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:
[0001]    This application claims priority from a Provisional Application, Serial No. 60/475,062, filed May 30, 2003. 
     
    
     
       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&#39;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&#39;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&#39; 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&#39;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&#39;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]    [0011]FIG. 1 is a perspective exploded view of a universal pneumatic ventricular assist device according to the present invention;  
         [0012]    [0012]FIG. 2 is a perspective exploded view of the ventricular assist device with an assembled disposable pump assembly;  
         [0013]    [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]    [0014]FIG. 4A is a elevation cross-sectional view of a valve portion of the ventricular assist device, taken along line  4 A- 4 A in FIG. 1;  
         [0015]    [0015]FIG. 4B is a perspective cross-sectional view of the valve portion of the ventricular assist device shown in FIG. 4A;  
         [0016]    [0016]FIG. 5A is a plan view of a disposable pump blood sac portion of the ventricular assist device;  
         [0017]    [0017]FIG. 5B is a cross-sectional view of the disposable blood sac taken along line  5 B- 5 B in FIG. 5A;  
         [0018]    [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]    [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&#39;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]    [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  74   a ,  74   b  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&#39; 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.