Pressure defined electromagnetic pulsatile pump

Abstract

A pump includes: a first pump body defining a first flow path; a first inlet check valve at an upstream end of the first flow path; a first outlet check valve at a downstream end of the first flow path; a first compressible container in flow communication with the flow path between the upstream and downstream ends; a first electromagnetic linear motor connected to the first compressible container such that extension of the first linear motor causes compression of the first compressible container; and an electronic controller configured supply a varying voltage or current to the first linear motor so as to provide a pulsatile flow at a controlled pressure and controlled pulse rate, where the pressure is independent of downstream flow resistance.

Description

PRESSURE DEFINED ELECTROMAGNETIC PULSATILE PUMPBACKGROUND

[0001] The present invention relates to pumps, and more particularly to pumps having a controlled pressure output.

[0002] Roller pump systems

[0003] Commercial organ transplant systems generally use roller pumps (also referred to as peristaltic pumps) primarily to provide motive force, but also to provide some pulsatility that, to a limited extent, emulates the cardiovascular waveform. A closed- loop control system typically adjusts the pressure going into the organ by adjusting the pump speed. Additional devices may be present to provide capacitance to the fluid system to dampen out pulse severity. While this system is fairly simple and economical, the pump speed control is a fairly crude tool that may work acceptably for normal or healthy organs, but could cause over pressure damage to capillaries if the resistance of the organ were to change. It also provides poor control for very small organs or organs with low flow acceptance. It does not provide for independent control of pulsation rate and flow rate. When the maximum tolerable systolic pressure is exceeded, damage or breakage of the capillary walls can occur. Even with pressure monitoring from a pressure sensor located at the organ, severely coagulated organs or very small organs can be a challenge to control the pump speed (with or without fluid bypasses) in such a way to avoid damage to the organ.

[0004] Centrifugal pump systems

[0005] Centrifugal pump systems such as MEDTRONIX or LEVITRONIX are popular for pumping blood in certain medical procedures such as organ transplant. However, these systems are not normally outfitted with systems for generating pulsatile waveforms and they generally provide constant flow rate or pressure during the procedure. Constant pressure flow does a poor job of emulating the pulsatile flow of human or animal hearts, w hich can result in capillary coagulation or blockage over time as pulsation is advantageous for red blood cells to pass through small capillaries.

[0006] Pressure regulator systems

[0007] Also known are systems that demonstrate improved organ performance when utilizing a combination of a centrifugal pump and an electronically piloted back pressure regulator ("BPR") system. The BPR system consists of an electronic pressure regulator (EPR) to generate a pulsatile air pressure signal. This signal is provided to a direct diaphragm sealing, multiple-onfice back pressure regulator (see for example U.S. Pat 8,329,450 for METHODS AND APPARATUS FOR ORGAN SUPPORT issued to BIOMEDINNOVATIONS of Denver, NC). In such systems, a constant flow pump such as the centrifugal examples mentioned below are used to generate an excess flow rate. The combination of an electronic pressure regulator ("EPR") and BPR are used to precisely circulate all additional fluid back to the pump supply system, thereby creating a pulsatile waveform that never exceeds the maximum pressure target. These systems provide exemplary performance yet require a number of separate components which make the system inconvenient for mobile use. For example, this system requires an air compressor, an EPR. the BPR. and a pump to generate the pressure waveform. A wetted pressure sensor may be desired to verify and adapt the EPR setpoint as well.

[0008] Despite the prior art devices described above, there remains a need for a pressure defined pump which will generate a pulsatile pressure wave similar to a human or animal heart, without exceeding the target pressure, regardless of downstream fluid conductance (inverse of flow resistance). Such a pumping device would simplify the prior art systems by:

[0009] 1) Providing precision pressure control to precisely and robustly avoid excess pressure thereby avoiding capillary damage for small and unhealthy organs (compared to roller pump systems).

[0010] 2) Providing precise pulsatile waveforms (compared to centrifugal systems).

[0011] 3) Eliminating several components required for pressure regulator systems.SUMMARY

[0012] A novel pumping mechanism is described to provide pressure-defined pulsatile flow for medical applications. The motive force is defined by a linear force from an electromagnetic device such as a linear motor. A compressible container such as a bellows translates the force into a pressure. Inlet and outlet check valves translate the pulsatile pressure into pulsatile flow, similar to heart check valves.BRIEF DESCRIPTION OF THE DRAWINGS

[0001] The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:

[0002] FIG. 1 is a schematic diagram of a pulsatile pump connected to a fluid system;

[0001] FIG. 2 is a graph showing a defined pressure pulse that is found directly at the exit of the heart;

[0003] FIG. 3 is graph showing a more damped pressure pulse that an organ may receive depending on the location of the organ in the body;

[0004] FIG. 4 is graph showing applied voltage and resulting pressure waveform at the application in psi;

[0005] FIG. 5 is graph showing applied voltage and resulting pressure waveform at the application in psi, where the rising wave is clipped with an angular feature, which is a very effective way of eliminating or reducing the inertial overshoot that can occur;

[0006] FIG. 6 is graph showing applied voltage and resulting pressure waveform at the application in psi, shows an exponential rise at constant voltage that is due to the compressible container moving and the solenoid core becoming closer to its "choke" location. As the core approaches the choke location the force increases exponentially (inversely exponential to the distance);

[0007] FIG. 7 is graph showing applied voltage and resulting pressure waveform at the application in psi, In FIG. 7. the hydraulic disruptions after the wave wereminimized by a combination of gentler down slope, and also inclusion of supply line resistance (upstream of the inlet check valve);

[0008] FIG. 8 shows a typical electromagnetic solenoid curve, with the inverse exponential drop-off in force with displacement (stroke);

[0009] FIG. 9 shows a typical improved force / displacement curve from a speaker coil linear motor (SCLM); and

[0010] FIG. 10 is a schematic diagram of an alternative pulsatile pump connected to a fluid system.DETAILED DESCRIPTION

[0013] Described herein is a linear motor driven pressure pump. A preferred embodiment includes a control system that monitors the pressure produced at an application and adapts through one of several control strategies to provide a desired pressure-defined waveform.

[0014] Definitions

[0015] "Linear motor": this term refers to an electromagnetic device that generates linear force from varying electrical current. Any linear force generator using electromagnetic force may be used. Preferred examples include speaker coil linear motors ("SCLM") and electromagnetic solenoids. SCLM devices provide much more linear force versus displacement characteristics, and are a preferred example. For definitional purposes, a SCLM is defined as a linear motor that includes both an electromagnetic coil and a permanent magnet. Alternatively, linear solenoids (containing no permanent magnets) are more economical and other suitable examples may utilize solenoids and compensate for the variance in force / displacement / (ampere- tum) in other ways. Examples of such compensation may include carefully selected springs, displacement monitoring to compensate for the variations in force / displacement, and feedback control mechanisms that can learn and adapt by observing the pressure curve (including machine learning).

[0016] "Compressible container": this term refers to a fluid container which translates an external force into fluid pressure. Preferably the compressible container may be a bellows having a pleated structure, but also may be a simple deformable container such as tubing or an enclosure bounded by an elastomeric material such as silicone. Another example of a compressible container is a cavity enclosed by a flexible diaphragm, such as is provided in a diaphragm pump. All similar geometries will be described as a "compressible container" for simplicity.

[0017] "Check valve": this term refers a means to permit fluid flow in one direction and to prevent back flow. Diaphragm type check or "duck bill" type check valves or other designs with very little pressure drop are preferred. Ball or poppet type check valves will also suffice. It is preferred that the selected check valve have a cracking pressure (opening differential pressure) < 0.5 psig (and highly preferred < 0.25 psi). The force of a linear motor or solenoid is related to the current flowing in it. While it is possible to control current directly, it is easier to control current in a winding by varying the voltage across it. With each reference to controlling voltage, it should be understood that this is a practical analog for current.

[0018] An example system 10 incorporating a pulsatile pump 12 is shown in FIG. 1. The reservoir 14 contains a fluid "F". The reservoir 14 is located upstream of the pump 12. The reservoir 14 may be positioned at a higher elevation than the pump 12 in order to provide a gravity7head for the fluid F. The pump 12 includes a pump body 16 defining a flow path 18 extending between an upstream end 20 and a downstream end 22. An inlet check valve 24 is positioned at the upstream end 20 of the flow path 18. An outlet check valve 26 is positioned at the downstream end 22 of the flow path 18. A compressible container 28 is disposed in flow communication with the flow path 18 between the upstream and downstream ends 20, 22. In the illustrated example, the compressible container 28 is a bellows formed with a number of pleats 29. The Shore D polymer construction offers variable force resistance as the pleats are compressed. An electromagnetic linear motor 30 is connected to the compressible container 28 such that extension of the linear motor 30 (i.e. upwards motion of a push rod or other movable portion as depicted in FIG. 1) causes compression of the compressible container 28.

[0019] An application "A", for example an animal organ to be perfused with fluid F, is positioned downstream of the pump 12. An appropriate flow path is defined from the reservoir 14 through the pump 12 and the application A. For example, flexible tubing may be used to interconnect the various components for this purpose. An outlet line 32 extends downstream of the application A. Fluid exiting the outlet line 32 may be discarded, collected in a container (not shown), or recirculated back into the reservoir 14.

[0020] One or more sensors are provided to measure physical parameters of the system 10 and generate a signal representative thereof. The illustrated example, a pressure transducer 34 is configured to measure a fluid pressure in the flow path downstream of the pump 12 and upstream of the application A.

[0021] An electronic controller 36 is provided. This is operable to receive one or more inputs, such as a pressure signal from pressure transducer 34, and provide variable voltage or current to the linear motor 30.

[0022] In operation, the linear motor 30 applies force to the compressible container 28, which translates the force into fluid pressure. A complexity is that the position of the linear motor actuator 30 also affects the force generated for a given current. Therefore, the linear motor performance can be modelled by a three-variable relationship between force, current, and position.

[0023] The compressible container 28 is connected to the inlet and outlet check valves 24, 26 such as in commercial diaphragm pumps (and in one chamber of the heart) to produce the pressure-defined motive pumping force.

[0024] For a given range of positions, pressure generated is approximately proportional to the electrical current provided to the linear motor 30. As current is approximately proportional to voltage according to the resistance of the windings (though resistance relationship varies with temperature), it is possible to utilize a voltage controller as a means to approximate force.

[0025] Therefore, a simple system is given by providing a voltage wave (which results in a current wave according to the inductance / resistance of the coil) in order to provide the required pressure wave.

[0026] Adaptive feedback control

[0027] A preferred embodiment includes pressure sensor 34 and provides adaptation of subsequent current waveforms based on analysis of the error waveform (whereas the error waveform is the difference between actual and ideal waveform).

[0028] Inadequate systolic pressure would be addressed in subsequent waveforms by increasing the maximum power to the linear motor 30.

[0029] Excessive overshoot would be compensated by increasing the smoothing, clipping, or damping of the power waveform change, or by creating a multiple step waveform move which compensates for the inertial effect, then moves to the full step after the inertial effect subsides.

[0030] Thie system and method described herein is capable of controlling the application or organ pressure precisely, independent of pulse rate, also through a wide range of organ conductance, such that a functioning system can accommodate a large variance in organ flow rate (such as 5: 1 or 10: 1) in real time while maintaining a controlled pressure and a controlled pulse rate. Such robust performance makes the system also useful for a wide variety of organs and organ sizes.

[0031] The inventive system is able to provide controlled pressure independent of organ flow rate acceptance (conductance) because the linear motor is controlled with an algorithm that compresses the compressible container with a force required to produce the desired pressure. If the organ or application conductance drops unexpectedly, the system has no expectations of linear motor stroke distance and continues its pressure cycles regardless of stroke movement. Depending on the embodiment utilized, any secondary or tertian’ effects on pressure from a flow excursion would be very minor and very short lived. The real-time control systemembodiment would have virtually no impact due to the inherent nature of high-speed closed-loop pressure control systems.

[0032] Most prior art systems discussed above do not exhibit this level of independence between application flow rate and other key variables such as pulse rate. For example, a prominent organ perfusion system uses a peristaltic pump (buffered by a bellows) along with motor speed controlled to keep the pressure in proper range. Such a system can accommodate varying flow rates, but pulse rate is affected, and such an approach is inherently less robust to unexpected changes in conditions. Other commercial systems using linear motors for ventrical assist devices also focus on controlling flow with pressure established boundaries. While the centrifugal pump with pressure regulator approach also excels at flow rate independence, this invention seeks to reproduce that performance in a more economical and / or mobile format.

[0033] Sources of variability that contnbute to the error waveform:

[0034] - Inertia effects of the mechanism will alter the pulsatile waveform.

[0035] - Fluid inertial effects can cause issues if there is a rapid change in velocity.

[0036] - Changes in organ resistance.

[0037] - Location and length of tubing to the organ.

[0038] - The pressure sensor 34 may optionally be located very close to the organ, allowing for the pump 12 to be located some distance away.

[0039] - Viscosity changes in the fluid.

[0040] - Changes in pressure head of the fluid coming into the inlet check valve 24.

[0041] - Small changes in the efficiency of the check valves 24, 26.

[0042] - Changes in the temperature of the linear motor windings.

[0043] Adaptation strategies

[0044] A variety of control strategies could be used, such as observing one or multiple prior waveforms as input to the formulation of the subsequent waveforms.Adaptations can be damped so that waveforms gradually conform over multiple cycles. Machine learning algorithms or neural networks can be utilized to create a more sophisticated mapping to minimize error.

[0045] Displacement monitoring and flow approximation

[0046] In one embodiment, a distance sensor (shown schematically at 38) may optionally be used to determine the displacement of the linear motor 30 and compressible container 28. A primary benefit of displacement monitoring is that it provides the opportunity to adapt the current to the linear motor 30 based on the know n characteristics of the force / displacement relationship.

[0047] Another benefit is to provide an approximation of the flow rate. The sensor 38 w ould track the linear movement at the interface between the linear motor 30 and the compressible container 28. By measuring the compressible container displacement, an approximation of the flow rate could be achieved. This embodiment w ould dramatically lower the cost of systems that require some indication of flow.

[0048] One potential failure mechanism for this embodiment is the potential for leakage back through check valves (such as would be cause by debris in the valve). A preferred solution to this issue is to incorporate a single or periodic test to verify good check valve qualify. By blocking the flow downstream of the pump 12 (by external clamp or by installation of a manual or automatic block valve), it is possible to verify' that the upstream check valve 24 has integrity by verifying that the compressible container 28 does not move under constant linear motor force. In order to verify' the downstream check valve 26, it would be possible to create a higher pressure downstream than in the compressible container 28, block the upstream of the pump 12, and observe movement in the compressible container 28 (indication of leakback of the downstream check valve 26).

[0049] Pressure approximation

[0050] In another embodiment, a force or pressure sensor (show n schematically at 40) is placed between the linear motor 30 and the compressible container 28 to sense the force that is generated by the linear motor 30. In a preferred example, this sensor 40 can be used as high-speed feedback to correct the force / displacement curve and adapt for other issues such as motor temperature. In most applications, a fluid pressure sensor 34 would still be provided at the application A. However, in one example, this force or pressure sensor 40 would serve as an economical proxy for application pressure, avoiding the required investment.

[0051] Hydraulic effects - application capacitance and resistance

[0052] Inertia of the mechanical moving components (such as linear motor magnet, solenoid core) can present undesirable artifacts in the pressure wave. Similarly, hydraulic inertia can also present undesirable pressure wave artifacts. A preferred example would include carefully tuned fluid restriction to prevent excessive fluid velocity, thereby minimizing fluid inertia artifacts. An example of such restriction w ould be a restriction in the suction tubing leading to the inlet (first) check valve 24 to avoid pressure artifacts from inertia in the supply tubing. A similar restriction may be optionally provided after the outlet check valve 26. but before the application A and pressure sensor 34, to avoid fluid inertia effects in the outlet tubing. Such optional restrictors are not shown in the drawings.

[0053] The t pical application would provide both resistance to fluid flow (increasing differential pressure (dP) with increasing flow, and hydraulic capacitance (ability to absorb additional volume of fluid with increasing pressure). In the example of an organ such as a kidney, the organ w ould typically accept more flow7through the vessels with increasing pressure, but also the organ would exhibit fluid capacitance by dampening pressure changes at its inlet because of the swelling of the capillaries with higher pressures. For example, as the pressure wave from the pump 12 lowers from the high to the low pressure phase, the organ would buffer the pressure drop due to its ow n capacitance. In an extreme example of capacitance, the organ may actually flow a small amount of fluid backwards if the pump system dropped the pressure rapidly.

[0054] Therefore, the determination of the ideal pressure waveform is a delicate balance between the needs of the application (flow rate, pressure waveforms), the properties of the application (resistance, capacitance), and also that of the fluid supply system (location and head of the supply container), and the properties of the tubing conduits (resistance primarily, but also capacitance if the tubing wall is thin or if any air bubbles are present).

[0055] In one embodiment of, a hydraulic capacitor (such as a separate compressible container, flexible tubing, or air pocket) may be provided near the inlet check valve 24 to minimize the impact of the hydraulic acceleration and deceleration on the system performance.

[0056] In a preferred embodiment, a hydraulic capacitance is provided to the system to dampen the changes in pressure to better emulate the biology of the organ blood flow. Such capacitance could be provided by a flexible fluid volume such as a separate compressible container, an elastomeric fluid conduit, or an air pocket (either exposed directly or separated by a flexible membrane from the fluid).

[0057] Example waveforms

[0058] The pump 12 is capable of approximately emulating a variety of pulsatile waveforms found in medical applications. Interestingly, most organs in the body do not receive the highly defined pressure pulse that is found directly at the exit of the heart (solid line in FIG. 2). Depending on the location of the organ in the body, they may receive a much more damped response (FIG. 3).

[0059] Several wave forms are presented to illustrate basic functionality of a simple system before implementation of a feedback control mechanism. In each chart, the date line is proportional to the applied voltage. The cell line is the pressure waveform at the application in psi. It will be noted that there is a delay between the onset of the voltage and the pressure sensed downstream in all charts.

[0060] The first waveform (FIG. 4) shows an artifact of inertia (mechanical and / or fluid) on the pressure rise. Also, also shown is a very strong fluid inertial wave after the compressible container 28 completes its refill (after the voltage drop).

[0061] In FIG. 5, the rising voltage wave is clipped with an angular feature, which is a very effective way of eliminating or reducing the inertial overshoot that can occur.

[0062] FIG. 6 also shows an exponential rise at constant voltage that is due to the compressible container 28 moving and the solenoid core becoming closer to its "choke" location. As the core approaches the choke location the force increases exponentially (inversely exponential to the distance).

[0063] In FIGS. 4-6, there is a hydraulic disruption after the end of the wave, where the pressure bounces up and down. This is largely hydraulic inertia as the tubing jumps around due to the rapid fluid velocity changes in both the upstream and downstream sets (separately due to the check valves).

[0064] In FIG. 7, the hydraulic disruptions after the wave were minimized by a combination of gentler down slope, and also inclusion of supply line resistance (upstream of the inlet check valve 24).

[0065] Examples of feedback control

[0066] Modeling of physical system

[0067] In one example of an adaptive control system, a mathematical model of a physical system is developed which provides for a transform to adapt the input power curve. The adaptation for physical mass inertia is an example of how the physical model could be used to establish an improved power waveform.

[0068] Machine learning

[0069] In another example, no specific understanding of a physical model is required, but a feedback model uses machine learning or neural network learning or other pattern matching algorithms available through artificial intelligence to examine theerror (desired - actual) and provide an adaptation to the power input curve to minimize error over several or many cycles. Referred to as "numerical techniques".

[0070] Real-time intra-wave wave control

[0071] In another embodiment, the current applied to the linear motor 30 is adapted in real time within a single pulsatile wave to avoid overshoot and by responding to or learning from the emerging pressure pattern. Such adaptation could be any of the above-mentioned control methods, but also including the widely used PID (proportional integral derivative) method. An error term is established as the difference between the desired pressure and the observed fluid pressure in real time. The PID algorithm is tuned to initiate, accelerate, and even decelerate the mechanism with very high PID calculation rates. The derivative term is helpful to avoid pressure overshoot from the physical mechanism deceleration. PID calculation intervals faster than 10 mS are preferred. Rates faster than 3 mS are highly preferred, with calculation rates faster than ImS are most highly preferred.

[0072] In addition to any other control logic implemented, it is highly preferred to include a high-speed shut-off that immediately cuts off voltage applied to the linear motor if the pressure (as detected by pressure sensor 34, for example) exceeds a pre- established maximum desired pressure.

[0073] While the example waves show a delay between the onset of power and the measurement of pressure at the application (roughly 300 msec), it is possible to minimize the delays by utilizing high speed signal processing (both input and output signal conversion), fast calculation intervals, judicious location of pressure sensors, or by using the pressure / force sensor option adjacent to the compressible container 28.

[0074] Double compressible container systems

[0075] In the above-mentioned example with a single compressible container 28, it is not possible to explicitly control the diastolic pressure while refilling the compressible container 28. It is practical to position the supply fluid above the application,providing hydraulic head pressure in such a way as to establish a base pressure (diastolic pressure) during compressible container recharge.

[0076] By adding a second compressible container, it is possible to explicitly control the diastolic pressure as well as the systolic pressure. FIG. 10 shows a system 110 including a second compressible container 128 and linear motor 130. Both compressible container 28. 128 have their own inlet and outlet check valves 24, 124, 26, 126, respectively and the fluid streams are teed together before and after the inlet and outlet check valves respectively.

[0077] In this embodiment, one compressible container provides the higher pressure and the other compressible container controls the lower pressure. The compressible containers are recharged in alternating patterns, each refilling when the other is discharging.

[0078] If the supply pressure from the upstream reservoir (alternatively could be from another pumped supply or pressurized supply) is not significantly above atmospheric pressure, then the compressible container should be mechanically linked to the linear motor in order to provide for suction (pulling in addition to pushing) to rapidly refill the compressible container, overcoming friction that may exist in the supply lines and the inlet check valve(s).

[0079] Alternative compressible container geometries

[0080] In another example, the compressible action of the compressible container may replaced by a cylinder or syringe with sliding seals.

[0081] Spring to linearize force versus displacement

[0082] Many solenoids are provided wi th springs integrated to provide for the return of the actuator and to alter the force versus displacement relationship. Because most commercial solenoids are intended to provide for simple push / pull actuation, the springs normally used with solenoids are not suitable for flattening the force / displacement curve.

[0083] All traditional solenoids have a non-linear relationship between force and displacement, with the highest force being when the center of the magnetic flux field is nearly centered with the center of magnetic attraction of the linear motor core. As the two centers are separated, the force generated degrades rapidly across the stroke.

[0084] By strategic selection of spring rates and spring lengths, it is possible to integrate a spring which significantly linearizes the response of the force / displacement relationship of the linear motor / spring system.

[0085] In one embodiment, a spring is provided which significantly linearizes the force / displacement curve of a linear motor (typically a solenoid), lowering the delta force across the active displacement range (at constant power) by at least 30%, and in a preferred embodiment, at least 50%.

[0086] In another embodiment, two springs are included to further optimize the overall performance of the linear motor (typically a solenoid), lowering the delta force across active displacement range (at constant power) by at least 30% and preferably at least 50%.

[0087] Appendix charts

[0088] FIG. 8 shows a typical electromagnetic solenoid curve, with the dramatic inverse exponential drop-off in force with displacement (stroke).

[0089] FIG. 9 shows aty pical improved force / displacement curve from a speaker coil linear motor (SCLM).

[0090] The foregoing has described a pulsatile pump. All of the features disclosed in this specification, and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0091] Each feature disclosed in this specification may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0092] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends, or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

WHAT IS CLAIMED IS:

1. A pump, comprising: a first pump body defining a first flow path; a first inlet check valve at an upstream end of the first flow path; a first outlet check valve at a downstream end of the first flow path; a first compressible container in flow communication with the flow path between the upstream and downstream ends; a first electromagnetic linear motor connected to the first compressible container such that extension of the first linear motor causes compression of the first compressible container; and an electronic controller configured supply a varying voltage or current to the first linear motor so as to provide a pulsatile flow- at a controlled pressure and controlled pulse rate, where the pressure is independent of downstream flow resistance.

2. The pump of claim 1, further comprising: a second pump body defining a second flow path; a second inlet check valve at an upstream end of the second flow path; a second outlet check valve at a downstream end of the second flow path; a second compressible container in flow communication with the flow path between the upstream and downstream ends; and a second electromagnetic linear motor connected to the second compressible container such that extension of the second linear motor causes compression of the second compressible container, wherein the electronic controller is configured to independently supply a varying voltage or current to the first linear motor and to the second linear motor so as to provide a pulsatile pressure, wherein the first and second linear motors operate out of phase with each other3. An apparatus, comprising: the pump of claim 2; a reservoir upstream of the pump; and an application downstream of the pump, wherein the first and second flow pathsare joined at locations upstream of the first and second inlet check valves and downstream of the first and second outlet check valves.

4. The apparatus of claim 3, further comprising a fluid pressure sensor configured to sense a pressure between the pump and the application and to provide a signal to the electronic controller.

5. The apparatus of claim 3, further comprising a distance sensor configured to sense a displacement of at least one of the linear motors and to provide a signal to the electronic controller.

6. The apparatus of claim 3, further comprising a force sensor disposed between one of the compressible container its respective linear motor and configured to sense a force generated by the corresponding linear motor and to provide a signal to the electronic controller.

7. The apparatus of claim 3, wherein, each of the check valves has a cracking pressure of less than 0.15 psi.

8. The apparatus of claim 3, wherein at least one of the first linear motor and the second linear motor is a has a permanent magnet and coil.

9. The apparatus of claim 3, wherein at least one of the compressible container is a pleated structure.

10. The apparatus of claim 3, where the electronic controller is configured in a is a high speed control loop which adapts the voltage or current in real time as compared with the error between desired and actual pressure.

11. The apparatus of claim 3, wherein the high speed control loop is a PID loop.

12. The apparatus of claim 3, wherein the electronic controller is configured to apply a mathematical transform to a desired pressure waveform, and apply the transformed waveform to the first and second linear motors.

13. The apparatus of claim 3, wherein the transformed waveform is adapted according to an error defined as a difference between an actual waveform property and a target waveform property, and the error is used to adjust the transform for a subsequent waveform.

14. The apparatus of claim 1 or claim 2 where the electronic controller is configured to maintain the controlled pressure and the controlled pulse rate, over a change in application flow rate through a range of 10:

115. The apparatus of claim 1 or claim 2 where the electronic controller is configured to maintain the controlled pressure and the controlled pulse rate, over a change in application flow rate through a range of 5: 1 .

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