Patent Publication Number: US-2022226633-A1

Title: Implantable pump system having an undulating membrane

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 16/557,711, filed Aug. 30, 2019, now U.S. Pat. No. 11,298,522, which is a continuation application of U.S. patent application Ser. No. 15/976,831, filed May 10, 2018, now U.S. Pat. No. 10,398,821, which is a divisional application of U.S. patent application Ser. No. 15/484,101, filed Apr. 10, 2017, now U.S. Pat. No. 9,968,720, which claims the benefit of the filing date of U.S. Provisional Patent Application No. 62/321,076 filed Apr. 11, 2016, the entire contents of each of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to heart pumps and more particularly to implantable pumps having an undulating membrane designed to reduce hemolysis and platelet activation. 
     BACKGROUND 
     The human heart is comprised of four major chambers with two ventricles and two atria. Generally, the right-side heart receives oxygen-poor blood from the body into the right atrium and pumps it via the right ventricle to the lungs. The left-side heart receives oxygen-rich blood from the lungs into the left atrium and pumps it via the left ventricle to the aorta for distribution throughout the body. Due to any of a number of illnesses, including coronary artery disease, high blood pressure (hypertension), valvular regurgitation and calcification, damage to the heart muscle as a result of infarction or ischemia, myocarditis, congenital heart defects, abnormal heart rhythms or various infectious diseases, the left ventricle may be rendered less effective and thus unable to pump oxygenated blood throughout the body. 
     The Centers for Disease Control and Prevention (CDC) estimate that about 5.1 million people in the United States suffer from some form of heart failure. Heart failure is generally categorized into four different stages with the most severe being end stage heart failure. End stage heart failure may be diagnosed where a patient has heart failure symptoms at rest in spite of medical treatment. Patients at this stage may have systolic heart failure, characterized by decreasing ejection fraction. In patients with systolic heart failure, the walls of the ventricle, which are typically thick in a healthy patient, become thin and weak. Consequently, during systole a reduced volume of oxygenated blood is ejected into circulation, a situation that continues in a downward spiral until death. A patient diagnosed with end stage heart failure has a one-year mortality rate of approximately 50%. 
     For patients that have reached end stage heart failure, treatment options are limited. In addition to continued use of drug therapy commonly prescribed during earlier stages of heart failure, the typical recommend is cardiac transplantation and implantation of a mechanical assist device. While a cardiac transplant may significantly prolong the patient&#39;s life beyond the one year mortality rate, patients frequently expire while on a waitlist for months and sometimes years awaiting a suitable donor heart. Presently, the only alternative to a cardiac transplant is a mechanical implant. While in recent years mechanical implants have improved in design, typically such implants will prolong a patient&#39;s life by a few years at most, and include a number of co-morbidities. 
     One type of mechanical implant often used for patients with end stage heart failure is a left ventricular assist device (LVAD). The LVAD is a surgically implanted pump that draws oxygenated blood from the left ventricle and pumps it directly to the aorta, thereby off-loading (reducing) the pumping work of the left ventricle. LVADs typically are used either as “bridge-to-transplant therapy” or “destination therapy.” When used for bridge-to-transplant therapy, the LVAD is used to prolong the life of a patient who is waiting for a heart transplant. When a patient is not suitable for a heart transplant, the LVAD may be used as a destination therapy to prolong the life, or improve the quality of life, of the patient, but generally such prolongation is for only a couple years. 
     Generally, a LVAD includes an inlet cannula, a pump, and an outlet cannula, and is coupled to an extracorporeal battery and control unit. The inlet cannula typically directly connected to the left ventricle, e.g., at the apex, and delivers blood from the left ventricle to the pump. The outlet cannula typically connected to the aorta distal to the aortic valve, delivers blood from the pump to the aorta. Typically, the outlet cannula of the pump is extended using a hose-type structure, such as a Dacron graft, to reach a proper delivery location on the aorta. Early LVAD designs were of the reciprocating type but more recently rotary and centrifugal pumps have been used. 
     U.S. Pat. No. 4,277,706 to Isaacson, entitled “Actuator for Heart Pump,” describes a LVAD having a reciprocating pump. The pump described in the Isaacson patent includes a housing having an inlet and an outlet, a cavity in the interior of the pump connected to the inlet and the outlet, a flexible diaphragm that extends across the cavity, a plate secured to the diaphragm, and a ball screw that is configured to be reciprocated to drive the plate and connected diaphragm from one end of the cavity to the other end to simulate systole and diastole. The ball screw is actuated by a direct current motor. The Isaacson patent also describes a controller configured to manage the revolutions of the ball screw to control the starting, stopping and reversal of directions to control blood flow in and out of the pump. 
     Previously-known reciprocating pump LVADs have a number of drawbacks. Such pumps often are bulky, heavy and may require removal of bones and tissue in the chest for implantation. They also require a significant amount of energy to displace the blood by compressing the cavity. Moreover, the pump subjects the blood to significant pressure fluctuations as it passes through the pump, resulting in high shear forces and risk of hemolysis. These pressure fluctuations may be exaggerated at higher blood flow rates. Further, depending on the geometry of the pump, areas of little or no flow may result in flow stagnation, which can lead to thrombus formation and potentially fatal medical conditions, such as stroke. Finally, the positive displacement pumps like the one described in the Isaacson patent are incapable of achieving pulsatility similar to that of the natural heart, e.g., roughly 60 to 100 beats per minute, while maintaining physiological pressure gradients. 
     LVADs utilizing rotary and centrifugal configurations also are known. For example, U.S. Pat. No. 3,608,088 to Reich, entitled “Implantable Blood Pump,” describes a centrifugal pump to assist a failing heart. The Reich patent describes a centrifugal pump having an inlet connected to a rigid cannula that is coupled to the left ventricular cavity and a Dacron graft extending from the pump diffuser to the aorta. A pump includes an impeller that is rotated at high speeds to accelerate blood, and simulated pulsations of the natural heart by changing rotation speeds or introducing a fluid oscillator. 
     U.S. Pat. No. 5,370,509 to Golding, entitled “Sealless Rotodynamic Pump with Fluid Bearing,” describes an axial blood pump capable for use as a heart pump. One embodiment described involves an axial flow blood pump with impeller blades that are aligned with the axes of the blood inlet and blood outlet. U.S. Pat. No. 5,588,812 to Taylor, entitled “Implantable Electrical Axial-Flow Blood Pump,” describes an axial flow blood pump similar to that of the Golding patent. The pump described in the Taylor patent has a pump housing that defines a cylindrical blood conduit through which blood is pumped from the inlet to the outlet, and rotor blades that rotate along the axis of the pump to accelerate blood flowing through the blood conduit. 
     While previously-known LVAD devices have improved, those pump designs are not without problems. Like reciprocating pumps, rotary and centrifugal pumps are often bulky and difficult to implant. Rotary pumps, while mechanically different from positive displacement pumps, also exhibit undesirable characteristics. Like positive displacement pumps, rotary pumps apply significant shear forces to the blood, thereby posing a risk of hemolysis and platelet activation. The very nature of a disk or blade rotating about an axis results in areas of high velocity and low velocity as well as vibration and heat generation. Specifically, the area near the edge of the disk or blade furthest from the axis of rotation experiences higher angular velocity and thus flow rate than the area closest to the axis of rotation. The resulting radial velocity profile along the rotating blade results in high shear forces being applied to the blood. In addition, stagnation or low flow rates near the axis of rotation may result in thrombus formation. 
     While centrifugal pumps may be capable generating pulsatile flow by varying the speed of rotation of the associated disk or blades, this only exacerbates the problems resulting from steep radial velocity profiles and high shear force. In common practice, the output of currently available rotary pumps, measured as flow rate against a given head pressure, is controlled by changing the rotational speed of the pump. Given the mass of the rotating member, the angular velocity of the rotating member, and the resulting inertia, a change in rotational speed cannot be instantaneous but instead must be gradual. Accordingly, while centrifugal pumps can mimic a pulsatile flow with gradual speed changes, the resulting pulse is not “on-demand” and does not resemble a typical physiological pulse. 
     Moreover, rotary pumps typically result in the application of non-physiologic pressures on the blood. Such high operating pressures have the unwanted effect of overextending blood vessels, which in the presence of continuous flow can cause the blood vessels to fibrose and become inelastic. This in turn can lead to loss of resilience in the circulatory system, promoting calcification and plaque formation. Further, if the rotational speed of a pump is varied to simulate pulsatile flow or increase flow rate, the rotary pump is less likely to be operated at its optimal operating point, reducing efficiency and increasing energy losses and heat generation. 
     LVADs may also be configured to increase blood flow to match the demand of the patient. Numerous publications and patents describe methods for adjusting LVAD pump flow to match that demanded by the patient. For example U.S. Pat. No. 7,520,850 to Brockway, entitled “Feedback control and ventricular assist devices,” describes systems and methods for employing pressure feedback to control a ventricular assist device. The system described in the Brockway patent attempts to maintain a constant filling of the ventricle by measuring ventricular pressure and/or ventricular volume. While such systems can achieve flow rates as high as 8 or 9 liters per minute, these flow rates generally are outside of the efficient range of operation for current rotary pumps, which are typically tuned to operate in a range of 4 to 6 liters per minute. Thus, increasing the flow rate in rotary pumps to match patient demanded results in non-optimal pump performance. 
     Pumps other than of the rotary and positive displacement types are known in the art for displacing fluid. For example, U.S. Pat. Nos. 6,361,284 and 6,659,740, both to Drevet, entitled “Vibrating Membrane Fluid Circulator,” describe pumps in which a deformable membrane is vibrated to propel fluid through a pump housing. In these patents, vibratory motion applied to the deformable membrane causes wave-like undulations in the membrane that propel the fluid along a channel. Different flow rates may be achieved by controlling the excitation applied to the membrane. 
     U.S. Pat. No. 7,323,961 to Drevet, entitled “Electromagnetic Machine with a Deformable Membrane”, describes a device in which a membrane is coupled in tension along its outer edge to an electromagnetic device arranged to rotate around the membrane. As the electromagnetic device rotates, the outer edge of the membrane is deflected slightly in a direction normal to the plane of the membrane. These deflections induce a wave-like undulation in the membrane that may be used to move a fluid in contact with the membrane. 
     U.S. Pat. No. 9,080,564 to Drevet, entitled “Diaphragm Circulator,” describes a tensioned deformable membrane in which undulations are created by electromechanically moving a magnetized ring, attached to an outer edge of a deformable membrane, over a coil. Axial displacement of magnetized ring causes undulations of membrane. Like in the &#39;961 patent, the membrane undulations can be controlled by manipulating the magnetic attraction. U.S. Pat. No. 8,714,944 to Drevet, entitled “Diaphragm pump with a Crinkle Diaphragm of Improved Efficiency” and U.S. Pat. No. 8,834,136 to Drevet, entitled “Crinkle Diaphragm Pump” teach similar types of vibrating membrane pumps. 
     None of the foregoing patents to Drevet describe a vibratory membrane pump suitable for use in a biological setting, or capable of pumping blood over extended periods that present a low risk of flow stagnation leading to thrombus formation. 
     What is needed is an energy efficient implantable pump having light weight, small size, and fast start and stop response that can operate efficiently and with minimal blood damage over a wide range of flow rates. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the drawbacks of previously-known LVAD systems and methods by providing an implantable pump system having an undulating membrane capable of producing a wide range of physiological flow rates while applying low shear forces to the blood, thereby reducing hemolysis and platelet activation relative to previously-known systems. 
     In accordance with one aspect of the invention, the implantable blood pump system includes an implantable pump, a controller and a rechargeable battery, each electrically coupled to one another. The system further may comprise a programmer that communicates with the controller to set and change pumping parameters. 
     The implantable blood pump constructed in accordance with the principles of the present invention may have an implantable housing configured to be implanted at a patient&#39;s heart, a membrane disposed within the implantable housing, and an actuator system also disposed within the implantable housing having a stationary component and a moving component. The moving component may be coupled to the membrane. The actuator system may receive an electrical signal to cause the moving component to reciprocate at varying frequencies and amplitudes relative to the stationary component, thereby causing the membrane to reciprocate at varying frequencies and amplitudes resulting in blood flow. 
     The implantable housing may include an inlet and an outlet. The membrane may be part of a membrane assembly disposed concentrically within the housing proximal to the outlet. The membrane may be a tensioned flexible circular membrane having a central aperture. The tensioned flexible membrane may be coupled to a rigid ring. The stationary part of the actuator system may include a stator assembly and an electromagnet assembly and the moving component may be a magnetic ring. The electromagnet assembly may selectively generate a magnetic field. The magnet ring may be coupled to the rigid ring and may be concentrically suspended around the actuator. The magnetic ring may reciprocate in response to the magnetic field generated by the electromagnet assembly. During operation of the implantable blood pump, blood may enter the inlet, flow around the actuator assembly and the magnetic ring, flow across the membrane and ultimately flow out of the outlet. 
     The magnetic ring may be coupled to the membrane assembly and the first and second suspension rings by three rigid posts spaced equidistant around the actuator assembly, such that the first and second suspension rings permit the magnetic ring to reciprocate over the actuator assembly but resist movement in other directions. The first and second suspension rings serve as springs that enable movement of the magnetic ring over the actuator assembly. The implantable blood pump may further include a housing fixation ring concentrically positioned around the actuator assembly and coupled to both the actuator assembly and the housing, which anchors the actuator assembly to the housing. 
     In accordance with the principles of the invention, the magnetic ring is configured to induce wave-like deformation in the circular membrane by reciprocating over the actuator assembly responsive to alternating excitation of first and second electromagnetic coils. This reciprocation induces wave-like deformations in the circular membrane, having a magnitude determined by the displacement and frequency of the magnetic ring movement. The wave-like deformations of the circular membrane in turn cause flow through the pump, capable of producing physiologic flow rates in a range between 4 and 10 liters per second. 
     In accordance with another aspect of the principles of the present invention, the controller may be programmed to vary the actuation of the actuator assembly to cause the pump to produce pulsatile flow. Methods for pumping blood from the left ventricle to the aorta using the implantable blood pump and system of the present invention also are provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an exemplary embodiment of the pump system of the present invention comprising an implantable pump, controller, battery, programmer and mobile device. 
         FIG. 2  is a perspective view of the implantable pump of  FIG. 1 . 
         FIGS. 3A and 3B  are, respectively, a perspective view and a schematic view of the electronic components of an exemplary embodiment of the controller of the present invention. 
         FIG. 4  is a plan view of an extracorporeal battery for use in the pump system of the present invention. 
         FIGS. 5A and 5B  are, respectively, a perspective view and a schematic view of the electronic components of an exemplary embodiment of the programmer of the present invention. 
         FIG. 6  is a perspective view of the pump assembly of the present invention. 
         FIG. 7  is a perspective, cut-away view of the implantable pump of the present invention. 
         FIG. 8  is an exploded view of the implantable pump of the present invention. 
         FIG. 9  is a perspective cross sectional view of the pump assembly of the present invention. 
         FIG. 10  is a perspective cross sectional view of the membrane assembly of the present invention. 
         FIG. 11  is a perspective cross section view of the moving components of the pump assembly according to a first embodiment of the present invention. 
         FIG. 12  is a cross sectional view of the implantable pump of the present invention. 
         FIG. 13  is a cross sectional view of a lower portion of the implantable pump depicting the flow channel and membrane assembly in a resting position. 
         FIG. 14  is a cross sectional view of a lower portion of the implantable pump depicting the flow channel and membrane assembly with the membrane undulating. 
     
    
    
     DETAILED DESCRIPTION 
     The implantable pump system of the present invention is particularly well-suited for use as a left ventricular assist device (LVAD), and includes an undulating membrane pump suitable for long-term implantation in a patient having end term heart failure. An implantable pump system constructed in accordance with the principles of the present invention includes an implantable pump and an extracorporeal battery, controller and programmer. The implantable pump includes a housing having an inlet, and outlet, a flexible membrane, and an actuator assembly. When configured as an LVAD, the housing includes an inlet cannula that is inserted into a patient&#39;s left ventricle near the apex and an outlet cannula that is surgically placed in fluid communication with the patient&#39;s aorta. By activating the actuator assembly within the implantable pump, membrane is induced to undulate, thereby causing blood to be drawn into the pump through the inlet cannula and expelled through the outlet cannula into the aorta. Flow rate and pulsatility may be manipulated by changing one or more of the frequency, amplitude and duty cycle of the actuator assembly. 
     Referring now to  FIG. 1 , pump system  10  constructed in accordance with the principles of the present invention is described. Pump system  10  includes implantable pump  20 , controller  30 , battery  40 , programmer  50  and optionally, a software module programmed to run on mobile device  60 . Implantable pump  20  is configured to be implanted within a patient&#39;s chest so that inlet cannula  21  is coupled to left ventricle LV of heart H. Outlet cannula  22  of pump  20  is configured to be coupled to aorta A. Inlet cannula  21  preferably is coupled to the apex of left ventricle LV, while outlet cannula  22  is coupled to aorta A in the vicinity of the ascending aorta, above the level of the cardiac arteries. Implantable pump  20  may be affixed within the patient&#39;s chest using a ring-suture or other conventional technique. Outlet cannula  22 , which may comprise a Dacron graft or other synthetic material, is coupled to outlet  23  of implantable pump  20 . 
     Referring now also to  FIG. 2 , implantable pump  20  in a preferred embodiment consists of upper housing portion  24  joined to lower housing portion  25  along interface  26 , for example, by threads or welding, to form fluid tight pump housing  27  that may have a cylindrical shape. Upper housing portion  24  includes inlet cannula  21  and electrical conduit  28  for receiving electrical wires from controller  30  and battery  40 . Lower housing portion  25  includes outlet  23  that couples to outlet cannula  22 , as shown in  FIG. 1 . Pump housing  27  is made of a biocompatible material, such as stainless steel, and is sized to be implanted within a patient&#39;s chest. 
     Referring again to  FIG. 1 , in one embodiment, controller  30  and battery  40  are extracorporeal, and are sized so as to be placed on a belt or garment worn by the patient. Both controller  30  and battery  40  are electrically coupled to implantable pump  20 , for example, via cable  29  that extends through a transcutaneous opening in the patient&#39;s skin and into electrical conduit  28  of pump housing  27 . Illustratively, battery  40  is electrically coupled to controller  30  via cable  41  that is integrated into belt  42 . In an alternative embodiment, controller  30  may be enclosed within a biocompatible housing and sized to be implanted subcutaneously in the patient&#39;s abdomen. In this alternative embodiment, controller  30  may include a wireless transceiver for bi-directional communications with an extracorporeal programming device and also include a battery that is continuously and inductively charged via extracorporeal battery  40  and an extracorporeal charging circuit. As will be understood, the foregoing alternative embodiment avoids the use of transcutaneous cable  29 , and thus eliminates a frequent source of infection for conventional LVAD devices. 
     Battery  40  preferably comprises a rechargeable battery capable of powering implantable pump  20  and controller  30  for a period of several days, e.g., 3-5 days, before needing to be recharged. Battery  40  may include a separate charging circuit, not shown, as is conventional for rechargeable batteries. Battery  40  preferably is disposed within a housing suitable for carrying on a belt or holster, so as not to interfere with the patient&#39;s daily activities. 
     Programmer  50  may consist of a conventional laptop computer that is programmed to execute programmed software routines, for use by a clinician or medical professional, for configuring and providing operational parameters to controller  30 . The configuration and operational parameter data is stored in a memory associated with controller  30  and used by the controller to control operation of implantable pump  20 . As described in further detail below, controller  30  directs implantable pump  20  to operate at specific parameters determined by programmer  50 . Programmer  50  preferably is coupled to controller  30  via cable  51  only when the operational parameters of the implantable pump are initially set or periodically adjusted, e.g., when the patient visits the clinician. 
     In accordance with another aspect of the invention, mobile device  60 , which may a conventional smartphone, may include an application program for bi-directionally and wirelessly communicating with controller  30 , e.g., via WiFi or Bluetooth communications. The application program on mobile device  60  may be programmed to permit the patient to send instructions to controller to modify or adjust a limited number of operational parameters of implantable pump  20  stored in controller  30 . Alternatively or in addition, mobile device  60  may be programmed to receive from controller  30  and to display on screen  61  of mobile device  60 , data relating to operation of implantable pump  20  or alert or status messages generated by controller  30 . 
     With respect to  FIGS. 3A and 3B , controller  30  is described in greater detail. As depicted in  FIG. 1 , controller  30  may be sized and configured to be worn on the exterior of the patient&#39;s body and may be incorporated into a garment such as a belt or a vest. Controller  30  includes input port  31 , battery port  32 , output port  33 , indicator lights  34 , display  35 , status lights  36  and buttons  37 . 
     Input port  31  is configured to periodically and removably accept cable  51  to establish an electrical connection between programmer  50  and controller  30 , e.g., via a USB connection. In this manner, a clinician may couple to controller  30  to set or adjust operational parameters stored in controller  30  for controlling operation of implantable pump. In addition, when programmer  50  is coupled to controller  30 , the clinician also may download from controller  30  data relating to operation of the implantable pump, such as actuation statistics, for processing and presentation on display  55  of programmer  50 . Alternatively, or in addition, controller  30  may include a wireless transceiver for wirelessly communicating such information with programmer  50 . In this alternative embodiment, wireless communications between controller  30  and programmer  50  may be encrypted with an encryption key associated with a unique identification number of the controller, such as a serial number. 
     Battery port  32  is configured to removably accept cable  41 , illustratively shown in  FIG. 1  as integrated with belt  42 , so that cable  41  routed through the belt and extends around the patient&#39;s back until it couples to controller  30 . In this manner, battery  40  may be removed from belt  42  and disconnected from controller  30  to enable the patient to periodically replace the battery with a fully charged battery. It is expected that the patient will have available to him or her at least two batteries, so that while one battery is coupled to controller  30  to energize the controller and implantable pump, the other battery may be connected to a recharging station. Alternatively, or in addition, battery port  32  may be configured to accept a cable that is coupled directly to a power supply, such a substantially larger battery/charger combination that permits the patient to remove battery  40  while lying supine in a bed, e.g., to sleep. 
     Output port  33  is electrically coupled to cable  29 , which in turn is coupled to implantable pump  20  through electrical conduit  28  of pump housing  27 . Cable  29  provides both energy to energize implantable pump  20  in accordance with the configuration settings and operational parameters stored in controller  30 , and to receive data from sensors disposed in implantable pump  20 . In one embodiment, cable  29  may comprise an electrical cable having a biocompatible coating and is designed to extend transcutaneously. Cable  29  may be impregnated with pharmaceuticals to reduce the risk of infection, the transmission of potentially hazardous substances or to promote healing where it extends through the patient&#39;s skin. 
     As mentioned above, controller  30  may include indicator lights  34 , display  35 , status lights  36  and buttons  37 . Indicator lights  34  may visually display information relevant to operation of the system, such as the remaining life of battery  40 . Display  35  may be a digital liquid crystal display that displays real time pump performance data, physiological data of the patient, such as heart rate, or operational parameters of the implantable pump, such as the target pump pressure or flow rate, etc. When it is determined that certain parameter conditions exceed preprogrammed thresholds, an alarm may be sounded and an alert may be displayed on display  35 . Status lights  36  may comprise light emitting diodes (LEDs) that are turned on or off to indicate whether certain functionality of the controller or implantable pump is active. Buttons  37  may be used to wake up display  35 , to set or quiet alarms, etc. 
     With respect to  FIG. 3B , the components of the illustrative embodiment of controller  30  of  FIG. 3A  are described. In addition to the components of controller  30  described in connection with  FIG. 3A , controller  30  further includes microprocessor  38 , memory  39 , battery  43 , optional transceiver  44  and amplifier circuitry  45 . Microprocessor may be a general purpose microprocessor, for which programming to control operation of implantable pump  20  is stored in memory  39 . Memory  39  also may store configuration settings and operational parameters for implantable pump  20 . Battery  40  supplies power to controller  30  to provide continuity of operation when battery  40  is periodically swapped out. Optional transceiver  44  to facilitates wireless communication with programmer  50  and/or mobile device  60  via any of a number of well-known communications standards, including BLUETOOTH™, ZigBee, and/or any IEEE 802.11 wireless standard such as Wi-Fi or Wi-Fi Direct. Controller  30  further may include amplifier circuitry  45  for amplifying electrical signals transferred between controller  30  and implantable pump  20 . 
     Referring now to  FIG. 4 , battery  40  is described. Battery  40  provides power to implantable pump  20  and also may provide power to controller  30 . Battery  40  may consist of a single battery or a plurality of batteries disposed within a housing, and preferably is sized and configured to be worn on the exterior of the patient&#39;s body, such as on belt  42 . Battery life indicator  46  may be provided on the exterior of battery  40  to indicate the degree to the remaining charge of the battery. Cable  41  may have one end removably coupled to battery  40  and the other end removably coupled to battery port of controller  30  to supply power to energize implantable pump  20 . In one embodiment, battery  40  may be rechargeable using a separate charging station, as is known in the art of rechargeable batteries. Alternatively, or in addition, battery  40  may include port  47  which may be removably coupled to a transformer and cable to permit the battery to be recharged using a conventional residential power outlet, e.g., 120 V, 60 Hz AC power. 
     Referring now to  FIGS. 5A-5B , programmer  50  is described. Programmer  50  may be conventional laptop loaded with programmed software routines for configuring controller  30  and setting operational parameters that controller  30  uses to control operation of implantable pump  20 . As discussed above, programmer  50  typically is located in a clinician&#39;s office or hospital, and is coupled to controller  30  via cable  51  or wirelessly to initially set up controller  30 , and then periodically thereafter as required to adjust the operational parameters as may be needed. The operation parameters of controller  30  set using the programmed routines of programmer  50  may include but are not limited to applied voltage, pump frequency, pump amplitude, target flow rate, pulsatility, etc. When first implanted, the surgeon or clinician may use programmer  50  to communicate initial operating parameters to controller  30 . Following implantation, the patient periodically may return to the clinician&#39;s office for adjustments to the operational parameters which may again be made using programmer  50 . 
     Programmer  50  may be any type of conventional personal computer device such as a laptop or a tablet computer having touch screen capability. As illustrated in  FIG. 5B , programmer  50  preferably includes processor  52 , memory  53 , input/output device  54 , display  55 , battery  56  and communication unit  57 . Memory  53  may include the operating system for the programmer, as well as the programmed routines needed to communicate with controller  30 . Communication unit  57  may include any of a number of well-known communication protocols, such as BLUETOOTH™, ZigBee, and/or any IEEE 802.11 wireless standard such as Wi-Fi or Wi-Fi Direct. As illustrated in  FIG. 5A , the programmed routines used to program and communicate with controller  30  also may provide data for display on the screen of programmer  50  identifying operational parameters with which controller  30  controls implantable pump  20 . The programmed routines also may enable programmer  50  to download from controller  30  operational data or physiologic data communicated by the implantable pump and to display that information in real time while the programmer is coupled to the controller via a wired or wireless connection. The transferred data may then be processed and displayed on the screen of programmer  50 . 
     Referring now to  FIGS. 6 and 7 , a preferred embodiment of pump assembly  70  and implantable pump  20  are illustrated. However, it is understood that pump assemblies and implantable pumps, and components included therein, may have different shapes and sizes than those illustrated in  FIGS. 6 and 7  without departing from the invention described herein. As is illustrated in  FIG. 7 , pump assembly  70  is configured to fit within pump housing  27 . To fix pump assembly  70  within pump housing  27 , pump assembly  70  may include fixation ring  71 , which may extend from and around stator assembly  72 , and may be captured between upper housing portion  24  and lower housing portion  25  when the housing portions are assembled, as illustrated in  FIG. 7 . In this manner, stator assembly  72  may be suspended within the pump housing in close-fitting relation to the interior walls of the pump housing. Fixation ring  71  preferably is a rigid annular structure that is disposed concentrically around stator assembly  72 , having a larger diameter than stator assembly  72 . Fixation ring  71  may be rigidly coupled to stator assembly  72  via struts  73 . Struts  73  may create gap  74  between fixation ring  71  and stator assembly  72 , which preferably is about 0.05 mm at its most restricted point. 
     As shown in  FIG. 7 , pump assembly  70  may be disposed in pump housing  27  such that fixation ring  71  is captured on step  75  formed between upper housing portion  24  and lower housing portion  25 . In this manner, stator assembly  72  may be suspended within, and prevented from moving within, pump housing  27 . Pump housing  27  preferably is sized and configured to conform to pump assembly  70  such that, stator assembly  72  does not contact the interior of the pump housing at any location other than at fixation ring  71 . 
       FIG. 8  is an exploded view of implantable pump  20 , depicting the arrangement of the internal components of pump assembly  70  arranged between upper housing portion  24  and lower housing portion  25 . In particular, pump assembly  70  may comprise stator assembly  72 , magnetic ring assembly  76 , first electromagnetic coil  77 , second electromagnetic coil  78 , fixation ring  71 , first suspension ring  79 , second suspension ring  80 , posts  81  and membrane assembly  82 . Stator assembly  72  may comprise tapered section  83 , electromagnetic coil holder portions  84 ,  85  and  86 , and flanged portion  87 . Magnetic ring assembly  76  may comprise magnetic ring  88  and magnetic ring holder portions  89  and  90 . First and second electromagnetic coils  77  and  78 , together with electromagnetic coil holder portions  84 ,  85  and  86  may form electromagnet assembly  91 . Electromagnet assembly  91  together with stator assembly  72  form an actuator assembly. The actuator assembly together with magnetic ring assembly  76  in turn forms the actuator system of implantable pump  20 . 
     First electromagnetic coil  77  and second electromagnetic coil  78  may be concentrically sandwiched between electromagnetic coil holder portions  84 ,  85  and  86  to form electromagnet assembly  91 . Tapered section  83 , which may be coupled to fixation ring  71  and first suspension spring  79 , may be located concentrically atop electromagnet assembly  91 . Magnetic ring  88  may be disposed with magnetic ring holder portions  89  and  90  to form magnetic ring assembly  76 , which may be concentrically disposed for reciprocation over electromagnet assembly  91 . Second suspension ring  80  may be disposed concentrically beneath electromagnet assembly  91 . Flanged portion  87  may be concentrically disposed below second suspension ring  80 . Posts  81  may engage first suspension ring  79 , magnetic ring assembly  76  and second suspension ring  80  at equally spaced locations around the actuator assembly. Membrane assembly  82  may be positioned concentrically below flanged portion  87  and engaged with posts  81 . 
     Further details of pump assembly  70  are provided with respect to  FIG. 9 . Specifically, actuator assembly  95  comprises stator assembly  72  and electromagnet assembly  91 , including first and second electromagnetic coils  77  and  78 . During use of implantable pump  20 , actuator assembly  95  remains stationary relative to pump housing  27 . First electromagnetic coil  77  and second electromagnetic coil  78  may be separated by electromagnetic holder portion  85 . Controller  30  and battery  40  are electrically coupled to electromagnetic coils  77  and  78  via cable  29  that extends through electrical conduit  28  of pump housing  27  to supply current to electromagnetic coils  77  and  78 . First electromagnetic coil  77  and second electromagnetic coil  78  may be in electrical communication with one another or may be configured to operate independently and have separate wired connections to controller  30  and battery  40  via cable  29 . 
     Electromagnetic coils  77  and  78  may be made of any electrically conductive metallic material such as copper and further may comprise of one or more smaller metallic wires wound into a coil. The wires of the electromagnetic coils are insulated to prevent shorting to adjacent conductive material. Other components of pump assembly  70 , such as stator assembly  72 , preferably also are insulated and/or made of non-conductive material to reduce unwanted transmission of the electrical signal. 
     Actuator assembly  95  may be surrounded by first suspension ring  79  and second suspension ring  80 . Suspension rings  79  and  80  may be annular in shape and fit concentrically around actuator assembly  95 . First suspension ring  79  preferably is rigidly affixed to tapered section  83  near a top portion of stator assembly  72  via struts  73  extending from the suspension ring to the stator assembly. As discussed above, struts  73  may also affix fixation ring  71  to stator assembly  72 . Fixation ring  71  and first suspension spring  79  may be sized and positioned such that a gap of no less than 0.5 mm exists between first suspension ring  79  and fixation ring  71 . Second suspension ring  80  similarly may be rigidly affixed via struts near the bottom of stator assembly  72 , below electromagnet assembly  91 . Suspension rings  79  and  80  preferably are sized and shaped such that when suspension rings  79  and  80  are positioned surrounding actuator assembly  95 , a gap of no less than 0.5 mm exists between actuator assembly  95  and suspension rings  79  and  80 . 
     First suspension ring  79  and second suspension ring  80  may comprise stainless steel having elastic properties and which exhibits a spring force when deflected in a direction normal to the plane of the spring. First suspension ring  79  and second suspension ring  80  may be substantially rigid with respect to forces applied tangential to the suspension ring. In this manner, first suspension ring  79  and second suspension ring  80  may exhibit a spring tension when deformed up and down relative to a vertical axis of the actuator assembly but may rigidly resist movement along any other axis, e.g., tilt or twist movements. 
     Magnetic ring assembly  76  may be annular in shape and concentrically surrounds actuator assembly  95 . Magnetic ring  88  may comprise one or more materials exhibiting magnetic properties such as iron, nickel, cobalt or various alloys. Magnetic ring  88  may be made of a single unitary component or comprise several magnetic components that are coupled together. Magnetic ring assembly  76  may be sized and shaped such that when it is positioned concentrically over actuator assembly  95 , a gap of no less than 0.5 mm exists between an outer lateral surface of actuator assembly  95  and an interior surface of magnetic ring assembly  76 . 
     Magnetic ring assembly  76  may be concentrically positioned around actuator assembly  95  between first suspension ring  79  and second suspension ring  80 , and may be rigidly coupled to first suspension ring  79  and second suspension ring  80 . Magnetic ring assembly  76  may be rigidly coupled to the suspension rings by more than one post  81  spaced evenly around actuator assembly  95  and configured to extend parallel to a central axis of pump assembly  70 . Suspension rings  79  and  80  and magnetic ring assembly  76  may be engaged such that magnetic ring assembly  76  is suspended equidistant between first electromagnetic coil  77  and second electromagnetic coil  78  when the suspension rings are in their non-deflected shapes. Each of suspension rings  79  and  80  and magnetic ring holder portions  89  and  90  may include post receiving regions for engaging with posts  81  or may be affixed to posts  81  in any suitable manner that causes suspension rings  79  and  80  and magnetic ring assembly  76  to be rigidly affixed to posts  81 . Posts  81  may extend beyond suspension rings  79  and  80  to engage other components, such as flanged portion  87  and membrane assembly  82 . 
     First electromagnetic coil  77  may be activated by controller applying an electrical signal from battery  40  to first electromagnetic coil  77 , thus inducing current in the electromagnetic coil and generating a magnetic field surrounding electromagnetic coil  77 . The direction of the current in electromagnetic coil  77  and the polarity of magnetic ring assembly  76  nearest electromagnetic coil  77  may be configured such that the first electromagnetic coil magnetically attracts or repeals magnetic ring assembly  76  as desired. Similarly, a magnetic field may be created in second electromagnetic coil  78  by introducing a current in the second electromagnetic coil. The direction of the current in second electromagnetic coil  78  and the polarity of magnetic ring assembly  76  nearest the second electromagnetic coil also may be similarly configured so that first electromagnetic coil  77  magnetically attracts or repels magnetic ring assembly  76  when an appropriate current is induced in second electromagnetic coil  78 . 
     Because magnetic ring assembly  76  may be rigidly affixed to posts  81 , which in turn may be rigidly affixed to first suspension ring  79  and second suspension ring  80 , the elastic properties of the suspension rings permit magnetic ring assembly  76  to move up towards first electromagnetic coil  77  or downward toward second electromagnetic coil  78 , depending upon the polarity of magnetic fields generated by the electromagnetic rings. In this manner, when magnetic ring assembly  76  experiences an upward magnetic force, magnetic ring assembly  76  deflects upward towards first electromagnetic coil  77 . As posts  81  move upward with magnetic ring assembly  76 , posts  81  cause the suspensions rings  79  and  80  to elastically deform, which creates a spring force opposite to the direction of movement. When the magnetic field generated by the first electromagnetic coil collapses, when the electrical current ceases, this downward spring force causes the magnetic ring assembly to return to its neutral position. Similarly, when magnetic ring assembly  76  is magnetically attracted downward, magnetic ring assembly  76  deflects downward towards second electromagnetic ring  78 . As posts  81  move downward with magnetic ring assembly  76 , posts  81  impose an elastic deformation of the first and second suspension rings, thus generating a spring force in the opposite direction. When the magnetic field generated by the second electromagnetic ring collapses, when the electrical current ceases, this upward spring force causes the magnetic ring assembly to again return to its neutral position. 
     Electromagnetic coils  77  and  78  may be energized separately, or alternatively, may be connected in series to cause the electromagnetic coils to be activated simultaneously. In this configuration, first magnetic coil may be configured to experience a current flow direction opposite that of the second electromagnetic coil. Accordingly, when current is induced to first electromagnetic coil  77  to attract magnetic ring assembly  76 , the same current is applied to second electromagnetic coil  78  to induce a current that causes second electromagnetic coil  78  to repel magnetic ring assembly  76 . Similarly, when current is induced to second electromagnetic coil  78  to attract magnetic ring assembly  76 , the current applied to first electromagnetic coil  77  causes the first electromagnetic coil to repel magnetic ring assembly  76 . In this manner, electromagnetic coils  77  and  78  work together to cause deflection of magnetic ring assembly  76 . 
     By manipulating the timing and intensity of the electrical signals applied to the electromagnetic coils, the frequency at which magnetic ring assembly  76  deflects towards the first and second electromagnetic coils may be altered. For example, by alternating the current induced in the electromagnetic coils more frequently, the magnetic ring assembly may be caused to cycle up and down more times in a given period. By increasing the amount of current, the magnetic ring assembly may be deflected at a faster rate and caused to travel longer distances. 
     Alternatively, first electromagnetic coil  77  and second electromagnetic coil  78  may be energized independently. For example, first electromagnetic coil  77  and second electromagnetic coil  78  may be energized at varying intensities; one may be coordinated to decrease intensity as the other increases intensity. In this manner, intensity of the signal applied to second electromagnetic coil  78  to cause downward magnetic attraction may simultaneously be increased as the intensity of the signal applied to first electromagnetic coil  77  causes an upward magnetic attraction that decreases. 
     In accordance with one aspect of the invention, movements of magnetic ring assembly  76  may be translated to membrane assembly  82  which may be disposed concentrically below stator assembly  72 . Membrane assembly  82  preferably is rigidly attached to magnetic ring assembly  76  by posts  81 . In the embodiment depicted in  FIG. 9 , posts  81  may extend beyond second suspension ring  80  and coupled to membrane assembly  82 . 
     Referring now to  FIG. 10 , one embodiment of membrane assembly  82  is described in greater detail. Membrane assembly  82  may comprise rigid membrane ring  96  and membrane  97 . Rigid membrane ring  96  exhibits rigid properties under typical forces experienced during the full range of operation of the present invention. Post reception sites  98  may be formed into rigid membrane ring  96  to engage membrane assembly  82  with posts  81 . Alternatively, posts  81  may be attached to rigid membrane ring  96  in any other way which directly translates the motion of magnetic ring assembly  76  to rigid membrane ring  96 . Rigid membrane ring  96  may be affixed to membrane  97  and hold the membrane in tension. Membrane  97  may be molded directly onto rigid membrane ring  96  or may be affixed to rigid membrane ring  96  in any way that holds membrane  97  uniformly in tension along its circumference. Membrane  97  alternatively may include a flexible pleated structure where it attaches to rigid membrane ring  96  to increase the ability of the membrane to move where the membrane is affixed to rigid membrane ring  96 . Membrane  97  may further include circular aperture  99  disposed in the center of the membrane. 
     In a preferred embodiment, membrane  97  has a thin, planar shape and is made of an elastomer having elastic properties and good durability. Alternatively, membrane  97  may have a uniform thickness from the membrane ring to the circular aperture. As a yet further alternative, membrane  97  may vary in thickness and exhibit more complex geometries. For example, as shown in  FIG. 10 , membrane  97  may have a reduced thickness as the membrane extends from rigid membrane ring  96  to circular aperture  99 . Alternatively, or in addition to, membrane  97  may incorporate metallic elements such as a spiral spring to enhance the spring force of the membrane in a direction normal to plane of the membrane, and this spring force may vary radially along the membrane. In yet another embodiment, membrane  97  may be pre-formed with an undulating shape. 
       FIG. 11  depicts moving portions of the embodiment of pump assembly  70  shown in  FIGS. 6-9  as non-grayed out elements. Non-moving portions of the pump assembly, including actuator assembly  95  and electromagnet assembly  91  (partially shown) may be fixed to pump housing  27  by fixation ring  71 . Moving portions of pump assembly  70  may include posts  81 , first suspension spring  79 , magnetic ring assembly  76 , second suspension spring  80  and membrane assembly  82 . As magnetic ring assembly  76  moves up and down, the movement is rigidly translated by posts  81  to membrane assembly  82 . Given the rigidity of the posts, when magnetic ring assembly  76  travels a certain distance upward or downward, membrane assembly  82  may travel the same distance. For example, when magnetic ring assembly  76  travels 4 mm from a position near first electromagnetic coil  77  to a position near second electromagnetic coil  78 , membrane assembly  82  may also travel 4 mm in the same direction. Similarly, the frequency at which magnetic ring assembly  76  traverses the space between the first and second electromagnetic coils may be the same frequency at which membrane assembly  82  travels the same distance. 
     Referring now to  FIG. 12 , in the embodiment of implantable pump  20  described in  FIGS. 6-9 , blood may enter implantable pump  20  from the left ventricle through inlet cannula  21  and flow downward along pump assembly  70  into delivery channel  100 , defined by the interior surface of pump housing  27  and exterior of pump assembly  70 . Delivery channel  100  begins at the top of stator assembly  72  and extends between tapered section  83  and the interior of pump housing  27 . As the blood moves down tapered section  83 , it is directed through gap  74  and into a vertical portion of delivery channel  100  in the area between pump housing  27  and actuator assembly  95 , and including in the gap between magnetic ring assembly  76  and electromagnet assembly  91 . Delivery channel  100  extends down to flanged portion  87  of stator assembly  72 , which routes blood into flow channel  101 , within which membrane assembly  82  is suspended. By directing blood from inlet cannula  21  through delivery channel  100  to flow channel  101 , delivery channel  100  delivers blood to membrane assembly  82 . By actuating electromagnetic coils  77  and  78 , membrane  97  may be undulated within flow channel  101  to induce wavelike formations in membrane  97  that move from the edge of the membrane towards circular aperture  99 . Accordingly, when blood is delivered to membrane assembly  82  from delivery channel  100 , it may be propelled radially along both the top and bottom of membrane  97  towards circular aperture  99 , and from there out of outlet  23 . 
     In accordance with one aspect of the present invention, the undulating membrane pump described herein avoids thrombus formation by placing all moving parts directly within the primary flow path, thereby reducing the risk of flow stagnation. Specifically, the moving components depicted in  FIG. 11 , including magnetic ring assembly  76 , suspension rings  79  and  80 , posts  81  and membrane assembly  82  all are located within delivery channel  100  and flow channel  101 . Flow stagnation may further be avoided by eliminating secondary flow paths that may experience significantly slower flow rates. 
     Turning now to  FIGS. 13 and 14 , a lower portion of implantable pump  20 , including flanged portion  87 , membrane assembly  82  and lower housing portion  23  is shown. Delivery channel  100  may be in fluid communication with membrane assembly  82  and flow channel  101  which is defined by a bottom surface of flanged portion  87  and the interior surface of lower housing portion  25 . Flanged portion  87  may comprise feature  102  that extends downward as the bottom of flanged portion  87  moves radially inward. The interior surface of lower housing portion  25  may also slope upward as it extends radially inward. The combination of the upward slope of the interior surface of lower housing portion  25  and the bottom surface of flanged portion  87  moving downward narrows flow channel  101  as the channel moves radially inwards from delivery channel  100  to circular aperture  99  of membrane  97 , which is disposed about pump outlet  23 . 
     As explained above, membrane assembly  82  may be suspended by posts  81  within flow channel  101  below the bottom surface of flanged portion  87  and above the interior surface of lower housing portion  25 . Membrane assembly  82  may be free to move up and down in the vertical direction within flow channel  101 , which movement is constrained only by suspension rings  79  and  80 . Membrane assembly  82  may be constrained from twisting, tilting or moving in any direction in flow channel  101  other than up and down by rigid posts  81  and by the suspension rings. 
     Flow channel  101  is divided by membrane  97  into an upper flow channel and a lower flow channel by membrane  97 . The geometry of membrane  97  may be angled such that when membrane assembly  82  is at rest, the top surface of membrane  97  is parallel to the bottom surface of flanged portion  87  and the bottom surface of membrane  97  is parallel to the opposing surface of lower housing portion  25 . Alternatively, membrane  97  may be sized and shaped such that when membrane assembly  82  is at rest, the upper and lower flow channels narrow as they move radially inward from delivery channel  100  to circular aperture  99  in membrane  97 . 
     Referring now also to  FIG. 14 , as rigid membrane ring  96  is caused by posts  81  to move up and down in flow channel  101 , the outermost portion of membrane  97  nearest rigid membrane ring  96 , moves up and down with rigid membrane ring  96 . Membrane  97 , being flexible and having elastic properties, gradually translates the up and down movement of the membrane portion nearest rigid membrane ring  96  along membrane  97  towards circular aperture  99 . This movement across flexible membrane  97  causes wavelike deformations in the membrane which may propagate inwards from rigid membrane ring  96  towards aperture  99 . 
     The waves formed in the undulating membrane may be manipulated by changing the speed at which rigid membrane ring  96  moves up and down as well as the distance rigid membrane ring  96  moves up and down. As explained above, the amplitude and frequency at which rigid membrane ring  96  moves up and down is determined by the amplitude and frequency at which magnetic ring assembly  76  reciprocates over electromagnet assembly  91  Accordingly, the waves formed in the undulating membrane may be adjusted by changing the frequency and amplitude at which magnetic ring assembly  76  is reciprocated. 
     When blood is introduced into flow channel  101  from delivery channel  100 , the undulations in membrane  97  cause blood to be propelled toward circular aperture  99  and out of pump housing  27  via outlet  23 . The transfer of energy from the membrane to the blood is directed radially inward along the length of the membrane towards aperture  99 , and propels the blood along the flow channel towards outlet  23  along both sides of membrane  97 . 
       FIG. 15  shows that when rigid membrane ring  96  moves downward in unison with magnetic ring assembly  76 , the upper portion of flow channel  101  near delivery channel  100  expands, causing blood from delivery channel  100  to fill the upper portion of the flow channel near the outer region of membrane  97 . As rigid membrane ring  96  moves upward, the upper portion of flow channel  101  begins to narrow near rigid membrane ring  96 , causing wave-like deformations to translate across the membrane. As the wave propagates across membrane  97 , blood in the upper portion of flow channel  101  is propelled towards circular aperture and ultimately out of pump housing  27  through outlet  23 . Simultaneously, as rigid membrane ring  96  moves upwards, the lower portion of flow channel  101  nearest the outer portion of membrane  97  begins to enlarge, allowing blood from delivery channel  100  to flow into this region. Subsequently, when rigid membrane ring  96  is again thrust downwards, the region of lower portion of flow channel  101  nearest outer portion of membrane  97  begins to narrow, causing wave-like deformations to translate across the membrane that propel blood towards outlet  23 . 
     By manipulating the waves formed in the undulating membrane by changing the frequency and amplitude at which magnetic ring assembly  76  moves up and down, the pressure gradient within flow channel  101  and ultimately the flow rate of the blood moving through flow channel  101  may be adjusted. Appropriately controlling the movement of magnetic ring assembly  76  permits oxygen-rich blood to be effectively and safely pumped from the left ventricle to the aorta and throughout the body as needed. 
     In addition to merely pumping blood from the left ventricle to the aorta, implantable pump  20  of the present invention may be operated to closely mimic physiologic pulsatility, without loss of pump efficiency. In the embodiment detailed above, pulsatility may be achieved nearly instantaneously by changing the frequency and amplitude at which magnetic ring assembly  76  moves, to create a desired flow output, or by ceasing movement of the magnetic ring assembly for a period time to create a period of low or no flow output. Unlike typical rotary pumps, which require a certain period of time to attain a set number of rotations per minute to achieve a desired fluid displacement and pulsatility, implantable pump  20  may achieve a desired flow output nearly instantaneously and similarly may cease output nearly instantaneously due to the very low inertia generated by the small moving mass of the moving components of the pump assembly. The ability to start and stop on-demand permits rapid changes in pressure and flow. Along with the frequency and amplitude, the duty cycle, defined by the percentage of time membrane  97  is excited over a set period of time, may be adjusted to achieve a desired flow output and pulsatility, without loss of pump efficiency. Even holding frequency and amplitude constant, flow rate may be altered by manipulating the duty cycle between 0 and 100%. 
     In accordance with another aspect of the invention, controller  30  may be programmed by programmer  50  to operate at selected frequencies, amplitudes and duty cycles to achieve a wide range of physiologic flow rates and with physiologic pulsatilities. For example, programmer  50  may direct controller  30  to operate implantable pump  20  at a given frequency, amplitude and/or duty cycle during a period of time when a patient is typically sleeping and may direct controller  30  to operate implantable pump  20  at a different frequency, amplitude and or duty cycle during time periods when the patient is typically awake. Controller  30  or implantable pump also may include an accelerometer or position indicator to determine whether the patient is supine or ambulatory, the output of which may be used to move from one set of pump operating parameters to another. When the patient experiences certain discomfort or a physician determines that the parameters are not optimized, physician may alter one or more of at least frequency, amplitude and duty cycle to achieve the desired functionality. Alternatively, controller  30  or mobile device  60  may be configured to alter one or more of frequency, amplitude and duty cycle to suit the patient&#39;s needs. 
     Implantable pump  20  further may comprise one or more additional sensors for adjusting flow output and pulsatility according to the demand of the patient. Sensors may be incorporated into implantable pump  20  or alternatively or in addition to may be implanted elsewhere in or on the patient. The sensors preferably are in electrical communication with controller  30 , and may monitor operational parameters that measure the performance of implantable pump  20  or physiological sensors that measure physiological parameters of the patients such as heart rate or blood pressure. By using one or more physiological sensors, pulsatile flow may be synchronized with a cardiac cycle of the patient by monitoring blood pressure or muscle contractions, for example, and synchronizing the duty cycle according to the sensed output. 
     Controller  30  may compare physiological sensor measurements to current implantable pump output. If it is determined by analyzing sensor measurements that demand exceeds current output, frequency, amplitude and/or duty cycle may be automatically adjusted to meet current demand. Similarly, the controller may determine that current output exceeds demand and thus alter output by changing frequency, amplitude and/or duty cycle. Alternatively, or in addition to, when it is determined that demand exceeds current output, an alarm may sound from controller  30 . Similarly, operational measurements from operational sensors may be compared against predetermined thresholds and where measurements exceed predetermined thresholds or a malfunction is detected, an alarm may sound from controller  30 . 
     Implantable pump  20  is sized and shaped to produce physiological flow rates, pressure gradients and pulsatility at an operating point at which maximum efficiency is achieved. Specially, implantable pump  20  may be sized and shaped to produce physiological flow rates ranging from 4 to 6 liters per minute at pressure gradients lower than a threshold value associated with hemolysis. Also, to mimic a typical physiological pulse of 60 beats per minute, implantable pump  20  may pulse about once per second. To achieve such pulsatility, a duty cycle of 50% may be utilized with an “on” period of 0.5 seconds and an “off” period of 0.5 seconds. For a given system, maximum efficiency at a specific operating frequency, amplitude and voltage may be achieved while producing a flow rate of 4 to 6 liters per minute at a duty cycle of 50% by manipulating one or more of the shape and size of blood flow channels, elastic properties of the suspension rings, mass of the moving parts, membrane geometries, and elastic properties and friction properties of the membrane. In this manner, implantable pump  20  may be designed to produce desirable physiological outputs while continuing to function at optimum operating parameters. 
     By adjusting the duty cycle, implantable pump  20  may be configured to generate a wide range of output flows at physiological pressure gradients. For example, for an exemplary LVAD system configured to produce 4 to 6 liters per minute at a duty cycle of 50%, optimal operating frequency may be 120 Hz. For this system, flow output may be increased to 10 liters per minute or decreased to 4 liters per minute, for example, by changing only the duty cycle. As duty cycle and frequency operate independent of one another, duty cycle may be manipulated between 0 and 100% while leaving the frequency of 120 Hz unaffected. 
     The implantable pump system described herein, tuned to achieve physiological flow rates, pressure gradients and pulsatility, also avoids hemolysis and platelet activation by applying low to moderate shear forces on the blood, similar to those exerted by a healthy heart. The moving components are rigidly affixed to one another and do not incorporate any parts that would induce friction, such as mechanical bearings or gears. In the embodiment detailed above, delivery channel  100  may be sized and configured to also avoid friction between moving magnetic ring assembly  76 , suspension rings  79  and  80 , posts  81  and lower housing portion  25  by sizing the channel such that clearances of at least 0.5 mm are maintained between all moving components. Similarly, magnetic ring assembly  76 , suspension rings  79  and  80 , and posts  81  all may be offset from stator assembly  72  by at least 0.5 mm to avoid friction between the stator assembly and the moving parts. 
     While various illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. For example, pump assembly  70  shown in  FIG. 9  may be ordered differently and may include additional or fewer components of various sizes and composition. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.