fig1 shows a flow - directed infusion catheter ( 100 ) made according to a preferred embodiment of the invention . the catheter ( 100 ) has an elongate tubular body with a proximal end ( 102 ) and a distal end ( 104 ) and an inner lumen ( 106 ) extending between those ends . for this variation of the inventive catheter ( 100 ), the tubular body has three segments ; a comparatively stiff proximal segment ( 108 ), a comparatively more flexible intermediate section ( 110 ), and a most flexible distal segment ( 112 ). between the proximal segment ( 108 ) and the mid segment ( 110 ) lies a tapering joint ( 114 ). similarly , between middle segment ( 110 ) and distal segment ( 112 ) lies a tapering joint ( 116 ). the flexible distal segment ( 112 ) may have one or more radiopaque bands ( 118 ) allowing clear visualization of the distal tip using fluoroscopy . the flexible distal segment ( 112 ) has an open end which allows for the infusion of diagnostic , therapeutic , or vasoocclusive agents into the target site . the flexible distal segment ( 112 ) may be made of a polymer which is inherently quite springy and flexible and biologically compatible such as polyvinylchloride ( pvc ), polyurethane , silicones , or various block copolymers of polyamides with these polymers or blends or alloys of them . this segment may be doped with radio - opaque materials such as barium sulfate , bismuth trioxide , bismuth subcarbonate , powdered tungsten , powdered tantalum , or the like . preferred is bismuth subcarbonate . it is typical that contents of this section may include between 10 % and 30 % by weight of the radiopaque material , preferably 20 - 25 %. the preferred polymers are polyurethane and pvc . most preferred is pvc . the range of hardness for the materials of this section are shore 55a to 75a , preferably 60a to 70a , and most preferably in the neighborhood of shore 65a . the distal segment ( 112 ) typically makes up between 5 % and 25 % of the total length of the tubular member and is generally between 5 and 40 cm . in length . most preferably , it is between 10 - 30 cm . in length . the outer diameter of distal segment ( 112 ) is preferably between 1 f and 2 . 5 f . most preferably is an outer diameter in the neighborhood of 1 . 6 f and 2 f , most preferred is 1 . 8 f . it should be noted that this is an extremely small catheter diameter . middle segment ( 110 ) may be made of the same general materials as is the distal segment . of course , the flexibility of the material making up the middle segment is preferably moderately more stiff than is the distal section . this is to say that the flexural modulus of the plastic making up the section is between shore 65a and 85a , preferably 67a and 77a , and most preferably about 72a . the length of midsection ( 110 ) is typically between 10 - 20 % of the overall length of the tubular member . the physical length is typically between 20 - 40 cm . and preferably between 20 — 30 cm . the outer diameter of middle section ( 110 ) desirably is between 2 f and 3 f , preferably between 2 . 2 f and 2 . 6 f . proximal segment ( 108 ) similarly may be made of a polymeric material such as those discussed above with regard to the other two segments . however , since it is relatively more stiff than the other two sections , it may also be produced of a material such as a polyamides ( nylon ) and polyethylene , e . g . high density , or polypropylene . preferably , on the basis of compatibility with the preferred polymers in the other segments , the proximal segment is pvc or polyurethane , preferably pvc . the proximal segment ( 108 ) may also comprise a braided shaft ( a polymer outer core with a metallic mesh inner core ) or a coil ( a helically wound wire or ribbon on a polymer core further covered by a polymer outer cover ). the proximal segment typically makes up between 60 - 80 % of the total length of the tubular member and is typically between 100 - 140 cm . in length , preferably 105 - 120 cm . in length . the outer diameter is larger than that of the middle section ( 110 ) and typically is between 2 . 9 f and 3 . 5 f , preferably 2 . 7 f to 3 . 2 f , and most preferably 3 f . the wall thickness is preferably between about 4 mils and 12 mils . the polymers used in proximal section ( 108 ) typically are blended to include some amount of one or more of the radiopaque powdered materials discussed above . highly preferred in this variation of the invention is the use of a distal section ( 112 ), midsection ( 110 ), and proximal section ( 108 ) which are of a substantially constant diameter and in which the joints ( 114 ) and ( 116 ) are tapered . use of tapered joints ( 114 ) and ( 116 ) provide for ease of assembly and allow for a smooth transition between the segments . a long stylet ( 120 ) is also shown . the stylet is shorter than the overall length of the catheter assembly ( 100 ) and unlike a guidewire does not precede the catheter through the vasculature , both because of its short length and absence of a taper or shapeable tip . stylet ( 120 ) is placed interior to the catheter assembly ( 100 ) during the time it is initially into the body . that is to say that the stylet provides sufficient stiffness to allow to be manipulated through a guiding catheter assembly to a region near the target site in the vasculature . the most proximal portion of the catheter includes the typical means ( 122 ) for joining the proximal end of the catheter to other devices using , e . g ., helically cut threads or the like . fig2 a shows one step in producing joints ( 114 ) and ( 116 ). fig2 a shows a tapered mandrel ( 200 ) which typically would be made of a metal such as stainless steel or other heat - resistant material . a smaller diameter polymeric tubing ( 202 ) and a larger diameter polymeric tubing ( 204 ) are shown placed therein . the overlap ( 206 ) between larger polymeric tubing ( 204 ) and smaller polymeric tubing ( 202 ) is shown therein . overlap ( 206 ) may be of any convenient length but we have found that for a catheter of this type , an overlap of 0 . 05 - 3 mm . is desirable . for pvc , an overlap of about 1 mm . is highly desirable . the ends ( 208 ) of the respective polymeric tubing ( 202 ) and ( 204 ) may be chamfered or rounded if so desired . the tapered mandrel is for the specific purpose of providing shape to the overlap ( 206 ) during the step of heating that overlap ( 206 ). fig2 b shows the overall shape of the overlap joint ( 206 ) as was shown prior to heating in fig2 a . a larger diameter ( 204 ) may be proximal section ( 108 ) where smaller diameter tubing ( 202 ) is midsection ( 110 ). similarly , large diameter tubing ( 204 ) may be middle segment ( 110 ) where smaller diameter tubing ( 202 ) is distal segment ( 112 ). overlap ( 206 ) may be either joint ( 114 ) or joint ( 116 ). the inner profile of overlap ( 206 ) generally follows that of tapered mandrel ( 200 ). the construction of overlap ( 206 ) during the heating step must be done with some care . we have found , for instance , that when fusing of a joint between two sections of shore 72a pvc having 23 % bismuth carbonate with a section of tubing having a shore hardness of 65 a also containing 23 % bismuth carbonate is readily formed at a temperature of 375 ° f . for 10 - 15 seconds . for harder materials , e . g ., a 1 mm . overlap joint of shore 77d pvc with 16 % bismuth carbonate and a smaller tubing of shore 72a pvc with 23 % bismuth carbonate , a heating step of 415 ° f . for 10 - 15 seconds is adequate . fig3 shows a variation of the distal portion ( 112 ) of the inventive catheter ( 100 ) in which that section ( 112 ) is of two different diameters . the section is of the same material however , throughout the section . the length of midsection taper ( 302 ) is usually the same as the tapers ( 114 , 116 ) between sections mentioned above . the diameter of the smaller portion ( 304 ) of the distal section ( 116 ) is typically about 50 % to 75 % of the diameter of the larger diameter portion ( 306 ) of that section ( 116 ). use of the same polymer in that section ( 116 ) provides for excellent softness and suppleness in flowing through arterial vasculature . we have also found that when using either pvc or a polyurethane , particularly when the pvc &# 39 ; s are infused with plasticizers such as epoxidized soybean oil , the catheter assembly is provided with substantial added flexibility and conformability where the catheter ( 100 ) is “ annealed ” after the tapered joints ( 104 ) and ( 106 ) have been produced . the exterior and interior surfaces of catheter assembly ( 100 ) may be treated with a hydrophilic covering much as recited in the patent to zenzen et al . ( u . s . pat . no . 5 , 538 , 512 ), the entirety of which is incorporated by reference . although preferred embodiments of the invention have been described herein , it will be recognized that a variety of changes and modifications .
this invention is to a minimally invasive surgical device . in particular , the invention relates to an infusion catheter which may be used in cardiovascular and endovascular procedures to deliver diagnostic , therapeutic , or vasoocclusive agents to a target site accessible through the vasculature . the device is a flow - directed infusion catheter having a variety of sections of different flexibilities with tapered junctions between those sections . the inventive catheter is directed to that target site by a flow of blood to the site .