Expansible tip catheters

Abstract

Expansible tip catheters in which the distal portion of a single lumen flexible plastic catheter tube is manufactured with a physical characteristic such that when fluid under pressure is introduced therein the wall of this distal portion begins to expand outwardly, and additional fluid pressure causes the wall to expand both outwardly and also along the longitudinal catheter axis.

Description

FIELD OF THE INVENTION

This invention relates to expansible tip catheters designed to be advanced through small passageways, a particular class of such catheters being embolectomy and thrombectomy catheters designed to remove emboli and thrombi from arterial and venous passageways. Other catheters of this general type are the occlusion catheter and dialysis shunt declotting catheters.

BACKGROUND OF THE INVENTION

For several years catheters have been available for surgically removing emboli and thrombi from the arterial and venous passageways. Such emboli and thrombi may result from natural causes such as myocardial infarction and thrombophlebitis and may be also induced as a result of other surgical techniques such as open heart surgery, catherization procedures and saphenous vein shunts for hemodialysis.

The most commonly used prior art catheter comprises a flexible tube having one or more apertures at its distal end. A balloon is secured at this distal end with the ends of the balloon sealed to the catheter on opposite sides of these apertures. A flexible guide wire may be temporarily positioned through the length of the catheter in order to provide support for the catheter while it is being extended through the body passageway. Otherwise, the very small flexible tube, typically having an O.D. of between 0.026 to 0.092 inches and a wall thickness in the range of 0.004 to 0.016 inches, tends to curl back rather than advancing through the artery or vein of the patient. After the tube is in place with the prior art catheter, this guide wire is removed. In use, the surgeon passes the distal end with the balloon deflated through the thrombus. A fluid or gas is then passed from the proximal end through the tube to inflate the balloon. The inflated catheter is then withdrawn, carrying with it the thrombus.

A disadvantage of this prior art catheter is that substantial care must be taken while inflating the balloon. A relatively high inflation pressure is required to inflate the balloon and if the surgeon is not very careful, the balloon may be overinflated, resulting in rupture of the balloon and discharge of the fluid or gas into the bloodstream of the patient. Even if the balloon does not rupture, such over inflation may sufficiently enlarge the outside diameter of the balloon so as to damage the wall of the body passageway.

The prior art catheter described above does not permit the balloon to be inflated while the insertion wire is in place. As a result, the catheter is substantially transparent to X-rays and therefore a radiopaque solution must usually be used to inflate the balloon if the surgeon wishes to determine the position of the catheter by an X-ray procedure. Another disadvantage of the prior art configuration is that if the surgeon wants to reinsert the guidewire after the catheter has been removed from the patient, the guidewire must be reinserted down the length of the catheter. This is a tedious and time consumming operation because of the small dimensions of the catheter and wire.

SUMMARY OF THE INVENTION

The catheter of the present invention is an improvement in the type of catheter which is constructed and arranged to be inserted, distal end first, into body fluid passages, such as arteries, veins, and the like. These catheters typically comprise an elongate flexible tube which is sealed at the distal end and is connected at the proximal end to a connector which, in use, is connected to a source of pressurized fluid for selectively injecting fluid under pressure into the tube. The improvement of this invention is that an elongate portion of the tube adjacent the distal end is made of a material which, either by its composition or its pre-treatment, e.g., prestretching, or both, is less resistant to lateral expansion, outwardly from the center, than is the remainder of the tube. Thus, upon injection of fluid under pressure into the tube during use the elongate distal end portion expands laterally first. This lateral expansion begins initially in the elongate distal end portion and progresses along said portion as additional fluid is injected into the tube in preference to the lateral expansion of the remainder of the tube. Typically, a flexible wire or other means extends through the length of the tube to prevent extension of the tube during use and to guide the tube during insertion.

Structurally, the catheter comprises a continuous flexible single lumen plastic tube which has a guide wire which extends through the tube and is secured at both the proximal and distal ends of the tube. The tube is sealed at the distal end and a small portion of the tube proximate the distal end of the single lumen, which may typically range from 0.5 to about 1.0 inch in length, differs from the remainder of the tube in that it has the physical properties or characteristics of being less resistant to lateral expansion outwardly away from the center of the lumen. Thus, when fluid under pressure is passed through the catheter from the proximal end to the distal end, the fluid causes the walls of this distal end portion of the plastic tube to expand outwardly. The expansion begins initially in this distal end portion and progresses along the distal end portion. The plastic tube which is more resistant to lateral expansion than the distal end portion does not expand during this procedure.

In both its non-inflated and inflated conditions, the catheter has marked differences over the prior art. In its non-inflated state, the catheter presents a substantially uniform outside diameter along its length and has the physical characteristics of a uniform length of small diameter flexible tube. The structural complexity of the superimposed balloon of the prior art and the difficulties attendant to the use of the prior art catheters are entirely obviated by the present invention.

Another important difference, with respect to the prior art catheters, is that the elongate distal end portion expands initially outwardly in preference to expansion of the remaining part of the catheter tube, but this distal end portion also expands laterally progressively along the longitudinal axis of the catheter the full length of the distal end portion. This longitudinal expansion capacity accommodates a considerable amount of excess fluid. One of the serious risks and disadvantages of the prior art, the difficulty in providing the proper amount of pressurized fluid for safe and effective use, has been obviated. Accordingly, if the surgeon should inadvertently overfill the catheter with fluid, the additional fluid is accommodated by longitudinal expansion of the distal end portion without substantial risk of rupturing the walls of the plastic tube.

The permanently attached guidewire provides several significant advantages. This wire prevents longitudinal extension of the catheter tube since both the distal and proximal ends of the tube are secured to opposite ends of the guidewire. The wire is radiopaque so that the surgeon may with X-ray technique determine the precise location of the catheter within the patient without having to use a radiopaque solution. The wire supports the small flexible plastic tube while it is being inserted and withdrawn from the patient. And, since the wire is permanently attached, there is no lost time caused by having to reinsert the wire through the catheter tube.

One practical advantage of catheters constructed according to this invention is that they may be shipped in smaller containers than is normally possible with catheters which embody an unsupported plastic tube. Since plastic catheters, if not supported by a guidewire, will take a permanent set if coiled, these catheters typically must be packaged and shipped in a flat condition. This requires long, bulky packages, with increased risk of damage during shipment. Storage of catheters in large numbers also occupies a great deal of valuable and limited space. In contrast, the catheters of this invention can be coiled and shipped in small boxes, since the guidewire does not take a permanent set and any set or deformation in the plastic has little if any effect upon the catheters characteristics during use.

Another feature of this invention is that in the event of over inflation and rupture of the expansible distal end portion of the catheter, an occurrence less likely with the present catheter than those of the prior art, the plastic tubing material remains integral and coherent. This reduces the possibility of foreign plastic material being left in the body fluid passageway after the catheter has been withdrawn.

FIG. 1 is a perspective view of the expansible tip catheter construction in accordance with the present invention;

FIG. 2 is a cross-sectional view of the preferred embodiment of the catheter shown in FIG. 1;

FIG. 4a shows the expansible tip catheter inflated to its normal position; FIG. 4b shows the expansible tip catheter overinflated; and FIG. 4c shows the expansible tip catheter grossly overinflated; and

FIGS. 5a through 5f show the various stages of construction of the expansible tip catheter of FIG. 3.

Referring first to FIG. 1, the basic structural components of the present invention are described. The expansible tip catheter 10 comprises a continuous flexible single lumen plastic tube 11 having an expansible tip portion 12 at its distal end and a luer connector 13 or like fluid coupling at its proximal end adapted to be connected to a syringe 14 or like source of fluid to which exterior pressure may be applied. After the distal tip has been advanced by the surgeon through a passageway to the desired location, the syringe 14 is connected to the coupling 13 and a predetermined amount of fluid is introduced under pressure into the catheter lumen. This fluid causes the wall of the distal end of the catheter to expand outwardly.

A cross-sectional view of one embodiment of the present invention is shown in FIG. 2. The proximal end 20 of the catheter tube 11 is permanently joined to the luer connector 13 by means of an inner bushing 22. At its distal end, the catheter is sealed by lacquer plug 23 and one or more suture ties 24. Extending completely through the lumen and permanently secured at the distal and proximal ends thereof is a flexible guidewire 25 having a pair of beads 26, 27 permanently secured to the distal end of the wire. As shown, the wall 28 of the flexible tube proximate those beads is drawn tightly into the valley between these beads and secured by one or more of the suture ties 24. At the proximal end, the wire 25 is permanently secured by a loop 29 extending through the stem wall 30 of the luer tip as shown.

The expansible distal end portion of the catheter is formed by modifying the lateral expansion characteristics of the distal end portion of the catheter lumen. In the simpliest form of the invention, the lumen 11 is an extrusion of a stretchable elastomeric material, for example block copolymers of styrene and butadiene. At the distal end, at a point 31 closely proximate the beads 26 and 27 of the wire 25, the tube is physically expanded along its longitudinal axis a predetermined amount during the manufacturing process. This pre-stretching or pre-extension permanently changes the characteristics of that portion of the tube so treated. When stretched a pre-determined amount and released, the tube will elastically recover its original unstretched dimensional configuration, but this portion is less resistant to lateral expansion than is the unextended material. It is not fully understood what physical changes occur in elastomer, but it is believed that the stretching changes the orientation of the polymeric components. The effect, in any event, is to lower the modulus of elasticity of the extended portion. Thus, although the material returns to its original unstretched dimensional configuration after being extended, it is less resistant to lateral expansion than it was before being extended. When fluid under pressure is introduced into the tube the material "remembers" the point 31 at which it was previously extended and the outward expansion of the tube begins at this point 31 and progresses longitudinally along the length of the pre-extended distal end portion of the tube.

A disadvantage of the simplified embodiment of the invention described hereinbefore is that the wall of the catheter may, by virtue of the internal fluid pressure, be induced to expand outwardly at some place other than its distal tip portion. For example, if the distal tip is inserted into a passageway that is too small for proper expansion, as the fluid pressure is increased such other portion of the catheter wall may be caused to expand outwardly at such point. Also, in this simplified embodiment, should any other portion of the catheter be inadvertently stretched during handling by the surgeon or his assistants, such portion would be as likely to expand as the distal end.

In the preferred embodiment of this invention shown in the cross-sectional view of FIG. 3, substantially the entire length of tubing 35 formed from material which is substantially resistant to expansion when pressure is applied to its interior wall. An exemplary material is a block polymer of styrene and butadiene filled with polypropylene. The distal expansible tip portion 12 is formed from a short length of tubing 36 having a different plastic configuration, which is less resistant to lateral expansion, having one end 37 abutted to and permanently joined to one end 38 of the substantially longer length of filled, more expansion resistant material. Advantageously, this distal tube 36 is formed of the unfilled styrene butadiene elastomer and has inside and outside diametral dimensions identical with the main catheter tube 35 so that the catheter is a continuous single lumen of uniform outside diameter (O.D.) and inside diameter (I.D.). In the manner described above, the distal end is stretched at a point 31 to impart a permanent physical characteristic to the unfilled plastic material. As a result, when fluid pressure is applied through the luer connector 13 at the proximal end through the first length of tube 35 and hence the second distal tube 36, the exterior wall of the distal portion is caused to expand outwardly beginning at the point 31 which has been physically stretched. The physical characteristics of the tube 35 inhibit expansion of any other portion of the catheter lumen.

The improved inflation characteristics of the invention are illustrated in FIGS. 4a, 4b and 4c. FIG. 4a illustrates the inflation of the expansible tip 12 to its normal expanded position, i.e., the form that it would normally assume during an embolectomy procedure, for example. As shown, beginning at the point 31, the point at which the catheter has been stretched, the wall of the distal tip has been caused to expand outwardly to a predetermined outside diameter. Only relatively small fluid pressures are required to reach and maintain this position.

A significant feature of this invention is that should the surgeon inadvertently overfill the catheter with fluid, such additional fluid is readily accommodated by the catheter in that the plastic tip may expand both outwardly in the direction of the arrows 40, 41, but also progressively along the longitudinal axis 42 of the catheter lumen to assume the configuration shown in FIG. 4b. In the embodiments of FIGS. 2 and 3, this additional expansion is accommodated by the portion of the distal tip 12 which either has not previously been stretched or not stretched to the same degree as the portion at point 31. As excess fluid is forced into the distal end, this unstretched or partially stretched portion is caused to stretch, thereby providing an appreciable expansion volume beyond the normal expanded state shown in FIG. 4a. As a result, the catheter of this invention can accommodate a substantial excess introduction of fluid without rupturing the wall of the expansible distal tip, even to a grossly distended state shown in FIG. 4c.

The single lumen construction of the present invention provides other important advantages as well. Thus, this construction provides a catheter of having a substantially uniform outside diameter along its entire length, thereby facilitating the advancement of the tube through the vascular system or similar passageway. For a given uninflated O.D., the O.D. of the expansible tip is relatively large. A ratio of 6.6 for the inflated O.D. to uninflated O.D. is easily achieved.

The permanently secured guidewire provides a nonremovable support for the catheter as it is advanced through a passageway. Accordingly, after the catheter is withdrawn, no time is lost in having to reinsert the guidewire. Also, the guidewire is radiopaque, thus relieving the surgeon from having to use a radiopaque solution when it is desired to locate the catheter position by X-ray. The wire prevents longitudinal extension of the catheter as fluid is forced therethrough to expand the distal tip. Another advantage exhibited by catheters constructed in accordance with this invention is that in the tests conducted to date, when the catheter was overfilled to force the expansible tip to rupture, the tip portion remained in one integral piece. This is of course desirable since it precludes leaving any foreign matter inside the body passageway.

The procedures involved in manufacturing the catheter shown in FIGS. 1-3 are illustrated in FIGS. 5a, 5b, 5c, 5d, 5e, and 5f. Referring to FIG. 5a, the proximal end of the filled poly-styrene-butadiene tube 35 is permanently bonded to the inner and outer bushings 21, 22. A suitable lacquer may serve as the bonding medium. An inner mandrel 50 is positioned through the entire length of the tube 35 so as to prevent the entry of any lacquer into the internal of the lumen. The end 37 of the distal unfilled poly-styrene-butadiene tube 36 is bonded to end 38 of tube 35 also by a suitable lacquer. The mandrel 50 is then removed. At this point of time during the manufacturing procedure, no physical stretching is applied to the distal tube 36.

As shown in FIG. 5b, the next step of the procedure is to insert the guidewire 25 through the entire length of the catheter lumen and through the stem wall 30 of the luer tip 13. As shown, the luer tip is held at an angle with the wire so that the wire pierces the wall of the stem as shown. The wire is then bent in the form of a loop as shown in FIG. 5c and the stem of the luer tip is lacquer bonded to the proximal end of the catheter lumen by means of the bushings 21, 22 as shown in FIG. 5d. This step permanently secures one end of the guidewire to the proximal end of the catheter.

Following the attachment of the wire at the proximal end of the catheter, the distal end of the catheter 10 is compressed so as to expose the pair of beads 26, 27 located on the wire. (See FIG. 5e) These beads are then liberally covered with the bonding lacquer and the catheter allowed to return to the original configuration, shown in FIG. 5d, thereby providing a lacquer bond between the inside wall of the distal end and the beads 26, 27 and the lacquer plug 23. One or more knots of suture thread 24 are then tied around the exterior of the catheter so as to compress the catheter wall 28 into the valley between the wire beads as shown in FIG. 3. The distal end including these suture ties is then dipped in lacquer to provide a relatively smooth surface over the distal end of the catheter 10.

The distal tube 36 is then stretched as shown in FIG. 5f. This may be manually performed by grasping the portion of the catheter overlying the bead 27 with the fingers of one hand and grasping the immediately adjacent catheter wall at point 31 with the fingers of the other hand and pulling the two apart a predetermined amount S. A single stretch of the predetermined dimensions is all that is required to give the material the permanent characteristic of being less resistant to lateral expansion while allowing the catheter material to elastically return to its original dimensional configuration after being released. The catheter is then tested by introducing air at the proximal end and causing the distal end to inflate to the desired configuration. After sterilization, the catheter is ready for surgical application.

By way of specific example only, embolectomy catheters in a range of O.D.'s may be constructed in accordance with this invention according to the following specifications; all dimensions being stated in inches.

__________________________________________________________________________ Guide Length Length Catheter Wire Bead of of Size O.D. I.D. O.D. Diameter Tube 35 Tube 36 S __________________________________________________________________________ 2F .026 .017 .008 .022 32 .3 1.0 to 1.5 3F .039 .024 .008 .022 32 .3 0.7 to 1.2 4F .052 .028 .015 .030 32 .3 0.4 to 0.9 5F .065 .037 .015 .030 32 .3 0.2 to 0.7 6F .078 .043 .015 .030 32 .3 0.2 to 0.7 7F .092 .060 .015 .030 32 .3 0.2 to 0.7 __________________________________________________________________________

There is no particular criticality of materials, since a number of polymeric materials exhibit the characteristic of being less resistant to expansion or stretch once having been stretched than in the unstretched or unextended condition.

It will be understood that other means of obtaining compatible materials having differing resistance to expansion can be used without departing from this invention. For example, it is known that irradiation of polymers by electrons, X-rays, gamma rays, etc., effects the degree and nature of polymerization and modifies the physical characteristics of most polymers. In general, irradiation tends to cross-link the polymer thus reducing its thermoplastic and/or elastic characteristics; however, irradiation under varying conditions with specific polymers can result in other changes. It is within the scope of this invention to modify part of the plastic tube either to increase or to decrease the resistance to expansion, depending upon the polymer system being used, to obtain the structure defined herein.

In addition, of course, the material must be sufficiently compatible with body fluids and tissues as to be usable in the fluid passages in the body without undue irritation or other complications arising from reaction of the material with body fluids or tissue. Again, however, a large number of materials have been found to be sufficiently biologically acceptable for this purpose. Indeed, most conventional polymers are sufficiently compatible for temporary use in the body. For example, the polyolefins, polyethylene and polypropylene, the polyacetals, poly-butadiene-styrene copolymers, the polyfluoro and polyfluorochloro-polymers, such as TEFLON and KEL-F and other polymers and copolymers are generally suitable, when properly processed and handled, for at least temporary residence in the body. While biological compatability of the guidewire is not particularly critical, since it is not normally in contact with body fluids, it is desirable to provide a material which has at least temporary compatability with body fluids and tissues. No. 302 stainless steel wire, and other stainless steel products as well as other alloys are suitable.

The medical literature on prosthetic devices give many examples of materials which have been found suitable for use in connection with body fluids and tissues both temporarily and on a long term basis.

One particularly suitable material is the KRATON polymers which are described as thermoplastic elastomers produced by Shell Chemical Co., Polymers Division, for pharmaceutical and medical applications. These KRATON products are block copolymers of butadiene and styrene which have rubbery properties but do not require vulcanization. The butadiene-styrene copolymers may be blended with fillers, such as polypropylene, to give more expansion resistant characteristics to the products. These polymers are fabricated and processed using conventional extrusion and molding techniques.

The polymers may be bonded by solvent welding or cemented using an appropriate lacquer. It is often convenient to prepare a lacquer which is composed of the polymer or polymers to be bonded dissolved in an appropriate solvent. Manufacturers literature and standard handbooks, such as MODERN PLASTICS ENCYCLOPEDIA, as well as the polymer literature generally, provide information as to the solubility of the various polymers in selected solvents. KRATON may be dissolved in toluene, methyl ethyl ketone or cyclohexanone in concentrations of from 5 percent to 10 percent to form a suitable lacquer. Upon evaporation of the solvent, only the polymer remains without loss of its biocompatability characteristics.

The connector elements may be made of any material which can be conveniently fabricated into the desired shapes. Copolymers of styrene and butadiene, blended or filled with polyproplene, or other stiffening material, are convenient since cohesive bonding usually is more easily accomplished than adhesive bonding.

The foregoing examples, are intended merely to illustrate the invention and are not limiting. Size, materials and details of fabrication of plastic and metal catheters and the like are well known and can be used in conjunction with the teachings of this patent. The extent and scope of the protection claimed hereunder is not to be limited to the specific examples set forth hereinbefore, but only by the scope of the following claims.

Claims

What is claimed is:

1. In an expansible tip embolectomy catheter of the type which is so constructed and arranged as to be inserted distal end first into blood passages in the body which comprise an elongate flexible tube sealed at the distal end and connected at the proximal end to a pressurized fluid source connector for supplying fluid under pressure into said tube during use, the improvement wherein:

said tube has an outside diameter from about 0.026 inches to about 0.092 inches;

an elongate portion of the tube adjacent the distal end is pre-stretched to be less resistant to lateral expansion than the remainder of the tube such that upon injection of fluid under pressure into said tube said elongate distal end portion expands laterally first, said lateral expansion beginning initially in and progressing along said elongate distal end portion in preference to lateral expansion of the remainder of said tube; and

including an elongate flexible wire secured to the connector and the distal end of the tube, extending through the tube to prevent extension and to guide the tube during insertion.

2. The improved expansible tip catheter defined in claim 1 wherein the outside diameter of the unexpanded tube is substantially uniform along the length thereof.

3. The improved expansible tip catheter defined in claim 1 wherein the tube is constructed in two sections, an elongate tip portion composed of a resilient polymer, and the remainder of the tube which is composed of flexible polymer, the resilient polymer tip portion being less resistant to lateral expansion than the remainder of the tube.