WO1995017219A1

WO1995017219A1 - Intra-aortic balloon pump device

Info

Publication number: WO1995017219A1
Application number: PCT/US1994/014721
Authority: WO
Inventors: William Edelman; Mark Thomas Kieras; Peter T. Majeski
Original assignee: St. Jude Medical, Inc.
Priority date: 1993-12-20
Filing date: 1994-12-19
Publication date: 1995-06-29
Also published as: CA2179510A1; EP0735903A1; JPH09511155A; EP0735903A4

Abstract

A large thin walled polyurethane balloon (20) for an intra-aortic balloon pump catheter (10) is coated with a hydrophilic lubricous coating (36) which includes a water-soluble polyvinyl pyrrolidone, preferably in a blend with a thermoplastic polyurethane, and a suitable organic solvent and then is dried and cured for a substantial period. The dried and cured balloon (20) is assembled into a catheter (10) and furled. The furled balloon (20f) demonstrates a high degree of slipperiness when hydrated in conjuction with insertion into a patient's vasculature, unfurls readily, and demonstrates flexibility, strength and toughness for use in intra-aortic pulsation operation.

Description

INTRA-AORTIC BALLOON PUMP DEVICE

FIELD OF THE INVENTION This invention relates to intra-aortic balloon pumps and particularly to improved intra-aortic balloon pump catheters.

BACKGROUND OF THE INVENTION Intra-aortic balloon pumps (IABP) are used to provide counter pulsation within the aorta of ailing hearts over substantial periods of time, e.g. to provide ventricular assistance during cardiogenic shock, low cardiac output in post-operative care, weaning from cardiopulmonary bypass, treatment for refractory unstable angina, and other circumstances of sub-normal cardiac function. Such pumps of the type involved in this invention include a flexible thin-walled balloon which is readily inflatable under low pressure to substantial size and displacement, mounted on a catheter device used for insertion of the balloon into a remote artery and through the intervening vascular system of the patient to the aortic pumping site while the balloon is deflated and furled. This requires insertion of the furled large capacity balloon through a small insertion passage, e.g., a small puncture opening or through an introducer cannula into the selected artery, and then sliding-threading of the catheter and furled balloon through tortuous lumen passageways of the patient's vascular system over a guidewire to the pumping site, e.g. from insertion into an artery in the groin area to the patient's descending aorta. At the pumping site, the balloon is unfurled and then successively and rapidly inflated and deflated in synchronism with the patient's cardiac pulsation rates over extended periods of time in a known counterpulsation technique to enhance cardiac output. Thus, use of an IABP requires forceful sliding insertion of a relatively large balloon through a small insertion opening and tortuous arterial lumens, which may be randomly narrowed by arteriosclerotic deposits of plaque, and subsequent unfurling and reliable pulsation operation at heart-beat rates over substantial periods of time, e.g. for several days. Moreover, the balloon may be subject to abrasion by plaque deposits or the like during the pulsation operation at the pumping site.

It will be appreciated that the circumstances and requirements of insertion and use of intra-aortic balloon pumps provide numerous conflicting parameters. Significant aspects of these conflicting parameters are related to the fact that the inflated but unstretched diameter of the balloon is much larger than the diameter of the insertion site, which may be percutaneous, and larger than at least portions of the lumen of the vascular system through which it is to be threaded. This requires that the balloons be furled for insertion through passageways which are of very small inside diameter (ID) relative to the size of the balloon when opened. Further, it is desirable that the furled balloon, as well as the related catheter mechanism should be slippery during insertion for ease of sliding movement through the insertion site, through small lumens and along changes of direction in tortuous pathways during its passage along the patient's vascular system from the point of entry to the aorta, with minimum risk of inducing morbidity during such insertion and passage and during use in the pumping phase. Moreover, the balloon should be dry and non-slippery during handling, furling, packaging, unpackaging and handling by the health care personnel up to the time of actual insertion into the patient's vascular system.

The related catheter equipment typically includes dual concentric lumens, including a center lumen passageway to serve functions such as engaging over a guidewire, sensing values in the aorta, e.g. arterial pressure, and/or administration of medicaments. A surrounding annular passageway between the inner and outer lumens must be of a size adequate to shuttle an operating gas such as helium at rates to obtain the rapid repetitious expansion and collapse of the balloon necessary for the pumping function in counterpulsation to the patient's heart.

Various coatings and other surface layers have been provided on different types of catheter devices to provide highly lubricous characteristics during insertion through a patient's vascular system. These have included, among others, the use of hydrophilic coatings which provide the beneficial characteristics of being dry and non-slippery during packaging and handling, and then becoming lubricous when wetted as upon contact with aqueous body fluids such as the blood within the patient's vascular system. Examples of such coatings and treatments are described, for instance, in U.S. Pat. Nos. 4,100,309, 4,119,094, 4,642,267 and 5,135,516. As described in certain of these patents, polyvinylpyrrolidone is a commercially available poly (N- vinyl lactam) hydrophilic polymer which has several characteristics making it useful and desirable in forming hydrophilic lubricous coatings on catheters and other invasive devices. The cited U.S. Pat. Nos. 4,100,309 and 4,119,094 describe coating of such devices by a two step procedure. First a solution of an isocyanate containing prepolymer and polyurethane is applied to the substrate of the device to be coated followed by a coating solution of polyvinylpyrrolidone. Polyurethane may be omitted from the isocyanate containing prepolymer when the substrate is polyurethane. In either event, this approach requires that reactive isocyanate be present. As pointed out subsequently in U.S. Pat. No. 4,642,267, the aforenoted approach provides certain shortcomings because of the necessary presence of the reactive isocyanates. The Patent No. 4,642,267 describes the use of another hydrophilic coating formed from a blend or alloy of thermoplastic polyurethanes with polyvinylpyrrolidone and/or other poly (N-vinyl lactams) . However, there is no suggestion for the use of this blend coating or other hydrophilic lubricous coatings on the balloons of intra-aortic balloon pumps or on other devices which are subject to the structural and functional requirements of such pump balloons.

U.S. Pat. No. 4,646,719 describes one beneficial structure and form of intra-aortic balloon pumps and includes a description of the manner of insertion and use of such pumps.

The disclosure of each of the aforecited U.S. patents 4,100,309, 4,119,094, 4,642,267 and 4,646,719 is incorporated herein by reference.

SUMMARY OF THE INVENTION It has been found that large thin-walled balloons of intra-aortic pumps can be coated with a hydrophilic lubricous coating to be very slippery when hydrated in use and still appear to maintain the flexibility, strength and toughness necessary to meet the stringent operational requirements for the balloons of such pumps. While these assemblies gain the benefits of a highly lubricous exposed surface of the furled balloon to increase the ease with which the balloon catheter is introduced into and passed through the vasculature, the coated balloons also unfurl readily and appear to retain reliability for extensive useful life in subsequent pumping operations. It also has been found that balloons so coated and while dry may be handled, manipulated, attached to catheters and furled in substantially a normal manner of production of balloon pump catheter assemblies.

In the preferred embodiment, it has been found that application of an outer surface coating of a blend of an organic solvent soluble thermoplastic polyurethane having no reactive isocyanate functionality and a poly (N-vinyl lactam) , specifically polyvinylpyrrolidone, in a suitable solvent, such as suggested in the U.S. Pat. No. 4,642,267, on an intra-aortic balloon provides a stable, highly lubricous surface while apparently preserving the functional physical characteristics of the balloon as a part of an intra-aortic balloon pump catheter device. This includes, for example, maintaining flexibility, bonding capacity, inflatability, aneurysm pressure, tensile strength and abrasion resistance to assure reliable pulsing operation over extended periods of intra-aortic pumping operation.

The coating may be readily applied to the balloon, which typically is of polyurethane, as by a casting or dip coating procedure to readily form a uniform film, and then dried to provide a dry non-slippery product for conventional handling, furling of the balloon, packaging and operation preparation purposes. The coating is self- activated upon contact with an aqueous solution, including blood, whereby the coating hydrates substantially instantaneously and thereby acquires a coefficient of friction much lower than that of an uncoated balloon catheter. The result is a very slippery external surface which provides ease of insertion of the intra-aortic balloon catheter through tissue or through an introducer cannula and through the patient's vasculature to facilitate placement in the aorta for counterpulsation therapy. The highly lubricous surface of the balloon facilitates insertion and positioning of the pump balloon with minimal forces and is believed to reduce morbidity in terms of thromboembolism and/or dissection of the arterial walls. The coating also may be pre-wetted just prior to insertion if preferred by the user, with the same beneficial effect. It is believed that the coating also reduces the impact of atherosclerotic lesions upon the balloon material, and thus aides in preserving the integrity of the balloon both during insertion and during use to enhance the necessary durability of the intra-aortic balloon pumping device.

An object of the invention is to provide intra-aortic balloon pump catheters which provide ease of insertion with minimum trauma while obtaining and maintaining good reliability and useful life of the balloon pump. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a simplified top view of an intra-aortic balloon catheter employing this invention.

Fig. 2 is an enlarged cross-sectional view taken along line 2-2 of Fig. 1.

Fig. 2A is a further enlarged schematic illustration of a cross-sectional segment of the balloon as in Fig. 2.

Fig. 3 is an enlarged side elevation view illustrating the balloon section of the pump device of Fig. 1 with the balloon furled and unsheathed, such as during insertion through a patient's vasculature.

Fig. 4 is a schematic side elevation of a tubular sheath for the furled balloon of Fig. 3.

Figs. 5A-5E schematically illustrate steps in one mode of applying the coating of the balloons of Figs. 1-3.

While the invention will be further described in connection with certain preferred embodiments, it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS As illustrated in Fig. 1, one embodiment of an intra-aortic balloon pump device 10 includes a flexible tubular outer lumen 12 and a co-axial flexible tubular inner lumen 14 attached to a wye connector 16. A single chamber intra-aortic balloon 20 is attached at its proximal end to the distal end of the outer lumen 12. The distal end of the balloon 20 is attached to the distal portion of the inner lumen 14. Each of these balloon-lumen attachments is a gas-tight adhesive bond connection between an end sleeve section 21,22 of the balloon and the outer surface of the respective lumen 12,14. As seen in the drawings, these end attachment sleeves are of substantially lesser diameter than the main displacement body section 23 of the balloon and are joined thereto by short tapered sections 24,25. The wye connector 16 provides access through the lateral branch 26 to an appropriate gas supply pump and control device (not shown) for inflating and deflating the balloon 20 by successively injecting and withdrawing a gas such as helium through the annular space between the lumens 12 and 14. The controller responds to the pulsing of the heart and effects inflation and deflation of the balloon in timed counterpulsation to the pumping action of the heart in a known manner. The axial section 27 of the wye provides axial access to the inner lumen for reception of a guide wire 28 as well as for sensing of arterial pressure and/or the injection of medicaments through the inner lumen. Tie downs 32 are included for affixation to the skin of the patient by suturing and/or taping for securing the catheter in its inserted operative pumping position.

The balloon 20 is a large flexible thin-film balloon of conventional appropriate size, i.e., on the order of about 0.5" to about 1.0" in diameter when in an inflated but unstretched condition and about 8" to 12" in length. Typical sizes are of 30cc, 40cc and 50cc displacement. The balloon may be formed of any suitable material, with polyurethane presently being preferred. A hydrophilic coating 36 covers the balloon. The coating forms a lubricous outer surface which is very slippery when wetted by an aqueous fluid, such as blood, while permitting processing and furling of the balloon and handling of the balloon and related pump mechanism in a normal manner when dry. Coatings which are available from Hydromer Inc., Whitehouse, New Jersey, and comprise polyvinylpyrrolidone have been found efficacious. These coatings comprise poly¬ vinylpyrrolidone and one or more polyurethane or isocyanate-containing prepolymers. It is reported that these polymers react with one another forming interpenetrating polymer networks which swell to varying degrees in the presence of water, depending on the concentration of the components, and that they have anti- thrombogenic properties. They swell immediately upon contact with water-based fluids but do not dissolve, becoming extremely lubricous and highly durable coatings e.g. typically of 0.2 - 0.5 mils thickness after drying. It has been found that such hydrophilic coatings can be applied to intra-aortic balloons 20 to gain the desirable slipperiness when wet without significantly impairing the normal physical properties and handlability of the balloons and assembled devices. The coated balloon 20 is furled, as illustrated schematically at 20f in Fig. 3. This minimizes its effective outer diameter during insertion into a patient's arterial system. The furling may be accomplished in a conventional manner. This includes applying a solution of silicone and freon on the outer surface such as by spraying to deposit silicone thereon, then evacuating the air from the balloon thereby causing the balloon to collapse into flat generally radially extending "wings", then rolling those wings tightly about the inner lumen 14 in mutually interleaved relation with one another. This winds the collapsed balloon "wings" into tightly packed spirals as viewed in cross-section, to minimize the effective outer diameter of the balloon during handling and during the insertion process. The silicone avoids surface-to-surface sticking of the furled layers. A thin tubular sheath 40 typically is placed over the furled balloon to maintain its radial compaction to a minimum effective outside diameter, e.g., 9 Fr. (about 0.117") during shipping and handling, up to the point and time of insertion into the patient. The wye and tubular lumena and related components and equipment may be of any suitable structure and size. However, by employing another development, to be set forth more fully in another application, the inner lumen may be a very thin-walled tube formed of Nitenol (a nickel- titanium alloy) to minimize the outside diameter of the inner lumen while maintaining the necessary functional inside diameter and strength characteristics, and the outer lumen may be a thin-walled tube formed by coextrusion of polyurethane around nylon, to provide space between the lumena of adequate cross-section for the pulsation gas flow while minimizing the outside diameter of the outer lumen. That improved lumen design will reduce the obstruction of the patient's access arteries by the catheter during operation of the intra-aortic pump, relative to current commercial catheter devices which also may employ coated balloons as in this invention. By way of example, such an improved inner lumen may be a nickel-titanium alloy tube 0.0283 " ID and 0.0347" OD, and the outer lumen may be 0.090 ± 0.001" ID and 0.105" to 0.111" OD (8 Fr.) .

The basic balloon 20, prior to coating, may be of the same material, configuration and size as uncoated balloons currently in use in intra-aortic balloon pumps. An example of a preferred embodiment includes a polyether based polyurethane balloon of about 0.003"-0.005" wall thickness formed by dip molding on an appropriately shaped mandrel. Such balloons have satisfactory flexibility and strength, with high elasticity, e.g., about 525% stretchability without rupture. One specific commercially available polyurethane which has proven satisfactory in such balloons, including those used in practicing this invention, is sold by B.F. Goodrich under the designation "Estane 58110".

It will be appreciated that the furled balloon typically represents the largest diameter portion of the catheter of an intra-aortic balloon pump. Therefore, maximizing the slipperiness as well as minimizing the effective outside diameter of the furled balloon are important considerations. The coated balloon 20 provides the desirable slipperiness without significantly compromising strength, reliability or durability and without requiring other modifications from current conventional modes of manufacture, packaging and use. Also, there may be a benefit of an increase in thrombo- resistance of the coated surface as compared to a polyurethane film surface.

Examples of Coated Balloons Polyurethane balloons as described above with a coating 36 comprising polyvinylpyrrolidone as the hydrophilic agent have provided beneficial results. The polyvinylpyrrolidone has been applied to the polyurethane balloon substrate in two forms. One was in a prepolymer solution containing isocyanate in an organic solvent. Evaporating the solvent is believed to form a polyvinylpyr- rolidone/polyurethane interpolymer coating on the substrate. This coating, herein designated as "Coating A", was of the following formulation:

Coating A (Hydromer. Inc. Designation 11-Aι 1.8% by weight Polyvinylpyrrolidone 0.6% by weight Polyisocyanate 80 pp Surfactants 97.6% by weight Solvent mixture of:

73.2% by weight Ethyl Lactate 24.4% by weight Cyclohexane

The second coating was a blend of thermoplastic polyurethane with polyvinylpyrrolidone in another organic solvent, with the following formulation, herein designated as "Coating B":

Coating B (Hydromer. Inc. Designation 11B or 503) 3.0% by weight Polyvinylpyrrolidone 0.1% by weight Polyurethane 13 ppm Surfactant

96.9% by weight Solvent mixture of: 93.9% by weight Diacetone Alcohol 0.8% by weight Tetrahydrofuran

2.2% by weight N-Methyl Pyrrolidone Other manners of coating with polyvinylpyrrolidone and related hydrophilic materials also are deemed to be operable.

The coating with an interpolymer blend as with Coating B presently is preferred. It is simple and easy to apply. It has no free isocyanates and therefore avoids the need to insure that reactive isocyanates are removed from the final product. It is believed that such isocyanates may introduce chemical instability and/or inactivate desirable additives such as pharmaceuticals surfactants and dyes. The balloons coated with Coating B seem to have better lubricity and flexibility.

The coating may be applied to the balloons in any suitable manner, such as spraying, dipping (immersion) or brushing. Figs. 5A-5E illustrate schematically a dipping process of coating balloons 20 in a one step coating process using the interpolymer blend of Coating B. In the system illustrated, the balloons are mounted on long slender mandrels 48 of racks 50, as in Fig 5A, by sliding them on from the lower end of the mandrel and gripping the proximal (upper) ends, such as by engaging the balloon necks 21 on barbs on the upper portions of the mandrels. The lower ends of the balloons remain sealed, from the mode of their manufacture. The balloons then are dipped into the coating solution 52 in an appropriate container 54 as illustrated in Fig. 5B, to a depth to insure that the proximal necks 21 are immersed at least to the length to which they will be trimmed later. The open upper ends are maintained above the coating liquid to avoid entry of coating into the balloons. The balloons then are withdrawn as in Fig. 5C and allowed to drip and dry for a minimum of 15 minutes. The viscosity of the coating solution, the insertion and withdrawal rates and the dwell time of immersion are adjusted to control the thickness of the coating. An immersion cycle of 10 seconds, with a dwell time of 1 second and withdrawal cycle of 10 seconds has been found to provide a satisfactory coating when using a Coating B at a viscosity of 19-24 sec. at 77°F as measured with an Zahn-type viscosity cup #2 per ASTM D4212-88 Standard Test Method for Viscosity by Dip-type Cups, where the Coating B was a product designated "Coating Solution 503" by the supplier Hydromer, Inc. of Whitehouse, New Jersey.

The coated balloons then are heated to evaporate the solvent, as by being placed in an oven 56 (Fig. 5D) at about 150°F. for 60 minutes. Upon removal from the oven the racks of balloons are allowed to cool under ambient room temperature conditions for a minimum of ten minutes. The balloons then are removed from the mandrels and each balloon is placed in a polyethylene sleeve 60, inspected and stored for curing at ambient room temperatures, e.g., about 70°F, for at least 7 days before use, as illustrated in Fig. 5E. The latter "curing" period appears to facilitate restoration of the strength of the balloon material following coating, perhaps by permitting further dissipation of any remaining solvent and/or completion of the interbonding of the substrate and the coating at the bonding interface therebetween.

The coated balloons are biocompatible and appear to retain substantially their original strength, flexibility and wearability after coating and curing as outlined above, while attaining a highly lubricous surface when ultimately wetted. Moreover, while dry they can be handled, furled, packaged in tubes 40, unpacked and prepared for insertion in the same manner as uncoated balloons. This includes tolerance to the heating step often employed following furling, wherein the furled balloons are heated to a temperature on the order of 135°F for about 12-16 hours to assist in setting and thereby sustaining the furling during insertion following removal from the tube 40. The coated balloons become very slippery promptly upon being wetted, with attendant benefits of ease of insertion and placement as well as reduction of trauma, and the coating does not appear to either prompt undesired unfurling prior to insertion or to hinder normal intentional unfurling when in place at the pumping site in the patient's aorta. The noted coatings are stable and apparently are of uniform characteristics throughout their thickness to maintain the same lubricity and inert characteristics despite reasonable wear during extended periods of use normally encountered with IABP devices. Also, the coating does not present a hazard to effective assembly of the complete balloon pump catheter devices. The aforedescribed specific embodiment with Coating B included polyether urethanes for the balloon substrate and in the coatings, and a compatible solvent, with beneficial results. However it is believed that acceptable results also would be obtained with balloons and coatings using other polyurethanes and appropriate compatible solvents.

Test Performance Using Balloons Coated Per the Invention and of IABP Incorporating the Coated Balloons Forty polyurethane balloons of 40cc capacity and twenty-eight of 30cc capacity were cleaned in an ultrasonic bath of isopropyl alcohol and coated by the coating supplier. The balloons were 80% submerged at one end in the cleaning bath for 5 minutes with the balloons correspondingly filled, and this step was repeated with the opposite ends submerged, followed by drying for 20±5 minutes in ambient room air and oven drying for 20±2 minutes at 65°± 2°C. All of the cleaned balloons were coated with the aforedescribed coating solution 503 of Hydromer, Inc. by dip coating generally as described above. Ten of the 30cc balloons were coated both externally and internally by immersion into and withdrawal from the coating solution at 1/6 in/sec with a bottom dwell time of 3 seconds. The other eighteen of the 30cc balloons and the thirty 40cc balloons were coated only externally by dip coating with immersion and withdrawal at 1/4 in/sec and 3 seconds bottom dwell time. All then were permitted to drip and dry in ambient room air for 20±5 minutes, followed by oven drying for 30±1 minutes at 65±2°C. At least seven days thereafter these balloons were subjected to numerous tests including those referred to below.

Half of the coated balloons were built into functional 9 Fr. catheters for performance testing, along with an equal number of control intra-aortic balloon pump devices with conventional polyurethane balloons. The other coated balloons were reserved for mechanical testing.

All of the test and control catheters were manufactured by the normal steps for manufacturing a current commercial IABP by the Cardiac Assist Division of St. Jude Medical, Inc. Post-furl pressure decay leak tests were performed upon return of the catheters from the sterilizer. Those which did not pass this test were not tested further.

All of the remaining catheters, with the balloons still in the packaging sheaths, were pressurized to 6 psi and submerged in water where a leak would manifest itself as a constant stream of bubbles and a decreasing pressure. The sheaths then were removed from five 40cc control catheters and five 40cc catheters incorporating the coated balloons and all were pressurized until their balloons aneurized. The pressure at which each aneurized was recorded. While the balloons were aneurized, these catheters were again immersed in water to determine if a leak had developed. The catheters subjected to these latter leak tests showed no leakage of the balloons or bonds under the initial 6 psi test or after aneurizing. The control catheters experienced balloon aneurysm at an average of 13.6 psi (range of 13.5-14 psi) while those with coated balloons aneurized at an average of 12.9 psi (range of 12.75-13 psi), all with no leakage of the balloons or the bonds.

Similar tests were conducted on fifty-nine other 9 Fr. IABP catheters similarly manufactured, namely thirty control catheters consisting of ten each with 30cc, 40cc and 50cc balloons and twenty-nine catheters having balloons coated with Coating B as follows: ten 30cc, ten 40cc and nine 50cc. All of these fifty-nine samples were aged for 45 days in a 65°C oven, simulating 2 years of shelf life. The average and range of aneurysm pressures observed were as follows, stated in psi:

Coated per the Invention Control

Average Range Average Range

30cc 14.13 14.00-14.25 14.15 13.75-14.25

40cc 13.78 13.50-14.25 13.75 13.50-14.00

50cc 12.42 12.50-12.75 12.40 12.25-12.50

The differences of the aneurysm pressures are not deemed to be clinically significant as the observed aneurysm pressures all were far above the normal usage pressure of about lδOmmHG or 2.9 psi, i.e. by a factor of more than four. Correspondingly, the calculated hoop stress on the balloon material during a usage pressure of 3 psi is about 190 to 220 psi for balloons of the above size range and about 0.0048 inches coated thickness whereas the noted aneurizing pressures calculate to a range of about 895 to 922 psi.

The ten 30cc balloons coated internally as well as externally and built into catheters were not furled and were not subjected to the in-sheath leak test. However, they were immersed in water for 7 days at room temperature and then subjected to the aneurysm test, with an average aneurysm pressure of 12.8 psi (range of 12.5-13 psi), with no leakage of the balloons or the bonds. This indicates that presence of the coating on the inner surface of the connection sleeves 21,22 would not impair the functionality of the catheter.

Five 30cc and five 40cc catheters with coated balloons, from the group first-noted above, were subjected to inflation testing, along with a corresponding number and size of control catheters. This consisted of loading each catheter into an inflate/deflate fixture, which was pressurized to 75mmHg, and connecting the catheter to a Model 700 pump marketed by the Cardiac Assist Division of St. Jude Medical, Inc. The pump then was operated in the "manual fill" mode. All five of the 40cc coated balloons and two of the 30cc coated balloons opened on the first cycle, and two more of the 30cc coated balloons opened on the third cycle. The remaining coated 30cc balloon opened in 22 cycles. These results were better than experienced with the corresponding control catheters. The catheters used for the foregoing inflation testing also were subjected to performance testing. After the inflation test, each was run through the autopurge cycle with the Model 700 controller and then cycled under several different operating parameters using the "neutral" timing setting, i.e. no lead or lag time bias relative to the cardiac cycle. These catheters were tested at 80 beats per minute (bpm) with 75mmHg back-pressure, with data taken at initiation and after one hour of operation. The same catheters were tested at 125 bpm with 75mmHg back-pressure and 80 bpm with lOOmmHg back-pressure. The following table reports the average time in milliseconds to inflate to 90% of the full volume, the average time to deflate from the peak volume to 90% deflated state, and the sum of the latter two as the average total cycle time for these balloons, with notes as to the range of the latter.

Total 90% Cycle time, ms

Inflate Deflate

Balloon Rate 90% ms 90% ms Average Range

30cc Control 80 bpm, 75 mm, 127 152.5 279.5 four: 240-282.5 t = 0 one: 335

30cc Coated 80 bpm, 75 mm, 1 12 136.5 248.5 four: 230-250 t = 0 one: 272.5

30cc Control 80 bpm, 75 mm, 132 142.5 274.5 four: 247.5-282.5 t = 1 hr one: 315

30cc Coated 80 bpm, 75 mm, 1 14 132 246 four: 237.5-247.5 t = 1 hr one: 265

30cc Control 125 bpm, 75 mm 123.13 128.13 251 .25 four: 240-262.5 one: n/a

30cc Coated 125 bpm, 75 mm 1 15 127 242 four: 235-240 one: 255

30cc Control 80 bpm, 100 mm 133.5 127 260.5 four: 255-272.5 one: 245

30cc Coated 80 bpm, 100 mm 125 123 248 four: 240-250 one: 260

40cc Control 80 bpm, 75 mm, 142 156.5 298.5 292.5-305.5 t = 0

40cc Coated 80 bpm, 75 mm, 134.5 154.5 289 277.5-300 t = 0

40cc Control 80 bpm, 75mm, 144 158 302 292-307.5 t = 1 hr

40cc Control 80 bpm, 75 mm, 140 157.5 292 287.5-297.5 t = 1 hr

40cc Control 80 bpm, 100 mm 156.5 144 300.5 290-320

40cc Coated 80 bpm, 100 mm 146.5 141 .5 288 280-295

40cc Control 125 bpm, 75 mm 129.5 135 264.5 four: 260-275 one: 252.5 * Recalculated 150.5 186.5 337 322.5-342.5

40cc Coated 125 bpm, 75 mm 129 135 264 four: 265-275 one: 250 * Recalculated 150.5 173 323.5 295-342.5

* Because the 40cc balloons did not reach full displacement at 125 bpm, the inflate and deflate times were recalculated for 90% of full displacement. This is believed to reflect more realistic cycle times. Tensile tests also were conducted on fifteen samples each of the control and coated balloon materials of the first-noted group, using ASTM 882 as the guide. The samples, which were sterilized in an ethylene oxide sterilizer, were 10mm wide and 4 inches minimum length; the gage length was 2 inches; and the crosshead speed was 20 inches per minute. The thickness of the samples was measured in two places in the test zone and the average of these values used for tensile strength calculations. The control samples had an average elongation at break of 17.5", with a standard deviation of 0.9", and a computed average tensile strength of 7420 psi, with a standard deviation of 545 psi. The coated samples had an average elongation at break of 16.4", with a standard deviation of 1.0", and a computed tensile strength of 6705 psi, with a standard deviation of 620 psi. Again, because the stresses at which intra-aortic balloons operate are well below these figures, it is believed to be clear that the coated balloons are functionally equivalent to the uncoated balloons in elongation and tensile strength.

Another set of tensile tests were conducted on ten sets each of control and coated balloon material which had been "aged" for 45 days at 65°C. These tests also followed the ASTM 882 guide, utilizing an Instron® tester. These tests showed an average yield strength of 979 psi for the coated balloon material and 955 psi for the uncoated balloon material, and ultimate tensile strength at failure of 5267 psi for the coated material and 6311 psi for the uncoated material. These results are deemed to confirm the previously noted tensile and aneurism results and observations.

Coated balloons which had been sterilized in a normal manner also passed bacterial endotoxin and MEM Cytotoxicity assay tests. A pin-on-disk tribo eter was used for further tests under an aqueous 25°C environment using an alumina pin and an aluminum disk with a five gram load at speeds of 5.08- 5.13 cm/sec for 35 minutes. These tests showed coefficients of friction (μ) substantially all well below 0.10 for coated balloons and from about 0.15 to over 0.40 for control balloons. Subjective observations and tactile examinations also have confirmed that the coated intra- aortic catheter balloons have a high degree of slipperiness when wetted, substantially exceeding that of wet balloons of uncoated polyurethane or similar materials.

It will be appreciated that improved intra-aortic balloon pump devices have been provided which meet the objects of this invention.

The invention has been described in considerable detail with reference to certain embodiments, and particularly with respect to the preferred embodiments thereof. However, it will be understood that variations, modifications and improvements may be made, particularly by those skilled in this art and in light of the teachings referred to herein, within the spirit and scope of the invention as claimed.

Claims

WHAT IS CLAIMED IS:

1. An intra-aortic balloon pump device including a vascular catheter and a pump balloon mounted on said catheter for insertion by said catheter into and through the vascular system of a patient and into the patient's aorta for repetitious pulse-rate inflation of said balloon over an extended time-span to assist the blood-pumping function of that patient's heart; said balloon being formed of flexible material, being of a cross sectional size and configuration as viewed generally normal to the longitudinal axis of said catheter to provide an unstretched inflated first diameter substantially greater than the passages through which it is to pass in the course of insertion into the patient's vascular system, and being furled to a substantially smaller second diameter for such insertion; and at least the externally exposed surface of said balloon comprising a hydrophilic material which is non-tacky when dry and becomes highly lubricous when contacted by an aqueous solution, including blood, whereby said balloon may be furled to said second diameter while dry and will become lubricous upon contact with an aqueous solution in the course of insertion into the patient's vascular system for ready passage therethrough and into the patient's aorta adjacent the heart in such furled condition, and thereafter for said repetitious inflation in the aorta.

2. The invention as in claim 1 wherein said hydrophilic material includes a poly (N-vinyl lactam) .

3. The invention as in claim 1 wherein said hydrophilic material includes water soluble polyvinylpyrro¬ lidone.

4. The invention as in claim 1 wherein said balloon is formed of a polyurethane and said hydrophilic material is a stable hydrophilic blend which consists essentially of a thermoplastic polyurethane and a water soluble polyvinyl¬ pyrrolidone.

5. The invention as in claim 1 wherein said balloon is furled.

6. The invention as in claim 1 wherein said balloon is furled, comprising flattened portions of said balloon wound about the longitudinal axis of said balloon.

7. The invention as in claim 1 wherein said device includes an element extending longitudinally through said balloon generally along the axis thereof, and said balloon is furled with flattened portions of said balloon wound about said element.

8. A method of making an intra-aortic balloon pump device which includes a vascular catheter with a pump balloon mounted thereon for insertion by said catheter into and through the vascular system of a patient and into the patient's aorta for repetitious pulse-rate inflation of said balloon over an extended time-span to assist the blood-pumping function of that patient's heart, comprising: providing an elongated intra-aortic pump balloon formed of flexible material and of a cross sectional size and configuration as viewed generally normal to the longitudinal axis thereof to provide an unstretched inflated first diameter substantially greater than the passages through which is to pass in the course of insertion into the patient's vascular system; covering the externally exposed surface of said intra- aortic balloon with a hydrophilic material in a liquid solution wherein said hydrophilic material is a material which is non-tacky when dry and becomes highly lubricous when contacted by an aqueous solution, including blood; evaporating the liquid from said solution on said balloon to form a dry coating of said hydrophilic material thereon; curing said balloon with said coating thereon for a plurality of days to enhance the strength and flexibility of the coated balloon; assembling said balloon in an intra-aortic balloon pump catheter having a longitudinal axis, with said longitudinal axes aligned with one another; furling said balloon about the longitudinal axis of said catheter while dry to a second diameter which is much smaller than said first diameter and suitable for insertion into and through a patient's vascular system; whereby said balloon becomes lubricous when contacted with an aqueous solution in conjunction with such insertion for ease of passage through the patient's vascular system and into the patient's aorta adjacent the heart in such furled condition while retaining substantially its original strength for said repetitious inflation in said aorta.

9. The invention as in claim 8 wherein said hydrophilic material includes a poly (N-vinyl lactam) .

10. The invention as in claim 8 wherein said covering step includes covering said balloon with a hydrophilic material which includes a water soluble polyvinylpyrroli¬ done in an organic solvent.

11. The invention as in claim 8 wherein said balloon is formed of a polyurethane and said hydrophilic material is a stable hydrophilic blend which consists essentially of a thermoplastic polyurethane and a water soluble polyvinyl¬ pyrrolidone.

12. The invention as in claim 8 wherein said balloon is formed of a polyurethane and said covering step includes covering said balloon with a stable hydrophilic blend which consists essentially of a thermoplastic polyurethane and a water soluble polyvinylpyrrolidone in an organic solvent which will solvate said polyurethanes.

13. The invention as in claim 8 wherein said curing step includes curing the coated balloon for at least seven days prior to furling same.