WO2024242960A1

Movatterモバイル変換

Info

Publication number: WO2024242960A1
Application number: PCT/US2024/029438
Authority: WO
Inventors: Nicholas Greatrex; Daniel Timms
Original assignee: Bivacor Inc
Current assignee: Bivacor Inc
Priority date: 2023-05-16
Filing date: 2024-05-15
Publication date: 2024-11-28
Anticipated expiration: 2025-11-16
Also published as: WO2024242960A9

Abstract

A heart pump including a housing forming a cavity including at least one inlet and at least one outlet, an impeller provided within the cavity, the impeller including vanes for urging fluid from the inlet to the outlet upon rotation of the impeller, a drive that rotates the impeller within the cavity and a magnetic bearing including at least one bearing coil that controls an axial position of the impeller within the cavity. One or more electronic processing devices are provided that are configured to determine a bearing indicator relating to axial forces on the impeller and use the bearing indicator to calculate at least one parameter.

Description

^_^^^^ ^ Speed in kRPM [kRPM]^ ^^{^}_^^^^^{^ ^^^^^} ^_^^^^^^^^{^ Speed normalized power}

#_^^^^ ^ #_$%& ' #_^((&^^= Position normalized^)um*^ ^_^^^^ ^ pk-pk pulse height normalized^)kRPM*^ ^_^^^^ ^ Hematocrit )%*^ ^_^^^^^ ^ inlet pressure difference )mmHg* [0186] If a VZP controller is not used or different tuning in used then the MB current could also be used to estimate inlet pressure difference, using the tilt on the rotor (measured via the MB current differences), or used in conjunction with rotor position to determine the inlet pressure difference. In this instance, an equation of the following form can be used: +,-./^01.2231.^4566.1.,7.

^ ^_^^^_^^^^^_^^^^ ^ ^_^^:_%^$&^ ^ ^_^^^^ ^ Speed in kRPM [kRPM]^ ^^{^}_^^^^^{^ ^^^^^} ^_^^^^^^^^{^ Speed normalized power}

#_^^^^ ^ #_$%& ' #_^((&^^= Position normalized^)um*^ ^_^^^^ ^ pk-pk pulse height normalized^)kRPM*^ ^_^^^^ ^ Hematocrit )%*^ :_%^$& ^ MB bias current^)A* [0187] Following this, left and right pump pressures can be calculated at step 830. Again, this can be achieved using equations of the following forms, with equation constants calculated experimentally: ;.6/^<3=<^<1.2231.

^ ^_^^^_^^^^^_^^^^ ^ ^_^^:_%^$& 15>?/^<3=<^<1.2231.

^ ^_^^^_^^^^^_^^^^ ^ ^_^^:_%^$&^ ^ ^_^^^^ ^ Speed in kRPM [kRPM] [0188] Having established these values, further hemodynamic parameters including vascular pressures can now be calculated at step 840. [0189] In this regard, it will be noted that whilst estimation of flow and pressure output of the LVAD is possible and established in the field, an LVAD is in parallel with left ventricle and in series with the right ventricle, so it is difficult to determine patient hemodynamics with only LVAD information. [0190] A TAH with 2 independent pumps could estimate the flow and the pressure head of each pump, however without information about the relative pressures of the left and right pump it is not possible to know the individual Systemic Vascular Resistance (SVR) and Pulmonary Vascular Resistance (PVR) only the total vascular resistance (SVR + PVR). [0191] In the case of a dual sided pump, the relative left and right atrial filling can be used to estimate the SVR and PVR of the patient. In this regard, as shown in Figure 12, knowing the left and right pump pressures, and the atrial pressure difference (given by the inlet pressure difference), allows the pulmonary and systemic pressure drops to be calculated. This in turn allows the SVR and PVR to be determined at step 850 as follows:

^{@A B )Systemic Pressure Drop*} S_{ystemic Flow}

^{@A B )Pulmonary Pressure Drop*} P_{ulmonary Flow} [0192] Furthermore, as all four of the relative inlet and outlet pressures can be estimated (Left in, Left out, Right in, Right out), then the absolute pressures can be determined at step 860 if one of the pressures is known. Clinically the easiest measurement would be central venous pressure (CVP), which would in turn allow calculation of left atrial pressure (LAP), pulmonary aterial pressure (PAP) and aortic pressure (AoP). [0193] Additionally, a measure of delivered oxygen can be more clinically relevant than the pressures. Delivered oxygen (DO₂) can be calculated using haemoglobin (Hb) / HCT, oxygen saturation (SaO2) and the oxygenation pressure in arterial blood (PaO2), one or more of which can be estimated using the drive and/or bearing indicator, and/or measured using other means. For example, SaO2 can be calculated from a pulse oximeter, which can be achieved using the pump described above operating in a pulsatile manner. [0194] The amount of delivered oxygen is given by the equation, where CO is the cardiac output: [0195] DO₂ = CO [ (Hb x SaO₂ x 1.34) + (PaO₂ x 0.0031) ] [0196] Again monitoring of delivered oxygen can be used to adjust pump operation, for example increasing / decreasing flow rates in the pulmonary or systemic circulatory systems. [0197] Additionally, the oxygenation level of the blood can change its viscosity values at different frequencies, and so monitoring at different frequencies can be used to allow oxygenation levels to be determined. [0198] It should be noted that in practice, the above calculations may need to be modified to account for bronchial shunt, which is a physiological phenomena in which lung tissue is perfused with oxygenated blood from the systemic circulation that is then returned in part to the pulmonary veins/left atrium, in contrast to typical flow patterns where the oxygenated blood from the aorta is returned to the right atrium. The bronchial shunt is another flow path that can be added into the above calculations, to thereby obtain more accurate pressure estimates. [0199] In healthy patients the bronchial shunt is only 1% of the total blood flow, whereas in heart failure patients it can be as high as 4%. Due to the nature of the shunt path, variation in the shunt resistance / flow does not significantly affect the left estimate, but can alter the right estimate. To account for this, in one example, the above calculations can be modified to include an assumed level of bronchial shunt, or alternatively, additional parameters could be used to estimate the shunt flow. [0200] At step 870, the controller 150 operates to control the pump, based on the determined pressures. This can include adjusting the drive and/or bearing as required. In one example, with accurate estimation of the pump outflow, it is possible to change the pressure flow relationship of the pump by modifying the speed as a function of flow or pressure, which can in turn be used to make the HQ curve steep or shallow (see next slides), as shown for example in Figures 13A, 13B, 13C and 13D, respectively. [0201] In this example, the controller is configured to predict head pressure, with an error being inputter as head pressure minus predicted head pressure. Proportional integral control is then used to control to a speed target, with autonomous changes to the speed would be limited to a defined safe range. [0202] It will be appreciated that the above arrangement therefore uses a combination of drive and bearing signals to provide a more accurate estimate of hemodynamic parameters, which can be further improved through the inclusion of hematocrit as an indication of fluid viscosity. Furthermore, in the case of a dual sided impeller BiVAD, this can be used to resolve absolute pressures within a patient given a clinical measure of a single pressure. [0203] The above described arrangement can be employed in wide range of circumstances and in different pump configurations. For example, this can be used when one or two pumps are used to provide assistance or replacement of the left or right ventricles, including in a TAH, when two rotary pumps to provide complete replacement of the native heart, in an LVAD/RVAD, when a single rotary pump is used to provide assistance to either the left or right ventricles, or in a BiVAD, when two rotary pumps to provide assistance to both the left or right ventricles. [0204] The controller and control process can be used in a device that uses an active magnetic bearing in conjunction with a zero power controller that controls the position of the rotor in response to a change of magnetic bearing current. Signal filtering techniques on the fundamental current signal with consideration to the zero power controller can return a feedback signal appropriate for use in the controller. [0205] An example of a single VAD heart pump will now be described with reference to Figures 14A to 14F. [0206] In this example, the heart pump 1400 includes a housing 1410 defining a cavity 1415. The housing can be of any suitable form but typically includes a main body, and left and right end caps which connect to the main body. The housing can be made of any suitable biocompatible material, and can be made of titanium, a polymer or the like. [0207] The housing 1410 includes an inlet 1411, for connection to the left atrium/pulmonary vein or right atrium/vena cava, or left or right ventricle, and an outlet 1412 for connection to the aorta or pulmonary artery, respectively. [0208] The heart pump 1400 includes an impeller 1420 provided within the cavity 1415. The impeller 1420 includes a rotor 1421 having vanes 1422 mounted thereon for urging fluid from the inlet 1411 to the outlet 1412 upon rotation of the impeller 1420. In this example, as the heart pump 1400 is a single ventricular assist device, the impeller includes a single set of vanes 1422 for urging fluid from the inlet 1411 to the outlet 1412. In this example, the vanes 1422 have a configuration similar to that described above, and these will not therefore be described in further detail, although it will be appreciated that other suitable vane configurations can be used. The impeller can also include an aperture 1424 extending therethrough to allow blood to flow around the rear surface of the impeller and thereby prevent stagnation and clotting of blood within the heart pump. Furthermore, the use of a magnetic bearing in this region allows for blood gaps in excess of 200-300^m, which can both reduces shear stress and thus red cell lysis, as well as promote greater rates of washout flow than otherwise anticipated in gaps created by hydrodynamic bearings. [0209] The heart pump 1400 further includes a drive 1430 that rotates the impeller 1420 within the cavity 1415. The drive 1430 can be of any appropriate form but typically includes a number of coils, each wound on a respective stator, supported by a mounting, allowing the drive 1430 to be coupled to the housing 1410. The drive cooperates with magnetic material 1434 mounted in the rotor 1421, with the magnetic material being in the form of a number of circumferentially spaced permanent drive magnets arranged proximate an outer circumferential edge of the rotor 1421. In one example, the coils and stators are wedge shaped and circumferentially spaced around the mounting, so as to provide twelve electromagnets radially aligned with the drive magnets 1434 in the rotor 1421, to thereby maximise a degree of magnetic coupling between the magnets in the rotor 1421 and the drive 1430. [0210] The heart pump 1400 can further include a magnetic bearing 1440 including at least one bearing coil 1441 that controls an axial position of the impeller within the cavity 1415. In one particular example, shown in more detail in Figure 14E, the magnetic bearing includes three bearing coils 1441, each of which is mounted on a first leg 1442.1 of respective U-shaped stators, with a second leg 1442.2 being positioned radially inwardly of the first leg 1442.1. The stators are mounted to or integrally formed with a support 1443 and circumferentially spaced 140° apart around the housing so that the first and second legs 1442.1 1442.2 align with respective magnetic material, such as bearing magnets 1444, 1445 within the impeller 1420, allowing an axial position of the impeller 1420 to be controlled. [0211] In one particular example, the bearing rotor assembly includes ferromagnetic core target 1444 mounted in the rotor, proximate an outer circumferential edge of the rotor 1421, and a permanent bearing magnet or ferromagnetic material 1445 mounted radially inwardly of the first ferromagnetic core target 1444, so that the ferromagnetic core target and bearing magnets 1444, 1445 align with respective legs 1442.1, 1442.2 of the stators. The ferromagnetic core target can be replaced with a second permanent magnet. However, the use of a magnetic bearing may not be required and can be replaced by a static physical bearing or hydrodynamic bearing, or the like. [0212] In this example, the drive 1430 and magnetic bearing 1440 are mounted at opposing ends of the housing 1410 so that the drive and bearing 1430, 1440 are provided proximate opposing surfaces of the rotor 1421 as shown for example in Figure 14B. In the current example the drive 1430 is mounted adjacent the side of the impeller 1420 that includes vanes so as to maximise the blood gap between the rotor, vanes and the casing. That is to say, only the vane tips are in closer proximity to the casing, however this blood gap can still be in the order of 200-300^m. Additionally, bearing and drive are configured so that the magnetic forces inherent between the drive 1430 and impeller 1420, and between the magnetic bearing 1440 and impeller 1420 and the hydraulic forces on the impeller 1420 define a balance position within the cavity under conditions of normal flow. This minimises the bearing current required to maintain the position of the impeller 1420 within the cavity under nominal flow conditions. [0213] Periodic patient signals such as breathing rate, breathing depth, vascular compliance, atrial contractility and ventricular contractility (in the case of an LVAD) can be detected through the magnetic bearing and drive signals, including allowing both a rate and magnitude of signals to be estimated. An example of this process will now be described with reference to Figure 15. [0214] In this example, at step 1500, the controller 150 operates to determine drive and/or bearing indicators, in a manner similar to that described above. [0215] Examples of the magnetic bearing signals monitored during a monitoring period are shown in Figure 16A, with a derived impeller position being shown in Figure 16B. Measured vascular resistance and derived pump inlet pressure differences are shown in Figure 16C and 16D. In these examples, changes in inlet pressure are shown at 1601, 1602, whilst periods of increased pulse magnitude caused by pumps speeds of 600RPM and 300RPM (as opposed to the default 100RPM), being shown at 1603, 1604. [0216] At step 1510 Fourier analysis is performed, to determine the magnitude of the signals at different frequencies. Figure 17 is an example of a waterfall plot resulting from Fourier analysis performed using the bearing indicator signals of Figure 16A. [0217] The plot shows peaks corresponding to the heart pulsatile flow harmonics at 1701, 1702, with the increased magnitude peaks caused by the increased rotation speed pulse magnitude being shown at 1702. A normal breathing rate is shown by the peaks 1711, whereas elevated breathing rate and magnitude is shown at 1712. It will be appreciated that this therefore allows information regarding a breathing rate to be determined. [0218] This can be facilitated at step 1520, for example by filtering out signals resulting from operation of the pump, thereby effectively removing the peaks 1701, 1702. [0219] At step 1530, one or more periodic parameters can be extracted from the results of the Fourier analysis, with these being monitored at step 1540, for example comparing these to desirable or expected ranges, to ascertain when parameters fall out of range. This can then be used to control the pump and/or generate a notification at steps 1550 or 1560. For example, if a breathing rate is high, this could indicate reduced oxygenation, and so pump speed could be increased. Alternatively and/or additionally, an alert could be generated to notify medical personnel that the values are out of range and an intervention is required. [0220] Thus, frequency domain analysis and filtering can be used to identify periodic subject signals, with breathing in particular being used to identify hazardous events, allowing clinical staff to be informed using alarms, messages, metrics, or the like, and also optionally allowing the pump operation to be controlled. Whilst this example has focussed on use of the bearing indicator, as described above this could also or alternatively use the drive indicator. [0221] The above described approaches can also be used to measure other parameters, such pump parameters or pump operational performance, specifically if there are any clots, thrombus, or occlusions that are upstream, inside, or downstream to the device and its vascular connections. One example of this would be to monitor for vibration of the rotor and if the vibration magnitude increases that could indicate that there is a thrombus attached to the rotor which is changing the rotational balance of the spinning rotor. An example of this is shown in Figure 18, in which there are increased peaks 1801 and a spread 1802 in different magnetic bearing signals, indicating the impeller is undergoing vibration, and hence indicating the presence of a thrombus. [0222] Monitoring the magnetic bearing signal, and in particular monitoring changes in the bearing parameter to detect thrombus can also be used to determine a location of the thrombus, for example determining whether this is attached to the impeller, and/or partially blocking an inlet or outlet of the pump, which in turn can be used to determine the best intervention for treatment. [0223] In one example, the above described arrangement uses a bearing indicator to calculate one or more of the following parameters: fluid viscosity, a presence of a thrombus or occlusion, location of a thrombus or occlusion, a breathing rate, a breathing depth, a vascular compliance (inflow or outflow), a ventricular contractility magnitude, an atrial contractility magnitude, an atrial contractility rate, a patient activity, such as running, sleeping, resting or the like, or postural changes. [0224] In one example, the above described arrangement uses both drive and bearing indicators to calculate one or more of the following parameters: a breathing rate, a breathing depth, a flow, a head pressure, a relative inlet pressure, an absolute pressure within a subject, a systemic / pulmonary vascular pressure, a systemic/pulmonary vascular resistance, a vascular compliance (inflow or outflow), a ventricular contractility magnitude, an atrial contractility magnitude, a level of delivered oxygen, specific events within cardiac cycle, such as aortic valve opening / closing, mitral valve opening / closing, a ratio of systemic and pulmonary vascular resistance, a ventricular contractility rate, an atrial contractility rate, a patient activity, such as running, sleeping, resting or the like, or postural changes. [0225] In one example, the above described arrangement uses a drive bearing indicator to calculate one or more of the following parameters: a breathing rate, a breathing depth, a vascular compliance (inflow or outflow), an atrial contractility magnitude, or an atrial contractility rate. [0226] Whilst the above parameters might be derivable for both total artificial hearts and ventricular assist devices, it will be noted that the configuration of the pump described in Figures 1 to 3, which uses a single dual sided impeller to provide pulmonary and systemic flows is particularly beneficial for deriving hemodynamic parameters, such as a flow, a head pressure, a relative inlet pressure, an absolute pressure within a subject, a systemic / pulmonary vascular pressure, a systemic/pulmonary vascular resistance, a ratio of systemic and pulmonary vascular resistance, or a patient activity. [0227] In connection with techniques described herein, it will be appreciated that the location / placement of the heart pump may make obtaining data regarding operation of the heart pump and the subject (including hemodynamic attributes of the subject) more technically challenging in some instances (e.g., because it is located inside the body of an individual). Accordingly, the ability to calculate one or more of the parameters described herein can be advantageous to providing improved therapy / therapeutic treatment for the subject. For example, by increasing the efficiency at which the heart pump operates. Or providing dynamic feedback to the individual or clinician. Or automatically controlling aspects of the heart pump based on one or more parameters. Thus, the techniques herein for calculating parameter(s) can be used to improve the health, well-being, and the like of individuals using heart pumps. The techniques can be used by clinicians to provide increased quality of care that is responsive or based on how the calculated parameter(s) change. The approach can also avoid the need to implant additional separate sensors, such as blood pressure sensors, or the like. [0228] It will be appreciated as in the previous example, the apparatus can further include a controller, and otherwise functions largely as previously described, and hence will not be described in further detail. [0229] Throughout this specification and claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers. As used herein and unless otherwise stated, the term "approximately" means ±20%. The above embodiments are to be understood as non- limiting illustrative examples of how the present invention, and aspects of the present invention, may be implemented. Further examples of the present invention are envisaged such as applying the invention to axial impellers including axial flow pumps. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the present invention, which is defined in the accompanying claims. [0230] It is to be noted that the term “or” as used herein is to be interpreted to mean “and/or”, unless expressly stated otherwise. Also, the phrase “at least one” means at least one of the elements listed rather than at least one of each of the elements listed, unless expressly stated otherwise.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1) A heart pump including: a) a housing forming a cavity including at least one inlet and at least one outlet; b) an impeller provided within the cavity, the impeller including vanes for urging fluid from the inlet to the outlet upon rotation of the impeller; c) a drive that rotates the impeller within the cavity; d) a magnetic bearing including at least one bearing coil that controls an axial position of the impeller within the cavity; and, e) one or more electronic processing devices that are configured to: i) determine a bearing indicator relating to axial forces on the impeller; and, ii) use the bearing indicator to calculate at least one parameter. 2) A heart pump according to claim 1, wherein the bearing indicator is indicative of at least one of: a) a tilt of the impeller; b) an electrical current used by the magnetic bearing; c) an axial position of the impeller within the cavity; d) a change in tilt of the impeller; e) a rate of change in tilt of the impeller; f) a change in bearing indicator; g) a rate of change in bearing indicator; h) a derivative of bearing indicator; i) an integral of bearing indicator; j) a magnitude in difference between maximum and minimum values of bearing indicator over a pulse period; k) a change in electrical current used by the magnetic bearing; l) a rate of change in electrical current used by the magnetic bearing; m) a derivative of electrical current used by the magnetic bearing; n) an integral of electrical current used by the magnetic bearing; o) a magnitude in difference between maximum and minimum values of electrical current used by the magnetic bearing over a pulse period; p) a change in axial position of the impeller within the cavity; q) a measure of vibration of the impeller; and, r) a rate of change in axial position of the impeller within the cavity. 3) A heart pump according to claim 1 or claim 2, wherein the one or more processing devices are configured to determine the bearing indicator based on at least one of: a) signals from a position sensor configured to detect an axial position of the impeller; b) signals from a position sensor configured to detect a radial position of the impeller; and, c) a current supplied to the at least one bearing coil. 4) A heart pump according to claim 1, wherein the one or more electronic processing devices are configured to: a) determine a drive indicator indicative of rotation of the impeller; and, b) use the drive indicator and the bearing indicator to calculate the at least one parameter. 5) A heart pump according to claim 4, wherein the drive indicator is indicative of at least one of: a) a current supplied to the drive; b) an expected rotational speed of the impeller; c) an actual rotational speed of the impeller; d) a magnitude of a rotational speed change of the impeller; e) a waveform of changes in rotational speed of the of the impeller; and, f) a ratio of high speed and low speed periods of the waveform. 6) A heart pump according to any one of the claims 4 or 5, wherein the one or more processing devices are configured to determine the drive indicator based on a magnitude of current signals applied to the drive. 7) A heart pump according to any one of the claims 4 to 6, wherein the one or more processing devices are configured to: a) determine a fluid viscosity indicator indicative of the viscosity of blood within the heart pump; and, b) calculate at least one hemodynamic parameter using the drive indicator, the bearing indicator, and the fluid viscosity indicator. 8) A heart pump according to claim 7, wherein the one or more processing devices are configured to determine the fluid viscosity indicator at least one of: a) based on user input commands; and, b) by estimating the fluid viscosity. 9) A heart pump according to any one of the claims 1 to 8, wherein the one or more processing devices are configured to estimate a fluid viscosity using at least one of: a) a plant transfer function; and, b) variations in the bearing indicator. 10) A heart pump according to any one of the claims 1 to 9, wherein the one or more processing devices are configured to estimate a presence or amount of air in the pump using at least one of: a) a plant transfer function; b) a fluid viscosity; and, c) variations in the bearing and/or drive indicators. 11) A heart pump according to any one of the claims 1 to 10, wherein the parameter includes at least one of: a) a subject parameter; b) a pump operating parameter; and, c) a hemodynamic parameter. 12) A heart pump according to claim 11, wherein the subject parameter includes at least one of: a) a periodic subject signal; b) a presence of a thrombus or occlusion; c) a location of a thrombus or occlusion; d) a breathing rate; e) a breathing depth; f) a subject activity level; g) a subject posture or subject posture change; and, h) at least one hemodynamic parameter, the at least one hemodynamic parameter including at least one of: i) a flow; ii) a head pressure; iii) a relative inlet pressure; iv) one or more absolute pressures within a subject; v) a systemic vascular pressure; vi) a pulmonary vascular pressure; vii) a systemic vascular resistance; viii) a pulmonary vascular resistance; ix) a ratio of systemic and pulmonary vascular resistance; x) vascular compliance; xi) a ventricular contractility magnitude; xii) a ventricular contractility rate; xiii) an atrial contractility magnitude; xiv) an atrial contractility rate; xv) a level of delivered oxygen; xvi) a cardiac event; xvii) aortic valve opening or closing; and, xviii) mitral valve opening or closing. 13) A heart pump according to any one of the claims 1 to 12, wherein the one or more processing devices are configured to: a) determine at least one clinically measured pressure parameter; and, b) calculate remaining absolute pressure parameters, wherein the pressure parameters include: i) central venous pressure (CVP); ii) left atrial pressure (LAP); iii) pulmonary aterial pressure (PAP); and, iv) aortic pressure (AoP). 14) A heart pump according to any one of the claims 1 to 13, wherein the one or more processing devices are configured to at least one of: a) control the heart pump at least in part using the at least one parameter; b) display an indication of the at least one parameter; c) record, to non-transitory memory, an indication of the at least one parameter; and, d) generate an alert or notification based on at least one parameter. 15) A heart pump according to claim 14, wherein the one or more processing devices are configured to control at least one of a rotational speed and an axial position of the impeller. 16) A heart pump according to any one of the claims 1 to 15, wherein the one or more processing devices are configured to control a rotational speed of the impeller to at least one of: a) control a blood flow rate through the heart pump; b) vary the rotational speed to induce pulsatile flow; c) vary the rotational speed to induce pulsatile flow that mimics a physiological pulse; d) vary the rotational speed to induce pulsatile flow that matches a physiological pulse when the heart pump is used as a ventricular assist device; e) vary the rotational speed to induce pulsatile flow in accordance with a pulse waveform; f) vary the rotational speed to alter a pulse waveform of pulsatile flow; g) vary the rotational speed to alter a pulse waveform to at least one of: i) alter a pulsatile frequency; ii) alter a pulsatile magnitude; and, iii) change a ratio of higher speed and lower speed parts of the pulse waveform; h) vary the rotational speed to selectively load a subject's heart when the heart pump is used as a ventricular assist device; i) vary the rotational speed to selectively load a subject's heart when the heart pump is used as a ventricular assist device to thereby promote recovery of the subject's heart; j) increase an effective pump flow curve gradient; and, k) decrease an effective pump flow curve gradient. 17) A heart pump according to any one of the claims 1 to 16, wherein the one or more processing devices are configured to: a) perform spectral analysis of at least one of a drive indicator and the bearing indicator; and, b) determine at least one subject parameter using results of the performed spectral analysis. 18) A heart pump according to claim 17, wherein the one or more processing devices are configured to perform the spectral analysis of at least one of: a) an electrical current applied to the drive; and, b) an electrical current applied to the bearing. 19) A heart pump according to claim 17 or claim 18, wherein the one or more processing devices are configured to perform filtering or signal processing to compensate for pulsatile operation of the heart pump. 20) A heart pump according to any one of the claims 1 to 19, wherein the one or more processing devices are configured to: a) determine a magnitude and/or frequency of periodic signals within at least one of a drive indicator and the bearing indicator; and, b) determine the parameter using the magnitude and/or frequency. 21) A heart pump according to any one of the claims 1 to 20, wherein the one or more processing devices are configured to: a) determine a waveform shape of signals within at least one of a drive indicator and the bearing indicator; and, b) determine the parameter using the waveform shape. 22) A heart pump according to claim 21, wherein when the pump is configured to act as an assist device for a subject, the one or more processing devices are configured to: a) identify parts of the subject's cardiac cycle using the waveform shape; and, b) determine the parameter using the parts of the cardiac cycle. 23) A heart pump according to any one of the claims 1 to 22, wherein the impeller includes first and second sets of vanes provided on a rotor body, the rotor being positioned within the cavity to define: a) a first cavity portion having a first inlet and a first outlet, the first set of vanes being provided within the first cavity portion so as to define a first pump that provides at least partial left ventricular function; and, b) a second cavity portion having a second inlet and a second outlet, the second set of vanes being provided within the second cavity portion so as to define a second pump that provides at least partial right ventricular function. 24) A heart pump according to claim 23, wherein the axial position of the impeller determines a separation between each set of vanes and a respective cavity surface, the separation being used to control the fluid flows from the inlets to the outlets. 25) A heart pump according to claim 23 or claim 24, wherein the first and second pumps have respective pump performance curves having different gradients so that a change in rotational speed of the pump causes a change in the relative flows of the first and second pumps. 26) A heart pump according to any one of the claims 1 to 25, wherein the drive includes: a) a number of circumferentially spaced permanent magnets mounted in the rotor of the impeller, adjacent magnets having opposing polarities; and, b) at least one drive coil that in use generates a magnetic field that cooperates with the magnetic material allowing the impeller to be rotated. 27) A heart pump according to any one of the claims 1 to 26, wherein the magnetic bearing includes: a) first and second annular magnetic bearing members mounted within and proximate a face of the rotor, the first magnetic bearing member being provided radially outwardly of the second magnetic bearing member; b) a number of circumferentially spaced substantially U-shaped bearing stators mounted in the housing proximate a second end of the cavity, each U-shaped bearing stator having first and second bearing stator legs substantially radially aligned with the first and second magnetic bearing members respectively; and, c) at least one bearing coil on each bearing stator that generates a magnetic field that cooperates with the magnetic bearing members to thereby at least one of: i) control an axial position of the impeller; and, ii) at least partially restrain radial movement of the impeller. 28) A heart pump according to any one of the claims 1 to 27, wherein the drive is positioned at a first end of the cavity and the magnetic bearing is positioned at a second end of the cavity. 29) A heart pump according to any one of the claims 1 to 28, wherein the heart pump is at least one of: a) a ventricular assist device; and, b) a total artificial heart. 30) A heart pump including: a) a housing including a cavity having first and second inlets and first and second outlets; b) an impeller provided within the cavity, the impeller including first and second sets of vanes; c) a drive configured to rotate the impeller within the cavity so that: i) the first set of vanes urges fluid radially from the first inlet to the first outlet; and, ii) the second set of vanes urges fluid radially from the second inlet to the second outlet; d) a magnetic bearing including at least one bearing coil that controls an axial position of the impeller within the cavity; and, e) one or more electronic processing devices that are configured to: i) determine a bearing indicator relating to axial forces on the impeller; and, ii) use the bearing indicator to calculate at least one parameter. 31) A controller for a heart pump, the controller being configured to calculate at least one hemodynamic parameter, wherein the heart pump includes: a) a housing forming a cavity including at least one inlet and at least one outlet; b) an impeller provided within the cavity, the impeller including vanes for urging fluid from the inlet to the outlet upon rotation of the impeller; c) a drive that rotates the impeller within the cavity; d) a magnetic bearing including at least one bearing coil that controls an axial position of the impeller within the cavity; and, e) the controller including one or more electronic processing devices that are configured to: i) determine a bearing indicator relating to axial forces on the impeller; and, ii) use the bearing indicator to calculate at least one parameter. 32) A method of calculating at least one parameter, wherein the method includes in one or more processing devices: a) determining a bearing indicator associated with a magnetic bearing including at least one bearing coil that controls an axial position of an impeller within a cavity of a heart pump, wherein the bearing indicator relates to axial forces on the impeller; and, b) using the bearing indicator to calculate at least one parameter. 33) A heart pump including: a) a housing forming a cavity including at least one inlet and at least one outlet; b) an impeller provided within the cavity, the impeller including vanes for urging fluid from the inlet to the outlet upon rotation of the impeller; c) a drive that rotates the impeller within the cavity; d) a magnetic bearing including at least one bearing coil that controls an axial position of the impeller within the cavity; and, e) one or more electronic processing devices that are configured to: i) determine a drive indicator indicative of rotation of the impeller; and, ii) use the drive indicator to calculate the at least one parameter. 34) A heart pump according to claim 33, wherein the drive indicator is indicative of at least one of: a) a current supplied to the drive; b) an expected rotational speed of the impeller; c) an actual rotational speed of the impeller; and, d) a magnitude of a rotational speed change. 35) A heart pump according to claim 33 or claim 34, wherein the one or more processing devices are configured to: a) perform spectral analysis of the drive indicator; and, b) determine the at least one subject parameter using results of the analysis. 36) A heart pump according to any one of the claims 33 to 35, wherein the one or more processing devices are configured to perform filtering to compensate for pulsatile operation of the heart pump. 37) A heart pump according to any one of the claims 33 to 36, wherein the one or more processing devices are configured to: a) determine a magnitude and/or frequency of periodic signals within at least one of a drive indicator and the bearing indicator; and, b) determine the parameter using the magnitude and/or frequency. 38) A heart pump according to any one of the claims 33 to 37, wherein the one or more processing devices are configured to: a) determine a waveform shape of signals within at least one of a drive indicator and the bearing indicator; and, b) determine the parameter using the waveform shape. 39) A heart pump according to claim 38, wherein when the pump is configured to act as an assist device, the one or more processing devices are configured to: a) identify parts of the cardiac cycle using the waveform shape; and, b) determine the parameter using the parts of the cardiac cycle. 40) A heart pump according to any one of the claims 33 to 39, wherein the parameter includes at least one of: a) a subject parameter; b) a pump operating parameter; and, c) a hemodynamic parameter. 41) A heart pump according to claim 40, wherein the subject parameter includes at least one of: a) a periodic subject signal; b) a presence of a thrombus or occlusion; c) a location of a thrombus or occlusion; d) a breathing rate; e) a breathing depth; f) a subject activity level; g) a subject posture or subject posture change; and, h) at least one hemodynamic parameter, the at least one hemodynamic parameter including at least one of: i) a flow; ii) a head pressure; iii) a relative inlet pressure; iv) one or more absolute pressures within a subject; v) a systemic vascular pressure; vi) a pulmonary vascular pressure; vii) a systemic vascular resistance; viii) a pulmonary vascular resistance; ix) a ratio of systemic and pulmonary vascular resistance; x) vascular compliance; xi) a ventricular contractility magnitude; xii) a ventricular contractility rate; xiii) an atrial contractility magnitude; xiv) an atrial contractility rate; xv) a level of delivered oxygen; xvi) a cardiac event; xvii) aortic valve opening or closing; and, xviii) mitral valve opening or closing. 42) A heart pump according to claim 40, wherein the subject parameter includes at least one of: a) a breathing rate; b) a breathing depth; and, c) at least one hemodynamic parameter, the at least one hemodynamic parameter including at least one of: i) vascular compliance; ii) an atrial contractility magnitude; and, iii) an atrial contractility rate. 43) A heart pump according to any one of the claims 33 to 42, wherein the one or more processing devices are configured to at least one of: a) control the heart pump at least in part using the at least one parameter; b) display an indication of the at least one parameter; c) record an indication of the at least one parameter; and, d) generate an alert or notification based on the at least one parameter. 44) A heart pump including: a) a housing including a cavity having first and second inlets and first and second outlets; b) an impeller provided within the cavity, the impeller including first and second sets of vanes; c) a drive configured to rotate the impeller within the cavity so that: i) the first set of vanes urges fluid radially from the first inlet to the first outlet; and, ii) the second set of vanes urges fluid radially from the second inlet to the second outlet; d) a magnetic bearing including at least one bearing coil that controls an axial position of the impeller within the cavity; and, e) one or more electronic processing devices that are configured to: i) determine a drive indicator indicative of rotation of the impeller; and, ii) use the drive indicator to calculate at least one parameter. 45) A controller for a heart pump, wherein the heart pump includes: a) a housing forming a cavity including at least one inlet and at least one outlet; b) an impeller provided within the cavity, the impeller including vanes for urging fluid from the inlet to the outlet upon rotation of the impeller; c) a drive that rotates the impeller within the cavity; d) a magnetic bearing including at least one bearing coil that controls an axial position of the impeller within the cavity; and, e) wherein the controller includes one or more one or more electronic processing devices that are configured to: i) determine a drive indicator indicative of rotation of the impeller; and, ii) use the drive indicator to calculate at least one parameter. 46) A method performed using one or more processing devices coupled to a heart pump of a patient, the method including: a) determining a drive indicator associated with a drive that includes at least one drive coil that rotates an impeller within a cavity of the heart pump; and, b) using the drive indicator to calculate at least one parameter. 47) A method of providing treatment for a subject with a heart pump, the heart pump including an impeller and a magnetic bearing, the impeller including vanes for urging fluid from an inlet of the heart pump to an outlet of heart pump upon rotation of the impeller, the magnetic bearing being configured to control an axial position of the impeller within the housing, the method including: a) determining an indicator relating to axial forces on the impeller or rotation of the impeller; b) calculating at least one parameter based on the determined indicator; and c) adjusting treatment for the subject based on the calculated at least one parameter. 48) The method of claim 47, wherein the indicator includes a bearing indictor relating to axial forces on the impeller. 49) The method of any one of claims 47 to 48, wherein the indicator includes a drive indicator indicative of rotation of the impeller. 50) The method of any one of claims 47 to 49, wherein the method further includes: a) comparing the at least one parameter to a defined threshold; and, b) wherein adjustment of treatment is further based on the comparing. 51) The method of any one of claims 47 to 50, wherein the at least one parameter includes a subject parameter. 52) The method of claim 51, wherein the subject parameter includes a hemodynamic parameter. 53) The method of any one of claims 47 to 52, wherein the at least one parameter includes an operating parameter for the heart pump. 54) The method of any one of claims 47 to 53, wherein adjusting the treatment includes controlling operation of the heart pump based on the calculated at least one parameter. 55) The method of any one of claims 47 to 54, wherein the method further includes: outputting, to a display screen, a display that includes an indication of the at least one parameter, wherein adjusting of treatment is based on the indication of the at least one parameter that is displayed. 56) The method of any one of claims 47 to 55, wherein the method further includes: storing, to non-transitory memory, an indication of the at least one parameter, wherein adjusting of treatment is based on the stored indication. 57) The method of any one of claims 47 to 56, wherein the method further includes: generating an alert or notification based on the at least one parameter, wherein adjusting of treatment is based on the alert or notification.