WO1998036792A1

WO1998036792A1 - Ball valve system for heart-assist device and method of manufacture

Info

Publication number: WO1998036792A1
Application number: PCT/AU1998/000103
Authority: WO
Inventors: Geoff Tansley; John Woodard; John Begg
Original assignee: Micromedical Industries Limited
Priority date: 1997-02-19
Filing date: 1998-02-19
Publication date: 1998-08-27
Also published as: AUPO522497A0

Abstract

A ball valve for a ventricular assist device wherein the ball valve includes a casing (22). The casing can include ribs (28-30) to provide a guide surface as the ball occluder moves between a valve closed position and a valve open position. In a particular form, in its open position the centre line of the ball occluder is offset from the valve casing centre line.

Description

BALL VALVE SYSTEM FOR HEART-ASSIST DEVICE

AND METHOD OF MANUFACTURE

The present invention relates to a ball valve system for a heart-assist device and a method of manufacture therefore and, more particularly, to such a system particularly suited for certain types of ventricular assist device .

Discussion of Prior Art

The ventricular assist device (VAD) is a particular type of heart-assist device which is utilised to provide a mechanically pumped bypass for at least a portion of the blood intended to flow through a ventricle (usually the left ventricle) .

The ventricular assist device is designed to provide a pulsatile flow in conformity with blood flow provided by a healthy human heart .

A common problem with all forms of ventricular assist device is the necessity to minimise deleterious effects upon the blood passed through the device. In this connection it is important to minimise the occurrence of thrombogenesis and of blood trauma.

One particular form of ventricular assist device (a Chang-type device) is illustrated in Fig. 2 and comprises a diaphragm type pump for urging the blood in a pulsatile manner in combination with one way valves at the entry and exit. It is no less important in this type of ventricular assist device than any other that the abovementioned problems of thrombogenesis and blood trauma are minimised. It is an object of the present invention to provide a ventricular assist device, a valve system therefore and a method of manufacture thereof which seek to address or minimise the abovementioned problems. Brief Description of Invention

Accordingly, in one broad form of the invention, there is provided a ball valve for a heart assist device, said ball valve comprising a casing including guide means adapted to allow a ball occluder located therein to move between a valve closed position and a valve open position. Preferably said guide means comprises a plurality of ribs extending inwardly so as to provide ball occluder supporting surfaces whereby said ball occluder is supported as it moves between said valve closed position on an inlet side of a centre line XX of said valve casing and a valve open position on an outlet side of said centre line XX of said valve casing.

Preferably three said ribs extend equicircumferentially from an inside surface of said valve casing.

Preferably a clearance of approximately 0.2mm is maintained between said ball occluder and said ribs. Preferably an interior surface of said casing includes a spline profile portion adapted to smooth out the blood flow variations in an axial direction.

In a further broad form of the invention there is provided in combination a ventricular assist device operating in combination with the ball valve of any previous claim. Preferably said ventricular assist device is a Chang-type ventricular assist device.

In an alternative preferred form said ventricular assist device is a bladder-type ventricular assist device. In yet a further broad form of the invention there is provided a method of manufacture of a ball valve housing for a heart assist device, said ball valve housing manufactured by a blow molding method and including a first step of providing a preform, heating said preform to a predetermined temperature in an even manner, applying pressure to the internal walls of said preform whereby said preform expands to conform against the walls of a die enclosing said preform.

Preferably said preform is heated evenly. In one preferred form even heating is achieved by rotation of said preformed during heating.

In an alternative preferred form even heating is achieved by use of a ring heater surrounding said preform. In yet a further broad form of the invention there is provided a pulsatile heart bypass pump comprising the combination of VAD and ball valve described above. Brief Description of Drawings

Embodiments of the invention will now be described with reference to the accompanying drawings wherein: Fig. 1 is a side section view of a prior art ball valve, Fig. 2 illustrates a VAD and valve combination in accordance with a first embodiment of the invention, Fig. 3 illustrates views of the design of a ball valve suitable for use with the VAD and ball valve combination of Fig. 2,

Fig. 4 illustrates apparatus suitable for the manufacture of a ball valve sleeve in accordance with an embodiment of the invention,

Fig. 5 illustrates perspective views of a ball valve sleeve made according to the method of Fig. 4 whilst retaining the functional dimensions of the ball valve of Fig. 3, and Fig. 6 illustrates side views of an alternative VAD which can be combined with the ball valve according to a further embodiment of the invention. Detailed Description of Preferred Embodiments

Fig. 1 illustrates a prior art ball valve 10 arrangement suitable for use in a flow line 11A,11B. This ball valve is described in biomaterials 16, 245-249 "Development of a Ceramic Conduit Valve Prosthesis for Corrective Cardiovascular Surgery" by C R Gentle and G D Tansley. The application of such a valve to a VAD, for example of the type generally illustrated in Fig. 2, is not a trivial matter.

The VAD can introduce swirling effects into the blood flow which, in turn, can cause instability in the ball occluder 12 rendering valve operation highly inefficient and, in the process, causing blood trauma.

In addition the combination of ball valve 10 and VAD must not introduce coagulation sites.

Desirable features of a ball valve and VAD combination include : Positive opening and closing operation of the valve;

Minimisation of regurgitant volume;

Minimise pressure drop;

Minimise shear;

Present stabilised flow at the valve output;

Minimise sites where thrombogenesis can occur.

With reference to Fig. 2 there is shown a VAD and ball valve combination 13 according to a first embodiment of the invention comprising a diaphragm pump 14 having a pump chamber 15 profiled in the style of the Chang device having a diaphragm 16 urged by an air chamber 17 supplied via air source 18. Under the influence of a vacuum applied to diaphragm 16 blood is drawn through inlet valve 19 into pump chamber 15. Under pressure applied to diaphragm 16 by air in air chamber 17 introduced via air source 18 blood is expelled through outlet valve 20 thereby bypassing to a predetermined extent the pumping operation of heart 21.

The VAD and ball valve combination 13 relies entirely on efficient one way valve operation of inlet valve 19 and outlet valve 20.

The design parameters to be applied to the valve casing 22 of the ball valves comprising inlet valve 19 and outlet valve 20 are illustrated diagrammatically in Fig. 3. A casing centre line XX is defined as shown in Fig. 3. This "centre line" XX lies in a plane where, with the ball occluder 35 aligned so its centre line coincides with the centre line XX the cross sectional area available for blood flow around the occluder 35 in this position is equal to the cross sectional area available for blood flow at the inlet side 38 of the valve casing 22. The centre line XX also coincides with an internal profile of the valve casing 22 which forms a cylindrical portion defined by second straight cross section 48. From this centre line position a series of spline points are defined as nominated in Fig. 3 from which a spline profile portion 23 of the internal circumferential wall 24 is defined. The balance of the wall is defined in a first straight cross section 25, second straight cross-section 48, a first radius cross section 26 and a second radius cross section 27.

Formed integrally with the internal circumferential wall 24 but protruding inwardly from it are first, second and third support ribs 28, 29 and 30 aligned in axial direction YY and placed equidistantly circumferentially within valve casing 22.

The cross sections of the three ribs are identical with the cross section of rib 30 clearly defined in Fig. 3 and comprising a linear runner portion 31 followed by a rising ramp portion 32 and culminating in a raised seat portion 33 on the outlet side 34 of valve casing 22.

The purpose of the ribs 28, 29, 30 is to provide a guide surface comprising the top surfaces of the three inwardly facing ribs for the ball occluder 35 as it traverses in axial direction YY from its closed position 36 on inlet side 38 of valve casing 22 through to its open position 37 near outlet side 34 of valve casing 22 at which position further axial movement in the direction of outlet side 34 is prevented by the raised seat portions 33 of the ribs 28, 29, 30 acting on the surface of ball occluder 35 against the urging of blood flow (not shown) from inlet side 38 to outlet side 34.

In its open position 37 the centre line SS of ball occluder 35 is offset from valve casing centre line XX in the direction of outlet side 34 by an offset distance OD. In a preferred embodiment the offset distance OD is approximately 2.5mm for a valve casing of the dimensions illustrated in Fig 3. With this offset in combination with the ribs extending from the inlet side 38 of valve casing centre line XX through to outlet side 34 and providing a guiding function throughout their length to the ball occluder 35 it has been found that stable opening and shutting of the ball valve 39 according to a first preferred embodiment is achieved notwithstanding swirling effects caused at inlet 38 by the action of the Chang-type VAD 40 particularly, but not exclusively when the ball valve 39 is utilised as outlet valve 20 (refer Fig. 2) .

With reference to Fig. 4 a method of manufacture of valve casing 22 is disclosed with reference to the apparatus shown. The underlying method is a blow molding operation wherein a preform 41 is first heated to a working temperature and then expanded under the action of compressed air acting on the inside walls of the preform so that it expands to conform to the shape of a die which encloses the preform 41.

In this example of the method heating is provided by a ring heater 42 applied to the outside of the preform 41 while it is slowly rotated between mandrels 43 mounted on a lathe 4 . Compressed air to blow the preform is provided through a slippering arrangement 45 which communicates via mandrel 43 with the interior of preform 41.

The die 46 is made in two halves 46A and 46B mounted in opposing relationship for closure about preform 41 prior to blowing of the preform by injection of compressed air from compressed air source 47.

The resulting ball valve 39 has smooth internal surfaces which conform to the dimensions and profiles provided with reference to Fig. 3 in a functional sense. However the blow molding process provides improved rounding and smoothness over what is illustrated in Fig. 3 whilst retaining the functionality inherent in the design features described with reference to Fig. 3.

The end result of the blow molding operation is a unitary valve casing 22 for the ball valve 39 having no internal abrupt edges as illustrated in Fig. 5. In this instance the preform is a tube of dimension 19mm internal diameter with a 1.5mm wall thickness and a length of approximately 60mm. Preferred materials are polyurethane or ABS or clear polycarbonate or clear acrylic. Dimensions may have to be adjusted depending on the material used and, of course, the dimensions of the valve casing 22.

In use the ball valve 39 is utilised as both an inlet valve 19 and an outlet valve 20 on a Chang-type VAD 40 as generally illustrated in Fig. 2 operating to pump blood in a pulsatile manner as described earlier in the specification.

Fig. 6 illustrates an alternative form of VAD 49 which provides pulsatile flow by alternate compression and decompression of a bladder 50 operating in conjunction with one way valves 51,52. The ball valve of the present invention, appropriately modified with respect to the dimension OD can be applied with advantage to this type of VAD.

In particular applications the combination of pulsatile VAD and ball valve as previously described can be applied with advantage as part of a pulsatile bypass pump system suitable for substitution of the heart's blood pumping function for example during heart surgery. This system has the advantage of providing a pulsatile flow of blood for the human body which more closely matches the behavior of blood pumped under the influence of the human heart . The above describes only some embodiments of the present invention and modifications obvious to those skilled in the art can be made thereto without departing from the scope and spirit of the present invention. Industrial Applicability Embodiments of the present invention particularly adapted to utilisation in ventricular assist devices for the mechanical assistance of a heart.

Claims

1. A ball valve for a heart assist device, said ball valve comprising a casing including guide means adapted to allow a ball occluder located therein to move between a valve closed position and a valve open position.

2. The ball valve of claim 1 wherein said guide means comprises a plurality of ribs extending inwardly so as to provide ball occluder supporting surfaces whereby said ball occluder is supported as it moves between said valve closed position on an inlet side of a centre line XX of said valve casing and a valve open position on an outlet side of said centre line XX of said valve casing.

3. The ball valve of claim 2 wherein three said ribs extend equicircumferentially from an inside surface of said valve casing.

4. The ball valve of any one of claims 1, 2 or 3 wherein a clearance of approximately 0.2mm is maintained between said ball occluder and said ribs.

5. The ball valve of any previous claim wherein an interior surface of said casing includes a spline profile portion adapted to smooth out the blood flow variations in an axial direction.

6. The ball valve of any previous claim wherein the centre line SS of said ball occluder is offset from said valve casing centre line XX in the direction of said outlet by an offset distance OD.

7. The ball valve of claim 6 wherein said offset distance OD is in the range 2 to 3mm.

8. In combination a ventricular assist device operating in combination with the ball valve of any previous claim.

9. The combination of claim 8 wherein said ventricular assist device is a Chang-type ventricular assist device.

10. The combination of claim 8 wherein said ventricular assist device is a bladder-type ventricular assist device.

11. A method of manufacture of a ball valve housing for a heart assist device, said ball valve housing manufactured by a blow molding method and including a first step of providing a preform, heating said preform to a predetermined temperature in an even manner, applying pressure to the internal walls of said preform whereby said preform expands to conform against the walls of a die enclosing said preform.

12. The method of claim 10 wherein said preform is heated evenly .

13. A pulsatile heart bypass pump comprising the combination of any one of claims 8-10.