Patent Publication Number: US-9835146-B2

Title: Method of producing air for ventricular assist system

Description:
RELATIONSHIP TO OTHER APPLICATION 
     This application is a divisional of U.S. Ser. No. 12/301,257 filed on Dec. 22, 2009, now U.S. Pat. No. 8,596,992 issued on Dec. 3, 2013. U.S. Ser. No. 12/301,257 is a §371 national stage application of International Application No. PCT/US2007/018276 filed on Aug. 17, 2007, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/838,902 filed on Aug. 18, 2006. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates generally to pump systems, and more particularly, to a four-head diaphragm pump arrangement that is particularly suited for use in portable medical devices, such as a ventricular assist system. 
     Description of the Related Art 
     Ventricular assist devices are life sustaining systems that preferably are sufficiently portable to be carried by a patient without undue weight or bulk. Preferably, such a system should be powered by compressed air, notwithstanding that compressed air in such an application would require that a significant head pressure be overcome. Although other gases of lower density would function in this application with reduced head pressure, such would require the use of a compressed gas stored in heavy tanks to supply the implanted blood pump of the ventricular assist device. The preferred gas therefore it is filtered room air, as it is readily available in an unlimited supply, and provides the additional safety aspect to the patient of not requiring the use of tanks that can lose pressure or run empty at inopportune times. 
     An air pump for the ventricular assist device application needs to be compact, light in weight, low in vibration, and electrically efficient. In addition, it is highly desirable that the pump arrangement to be quiet in its operation, and particularly that the noise at the intake be maintained at a minimum to eliminate the need for cumbersome muffler systems. Intake air noise is a major contributor to overall sound output. Finally, it is essential that the pump arrangement to be reliable, and that it operate at reduced temperatures to achieve an extended lifespan. It is often desirable to maintain the maximum operating temperature of a device that will contact human skin to below 40° C. 
     It is, therefore, an object of this invention to provide a battery powered air pump arrangement that is suited for powering a portable ventricular assist device. 
     It is another object of this invention to provide an air pump arrangement that operates quietly and pneumatically efficiently. 
     It is also an object of this invention to provide an air pump arrangement that operates with minimal vibration. 
     It is a further object of this invention to provide an air pump arrangement that operates electrically efficiently. 
     It is additionally an object of this invention to provide an air pump arrangement that is reliable with redundant subsystems and can achieve powering of a ventricular assist device to a life-sustaining degree notwithstanding at least one subsystem failure. 
     It is yet a further object of this invention to provide an air pump arrangement that can achieve powering of a ventricular assist device to a heart rate of approximately 180 beats per minute. 
     It is yet an additional object of this invention to provide an air pump arrangement that can achieve low vibration powering of a ventricular assist device over a broad range of a heart rate, illustratively between approximately 40 to 180 beats per minute. 
     It is also another object of this invention to provide an air pump arrangement that can achieve inflation of a ventricular assist device in approximately 150 ms. 
     SUMMARY OF THE INVENTION 
     The foregoing and other objects are achieved by this invention which provides a pump arrangement having a rotatory shaft and a rotatory drive arrangement coupled to the rotatory shaft for applying rotatory energy thereto. There are additionally provided first, second, third, and fourth pump arrangements coupled to the rotatory shaft, each pump arrangement pumping a pulse of air during each rotation of the rotatory shaft, the first, second, third, and fourth pump arrangements pumping a corresponding pulse of air sequentially during each rotation of the rotatory shaft. 
     In one embodiment, the rotatory shaft has a first end, a second end, and a central region therebetween, and the rotatory drive arrangement includes an electric motor coaxially arranged about the central region of the rotatory shaft. The first and third pump arrangements are coupled to the first end of the rotatory shaft, and the second and fourth pump arrangements are coupled to the second end of the rotatory shaft. In addition, there is provided a first eccentric coupler for coupling the first and third pump arrangements to the first end of the rotatory shaft; and a second eccentric coupler for coupling the second and fourth pump arrangements to the second end of the rotatory shaft, the first and second eccentric couplers being angularly displaced on the rotatory shaft with respect to each other 
     In an advantageous embodiment of the invention, the first eccentric coupler arrangement has first and second eccentric portions angularly displaced with respect to one another for engaging with the first and third pump arrangements, respectively, and the second eccentric coupler arrangement has third and fourth eccentric portions angularly displaced with respect to one another for engaging with the second and fourth pump arrangements, respectively. In this manner, the first, second, third, and fourth pump arrangements pump a corresponding pulse of air at respective predetermined angular points during each rotation of the rotatory shaft. Further in accordance with this embodiment, the first, second, third, and fourth pump arrangements pump a respective pulse of air sequentially during each rotation of the rotatory shaft. In a highly advantageous embodiment, the first, second, third, and fourth pump arrangements pump a respective pulse of air sequentially every 90° during each rotation of the rotatory shaft. 
     In a specific illustrative embodiment of the invention, the first, second, third, and fourth pump arrangements each are respective ones of first, second, third, and fourth diaphragm pumps. Each of the first, second, third, and fourth diaphragm pumps has a respectively associated air inlet and a respectively associated compressed air outlet, and there is further provided a pneumatic coupling arrangement for coupling the respective air outlets of the first, second, third, and fourth diaphragm pumps to a combined compressed air outlet. Preferably, an outlet air capacity at the combined compressed air outlet is approximately between 2 liters/minute and 11 liters/minute at approximately 6 psi, and the rotatory drive arrangement consumes a maximum of approximately 1.45 Amps at 11 Volts (approximately 16 Watts). 
     In a further embodiment of the invention, each of the first, second, third, and fourth diaphragm pumps is provided with a diaphragm pump head arrangement, each diaphragm pump head arrangement having a respective inlet air diaphragm and a respective outlet air diaphragm. 
     In a particularly advantageous embodiment, the second, third, and fourth pump arrangements pump a respective pulse of air sequentially every 90° during each rotation of said rotatory shaft. In one embodiment, the first, second, third, and fourth pump arrangements are arranged in opposed pairs of pump arrangements. The first and third pump arrangements form a first pair of pump arrangements, and the second and fourth pump arrangements form a second pair of pump arrangements. 
     In a preferred embodiment, the first, second, third, and fourth pump arrangements are arranged in substantially coplanar relation. 
     In accordance with a method aspect of the invention, there are provided the steps of:
         coupling first, second, third, and fourth pump arrangements to a rotatory shaft each at a preselected angle; and   rotating the rotatory shaft whereby each of the first, second, third, and fourth pump arrangements issues a pulse of compressed air at the preselected angle of rotation of the rotatory shaft.       

     In one embodiment, the step of coupling comprises the further step of orienting respective ones of first and second eccentric couplers in response to the preselected angles of at least two of the first, second, third, and fourth pump arrangements. In a further embodiment, the step of coupling comprises the further step of orienting respective ones of third and fourth eccentric couplers in response to the preselected angles of the remaining two of the first, second, third, and fourth pump arrangements. 
     There is provided in a further embodiment the step of combining the pulses of compressed air to form the stream of compressed air. 
     In a highly advantageous embodiment of the invention, the step of coupling comprises the step of coupling first, second, third, and fourth pump arrangements to a rotatory shaft each at a preselected angle that differs from that of the other pump arrangements, whereby the first, second, third, and fourth pump arrangements issue respective pulses of compressed air sequentially in response to the step of rotating. Preferably, the respective sequential pulses of compressed air are distributed symmetrically in response to the step of rotating, and may be distributed every 90° in response to the step of rotating. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Comprehension of the invention is facilitated by reading the following detailed description, in conjunction with the annexed drawing, in which: 
         FIG. 1  is a plan view of a specific illustrative embodiment of the invention; 
         FIG. 2  is a plan view of elements of an illustrative prior art diaphragm head arrangement useful in the embodiment of  FIG. 1 ; 
         FIG. 3 , is a plan view of the underside of one of the elements of the illustrative prior art diaphragm head arrangement shown in  FIG. 1 ; 
         FIG. 4  is a schematic representation of the first and third pump arrangements coupled to the first end of the motor shaft that serves as the rotatory shaft; 
         FIG. 5  is a schematic representation of a prior art diaphragm head arrangement useful in the embodiment of  FIG. 1 ; 
         FIG. 6  is an isometric schematic representation of the prior art diaphragm head arrangement of  FIG. 5 ; 
         FIG. 7  is a partially cross-sectional representation of a prior art diaphragm employed in the prior art head arrangement of  FIG. 6 ; 
         FIG. 8  is a partially cross-sectional representation of the prior art diaphragm employed in the prior art head arrangement of  FIG. 6  shown in a closed position; 
         FIG. 9  is a partially cross-sectional representation of the prior art diaphragm employed of  FIG. 8  shown in an open position; 
         FIG. 10  is a partially fragmented and partially transparent perspective representation of a four-head pump arrangement constructed in accordance with the principles of the invention; 
         FIG. 11  is a graphical representation that compares pump flow versus power consumption for various pump configurations, including the specific illustrative embodiment of the invention described herein; and 
         FIG. 12  is a bar graph representation that compares output flow versus noise level output for various pump configurations, including the specific illustrative embodiment of the invention described herein. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a plan view of a specific illustrative embodiment of a pump arrangement  100  constructed in accordance with the principles of the invention. Pump arrangement  100  is shown to have a rotatory shaft  110  having a first end  112  and a second end  114 . An electric motor  116  is coaxially arranged about rotatory shaft  110  in a central region (not specifically designated) intermediate of first and second ends  112  and  114 . The electric motor is powered via electric conductors  117 . 
     Pump arrangement  100  is additionally provided with first through fourth pump arrangements that are respectively generally designated  120 ,  122 ,  124 , and  126 . Portions of a diaphragm head arrangement, such as that which is shown to be associated with pump arrangement  126 , is designated as diaphragm head arrangement  200 , and is further shown and described in connection with  FIGS. 2 and 3 , the operation of which is described in detain in connection with  FIGS. 5-9 . 
     Referring once again to  FIG. 1 , each of pump arrangements  120 ,  122 ,  124 , and  126  is shown to be coupled to rotatory shaft  110  by a respectively associated one of connector rods  130 ,  132 ,  134 , and  136 . In this specific illustrative embodiment of the invention, each of the connector rods is coupled to rotatory shaft  110  by a respective eccentric coupler, as will be described below in connection with  FIG. 4 . The eccentric couplers are angularly displaced with respect to each other on the rotatory shaft, whereby in this specific illustrative embodiment of the invention each of pump arrangements  120 ,  122 ,  124 , and  126  issues pulses of compressed air in a predetermined sequence as rotatory shaft  110  is rotated. In a highly advantageous embodiment, the eccentric couplers are angularly arranged such that the pulses of compressed air are issued each 90° of the rotation of rotatory shaft  110 . 
     There is additionally shown in  FIG. 1  a counterweight  140  that provides a balancing effect to pump arrangement  100  as rotatory shaft  110  is rotated. Preferably, a second counterweight is provided at the other end of rotatory shaft  110 . However, the second counterweight is not shown in this figure to enhance the clarity of the present disclosure. 
     Support bearings  142  and  146 , arranged on opposite ends of rotatory shaft  100  and intermediate of adjacent ones of the connector rods, provide additional support to the rotatory shaft. The support bearings are arranged to be affixed to top and/or bottom cover plates (not shown in this figure) that complete the enclosure of pump arrangement  100 . In this embodiment, the pump arrangements are interconnected pneumatically, illustratively by conduits such as conduit  150 , to produce a combined stream of compressed air at outlet  152 . 
     As can be seen in  FIG. 1 , pump arrangements  120 ,  122 ,  124 , and  126  are arranged in substantially coplanar relation. More specifically, pump arrangements  120  and  124  are arranged in opposition to one another, and pump arrangements  122  and  126  oppose one another in this substantially coplanar arrangement. 
       FIG. 2  is a plan view of elements of an illustrative prior art diaphragm head arrangement  200  useful in the embodiment of  FIG. 1 . It is to be understood that the practice of the invention herein disclosed is not limited to the illustrative prior art diaphragm head arrangement shown in  FIGS. 2-9  and described herein in connection with those figures. Referring to  FIG. 2 , there is shown a valve seat support  202  having thereon valve seats  17   a  and  17   b . The valve seats and the diaphragms (not specifically designated) installed therein will be described in greater detail in connection with the schematic representations of  FIGS. 5 and 6 . 
     A valve seat cover arrangement  204  is shown to have a polymeric seal  204  installed thereon. Valve seat cover arrangement  204 , when assembled with valve seat support  202 , includes the polymeric seal interposed therebetween. 
       FIG. 3 , is a plan view of the underside of valve seat support  202  of the illustrative prior art diaphragm head arrangement shown in  FIG. 1 . This figure shows the underside of valve seats  17   a  and  17   b.    
       FIG. 4  is a schematic representation of the first pump arrangement  120  and third pump arrangement  124  coupled to first end  112  of the rotatory shaft  110  that serves as the rotatory shaft. Elements of structure that have previously been discussed are similarly designated. In contrast to the embodiment described above in connection with  FIG. 1 , the present embodiment of  FIG. 4  employs a single eccentric coupler  300  that is shared in this specific illustrative embodiment of the invention by connector rods  130  and  134 . As shown, connector rods  130  and  134  are coupled to eccentric coupler  300  by respective bearings that are, in this embodiment, pressed onto the eccentric coupler and into the connector rods, such as bearing  302  associated with connector rod  130 . A counterweight  140   a  serves to achieve a dynamic balance. 
     In the operation of the specific illustrative embodiment of  FIG. 4 , the sharing of eccentric coupler  300  by connector rods  130  and  134  results in the first and third pump arrangements operating 180° apart. That is, when the first pump arrangement is at top dead center, the third pump arrangement is at bottom dead center. Therefore, in embodiments of the invention where it is desired to operate pump arrangements  120 ,  122 ,  124 , and  126  in sequence, the second eccentric coupler (not shown in this figure) disposed on the second end (not shown in this figure) of rotatory shaft  110  would be angularly displaced on the rotatory shaft to some angle other than 0° (parallel to the angular position of eccentric coupler  300 ) or 180° (diametrically opposite to the angular position of eccentric coupler  300 ). Installing the second eccentric coupler at a corresponding 90° or 270° would result in a four head pump arrangement that issues pulses of compressed air every 90° of the rotation of rotatory shaft  110 . 
       FIG. 5  is a schematic representation of a prior art diaphragm head arrangement useful in the embodiment of  FIG. 1 .  FIG. 6  is an isometric schematic representation of the prior art diaphragm head arrangement of  FIG. 5 . The operation of the prior art diaphragm head arrangement shown in  FIGS. 5-9  is described in detail in U.S. Pat. No. 5,803,122, the disclosure of which is incorporated herein by reference. It is understood, however, that the present invention is not limited to the use of this known diaphragm head arrangement. Elements of structure that have previously been discussed in connection with  FIGS. 2-4  are similarly designated. 
     Referring to  FIGS. 5 and 6 , inlet and outlet valves  16   a  and  b  are each disposed in valve seats  17   a  and  b , respectively, facing opposite directions. Because inlet and outlet valves  16   a  and  b  are identical in all respects except for their orientation in pump  10 , description will be made of only one valve  16  which will be equally applicable to both 
       FIG. 7  is a partially cross-sectional representation of a prior art diaphragm employed in the prior art head arrangement of  FIG. 6 . As shown in this figure, the interior of raised rim  22  defines a circular valve face  50  which is indented into a downstream side  47  of valve seat  17  from raised rim  22 . In the preferred embodiment, valve face  50  has a frusto-conical shape made up of a central, circular, flat surface  54  which is surrounded by an angled, conical surface  56 . Circular flat surface  54  is indented into valve seat  17  from raised rim  22  to bow diaphragm  20  as will be described in more detail below. The frusto-conical shape of valve face  50  is oriented so that angled conical surface  56  extends into valve seat  17  such that the depth of surface  56  is greatest at its outermost perimeter. Thus, valve face  50  is indented into valve seat  17  a maximum extent adjacent raised rim  22 . While a frusto-conical shape is preferred, it will be understood that valve face  50  may have a variety of different shapes other than frusto-conical. For example, valve face  50  may not include a circular flat surface  54 , but instead might solely include an angled, conical surface. As other alternatives, valve face  50  may be substantially planar, valve face  50  may be a curved concave shape, or valve face  50  may have a plurality of angled flat surfaces instead of angled, conical surface  56 . It is contemplated that the most preferred configuration is any angled shape of valve face  50  wherein the depth of valve face  50  is greatest at its outermost perimeter. Such shapes support the diaphragm during the reverse cycle of fluid flow along a center area of valve face  50  which expands outwardly as the reverse fluid pressure is increased. Such shapes also substantially prevent diaphragm  20  from contacting valve face  50  at its deepest perimeter adjacent raised rim  22 . 
       FIG. 8  is a partially cross-sectional representation of the prior art diaphragm employed in the prior art head arrangement of  FIG. 6  shown in a closed position. A plurality of cylindrical channels  18  are defined in valve face  50  of valve seat  17 . In the illustrated embodiment, six channels  18  are defined in valve seat  17  and are oriented to intersect angled, conical surface  56  of valve face  50  in a circular fashion. A center support  24  is axially oriented in the center of each channel  18 . Center supports  24  include an angled downstream end  64  that is angled approximately the same as angled, conical surface  56  so as to lie generally in the same plane as that region of valve face so immediately adjacent channel  18 . Center supports  24  are secured to valve seat  17  by a bridge ring  62  substantially concentric to circular valve face  50  and disposed adjacent an upstream side  46  of valve seat  17  ( FIG. 8 ). Bridge ring  62  is thus removed from valve face  50 . Center supports  24  are connected to bridge ring  62  upstream of angled downstream ends  64 . Center supports  24  each provide a point of contact that support diaphragm  20  during the reverse cycle of fluid flow so that diaphragm  20  is not excessively deformed across channels  18 . The support provided by supports  24  enables diaphragm  20  to be made thinner than that which could otherwise span channels  18  without being drawn down into channels  18  on the reverse stroke, and thus provide sufficient durability to repeated high speed cycling of the valve  10 . The thinness of diaphragm  20  also decreases power consumption and speeds response time. In the preferred embodiment, center supports  24  have a circular cross-sectional shape that is substantially concentric to the circular cross-sectional shape of channels  18 . In an alternative embodiment, the span of bridge ring  62  across each channel  18  is recessed into the inlet plenum or chamber in order to reduce constriction at the entry into channels  18 . 
     A plug recess  66  is defined in valve seat  17  in the center of valve face  50  ( FIGS. 5-7 ). Plug recess  66  is surrounded concentrically by flat surface  54  of valve face  50 . Plug recess  66  is shaped to securely receive a plug  68  on diaphragm  20 . When diaphragm  20  is secured to valve seat  17  via the securing of plug  68  in plug recess  66 , an upstream surface  70  of diaphragm  20  extends over all of valve face  50 , including channels  18  therein, and onto and beyond raised rim  22 . Because diaphragm  20  is secured to valve seat  17  in a position indented from raised rim  22 , diaphragm  20  is bowed by its contact with raised rim  22 . The bowing of diaphragm  20  biases diaphragm  20  toward a closed position, i.e. a position where upstream surface  70  of diaphragm  20  contacts and is fluidly sealed near its perimeter against raised rim  22 . The bowing of diaphragm  22  gives valve  16  a better response characteristic by snapping closed more quickly upon a drop in forward fluid pressure (i.e. during the return stroke). This characteristic is especially important in a high-speed reciprocating environment. 
       FIG. 9  is a partially cross-sectional representation of the prior art diaphragm employed in the embodiment of  FIG. 8 , shown in an open position. When pump  10  is shut off and valve  16  is in a rest position, upstream surface  70  of diaphragm  20  is spaced a small distance away from angled downstream ends  64  of center supports  24 . Only during the return stroke of pump  10 , when the fluid pressure is greater on a downstream surface  72  of diaphragm  20  than upstream surface  70 , will diaphragm  20  contact center supports  24 , and then typically only along a portion. The space between diaphragm  20  and center supports  24  allows the fluid upstream of diaphragm  20  to exert pressure against upstream surface  70  of diaphragm  20  over a greater area than would otherwise be possible without this space. With the fluid exerting pressure over a greater area, diaphragm  20  will experience a greater forward opening force during the forward cycle, and less pressure will therefore be required to open valve  16 . Consequently less energy will be consumed by valve  16  and a faster response time will be produced. 
     Diaphragm  20  is made of a pliable yet durable material in order to require minimal energy to open and yet withstand the pressures of a high-speed environment. Resilient, elastomeric materials are suitable, and in the preferred embodiment diaphragm  20  is made of neoprene. Alternatively diaphragm  20  may be made of Latex, Silicone, Buna-N, EPDM, Viton, or other suitable resilient elastomeric material. 
     During the return fluid cycle, valve  16  will be closed and pushed against a portion of downstream ends  64  of center supports  24 . Because of the frusto-conical shape of surface  52  in combination with raised rim  22 , diaphragm  20  will not contact all of the frusto-conical surface of valve face  50  nor necessarily all of downstream ends  64  of center supports  24 . The area of upstream surface  70  of diaphragm  20  against which the fluid can exert pressure will therefore be greater than the sum of the cross-sectional areas of channels  18  (minus the center support cross-sectional areas). Consequently, less energy will be consumed to crack open valve  16  from a reverse cycle position. It can therefore be seen that valve  16  is both energy efficient and durable as a result of its unique configuration. 
     While the prior art diaphragm valve arrangement described herein finds applicability in valves having a range of dimensions, the relative dimensions of valve  16  in one embodiment of a 15 liters per minute valve are as follows: the diameter of diaphragm  20  is 0.687 inches; diaphragm  20  has a thickness of 0.017 inches; the diameter of valve face  50  is 0.625 inches; the depth of raised rim  22  is 0.021 inches; the diameter of channels  18  is 0.156 inches; the diameter of center supports  24  is 0.063 inches; and the diameter of bridge ring  62  is 0.405 inches. 
       FIG. 10  is a partially fragmented and partially transparent perspective representation of a four-head pump arrangement constructed in accordance with the principles of the invention. Elements of structure that have previously been discussed are similarly designated. As shown in this figure, connector rod  130  has bearing  302  installed therein. The embodiment of  FIG. 10  is similar to that of  FIG. 1  in that each connector rod has an associated eccentric coupler (not shown in this figure) whereby the specific angle of rotation of the rotatory shaft at which each pump arrangement will issue a pulse of compressed air can individually be preselected. 
       FIG. 11  is a graphical representation that compares pump flow versus power consumption for various pump configurations, including the specific illustrative embodiment of the invention described herein. As shown in this figure, the four head design of the present specific illustrative embodiment of the invention (not shown in this figure), which employs a 90° air pulse timing, as described above, exhibits reduced power consumption as compared to four head designs that employ 180° air pulse timing. More specifically, graph trace  402 , which corresponds to the four head design of the present specific illustrative embodiment of the invention, using 90° timing and low speed eccentric, consumes less power at almost all flow rates (graphical trace  404 ) than a high speed eccentric (graphical trace  406 ). In addition, the 90° timing achieves reduced noise and low vibration. The term “low speed eccentric,” as used herein refers to a stroke length design that is longer than the stroke length of the high speed eccentric, and therefore can be rotated at a slower speed. The stroke length refers to the offset from the centerline of the piston bearing assembly, which determines the length of the stroke. Lower speeds tend to vibrate more, but run quieter. 
       FIG. 12  is a bar graph representation that compares output flow versus noise level output for various pump configurations, including the specific illustrative embodiment of the invention described herein. As shown in this figure, the four head design of the present specific illustrative embodiment of the invention (not shown in this figure), which employs a 90° air pulse timing, exhibits reduced noise output at each of several flow rates, as compared to the four head design (not shown) operated using a high speed eccentric. The noise output is comparable to that of the four head design (not shown) operated using a low speed eccentric. 
     Although the invention has been described in terms of specific embodiments and applications, persons skilled in the art may, in light of this teaching, generate additional embodiments without exceeding the scope or departing from the spirit of the invention described and claimed herein. Accordingly, it is to be understood that the drawing and description in this disclosure are proffered to facilitate comprehension of the invention, and should not be construed to limit the scope thereof.