this invention is a kink - resistant catheter section or a catheter . if a catheter , it is a composite device having at least one section including at least one helically wound ribbon stiffener coaxial to and adhesively attached to at least one polymeric outer section . the ribbon forms the inner lumen of the catheter section . the catheter is configured so that at least the distal portion of the catheter has a critical bend diameter of no more than 3 . 5 mm , preferably no more than 2 . 5 mm , more preferably no more than 1 . 5 mm , and most preferably no more than 1 . 0 mm . i have additionally found that the radial compression strength of the section is quite high as compared to distal sections found on comparable catheters . a typical multi - section catheter ( 100 ) which may incorporate the concepts of this invention is shown in fig1 . such a catheter is described in more detail in u . s . pat . no . 4 , 739 , 768 , to engelson , ( the entirety of which is incorporated by reference ) and is particularly suitable for neurological and peripheral vascular applications . clearly , then , it is also suitable for less demanding service such as might be encountered in access and treatment of the heart . one difficulty which has arisen as higher demands for length have been placed on these catheters is that the diameter of the distal section necessarily becomes smaller and smaller . this is so since the longer catheters must reach ever more smaller vascular areas . this smaller diameter requires a concomitant thinning of the wall section . the thinner section walls may kink or ripple when actively pushed along the guidewire or when vasoocclusive devices are pushed through the catheter &# 39 ; s lumen . the typical configuration shown in fig1 has a distal section ( 102 ) having significant flexibility , an intermediate section ( 104 ) which is typically less flexible , and a long proximal section ( 106 ) which in turn is least flexible . the distal section ( 102 ) is flexible and soft to allow deep penetration of the extraordinary convolutions of the neurological vasculature without trauma . various known and often necessary accessories to the catheter assembly , e . g ., one or more radiopaque bands ( 108 ) at the distal region to allow viewing of the position of the distal region under fluoroscopy and a luer assembly ( 110 ) for guidewire ( 112 ) and fluids access , are also shown in fig1 . the typical dimensions of this catheter are : obviously , these dimensions are not particularly critical to this invention and are selected as a function of the malady treated and its site within the body . however , as will be discussed below , use of the spiral wound ribbon permits the walls of the catheter to be somewhat thinner with no diminution of performance , e . g ., crush strength or flexibility , and , indeed , usually provides an improvement in performance . fig2 shows a magnified cross - section of a catheter body or section ( 200 ) showing the most basic aspects of one variation of the invention . as shown there , the catheter body or section has a helically wound ribbon ( 202 ) and an adhesive ( 204 ) on at least an outer portion of the ribbon ( 202 ). typically , the outer tubing member ( 206 ) is polymeric . preferably , the outer tubing member ( 206 ) is , produced of a polymer which is heat shrinkable onto the adhesive ( 204 ). such polymers include known materials such as polyethylene , polyvinylchloride ( pvc ), ethylvinylacetate ( eva ), polyethylene terephalate ( pet ), and their mixtures and copolymers . one very useful class of polymers are the thermoplastic elastomers , particularly polyesters . typical of this class is hytrel . similarly , the adhesive ( 204 ) is desirably a thermoplastic which may be coated onto the inner lumen of the outer tubing member ( 206 ), the outer surface of the coil ( as wound ), the ribbon itself , or may be formed in situ by the use of a mixture of polymers such as polyethylene and eva , which when heated to a proper temperature exude the eva onto the ribbon . a very highly desirable combination -- from an assembly point of view -- is the use of an thermoplastic adhesive ( 204 ) having a softening temperature between the temperature for heat shrinking the outer tubing ( 206 ) onto the adhesive ( 204 ) and the melting temperature of that outer tubing ( 206 ). i have found that an outer covering of eva having a suitable softening / heat shrinking temperature is an excellent choice for securing a strong bond to the ribbon particularly with an adhesive such as polyester or polyimide . the eva ( obviously , with or without other mixed polymers and fillers ) is typically extruded into a taking of an appropriate size and thickness and cross - linked to raise the melt temperature of the resultant tubing . the tubing is then inflated and , perhaps , stretched to give the included polymer molecular orientation . the tubing may then be heat - shrunk onto the catheter . a suitable eva would have significant adhesive properties at about 300 ° f . this is not to exclude the use of other polymers , depending on the section of the catheter in which the section is used . for instance , the tubing may be of any of a variety of polymers , variously stiff or flexible . for instance , if the section ( 200 ) is used as a proximal section , the outer tubing member ( 206 ) may be a polyimide , polyamides such as the nylons , high density polyethylene ( hdpe ), polypropylene , polyvinylchloride , various fluoropolymers ( for instance : ptfe , fep , vinylidene fluoride , mixtures , alloys , copolymers , block copolymers , etc . ), polysulfones or the like . blends , alloys , mixtures , copolymers , block copolymers , of these materials are also suitable , if desired . if a more flexible section is required , the outer tubing member ( 206 ) may be a polyurethane , low density polyethylene ( ldpe ), polyvinylchloride , thy , etc . and other polymers of suitable softness or modulus of elasticity . although it is quite difficult to accomplish , the inventive catheter design allows the use in the distal portion of the catheter , thin - walled tubing of inherently more slippery polymers , such as ptfe and fep and their mixtures , which have the benefit of being lubricious but otherwise would have been used in a somewhat greater thickness . production of a good adhesive joint between the helically wound ribbon ( 202 ) and the adhesive ( 204 ) is not an easy task . clearly , greater thickness tubing of these polymers results in the resulting catheter section being somewhat stiffer . the wall thickness of the outer tubing member ( 206 ) may be as thin as 0 . 5 mil and as thick as 10 mil , depending upon catheter usage , portion of the catheter chosen , polymer choice , and the style of catheter . typically , the wall thickness of the tubing member will be between 0 . 5 and 3 . 0 mils . this dimension is obviously only a range and each catheter variation must be carefully designed for the specific purpose to which it is placed . preferred combinations of polymers for catheter configurations will also be discussed below . it should also be noted at this point that each of the polymers discussed herein may be used in conjunction with radiopaque material such as barium sulfate , bismuth trioxide , bismuth carbonate , powdered tungsten , powdered tantalum , or the like so that the location of the various pieces of tubing may be radiographically visualized within the vessel . the spiral wound ribbon ( 202 ) shown in fig2 may also be of a variety of different materials . although metallic ribbons are preferred because of their strength - to - weight ratios , fibrous materials ( both synthetic and natural ) may also be used . preferred , because of cost , strength , and ready availability are stainless steels ( ss308 , ss304 , ss318 , etc .) and tungsten alloys . in certain applications , particularly smaller diameter catheter sections , more malleable metals and alloys , e . g ., gold , platinum , palladium , rhodium , etc . may be used . a platinum alloy with a few percent of tungsten is preferred partially because of its radiopacity . the class of alloys known as super - elastic alloys is also a desirable selection . preferred super - elastic alloys include the class of titanium / nickel materials known as nitinol -- alloys discovered by the u . s . navy ordnance laboratory . these materials are discussed at length in u . s . pat . no . 3 , 174 , 851 to buehler et al ., u . s . pat . no . 3 , 351 , 463 to rozner et al ., and u . s . pat . no . 3 , 753 , 700 to harrison et al . these alloys are not readily commercially available in the small ribbons required by the invention described here , but for very high performance catheters are excellent choices . when using a superelastic alloy , an additional step is usually necessary to preserve the helical shape of the stiffening member . i have purchased nitinol wire and rolled it into a 1 × 4 mil ribbon . the ribbon is then helically wound onto a mandrel , usually metallic , of an appropriate size . the winding is then heated to a temperature of 650 °- 750 ° f . for a few minutes , presumably annealing the ribbon . the helical coil then retains its shape . metallic ribbons ( 202 ) that are suitable for use in this invention are desirably between 0 . 5 mil and 1 . 5 mil in thickness and 2 . 5 mil and 8 . 0 mil in width . by the term &# 34 ; ribbon &# 34 ;, i intend to include elongated shapes , the cross - section of which are not square or round and may typically be rectangular , oval or semi - oval . they should have an aspect ratio of at least 0 . 5 ( thickness / width ). in any event , for superelastic alloys , particularly nitinol , the thickness and width may be somewhat finer , e . g ., down to 0 . 30 mil and 1 . 0 mil , respectively . currently available stainless steel ribbons include sizes of 1 mil × 3 mil , 2 mil × 6 mil , and 2 mil × 8 mil . suitable non - metallic ribbons include high performance materials such as those made of polyaramids ( e . g ., kevlar ) and carbon fibers . it should be observed that the preferred manner of using non - metallic ribbons in this invention is typically in combination with metallic ribbons to allow &# 34 ; tuning &# 34 ; of the stiffness of the resulting composite . finally , in fig2 may be seen an outer layer ( 208 ) of a lubricious material such as a silicone or other , perhaps hydrophilic , material such as a polyvinylpyrrolidone composition . these compositions are well known and do not form a critical portion of the invention . typical of the catheter made using this invention are those in the 3 french to 5 french range . the inner diameter of such catheters is then 20 mils to 42 mils . however , i have made micro - catheters ( discussed in more detail below ) having outside diameters of 18 mils to 34 mils . the inner diameter of those catheters was 11 mils to 20 mils . the invention is not limited to such sizes , however . fig3 shows a variation of the inventive catheter ( 210 ) in which the cross - sections of the ribbons ( 212 & amp ; 214 ) are generally oval rather than rectangular than as shown in fig2 . either cross - section is acceptable but the oval section has less of a tendency to bind with guidewires passing through the lumen . additionally , the fig3 variation shows the use of two ribbons ( 212 & amp ; 214 ) wound side - by - side so to form a single layer of ribbon inside the outer tubing cover ( 206 ). the dual ribbons may be of the same composition or of differing compositions . they may be of the same size or of differing sizes . the number of ribbons may be of any convenient configuration so long as the specific stiffness and kink - resisting criteria are met . fig4 shows another variation in which catheter sections made according to this invention are used in axial conjunction . section ( 220 ) is generally as described in fig3 and 4 above , but section ( 222 ) is more proximal and enjoys two outer covering layers ( 224 ) and ( 226 ). covering ( 224 ) is simply a proximal extension of the polymeric covering in section ( 220 ); polymeric covering ( 226 ) is placed directly on the outer surface of the helically - wound coil ( 228 ). as has been noted elsewhere , coil ( 228 ) may be the same as or different than the coil found in the more distal section ( 220 ). other methods for changing the stiffness of various sections of a catheter made using sections of the inventive catheter section are shown in fig5 , and 7 . for instance , fig5 shows a distal section ( 230 ) having a helically - wound ribbon ( 232 ), an outer polymeric covering ( 234 ), and a radiopaque band ( 236 ). in this variation , the ribbon ( 232 ) is wound in such a fashion that adjacent turns are not contiguous . this allows the distal catheter section ( 230 ) to be quite flexible and kink - resistant . the intermediate section ( 238 ) retains the same outer covering ( 234 ), but the pitch of the coil has been narrowed so that the flexibility of the midsection ( 238 ) is not as high as was the distal section ( 230 ). the most proximal section ( 240 ) has no helically - wound ribbon at all , but instead uses a variety of polymeric or other tubing materials to form the stiffest portion of the catheter assembly . in this instance , the outer layer remains as found in the most distal section ( 230 ) and the midsection ( 238 ). the inner layer in this instance is a stiffer material , such as polyimide , polypropylene , or a stainless steel tube , known as a &# 34 ; hypotube &# 34 ;. fig6 shows still another variation of forming the distal section of a catheter assembly which is flexible and yet provides a greater stiffness for other sections of the catheter assembly . for instance , in fig6 the intermediate section ( 242 ) utilizes double layers of polymeric material , e . g ., the outer tubing ( 234 ) ( discussed above ) on the outer surface and an inner tubing of similar or stiffer material ( 244 ) in contiguous relationship along the length of the section ( 242 ). the most proximal section ( 246 ) shows only a short overlap between stiff distal tube ( 248 ) ( perhaps made of the polyimide , polypropylene , nylon , or hypotube materials discussed above ) and the outer layer ( 234 ). this is a simple arrangement and may be used , for instance , where cost is at a premium . fig7 shows still a further variation in which the most distal section is a composite of polymeric layers ( 252 ) and a braid ( 254 ). the composition of the mid and proximal sections are not critical to the invention . they may be of one type or the other depending upon the requirements of the particular application . the most significant of benefits is accrued when , however , the distal section is of the type specified herein . nevertheless , a variation shown in fig8 depicts an instance in which the non - kinking criteria of this invention is applied in a mid - section . catheter ( 256 ) uses a distal section having only tubing ( 260 ) extending distally of the mid - section ( 262 ). mid - section ( 262 ) comprises both outer tubing ( 260 ) and helically - wound ribbon ( 264 ) easily held in place according to this invention . proximal section ( 266 ) is made stiffer by incorporating multiple layers of tubing , as discussed above . although the exemplified catheter assemblies in fig1 , 6 , 7 , and 8 each utilize three sections , it should be understood that this invention is not so limited . the number of sections is selected by the designer when conceptualizing a specific use for a chosen device . often , the optimum number of sections ends up being three simply because of the physiology of the human body , however , three or more may be involved in this invention . the sections additionally need not be of constant stiffness . they may also vary in stiffness -- typically as the distal end of a section is approached , the section becomes more flexible . as was noted above , i have found that use of this method of construction allows use of significantly smaller diameter catheters which still remain kink - free and yet are quite useable . for instance , fig9 shows a short cross - section of a distal end of a vascular catheter ( 270 ) in which the outer section comprises an outer cover ( 206 ) and a helically - wound ribbon ( 204 ) generally as shown in fig2 . within the lumen defined by a helically - wound coil ( 204 ) may be found yet a smaller catheter device covering ( 272 ) and a helically - wound coil ( 274 ). again , it is desireable that helically - wound coil ( 274 ) and covering ( 272 ) be adhesively attached to each other to lessen the chance of any kinking taking place . within the lumen of the inner catheter is a guidewire ( 276 ) which , just as an inner catheter ( 275 ), is slidable within outer catheter ( 270 ), is slidable within the inner catheter ( 275 ). for instance , a guidewire ( 276 ) may have an outside diameter of 5 to 7 mils in this distal region and the outer diameter of inner catheter ( 275 ) may have an outer diameter of 121 / 2 to 14 mils . as was noted above , the most distal portion of the distal section of this catheter ( and preferably other sections as well ) have a critical bend diameter of no more than 3 . 5 mm , preferably no more than 2 . 5 mm , more preferably no more than 1 . 5 mm , and most preferably no more than 1 . 0 mm . to some extent , the critical band diameter is also dependent upon the diameter of the catheter section and its components . for instance , i have made 3 french catheter section of the type shown in fig2 ( of stainless steel ribbon ) with critical bond diameters less than 2 . 5 mm . similarly , i have made catheter sections such as the inner catheter ( 275 ) shown in fig9 with an outer diameter of 0 . 018 &# 34 ; ( of platinum - tungsten alloy ribbon ) with band diameters less than 1 . 0 mm . the test we utilize for critical bend diameter determination uses a test shown schematically in fig1 a and 10b . in general , as shown in fig1 a , a catheter section ( 300 ) is placed between two plates ( desirably of plastic or glass or the like for visibility ) and often with an optional peg ( 302 ) to hold the catheter section ( 300 ) loop in place . the ends of the catheter are then pulled until a kink appears in the body of the catheter . alternatively , the ratio of the outer diameters ( major diameter : minor diameter ) as measured at apex ( 304 ) reaches a value of 1 . 5 . fig1 b shows the cross section of the catheter sector at ( 304 ) and further shows the manner in which the major diameter and the minor diameter are measured . these two methods provide comparable results although the latter method is more repeatable . many times herein , we refer to the &# 34 ; region &# 34 ; section of the catheter . where the context permits , by &# 34 ; region &# 34 ; we mean within 15 % of the point specified . for instance , &# 34 ; the distal region of the distal section &# 34 ; would refer to the most distal 15 % in length of the distal section . this invention has been described and specific examples of the invention have portrayed . the use of those specifics is not intended to limit the invention in any way . additionally , to the extent that there are variations of the invention which are within the spirit of the disclosure and yet are equivalent to the inventions found in the claims , it is our intent that this patent cover those variations as well .
this invention is a surgical device . in particular , it is a catheter suitable for accessing a tissue target within the body , typically a target which is accessible through the vascular system . central to the invention is the use of a stiffener ribbon , typically metallic , wound within the catheter body in such a way as to create a catheter having controllable stiffness . the stiffener ribbon is adhesively bonded to a flexible outer tubing member so to produce a thin wall catheter section which is exceptionally flexible but highly kink resistant . the catheter sections made according to this invention may be used in conjunction with other catheter sections either using the concepts shown herein or made in other ways . because of the effective strength and ability to retain a generally kink - free form , these catheters may be effectively used in sizes which are quite fine , e . g ., 0 . 015 &# 34 ; to 0 . 020 &# 34 ; in diameter , and usable within typical vascular catheters .