VENTRICULAR ASSIST DEVICE

Abstract

A control device (100) for controlling the rotational speed (n.sub.VAD(t)) of a non-pulsatile ventricular assist device, VAD, (50) uses an event-based within-a-beat control strategy, wherein the control device is configured to alter the rotational speed of the VAD within the cardiac cycle of the assisted heart and to synchronize the alteration of the rotational speed with the heartbeat by at least one sequence of trigger signals (σ(t)) that is related to at least one predetermined characteristic event in the cardiac cycle. Further, a VAD (50) for assistance of a heart comprises the control device (100) for controlling the VAD, wherein the VAD is preferably a non-pulsatile rotational, for example catheter-based, blood pump.

Claims

1. A control device for controlling a rotational speed (n.sub.VAD(t)) of a non-pulsatile ventricular assist device (VAD), by an event-based within-a-beat control strategy, wherein the control device is configured to: alter the rotational speed (n.sub.VAD(t)) of the VAD within a cardiac cycle of an assisted heart; and synchronize the alteration of the rotational speed (n.sub.VAD(t)) with a heartbeat by at least one sequence of trigger signals (σ(t)) that is related to at least one predetermined characteristic event in the cardiac cycle, wherein the control device is configured to control the rotational speed (n.sub.VAD(t)) of the VAD such that, in a diastolic phase of the cardiac cycle of the assisted heart, the amount of blood ejected into an artery of interest is such that a blood volume remains in a corresponding ventricle and co-ejection from the VAD and from the corresponding ventricle during systole results in a predetermined total peak blood flow (Q.sub.total|max(h)).

2. The control device of claim 1, wherein the control device is configured to alter the rotational speed (n.sub.VAD(t)) of the VAD for a predetermined pulse duration (τ.sup.pulse(h)) or a heart rate dependent pulse duration (τ.sup.assist(h)) to restore and/or maintain at least a predetermined pulsatility (Δ(h)) in the artery of interest within the cardiac cycle, and to synchronize at least one of a beginning and an end of the rotational speed alteration by the at least one sequence of trigger signals (σ(t)).

3. The control device of claim 2, wherein the control device is configured to generate a speed command signal (n.sub.VAD.sup.set(t)) for the alteration of the rotational speed (n.sub.VAD(t)) of the VAD (50) so that the predetermined pulsatility (Δ(h)) is achieved, either in a first setup by an open-loop control, wherein the speed command signal (n.sub.VAD.sup.set(t)) is alternated between predefined rotational speed levels using a command signal generator, or in a second setup by a closed-loop pressure control in a feedback system, wherein the speed command signal (n.sub.VAD.sup.set(t)) is automatically set for each heartbeat (h).

4. The control device of claim 3, wherein the control device is configured to adjust the speed command signal (n.sub.VAD.sup.set(t)) to achieve the predetermined pulsatility (Δ(h)) in the second setup.

5. The control device according to claim 2, wherein the control device is configured to alter the rotational speed (n.sub.VAD(t)) of the VAD to generate the predetermined pulsatility (Δ(h)) only in y out of x consecutive cardiac cycles of the assisted heart, wherein x is an integer greater than 2 and y is an integer with y≤x.

6. The control device according to claim 5, wherein the control device is configured to set the rotational speed (n.sub.VAD(t)) of the VAD (50) during at least y of the other x minus y consecutive cardiac cycles of the assisted heart, so that the mean arterial blood pressure per heartbeat (AoP(h)) remains above the predetermined threshold value (AoP.sub.thr(h)).

7. The control device according to claim 2, wherein the control device is further configured to adjust the speed command signal (n.sub.VAD.sup.set(t)) so that a mean arterial blood pressure per heartbeat (AoP(h)) remains above a predetermined threshold value (AoP.sub.thr(h)).

8. The control device according to claim 2, wherein the control device is configured to initialize an adjustment of a speed command signal (n.sub.VAD.sup.set(t)) a predetermined first time interval (τ.sup.incr(h)) before one of the at least one predetermined characteristic event occurs.

9. The control device according to claim 8, wherein the control device is configured to end the adjustment of the speed command signal (n.sub.VAD.sup.set(t)) in accordance with at least one of: after the predetermined pulse duration (τ.sup.pulse(h))), after the heart rate dependent pulse duration (τ.sup.assist(h)), with an occurrence of one of the at least one predetermined characteristic event in the cardiac cycle, and a predetermined second time interval (τ.sup.red(h)) before or when the at least one predetermined event in the cardiac cycle occurs.

10. The control device according to claim 1, wherein the control device is configured to derive one of the at least one sequence of trigger signals (σ(t)) from an electrical current which is supplied to an actuator of the VAD.

11. The control device according to claim 10, wherein the control device is configured to distinguish changes in the electrical current due to the alteration of the rotational speed (n.sub.VAD(t)) of the VAD from changes in the electrical current caused by the assisted heart passing through the cardiac cycle.

12. The control device according to claim 1, wherein the control device is configured to derive the at least one sequence of trigger signals (σ(t)) from at least one signal being a processed measuring signal, with the processed measuring signal representing at least one of the following physical quantities: a blood pressure difference between an outlet of the VAD for blood ejection and an inlet of the VAD for sucking blood in, a blood pressure in a ventricle of the assisted heart, a blood pressure in the aorta adjacent to the assisted heart, a blood pressure in the vena cava adjacent to the assisted heart, and a blood pressure in the pulmonary artery adjacent to the assisted heart.

13. The control device according to claim 1, wherein the control device is configured to: determine from at least one of the at least one processed measuring signal characteristic information about the circulatory system within a cardiac cycle; and derive or predict the at least one predetermined characteristic event for an upcoming cardiac cycle based on characteristic information determined during previous cardiac cycles.

14. The control device according to claim 13, wherein the control device is configured to determine from at least two processed measuring signals an impact of the alteration of the rotational speed (n.sub.VAD(t)) of the VAD when deriving or predicting the at least one predetermined characteristic event.

15. The control device according to claim 1, wherein the artery of interest is the aorta or the pulmonary artery and the predetermined total peak blood flow (Q.sub.total|max(h)) is at least 6 L/min.

16. The control device according to claim 1, wherein the control device is configured to perform at least one of the following: increase the rotational speed (n.sub.VAD(t)) of the VAD during systole of the assisted heart and/or to reduce the rotational speed (n.sub.VAD(t)) of the VAD during diastole of the heart.

17. The control device according to claim 1, wherein the control device is configured to alter the rotational speed of the VAD only when an average VAD-induced blood flow can be set above a currently required minimum blood flow demand of the assisted heart.

18. A non-pulsatile ventricular assist device (VAD) for assistance of a heart, comprising a control device for controlling a rotational speed (n.sub.VAD(t) of the VAD, by an event-based within-a-beat control strategy, wherein the control device is configured to: alter the rotational speed (n.sub.VAD(t)) of the VAD within a cardiac cycle of an assisted heart; and synchronize the alteration of the rotational speed (n.sub.VAD(t)) with a heartbeat by at least one sequence of trigger signals (σ(t)) that is related to at least one predetermined characteristic event in the cardiac cycle, wherein the control device is configured to control the rotational speed (n.sub.VAD(t)) of the VAD such that, in a diastolic phase of the cardiac cycle of the assisted heart, the amount of blood ejected into an artery of interest is such that a blood volume remains in a corresponding ventricle and co-ejection from the VAD and from the corresponding ventricle during systole results in a predetermined total peak blood flow (Q.sub.total|max(h)).

19. (canceled)

20. The control device according to claim 8, wherein the at least one predetermined characteristic event is at least one of a beginning of ventricular contraction and an occurrence of the R-wave (R) in an electrocardiogram (ECG) signal led from the patient with the assisted heart.

21. The control device according to claim 9, wherein the at least one predetermined characteristic event in the cardiac cycle is at least one of a beginning of ventricular relaxation of the assisted heart and a closing of the aortic valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0089] Hereinafter the invention will be explained by way of examples with reference to the accompanying drawings; in which

[0090] FIG. 1 shows one exemplary embodiment of a VAD placed through the aorta and extending through the aortic valve into the left ventricle of a heart, and a block diagram of an exemplary embodiment of the control device for the VAD;

[0091] FIG. 2 shows a side view of the exemplary VAD of FIG. 1 in more detail;

[0092] FIG. 3 shows a diagram with exemplary signal waveforms that represent, a) the aortic pressure (AoP(t)), b) the left ventricular pressure (LVP(t)), c) an ECG (ECG(t)), and d) a speed command signal trajectory (n.sub.VAD.sup.set(t)), and with e) a corresponding sequence of trigger signals (σ(t)), for illustrating the principle of pulsatile speed control to restore and/or maintain blood pulsatility by means of the VAD of FIGS. 1 and 2 under control of the control device of FIG. 1;

[0093] FIG. 4 shows an electrical equivalent circuit of an electrical model approximating the so-called Windkessel effect in the aorta;

[0094] FIG. 5 shows the results of five different simulation scenarios with respect to the blood flow of the heart Q.sub.heart(t) and blood flow of the pump Q.sub.pump(t) (upper plots) and aortic pressure AoP(t) (lower plots).

DETAILED DESCRIPTION

[0095] FIG. 1 shows a catheter-based rotational blood pump (in the following called “blood pump”) on the left hand side, which is described herein as one exemplary embodiment of a VAD. This exemplary blood pump is shown in more detail in FIG. 2.

[0096] As noted above, one important physical prerequisite which was found by the inventors to be fulfilled by the VAD to be used for the applications proposed herein is the absence of any relevant inertia. The rotary blood pumps such as a blood pump of the catheter-based pump type shown in FIG. 2 do not have any relevant inertia which would hinder the implementation of the proposed speed control scenarios with within-a-beat speed modulation.

[0097] The blood pump is based on a catheter 10 (catheter-based blood pump), by means of which the blood pump is temporarily introduced through the aorta 12 and the aortic valve 15 into the left ventricle 16 of a heart. As shown in more detail in FIG. 2, the blood pump comprises in addition to the catheter 10 a rotary pumping device 50 fastened to the end of a catheter tube 20. The rotary pumping device 50 comprises a motor section 51 and a pump section 52 located at an axial distance therefrom. A flow cannula 53 is connected to the pump section 52 at its one end, extends from the pump section 52 and has an inflow cage 54 located at its other end. The inflow cage 54 has attached thereto a soft and flexible tip 55. The pump section 52 comprises a pump housing with outlet openings 56. Further, the pumping device 50 comprises a drive shaft 57 protruding from the motor section 51 into the pump housing of the pump section 52. The drive shaft 57 drives an impeller 58 as a thrust element by means of which, during operation of the blood pump, blood can be sucked through the inflow cage 54 and discharged through the outlet openings 56.

[0098] The pumping device 50 can also pump in the reverse direction when adapted accordingly, e.g. as required when the blood pump is placed in the right heart. In this regard and for the sake of completeness, FIG. 1 shows the rotary blood pump as one particular example of a VAD located in and for assistance of the left heart. For assistance of the right heart, the rotary blood pump of the present example may be temporarily introduced into the right heart from the vena cava and located in the right heart so that blood can be ejected into the pulmonary artery. In this configuration, the blood pump may be configured for sucking in blood from the vena cava or from the right ventricle and for ejecting the blood into the pulmonary artery. That is to say, the principles and functionalities described by the one particular embodiment may be transferred correspondingly for right-sided heart assistance. Thus, no detailed description is required.

[0099] In FIGS. 1 and 2, three lines, two signal lines 28A and 28B and a power-supply line 29 for suppling an electrical current to the motor section 51, pass through the catheter tube 20 of the catheter 10 to the pumping device 50. The two signal lines 28A, 28B and the power-supply line 29 are attached at their proximal end to a control device 100. It goes without saying that there may be additional lines for further functions; for example, a line for a purge fluid (not shown) may pass through the catheter tube 20 of the catheter 10 to the pumping device 50 as well. Additional lines may be added based on different sensing technologies.

[0100] As shown in FIG. 2, the signal lines 28A, 28B are parts of blood pressure sensors with corresponding sensor heads 30 and 60, respectively, which are located externally on the housing of the pump section 52. The sensor head 60 of the first pressure sensor is associated with signal line 28B. The signal line 28A is associated with and connected to the sensor head 30 of the second blood pressure sensor. The blood pressure sensors may, for example, be optical pressure sensors functioning according to the Fabry-Perot principle as described in U.S. Pat. No. 5,911,685 A, in which case the two signal lines 28A, 28B are optical fibers. However, other pressure sensors may be used instead. Basically, signals of the pressure sensors, which carry the respective information on the pressure at the location of the sensor and which may be of any suitable physical origin, e.g. of optical, hydraulic or electrical, etc., origin, are transmitted via the respective signal lines 28A, 28B to corresponding inputs of a data processing unit 110 of the control device 100. In the example shown in FIG. 1, the pressure sensors are arranged so that the aortic pressure AoP(t) is measured by sensor head 60 and the left ventricular pressure LVP(t) is measured by sensor head 30.

[0101] The data processing unit 110 is configured for acquisition of all external and internal signals, for actual signal processing, which includes for example calculation of a difference between two pressure signals as a basis for estimating pump flow, for signal analysis to detect characteristic events during the cardiac cycle based on the acquired and calculated signals, and for generating a sequence of trigger signals σ(t) by means of a trigger signal generator, for triggering a speed command signal generator 120 (see details below).

[0102] The data processing unit 110 is connected via corresponding signal lines to additional measurement devices 300, such as a patient monitoring unit 310 and an electrocardiograph 320; these devices are just two examples, i.e. other measuring devices may provide useful signals and therefore be used as well. The electrocardiograph 320 provides an ECG signal ECG(t) to the data processing unit 110.

[0103] The control device 100 further comprises a user interface 200 comprising a display 210 and a communication interface 220. On the display 210, setting parameters, monitored parameters, such as measured pressure signals, and other information is displayed. Further, by means of the communication interface 220, the user of the control device 100 can communicate with the control device 100, e.g. to change settings of the whole system.

[0104] The data processing unit 110 is particularly configured to derive or predict the time of occurrence of one or more predefined characteristic events during the cardiac cycle of the assisted heart by means of real-time analysis of current signal values which are used for generation of a sequence of trigger signals σ(t) by means of a trigger signal generator. The resulting sequence of trigger signals σ(t) is forwarded to the speed command signal generator 120 to trigger speed command signal changes.

[0105] Further, the data processing unit 110 is configured to analyze previous values of these speed command signals n.sub.VAD.sup.set(t), as well. That is, the data processing unit 110 is also configured to predict the time of occurrence of the at least one predefined characteristic event in the upcoming cardiac cycle based on the stored information about the characteristic events occurring during the current and/or previous cardiac cycles.

[0106] One particular characteristic event of the cardiac cycle may be the beginning of contraction of the heart at the beginning of the systolic phase. The detected occurrence or the predicted occurrence of such characteristic event is used as an event for synchronizing the pulse of the speed command signal n.sub.VAD.sup.set(t) as proposed herein with the cardiac cycle.

[0107] The speed command signal generator 120 is configured to generate and adjust the speed command signal n.sub.VAD.sup.set(t) of the pumping device 50 and to provide it to a speed control unit 130 either in a feedforward setup as an event-based command signal generator (first setup) or in an outer feedback closed-loop setup for pressure control (second setup).

[0108] In the first setup, the speed command signal generator 120 is triggered by at least one sequence of trigger signals σ(t) which is provided by the data processing unit 110. In the second setup, the speed command signal n.sub.VAD.sup.set(t) is provided by a pressure control algorithm (as the command signal generator 120) which operates in an outer feedback loop and is fed with external and internal signals by the data processing unit 110, and triggered by at least one sequence of trigger signals σ(t) provided by the data processing unit 110 to achieve the desired minimum pulsatility Δ(h).

[0109] Accordingly, the speed control unit 130 controls the speed n.sub.VAD(t) of the VAD, in accordance with the speed command signal n.sub.VAD.sup.set(t), by supplying a motor current I.sub.VAD(t) to the motor section 51 of the pumping device 50 via the power-supply line 29 that leads through the catheter tube 20. The current level of the supplied motor current I.sub.VAD(t) corresponds to the electrical current currently required by the pumping device 50 to establish the target speed level as defined by the speed command signal n.sub.VAD.sup.set(t). Via the power-supply line 29, the pump also communicates with the control unit 100.

[0110] A measuring signal such as the supplied motor current I.sub.VAD(i) which is used as a representative signal of an internal signal of the control device 100 is provided to the data processing unit 110 for further processing.

[0111] According to the first aspect of the present invention, the control device 100 is configured for altering the speed of the blood pump of FIGS. 1 and 2 as an exemplary embodiment of a VAD for heart assistance.

[0112] The control device 100 is particularly configured to alter the speed of the blood pump 50 within a cardiac cycle of the assisted heart, resulting in a change of the blood flow through the pump, the speed alteration of which is synchronized with the heartbeat by means of at least one event per cardiac cycle which is related to a predetermined event in the cardiac cycle. That is to say, the speed command signal generator 120 may be triggered by at least one sequence of trigger signals σ(t) provided by the trigger signal generator of the data processing unit 110 which obtains information on at least one particular event in the cardiac cycle the occurrence of which is detected, the corresponding signal information being used to set the sequence of trigger signals σ(t).

[0113] But it should be noted that the trigger signal generator which provides the sequence of trigger signals σ(t) may rely on more than one event in the cardiac cycle to be detected during each cardiac cycle and to be analyzed to derive a corresponding sequence of trigger signals σ(t) for adjusting the command signal n.sub.VAD.sup.set(t) and, thus, for altering the speed n.sub.VAD(t) of the blood pump 50.

[0114] As discussed above, the blood pump comprises the rotary pumping device 50, with the (rotational) speed n.sub.VAD(t) of the impeller being controlled by speed control unit 130. The speed command signal n.sub.VAD.sup.set(t) of the blood pump is adjusted by the command signal generator 120.

[0115] According to a first embodiment of the proposed change of blood flow produced by the blood pump, the control device 100, in particular the speed command signal generator 120, is configured to adjust the speed command signal n.sub.VAD.sup.set(t) of the rotary pumping device 50 so that the resulting speed n.sub.VAD(t) of the VAD is altered to generate a VAD-induced blood flow Q.sub.VAD(t), which induces a pressure pulse within each cardiac cycle.

[0116] For a better understanding, an example of the potential effect of the speed alteration is illustrated in FIG. 3. FIG. 3 shows a diagram with exemplary waveforms.

[0117] The waveforms in FIG. 3a) represent the aortic pressure signal distinguishing between physiological (non-assisted) aortic pressure AoP(t) (dashed line) and desired (assisted) aortic pressure (t) (solid line).

[0118] The waveform in FIG. 3b) represents the signal for the left ventricular pressure LVP(t) with examples for characteristic pressure values and/or events in the cardiac cycle which may be used for generating or deriving a sequence of trigger signals σ(t).

[0119] The waveform in FIG. 3c) represents an ECG signal.

[0120] The diagram of FIG. 3 illustrates by way of one example the principle of a pulsatile blood pressure restoration and maintenance using the blood pump of FIGS. 1 and 2 under control of the control device 100 in FIG. 1.

[0121] To this end, FIG. 3d) shows one particular example of a speed command signal n.sub.VAD.sup.set(t).

[0122] In FIG. 3e), a corresponding sequence of trigger signals σ(t) is illustrated.

[0123] The speed command signal n.sub.VAD.sup.set(t) is used for the pump speed alteration which corresponds to the signal output of the speed command signal generator 120, and which is forwarded to the speed control unit 130. The sequence of trigger signals σ(t) is the basis for the event-based speed command signal generation or the event-based closed-loop pressure control resulting in an altered speed command signal n.sub.VAD.sup.set(t), the alteration of which is synchronized with the heartbeat.

[0124] The command signal n.sub.VAD.sup.set(t) represents a speed increase from a basic speed level

n.sub.VAD.sup.set(t)=n.sub.VAD.sup.set,basic(j)

to an increased speed level

n.sub.VAD.sup.set(t)=n.sub.VAD.sup.set,basic(j)+Δn.sub.VAD.sup.set(j)

at the beginning of a speed pulse, wherein Δn.sub.VAD.sup.set(j) represents the speed difference during the speed pulse.

[0125] In FIG. 3, the beginning of the speed pulse is synchronized with the end of diastole. Further, the speed decrease from the increased speed level

n.sub.VAD.sup.set(t)=n.sub.VAD.sup.set,basic(j)+Δn.sub.VAD.sup.set(j)

back to the basic speed level

n.sub.VAD.sup.set(t)=n.sub.VAD.sup.set,basic(j)

at the end of the speed pulse is also shown.

[0126] In FIG. 3, the end of the speed pulse is synchronized with the end of systole. These speed alterations each represent possible implementations of speed alteration for achieving the desired minimum pulsatility as discussed in the general section herein.

[0127] The speed decrease is triggered so that a pulse of the speed command signal n.sub.VAD.sup.set(t) after a heart rate dependent pulse duration τ.sup.assist(h), i.e., the pulse duration is adapted to the heart rate HR(h). That is to say, the command signal generator 120 is configured to generate a speed pulse with a heart rate dependent pulse duration.

[0128] Alternatively, the speed decrease can be triggered so that a predetermined pulse duration τ.sup.pulse(j) is achieved. To this end, the command signal generator 120 can be configured to generate a speed pulse with a predetermined pulse duration τ.sup.pulse(j).

[0129] In the shown example (FIG. 3d), the speed increases by the speed difference Δn.sub.VAD.sup.set(j) at the beginning of the speed pulse ends here e.g. at time point t.sup.LVP.sub.j,ED, and the speed decrease at the end of the speed pulse ends here e.g. at time point t.sup.AoP.sub.j,ES.

[0130] Preferably, in operation, the speed command signal generator 120 is configured to control pulsatility ΔAoP(h) by adjusting the speed difference Δn.sub.VAD.sup.set(h) accordingly. As discussed above, a desired minimum pulsatility in the range of Δ(h)=[15 . . . 30] mmHg is considered as sufficient so that a deficiency in the vWF may not occur and/or microvascular perfusion may be improved.

[0131] Further, as discussed above, the data processing unit 110 is configured to measure and/or calculate the current mean arterial blood pressure per heartbeat AoP(h) and to supply the current value to the speed command signal generator 120. To this end, the speed command signal generator 120 is further configured to adjust the speed command signal n.sub.VAD.sup.set(t) to preferably avoid a drop of the arterial blood pressure below a predetermined threshold value AoP(h)≥AoP.sub.thr(h).

[0132] As discussed in the general section, restoration and/or maintenance of a sufficient minimum blood pressure pulsatility can be achieved by altering the speed of the rotary pumping device 50 so that the VAD-induced blood flow Q.sub.VAD(t) is reduced substantially during diastole of the cardiac cycle and/or is increased substantially during systole of the cardiac cycle. Thus, in particular embodiments, the speed command signal generator 120 is configured to adjust the speed command signal n.sub.VAD.sup.set(t) so that in the diastolic phase of the cardiac cycle of the assisted heart the blood volume ejected to the aorta (or pulmonary artery) is low such that a predetermined volume remains in the left (right) ventricle and the rotary pumping device 50, together with the left (right) ventricle, co-ejects appropriate blood volumes during systole. In other words, the diastolic speed reduction also allows the heart to fill adequately, so that a systolic co-ejection of blood from the rotary pumping device 50 and the native heart is possible. In this regard, the inventors have found that the pump and the native heart should induce a total peak flow during systole of

Q.sub.total|max(h)=Q.sub.heart|max(h)+Q.sub.pump|max(h)>6 L/min . . . 10 L/min,

resulting in total ejected volumes of

EV(h)=EV.sub.heart(h)+EV.sub.pump(h)=40 . . . 70 ml,

so that the desired minimum pulsatility Δ(h)≥15 . . . 30 mmHg can be achieved. Nevertheless, the targeted desired minimum pulsatility Δ(h) will not be a fixed value, but may vary based on the recruitment of vWF. Moreover, if the native pulsatility of a weakened heart is already higher than the desired minimum pulsatility, then the pulsatility will of course not necessarily be reduced.

[0133] The inventors have validated the values stated for peak flows per heartbeat of the pump Q.sub.pump|max(h) and the heart Q.sub.heart|max(h) and the corresponding total ejection volumes per heartbeat of the pump EV.sub.pump(h) and the heart EV.sub.heart(h) by means of a mathematical model of an electrical equivalent circuit. The model used is illustrated in FIG. 4.

[0134] FIG. 4 shows the circuit of the electrical model approximating the dynamics of the so-called Windkessel effect in the aorta when blood is ejected by the heart. The electrical model consists of a resistor (R.sub.1=0.05 Ohm) representing the resistance of the aortic valve in series with a series connection of another resistor (R.sub.2=1.32 Ohm) representing the resistance of the peripheral system of the arteries, and a capacitor (C.sub.2=1.7 F) representing the arterial compliance. Further, in the model, the (residual) cardiac output Q.sub.heart(h) and the blood flow of the pump Q.sub.pump(h) are assumed as current sources. Representing a rotatory blood pump, a standard pump Impella 5.0 was used; for more details, reference is made to Catanho et al., “Model of Aortic Blood Flow Using the Windkessel Effect”, Beng 221, Mathematical Methods in Bioengineering, Report, 2012.

[0135] FIG. 5 represents the results of five different simulation scenarios. The table below shows the results of the five different simulation scenarios with additional information on total blood flow for a heartbeat j (Q.sub.total(j)) and corresponding pulsatility (ΔAoP(j)).

[0136] In FIG. 5, from the left to the right, the considered scenarios {circle around (1)} to {circle around (3)} were the following:

[0137] Scenario {circle around (1)}—“healthy heart”: A native heart function is assumed, resulting in peak flows of the heart Q.sub.heart|max(j)=15 L/min and a pulsatility of ΔAoP(j)=40 mmHg (120/80 mmHg) with a common mean aortic blood pressure AoP(j)=105.4 mmHg.

[0138] Scenario {circle around (2)}—“weakened heart, no assistance”: The heart function is reduced to a third of the native function, resulting in a peak flow of the heart Q.sub.heart|max(j)=5.4 L/min and a very low pulsatility of ΔAoP(j)=14.5 mmHg (42/28 mmHg) with an unphysiologically low mean aortic blood pressure of AoP(j)=36.8 mmHg while no pump is implanted.

[0139] Scenario {circle around (3)}—“full unloading (P4)”: The weakened heart is assisted by a pump at speed level P4 with the aim of generating maximum flow, resulting in a total peak flow of Q.sub.total|max(V)=Q.sub.heart|max(j)+Q.sub.pump|max(j)=8.5 L/min and a moderate pulsatility of ΔAoP(j)=17.2 mmHg (96/79 mmHg) with a physiologically mean aortic blood pressure of AoP(j)=89.8 mmHg.

[0140] Scenario {circle around (4)}—“low pulsatility (P4/P2)”: The weakened heart is assisted by a pump, the speed of which is altered with the speed of scenario {circle around (3)} (P4) at systole and low speed (P2) at diastole, resulting in a total peak flow of Q.sub.total|max(j)=Q.sub.heart|max(j)+Q.sub.pump|max(j)=8.5 L/min and a higher moderate pulsatility of ΔAoP(j)=20.4 mmHg (78/58 mmHg) compared to scenario {circle around (3)} at a lower mean aortic pressure of AoP(j)=70.6 mmHg.

[0141] Scenario {circle around (5)}—“high pulsatility (P9/P2)”: The weakened heart is assisted by a pump, the speed of which is altered with the highest possible speed (P9) at systole and low speed (P2) at diastole, resulting in a high total peak flow of Q.sub.total|max(j)=Q.sub.heart|max(j)+Q.sub.pump|max(j)=10.3 L/min and the highest possible pulsatility of ΔAoP(j)=27.4 mmHg (95/69 mmHg) at a moderate mean aortic pressure of AoP(j)=85.2 mmHg.

[0142] It should be noted that in Scenario {circle around (3)}-{circle around (5)} it is assumed that the heart ejects the same amount during systole despite varying degrees of diastolic unloading by the pump.

TABLE-US-00001 Values for heartbeat j Q.sub.heart|.sub.max Q.sub.pump|.sub.max Q.sub.total EV.sub.heart EV.sub.pump ΔAoP AoP Scenario [L/min] [L/min] [L/min] [ml] [ml] [mmHg] [mmHg] {circle around (1)} “healthy heart” 15.0 0.0 4.34 72.3 0.0 40.0 105.4 {circle around (2)} “weakened heart, 5.4 0.0 1.51 25.2 0.0 13.5 36.8 no assistance” {circle around (3)} “full unloading 5.4 3.1 3.81 25.2 38.2 17.2 89.8 (P4)” {circle around (4)} “low pulsatility 5.4 3.1 2.94 25.2 23.8 20.4 70.6 (P4/P2)” {circle around (5)} “high pulsatility 5.4 4.9 3.54 25.2 33.8 27.4 85.2 (P9/P2)”

[0143] In summary, the simulation results underline the fact that the speed alteration can either focus on increased pulsatility while accepting reduced mean aortic pressure or focus on increased mean aortic pressure while accepting reduced pulsatility. Physical and physiological constraints were taken into consideration here, such as very low inertia and hemolysis.

[0144] In particular, the data processing unit 110 is configured to trigger the speed command signal generator 120 so that the pulse of the speed command signal n.sub.VAD.sup.set(t) begins and/or ends at the detected or predicted time of occurrence of at least one predetermined event in the cardiac cycle. The at least one sequence of trigger signals σ(t) which is generated by the trigger signal generator of the data processing unit 110 is provided to the speed command signal generator 120.

[0145] In a preferred embodiment and as illustrated in FIG. 3, the speed command signal generator 120 is configured to initialize the increase of the speed command signal n.sub.VAD.sup.set(t) a predetermined time interval τ.sup.incr(h) before a characteristic event of the cardiac cycle occurs, which is used as a basis for generating the sequence of trigger signals σ(t). This sequence of trigger signals σ(t) can be used to change the pump speed in a moderate manner to avoid suction, blood damage, etc., or to allow the pump speed increase in a timely manner to address the phase shift between a change in speed and the resulting change in pressure (compliance of vasculature and inertia of blood) for the systolic co-ejection.

[0146] In the example illustrated in FIG. 3, the starting time of contraction of the left ventricle is used as the characteristic time taken into account for the sequence of trigger signals σ(t) generated by the trigger signal generator. The contraction of the left ventricle starts immediately after the R-wave occurs in the corresponding ECG signal. Thus, the speed command signal generator 120 may be configured to derive a sequence of trigger signals σ(t) based on the ECG signal, which is provided to the data processing unit 110. The data processing unit 110 may be configured to receive the ECG signal from an (external) ECG device 320 and to generate the sequence of trigger signals σ(t) by means of the trigger signal generator.

[0147] As mentioned above, another measuring signal may be used by the data processing unit 110 for generating the sequence of trigger signals σ(t), showing e.g. the beginning of left atrial contraction which can be used as an event, the time of occurrence of which precedes the beginning of the systolic ejection phase. For example, in FIG. 3b) some characteristic values and times are marked as examples on the signal for the left ventricular pressure LVP(t), namely the minimum value LVP.sub.min(j), the maximum value LVP.sub.max(j), its maximum change over time dLVP(j)/dt|.sub.max, and its minimum change over time dLVP(j)/dt|.sub.min.

[0148] To sum up, the speed command signal generator 120 synchronizes the adjustment of the speed command signal n.sub.VAD.sup.set(t) with the cardiac cycle by means of at least one sequence of trigger signals σ(t) which is provided by the data processing unit 110 such that the speed pulse is initialized before the beginning of ventricular contraction and/or the occurrence of the R-wave in the ECG signal.

[0149] The predetermined time interval τ.sup.incr(h) for initializing the increase of the speed command signal n.sub.VAD.sup.set(t) may be set, for example, to about τ.sup.incr(h)=150 ms, preferably τ.sup.incr(h)=100 ms, most preferably τ.sup.incr(h)≤100 ms before the associated characteristic event in the cardiac cycle. The inventors have further found that it can be ensured by the predetermined time interval τ.sup.incr(h) that the blood flow is not accelerated too fast, which is assumed to reduce the likelihood of blood damage and/or of undesired hemodynamic effects. Thus, the speed command signal generator 120 is configured to adjust the speed command signal n.sub.VAD.sup.set(t) such that the speed n.sub.VAD(t) of the VAD is altered smoothly.

[0150] As one particular example, FIG. 3d) shows a speed command signal n.sub.VAD.sup.set(t) with a ramp for increasing or decreasing the speed n.sub.VAD(t) of the VAD linearly, but other forms may be possible as well, such as an exponential speed increase or decrease.

[0151] Finally, the speed command signal generator 120 is configured to adjust the speed n.sub.VAD(t) of the VAD back to the initial speed level n.sub.VAD.sup.set,basic(t) to end a current speed pulse after the predetermined pulse duration Σ.sup.pulse (h).

[0152] Alternatively or additionally, the speed command signal generator 120 is configured to adjust the speed command signal n.sub.VAD.sup.set(t) for altering the speed n.sub.VAD(t) of the VAD to end a current speed pulse when a predetermined characteristic event of the cardiac cycle occurs.

[0153] In a preferred embodiment, the predetermined event is the beginning of relaxation of the assisted heart and/or the closing of the aortic valve. Here, the predetermined time interval τ.sup.red(h) for initializing the reduction of the speed command signal n.sub.VAD.sup.set(t) before, during or after a predetermined characteristic event in the cardiac cycle may also be taken into account. Preferably, the trigger for terminating the speed pulse is part of the sequence of trigger signals σ(t) and is provided by the data processing unit 110 a time interval τ.sup.red(h) before ventricular relaxation begins. Preferably, this trigger signal is based on a prediction of the beginning of ventricular relaxation detected during previous cardiac cycles.

[0154] For example, the closing of the aortic valve can be determined when the left ventricular pressure LVP(t) drops below the aortic pressure AoP(t) or, correspondingly, when the pressure difference between the inlet 54 and the outlet 56 of the flow cannula 53 becomes lower than zero.

[0155] The data processing unit 110 is further configured to derive the sequence of trigger signals σ(t) from at least one signal that comprises information relating to the closing of the aortic valve of the assisted heart as a characteristic event in the cardiac cycle.

[0156] For example, useful signals may be a measuring signal representing a left ventricular pressure LVP(t) of the assisted heart and/or the aortic pressure AoP(t) adjacent to the assisted heart. If the blood pump is configured for assistance of and placement into the right side of the heart, the signal may be a measuring signal representing a blood pressure in the vena cava CVP(t) adjacent to the assisted heart and/or right ventricular pressure RVP(t) and/or a blood pressure in the pulmonary artery PAP(t) adjacent to the assisted heart.

[0157] The data processing unit 110 is configured to derive a sequence of trigger signals σ(t) from a required motor current I.sub.VAD(t) that is provided by the speed control unit 130 to the rotary pumping device 50. As discussed elsewhere herein, the required motor current I.sub.VAD(t) reflects the energy required by the rotary pumping device 50 to follow the set speed value. Thus, the command signal generator 120 may be triggered by a corresponding sequence of trigger signals σ(t) provided by the data processing unit 110.

[0158] Preferably, the data processing unit 110 is configured to receive, store and analyze at least one measuring signal containing characteristic information of the circulatory system and of the cardiac cycle in order to predict at least one event per heartbeat based on analysis results of previous cardiac cycles. Most preferably, the data processing unit 110 is configured to analyze at least two measuring signals to filter the impact of the pump-induced pressure changes so that characteristic events in the cardiac cycle may be reliably detected.