VENTRICULAR ASSIST DEVICE CONTROL

Abstract

A control device for a ventricular assist device (VAD) with settable speed levels. The control device includes an input configured to receive at least one measuring signal related to a physiological condition of the circulatory system of a patient receiving heart assistance by the VAD, where the control device is configured to derive an actual value of at least one characteristic parameter of the heart from one or more of the at least one measuring signal and to provide a refined actual value of the at least one characteristic parameter in which effects of physiologically caused fluctuations are eliminated or reduced. The control device further includes an output configured to output an updated setting value for the speed level, where the control device is configured to produce the updated setting value based on the refined actual value and a predeterminable set-point value.

Claims

1. A control device for a ventricular assist device (VAD) with settable speed levels, the control device comprising: an input configured to receive at least one measuring signal related to a physiological condition of the circulatory system of a patient receiving heart assistance by the VAD, wherein the control device is configured to derive an actual value of at least one characteristic parameter of the heart from the at least one measuring signal and to provide a refined actual value of the at least one characteristic parameter in which effects of physiologically caused fluctuations are eliminated or reduced; and an output configured to output an updated setting value for the speed level, wherein the control device is configured to produce the updated setting value based on the refined actual value and a predeterminable set-point value.

2. The control device according to claim 1, wherein the control device is configured to process at least one of the at least one measuring signal or the actual value to provide the refined actual value.

3. The control device according to claim 1, wherein the control device is configured to process a plurality of actual values within a moving time interval that includes a current actual value and historical actual values.

4. The control device according to claim 1, wherein the refined actual value is a moving average of a plurality of actual values and/or is based on a moving average of the at least one measuring signal.

5. The control device according to claim 1, wherein the control device is configured to determine a breathing or ventilation frequency based on the at least one measuring signal, historical actual values, or a measuring signal of a ventilation pressure.

6. The control device according to claim 1, wherein the control device is configured to: process the at least one measuring signal or a sequence of actual values by applying a moving average filter having a size related to a periodicity of the physiologically caused fluctuations to be eliminated; or process the at least one measuring signal or the sequence of actual values by applying a high-pass filter having a characterizing cut-off frequency related to the physiologically caused fluctuations to be eliminated.

7. The control device according to claim 1, wherein the at least one measuring signal is includes at least one pressure in the circulatory system of the patient.

8. The control device according to claim 1, wherein the at least one characteristic parameter is a pressure gradient between two intracardiac pressures at two particular events during one cardiac cycle.

9. The control device according to claim 1, wherein the at least one characteristic parameter is a filling gradient of the left ventricular pressure during the diastolic phase of a cardiac cycle between the opening of the mitral valve and the closing of the mitral valve.

10. The control device according to claim 1, wherein the control device is further configured to: calculate an actual heart rate based on the time interval between an occurrence and a consecutive recurrence of one of the at least one characteristic parameter; or calculate an actual blood flow produced by the VAD.

11. The control device according to claim 1, wherein the control device is configured to: update the setting value each time there is a predetermined difference between a refined actual value and a corresponding set-point value; update the setting value when a new refined actual value has been produced; or update the setting value periodically with a predetermined frequency.

12. The control device according to claim 1, wherein control device is further configured to: display the refined actual value on a display; or provide the refined actual value at an output.

13. A system for assistance of a heart, the system comprising: a ventricular assist device (VAD) with settable speed levels, wherein the VAD comprises a rotor and an electric motor having a shaft, and wherein the shaft is coupled to the rotor and configured to drive the rotor; and a control device configured to: receive at least one measuring signal related to a physiological condition of the circulatory system of a patient receiving heart assistance by the VAD; derive an actual value of at least one characteristic parameter of the heart from the at least one measuring signal; process the actual value or the at least one measuring signal to derive a refined actual value in which physiologically caused fluctuations are eliminated or reduced; and update a setting value for a speed level of the VAD based on the refined actual value and a predeterminable set-point value.

14. A method for obtaining a refined actual value of at least one characteristic parameter of a heart, the method comprising receiving, with one or more processors, at least one measuring signal related to a physiological condition of the circulatory system of a patient; deriving, with the one or more processors, an actual value of at least one characteristic parameter of the heart from the at least one measuring signal; and processing, with the one or more processors, the actual value or the at least one measuring signal to provide a refined actual value in in which physiologically caused fluctuations are eliminated or reduced.

15. The method of claim 14 further comprising producing, with the one or more processors, an updated setting value for the speed level based on the refined actual value and a predeterminable set-point value.

16. The control device according to claim 1, wherein the physiologically caused fluctuations to be eliminated or to be reduced are correlated with pressure fluctuations in the thorax of the patient.

17. The control device according to claim 1, wherein the physiologically caused fluctuations to be eliminated or to be reduced are correlated with pressure fluctuations caused by autonomous or assisted breathing of the patient, pressure fluctuations caused by an intra-aortic balloon pump in the aorta of the patient, pressure fluctuations caused by an external counter-pulsation therapy applied to the patient, or pressure fluctuations caused by a change of the patient's positioning.

18. The control device according to claim 1, wherein the physiologically caused fluctuations to be eliminated or to be reduced are correlated with pressure fluctuations caused by an intra-aortic balloon pump in the aorta of the patient.

19. The control device according to claim 8, wherein the pressure gradient is a filling gradient, a systolic contraction, or a diastolic relaxation of the heart.

20. The control device according to claim 9, wherein the control device is configured to produce the updated setting values so that the filling gradient becomes or is kept positive and close to zero.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Hereinafter the invention will be explained by way of examples with reference to the accompanying drawings; in which

[0070] FIG. 1 shows a catheter-based intravascular blood pump as an example of a VAD which is placed through the aorta and extending through the aortic valve into the left ventricle of a heart, and a simplified block diagram of an embodiment of a control device for the blood pump;

[0071] FIG. 2 shows a side view of the VAD of FIG. 1 with some details;

[0072] FIG. 3 shows the control device of FIG. 1 in an application context of a patient receiving heart assistance by the VAD and receiving breathing assistance by a lung ventilation device;

[0073] FIG. 4 illustrate physiologically caused fluctuations due to lung ventilation (FIG. 4C) on detected end-diastolic pressure values (FIG. 4A) and an end-diastolic pressure signal in which the physiologically caused fluctuations are reduced (FIG. 4A) and the rotational speed of the blood pump (FIG. 4B) under control of the control device;

[0074] FIG. 5 illustrate the detection of end-diastolic pressure values in the left ventricular pressure signal;

[0075] FIG. 6 show a diagram (FIG. 6A), of the left ventricular pressure signal during two cardiac cycles illustrating pressure gradients, such as the filling gradient (FIG. 6B), systolic contraction, and the diastolic relaxation, and particularly the filling gradient without VAD assistance (FIG. 6B), and the effect of a speed level control based on the filling gradient (FIG. 6C);

[0076] FIG. 7 further illustrates the effect of the VAD assistance of FIG. 6C by means of several pV-loops; and

[0077] FIG. 8 is a diagram with characteristic curves indicating the relationship between an actual pressure difference ΔP.sub.pump between preload and afterload at a rotary blood pump, an actual blood pump speed n.sub.pump, and a corresponding blood flow produced by the blood pump Q.sub.pump.

[0078] Now with reference to FIGS. 1 and 2, 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, while the exemplary blood pump is shown in more detail in FIG. 2.

[0079] The blood pump is based on a catheter 10, 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 having 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 rotary pumping device, blood can be sucked through the inflow cage 54 and discharged through the outlet openings 56.

[0080] 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 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.

[0081] 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.

[0082] 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, wherein 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 is measured by sensor head 60 and the left ventricular pressure LVP is measured by sensor head 30.

[0083] The data processing unit 110 is connected via an input 101 with the respective signal lines 28A, 28B to receive the corresponding measuring signals AoP.sub.meas for the aortic pressure AoP and LVP.sub.meas the left ventricular pressure LVP.

[0084] The data processing unit 110 is configured for acquiring external and internal signals, for signal processing, such as calculation of a difference between two pressure signals as a basis for estimating pump flow, for signal analysis, such as deriving an actual value of an at least one characteristic parameter σ, such as the end-diastolic left ventricular pressure EDLVP or a filling gradient FG of the heart which is to be forwarded to a speed command signal generator 120.

[0085] The data processing unit 110 is connected via corresponding signal lines at inputs 102, 103 to additional measurement devices 300, e.g. an electrocardiograph (ECG) 310. The ECG 310 provides an ECG signal to the data processing unit 110. The device 310 is exemplary and not limiting, i.e. other external measuring devices represented by device 320 may supply useful signals and may be used as well.

[0086] The control device 100 further comprises a user interface 200 comprising a display 210 as an output means and an input device 220 as input means such as a keyboard, buttons etc. The display device 210 and the input device 220 are integrated partly together in form of a touch screen device. On the display 210, setting parameters, monitored parameters, such as measured pressure signals, and other information, such as setting menus etc., can be displayed. Particularly, refined actual values, such as the EDLVP* or FG*, of the at least one characteristic parameter 6 may be displayed via the display device 210 to a user. Further, by means of the user interface 220, the user of the control device 100 and the VAD can interact with the control device 100, e.g. by changing desired settings of the system.

[0087] Further, the refined actual values, such as the EDLVP*, FG*, of the at least one characteristic parameter 6, in which effects of physiologically caused fluctuations are eliminated or reduced, are provided at output 104 for external use as needed.

[0088] The data processing unit 110 is also configured to provide the refined actual value, such as e.g. EDLVP* or FG*, of the at least on characteristic parameter 6. The refined actual value of the at least on characteristic parameter 6 is forwarded to a speed command signal generator 120.

[0089] The speed command signal generator 120 is configured to generate and adjust, i.e. update, an actual speed command signal n.sub.VAD.sup.set and to supply it to a speed control unit 130. The speed command signal n.sub.VAD.sup.set is provided by the command signal generator 120 operating in an outer feedback loop in which the command signal generator 120 is continuously fed with the refined actual value of the at least on characteristic parameter 6.

[0090] The command signal generator 120 also receives a corresponding set-point value SP, such as EDLVP.sub.set or FG.sub.set, for the at least one characteristic parameter 6. The set-point value SP is also provided by the data processing unit 110. The command signal generator 120 is configured to generate based on an error signal ERR (cf. FIG. 3) corresponding to an actual difference between the refined actual value, such as the EDLVP* or FG*, of the at least on characteristic parameter 6 and the corresponding set-point value SP the actual speed command signal n.sub.VAD.sup.set For example, the actual speed command signal n.sub.VAD.sup.set may be generated based on the error signal in the manner of proportional-integral-derivative (PID) controller 125 (cf. FIG. 3), or any other alternative controller such as a fuzzy controller. The generated actual speed command signal n.sub.VAD.sup.set is forwarded to the speed control unit 130.

[0091] Accordingly, the speed control unit 130 controls the speed n.sub.VAD of the VAD, in accordance with the received speed command signal n.sub.VAD.sup.set. With reference the rotational blood pump as an exemplary VAD, the speed control unit 130 supplies a motor current I.sub.VAD to the motor section 51 of the pumping device 50 via the power-supply line 29 that leads through the catheter tube 20. The actual level of the supplied motor current I.sub.VAD corresponds to the electrical current required by the pumping device 50 to establish the target speed level defined by the actual speed command signal n.sub.VAD.sup.set Via the power-supply line 29, the pumping device 50 may communicate with the control unit 100, i.e. may provide a signal corresponding to the actual rotational speed.

[0092] A measuring signal of the supplied motor current I.sub.VAD is an example of an internal signal to the control device 100 which is also provided to the data processing unit 110 for further processing and use.

[0093] According to the first aspect the control device 100 for pumping device 50 as an embodiment of a VAD with settable speed levels comprises the input 101 that is configured to receive the measuring signal LVP.sub.meas of the left ventricular pressure LVP that represents a physical value related to the circulatory system of the patient receiving heart assistance by the VAD.

[0094] The control device 100 is configured to provide a refined actual value EDLVP* or FG* of at least one characteristic parameter in which physiologically caused fluctuations are eliminated or at least reduced. To this end, in the embodiment shown, the data processing unit 110 is configured to derive an actual value of the EDLVP as an actual value of at least one characteristic parameter 6 of the heart from the measuring signal LVP.sub.meas.

[0095] The data processing unit 110 is further configured to process the measuring signal LVP.sub.meas or the actual value EDLVP or FG in order to provide the refined actual value EDLVP* or FG* in which the physiologically caused fluctuations are eliminated. An output of the data processing unit 110 forwards the refined actual value EDLVP* or FG* of the at least one characteristic parameter 6 to the speed command unit 120.

[0096] The speed command unit 120, in turn, provides at output 105 a correspondingly updated speed command signal n.sub.VAD.sup.set as the current setting value to the motor control unit 130.

[0097] The motor control unit 130 supplies a corresponding motor current I.sub.VAD required by the pumping device 50 to establish the target speed level as defined by the speed command signal n.sub.VAD.sup.set.

[0098] FIG. 3 shows an embodiment of an application of the improved control device 100 of FIG. 1 in the context of a patient P receiving heart assistance by the VAD 50 and breathing assistance by a lung ventilation device 70.

[0099] To start with, on the right-hand side of FIG. 3 a broken line box depicts the patient P. Further, box H depicts the heart of the patient P. For sake of simplicity, the lower half of the box H corresponds to the left ventricle 16 in which the flow cannula 53 with the inflow cage 54 of the pumping device 50 of FIGS. 1 and 2 as well as the sensor head 30 of one of the pressure sensors are located. The motor section 51, the pump section 52 and the pump housing 56 are located in the aorta after the aortic valve 15. The motor section 51 of the pumping device 50 produces the pumping speed of the pumping device 50. By supplying the necessary motor current I.sub.VAD via the power-supply line 29 by the motor control unit 130 of the control device 100 the speed of the VAD can be controlled based on the refined actual value EDLVP* or FG* as the at least one characteristic parameter 6.

[0100] Further shown in the box P is a box representing the lung L of the patient P. In the example, the patient P having an insufficient heart function receives heart assistance by the pumping device 50 and also ventilation assistance to the lung L by the ventilation device 70.

[0101] Due to the ventilation, the lung L is inflated and deflated. Thereby, the pressure in the thorax of the patient P is affected resulting in a synchronized variation of the intracardiac pressures. Thus, the measured left ventricular pressure LVP comprises corresponding physiologically caused fluctuations.

[0102] By means of a ventilation pressure sensor 72, the control device 100 receives a pressure signal sensed by the ventilation pressure sensor 72 being a measuring signal for the ventilation pressure VentP.sub.meas.

[0103] The data processing unit 110 of the control device 100 is configured to perform continuously signal processing on the received measuring signal LVP.sub.meas to produce the refined actual value EDLVP* or FG* of the characteristic parameter □ in which physiologically caused fluctuations are eliminated or at least reduced. Additionally the data processing unit 110 is configured to perform continuously signal processing on the received measuring signal of the ventilation pressure VentP.sub.meas.

[0104] For the control of the pump speed of the pumping device 50, the data processing unit 110 is configured to derive and process the actual values of the EDLVP detected in or derived from the corresponding measuring signal LVP.sub.meas.

[0105] A refined actual value EDLVP* of the EDLVP or FG* as the characteristic parameter σ is forwarded to the speed command unit 120. The speed command unit 120 is configured to perform a comparison with the settable set-point value SP, such as EDLVP.sub.set or FG.sub.set, for the EDLVP or FG and to generate a corresponding speed command signal n.sub.VAD.sup.set supplied to the motor control unit 130, which, in turn, adjusts the motor current supplied to the electrical motor of the pumping device 50 accordingly.

[0106] As illustrated in FIGS. 5A and 5B, to this end, the data processing unit 110 is configured to determine the actual value EDLVP based on a filtered (or smoothed) version FV of the first derivative dLVP.sub.meas/dt of the measuring signal LVP.sub.meas of the left-ventricular pressure.

[0107] For example, when it is determined that the first derivative dLVP.sub.meas/dt of the measuring signal LVP.sub.meas of the left ventricular pressure is equal a predetermined threshold value v.sub.threshold (and/or that further conditions are valid), the current actual value of the LVP is determined as the current actual value of the EDLVP.

[0108] Alternatively or additionally, the control device 100 may use the ECG signal provided by the ECG device 310. Here, the data processing unit 110 is configured to check as a further condition whether the ECG signal shows the R-wave. Further, with the ECG signal, the control device 100 can be configured to adjust the predetermined threshold value v.sub.threshold based on R-wave occurring in the ECG signal so that the actual value of the EDLVP can be determined based on the first derivative of LVP.sub.meas as discussed above.

[0109] In operation of the VAD, the control of the blood pump speed level is based on the refined actual value EDLVP* of the EDLVP and the corresponding set-point value SP. The speed command unit 120 is configured to calculate an error signal ERR based on the refined actual value EDLVP* and the set-point value SP. The speed command unit 120 is further configured to generate in the manner of a PID controller 125 based on the error signal ERR a correspondingly updated speed command signal n.sub.VAD.sup.set supplied to the motor control unit 130.

[0110] The afore-discussed control principle for the speed level of the VAD based on the LVP as measuring signal representing a physical quantity related to the circulatory system can be modified to be based on any one or more other measuring signals representing physical quantities related to the circulatory system. For example, another or further vascular and/or intracardiac pressures, such as the aortic pressure AoP, the central venomous pressure CVP and/or the pulmonary artery pressure PAP for right-sided heart assistance, and the ECG signal may be used.

[0111] As mentioned above, due to ventilation the lung L is inflated and deflated by ventilation device 70. Thereby, the pressure in the thorax of the patient P is affected resulting in a corresponding variation of the measuring signal LVP.sub.meas. Consequently, during the inspiration phase, the derived EDLVP increases during the inspiration phases and decreases during the expiration phases. This causes corresponding physiologically caused fluctuations in the control of the speed level of the VAD.

[0112] FIGS. 4A to 4C illustrate the ventilation induced variation of the derived actual values EDLVP. In FIG. 4A the measuring signal LVP.sub.meas (solid line) is drawn and the derived actual values EDLVP are marked by triangles. FIG. 4C shows the ventilation pressure VentP which causes corresponding fluctuations in the EDLVP values over time.

[0113] To eliminate these physiologically caused fluctuations, as a first approach, the data processing unit 110 is configured to apply an average filter on the derived actual values EDLVP.

[0114] Regarding the setup of the average filter, the data processing unit 110 may be configured to determine continuously, or every now and then, or periodically the ventilation frequency VF based on the measuring signal of the ventilation pressure VentP.sub.meas.

[0115] It has been found that a filter size (or filter window) corresponding to the reciprocal value of the ventilation frequency VF, i.e. 1/VF, is effective to compensate for the effect of the ventilation. In other words, the data processing unit 110 can be configured to calculate for each point in time the actual mean value of the derived actual values EDLVP for a time interval related to the ventilation frequency VF.

[0116] For example, the time interval may be defined by the reciprocal value of the ventilation frequency VF or a multiple n thereof,

[00003]$i.e.\frac{n}{VF}$

with n=1, 2, 3, . . . .

[0117] Alternatively, the data processing unit 110 can be configured to calculate the ventilation frequency VF by the time interval between two consecutive maxima or minima of the actual values EDLVP as discussed herein above.

[0118] Alternatively, instead of the moving average filter the applied filter may be a high-pass filer having a characteristic cut-off frequency set so that the physiologically caused fluctuations to be eliminated disappear. Particularly, the control device may be configured to set the characteristic cut-off frequency of the high-pass filter to the determined ventilation frequency VF.

[0119] As regards the speed level control of the VAD, the signal processing unit 110 of the control device 100, can be further or alternatively configured to determine the beginning and end of the heart contraction phases and the heart relaxation phases, respectively. The implemented value detection algorithm, which will be roughly explained in the following, is based on the measuring signals of the left ventricular pressure LVP and/or the aortic pressure AoP. Based on the determined begin and end of the respective heart contraction phase and heart relaxation phase, the contractility and heart relaxation can be calculated based thereon.

[0120] FIG. 6A shows a diagram of the pressure in the left ventricle LVP and in the aorta AoP during two cardiac cycles j, j+1 for illustration of the filling gradient FG, the systolic contraction SC, and the diastolic relaxation DR of the heart. These pressure gradients FG, SC, DR may also (alternatively or additionally) be used as a characteristic parameter in the control of the speed level of the VAD.

[0121] The term “cardiac cycle” used herein embraces the dynamic behavior of the heart during one heartbeat including e.g. the time-dependent changes of blood pressure and ventricular volume. The heartbeat herein is defined to start with the evocation of the atrial contraction, and to end right before the following atrial contraction, distinguishing between systole and diastole. The systole of the heart (also called the ejection phase of the heart) is the phase between the closing of the mitral valve and the closing of the aortic valve. The diastole (also called the filling phase of the heart) is the phase between the closing of the aortic valve and the closing of the mitral valve of the following heart cycle. The frequency of the heart passing through the cardiac cycle is known as the heart rate.

[0122] The respective points 1 to 4 in FIG. 6A mark respective particular characteristic events in each of the two shown cardiac cycles j, j+1, namely the closing of the mitral valve (point 1, CMV), the opening of the aortic valve (point 2, OAV), the closing of the aortic valve (point 3, COV), and the opening of the mitral valve (point 4, OMV). The following discussion is based on the cardiac cycle j.

[0123] Accordingly, the pressure gradient of the left ventricular pressure LVP during the systolic phase of the cardiac cycle between closing of the mitral valve (point 1) and opening of the aortic valve (point 2), which is defined as

[00004]${\frac{\Delta LVP}{\Delta t}.Math.}_{\mathrm{SC}}=\frac{LVP\left(t_{\mathrm{OAV},j}\right)-LVP\left(t_{\mathrm{CMV},j}\right)}{t_{\mathrm{OAV},j}-t_{\mathrm{CMV},j}}$

describes the systolic contraction SC, i.e. contractility of the heart, which may be used as a measure of cardiac pump performance, the degree to which muscle fibers can shorten when activated by a stimulus independent of preload and afterload; it is a major determinant of cardiac output and an important factor in cardiac compensation. The data processing unit 110 may be configured to calculate the actual systolic contraction SC as a characteristic parameter σ.

[0124] The pressure gradient of the left ventricular pressure LVP during the diastolic phase of the cardiac cycle between the closing of the aortic valve (point 3, COV) and the opening of the mitral valve (point 4, OMV), which is defined as

[00005]${\frac{\Delta LVP}{\Delta t}.Math.}_{DR}=\frac{LVP\left(t_{\mathrm{OMV},j}\right)-LVP\left(t_{\mathrm{CAV},j}\right)}{t_{\mathrm{OMV},j}-t_{\mathrm{CAV},j}}$

describes the diastolic relaxation DR of the heart, which may be used to identify diastolic dysfunction, i.e. an abnormality in the relaxation phase of the heartbeat during which the heart is filling with blood in preparation for the next ejection. The data processing unit 110 may be configured to calculate the actual diastolic relaxation DR of the heart as a characteristic parameter 6.

[0125] Finally, the pressure gradient of the left ventricular pressure LVP during the diastolic phase of the cardiac cycle between the opening of the mitral valve (point 4, OMV) in the cardiac cycle j and the closing of the mitral valve (point 1, CMV) in the following cardiac cycle j+1, which is defined as

[00006]${\frac{\Delta LVP}{\Delta t}.Math.}_{FG}=\frac{LVP\left(t_{\mathrm{CMV},j+1}\right)-LVP\left(t_{\mathrm{OMV},j}\right)}{t_{\mathrm{CMV},j+1}-t_{\mathrm{OMV},j}}$

is called filling gradient FG, which may be used as a measure describing whether the left ventricle does not properly relax and becomes stiff meaning the ventricle cannot fill with blood properly. The data processing unit 110 may be configured to calculate the actual filling gradient FG as a characteristic parameter 6.

[0126] FIGS. 6B and 6C illustrate the effect of VAD speed control based on monitoring the filling gradient FG as the at least one characteristic parameter 6. To this end, the data processing unit 110 is configured to calculate the above discussed quotient of the difference of the left ventricular pressure value observed at the moment of opening of the mitral valve in an ending cardiac cycle j and at the moment of closing of the mitral valve in the consecutive following cardiac cycle j+1 divided by the time span therebetween.

[0127] FIG. 6B depicts the waveform of the LVP of an insufficient heart which is still loaded, i.e. not sufficiently assisted by application of a VAD. The left ventricle does not properly relax and becomes stiff so that the left ventricle cannot fill with blood properly. This is identified by thee filling gradient FG (dashed line in FIG. 6B) being positive and inclined, i.e. greater than zero.

[0128] FIG. 6C shows the effect of well-adjusted heart assistance by the VAD, in which the control of the VAD speed is based on monitoring of the filling gradient FG and the correspondingly adjusted speed of the VAD so that the amount of assistance provided by the VAD to the heart is such that the filling gradient becomes positive, but not negative to avoid suction. It is assumed that monitoring of the filling gradient FG and keeping it close to or equal to zero marks the suitable amount of heart assistance to unload the weakened heart and to support the heart in recovering.

[0129] FIG. 7 further illustrates the effect of the heart assistance by the pumping device 50 based on the filling gradient FG (FIG. 6) as the at least one characteristic parameter 6 on the variation of the left ventricular pressure LVP and the absolute left ventricular volume LVV during one cardiac cycle, which is called the characteristic pV-loop.

[0130] The effect on the shape and position of the pV-loop of the assisted heart is correlated with the amount of assistance provided by the VAD, such as the exemplary blood pump, which is correlated with the blood pump speed. It is noted, since blood flow produced by the pumping device of the VAD depends on the pressure difference between afterload and preload of the VAD, there is no linear relationship between the speed of the VAD and the produced blood flow and the provided assistance as well. But it is roughly correct to say that the amount of assistance may be increased by increasing the speed of the VAD.

[0131] The shown diagram of FIG. 7 starts in the situation of no support provided by the VAD (corresponding to FIG. 6B), which is reflected by the tall pV-loop (thick line) located in the middle and more to the right side of the diagram. With increasing support by the VAD, i.e. by the pumping device 50, the center of the pV-loop waveforms, connected to each other like a spiral, are shifted to the left side of the diagram, while the area of the respective pV-loop is becoming smaller and smaller. The area of the pV-look reflects the actual work produced by the heart itself, i.e. the actual load imposed on the heart. Thus, FIG. 7 illustrates the unloading of the heart by the pumping device 50. The clue is not the fact that the heart can be unloaded by assistance provided by the VAD. The clue is to find, maintain and adjust the actual amount of assistance so that the heart is just sufficiently unloaded to support the recovery thereof.

[0132] This can be done based on the herein-proposed speed level control using a suitable characteristic parameter 6 such as the filling gradient FG discussed and illustrated in connection with FIG. 6.

[0133] For sake of completeness, it is known that the absolute volume of the left ventricle V.sub.LV may be monitored by means of an echocardiography device.

[0134] FIG. 8 is an exemplary diagram showing a set of characteristic curves representing the relationship between the actual pressure difference between the preload and the afterload of the blood pump ΔP.sub.pump, the actual blood pump speed n.sub.pump, and the blood flow through the blood pump Q.sub.pump for the exemplary intravascular rotational blood pump as the herein used example of a VAD.

[0135] The actual blood flow Q.sub.pump through the blood pump can be determined as a function of the pressure difference ΔP.sub.pump and the actual pump speed n.sub.pump, Q.sub.pump=f(ΔP.sub.pump, n.sub.pump), based on the set of characteristic curves. The actual pressure difference ΔP.sub.pump can be determined by means of the pressure sensors 30, 60 in FIG. 2. The actual blood pump speed is known to the data processing unit 110, particularly in the speed command unit 120 and/or the motor control unit 130. Thus, the actual blood flow Q.sub.pump can be ascertained by the data processing unit 110. The relationship between the above-discussed values ΔP.sub.pump, Q.sub.pump, and n.sub.pump described by the set of characteristic curves shown in FIG. 8 can be stored in a storage as a look-up table in the control device 100, e.g. a read only memory of the data processing unit 110 or in a storage on a chip in the blood pump or in the motor control unit 130.

Further Embodiments

[0136] The present invention in particular concerns the following embodiments as defined in the following numbered items:

1. A control device (100) for a ventricular assist device, VAD (50), with settable speed levels, the control device (100) comprising an input (101) configured to receive at least one measuring signal (LVP.sub.meas) related to a physiological condition of the circulatory system of a patient (P) receiving heart assistance by the VAD (50), wherein the control device (100) is configured to derive an actual value (EDLVP; FG) of at least one characteristic parameter of the heart (H) from one or more of the at least one measuring signal (LVP.sub.meas) and to provide a refined actual value (EDLVP*; FG*) of the at least one characteristic parameter in which physiologically caused fluctuations are eliminated; and an output (105) configured to output an updated setting value (n.sub.VAD.sup.set) for the speed level, wherein the control device (100) is configured to produce the updated setting value (n.sub.VAD.sup.set) based on the refined actual value (EDLVP*; FG*) and a predeterminable set-point value (EDLVP.sub.set; FG.sub.set).
2. The control device (100) according to item 1, wherein the control device (100) is configured to process the one or more of the at least one measuring signal (LVP.sub.meas) and/or a time series of actual values (EDLVP, FG) to provide the refined actual value (EDLVP*; FG*).
3. The control device (100) according to item 1 or 2, wherein the control device (100) is configured to process a plurality of actual values (EDLVP; FG) within a moving time interval that includes a current actual value (EDLVP; FG) and further historical actual values.
4. The control device (100) according to any one of the items 1-3, wherein the refined actual value (EDLVP*; FG*) is a moving average of a plurality of actual values (EDLVP; FG) and/or is based on a moving average of the one or more of the at least one measuring signal (LVP.sub.meas).
5. The control device (100) according to any one of the items 1-4, wherein the control device (100) is configured to determine a breathing or ventilation frequency (VF) based on the at least one measuring signal (LVP.sub.meas) and/or consecutive actual values (EDLVP; FG) and/or a measuring signal of a ventilation pressure.
6. The control device (100) according to any one of the items 1-5, wherein the control device (100) is configured to process the one or more of the at least one measuring signal (LVP.sub.meas) or a sequence of actual values (EDLVP; FG) by applying a moving average filter having a size related to a periodicity of the physiologically caused fluctuations to be eliminated or to be reduced; and/or

[0137] to process the one or more of the at least one measuring signal (LVP.sub.meas) or the sequence of actual values (EDLVP; FG) by applying a high-pass filter having a characterizing cut-off frequency related to the physiologically caused fluctuations to be eliminated or to be reduced.

7. The control device (100) according to any one of the items 1-6, wherein at least one of the at least one measuring signal (LVP.sub.meas) is at least one pressure in the circulatory system of the patient, namely at least one of a left ventricular pressure (LVP), an aortic pressure (AoP), a central venomous pressure (CVP), a pulmonary artery pressure (PAP), and/or an ECG signal of the patient.
8. The control device (100) according to any one of the items 1-7, wherein the at least one characteristic parameter is at least one of: a particular value of a vascular and/or an intracardiac pressure at a predetermined event of the cardiac cycle; a pressure gradient (SC, DR, FG) between two intracardiac pressures at two particular events during one cardiac cycle.
9. The control device (100) according to any one of the items 1-8, wherein the at least one characteristic parameter is a filling gradient

[00007]${\frac{\Delta \mathrm{LVP}}{\Delta t}.Math.}_{FG}$

(FG) of the left ventricular pressure (LVP) during the diastolic phase of the cardiac cycle between the opening of the mitral valve (OMV) and closing of the mitral valve (CMV), which is defined as

[00008]${FG=\frac{\Delta LVP}{\Delta t}.Math.}_{FG}=\frac{LVP\left(t_{\mathrm{CMV},j+1}\right)-LVP\left(t_{\mathrm{OMV},j}\right)}{t_{\mathrm{CMV},j+1}-t_{\mathrm{OMV},j}}$

and wherein the control device (100) is configured to produce the updated setting values (n.sub.VAD.sup.set) so that the filling gradient

[00009]${\frac{\Delta \mathrm{LVP}}{\Delta t}.Math.}_{FG}$

becomes or is kept positive and close to zero, preferably zero.
10. The control device (100) according to any one of the items 1-9, wherein control device (100) is further configured

[0138] to calculate an actual heart rate based on the time interval between an occurrence and a consecutive recurrence of one of the at least one characteristic parameter (EDLVP; FG) and/or

[0139] to calculate an actual blood flow produced by the VAD (50).

11. The control device (100) according to any one of the items 1-10,

[0140] wherein control device (100) is configured to produce an updated setting value (n.sub.VAD.sup.set) each time there is a predetermined difference between the refined actual value (EDLVP*; FG*) and the corresponding set-point value (EDLVP.sub.set; FG.sub.set); and/or

[0141] wherein control device (100) is configured to update the setting value (n.sub.VAD.sup.set) when a new refined actual value (EDLVP*, FG*) has been produced; and/or

[0142] wherein control device (100) is configured to update the setting value (n.sub.VAD.sup.set) periodically with a predetermined frequency.

12. The control device (100) according to any one of the items 1-10, wherein control device (100) is configured to display the refined actual value (EDLVP*; FG*) on a display (210) and/or to provide the refined actual value (EDLVP*) at an output (104) of the control device (100).
13. A VAD (50) for assistance of a heart, comprising the control device (100) of any one of items 1 to 12,

[0143] wherein the VAD (50) is preferably a non-pulsatile rotational blood pump;

[0144] wherein further preferably the blood pump is catheter-based; and

[0145] wherein most preferably the VAD (50) is a low-inertia device by featuring one or more of the following: moving, in particular rotating, parts, for example a rotor or impeller, of the VAD comprise low masses by being made of a low-weight material, for example plastic; a driving means, such as an electric motor, is arranged near, preferably very near, most preferably adjacent, to a part, for example a rotor or impeller, driven by the motor, and, if catheter-based, preferably having no rotational drive cable; a coupling or connection, for example a shaft, of the motor with a part, for example a rotor or impeller, driven by the motor is short; all moving, in particular rotating, parts of the VAD have small diameters.

14. A method for obtaining a refined actual value of at least one characteristic parameter of the heart (H), the method comprising

[0146] receiving at least one measuring signal (LVP.sub.meas) related to a physiological condition of the circulatory system of a patient (P);

[0147] deriving an actual value (EDLVP; FG) of at least one characteristic parameter of the heart (H) from one or more of the at least one measuring signal (LVP.sub.meas);

[0148] processing the actual value (EDLVP; FG) or one or more of the at least one measuring signal (LVP.sub.meas) to provide the refined actual value (EDLVP*; FG*) in which physiologically caused fluctuations are eliminated or reduced.

15. A method for controlling the speed level of a ventricular assist device, VAD (50), with settable speed levels, the method comprising

[0149] obtaining a refined actual value of at least one characteristic parameter of the heart (H) by the method according to item 14; and

[0150] producing an updated setting value (n.sub.VAD.sup.t) for the speed level based on the refined actual value (EDLVP*; FG*) and a predeterminable set-point value (EDLVP.sub.set; FG.sub.set).

16. The method of item 14, further comprising processing the one or more of the at least one measuring signal (LVP.sub.meas) or a time series of the actual values (EDLVP, FG) to provide the refined actual value (EDLVP*; FG*).
17. The method of item 14 or 15, further comprising processing a plurality of actual values (EDLVP; FG) within a moving time interval that includes a current actual value (EDLVP; FG) and further historical actual values.
18. The method of any one of the items 14-17, further comprising determining a breathing or ventilation frequency (VF) of the patient (P) based on the at least one measuring signal (LVP.sub.meas) and/or consecutive actual values (EDLVP; FG) and/or a measuring signal of a ventilation pressure.
19. The method of any one of the items 14-18, further comprising

[0151] processing the one or more of the at least one measuring signal (LVP.sub.meas) or a sequence of actual values (EDLVP; FG) by applying a moving average filter having a size related to a periodicity of the physiologically caused fluctuations to be eliminated or to be educed; and/or

[0152] processing the one or more of the at least one measuring signal (LVP.sub.meas) or the sequence of actual values (EDLVP; FG) by applying a high-pass filter having a characterizing cut-off frequency related to the physiologically caused fluctuations to be eliminated or to be reduced.

20. The method of any one of the items 14-19, wherein at least one of the at least one measuring signal (LVP.sub.meas) is at least one pressure in the circulatory system of the patient, namely at least one of a left ventricular pressure (LVP), an aortic pressure (AoP), a central venomous pressure (CVP), a pulmonary artery pressure (PAP), and/or an ECG signal of the patient.

[0153] 21. The method of any one of the items 14-20, wherein the at least one characteristic parameter is at least one of: a particular value of a vascular and/or intracardiac pressure at a predetermined event of the cardiac cycle; a pressure gradient between two intracardiac pressures at two particular events during one cardiac cycle.

22. The method of any one of the items 14-21, wherein the at least one characteristic parameter is a filling gradient

[00010]${\frac{\Delta \mathrm{LVP}}{\Delta t}.Math.}_{FG}$

(FG) of the left ventricular pressure (LVP) during the diastolic phase of the cardiac cycle between the opening of the mitral valve (OMV) and closing of the mitral valve (CMV), which is defined as

[00011]${FG=\frac{\Delta LVP}{\Delta t}.Math.}_{FG}=\frac{LVP\left(t_{\mathrm{CMV},j+1}\right)-LVP\left(t_{\mathrm{OMV},j}\right)}{t_{\mathrm{CMV},j+1}-t_{\mathrm{OMV},j}}$

and wherein the control device (100) is configured to produce the updated setting values (n.sub.VAD.sup.set) so that the filling gradient

[00012]${\frac{\Delta \mathrm{LVP}}{\Delta t}.Math.}_{FG}$

(FG) becomes or is kept positive and close to zero, preferably zero.
23. The method of any one of the items 14-21, further comprising calculating an actual heart rate based on the time interval between an occurrence and a consecutive recurrence of one of the at least one actual value (EDLVP; FG) and/or calculating an actual blood flow produced by the VAD (50).
24. The method of any one of the items 14-23, further comprising

[0154] updating the setting value (n.sub.VAD.sup.set) each time there is a predetermined difference between the refined actual value (EDLVP*; FG*) and the corresponding set-point value (EDLVP.sub.set; FG.sub.set); and/or

[0155] updating the setting value (n.sub.VAD.sup.set) when a new refined actual value (EDLVP*; FG*) has been produced; and/or

[0156] updating the setting value (n.sub.VAD.sup.set) periodically with a predetermined frequency.

25. The control device (100) according to any one of the items 1-12 or the method according to any one of the items 14-24, wherein the physiologically caused fluctuations to be eliminated or to be reduced are correlated with at least one of pressure fluctuations in the thorax of the patient (P), pressure fluctuations caused by autonomous or assisted breathing of the patient (P), pressure fluctuations caused by an intra-aortic balloon pump in the aorta of the patient, pressure fluctuations caused by an external counter-pulsation therapy applied to the patient, pressure fluctuations caused by a change of the patient's positioning, for example into such as the Trendelenburg position.