WO1991008014A1

WO1991008014A1 - Low profile catheter

Info

Publication number: WO1991008014A1
Application number: PCT/US1990/006775
Authority: WO
Inventors: Bandula Wijay; Paolo Angelini
Original assignee: Leocor, Inc.
Priority date: 1989-11-28
Filing date: 1990-11-19
Publication date: 1991-06-13
Also published as: EP0502958A1; JPH05501658A; EP0502958A4

Abstract

An angioplasty catheter comprising an inner (10) and outer (12) tubular members, each having a proximal and distal segment. The distal segment (20) of the outer body member (12) is softer than the proximal segment (18) of the outer body member (12). Similarly, the distal segment (16) of the inner body member (10) is softer than the proximal segment (14) of the inner body member (10). The proximal segment of the inner body member is harder than the proximal segment of the outer body member. The distal segment (20) of the outer body member (12) is softer than the distal segment (16) of the inner body member (10). A balloon (26) spans the distal segments (16, 20) of the inner and outer body members, effectively closing off an annulus created between the nested inner and outer body members. The combination of hardnesses provides for sufficient body strength to allow pushability, combined with sufficient distal softness to avoid trauma to the arterial walls during insertion.

Description

TITLE: LOW PROFILE CATHETER

FIELD OF THE INVENTION

The invention relates to the field of surgery, and more particularly to instruments for facilitating the performance of surgical procedures involving the flow of blood. This technique has been generally de¬ scribed as percutaneous transluminal angioplasty.

BACKGROUND OF THE INVENTION

Obstructive coronary artery disease is generally regarded as a serious health problem in the United States and most of the western world. When drug treat¬ ment fails or inadequately controls angina pectoris, coronary artery bypass graft surgery is generally used. In 1964 a translumenal coaxial catheter dilation method for dilating atheromatous lesions in peripheral arteries was introduced by Dotter and Judkins. This technique required sequential dilation of stenotic lesions and employed progressively larger dilating catheters. Sub¬ sequently, in 1971 a "Fogarty balloon catheter" was used to perform translumenal arterioplasty. Subsequently, Gruntzig employed earlier techniques using a single double lumen catheter with a nondistensible balloon segment at its tip which was positioned in the lumen at the stenotic segment of a peripheral artery. The elas¬ tic balloon segment was then inflated, resulting in compression of the atheromatous lesion in a manner per¬ pendicular to the vessel thus dilating the lumen. The balloon remained inflated for ten to fifteen seconds at seven atmospheres internal pressure and was then de¬ flated. As a result, there was a significant reduction in complications due to endothelial damage, such as that caused by earlier known coaxial translumenal dilation techniques and thus a marked improvement in vessel pat¬ ency through the use of the Gruntzig catheter was achieved.

SUBSTITUTE SHEET In earlier designs, the amount of pressure which could be applied through a balloon type expander was limited and thus insufficient to dilate certain stenotic lesions. This shortcoming was due to the use of poly- vinylchloride balloons which had structural limitations that limited internal pressures to approximately seven atmospheres.

Other catheter designs resulted in a total cessa¬ tion of blood flow distal to the site of the treatment. Studies in living dogs with normal coronary arteries have shown that coronary translumenal angioplasty may be associated with brief, self-limited ventricular tachy¬ cardia. During the inflation of the balloon, distal coronary pressure, falls to zero. Because of the lack of blood flow and the pressure distal to the treatment site the period of use such known catheters must be rela¬ tively short to prevent complications due to the lack of blood supply. This limitation on inflation time tended to reduce the success rate of the coronary trans- lumenal angioplasty.

The translumenal coronary angioplasty technique consists of a catheter system introduced via the femoral artery under local anesthesia. A preshaped guiding catheter is positioned into the orifice of the coronary artery and through this catheter a dilation catheter is advanced into the branches of the coronary artery. The dilation catheter had an elliptical-shaped relatively non-distensible balloon portion near its tip which could be inflated and deflated. After traversing the stenotic lesion of the coronary artery, the balloon portion was inflated with fluid which compressed the atherosclerotic material in a direction generally perpendicular to the wall of the vessel thereby dilating the lumen of the vessel. Peripheral arterial lesions treated by this technique have demonstrated that the atheroma can be compressed leaving a smooth luminal surface. Studies have shown that the patency rate two years following the dilation of the iliac and femoropopliteal atheroscler¬ otic lesions was greater than seventy percent.

Although guiding catheters are used in placement of angioplasty (dilation) catheters, the angioplasty catheter can be placed in a stenotic lesions using solely the wire guide if the lesion is proximately lo¬ cated to the point of entry in the body. The word "guide" as referred to in this application is directed to both wire guides and guiding catheters separately or as used in tandem. Typically a guide of appropriate size is advanced through the stenotic lesion and the balloon catheter is threaded over it and advanced to the area of the stenosis. Once the area of the stenosis is reached, the balloon in the catheter is inflated to a high pressure depending on the size of the balloon and the type of stenosis, and the pressure is held for a period of time. During the procedure the distal and proximal pressure is measured to evaluate the physiolog¬ ical conditions of the organ. More specifically, the pressure differential is measured after deflating the balloon and is used as an indication of the degree of dilation achieved.

Past designs have employed a stiff catheter tip on the angioplasty catheter which often resulted in pulling the guide out of the stenotic lesion as the catheter was advanced toward the lesion. Separately, in using the angioplasty catheter, it was often neces¬ sary to measure the pressure distal to the catheter. Past designs employed a guide closely fitting to the internal cross section of the distal lumen in the cathe¬ ter thereby making it difficult to obtain adequate pres¬ sure measurements due to the large pressure drops in¬ volved as a result of the usage of close clearances. The pressure measurements were of the nature of a dy- namic measurement, the accuracy and frequency response of which was greatly and adversely affected by the pres¬ sure drops within the catheter measurement lumen. It

SUBSTITUTE SHEET was frequently required that the guide be retracted and replaced in order to achieve accurate pressure measure¬ ment.

Angioplasty catheters used in the past had rela- tively large catheter body diameters which tended to oc¬ clude the artery of concern causing reduced blood flow to the lesion or the organ it supplies. Once such cath¬ eter is disclosed in U.S. Patent 4,323,071 (Fig 4). Other catheters although using a tapered body, employed a rigid tip which, if the arterial path was particularly tortuous, tended to pull the guide wire from the steno¬ sis. One such catheter is disclosed in U.S. Patent 4,413,989 (Fig. 8).

Flexible tips attached to the distal end of an angiography catheter have been used to inject radiopaque contrast or medicaments into the femoral artery as part of diagnostic or treatment procedures. Such deformable tips had the object of preventing punctures of the wall of the aorta and have been provided to have a larger cross-sectional profile than the catheter body to which they are attached. Some designs even featured means to inflate the deformable tip to increase the contact area between the tip and the body tissue to reduce the pres¬ sure per unit area applied to the tissue. One such de- sign is disclosed in U.S. Patent 4,531,943.

In past designs it was often difficult to esti¬ mate the location of the tip of the catheter. Prior designs employed the use of a gold band near the distal end of the catheter thereby marking that portion of the catheter visible under an x-ray machine. However, be¬ cause it was risky to attach such rings at the extreme distal end of the catheter, the extreme distal tip of the catheter was not visible under x-ray and often the physician performing the procedure had to guess as to its location.

Known angioplasty catheters have dilation bal¬ loons attached to the catheter body by adhesives or by

SUBSTITUTE SHEET heat sealing. Most often, these balloons are made out of polyvinylchloride or irradiated polyethylene. Poly- vinylchloride balloons are normally solvent or adhesive bonded to catheter bodies of the same material and poly- ethylene balloons are adhesive bonded or heat shrunk to catheter bodies of the same material, or a blend of polyethylene and polypropylene, so as to obtain catheter body stiffness. Most such catheters have relatively stiff tips as their distal end which often causes the preplaced guide to be pulled out of the lesion area during catheter advancement in tortuous arteries as well intimal damage. Known catheters also contain relatively stiff bodies to carry the balloon adjacent the distal end of the catheter. The stiffness of the catheter body continues in the area of the balloon up to the distal end of the catheter.

Known catheters contain balloon lumen bleed holes whereby air can be removed directly out of the balloon cavity and out of the catheter during the filing of the balloon. These additional lumens either in the form of small metal tubes or as a multilumen catheter tube, con¬ sumed valuable cross-sectional area of the catheter tube that otherwise could be used for other purposes such as pressure measurements. Known catheter designs have employed an inner and outer tube wherein in the outer tube contains the bal¬ loon as an integral portion thereof or a separate bal¬ loon which is bonded to the outer tube. The annulus between the inner and outer tubes is used for inflation of the balloon.

Known angioplasty catheters have been shipped in a sterilized condition to doctors and hospitals with the balloon in a deflated condition and having gas entrained therein. Prior to using such catheters, doctors or technicians had to inject a contrast fluid into the balloon to displace the gases therein. This procedure involved sequential filing and evacuation of balloon

SUBSTITUTESHEET using a plunger connected to the proximal end of the catheter. Such catheters were shipped to doctors and hospitals with the balloon in a wing-folded condition. Essentially wing folding involved flattening of the balloon along the catheter body and folding the balloon over onto the catheter body in two segments which resem¬ ble wings coming from a fuselage. In the past, the catheters were wing-folded in the factory prior to ship¬ ment. However, in to order remove the entrained gases, the doctor or technician had to unfold the wings and fill the balloon with contrast fluid while evacuating gases therefrom. As a result, the advantage of the balloon tending to retain its wing-folded position after shipment was lost. The doctor or technician after fill- ing the balloon with contrast fluid had to again attempt to manipulate the balloon with his or. her fingers to reachieve the wing-folded position which reduced the profile of the catheter.

It is an object of this invention to provide a soft atraumatic catheter tip in which radiopaque fillers such as bismuth-oxychloride or bismuth-subcarbonate are incorporated.

It is an object of the invention to provide a relatively soft catheter tip to minimize the tendency of the catheter to dislocate a guide out of a stenosis when the catheter is advanced in a tortuous path, and also minimize intimal damage.

It is another object of this invention to provide a catheter tip which can be insert molded, heat bonded, or adhesive bonded to the relatively stiff catheter body proximal to it. It is a further object of this inven¬ tion to use material such as nylon, polyvinylchloride, polyurethane, of different stiffnesses that are readily bondable using the aforementioned methods. It is a further object of this invention to pro¬ vide an inner tube that is relatively large in its in¬ ternal diameter and that is necked down in the region of the balloon and for several centimeters proximal to the balloon in order to provide a large lumen for pressure measurement. The catheter provides an improved fre¬ quency response without sacrificing the total overall outside diameter and maintaining a relatively small diameter in the region of the balloon thereby maintain¬ ing a low profile catheter design.

It is a further object of this invention to pro¬ vide, in one embodiment, an opening into the balloon cavity at its extreme distal end thereby facilitating the removal of gases during filling with contrast fluid. The inner and outer tubular members of the cathe¬ ters of this invention can be formed from a number of flexible, biologically safe, elastomeric or polymeric materials. Preferably, the inner and outer tubular members are formed from polymeric materials which com¬ prise a blend of a hard nylon compound, i.e., including a polyamide, as exemplified by a nylon such as nylon- 11, nylon-12, etc., and a soft nylon compound comprising a block copolyamide, such as a polyether-polyamide co- polymer, as exemplified by a polyether-nylon-12 copoly- mer. If desired, the outer tubular member of this in¬ vention also can be formed using a polymeric composition comprising solely a polyether-polyamide copolymer, such as the previously mentioned polyether-nylon-12 copoly¬ mer.

SUMMARY OF THE INVENTION

The apparatus of the present invention is an angioplasty catheter comprising an inner and outer tubu¬ lar members, each having a proximal and distal segment. The distal segment of the outer body member is softer than the proximal segment of the outer body member. Similarly, the distal segment of the inner body member is softer than the proximal segment of the inner body member. The proximal segment of the inner body member is harder than the proximal segment of the outer body member. The distal segment of the outer body member is softer than the distal segment of the inner body member. A reducing taper is provided between the proximal and distal segments of the inner body member. A similar reduction is provided between the proximal and distal segments of the outer body member. The distal segment of the inner body member extends beyond the distal seg¬ ment of the outer body member. A balloon spans the distal segments of the inner and outer body members, effectively closing off an annulus created between the nested inner and outer body members. The balloon can be selectively inflated during the angioplasty procedure. The catheter presents a low profile. The combination of hardnesses provides for sufficient body strength to allow pushability and torque resistance, combined with sufficient distal softness to avoid trauma to the arter¬ ial walls during insertion.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional view of the catheter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The catheter C is shown in Figure 1. Catheter C has a tubular inner body member, designated generally as 10, and a tubular outer body member, designated gener¬ ally as 12. Inner body member 10 has a proximal segment 14 and a distal segment 16. Outer body member 12 has a proximal segment 18 and a distal segment 20.

In the preferred embodiment, tapers 22 and 24 are located, respectively, on the inner body member 10 and outer body member 12. Taper 22 is located between seg¬ ments 14 and 16, while taper 24 is located between seg¬ ments 18 and 20. Tapers 22 and 24 are preferably lo¬ cated within close proximity to each other. As seen in Figure 1, segment 16 extends beyond segment 20. A bal¬ loon 26 spans between segments 20 and 16. Balloon 26 has a distal neck 28 mounted to segment 16. In the

SUBSTITUTE SHEET preferred embodiment, distal neck 28 ends contempo¬ raneously with the end of segment 16. The distal end of segment 20 contains a reduced-profile shoulder 30. The proximal neck 32 is mounted to shoulder 30. The result is that when the balloon 26 is deflated, the profile of the catheter C distally of taper 24 does not exceed the profile of segment 20, which preferably is less than 0.0420".

A radiopaque band 34, preferably made from rhen- ium and tunsten, is mounted to segment 16. The purposes of facilitating proper location of the balloon during the angioplasty procedure.

The balloon 26 can preferably be made of a poly¬ ethylene or polyester material, with a wide variety of wall thicknesses, including but not limited to 2, 2- 1/2, 3 and 3-1/2 mm.

In the preferred embodiment, segment 14 is made from a material that is 70 percent hard nylon compound. The preferred hard nylon compound, containing 30 percent bismuth oxychloride and color additive, as used in this specification refers to a product available from Huels Corporation which contains "nylon 12-L2101F." Its typi¬ cal Shore D hardness is 75 and the tensile stress is in the range of 7300 psi. The nylon in the hard nylon compound, which is preferably nylon 12, is based on the lauryl lactum monomer. Different grades are derived through variations in the molecular weight of the homo¬ polymers; i.e., high-viscosity extrusion grades, as well as low-viscosity grades for injection molding. The lauryl lactum is copolymerized with various components to yield the approximate Shore D hardness of 75 and tensile strength of 7300 psi. It is understood that the percentage of hard nylon compound can vary in a range from 70 percent by plus or minus 10 percent. The other ingredient is soft nylon compound, containing 30 percent bismuth oxychloride and color additive. The preferred nylon in the soft nylon compound as used in this

SUBSTITUTE SHEET application is preferably nylon E47M-S3 made by the Huels Corporation of Piscataway, NJ. This material is chemically characterized as block copolyamides. The polymer chains consist of alternating rigid polyamide 12 segments and flexible polyether segments. By varying the proportions of the polyamide 12 to the polyether segments, grades of different hardnesses and flexibility can be obtained. The preferred embodiment is a material having a Shore D hardness of 47 and tensile stress of about 2900 psi. Each of the components of the catheter, except the balloon 26, are made from a blend of hard and soft nylon compounds, as indicated in this application. Where the percentage is given as hard nylon compound, the balance of the material is soft nylon compound. The opposing segment 18 on the outer body member 12 is pref¬ erably made of 40 percent, plus or minus 10 percent, hard nylon compound. The preferred Shore D hardness of segment 14 is 67, plus or minus 10; the preferred hard¬ ness for segment 18 on the Shore D scale is 58, plus or minus 10.

The preferred hardness on the Shore D scale for segment 16 is 52, plus or minus 10, while the preferred hardness on the Shore D scale for segment 20 is 47, plus or minus 10. The preferred tensile strengths of segments 14,

16, 18 and 20 are of the order of 5900, 4600, 4600, and 2900 psi, respectively. The material composition with respect to the hard nylon compound found in the various segments can range in hard nylon compound content plus or minus 5 percent, with the exception of segment 20, in which the hard nylon compound content can range between about 0-5 percent. It should be noted that segment 20 is preferably made of 100 percent soft nylon compound, while segment 16 is preferably 17 percent hard nylon compound.

Another feature regarding the softness of the tip of the catheter is the length of segment 20. The pre-

SUBSTITUTE SHEET ferred range is 3-15 cm. Lengthening segment 20 length¬ ens segment 16 and vice versa.

The net result of the catheter disclosed above is a low-profile angioplasty catheter that has sufficient body strength to have good pushability characteristics, and further having a soft distal end to improve track- ability and decrease the possibilities of patient trauma on the arterial wall; such soft distal end also prevents the pulling out of the guidewire. It should be noted that segment 14 can be con¬ nected to segment 16 by virtue of a discrete joint or, alternatively, by a gradual blending of one material into another. The same applies for the material change between segments 18 and 20. Segment 16 is of sufficient strength so that it does not inwardly distend during inflation of balloon 26. Tubular inner body member 10 has a central lumen 36, which extends for the length of the catheter. Lumen 36 can be used to advance the catheter C over a guide- wire as large as about 0.020" (not shown). Alterna¬ tively, with the guidewire removed, lumen 36 can be used to perfuse fluids distally of inflated balloon 26. The patient's own blood may be recycled through a suitable blood pump (not shown) through lumen 36 and distally of inflated balloon 26 during balloon, angioplasty. Tube 16 is sufficiently strong to avoid being distended, thereby constricting lumen 36 during inflation of balloon 26. At the same time, the portion of the catheter C distally of tapers 22 and 24 as an assembly is relatively soft to increase trackability and reduce trauma. The softness of the assembly referred to in the previous sentence can also be varied by adjusting the length of segment 20 in the preferred range of about 3-15 cm. The longer the length of segment 20, the more flexible is the overall tip assembly of the catheter C.

Other advantages and uses of the above design are disclosed in earlier-filed U.S. Applications Serial No.

SUBSTITUTE SHEET 100,363 filed September 23, 1987; a related earlier application No. 06/811,162 filed December 19, 1985, which is now abandoned; application No. 164,870, filed March 7, 1988; PCT application No. PCT/US89/00725, filed February 28, 1989; and application filed September 28, 1989, for which a number has not yet been issued. The disclosures of these earlier applications are incorpo¬ rated in this disclosure as if fully set forth.

In an alternative preferred embodiment, segment 18 is made from a substantially similar material as segment 20, preferably 40 percent hard nylon compound. Therefore, as previously stated, proximal outer body member 18 would be of the composition previously de¬ scribed in the other preferred embodiment, while distal segment 20 would be substantially the identical mate¬ rial. In this type of construction, there would be no joint between segments 18 and 20. This is distinguished from the other preferred embodiment where there would be a transition of materials between proximal outer body segment 18 and distal outer body segment 20. This tran¬ sition would occur adjacent and proximally of taper 24. The transition between proximal inner body member 14 and distal inner body member 16 will occur proximally and adjacent to taper 22. Thus, in the alternative prefer- red embodiment, the distal outer body member 20 is actu¬ ally harder than the distal inner body member 16. The relationship between the proximal inner and outer body members in this alternative preferred embodiment is the same as in the previously described embodiment. Stated differently, there has been no change in the preferred materials with this second alternative insofar as the proximal inner body member 14 and the proximal outer body member 18 are concerned. This alternative prefer¬ red embodiment provides a little bit more stiffness at the distal end of the catheter, coupled with sufficient flexibility to minimize patient trauma and improve trackability.

SUBSTITUTE SHEET The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.

SUBSTITUTE SHEET

Claims

1. A catheter comprising: a tubular outer body member having a proximal and distal segment; a tubular inner body member having a proximal and distal segment defining a lumen therethrough; said inner body member nested at least in part in said outer body member to define an annulus therebe- tween; a balloon connected to both said inner and outer body members spanning said annulus at one end, effec¬ tively closing it off, said balloon selectively distens¬ ible from an inflated to a deflated position; and said proximal segment of said inner body member is harder than said distal segment of said inner body member.

2. The catheter of claim 1, wherein: said proximal segment of said outer body member is harder than said distal segment of said outer body member.

3. The catheter of claim 2, wherein: said proximal segment of said inner body member is harder than said proximal segment of said outer body member.

4. The catheter of claim 3, wherein: said distal segment of said inner body member is harder than said distal segment of said outer body mem¬ ber.

5. The catheter of claim 4, further comprising: a reducing transition between said proximal and distal segments of said inner body member;

SUBSTITUTE SHEET a reducing transition between said proximal and distal segments of said outer body member; said transitions resulting in a reduced profile of the catheter.

6. The catheter of claim 1, further comprising: a reducing transition between said proximal and distal segments of said inner body member; a reducing transition between said proximal and distal segments of said outer body member; said transitions resulting in a reduced profile of the catheter.

7. The catheter of claim 6, wherein: said proximal segment of said outer body member is harder than said distal segment of said outer body member.

8. The catheter of claim 7, wherein: said proximal segment of said inner body member is harder than said proximal segment of said outer body member.

9. The catheter of claim 8, wherein: said distal segment of said inner body member is harder than said distal segment of said outer body mem¬ ber.

10. The catheter of claim 6, further comprising: a shoulder at the distal end of said distal seg¬ ment of said outer body member; said balloon having a proximal neck mounted to said shoulder so that the profile of the catheter in the area of said balloon during balloon deflation does not exceed the profile of said distal segment of said outer body member, measured proximally to said shoulder.

11. The catheter of claim 5, further comprising: a shoulder at the distal end of said distal seg¬ ment of said outer body member; said balloon having a proximal neck mounted to said shoulder so that the profile of the catheter in the area of said balloon during balloon deflation does not exceed the profile of said distal segment of said outer body member, measured proximally to said shoulder.

12. A catheter comprising: a tubul.ar outer body member having a proximal and distal segment; a tubular inner body member having a proximal and distal segment defining a lumen therethrough; said inner body member nested at least in part in said outer body member to define an annulus therebe¬ tween; a balloon connected to both said inner and outer body members spanning said annulus at one end, effec- tively closing it off, said balloon selectively distens¬ ible from an inflated to a deflated position; and said distal segment of said outer body member is softer than said proximal segment of said outer body member.

13. A catheter comprising: a tubular outer body member having a proximal and distal segment; a tubular inner body member having a proximal and distal segment defining a lumen therethrough; said inner body member nested at least in part in said outer body member to define an annulus therebe¬ tween; a balloon connected to both said inner and outer body members spanning said annulus at one end, effec¬ tively closing it off, said balloon selectively distens¬ ible from an inflated to a deflated position; and said proximal segment of said outer body member is softer than said proximal segment of said inner body member.

14. A catheter comprising: a tubular outer body member having a proximal and distal segment; a tubular inner body member having a proximal and distal segment defining a lumen therethrough; said inner body member nested at least in part in said outer body member to define an annulus therebe¬ tween; a balloon connected to both said inner and outer body members spanning said annulus at one end, effec- tively closing it off, said balloon selectively distens¬ ible from an inflated to a deflated position; and said distal segment of said inner body member is harder than said distal segment of said outer body mem¬ ber.

15. The catheter of claim 12, wherein: a reducing transition between said proximal and distal segments of said inner body member; a reducing transition between said proximal and distal segments of said outer body member; said transitions resulting in a reduced profile of the catheter.

16. The catheter of claim 13, further comprising: a reducing transition between said proximal and distal segments of said inner body member; a reducing transition between said proximal and distal segments of said outer body member; said transitions resulting in a reduced profile of the catheter.

17. The catheter of claim 14, further comprising: a reducing transition between said proximal and distal segments of said inner body member; a reducing transition between said proximal and distal segments of said outer body member; said transitions resulting in a reduced profile of the catheter.

18. The apparatus of claim 15, further comprising: a shoulder at the distal end of said distal seg- ment of said outer body member; said balloon having a proximal neck mounted to said shoulder so that the profile of the catheter in the area of said balloon during balloon deflation does not exceed the profile of said distal segment of said outer body member, measured proximally to said shoulder.

19. The apparatus of claim 16, further comprising: a shoulder at the distal end of said distal seg¬ ment of said outer body member; said balloon having a proximal neck mounted to said shoulder so that the profile of the catheter in the area of said balloon during balloon deflation does not exceed the profile of said distal segment of said outer body member, measured proximally to said shoulder.

20. The apparatus of claim 16, further comprising: a shoulder at the distal end of said distal seg¬ ment of said outer body member; said balloon having a proximal neck mounted to said shoulder so that the profile of the catheter in the area of said balloon during balloon deflation does not exceed the profile of said distal segment of said outer body member, measured proximally to said shoulder.

21. The apparatus of claim 17, further comprising: a shoulder at the distal end of said distal seg¬ ment of said outer body member;

SUBSTITUTE SHEET said balloon having a proximal neck mounted to said shoulder so that the profile of the catheter in the area of said balloon during balloon deflation does not exceed the profile of said distal segment of said outer body member, measured proximally to said shoulder.

22. The catheter of claim 1, wherein: said lumen in said inner body member is large enough to accommodate a 0.020" guidewire; and the distal segment of said outer body member is less than 0.042" outside diameter.

23. The catheter of claim 12, comprising: said lumen in said inner body member is large enough to accommodate a 0.020" guidewire; and the distal segment of said outer body member is less than 0.042" outside diameter.

24. The catheter of claim 13, comprising: said lumen in said inner body member is large enough to accommodate a 0.020" guidewire; and the distal segment of said outer body member is less than 0.042" outside diameter.

25. The catheter of claim 14, comprising: said lumen in said inner body member is large enough to accommodate a 0.020" guidewire; and the distal segment of said outer body member is less than 0.042" outside diameter.

26. The catheter of claim 1, wherein: said proximal segment and distal segment of said outer body member are of substantially the same hard¬ ness.

27. The catheter of claim 26, wherein:

SUBSTITUTE SHEET said proximal segment of said inner body member is harder than said proximal segment of said outer body member.

28. The catheter of claim 27, wherein: said distal segment of said inner body member is softer than said distal segment of said outer body mem¬ ber.

29. The catheter of claim 28, further comprising: a reducing transition between said proximal and distal segments of said inner body member; a reducing transition between said proximal and distal segments of said outer body member; said transitions resulting in a reduced profile of the catheter.

30. The catheter of claim 29, further comprising: a shoulder at the distal end of said distal seg- ment of said outer body member; said balloon having a proximal neck mounted to said shoulder so that the profile of the catheter in the area of said balloon during balloon deflation does not exceed the profile of said distal segment of said outer body member, measured proximally to said shoulder.

31. A catheter comprising: a tubular outer body member having a proximal and distal segment; a tubular inner body member having a proximal and distal segment defining a lumen therethrough; said inner body member nested at least in part in said outer body member to define an annulus therebe¬ tween; a balloon connected to both said inner and outer body members spanning said annulus at one end, effec-

SUBSTITUTE SHEET tively closing it off, said balloon selectively distens¬ ible from an inflated to a deflated position; and said distal segment of said inner body member is softer than said distal segment of said outer body mem- ber.

32. The catheter of claim 31, further comprising: a reducing transition between said proximal and distal segments of said inner body member; a reducing transition between said proximal and distal segments of said outer body member; said transitions resulting in a reduced profile of the catheter.

33. The catheter of claim 32, comprising: said lumen in said inner body member is large enough to accommodate a 0.020" guidewire; and the distal segment of said outer body member is less than 0.042" outside diameter.

34. The catheter of claim 26, comprising: said lumen in said inner body member is large enough to accommodate a 0.020" guidewire; and the distal segment of said outer body member is less than 0.042" outside diameter,

35. The catheter of claim 30, comprising: said lumen in said inner body member is large enough to accommodate a 0.020" guidewire; and the distal segment of said outer body member is less than 0.042" outside diameter.

SUBSTITUTE SHEET