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 . fig1 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 . fig2 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 fig2 at least one filament 100 follows a generally helical path . also in the embodiment of fig2 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 fig2 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 fig1 . 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 . fig2 is an enlarged , partial cross - section illustrating second portion 44 of support member 40 . as shown in fig2 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 fig2 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 fig2 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 fig2 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 fig2 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 fig2 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 fig2 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 fig2 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 fig2 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 fig2 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 fig2 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 . fig3 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 fig3 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 fig3 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 fig3 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 . fig4 is a plan view of the assembly of fig3 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 . fig5 is a plan view of the assembly of fig4 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 fig5 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 . fig6 is a plan view of the assembly of fig5 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 fig3 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 fig3 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 fig3 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 fig6 . 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 fig6 . 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 .