Universal pneumatic ventricular assist device

Abstract

A pneumatic ventricular assist device is designed for use in any circulatory support application including RVAD, LAVD, or BIVAD, trans-operative, short-term or long-term, tethered implantable or extracorporeal. It consists of a soft contoured pumping shell and a disposable pumping unit, which includes a pump sac, two one-way valves, and tubing connectors. The pumping unit is specially designed to allow continuous and fluid movement of blood and to limit blood-contacting surfaces, and is made of a supple and elastic material such as silicone. The components can be inexpensively and reliably manufactured by injection molding. Also, the pumping shell and pumping unit include complementary features that quickly and securely hold the pumping unit, and any attached cannulae, in place.

Description

FIELD OF THE INVENTION

[0002] The present invention relates to blood pumping devices, and, more particularly, to ventricular assist devices.

BACKGROUND

[0003] A ventricular assist device (“VAD”) is used to help supplement the heart's pumping action both during and after certain kinds of surgery, in situations where a complete cardiopulmonary bypass (using a heart-lung machine) is neither needed nor advisable in light of the serious side effects associated therewith. Ventricular assist devices typically comprise a pair of cannulae or other tubing and some sort of pump operably connected to the cannulae. In use, the cannulae are attached to either the left side of the heart (a left ventricular assist device) or to the right side of the heart (a right ventricular assist device) “in parallel,” i.e., the pump supplements the heart's pumping action but does not completely bypass it, and the pump is activated. Alternatively, a pump may be directly implanted into the body.

[0004] Originally, ventricular assist devices were air powered, wherein fluctuating air pressure, provided by a simple mechanical air pump machine, was applied to a bladder-like sac. The bladder had input and output valves, so that blood would enter the bladder through the input valve when the pressure on the bladder was low, and exit the bladder through the output valve when the pressure on the bladder was high. Unfortunately, these pneumatic ventricular assist devices were complicated, and used expensive mechanical valves that were prone to failure, subject to “clogging,” and that caused blood trauma or damage because of hard, metal edges and the like.

[0005] To overcome these problems, other types of ventricular assist devices were developed, including axial flow pumps for temporary insertion directly into the heart, and centrifugal pumps. The former are based on the Archymides' Principle, where a rod with helical blades is rotated inside a tube to displace liquid. In use, a catheter-mounted, miniature axial flow pump is appropriately positioned inside the heart, and is caused to operate via some sort of external magnetic drive or other appropriate mechanism. With high enough RPM's, a significant amount of blood can be pumped. In the case of centrifugal pumps, blood is moved by the action of a rapidly rotating impeller (spinning cone or the like), which causes the blood to accelerate out an exit. Both of these categories of ventricular assist devices are generally reliable and implantable, but are very expensive, not particularly durable, and are not useful in situations where a patient needs a true pulsating blood supply. Specifically, axial and centrifugal pumps are typically left on in a continuous operation mode, where a steady stream of blood is supplied on a continuous basis, as opposed to the natural rhythm of the heart, which acts on a periodic, pulse-producing basis. In addition, such pumps are still largely in the developmental or trial phase.

[0006] Accordingly, a primary object of the present invention is to provide a pneumatic ventricular assist device that offers the advantages of pneumatic operation without the drawbacks associated with prior pneumatic devices.

SUMMARY

[0007] A pneumatic ventricular assist device (“VAD”) is for use in any circulatory support application including RVAD, LAVD, or BIVAD, trans-operative, short-term or long-term, tethered implantable or extracorporeal. The VAD comprises a soft-contoured (rounded, low-profile) pumping shell and a disposable pumping unit that includes a blood sac, two one-way valves, and two tubing connectors. The pumping unit is specially designed to allow continuous and fluid movement of blood and to limit blood-contacting surfaces, and is made of a supple and elastic material such as silicone. The components can be inexpensively and reliably manufactured by injection molding. Also, the design of the VAD, according to the present invention, facilitates priming, de-bubbling, and connection to the body.

[0008] For assembly, the pumping shell is opened (it includes two halves in a clam shell-like arrangement), the pumping unit is positioned inside, and the shell is closed. The interior of the shell is complementary in shape to the pumping unit: a pumping chamber portion holds the blood sac, and two pump inlets are shaped to securely hold the valves and tubing connectors. A disposable seal rests between the two clamshell halves for sealing the connection there between.

[0009] In use, the VAD is connected to a patient's heart by way of two cannulae connected to the tubing connectors (the cannulae are connected to the heart at appropriate locations according to standard surgical practices). Then, a pneumatic drive unit is attached to an air inlet in the pumping shell by way of an air line or the like. Subsequently, the drive unit is activated to cause the blood sac to move in and out, in a gentle pumping action, by way of controlled periodic air pressure introduced into the pumping shell through the air inlet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] These and other features, aspects, and advantages of the present invention will become better understood with respect to the following description, appended claims, and accompanying drawings, in which:

[0011] FIG. 1 is a perspective exploded view of a universal pneumatic ventricular assist device according to the present invention;

[0012] FIG. 2 is a perspective exploded view of the ventricular assist device with an assembled disposable pump assembly;

[0013] FIG. 3 is a perspective, partially exploded view of the ventricular assist device in place against a lower half of a pumping shell portion of the ventricular assist device;

[0014] FIG. 4A is a elevation cross-sectional view of a valve portion of the ventricular assist device, taken along line 4A-4A in FIG. 1;

[0015] FIG. 4B is a perspective cross-sectional view of the valve portion of the ventricular assist device shown in FIG. 4A;

[0016] FIG. 5A is a plan view of a disposable pump blood sac portion of the ventricular assist device;

[0017] FIG. 5B is a cross-sectional view of the disposable blood sac taken along line 5B-5B in FIG. 5A;

[0018] FIGS. 6A-6C show various elevation views of how the ventricular assist device is placed and connected for use with a patient; and

[0019] FIG. 7 is a perspective view of two of the ventricular assist devices in use extracorporeally with a patient.

DETAILED DESCRIPTION

[0020] With reference to FIGS. 1-7, a ventricular assist device (VAD) 10 includes: a reusable pumping shell 12 having a first or upper “clamshell” half 14 and a second or lower clamshell half 16 removably attachable to the first half 14; a disposable seal 18 that fits between the two pumping shell halves 14, 16; and a disposable pumping unit 20 that includes: a disposable blood sac 22 that fits in the pumping shell 12; two disposable, one-way injection-molded valves 24, 26 attached to the blood sac 22; and two tubing connectors 28, 30 attached to the valves. Although the valves 24, 26 are identical, one valve 26 is positioned to act as an inlet valve, and the other valve 24 is positioned to act as an outlet valve (i.e., blood can only flow through the valves 24, 26 as indicated by the arrows in FIG. 3).

[0021] For assembly, the disposable pumping unit 20 is placed against the lower pumping shell half 16, the seal 18 is positioned in place, and the upper pumping shell half 14 is placed against and connected to the lower pumping shell half 16 (by way of screws or other fasteners). In use, the ventricular assist device 10 is appropriately connected to a patient's heart by way of a ventricular (or atrial) cannula 32 and an arterial cannula 34 respectively connected to the tubing connectors 28, 30. Then, a pneumatic drive unit 36 is operably attached to an air inlet 38 in the ventricular assist device 10 by a pneumatic line 40 or the like (see FIG. 7). Subsequently, the drive unit 36 is activated to cause a portion of the disposable blood sac 22 to move in and out, in a gentle pumping action, by way of controlled fluctuating air pressure introduced into the pumping shell 12 through the air inlet 38.

[0022] The pumping shell 12 is either molded or machined from a hard material that may or may not be implantable in the human body, and may or may not be reusable. The pumping shell 12 comprises the two halves 14, 16 (generally similar to one another), which mate together like a clamshell and together define a rounded pumping chamber 42 and two generally cylindrical pump inlets 44, 46 into the pumping chamber. As best seen in FIGS. 2 and 3, the pump inlets 44, 46 are provided with annular contours or shoulders 37 for holding the connectors 28, 30 (i.e., each pump shell half includes a semi-annular shoulder which, when the two halves are connected, together define an annular shoulder). In addition, the lower shell half 16 includes the air inlet 38, which is a small hole or channel extending from the outer surface of the shell through the shell wall to the pumping chamber 42. The outer surfaces of the shell halves 14, 16 are rounded, while the peripheral inner surfaces are flat so that the shell halves fit snugly against one another. The shape of the pumping shell is generally flat and softly contoured (i.e., rounded, ellipsoidal) so that it may be comfortably implanted.

[0023] As mentioned, the pumping shell pump inlets 44, 46 are generally cylindrical and dimensioned to hold and support the entireties of the cylindrical valves 24, 26 therein. As should be appreciated, having the valves enclosed within the confines of the complementary-shaped pump inlets maximizes support of the valves, thereby enhancing their performance and durability. It also reduces the likelihood of the valves becoming dislodged or loose during use.

[0024] The blood sac 22, valves 24, 26, and cannulae 32, 34 are specially designed to allow continuous and fluid motion of blood and to limit blood contacting surfaces. These components are made of a supple elastomer such as silicone that will stretch and deform to pressure gradients reducing the damage to blood cells. With reference to FIGS. 4A and 4B, the valves 24, 26 are hinge-less and have valve leaflet portions 50 that are flexible and elastic, simulating the action of natural heart valves, and improving their reliability and durability. The valves are injection molded in four piece molds reducing the manufacturing cost compared to biological or mechanical valves. In use, blood can flow through the valves in one direction only, from the valve inlet 52 to the valve outlet 54, i.e., in the direction of the arrows in the figures. Specifically, when the pressure is greater on the valve inlet side 52, the valve leaflets 50 respectively flex upwards and downwards, allowing blood to pass. However, when the pressure is greater on the valve outlet side 54, the leaflets are gently but forcibly compressed together, preventing blood from flowing back through the valve. Because the valves are each one-piece, are made from silicone (or another suitable material), and have rounded or contoured inner surfaces, they are very reliable, perform well, and minimize damage to blood. For example, as shown in FIG. 4B, note that the valve wall 53 leading up to the leaftlets 50 is rounded/sloped to minimize blood disturbance.

[0025] As indicated in FIG. 4A, the sac 22 and connectors 28 are configured to fit within the entrance and exit ends of the valves 24, 26 and against interior, circumferential shoulders 55 provided in the valves. This produces a continuous surface between the various elements and eliminates any sharp lips or ridges in the blood flow path, reducing blood damage.

[0026] FIGS. 5A and 5B (in addition to FIGS. 1-3) show the pumping sac 22. The pumping sac is bilaterally symmetric and includes circular/tubular inlets 70, 72 connected to a main pumping chamber 73. The pumping chamber 73 sports a gently rounded or circular profile, which has been found to maximize pumping effectiveness and to reduce blood trauma during the pumping action. More specifically, the pumping chamber 73 is generally shaped like a semi-flattened ellipsoid, i.e., flat, circular top and bottom walls 74a, 74b interconnected by a rounded sidewall 75.

[0027] The blood sac, valves, and/or cannulae may be coated with lubricant, hydrophobic, antibacterial and/or antithrombotic coatings, including but not limited to PTFE coatings, heparin bonded coatings, fluorinated coatings, treclosan and silver compound coatings, and anti-calcification agent releasing coatings such as previously described to improve blood compatibility and non thrombogenicity.

[0028] The connectors 28, 30 are made of a hard material (e.g., plastic, stainless steel, titanium), molded or machined, that will secure the connection between the valves 24, 26 and the cannulae 32, 34. The tubing connectors 28, 30 each include a cylindrical through-bore, a cylindrical fore-portion that fits into the valves 24, 26, an annular flange 76 which corresponds in shape to the pump inlet shoulders 37, and a rear-portion dimensioned to accommodate a cannula. In use, when the pumping unit 20 is placed in the pumping shell 12, the valves' annular flanges 76 lie against the pump inlet shoulders, securely holding the tubing connectors 28, 30 in place and preventing their removal from the pumping shell.

[0029] The seal 18 is made of a soft elastomer like the pumping sac and valves, but will not be in contact with blood and is only used to insure an airtight fit of the pumping shell halves 14, 16. The disposable pumping unit 20 (blood sac, valves and connectors and seal) may be preassembled and coated as a single disposable part.

[0030] To ensure that the cannulae 32, 34 remain securely connected to the connectors 28, 30, the inlet portions 44, 46 of each pumping shell half are provided with protruding, semi-annular gripping ridges 60 (see FIG. 2). In use, when the pumping unit 20 is placed in the lower pumping shell half 16, as shown in FIG. 3, the cannulae 32, 34 contact the gripping ridges of the lower half 16. Then, when the upper half 14 is placed against and connected to the lower half 16, the gripping ridges 60 of both halves bite into and engage the cannulae, securing them in place.

[0031] The whole system has been designed to be used in a wide range of applications of circulatory support, by simply selecting the appropriate cannulae and accessories. Intended applications include short term trans-operative support (a few hours), acute and post-cardiotomy support (up to a couple of weeks), bridge to transplant (˜3-6 months), bridge to recovery (˜several years) and destination therapy (until death). The device is also designed to be used as either a right VAD (FIG. 6B), a left VAD (FIG. 6A), or for bi-ventricular use (FIG. 6C), and to be used as a tethered implant(s), paracorporealy, or extracorporealy (FIG. 7).

[0032] To install the system, first the cannulae are sewn to the atrium, ventricle or outflowing artery of the compromised side of the heart, as applicable. The cannulae are then connected to the disposable pumping unit 20, while carefully removing any air bubbles in the system. The blood sac assembly is supple and flexible, facilitating its priming and de-bubbling. The connectors 28, 30 are also made to be easily connected and disconnected, facilitating this procedure. Once the system has been properly purged and connected, the pumping shell 12 is locked closed over the pumping unit. The blood sac assembly is symmetrical so that it can be placed either with the inflow valve on the left or on the right, making its design more adaptable to different applications. The connectors fit inside the pumping shell so that when the latter is closed it will crimp down on the cannulae connections preventing an accidental disconnection, as mentioned above. The device can then be placed in the abdomen or outside the body and the drive unit can be activated to start pumping.

[0033] Although the ventricular assist device of the present invention has been illustrated as having a pumping shell with two separate halves 14, 16, the halves could be hinged together or otherwise permanently connected without departing from the spirit and scope of the invention. Also, although the pumping unit has been described as comprising separate components connected together, the pumping unit could be provided as a single unit, i.e., a unitary piece of molded silicone. This also applies to the valves 24, 26 and connectors 28, 30, i.e., the connectors could be provided as part of the valves.

[0034] Although the valves 24, 26 have been characterized as being identical and each having two leaflets, it should be appreciated that the valves 24, 26 could have a different number of leaflets, e.g., 1 leaflet, or 3 leaflets, and the two valves 24, 26 could be different from one another. More specifically, where operating pressures on the two valves may be different (because one is acting as an inlet valve and the other acting as an outlet valve), it may be advantageous to utilize valves with different characteristics.

[0035] Since certain changes may be made in the above-described universal pneumatic ventricular assist device, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.

Claims

1. A pneumatic ventricular assist device comprising: a. a pumping shell comprising an upper pumping shell half and a lower pumping shell half, wherein: the upper and lower pumping shell halves are configured to fit against one another to together define a rounded, interior pumping chamber and two generally-cylindrical pump inlets extending from the pumping chamber to the pumping shell exterior; and the pumping shell includes an air inlet extending from the pumping shell exterior through to the pumping chamber; and b. a pumping unit comprising: i. a flexible blood sac configured to reside in the pumping chamber and having an interior and first and second tubular inlets; ii. first and second one-way valves dimensioned to fit in the pumping shell pump inlets and respectively connected to the first and second tubular inlets of the blood sac, said valves including tubular inlets and outlets each with an outwards-facing annular shoulder, wherein end portions of the blood sac tubular inlets fit inside the valve inlets and outlets and against the annular shoulders thereof to form a substantially-continuous internal surface between the blood sac interior and valve inlets and outlets for minimizing blood trauma; and iii. first and second tubing connectors dimensioned to at least partially fit in the pumping shell pump inlets and respectively connected to the first and second valves, said tubing connectors each having an annular flange, wherein the tubing connectors include cylindrical fore portions that fit inside the valve inlets and outlets and against the annular shoulders thereof to form respective substantially-continuous internal surfaces between the tubing connector interiors and valve inlets and outlets for minimizing blood trauma; c. wherein the pumping shell pump inlets each include: (i) an annular, inwards-facing shoulder against which the annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place; and (ii) an annular gripping ridge for securing cannulae connected to the tubing connectors in place when the pumping shell halves are connected together.

2. The pneumatic ventricular assist device of claim 1 wherein the pumping shell has a rounded, generally-flattened, ellipsoid-shaped outer surface for facilitating implantation.

3. The pneumatic ventricular assist device of claim 1 wherein the first and second one-way valves are flexible, one-piece, hinge-less valves each having two flexible valve leaflet portions separating the valve inlet and outlet, wherein the leaflet portions: (i) compress together, preventing blood from flowing back through the valve, when blood pressure is greater on the valve outlet side than on the valve inlet side; and (ii) flex outwards, allowing blood to pass through the valve, when blood pressure is greater on the valve inlet side than on the valve outlet side.

4. A pneumatic ventricular assist device comprising: a. a pumping shell having two pumping shell halves that together define an interior pumping chamber and two pump inlets when connected; and b. a pumping unit comprising: a flexible blood sac configured to reside in the pumping chamber and having first and second sac inlets; first and second one-way valves dimensioned to fit in the pumping shell pump inlets and respectively connected to the first and second sac inlets; and first and second tubing connectors dimensioned to at least partially fit in the pumping shell pump inlets and respectively connected to the first and second valves; c. wherein the pumping shell pump inlets each include an annular gripping ridge for securing cannulae connected to the tubing connectors in place when the pumping shell halves are connected together.

5. The pneumatic ventricular assist device of claim 4 wherein the pumping shell pump inlets each include an annular, inwards-facing shoulder against which annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place.

6. The pneumatic ventricular assist device of claim 4 wherein the pumping shell has a rounded, generally-flattened, ellipsoid-shaped outer surface for facilitating implantation.

7. The pneumatic ventricular assist device of claim 4 wherein the first and second one-way valves are one-piece, hinge-less valves each having a valve inlet side, a valve outlet side, and two flexible valve leaflet portions separating the valve inlet and outlet sides, wherein the leaflet portions: (i) compress together, preventing blood from flowing back through the valve, when blood pressure is greater on the valve outlet side than on the valve inlet side; and (ii) flex outwards, allowing blood to pass through the valve, when blood pressure is greater on the valve inlet side than on the valve outlet side.

8. A pneumatic ventricular assist device comprising: a. a pumping shell having an interior pumping chamber and two pump inlets; and b. a pumping unit comprising: a flexible blood sac configured to reside in the pumping chamber and having first and second sac inlets; first and second one-way valves dimensioned to fit in the pumping shell pump inlets and respectively connected to the first and second sac inlets; and first and second tubing connectors dimensioned to at least partially fit in the pumping shell pump inlets and respectively connected to the first and second valves; c. wherein the pumping shell pump inlets each include an annular, inwards-facing shoulder against which annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place.

9. The pneumatic ventricular assist device of claim 8 wherein: the pumping shell comprises two pumping shell halves that together define the interior pumping chamber and two pump inlets when connected; and the pumping shell pump inlets each include an annular gripping ridge for securing cannulae connected to the tubing connectors in place when the pumping shell halves are connected together.

10. The pneumatic ventricular assist device of claim 8 wherein the pumping shell has a rounded, generally-flattened, ellipsoid-shaped outer surface for facilitating implantation.

11. The pneumatic ventricular assist device of claim 8 wherein the first and second one-way valves are one-piece, hinge-less valves each having a valve inlet side, a valve outlet side, and two flexible valve leaflet portions separating the valve inlet and outlet sides, wherein the leaflet portions: (i) compress together, preventing blood from flowing back through the valve, when blood pressure is greater on the valve outlet side than on the valve inlet side; and (ii) flex outwards, allowing blood to pass through the valve, when blood pressure is greater on the valve inlet side than on the valve outlet side.

12. A pneumatic ventricular assist device comprising: a. a pumping shell having an interior pumping chamber and two pump inlets; and b. a pumping unit comprising: i. a flexible blood sac configured to reside in the pumping chamber and having an interior and first and second inlets into the sac interior; ii. first and second generally-cylindrical, one-way valves dimensioned to fit in the pumping shell pump inlets and respectively connected to the first and second sac inlets, said first and second valves each having a tubular inlet with an outwards-facing annular shoulder and a tubular outlet with an outwards-facing annular shoulder, wherein end portions of the blood sac inlets fit inside the valve inlets and outlets and against the annular shoulders thereof to form a substantially-continuous internal surface between the blood sac interior and valve inlets and outlets for minimizing blood trauma; and iii. first and second tubing connectors dimensioned to at least partially fit in the pumping shell pump inlets and respectively connected to the first and second valves, wherein the tubing connectors include cylindrical fore portions that fit inside the valve inlets and outlets and against the annular shoulders thereof to form respective substantially-continuous internal surfaces between the tubing connector interiors and valve inlets and outlets for minimizing blood trauma.

13. The pneumatic ventricular assist device of claim 12 wherein the pumping shell pump inlets each include an annular, inwards-facing shoulder against which annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place.

14. The pneumatic ventricular assist device of claim 12 wherein: the pumping shell comprises two pumping shell halves that together define the interior pumping chamber and two pump inlets when connected; and the pumping shell pump inlets each include an annular gripping ridge for securing cannulae connected to the tubing connectors in place when the pumping shell halves are connected together.

15. The pneumatic ventricular assist device of claim 12 wherein the pumping shell has a rounded, generally-flattened, ellipsoid-shaped outer surface for facilitating implantation.

16. A pneumatic ventricular assist device comprising: a. a pumping shell comprising a first pumping shell half and a second pumping shell half that fit together to define an interior pumping chamber and two elongated, generally-cylindrical pump inlets; and b. a pumping unit comprising: i. a flexible blood sac dimensioned to fit in the pumping shell and having an interior and two tubular inlets; ii. two flexible, one-piece, one-way, hinge-less valves respectively connected to the blood sac inlets, wherein the valves have cylindrical outer surfaces and are dimensioned to fit entirely within and against the elongated pump inlets for enhancing support of the valves and preventing their removal or dislodgement from the pumping shell during use of the pneumatic ventricular assist device; and iii. two tubing connectors respectively connected to the two valves and dimensioned to fit at least partially in the pumping shell pump inlets.

17. The pneumatic ventricular assist device of claim 16 wherein the pumping shell pump inlets include inwards-facing, annular shoulders against which annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place.

18. The pneumatic ventricular assist device of claim 16 wherein the pumping shell pump inlets include annular gripping ridge for securing cannulae connected to the tubing connectors in place when the first pumping shell half and second pumping shell half are fit together.

19. The pneumatic ventricular assist device of claim 16 wherein: the pumping shell pump inlets include inwards-facing, annular shoulders against which annular flange portions of the tubing connectors respectively rest to hold the tubing connectors in place; and the pumping shell pump inlets include annular gripping ridge for securing cannulae connected to the tubing connectors in place when the first pumping shell half and second pumping shell half are fit together.

20. A disposable pumping unit for a pneumatic ventricular assist device, said pumping unit comprising: a. a flexible blood sac having an interior and first and second tubular sac inlets; b. a first cylindrical-shaped, one-way valve having a tubular inlet side with an outwards-facing, annular shoulder and a tubular outlet side with an outwards-facing, annular shoulder, wherein: the outlet side of the first valve is connected to the first tubular sac inlet; and the first tubular sac inlet abuts the annular shoulder of the outlet side of the first valve to form a substantially-continuous internal surface between the first tubular sac inlet and the interior of the outlet side of the first valve; c. a first tubing connector having a tubular fore-portion connected to the tubular inlet side of the first valve, wherein the tubular fore-portion of the first tubing connector abuts the annular shoulder of the inlet side of the first valve to form a substantially-continuous internal surface between the interior of the inlet side of the first valve and the interior of the first tubing connector; d. a second cylindrical-shaped, one-way valve having a tubular inlet side with an outwards-facing, annular shoulder and a tubular outlet side with an outwards-facing, annular shoulder, wherein: the inlet side of the second valve is connected to the second tubular sac inlet; and the second tubular sac inlet abuts the annular shoulder of the inlet side of the second valve to form a substantially-continuous internal surface between the second tubular sac inlet and the interior of the inlet side of the second valve, to minimize trauma of blood passing through the pumping unit; and e. a second tubing connector having a tubular fore-portion connected to the tubular outlet side of the second valve, wherein the tubular fore-portion of the second tubing connector abuts the annular shoulder of the outlet side of the second valve to form a substantially-continuous internal surface between the interior of the outlet side of the second valve and the interior of the second tubing connector, to minimize trauma of blood passing through the pumping unit.