fig1 is a general view showing a catheter assembly , generally designated ( 11 ), that includes the invention catheter ( 12 ) in combination with a guidewire ( 13 ). the details of the catheter construction that distinguish it from prior structures are not shown in fig1 . the assembly includes a standard fitting ( 14 ) through which the guidewire is received and to which the proximal end ( 15 ) of the catheter is removably attached . as depicted , the catheter is a continuous tubular body that extends from proximal end ( 15 ) to distal end ( 16 ) and through which the guidewire extends . the distal end of the guidewire extends outwardly of the distal end ( 16 ) of the catheter . the distal region of the catheter typically carries one or more radiopaque bands ( 17 ) so that the location of the distal region of the catheter within the vessel may be visualized radiographically . details of the structure of catheter ( 12 ) are shown in fig2 . it is composed of an outer tube ( 18 ) and two or more inner coaxial tubular sections ( 19 ) and ( 20 ). as shown , the two inner coaxial tubular sections are disposed in tandem within the outer tube and are contiguous to each other ( i . e . their respective ends abut each other ). the outer tube ( 18 ) extends continuously over the entire length of the catheter , which typically will be over 50 to 210 cm , more usually 60 to 150 cm . the outer diameter of tube ( 18 ) ( as measured at proximal end ( 15 )) will normally be 0 . 75 to 2 . 00 mm , preferably 0 . 85 to 1 . 30 mm . as seen in fig2 the outer tube may neck down at its distal end ( 16 ) and its outer diameter at the distal end may be slightly smaller than at its proximal end . the outer tube will normally have a wall thickness of about 0 . 08 to 0 . 16 mm , preferably about 0 . 10 to 0 . 13 mm . it is made from a polymer having a flexural modulus ( as measured by astm d - 790 ) of about 5 , 000 to 30 , 000 psi ( 35 , 000 to 210 , 000 kpa ), such as low density polyethylene . the proximal inner tubular segment extends from the proximal end ( 15 ) of the catheter to junction ( 22 ). this distance will normally be 60 to 150 cm , more usually 40 to 120 cm , and preferably about 100 cm . its wall thickness is about 0 . 08 to 0 . 18 mm , preferably about 0 . 10 to 0 . 13 mm , an it is made of a polymer having a flexural modulus of about 220 , 000 to 260 , 000 psi ( 1 , 500 , 000 to 1 , 800 , 000 kpa ) such as polypropylene . the portion of the catheter from proximal end ( 15 ) to junction ( 22 ) is thus the stiffest portion of the catheter . the inner diameter of section ( 19 ) will normally be 0 . 45 to 0 . 75 mm . distal inner tubular section ( 20 ) extends from the distal end of section ( 19 ) ( junction ( 22 )) to junction ( 23 ). that distance will normally be 1 to 30 cm , more normally 1 to 20 cm , preferably about 10 cm . this section is less stiff than section ( 19 ). accordingly , its wall thickness is less than section ( 19 ) and / or it is made of a polymer with a lower flexural modulus than the polymer forming section ( 19 ). in a preferred embodiment , it is made of a continuous length of tubing having an appropriately tapered outer diameter . typically , the flexural modulus of the polymer forming section ( 20 ) will be 20 , 000 to 50 , 000 psi ( 140 , 000 to 350 , 000 kpa ) more usually 30 , 000 to 40 , 000 psi ( 210 , 000 to 280 , 000 kpa ). the wall thickness of section ( 20 ) will normally be 0 . 05 to 0 . 10 mm , preferably 0 . 06 to 0 . 09 mm . the inner diameter of section ( 20 ) is preferably substantially the same as that of section ( 19 ). the distal section ( 21 ) of the outer coaxial tube ( 18 ) extends from the distal end of section ( 20 ) ( junction ( 23 )) to the balloon portion of the catheter . the distance from junction ( 23 ) to the balloon will usually be 1 to 20 cm , more usually 1 to 10 cm , preferably about 5 cm . the distance from proximal end ( 15 ) to junction ( 22 ) will be greater than about 50 % of the entire length of catheter ( 12 ), more usually greater than about 75 % of the entire catheter length . although joint ( 22 ) is depicted as a butt joint in the drawing , the joint may be an overlap joint . the invention catheter thus has three sections of different flexibility / stiffness and becomes increasingly flexible from segment - to - segment distally . the axial flexibility / stiffness gradient of the invention is thus more gradual than in the two - segment embodiment of u . s . pat . no . 4 , 739 , 768 and the change in flexibility stiffness between segments is not as great as in a two segment embodiment . in particular , the inclusion of section ( 20 ) allows the distal end of the catheter to be tracked around sharp bends with less likelihood of kinking occurring at the transition between the outer tube and the distal end of the inner coaxial tubing . further , the structure reduces the likelihood of fatigue stress failure , delamination , or other structural failure at the transition . the balloon ( 24 ) of the catheter is defined by a portion of the thin - walled distal segment of the catheter tube . in its deflated configuration , it has a diameter that approximates the diameter of the tube proximal to it . it will normally be inflatable to a maximum diameter with a range of sizes 1 . 5 , 2 . 0 , 2 . 5 , 3 . 0 , 3 . 5 and 4 . 0 mm . the valve portion ( 30 ) of the catheter assembly is preferably inserted into the portion of the balloon having relatively constant inner diameter . it is held in place by heat welding or gluing or other suitable process . the valve may be made up of a simple tube having a metal band so as to form a valve surface proximally of the metal band on the interior of the lumen and a valve surface proximally or distally of the band . the guidewire contains the valve plug , the shape of which is relatively unimportant so long as it meshes adequately with the valve surfaces formed in the valve region . fig3 shows the guidewire ( 35 ) with a plug ( 40 ) that seats on the proximal side of the valve portion ( 30 ). in such a configuration , the guidewire ( 35 ) can be removed once the procedure is completed . fig4 shows the guidewire ( 35 ) with a plug ( 50 ) that seats on the distal side of the valve portion ( 30 ). accordingly , the guidewire ( 35 ) can only be withdrawn when the catheter is withdrawn . the catheter assembly of the invention is operated in similar fashion to other valve balloon catheters . in such operation , the guidewire is advanced into the vasculature to a desired site , and the catheter body is tracked over the guidewire . the location of the guidewire and the balloon within the vessel may be determined by conventional radiology techniques . once the balloon is at the desired site within the vessel , the catheter lumen is flushed by injecting fluid through the catheter lumen , the valve plug is seated against the distal valve surface or the proximal valve surface , depending upon the end from which the guidewire was introduced , by axially manipulating the guidewire . the valve plug blocks the distal opening of the catheter tube . the balloon is then inflated by injecting fluid through the catheter lumen . if desired , controlled distal leakage of the fluid from the catheter tip may be achieved by a slight adjustment in the tightness of the seating between the valve plug and the respective seating areas . the balloon may be deflated by withdrawing fluid from the catheter lumen . modifications of the above - described embodiments of the catheter and catheter assembly that are obvious to those of skill in the fields of catheter design and manufacture , materials science and related fields are intended to be within the scope of the following claims .
this invention is a single - lumen balloon catheter and assembly having a variable stiffness shaft that allows for greater guidewire trackability and proximal pushability than previous designs . the catheter has an elongate tubular body that is made of inner and outer coaxial tubes , the inner tube being made of proximal and distal sections , the proximal section being stiffer than the distal section and the distal section being stiffer than the outer tube .