Abstract:
A reinforced intravascular catheter adapted for use in performing minimally invasive medical procedures. A catheter, in accordance with the present invention, comprising an inner tubular member having an outer surface, a proximal end, a distal end, and a lumen extending therethrough. The catheter further including a support member overlaying the inner tubular member and conforming to the outer surface thereof, the support member including at least one filament forming a plurality of turns. The support member further including at least one multi-layered portion having a first layer and a plurality of additional layers, each layer comprising a plurality of turns formed by at least one filament, the plurality of additional layers each overlaying at least the first layer. The catheter also including an outer layer overlaying both the support member and the inner tubular member. A method of fabricating a catheter in accordance with the present invention is also disclosed.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to catheters for performing medical procedures. More particularly, the present invention relates to reinforced intravascular catheters. 
     BACKGROUND OF THE INVENTION 
     Intravascular catheters are currently utilized in a wide variety of minimally invasive medical procedures. Generally, an intravascular catheter enables a physician to remotely perform a medical procedure by inserting the catheter into the vascular system of the patient at a location that is easily accessible and thereafter navigating the catheter to the desired target site. By this method, virtually any target site in the patient&#39;s vascular system may be remotely accessed, including the coronary, cerebral, and peripheral vasculature. 
     Typically, the catheter enters the patient&#39;s vasculature at a convenient location such as a blood vessel in the neck or near the groin. Once the distal portion of the catheter has entered the patient&#39;s vascular system, the physician may urge the distal tip forward by applying longitudinal forces to the proximal portion of the catheter. For the catheter to effectively communicate these longitudinal forces, it is desirable that the catheter have a high level of pushability and kink resistance. 
     Frequently, the path taken by a catheter through the vascular system is tortuous, requiring the catheter to change direction frequently. It may also be necessary for the catheter to double back on itself. Physicians often apply torsional forces to the proximal portion of the catheter to aid in steering the catheter. To facilitate the steering process, it is desirable that an intravascular catheter have a relatively high level of torquability. Furthermore, in order for the catheter to conform to a patient&#39;s tortuous vascular system, it is desirable that intravascular catheters be very flexible. 
     The distance between the access site and the target site is often in excess of 100 cm. The inside diameter of the vasculature at the access site is often less than 5 mm. In light of the geometry of the patient&#39;s body, it is desirable to combine the features of torqueabity, pushability, and flexibility into a catheter which is relatively long and has a relatively small diameter. 
     Ideally, the distal end of an intravascular catheter will be adapted to reduce the probability that the vascular tissue will be damaged as the catheter is progressed through the vascular system. This is sometimes accomplished by bonding or welding a relatively soft tip member to the distal end of an intravascular catheter. 
     After the intravascular catheter has been navigated through the patient&#39;s vascular system so that its distal end is adjacent the target site, the catheter may be used for various diagnostic and/or therapeutic purposes. One example of a diagnostic use for an intravascular catheter is the delivery of radiopaque contrast solution to enhance fluoroscopic visualization. In this application, the intravascular catheter provides a fluid path leading from a location outside the body to a desired location inside the body of a patient. In order to maintain a fluid path, it is desirable that intravascular catheters be sufficiently resistant to kinking. In addition, because such fluids are delivered under pressure, it is also desirable that intravascular catheters be sufficiently resistant to bursting or leaking. 
     One useful therapeutic application of intravascular catheters is the treatment of intracranial aneurysms in the brain. Approximately 25,000 intracranial aneurysms rupture each year in North America. An aneurysm which is likely to rupture, or one which has already ruptured, may be treated by delivering an embolic device or agent to the interior of the aneurysm. The embolic device or agent encourages the formation of a thrombus inside the aneurysm. The formation of a thrombus reduces the probability that an aneurysm will rupture. The formation of a thrombus also reduces the probability that a previously ruptured aneurysm will re-bleed. Thrombus agents which may be used include liquid thrombus agents such as cyanocrylate, and granulated thrombus agents such as polyvinyl alcohol. An additional type of thrombus agent which is frequently used is a tiny coil. Any of the thrombus agents described above may be delivered using an intravascular catheter. 
     When treating an aneurysm with the aid of an intravascular catheter, the catheter tip is typically positioned proximate the aneurysm site. The thrombus agent is then urged through the lumen of the intravascular catheter and introduced into the aneurysm. Shortly after the thrombus agent is placed in the aneurysm, a thrombus forms in the aneurysm and is shortly thereafter complemented with a collagenous material which significantly lessens the potential for aneurysm rupture. It is desirable that the lumen of the catheter provides a path for delivering embolic devices to an aneurysm. To this end, it is desirable that the pathway through the catheter have a low friction surface. 
     The blood vessels in the brain frequently have an inside diameter of less than 3 mm. Accordingly, it is desirable that intravascular catheters intended for use in these blood vessels have an outside diameter which allows the catheter to be easily accommodated by the blood vessel. The path of the vasculature inside the brain is highly tortuous, and the blood vessels are relatively fragile. Accordingly, it is desirable that distal portion of a catheter for use in the brain be adapted to follow the highly torturous path of the neurological vasculature. 
     As described above, it is desirable to combine a number of performance features in an intravascular catheter. It is desirable that the catheter have a relatively high level of pushability and torqueability, particularly near its proximal end. It is also desirable that a catheter be relatively flexible, particularly near its distal end. The need for this combination of performance features is sometimes addressed by building a catheter which has two or more discrete tubular members having different performance characteristics. For example, a relatively flexible distal section may be bonded to a relatively rigid proximal section. When a catheter is formed from two or more discrete tubular members, it is necessary to form a bond between the distal end of one tubular member and the proximal end of another tubular member. 
     SUMMARY OF THE INVENTION 
     The present invention relates generally to catheters for performing medical procedures. More particularly, the present invention relates to reinforced intravascular catheters. A catheter in accordance with the present invention includes an elongate shaft. A hub may be fixed to the proximal end of the elongate shaft. The elongate shaft is comprised of an inner tubular member having a first layer, a second layer, an outer surface, and a distal end. 
     A support member overlies at least a portion of the inner tubular member and conforms to the surface thereof. The support member has a first portion, a second portion, and a third portion. The first portion, second portion, and third portion each have a distal end and a proximal end. The first portion of the support member being disposed proximate the distal end of the inner tubular member. The first portion of the support member is comprised of at least one filament which is circumferentially disposed about the inner tubular member in a helical manner. The at least one filament generally conforms to the shape of the outer surface of the inner tubular member and forms a plurality of turns. 
     In a presently preferred embodiment, a ring is circumferentially disposed about the outer surface of the inner tubular member proximate the distal end thereof. In a presently preferred embodiment, the ring is comprised of a radiopaque material. In this presently preferred embodiment, the ring produces a relatively bright image on a fluoroscopy screen during a medical procedure. This relatively bright image aids the user of the catheter in determining the location of the distal end of the elongate shaft. 
     In one embodiment of the present invention, a distal portion of the at least one filament is disposed between the outer surface of the inner tubular member and the ring. Placing the distal portion of the filament in this position has the advantage of retaining the distal portion of the filament while the remainder of the filament is wound around the inner tubular member. 
     The second portion of the support member is circumferentially disposed about the inner tubular member, with its distal end proximate the proximal end of the first portion of the support member. In one embodiment of the present invention, the second portion of the support member is comprised of a lattice structure having a first layer, a second layer, and a third layer. Each layer being comprised of a plurality of turns, formed by at least one filament. 
     The third portion of the support member is comprised of a plurality of turns formed by at least one filament. In a presently preferred embodiment, the filaments forming the support member are all coextensive. 
     In a presently preferred embodiment, the elongate shaft includes a flare disposed proximate the proximal end thereof. The hub may be formed over the proximal end of the elongate shaft. In a presently preferred embodiment, the hub is formed using an insert molding process. In this presently preferred embodiment, the single filament includes a distal end and a proximal end. In this presently preferred embodiment, it is unlikely that the distal end of the filament will protrude through the outer layer of the catheter since the distal portion of the filament is retained by a ring, as described above. Likewise, it is unlikely that the proximal end of the filament will protrude from the catheter since a hub is disposed over the proximal end of the elongate shaft. 
     An outer layer overlays both the support member, and the inner tubular member. In a presently preferred embodiment, the material of the outer layer fills any interstitial spaces in the support member. Also in a presently preferred embodiment, the outer layer is comprised of a distal portion, a middle portion, and a proximal portion. 
     In one embodiment of the present invention, the proximal end of the distal portion of the outer layer is fused to the distal end of the middle portion thereof. Likewise, the proximal end of the middle portion of the outer layer is fused to the distal end of the proximal portion. In this presently preferred embodiment, the distal portion, the middle portion, and the proximal portion combine to form an outer layer which is substantially continuous. 
     In one aspect of the present invention, the outer diameter of the proximal portion of the outer layer is large enough to substantially cover the layers of the second portion of the support member. Likewise, in another aspect of the present invention, the outer diameter of the distal portion of the outer layer is large enough to substantially cover the first portion of the support member. In a presently preferred embodiment, the outer diameter of the distal portion of the outer layer is smaller than the outer diameter of the proximal portion of the outer layer. It may be appreciated that the single layer construction of the first portion of the support member facilitates having an outer diameter of the distal portion which is smaller than the outer diameter of the proximal portion. 
     In one embodiment of the present invention, the plurality of turns forming the first portion of the support member are disposed at a first pitch. Also in this embodiment, the turns of the second portion of the support member are disposed at a second pitch different than the first pitch. Finally, in this embodiment, the turns of the third portion of the support member are disposed at a third pitch. In a presently preferred embodiment, the pitches of the first, second, and third portions of the support member may be selected to impart desired performance characteristics upon the catheter. For example, the third pitch may be relatively coarse so that it does not hinder the formation of a flare at the proximal end of the elongate shaft. 
     In a presently preferred embodiment, the distal end of the first portion of the support member is disposed proximate the distal end of the elongate shaft. An atraumatic tip is formed from the inner tubular member and the outer layer. In this presently preferred embodiment, the atraumatic tip is disposed distally of the distal portion of the first portion of the support member. In this presently preferred embodiment, the atraumatic tip has a level of flexibility which makes it unlikely to damage the blood vessels of a patient. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a catheter in accordance with an exemplary embodiment of the present invention; 
     FIG. 2 is a cross-sectional plan view of an elongate shaft in accordance with an exemplary embodiment of the present invention; 
     FIG. 3 is a plan view of an assembly including an inner tubular member and a filament in accordance with an exemplary embodiment of the present invention, the filament being circumferentially disposed about the inner tubular member following a generally helical path and forming a plurality of turns comprising a support member; 
     FIG. 4 is a plan view of the assembly of FIG. 3, to which a second layer has been added to a portion of the support member to form a lattice; 
     FIG. 5 is a plan view of the assembly of FIG. 4, to which a third layer has been added to a portion of the support member; and 
     FIG. 6 is a plan view of the assembly of FIG. 5, in which a plurality of portions forming an outer layer are circumferentially disposed over the support member and the inner tubular member. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered identically. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. 
     Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements. All other elements employ that which is known to those of skill in the field of the invention. Those skilled in the art will recognize that many of the examples provided have suitable alternatives which may be utilized. 
     FIG. 1 is a plan view of a catheter  10  in accordance with the present invention. Catheter  10  includes an elongate shaft  12  having a distal end  14 , a proximal end  16 , an outer surface  18 , and a lumen  20  extending therethrough. Catheter  10  further includes a hub  26  and a strain relief  28  disposed proximate proximal end  16  of elongate shaft  12 . Hub  26  and strain relief  28  enable a physician to connect other devices to catheter  10 . Hub  26  and strain relief  28  also provide a convenient place for a physician to apply longitudinal or rotational forces in order to manipulate catheter  10 . 
     FIG. 2 is a cross-sectional plan view of elongate shaft  12  of catheter  10 . Elongate shaft  12  is comprised of an inner tubular member  30  having a first layer  32 , a second layer  34 , an outer surface  36 , and a distal end  38 . In a presently preferred embodiment, first layer  32  of inner tubular member  30  is comprised of PTFE (polytetrafluoroethylene). PTFE is a preferred material because it creates a smooth, low-friction surface for the passage of other devices or fluids through the catheter. Also in a presently preferred embodiment, second layer  34  of inner tubular member  30  is comprised of polyether block amide (PEBA). Polyether block amide is commercially available from Atochem Polymers of Birdsboro, Pa., under the trade name PEBAX. Those of skill in the art will appreciate that inner tubular member  30  may be comprised of a single layer or a plurality of layers without deviating from the spirit and scope of the present invention. Those of skill in the art will appreciate that other materials may be suitable for the layer(s) of inner tubular member  30 . Examples of materials suitable in some applications include polyolefins, polyamides, and polyimides. 
     A support member  40  overlies inner tubular member  30  and conforms to the surface thereof Support member  40  has a first portion  42 , a second portion  44 , and a third portion  46 . First portion  42 , second portion  44 , and third portion  46  each have a distal end  52 ,  54 , and  56  respectively. In addition, first portion  42 , second portion  44 , and third portion  46  each have a proximal end  62 ,  64 , and  66  respectively. 
     First portion  42  of support member  40  is disposed proximate distal end  14  of inner tubular member  30  and is comprised of at least one filament  100  which is circumferentially disposed about inner tubular member  30 . At least one filament  100  generally conforms to the shape of outer surface  36  of inner tubular member  30  and forms a plurality of turns  102  in a helical pattern. 
     In the embodiment of FIG. 2, at least one filament  100  follows a generally helical path. Also in the embodiment of FIG. 2, one filament  100  is illustrated. Those of skill in the art will appreciate, however, that two or more filaments could be circumferentially disposed about inner tubular member  30  without departing from the spirit or scope of the present invention. For example, two filaments  100  could be wound around inner tubular member  30 , each filament following a generally helical path, such that the two filaments create a double helix. 
     A ring  70  is circumferentially disposed about outer surface  36  of inner tubular member  30  proximate the distal end thereof. In a presently preferred embodiment, ring  70  is comprised of a radiopaque material. In this presently preferred embodiment, ring  70  produces a relatively bright image on a fluoroscopy screen during a medical procedure. This relatively bright image aids the user of catheter  10  in determining the location of distal end  14  of elongate shaft  12 . A number of radiopaque materials are acceptable for use in fabricating ring  70 . Acceptable materials included gold, platnium, and a plastic material loaded with a radiopaque filler. 
     In the embodiment of FIG. 2, a distal portion  104  of at least one filament  100  is disposed between outer surface  36  of inner tubular member  30  and radiopaque ring  70 . Placing distal portion  104  of filament  100  in this position has the advantage of retaining distal portion  104  of filament  100  while the remainder of filament  100  is wound around inner tubular member  30 . 
     Second portion  44  of support member  40  is circumferentially disposed about inner tubular member  30 , with its distal end  54  proximate proximal end  62  of first portion  42  of support member  40 . Second portion  44  of support member  40  is comprised of a first layer  82 , a second layer  84 , and a third layer  86 . Each layer  82 ,  84 , and  86  is comprised of a plurality of turns  92 ,  94 , and  96 , respectively. Turns  92 ,  94 , and  96  are formed of filaments  112 ,  114 , and  116 , respectively. In a presently preferred embodiment, filaments  100 ,  112 ,  114 , and  116  are all coextensive. 
     Third portion  46  of support member  40  is comprised of a plurality of turns  122  formed by at least one filament  120 . In a presently preferred embodiment, filament  120  is coextensive with both filaments  100 ,  112 ,  114  and  116 . Third portion  46  of support member  40  is disposed with its distal end  56  proximate proximal end  64  of second portion  44 . 
     In a presently preferred embodiment, elongate shaft  12  includes a flare  22  disposed proximate proximal end  16  thereof. Hub  26  may be formed over proximal end  16  of elongate shaft  12  as shown in FIG.  1 . In a presently preferred embodiment, hub  26  is formed using an overmolding process. Also in a presently preferred embodiment, support member  40  is formed of a single filament  200 . In this presently preferred embodiment, filament  200  is comprised of filaments  100 ,  112 ,  114 ,  116 , and  120 , all of which are coextensive. In this presently preferred embodiment, filament  200  includes a distal end  202  and a proximal end  204 . In this presently preferred embodiment, it is unlikely that distal end  202  of filament  200  will protrude through the outer layer of catheter  10  since the distal portion of filament  200  is retained by ring  70 , as described above. Likewise, it is unlikely that proximal end  204  of filament  200  will protrude from catheter  10 , since hub  26  is formed over proximal end  16  of elongate shaft  12 . 
     FIG. 2 is an enlarged, partial cross-section illustrating second portion  44  of support member  40 . As shown in FIG. 2, second layer  84  of second portion  44  of support member  40  overlays first layer  82 . Likewise, third layer  86  of second portion  44  of support member  40  overlays second layer  84 . Referring again to FIG. 2, it can be appreciated that an outer layer  190  overlays both support member  40  and inner tubular member  30 . In a presently preferred embodiment, the material of outer layer  190  fills in any interstitial spaces in support member  40 . Also in a presently preferred embodiment, outer layer  190  is comprised of a distal portion  192 , a middle portion  194 , and a proximal portion  196 . 
     In the embodiment of FIG. 2, the proximal end of distal portion  192  of outer layer  190  has been fused to the distal end of middle portion  194 . Likewise, the proximal end of middle portion  194  of outer layer  190  has been fused to the distal end of proximal portion  196 . In this presently preferred embodiment, distal portion  192 , middle portion  194 , and proximal portion  196  combine to form an outer layer  190  which is substantially continuous. 
     As shown in FIG. 2, proximal portion  196  of outer layer  190  has an outer diameter A, and distal portion  192  has an outer diameter D. In the embodiment of FIG. 2, middle portion  194  of outer layer  190  includes a first outer diameter B substantially equal to outer diameter A of proximal portion  196  and a second outer diameter C substantially equal to outer diameter D of distal portion  192 . Middle portion  194  also includes a taper  98  extending between outer diameter B and outer diameter C of middle portion  194 . 
     In the embodiment of FIG. 2, distal end  54  of second portion  44  of support member  40  is disposed proximate taper  98  of middle portion  194  of outer layer  190 . Those of skill in the art will appreciate that other embodiments are possible without deviating from the spirit or scope of the present invention. For example, distal end  54  of second portion  44  of support member  40  may be disposed proximal to taper  98  of middle portion  194  of outer layer  190 . 
     Also in the embodiment of FIG. 2, outer diameter A of proximal portion  196  of outer layer  190  is large enough to substantially cover layers  82 ,  83 , and  84  of second portion  44  of support member  40 . Likewise, outer diameter D of distal portion  192  of outer layer  190  is large enough to substantially cover first portion  42  of support member  40 . In a presently preferred embodiment, outer diameter D of distal portion  192  is smaller than outer diameter A of proximal portion  196 . It may be appreciated that the single layer construction of first portion  42  of support member  40  facilitates having an outer diameter D of distal portion  192  which is smaller than outer diameter A of proximal portion  96 . 
     As described previously, in a presently preferred embodiment, distal end  202  of filament  200  is retained by ring  70 , and proximal end  204  of filament  200  is disposed within hub  26  of catheter  10 . In this presently preferred embodiment, diameters A and D do not need to be enlarged to prevent distal ends  202  and  204  from protruding out of catheter  10 . 
     In the embodiment of FIG. 2, the plurality of turns  102  forming first portion  42  of support member  40  are disposed at a first pitch  152 . Also in the embodiment of FIG. 2, the turns  82 ,  84 , and  86  of second portion  44  of support member  40  are disposed at a second pitch  154  different than first pitch  152 . Finally, in the embodiment of FIG. 2, turns  122  of third portion  46  of support member  40  are disposed at a third pitch  156 . In a presently preferred embodiment, pitches  152 ,  154 , and  156  of support member  40  may be selected to impart desired performance characteristics upon catheter  10 . For example, third pitch  156  may be relatively coarse to so that it does not hinder the formation of flare  22 . 
     In a presently preferred embodiment, distal end  52  of first portion  42  of support member  40  is disposed proximate distal end  14  of elongate shaft  12 . An atraumatic tip  150  is formed of inner tubular member  30  and outer layer  190 . In the embodiment of FIG. 2, atraumatic tip  150  is disposed distally of distal portion  52  of first portion  42  of support member  40 . In this presently preferred embodiment, atraumatic tip  150  has a level of flexibility which makes it unlikely to damage the blood vessels of a patient. 
     As described previously, filaments  100 ,  112 ,  114 ,  116 , and  120  of support member  40  are coextensive in a presently preferred embodiment. In a presently preferred embodiment, filaments  100 ,  112 ,  114 ,  116 , and  120  comprise metal wire. In a presently most preferred embodiment, filaments  100 ,  112 ,  114 ,  116 , and  120  are comprised of stainless steel wire. Those of skill in the art will appreciate that filaments  100 ,  112 ,  114 ,  116 , and  120  may be comprised of other materials without deviating from the spirit or scope of the present invention. Those of skill in the art will also appreciate that filaments  100 ,  112 ,  114 ,  116 , and  120  may be comprised of metallic or non-metallic materials. Examples of materials which may be suitable in some applications include: nickel titanium alloy, nylon, KEVLAR, and carbon fibers. 
     Also in a presently preferred embodiment, outer layer  190  is comprised of polyether block amide (PEBA). Polyether block amide is commercially available from Atochem Polymers of Birdsboro, Pa., under the trade name PEBAX. In a presently most preferred embodiment, distal portion  192 , middle portion  194 , and proximal portion  196  of outer tubular layer are comprised of a PEBA polymer having durometers of about  35 ,  63 , and  72  respectively. 
     Outer layer  190  may be comprised of other materials without departing from the spirit of scope of this invention. Examples of materials which may be suitable in some applications include polyethylene (PE), polypropylene (PP), polyvinylchloride (PVC), polyurethane, and polytetrafluoroethylene (PTFE). It should be understood that additives, loading agents, or fillers may be added to the material of outer layer  190  without deviating from the spirit or scope of the present invention. These additional materials may include color pigments, radiopaque materials, lubricants, or fillers. 
     FIG. 3 is a plan view of an assembly including inner tubular member  30  and a filament  300 . A ring  70  is circumferentially disposed about outer surface  36  of inner tubular member  30  proximate its distal end  38 . A distal portion  301  of filament  300  is disposed between outer surface  36  of inner tubular member  30  and radiopaque ring  70 . 
     First portion  42  of support member  40  is disposed proximate distal end  38  of inner tubular member  30  and is comprised of at least one filament  300 . Filament  300  is circumferentially disposed about inner tubular member  30  and generally conforms to the shape of outer surface  36 . In the embodiment of FIG. 3, filament  300  follows a generally helical path and forms a plurality of turns  302 . 
     Those of skill in the art will appreciate, however, that two or more filaments could be circumferentially disposed about inner tubular member  30  without departing from the spirit or scope of the present invention. If two filaments were utilized, for example, they would form a double helix. 
     Turns  302  of first portion  42  are disposed at a first pitch  152  and combine to form the first portion  42  of a support member  40 . In a presently preferred embodiment, turns  302  are disposed at a first pitch  152  of between about 0.020 inches per turn and 0.002 inches per turn. In a presently most preferred embodiment, turns  302  are disposed at a first pitch  152  of about 0.006 inches per turn. 
     As shown in FIG. 3, filament  300  extends beyond first portion  42  of support member  40  to form the first layer  82  of a second portion  44  of support member  40 . Filament  300  is circumferentially disposed about inner tubular member  30  and follows a generally helical path, forming a plurality of turns  304 . Turns  304  of second portion  44  are disposed at a second pitch  154 . In a presently preferred embodiment, turns  304  are disposed at a second pitch  154  of between about 0.050 inches per turn and 0.005 inches per turn. In a presently most preferred embodiment, turns  304  are disposed at a second pitch  154  of about 0.018 inches per turn. 
     In the embodiment of FIG. 3, first pitch  152  is generally finer than second pitch  154 . Those of skill in the art will recognize that a number of values may be used for first pitch  152  and second pitch  154  without deviating from the spirit and scope of the present invention. For example, embodiments of the present invention have been envisioned in which first pitch  152  and second pitch  154  are substantially equal. 
     FIG. 4 is a plan view of the assembly of FIG. 3, in which a second layer  84  has added to second portion  44  of support member  40 . Second layer  84  is comprised of a plurality of turns  306  which overlay first layer  82  of second portion  44  of support member  40 . Turns  306  are formed by filament  300  which is disposed along a generally helical path overlaying first layer  82  of second portion  44  of support member  40 . 
     FIG. 5 is a plan view of the assembly of FIG. 4, in which a third layer  86  has added to second portion  44  of support member  40 . Third layer  86  is comprised of a plurality of turns  308  which overlay second layer  84  of second portion  44  of support member  40 . Turns  308  are formed by filament  300  which is disposed along a generally helical path overlaying second layer  84  of second portion  44  of support member  40 . 
     In the assembly of FIG. 5, filament  300  extends beyond second portion  44  of support member  40  to form a third portion  46  of support member  40 . Filament  300  is circumferentially disposed about inner tubular member  30  and follows a generally helical path, forming a plurality of turns  310 . Turns  310  of third portion  46  are disposed at a third pitch  156 . In a presently preferred embodiment, third pitch  156  is generally more coarse than first pitch  152  and second pitch  154 . 
     FIG. 6 is a plan view of the assembly of FIG. 5, in which portions  192 ,  194 , and  196  forming outer layer  190  of elongate shaft  12  are circumferentially disposed over support member  40  and inner tubular member  30 . 
     Having thus described the figures, a method of manufacturing catheter  10  may now be described with reference thereto. A method in accordance with the present invention typically begins with the step of temporarily or permanently securing distal portion  192  of filament  300  to inner tubular member  30  proximate its distal end. In a presently preferred method, distal portion  192  of filament  300  is secured by ring  70 . As seen in FIG. 3, ring  70  is circumferentially disposed about inner tubular member  30  proximate its distal end  38 , while distal portion  192  of filament  300  is disposed between ring  70  and outer surface  36  of inner tubular member  30 . In a presently preferred method in accordance with the present invention, a distal end  350  of filament  300  is tied off. In this presently preferred embodiment, a location for tying off distal end  350  of filament  300  is provided as part of an apparatus for winding filament  300 . 
     Those of skill in the art will appreciate that other methods of fixing distal portion  192  of filament  300  to inner tubular member  30  may be used without deviating from the spirit or scope of the present invention. Methods which may be acceptable in some applications include welding, gluing, and tying. The use of adhesive tape or mechanical fasteners may also be applicable to some embodiments of the present invention. 
     Filament  300  may be wound around inner tubular member  30  following a generally helical path to form a plurality of turns. First portion  42  of support member  40  is comprised of a plurality of turns  302 . In a presently preferred embodiment, turns  302  of first portion  42  of support member  40  are wound at a first pitch  152 . 
     In a presently preferred method, filament  300  is wound beyond first portion  42  to form first layer  82  of second portion  44  of support member  40 . In a presently preferred embodiment, turns  304  of second portion  44  are wound at a second pitch  154 . Those of skill in the art will appreciate that first portion  42  and second portion  44  may be wound at the same pitch without deviating from the spirit and scope of the present invention. 
     In the embodiment of FIG. 3, the winding of filament  300  proceeds in a proximal direction. When the path of filament  300  reaches a desired point, the direction of winding travel is reversed so that filament  300  begins forming turns  306  which overlay turns  304  of first layer  82 . In this manner, second layer  84  of second portion  44  of support member  40  is formed. As shown in FIG. 3, second layer  84  is comprised of turns  306  formed from filament  300 . 
     The winding of filament  300  proceeds in a distal direction until the path of filament  300  reaches distal end  54  of second portion  44  of support member  40 . At this point, the direction of winding travel is reversed so that filament  300  begins forming turns  308  which overlay turns  306  of second layer  84 . In this manner, third layer  86  of second portion  44  of support member  40  is formed. 
     Third portion  46  of support member  40  may be formed by proceeding to wind filament  300  along a generally helical path in a proximal direction beyond proximal end  65  of second portion  44  of support member  40 . After the formation of third portion  46  is complete, filament  300  may be cut off at a desired location, to separate it from the spool it was dispensed from. 
     The steps involved in forming outer layer  190  of elongate shaft  12  are best illustrated in FIG.  6 . In a presently preferred method, proximal portion  196 , middle portion  194 , and distal portion  192  of outer layer  190  are all slid over support member  40  and inner tubular member  30 . After positioning, portions  192 ,  194 , and  196  are all circumferentially disposed over support member  40  and inner tubular member  30 , as shown in FIG.  6 . 
     A sleeve  360  (not shown) may then be placed over the assembly. In a presently preferred method, sleeve  360  is comprised of polytetrafluoroethylene (PTFE). PTFE is preferred because it provides a substantially non-stick surface. In a presently most preferred embodiment, sleeve  360  is comprised of PTFE shrink tubing. Suitable PTFE shrink tubing is commercially available Zeus Industries of Orangeburg, S.C., and Raychem Corporation of Menlo Park, Calif. 
     After placing sleeve  360  in the desired position, heat may be applied to sleeve  360  causing it to shrink. After shrinking, sleeve  360  substantially conforms to the outer surfaces of proximal portion  196 , middle portion  194 , and distal portion  192 . A number of methods may be used to heat sleeve  360 , including convection heating, radiation heating, and heating by conduction. In a presently preferred embodiment, sleeve  360  is heated by directing a flow of hot air from a hot air gun so that it impinges on sleeve  360 . Hot air guns suitable for this application are commercially available from Leister Elektro-Geratebau of Lucerne, Switzerland. 
     After shrinking, sleeve  360  serves to retain the position of proximal portion  196 , middle portion  194 , and distal portion  192 . Sleeve  360  also applies radially constrictive pressure to the outer surfaces of proximal portion  196 , middle portion  194 , and distal portion  192 . It should be understood that the steps of overlaying sleeve  360  over the assembly and shrinking sleeve  360  may be omitted without deviating from the spirit and scope of the present invention. Methods in accordance with the present invention have been envisioned which do not utilize sleeve  360 . Methods in accordance with the present invention have also been envisioned in which the assembly is heated during subsequent steps, and the step of applying heat to sleeve  360  is omitted. 
     In a presently preferred method in accordance with the present invention, distal portion  192 , middle portion  194 , and proximal portion  196  are heated to a temperature near their melting point, causing them all to fuse together forming outer layer  190 . The elevated temperature also causes outer layer  190  to be securely bonded to support member  40  and inner tubular member  30 . In a presently preferred embodiment, the material of outer layer  190  fills in any interstitial spaces in support member  40 . 
     A number of methods may be used to heat the assembly, including convection heating, radiation heating, and heating by conduction. An example of heating with radiant energy is directing infrared energy from an infrared heat source at the assembly. Infrared energy sources suitable for this process are commercially available from Research Incorporated of Minnetonka, Minn. A second example of heating with radiant energy is exposing the regions to be heated to radio frequency energy. 
     An example of heating with convection includes placing the assembly being heated in a temperature chamber. Temperature chambers suitable for this process are commercially available from Thermotron Corporation of New Holland, Mich. 
     An example of heating with conduction is placing a heated tool in direct contact with the assembly. Suitable heated tools may be comprised of a number of materials including stainless steel. Electric heaters suitable for heating a heated tool are commercially available from Watlow Incorporated of St. Louis, Mo. 
     Having formed outer layer  190 , the assembly may be allowed to cool. To speed cooling, the assembly may be submersed in a relatively cool fluid. Examples of fluids which may be suitable for some applications include water and air. In one method in accordance with the present invention, a temperature chamber with both heating and cooling capabilities is utilized. This temperature chamber is capable of producing an elevated temperature environment for heating and a low temperature environment for cooling. Temperature chambers with this capability are commercially available from Thermotron Corporation of New Holland, Mich. A flow of relatively cool air may also be directed at the assembly to speed cooling. Cold air generators suitable for this purpose are commercially available from ITW Vortec of Cincinnati, Ohio, and Exair Corporation of Cincinnati, Ohio. 
     After the assembly has cooled, sleeve  360  may be removed. This may be accomplished by scoring sleeve  360  with a cutting tool, and peeling it away from outer layer  190 . In a presently preferred method, sleeve  360  is comprised of polytetrafluoroethylene (PTFE). PTFE is preferred because it provides a substantially non-stick surface. This substantially non-stick surface aids in the removal of sleeve  360  from outer layer  190 . 
     In one method in accordance with the present invention, a mandrel is placed in lumen  20  of inner tubular member  30 . If a mandrel has been used, it may also be removed after the assembly has cooled. It should be understood that steps may be omitted from this process without deviating from the spirit or scope of the invention. For example, alternate methods have been envisioned, in which the use of sleeve  360  is not required. 
     Having thus described the preferred embodiments of the present invention, those of skill in the art will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. 
     Numerous advantages of the invention covered by this document have been set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.