In another example, the various catheter types in combination with guiding catheters or sheaths can be used to assist with the removal of thrombus, emboli, or debris present in the vasculature through the guiding catheter/sheath by applying a vacuum at the proximal end of the guiding catheter/sheath via a hemostasis valve adaptor. Alternatively, other catheter implementations are contemplated. 
     As shown in  FIGS. 2A and 2B , various embodiments of an extension catheter (generally shown at  10 ) as disclosed and contemplated herein can be used in conjunction with any conventional guiding catheter  12  for purposes of the various procedures described above. Generally, the distal end of the extension catheter  10  is positioned through and extended distally from the distal end of the conventional guiding catheter  12 . As best shown in  FIG. 2B , the various catheter embodiments, including catheter  10  as shown, have two basic parts: a distal portion that is a comparatively large diameter tube (generally indicated at  14 ) defining a lumen  18  and adapted to extend through and beyond the distal end of the guiding catheter; and a proximal portion that is a comparatively smaller diameter elongate member, also referred to herein as a “manipulation shaft” (generally indicated at  16 ), connected to the tubular portion  14  at a junction. 
     In the various implementations disclosed or contemplated herein, the proximal elongated shaft  16  is made up of at least two rods. In certain embodiments, the proximal shaft also has a sheath disposed around the at least two rods, such that the two rods are disposed within or through the sheath. The sheath is any structure that forms a lumen that is configured to receive the two or more rods of the proximal shaft (such as shaft  16 ) as disclosed or contemplated herein, and can also be referred to herein as a “tube.” In further embodiments, the sheath is discontinuous. That is, in those embodiments, at least one length of the two rods is not disposed within the sheath. In other implementations, the sheath can cover the entire length of the at least two rods. 
     In addition to serving as a mechanism for advancing the catheter in certain implementations, a manipulation shaft with at least two rods within a discontinuous sheath can have desirable torsional compliance characteristics, as will be explained in detail below. The torsional compliance characteristics of these embodiments can help to reduce incidence of stress at the joint or connection between the manipulation shaft and distal tube, thereby reducing the incidence of failure of that joint. 
     One example of an extension catheter embodiment  10  with a manipulation shaft  16  made up of two elongate members  30 ,  32  and a sheath segment  34  is shown in further detail in  FIGS. 3A-3C . The elongate members  30 ,  32  can be rods, tubes, or any other type of elongate member that can be used to advance a catheter or other similar medical device. The two elongate members  30 ,  32  in this embodiment are rods  30 ,  32  that do not contain lumens and are positioned generally adjacent to each other. The sheath segment  34  is positioned around the two rods  30 ,  32  such that the two rods  30 ,  32  are positioned through the lumen  36  formed in the segment  34 . In this implementation, the sheath segment  34  has a length that is shorter than the length of the two rods  30 ,  32  such that the entire length of the rods  30 ,  32  is not covered by the sheath segment  34 . That is, in this embodiment, the rods  30 ,  32  have an uncovered (or “unsheathed”) distal portion  38 A and an unsheathed proximal portion  38 B, with the sheath segment  34  positioned between the two unsheathed segments  38 A,  38 B. 
     In this implementation, each of the rods  30 ,  32  has a full diameter portion  30 A,  32 A and a reduced diameter portion  30 C,  32 C, with a transition portion  30 B,  32 B therebetween. As shown, the transition portions  30 B,  32 B in this embodiment are tapered portion  30 B,  32 B. In accordance with one implementation, the reduced diameter portions  30 C,  32 C can provide enhanced flexibility and are sized such that the diameter of the rods  30 ,  32  at their reduced diameter portions  30 C,  32 C can be positioned within the wall  40  of the distal tube  14  as described below. 
     In this implementation, the manipulation shaft  16  is coupled to the distal tube  14  at a point or area of the wall  40  of the tube  14 . More specifically, as best shown in  FIG. 3A , a distal portion of the shaft  16  is coupled to and integral with the wall  40  of the distal tube  14  at a connection zone  42 . The connection zone (also referred to as the “coupling zone” or “transition zone”)  42  is the portion or length of the proximal end of the distal tube  14  in which a length of the manipulation shaft  16  is coupled or otherwise positioned. In this specific embodiment, as best shown in  FIG. 3A , the two rods  30 ,  32  extend into the distal tube  14 . More specifically, the distal portion  44  of rod  30  is disposed in one portion of the wall  40  in the connection zone  42  of the distal tube  14  while the distal portion  46  of rod  32  is disposed in another portion of the wall  40 , as will be described in further detail below. 
     Further, in this implementation as best shown in  FIG. 3A , both distal portions  44 ,  46  are positioned in the connection zone  42  in a specific configuration. More specifically, each of the distal portions  44 ,  46  has an angled portion  48 ,  50  that extends at an angle in relation to the longitudinal axis of the tube  14  and an axial portion  52 ,  54  that extends axially for some distance as well, as shown. As shown, in this configuration, the proximal ends of the distal portions  44 ,  46  in the connection zone  42  are substantially adjacent to each other in the wall  40 . In contrast, the angled portions  48 ,  50  of the distal portions  44 ,  46  are farther apart from each other. That is, the distal portions  44 ,  46  of the rods  30 ,  32  are positioned such that they are farther apart from each other at the distal ends of the distal portions  44 ,  46  in comparison to the proximal ends. Thus, in accordance with one implementation, the axial portions  52 ,  54  of the distal portions  44 ,  46  are positioned in the wall  40  contralaterally in relation to each other. That is, the axial portion  52  of rod  30  is disposed in the wall  40  on one side of the tube  14  while the axial portion  54  is disposed in the wall  40  on the other side of the tube  14  such that the portions  52 ,  54  are positioned across the lumen  18  from each other. 
     Further, according to certain embodiments, the distal portions  44 ,  46  positioned in the connection zone are configured to be substantially flat or have a reduced cross-sectional profile that allows the distal portions  44 ,  46  to be positioned within the wall  40  of the tube  14  as described herein. Alternatively, other configurations are also contemplated. 
     For example,  FIGS. 4A and 4B  depict alternative embodiments of the distal portions  44 ,  46  of rods  30 ,  32 . It should be noted that while these two embodiments are depicted without any sheaths or sheath segments, it is understood that either or both can have one or more sheath segments or a single sheath that extends along the entire length of the rods  30 ,  32  or any portion thereof. In  FIG. 4A , the distal portions  44 ,  46  in the connection zone  42  are straight. That is, there are no angled or curved portions. Alternatively, in  FIG. 4B , the distal portions  44 ,  46  have a gradual curve configuration. As shown, the rods  30 ,  32  in  FIGS. 4A and 4B  are round. Alternatively, the distal portions  44 ,  46  can be flattened or have a reduced cross-sectional profile. Further, in certain implementations, the distal portions  44 ,  46  can have geometrical features (such as barbs, notches, holes, etc.) that may enhance the retention of the rods  30 ,  32  within the tube. In further alternatives, the distal portions  44 ,  46  can have multiple curves or bends and can either be round or flattened. 
     In accordance with one implementation, the positioning and configuration of the distal portions  44 ,  46  of the rods  30 ,  32  in the connection zone  42  in the wall  40  of the distal tube  14 , according to any of the embodiments depicted in  FIGS. 3A-4B , can enhance the kink resistance of that portion of the tube  14  as well as assisting in transmitting a distal or proximal force to the distal tube  14  in a more even fashion during use of the catheter  10 . Further, in a similar fashion to the geometrical features discussed above, the configuration of the distal portions  44 ,  46  can also enhance the retention strength of the connection between the manipulation shaft  16  and the distal tube  14  by increasing the surface area of the connection and thereby further distributing the stresses placed upon the connection when forces are applied to the manipulation shaft  16  (or the distal tube  16 ). 
     As discussed above, the rods  30 ,  32  in the embodiments depicted in  FIGS. 3A-3C and 4B  are solid rods (that is, they do not have lumens therein). In another embodiment as shown in  FIG. 4A , the rods  30 ,  32  are tubes  30 ,  32 , with each of the tubes  30 ,  32  having lumens defined therein. Further, in the embodiment of  FIGS. 3A-3C  as best shown in  FIG. 3C , the two rods  30 ,  32  are disposed within the sheath  34  such that the sheath segment  34  has a lumen  36 . More specifically, this particular configuration of the sheath  34  with two rods  30 ,  32  positioned adjacent to each other within the sheath  34  has two lumens  36 A,  36 B. 
     In alternative implementations, other configurations of the manipulation shaft  16  are possible, as shown in  FIGS. 5A-5N . For example, as shown in  FIG. 5A , the two rods  30 ,  32  can have lumens  56 ,  58  defined therein (rather than being solid rods). In this implementation, the rods  30 ,  32  can be hypotubes  30 ,  32 , with each having a lumen  56 ,  58  defined therein. In addition, like the solid rods  30 ,  32  depicted in  FIG. 3C , the sheath segment  34  also has two lumens  36 A,  36 B defined between the rods  30 ,  32  and the sheath  34 . Further, it is understood that any of the sheath segment embodiments disclosed or contemplated herein with two or more elongate members may also have lumens in the spaces created by the elongate members disposed therein. 
     Further,  FIGS. 5B-5N  show that the shaft  16  can, in certain embodiments, have various configurations relating to the number, shape, and size of the elongate members. For example, in the implementation of  FIG. 5B , the shaft  16  has a sheath segment  60  with two large rods  62 ,  64  and one small rod  66 . Further, the sheath  60  also has lumens  70 A,  70 B,  70 C,  70 D defined within the sheath  60  as a result of the configuration of the rods  62 ,  64 ,  66 . Each elongate member  62 ,  64 ,  66  disposed within the sheath  60  provides additional support or reinforcement to the shaft  16  while also resulting in multiple lumens within the segment  60 . Alternatively, as shown in  FIG. 5C , the shaft  16  can have the same configuration, except that the small rod  66  is a tube  66  having a lumen  68 . Additional configurations are shown in  FIGS. 5D-5N , including configurations with rods that are not round, but instead are square, rectangular, triangular, hexagonal, or other shapes or combinations thereof. Alternatively, any of the rods can be any known shape. As shown in these figures, the configuration, shape, and number of rods can also influence the cross-sectional shape or profile and the torsional characteristics of the segment  60 . 
     In the various implementations disclosed or contemplated herein, the one or more lumens defined within the sheath segments (such as lumens  36 A,  36 B and lumens  70 A,  70 B,  70 C,  70 D described above) extend along the entire length of the sheath segment (such as segment  34  and segment  60 ). 
     According to certain embodiments, a filler material such as an adhesive, binding material, or polymer can be injected or otherwise positioned within one or more of the lumens (such as lumens  36 A,  36 B, or  70 A,  70 B,  70 C,  70 D) and serve as a bonding agent. The filler material can provide additional structural support for the shaft  16 . Alternatively, the filler material can be a lubricant. The filler material can fill an entire lumen of a sheath segment (such as one or more of the lumens  36 A,  36 B or lumens  70 A,  70 B,  70 C,  70 D), the entire length of all of the lumens of a segment and/or all the segments, a portion of each of the lumens of each segment, only a portion of the length of any segment, or two or more portions of the length of any segment or all segments. Further, it is understood that the filler material can fill one sheath segment (such as one sheath segment of segments  88 A,  88 B of  FIG. 6D , segments  92 A,  92 B,  92 C,  92 D of  FIG. 6E , or segments  96 A,  96 B of  FIG. 6F , for example), two sheath segments (such as two segments of segments  88 A,  88 B, segments  92 A,  92 B,  92 C,  92 D, or segments  96 A,  96 B, for example), or any other number of segments. In addition, it is also understood that the filler material can fill all sheath segments on a device. 
     In accordance with certain alternative implementations as will be described in further detail below, the one or more lumens (such as lumens  36 A,  36 B or  70 A,  70 B,  70 C,  70 D), including, for example, the lumens in the elongate members (such as lumens  56 ,  58  as shown in  FIG. 5A ), can be configured to receive a fluid (such as, for example, a contrast solution) such that the fluid can be urged from the proximal end to the distal end of the segment (such as segment  34  or  60 ) and thereby dispense or deliver the fluid out of the distal end of the segment. 
     There can be benefits of a proximal shaft having a lumen. As discussed above, it allows for transmission of fluid through a conduit that is smaller in diameter than the guiding catheter. In certain embodiments, the lumen is sized specifically to conduct the desired amount of a specific fluid into the distal tube, into an area proximal to the opening of the distal tube, into a wall of the distal tube, out of the wall of the distal tube through an opening somewhere along the length of the tube, or out of the distal end of the distal tube. The control of the lumen size can allow for transmission of more or less fluid, depending on what is desired. For example, less fluid can be desirable when the fluid is contrast solution that is typically used in several catheter-based procedures, because greater amounts of contrast solution can cause harm to the patient. 
     According to various embodiments, the manipulation shaft  16  can have a diameter that ranges from about 0.008 inches to about 0.07 inches. Alternatively, the shaft  16  can have a diameter that ranges from about 0.01 inches to about 0.04 inches. Further, the shaft  16  can have a size that ranges from about ¼ French to about 3 French. The various inner elongate members can be made of at least one metal and/or at least one polymer. The metal can be stainless steel, nitinol, or other similar metals. Specific examples of stainless steel include 304 or 316 grade stainless steel. In those embodiments with inner elongate members, the outer wall, sheath, or sheath segment of the shaft  16  is made of polymeric materials such as PET, PTFE, Teflon, FEP, PE, PEBA, or other similar materials. 
     The various manipulation shaft or sheath embodiments as discussed in further detail elsewhere herein provide for a gradual change in flexibility from the proximal end of the shaft to the distal end. Further, certain shaft implementations are configured such that the distal portion of the shaft couples with the distal tube in such a way as to maximize the inner diameter of the distal tube. That is, in certain implementations, the various catheter implementations disclosed or contemplated herein require a sufficiently accessible opening at the proximal end of the distal tube to allow for the lumen to be accessible for medical devices. In other words, the opening must be large enough and/or have sufficient clearance to allow for easy insertion of various medical devices into the opening such that the devices can be urged distally through the tube and out of the opening at the distal end of the tube. In certain of these embodiments, clearance at the opening at the proximal end of the distal tube can be optimized by minimizing the profile (by reducing the diameter, etc.) of the manipulation shaft according to various configurations as disclosed herein. 
     As mentioned above, in accordance with some embodiments, the distal portion of the manipulation shaft is integrated or embedded in the proximal end of the distal tube. For example, in certain implementations, the distal tube is molded over the distal end of the manipulation shaft, thereby creating a connection zone as discussed elsewhere herein. 
     Returning to  FIG. 3A , the larger diameter distal tube  14  is, according to one embodiment, made generally from flexible polymeric materials. In certain implementations, the tube  14  is constructed with at least two layers. For example, the tube  14  can have two layers: a PEBAX, polyurethane, or NYLON outer layer, and a PTFE inner layer. Alternatively, the tube  14  can include a third polymeric layer (or more than three such layers). The tube  14  may also incorporate another layer comprised of re-inforcing coil or mesh. Such a coil or mesh layer can provide enhanced flexibility and/or strength. The tube  14  may also incorporate radiopaque markers (such as markers  274 ,  276 ,  278  as shown in  FIGS. 12A-C  and discussed below) on the tube  14 . The manipulation shaft  16  may also incorporate one or more visual markers, including radiopaque markers. 
     The number and configuration of the elongate members and the one or more sheath segments (and any filler material positioned therein) in the manipulation shaft can influence the physical characteristics of the catheter. More specifically, these components can directly influence the torsional compliance characteristics of the device. It is understood that for purposes of this application, “torsional compliance” is intended to mean the angular or rotational flexibility of the shaft along its length. As an example, a shaft with high torsional compliance will transmit less torque or rotation from one end to the other end, while a shaft with low torsional compliance will transmit more torque from one end to the other. A shaft with low torsional compliance will have higher torque transmission characteristics than one with high torsional compliance. As discussed above, certain known extension catheters have high torque transmission characteristics (and thus low torsional compliance characteristics) that can cause sufficient stress on the connection between the proximal shaft and distal tube to cause failure or separation at the connection point. Non-limiting examples of extension catheters having low torsional compliance can include catheters having a proximal shaft comprised of a single elongate member having a solid square or rectangular cross-section, a solid round cross-section, or a round cross-section with a lumen (such as a hypotube). 
     In contrast, the use of two or more elongate members in combination with different sheath segment configurations can produce higher torsional compliance (and thus lower torque transmission) than proximal shafts that are not configured as such. More specifically, without being limited by theory, the capability of the two or more elongate members to move independently in relation to each other helps to increase torsional compliance/reduce torque transmission when the manipulation shaft is turned at its proximal end by the user to cause rotation of the distal tube or when torsion is induced in the shaft as a result of pushing (or pulling) the catheter through a guiding catheter and through a tortuous vessel. In a related fashion, a sheath segment that covers only a portion of the length of the elongate members (instead of the entire length thereof) also maintains some independent movement of the elongate members, thereby maintaining lower torque transmission in comparison to any configuration that includes a sheath that covers the entire length of the elongate members. In contrast, in those situations in which it is desirable, the addition of a filler material that acts as a bonding agent in one or more lumens of the sheath segment can decrease the torsional compliance characteristics (and thus increase the torque transmission characteristics), while a filler material that constitutes a lubricant can increase torsional compliance characteristics less than a bonding agent. As discussed above, the amount of filler can also influence the torsional compliance characteristics, including whether the filler fills the entire length of a sheath segment, a portion of the segment, more than one portion of the segment, or more than one segment. 
     Thus, it is understood that torsional compliance of any given device or shaft can be determined based on a number of factors, including the number and length of any sheath segments, the number and length of any unsheathed segments, the amount of filler, the type of filler, the cross-sectional shape of the two or more elongate members, the number of elongate members, and other known factors. 
     These concepts are best captured in  FIG. 6A , which depicts a shaft  80  configuration with round rods  82 ,  84  having a sheath segment  86  and an unsheathed segment  87 . The unsheathed segment  87  allows for the independent movement of two round elongate members  82 ,  84 , thereby increasing torsional compliance as described above. That is, as shown by the fact that the proximal portions of the elongate members are wound together, the two elongate members can move independently in relation to each other—including being in sliding and rolling contact along their lengths—thereby increasing the torsional compliance of the shaft  80 . In contrast, non-round elongate members would not be capable of rolling or rotating in relation to each other as easily, thereby resulting in decreased torsional compliance as a result of the contact between elongate members being merely slidable in nature (rather than both sliding and rolling/rotating). Further, the sheathed segment  86  reduces the amount of relative movement of the two rods  82 ,  84  such that their independent movement in relation to each other is more limited in comparison to the length of rods  82 ,  84  in the unsheathed segment  87 , thereby resulting in decreased torsional compliance. Of course, it is understood that the two rods  82 ,  84  in the sheathed segment  86  can also be in sliding and rolling contact along their lengths, but it is also understood that the rods  82 ,  84  in the sheath  86  are not capable of rolling or rotating in relation to each other as easily as rods  82 ,  84  of an unsheathed segment (such as segment  87 ). And a filler injected into the segment  86  can further influence the torsional compliance as explained above. 
     Further,  FIGS. 6B-6F  depict various different additional manipulation shaft implementations, wherein each of the different configurations has a different impact on the torque transmission characteristics of the resulting device. More specifically, each of these figures shows a different embodiment of a manipulation shaft  80  having two elongate members  82 ,  84 , with each embodiment having a different sheath segment configuration. 
     For example,  FIG. 6B  depicts a manipulation shaft  80  with the two elongate members  82 ,  84 , but having no sheath segment. As described above, this shaft  80  would exhibit high torsional compliance (or low torque transmission) for the reasons set forth above. 
       FIG. 6C  shows a manipulation shaft  80  with two elongate members  82 ,  84  and a sheath segment  86  that is disposed around the two elongate members  82 ,  84  for a substantial amount of the length of the members  82 ,  84 . That is, the sheath segment  86  extends from a proximal portion of the members  82 ,  84  to a distal portion of the members  82 ,  84 . In this embodiment, the shaft  80  exhibits lower torsional compliance characteristics than any of the other embodiments in  FIGS. 6A-6F , because the sheath  86  is disposed around a greater length of the two members  82 ,  84  than any other embodiment, thereby limiting the freedom of the two members  82 ,  84  to move in relation to each other. Alternatively, the sheath segment  86  can be disposed around the elongate members  82 ,  84  for any length of those members  82 ,  84 , including the entire length thereof. Further, as is true with any of the embodiments shown in  FIGS. 6A-6F  and elsewhere in this application, a bonding agent filler injected into the segment  86  will cause even lower torsional compliance characteristics (while a lubricant filler would have torsional compliance characteristics that are not as low as those created by a bonding agent). 
     The manipulation shaft  80  embodiments in  FIGS. 6D-6F  all have at least two sheath segments disposed around two elongate members  82 ,  84 . More specifically,  FIG. 6D  depicts a first or distal sheath segment  88 A, and a second or proximal sheath segment  88 B, with an unsheathed segment  90  between the two segments  88 A,  88 B. The shaft  80  in  FIG. 6E  has four sheath segments  92 A,  92 B,  92 C,  92 D with three unsheathed segments  94 A,  94 B,  94 C disposed therebetween. Further,  FIG. 6F  has two sheath segments  96 A,  96 B with an unsheathed segment  98  between the two segments  96 A,  96 B. The unsheathed segment  98  in  FIG. 6F  has a greater length than the unsheathed segment  90  in  FIG. 6D , which means that the shaft  80  in  FIG. 6F  exhibits lower torque transmission than the shaft  80  in  FIG. 6D . In a further alternative, the shaft  80  can have a sheath that is disposed around the two elongate members  82 ,  84  and extends for the entire length of the shaft  80 , thus constituting a unitary or non-segmented sheath. Further, it is understood that the sheath or segments can have any length and cover any portion of the length of the shafts. It is also understood that there can be any number of sheath segments or unsheathed segments. In addition, certain embodiments can have at least two segments that are disposed around the at least two elongate members and adjacent to each other such that they in contact with each other such that there are no unsheathed segments between the at least two segments. 
       FIGS. 7A-7C  depict another embodiment of a catheter  100  with a manipulation shaft  104  that is coupled to the distal tube  102  in an eccentric manner, rather than a concentric manner. That is, the shaft  104  is joined to the distal tube  102  at one point or in one zone of the periphery or circumference of the distal tube  102  or along an extension  142  of the distal tube  102  as discussed in further detail below. For example, in one implementation as shown in  FIGS. 7A-7C , the manipulation shaft  104  is coupled to the distal tube  102  at a point or area of the wall  106  of the tube  102 . 
     The shaft  104  in this embodiment is made up of two rods  108 ,  110  positioned within the lumen  114  of the sheath  112  disposed around the rods  108 ,  110 , as best shown in  FIG. 7C . In this embodiment, the rods  108 ,  110  are solid (that is, they do not have lumens). Alternatively, as discussed above, the rods  108 ,  110  can be hypotubes  108 ,  110 , with each having a lumen defined therein, and/or can have a shape other than round. 
     As best shown in  FIGS. 7A and 7B , this specific implementation has a distal portion of the shaft  104  that is similar to the configuration of  FIG. 3A  as discussed above, because the shaft  104  is coupled to and integral with the wall  106  of the distal tube  102  at the connection zone  116 . Further, as best shown in  FIG. 7A , like the device  10  in  FIGS. 3A-3C , the two rods  108 ,  110  extend from the distal portion of the shaft  104  such that the distal portions  118 ,  120  of the rods  108 ,  110  extend into the distal tube  102 . More specifically, the distal portions  118 ,  120  are positioned in the wall  106  contralaterally in relation to each other. That is, the distal portion  118  is disposed in the wall  106  on one side of the distal tube  102  while the distal portion  120  is disposed in the wall  106  on the other side of the tube  102  such that the portions  118 ,  120  are positioned across the lumen  122  from each other. As with every embodiment having contralateral distal portions, the distal portions  118 ,  120  can be directly opposite each other across the lumen  122 , but in other implementations, they are not directly opposite each other. 
     Further, as best shown in  FIG. 7B , both distal portions  118 ,  120  (only  120  is visible in  FIG. 7B  because of the location of distal portion  118  behind distal portion  120  in the figure) have angled portions  124 ,  126  that extend at an angle in relation to the longitudinal axis of the tube  102  and axial portions  128 ,  130  that extend axially along that position for some distance as well as shown. Alternatively, the distal portions  118 ,  120  can have only angled portions (similar to portions  124 ,  126 ) and no straight or axial portions. In accordance with one implementation, the positioning and configuration of the distal portions  118 ,  120  of the rods  108 ,  110  in the wall  106  of the distal tube  102  enhance the kink resistance of that portion of the tube  102  as well as assisting in more evenly transmitting an axial force to the distal tube  102  in a more even fashion during use of the catheter  100 , while maintaining a low torque transmission. 
     In this specific implementation, both of the distal portions  118 ,  120  of the rods  108 ,  110  have a round configuration. Alternatively, they could have a flat configuration, thereby reducing their profiles within the distal tube  102 . 
     In addition, in this implementation, as best shown in  FIG. 7B , the distal tube  102  has a tapered proximal opening  140  and a proximal extension  142  that is configured to receive the manipulation shaft  104  as shown. In one implementation, the tapered proximal opening  140  provides easier access and insertion for any device being positioned through the lumen  122  of the distal tube  102 , while the proximal extension  142  provides enhanced strength to the connection between the manipulation shaft  104  and the distal tube  102 . 
     According to a further embodiment depicted in  FIGS. 8A and 8B , the device  150  has a manipulation shaft  154  that is made up of two rods  156 ,  158  and a tube  160  positioned between the two rods  156 ,  158  (as best shown in  FIG. 8B ).  FIG. 8A  is a side view, while  FIG. 8B  is a top view. In this implementation, the shaft  154  has a polymeric sheath segment  162  such as polyester and/or PET that is disposed around the two rods  156 ,  158  and tube  160 . A distal portion of the shaft  154  is coupled to and integral with an outer wall  166  of the distal tube  152  at the connection zone  164 , and more specifically is coupled to a proximal extension  186  of the tube  152 . Further, the two rods  156 ,  158  extend distally such that the distal portions  168 ,  170  of the rods  156 ,  158  extend into the distal tube  152 . The distal portions  168 ,  170  are positioned in the wall  166  contralaterally in relation to each other. That is, the distal portion  168  is disposed in the wall  166  on one side of the tube  152  while the distal portion  170  is disposed in the wall  166  on the other side of the tube  152  such that the portions  168 ,  170  are positioned across the lumen  180  from each other. Further, as best shown in  FIG. 8A , both distal portions  168 ,  170  (only  170  is visible in  FIG. 8A  because of the location of distal portion  168  behind distal portion  170  in the figure) have angled portions  172 ,  174  that extend at an angle in relation to the longitudinal axis of the tube  152  and axial portions  176 ,  178  that extend axially along that position for some distance as well as shown. In this specific implementation, both of the distal portions  168 ,  170  of the rods  156 ,  158  have a round configuration. Alternatively, they could have a flat configuration, thereby reducing their profiles within the distal tube  152 . 
     In addition, in this implementation, the tube  160  positioned between the two rods  156 ,  158  has a proximal end of the tube  160  extending proximally of the distal tube  152  and the distal end extending into the distal tube  152  as shown. It is understood that the proximal end of the tube  160  can be positioned at any point along the length of the manipulation shaft  154 . Alternatively, the proximal end of the tube  160  can extend to the proximal end of the manipulation shaft  154 . According to one embodiment, the tube  160  has a lumen (not shown) in fluid communication with the lumen  182  of the sheath segment  162  and further in fluid communication with the lumen  180  of the distal tube  152 . Alternatively, the tube  160  can have a lumen (not shown) that is not in fluid communication with the lumen  182  or the lumen  180 . In yet another alternative, the tube  160  has no lumen. Further, in this embodiment, two marker bands  184  are positioned around the rods  156 ,  158 . 
     As mentioned above, in this embodiment, the tube  160  extends distally into the distal tube  152  such that the lumen (not shown) of the tube  160  is in fluid communication with the lumen  180  of the distal tube  152 . Alternatively, the tube  160  extends distally out of the sheath  162  such that the distal end of the tube  160  is positioned in the tapered opening  188  of the distal tube  152  (described in further detail below). In that embodiment, the lumen is in fluid communication with an area external to and proximal to the lumen  180  of the distal tube  152 . In a further alternative, the tube  160  can extend distally to or beyond the distal end of the distal tube  152  such that the lumen (not shown) of the tube  160  is in fluid communication with an area external to and distal to the distal tube  152 . In a further embodiment. 
     In addition, in this implementation (like the embodiment depicted in  FIGS. 7A and 7B ), as best shown in  FIG. 8A , the distal tube  152  has a proximal extension  186  configured to receive the manipulation shaft  104  as shown and a tapered proximal opening  188 . The tapered proximal opening  188  in this embodiment has levels of tapering as shown, including a sharp tapered portion  188 A, a curved tapered portion  188 B, an axial portion  188 C, and a second sharp tapered portion  188 D. The tapered opening  188  provides easier access and insertion for any device being positioned through the lumen  180  of the distal tube  152 , while the proximal extension  186  provides enhanced strength to the connection between the manipulation shaft  154  and the distal tube  152 . 
     As shown in  FIG. 9A , according to certain implementations, a manipulation shaft  200  can terminate in a proximal fitting  202 . In accordance with one embodiment, the fitting  202  is adapted for connection to a fluid source. In certain embodiments, the fitting  202  is a standard female luer connection that is made from plastic. The fitting  202  can be bonded to the manipulation shaft  200  with adhesive, or it can be insert-molded over the manipulation shaft  200 . In the embodiment shown in  FIG. 9A , there is an optional strain-relief segment  204  disposed between the manipulation shaft  200  and the proximal fitting  202 . The strain relief segment  204  provides a flexible transition from the manipulation shaft  200  to the proximal fitting  202 . In this embodiment, the lumen  206  of the shaft  200  extends through the proximal fitting  202  as shown. 
     Alternatively, in  FIG. 9B , the proximal end of the lumen  206  in the shaft  200  does not have an opening. That is, the proximal end of the lumen  206  is not in fluid communication with any opening at the proximal end of the shaft  200 . 
     As discussed above, certain proximal shaft implementations have a sheath defining a lumen in which two separate inner elongate members are positioned. For example, the manipulation shaft  220  shown in  FIG. 10  has a sheath  226  defining a lumen  228  with two inner elongate members  222 ,  224  positioned therein, wherein each of the elongate members  222 ,  224  have lumens. In this embodiment, both of the elongate members  222 ,  224  have reduced diameter portions  222 A,  224 A as shown. In this exemplary embodiment, each elongate member  222 ,  224  has a connection section  222 B,  224 B between the full diameter section  222 C,  224 C and the reduced diameter section  222 A,  224 A that involves a narrowing or neck around the full circumference of the members  222 ,  224  as shown. 
     Alternatively, the manipulation shaft  240  shown in  FIG. 11  has sheath  246  defining a lumen  248  with two inner elongate members  242 ,  244  positioned therein. The sheath  240  has a tapered section  246  in which both of the elongate members  242 ,  244  have tapered sections  242 B,  244 B as shown. In this exemplary embodiment, each elongate member  242 ,  244  has an extended taper from the full diameter section  242 C,  244 C to the reduced diameter section  242 A,  244 A. 
     As shown in  FIGS. 12A-12C , certain embodiments of a distal tube  260  can have three segments or more of differing flexibilities: low flexibility at the proximal end  264  of the tube  260 , medium flexibility in the middle  266  of the tube  260 , and high flexibility at the distal end  268 . More segments of varying flexibilities can also be used. In fact, the connection zone  270  (the area of overlap in which the manipulation shaft  262  is coupled to the larger tube  260 ) has varying flexibility in that zone  270 . The differing flexibilities can be accomplished through combinations of differing materials, configurations, or geometries—as is known in the art (e.g. mesh or coil reinforcing, different PEBAX varieties, etc.). Moreover, different lengths can be selected for the segments  264 ,  266 ,  268  and the connection zone  270  according to design considerations. This permits more flexibility along a greater length of the device  258  as needed to deal with anticipated curvature in the path the catheter  258  must follow. In another implementation, the at least three segments have differing flexibilities as follows: low flexibility at the proximal end  264 , high flexibility in the middle  266 , and low flexibility at the distal end  268 . Any other combination of flexibilities is also possible. 
     As mentioned above, the flexible tube  260  can have radiopaque markers embedded in the tube  260  and/or placed along the length of the tube  260  for various purposes. For example, marker  274  can be used at or near the distal tip  280  of the tube  260  to help the doctor locate the position of the tip  280 . Another marker  276  could be used at or near the proximal end  282  of the tube  260  to assist the doctor in locating that end  282  of the tube  260  relative to the end of the guiding catheter or to assist in visualizing the location of the proximal opening of the tube  260 . In one embodiment, the marker band  276  can be located near the proximal end  282  of the tube but at a position on the tube  260  that is distal to the end  282 , as shown in  FIGS. 12A-12C . 
     Further, in certain embodiments, a radiopaque marker (not shown) can be located anywhere in or near the connection zone  270  (e.g. on the manipulation shaft  262  in or near the connection zone  270  or in the distal tube  260  in the connection zone  270 ). Further, any of the markers  274 ,  276 ,  278  can be non-cylindrical. For example, one or more of the markers  274 ,  276 ,  278  can be strips or other known configurations. 
     One or more of these markers  274 ,  276 ,  278  can be helpful to indicate to the doctor or surgeon the location of the proximal end  282  of the tube  260  in relation to the guiding catheter (not shown) so that they do not insert or push the proximal end  282  past the distal end of the guiding catheter. In this regard, certain embodiments include a third marker  278  located at some optimal point along the tube  260  in between the other two markers  274  and  276 , as shown in  FIGS. 2B, 12B, and 12C . As best shown in  FIG. 2B , the doctor or surgeon can use this third marker  278  to track how far the tube  260  is extending beyond the guiding catheter  12 . That is, the third marker  278  can be used in certain circumstances as a limit indicator. For example, in a specific embodiment having a tube  260  that is 35 cm in length, the third marker band  278  may be located 15 cm from the distal end  280  of the tube  260  in order to indicate this predetermined distance to the doctor, such that the doctor knows the distance that the distal end  280  extends beyond the guide catheter  12 . Depending on the specific configuration of the catheter  258 , the third marker band  278  can be disposed in the low flexibility segment  264 , the middle flexibility segment  266 , or possibly even in the high flexibility segment  268 . 
     It is understood that the distal tube  260  can have one, two, three, or more markers as described above. It is further understood that any marker arrangement of one or more markers, including the three marker arrangement, can be used in connection with a variety of catheter configurations, including those having a solid rail (e.g. a flat or round wire) or a hollow rail or proximal section with a lumen, such as a tube. In other implementations, one or more markers can be positioned on the manipulation shaft  262 . 
     In further embodiments, the proximal shaft  262  can have greater longitudinal flexibility than the distal tube  260  or any portion thereof. 
     According to certain implementations, the proximal shaft  262  can have a lumen  272  that extends along the length of the proximal shaft  262 . As shown, the lumen  272  has an distal opening  273  that is in fluid communication with an area external to and proximal to the distal tube  260 . In alternative embodiments, the shaft  262  can extend distally into the distal tube  260  such that the lumen  272  is in fluid communication with the lumen of the distal tube  260  via the opening  273 . In a further alternative, the shaft  262  can extend distally through the distal tube  260  such that the lumen is in fluid communication with an area external to and distal to the distal tube  260 . In yet another alternative, the proximal shaft  262  has no lumen. 
     Other embodiments include additional support structure in the distal tube that can provide mechanical advantage similar to that provided by the support coil.  FIG. 13A  depicts a device  300  having a distal tube  302  with a support member  304  positioned in the connection zone  306  that is configured to assume at least some of the mechanical loads. Alternatively,  FIG. 13B  depicts another embodiment of a support member  308  positioned in the connection zone  306  of a distal tube  302 , while  FIG. 13C  shows a further implementation of a support member  310 . In a further alternative, the tube  302  can have two or more support members. In certain embodiments, the support member (including the support members  304 ,  308 ,  310  depicted in  FIGS. 13A-13C ) can be the distal portion of the rod or tube extending distally from the shaft  312 . 
     As mentioned above, certain additional embodiments as disclosed and contemplated herein relate to an improved catheter tip that can be incorporated into any known multi-layer catheter, including any catheter disclosed herein or any other catheter for use in a human patient. As will be explained in further detail below, the various catheter tip embodiments disclosed herein have a protective wrap disposed at the tip of the catheter that eliminates any exposed ends of the tubular layers. 
     One embodiment of catheter tube  340  with an improved catheter tip  342  is depicted in  FIG. 15 . The tube  340  has a first layer (which, in this example, is also an inner layer)  344  and a second layer (which, in this example, is also an outer layer)  346 . The two layers  344 ,  346  are positioned adjacent to each other and are adhered, coupled, or otherwise attached to each other along a substantial length of each. The inner layer  344  also has a protective wrap (also referred to as an “extended portion,” “extension,” “distal wrap,” or “protective tip”)  348  that extends beyond the length of the outer layer  346  and, in this implementation, is wrapped around the distal end of the outer layer  346  such that the external portion (also referred to as “outer portion” or “distal portion”) of the extended portion  348  extends toward the proximal end of the tube  340  and is positioned against or adjacent to the exterior surface of the outer layer  346 . This configuration creates a fold  350  (also referred to herein as a “distal fold”) of the extended portion  348  at the catheter tip  342  that facilitates protection of the tube layers at the tip  342 . In other words, the positioning of the extended portion  348  as shown ensures that the ends of the layers  344 ,  346  are not exposed at the distal end of the tube  340 , thereby reducing the risk of delamination and the problems related thereto. 
     In this particular embodiment, the protective wrap  348  is integral with and is an extended portion of the inner layer  344 . Alternatively, in any of the catheter tip embodiments disclosed or contemplated herein, the protective wrap (such as protective wrap  348 ) can be a separate component that is coupled to the distal ends of the inner layer (in this example, the inner layer  344 ) and the outer layer (in this case, the outer layer  346 ). In a further alternative, in any of the catheter tip embodiments disclosed or contemplated herein, the protective wrap (such as protective wrap  348 ) can be integral with and an extended portion of the outer layer (such as outer layer  346 ). 
       FIG. 16  shows another embodiment of a catheter tube  360  with an improved catheter tip  362 . The tube  360  has a first (or “inner”) layer  364  and a second (outer) layer  366  that are positioned adjacent to each other and are attached to each other along a substantial length thereof. In this implementation, the protective wrap  368  is an extended portion  368  of the inner layer  364  that extends beyond the length of the outer layer  366  and, in this implementation, is folded such that the external portion or outer portion (also referred to herein as the “distal portion”)  368 A of the extended portion  368  is positioned against or adjacent to the internal portion or inner portion (also referred to herein as the “proximal portion”)  368 B and the distal end  370  of the external portion  368 A is positioned against or attached to the distal end  372  of the outer layer  366 . This configuration creates a fold  374  (also referred to herein as a “distal fold”) of the extended portion  368  at the catheter tip  362  that facilitates protection of the tube layers at the tip  362 . Like the embodiment depicted in  FIG. 15 , the configuration of the protective wrap  368  as shown ensures that the ends of the layers  364 ,  366  are not exposed at the distal end of the tube  360 , thereby reducing the risk of delamination and the problems related thereto. 
     A further implementation of a catheter tube  380  with an improved catheter tip  382  is depicted in  FIG. 17 . The tube  380  has a first (inner) layer  384  and a second (outer) layer  386  that are positioned adjacent to each other and are attached to each other along a substantial length thereof. The protective wrap  388  in this embodiment is an extended portion  388  of the inner layer  384  that extends beyond the length of the outer layer  386  and, in this implementation, is wrapped around the distal end of the outer layer  386  such that the external portion of the extended portion  388  extends toward the proximal end of the tube  380  and is positioned against or adjacent to the exterior surface of the outer layer  386 . This configuration creates a fold  390  (also referred to herein as a “distal fold”) of the extended portion  388  at the catheter tip  382  that facilitates protection of the tube layers at the tip  382 . However, unlike the embodiment in  FIG. 15 , in this implementation, the external portion of the extended portion  388  is positioned in a recess  392  or other type of configuration formed or defined in the external surface of the outer layer  386  such that the external portion of the extended portion  388  is “flush” with the outer layer  386 . In other words, the external portion of the extended portion  388  is positioned in the recess  392  such that the external diameter of the tube  380  along the length in which the external portion of the extended portion  388  is positioned in the recess  392  is the same as (or similar to) the external diameter along the length made up solely of the inner  384  and outer layers  386 . 
     In an alternative implementation, the recess (such as recess  392 ) can be created by a third layer (not shown), which is an additional outer layer that is external to the outer layer  386  and is positioned to create the recess  392 . In other words, in this alternative, the layer  386  as shown in  FIG. 17  is no longer an outer layer but instead is a middle layer that has no recess defined therein. Instead, the third layer is positioned over the middle layer but is shorter than the middle layer, thus leaving a portion of the middle layer exposed near the distal end, thereby creating the recess  392 . 
     In this embodiment of  FIG. 17 , the placement or disposition of the external portion of the protective wrap  388  in the recess  392  can create a smooth (also referred to as “non-catching” or “non-snagging”) outer surface of the tube  380  that reduces or prevents the occurrence of friction or snagging of the outer surface of the tube  380  within a mating (telescopic) second catheter or within a lumen or blood vessel in a patient during advancement or retraction of the tube  380 . In other words, the smooth outer surface means that there is no catch point formed by the protective wrap  388  that could potentially cause difficulties or damage in advancing or removing the device in relation to a patient. 
     In accordance with a further implementation, any of the improved catheter tips as discussed above with respect to  FIGS. 15-17  or contemplated elsewhere herein can also have variable stiffnesses along the length of the tip. For example, as shown with respect to  FIG. 17 , in some embodiments, a distal portion  394  of the distal end of the tube  380  can be relatively stiffer than a proximal portion  396  of the distal end of the tube  380 . In certain specific implementations, the greater stiffness of the distal portion  394  is caused by the composition or materials of the distal portion  394  having a higher durometer than the composition or materials of the proximal portion  396 . Alternatively, the greater stiffness of the distal portion  394  can be accomplished in any known fashion. It is understood that the length of the tube  380  that is considered the distal portion  394  (and thus the proximal portion  396 ) can vary, and that the specific lengths depicted in  FIG. 17  are merely exemplary. 
     One of ordinary skill in the art would understand that any of the above multi-layer catheter embodiments or any other embodiments contemplated herein can have more than two layers. For example, in certain implementations, the catheter can have 3 layers. Alternatively, the catheter can have 4 layers. In further embodiments, the catheter can have 5 or more layers. 
     It is further understood that the tubes of the multi-layer catheter embodiments can be made of one or more additional known polymeric, metal, or other materials that are typically used in catheters. Further, any tube embodiment can also include one or more radioopaque markers, including the examples described in further detail below. Further, the various tube implementations can also include a metal braid or coil configuration in the tube for additional reinforcement. 
     As discussed above, it is also understood that the catheter tip embodiments disclosed or contemplated herein can be incorporated into any known multi-layer catheter devices. For example, in one implementation, a catheter tip embodiment could be incorporated into a guiding catheter, including, for example, the guiding catheter  12  depicted in  FIG. 1  and discussed above. Alternatively, any of the catheter tip embodiments can be incorporated into any extension catheter such as those extension catheter embodiments disclosed or contemplated elsewhere herein. For example, any of the catheter tip embodiments disclosed or contemplated herein can be incorporated into the boosting catheter  10  as shown in  FIGS. 2A and 2B , the extension catheters depicted in  FIGS. 3A-3C  and  FIGS. 4A-4B , catheters having various manipulation shaft implementations such as those depicted in  FIGS. 6A-6F , and the boosting catheters  258  of  FIGS. 12A-12C , and any other catheter embodiments disclosed or contemplated herein. In addition, the various catheter tip embodiments disclosed herein can also be integrated into or combined with any known catheter. Further, it is understood that any of the improved catheter tip embodiments disclosed or contemplated herein can be integrated into or combined into a distal tip, including the distal end of any distal tube, of any of the various catheter implementations, such as guiding catheters, sheaths, delivery catheters (including stent delivery systems), snares, and arthorectomy catheters. 
     Further, it is understood that any of the various improved catheter tip embodiments disclosed or contemplated herein can be integrated into or combined with any boosting catheter, including the boosting catheter disclosed and claimed in U.S. application Ser. No. 14/210,572, entitled “Boosting Catheter and Related Systems and Methods,” which is hereby incorporated herein by reference in its entirety. 
     In addition, any of the various catheter embodiments disclosed herein, including the various implementations having a segmented catheter structure and the various implementations having an improved catheter tip can have an external lubricious coating. The external lubricious coating can be positioned around or integral with an entire length of the distal tube (or any portion thereof), an entire length of the proximal shaft (or any portion thereof), or an entire length of both the distal tube and the proximal shaft (or any portions thereof). In some implementations, the lubricious coating can be hydrophobic, while in other embodiments it can be hydrophilic. 
     Further, any of the various catheter embodiments disclosed herein, including the various implementations having a discontinuous or segmented catheter structure and the various implementations having an improved catheter tip, can also have an outer support membrane (also referred to as a “support membrane” or “support layer”) disposed around a proximal portion of the distal tube. It is also understood that any embodiment of the support membrane as disclosed or contemplated herein can also be incorporated into any other known catheter.  FIG. 18  depicts one embodiment of a catheter  400  in which the distal tube  404  has a support membrane  406  disposed around and coupled to the external wall  408  of the distal tube  404 . More specifically, in this exemplary embodiment, the membrane  406  is disposed around a portion of the wall  408  and extends longitudinally along the length of the tube  404  such that the proximal end of the membrane  406  does not extend to the proximal end  410  of the tube  404 . That is, the membrane  406  is positioned such that it is spaced from the proximal end  410  of the tube  404 . Alternatively, the membrane  406  can extend to the proximal end  410  of the tube  404 . According to certain implementations, the membrane  406  is disposed in the connection zone (or region) of the distal tube  404  in which the manipulation shaft  402  is coupled to the tube  402  (similar to the connection zone  42  discussed above with respect to  FIG. 3A ). 
     The membrane  406  (and any other membrane embodiment disclosed or contemplated herein) can wrap or otherwise be disposed around a portion of the circumference of the tube  404  as shown. Alternatively, the membrane can be an additional tube or tube layer that is disposed around the entire circumference of the tube  404 . In a further alternative, the membrane can be disposed around ¼, ½, or ¾ of the circumference of the tube  404 . In yet another alternative, as best shown in  FIG. 19 , the membrane  406  can be disposed around any amount of the circumference of the tube  404 . That is, the membrane  406  can cover any amount of the circumference of the tube  404  from about 30 degrees to about 360 degrees of the circumference. It is understood that these characteristics can apply to any membrane embodiment disclosed or contemplated herein that is disposed around any tube, including any catheter tube. 
     The membrane  406  (and any other membrane embodiment disclosed or contemplated herein) can have any size, shape, or configuration. In certain implementations, the membrane can be circular, oval, or an ellipse. Further, any of the membrane embodiments disclosed or contemplated herein is not necessarily a unitary, uniform component. Instead, any membrane embodiment can have one or more openings defined therein. In certain implementations, the one or more openings can be one or more channels defined in the membrane. Alternatively, membrane can have any pattern, feature, or configuration that forms any shape or shapes. 
     The various membrane embodiments disclosed herein (including membrane  406 ) can be made of any polymeric or non-polymeric material or any other known material that can be positioned around a catheter tube and is high strength and/or puncture resistant. For example, in one embodiment in which the material is polymeric, the material can be PTFE (etched or non-etched), PET, or PEEK or any other known polymeric material with the appropriate high strength and/or puncture resistance characteristics. In one embodiment, the membrane (such as membrane  406 ) has a thickness ranging from about 0.00025 inches to about 0.2 inches. Alternatively, the membrane can have a thickness ranging from about 0.001 inches to about 0.005 inches. 
     The membrane  406  (or any other membrane implementation disclosed or contemplated herein) can be attached to the external wall (such as wall  408 ) of the tube (such as tube  404 ) in a reflow process (in which the tube materials are heated/melted and the membrane is heat bonded to the tube), via adhesive bonding, or any other known method of attachment. 
       FIG. 20  shows another embodiment of a catheter  420  with a membrane  426  disposed around the connection zone of the manipulation shaft  422  and the distal tube  424 . In this embodiment, the membrane  426  covers more of the circumference of the tube  424  in comparison to the membrane  406  discussed above and depicted in  FIG. 19 . Further, in this implementation, the membrance extends longitudinally along the length of the tube  424  such that the proximal end of the membrane  426  extends to the proximal end  428  of the tube  424 . That is, the proximal end of the membrane  426  is positioned at the proximal end  428  of the tube  424 . Alternatively, the membrane  426  can be spaced from the proximal end  428  of the tube  424 . 
     A side view of another embodiment is shown in  FIG. 21  in which the membrane  446  is positioned around the connection zone of the manipulation shaft  442  and the distal tube  444  of the catheter  440 . 
     As mentioned above, any embodiment of the support membrane can also be incorporated into any other known catheter. For example, in another implementation as depicted in  FIG. 22 , the membrane  456  is positioned around the connection zone of the manipulation shaft  452  and the distal tube  454  of the catheter  450 . In this embodiment, the manipulation shaft  452  is a flat or substantially square shaft or wire  452 . Alternatively, the shaft  452  can have any known cross-sectional shape for a known component of a catheter. In further implementations, the shaft  452  can be tapered along some portion of its length or the entire length thereof. 
     In a further embodiment as shown in  FIG. 23 , the membrane  466  can be positioned around another known catheter. In this implementation, the catheter  460  has a manipulation shaft  462  that can be a solid wire or hollow tube that is further joined to a cylindrical or partially-cylindrical structure  463 . The structure  463  is embedded within, or joined to, the wall at the proximal end of the distal tube  464 . In certain embodiments, the structure  463  can be slotted or have a pattern formed therein to enhance attachment and flexibility. The support membrane  466  is positioned around the circumference or a portion of the circumference of the distal tube  464  in the connection zone extending distally on the distal tube from the structure  463 . In certain embodiments, the support membrane  466  can enhance or strengthen the attachment of the structure  463  and the distal tube  464 . 
     In yet another implementation as shown in  FIG. 24 , the membrane  476  can be positioned around another known catheter. That is, the membrane  476  is positioned around the connection zone of the manipulation shaft  472  and the distal tube  474  of the catheter  470 . In this embodiment, the manipulation shaft  472  has an extension  478  that extends into and is embedded within the proximal end of the distal tube  474  as shown. The extension  478  in this embodiment has a configuration or features that strengthen the connection between the manipulation shaft  472  and the tube  474 , thereby reducing the risk of separation of those two components. 
     Without being limited by theory, it is believed that the membrane embodiments disclosed herein provide a higher strength bond for the proximal portion of the distal tube that the membrane is disposed around, along with enhanced torque, peel, and shear strength. In those implementations in which the membrane disposed around the proximal portion is disposed around the connection zone of the catheter, the added strength bond can increase tensile strength and help prevent or reduce the risk of delamination, thereby preventing or reducing the risk of separation of the proximal manipulation shaft from the distal tube. That is, the membrane can provide fatigue resistance at the connection zone. In known fatigue testing of known catheters, application of repeated stress to the connection zone of the catheters caused the proximal shaft to separate from the distal tube (which could result in detachment proximal shaft from the distal tube or embolization during use). The membrane embodiments disclosed herein can reduce or prevent the risk of such separation. In addition, the membrane embodiments can also provide enhanced lubricity and additional strain relief properties. 
     In certain embodiments as discussed above, the membrane is disposed around a portion of the circumference of the tube, rather than the entire circumference. According to certain implementations, any membrane disposed around less than the entire circumference can be called a “partial circumference membrane.” One advantage of a partial circumference membrane made of a high strength material such as those discussed above is that it provides support without fully encircling the tube. It is understood that a membrane made of a high strength material (such as PTFE or PEEK) that fully encircles the catheter tube could cause the catheter tube to malfunction or not function properly. That is, the high strength material positioned entirely around the tube could render that portion of the tube too inflexible or otherwise inoperable for its desired purpose. Thus, in those circumstances, a partial circumference membrane can utilize a high strength material while not rendering the catheter tube hindered or inoperable. 
     Further, a partial circumference membrane can also have the advantage of providing the thinnest thickness (or lowest profile) possible when adding an additional layer to a tube. That is, a membrane that encircles the entire circumference of a tube will add more outer diameter to the tube than a partial circumference membrane. As such, any partial circumference membrane can minimize the additional circumference of a tube when the membrane is added thereto. 
     Certain additional embodiments as disclosed and contemplated herein relate to an improved proximal portion of a catheter tube that can be incorporated into any known multi-layer catheter, including any catheter disclosed herein or any other catheter for use in a human patient. As will be explained in further detail below, the various improved proximal tube portion embodiments disclosed herein have a protective wrap disposed at the proximal portion of the tube that eliminates any exposed ends of the tubular layers. It is understood that the improved proximal tube portion embodiments are substantially similar to the improved catheter tip embodiments discussed above. 
     One embodiment of catheter tube  500  with an improved proximal portion  502  is depicted in  FIG. 25 . The tube  500  has a first layer (which, in this example, is also an inner layer)  504  and a second layer (which, in this example, is also an outer layer)  506 . The two layers  504 ,  506  are positioned adjacent to each other and are adhered, coupled, or otherwise attached to each other along a substantial length of each. At least a portion of the inner layer  504  is a protective wrap (also referred to as an “extended portion,” “extension,” “distal wrap,” or “protective tip”)  508  that extends beyond the length of the outer layer  506  and, in this implementation, is wrapped around at least a portion of the distal end of the outer layer  506  as shown such that the external portion (also referred to as “outer portion” or “distal portion”) of the extended portion  508  extends toward the distal end of the tube  500  and is positioned against or adjacent to the exterior surface of the outer layer  506 . This configuration creates a fold  510  (also referred to herein as a “distal fold”) of the extended portion  508  along at least a portion of the proximal end  512  of the tube  500  that facilitates protection of the tube layers at the end  512 . In other words, the positioning of the extended portion  508  as shown ensures that the ends of the layers  504 ,  506  are not exposed along that portion of the proximal end  512  of the tube  500  covered by the wrap  508 , thereby reducing the risk of delamination and the problems related thereto. 
     In this particular embodiment, the protective wrap  508  is integral with and is an extended portion of the inner layer  504 . Alternatively, in any of the improved proximal tube portion embodiments disclosed or contemplated herein, the protective wrap (such as protective wrap  508 ) can be a separate component that is coupled to at least a portion of the distal ends of the inner layer (in this example, the inner layer  504 ) and the outer layer (in this case, the outer layer  506 ). In a further alternative, in any of the proximal tube portion embodiments disclosed or contemplated herein, the protective wrap (such as protective wrap  508 ) can be integral with and an extended portion of the outer layer (such as outer layer  506 ). 
       FIG. 26  shows another embodiment of a catheter tube  520  with an improved proximal tube portion  522 . The tube  520  has a first (or “inner”) layer  524  and a second (outer) layer  526  that are positioned adjacent to each other and are attached to each other along a substantial length thereof. In this implementation, the protective wrap  528  is an extended portion  528  of the inner layer  524  that extends beyond the length of the outer layer  526  and, in this implementation, is folded such that the external portion or outer portion (also referred to herein as the “distal portion”)  528 A of the extended portion  528  is positioned against or adjacent to the internal portion or inner portion (also referred to herein as the “proximal portion”)  528 B along at least a portion of the circumference of the end  536  and the distal end  530  of the external portion  528 A is positioned against or attached to the proximal end  532  of the outer layer  526 . This configuration creates a fold  534  (also referred to herein as a “distal fold”) of the extended portion  528  at the proximal end  536  along at least a portion of the end  536  that facilitates protection of the tube layers at the end  536 . Like the embodiment depicted in  FIG. 25 , the configuration of the protective wrap  528  as shown ensures that at least a portion of the ends of the layers  524 ,  526  are not exposed at the proximal end  536  of the tube  520 , thereby reducing the risk of delamination and the problems related thereto. 
     Additional implementations similar to those discussed above with respect to  FIGS. 15-17  and any other embodiments contemplated in the discussion above are also contemplated for the proximal tube end improvements. That is, any features or configurations of the improved distal tip embodiments discussed above and depicted in  FIGS. 15-17  can also be incorporated into any of the embodiments of the improved proximal portions as discussed above and depicted in  FIGS. 25-26 . However, in certain embodiments of the improved proximal portion as noted above, the protective wrap does not extend around the entire circumference of the proximal end of the tube. As discussed above, it is also understood that the improved proximal end embodiments disclosed or contemplated herein can be incorporated into any known multi-layer catheter devices. Further, it is understood that any of the various improved proximal end embodiments disclosed or contemplated herein can be integrated into or combined with any boosting catheter, including the boosting catheter disclosed and claimed in U.S. application Ser. No. 14/210,572, entitled “Boosting Catheter and Related Systems and Methods,” which is hereby incorporated herein by reference in its entirety. 
     While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.