Adaptive speed control algorithm and controller for optimizing flow in a ventricular assist device

Abstract

The present invention provides adaptive speed control algorithms and controllers for optimizing flow in a ventricular assist device. Methods and systems control a rotational speed of a blood pump during ventricular diastole. The method includes controlling the blood pump according to a first segment operating mode. The controller monitors a blood flow rate through the blood pump. The controller determines whether continuing to control the blood pump according to the first segment operating mode will result in the blood flow rate through the blood pump being less than a target minimum blood flow rate based on the blood flow rate. In response to determining that continuing to control the blood pump according to the first segment operating mode will result in the blood flow rate through the blood pump being less than the target minimum blood flow rate, the controller controls the rotational speed of the blood pump such that the blood flow rate through the blood pump approaches the target minimum blood flow rate.

Description

[0001] This application is a divisional application of PCT international application number PCT / US2019 / 048284, international application date August 27, 2019, and Chinese national phase application number 201980074331.0, entitled "Adaptive velocity control algorithm and controller for optimizing flow in ventricular assist devices".

[0002] Cross-referencing of relevant application data

[0003] This application claims the benefit of U.S. Provisional Application No. 62 / 736,013, filed September 25, 2018, under 35 USC §119(e), the full disclosure of which is incorporated herein by reference in its entirety for all purposes. Background Technology

[0004] A ventricular assist device, known as a VAD, is an implantable blood pump used for both short-term (i.e., days, months) and long-term (i.e., years, or a lifetime) applications for patients whose hearts cannot provide enough circulation (commonly referred to as heart failure or congestive heart failure). According to the American Heart Association, more than 5 million Americans suffer from heart failure, with approximately 670,000 new cases diagnosed each year. People with heart failure often experience shortness of breath and fatigue. Years of living with blocked arteries or high blood pressure can weaken the heart to the point that it cannot pump enough blood to the body. As symptoms worsen, it develops into advanced heart failure.

[0005] Patients with heart failure (also known as congestive heart failure) can use VADs while awaiting a heart transplant or as a long-term destination therapy. In another example, patients can use VADs while their own natural heart is recovering. Therefore, VADs can supplement a weakened heart (i.e., provide partial support) or effectively replace the function of a natural heart. VADs can be implanted in the patient and powered by a power source inside or outside the patient's body. Summary of the Invention

[0006] The following is a simplified overview of some embodiments of the invention to provide a basic understanding of the invention. This summary is not a broad overview of the invention. It is not intended to identify key / determining elements of the invention or to describe its scope. Its sole purpose is to present some embodiments of the invention in a simplified form as a prelude to the detailed implementation that follows.

[0007] Methods for controlling the rotational speed of a continuous-flow blood pump and related mechanical circulatory support systems adjust the pump's rotational speed based on the pump's blood flow rate to prevent the flow rate through the pump from dropping below a target minimum flow rate during ventricular diastole. For a given rotational speed, the flow rate through a continuous-flow blood pump (such as a centrifugal or axial-flow pump) decreases in response to an increase in the pressure differential across the pump. For left ventricular assist devices, the pressure differential across the pump is essentially equal to the pressure differential between the left ventricular pressure and the aortic pressure. For right ventricular assist devices, the pressure differential across the pump is essentially equal to the pressure differential between the right ventricular pressure and the pulmonary artery pressure. During ventricular diastole, the pressure within the ventricles decreases, thereby increasing the pressure differential across the pump and resulting in a decrease in the flow rate through the pump. In some cases, a patient's systemic blood pressure can vary over time, causing the pressure differential across the pump to be significantly higher during ventricular diastole, thus significantly reducing the flow rate through the pump during ventricular diastole. By adjusting the rotational speed of the blood pump based on the blood flow rate, it is possible to prevent the blood flow rate through the pump from dropping below the target minimum blood flow rate within an appropriate range of changes in the patient's blood pressure.

[0008] Therefore, in one aspect, a method for controlling the rotational speed of a continuous-flow blood pump in a ventricular assist device to control the blood flow rate through the pump during ventricular diastole includes: pumping blood from the patient's ventricle to the patient's artery via the ventricular assist device during a first segment of the patient's cardiac cycle. The rotational speed of the blood pump during the first segment is controlled by a controller according to a first-segment operating mode of the blood pump. The blood flow rate through the blood pump is monitored by the controller. The controller determines, based on the blood flow rate through the blood pump, whether continuing to control the rotational speed of the blood pump according to the first-segment operating mode during a second segment of the cardiac cycle would result in a blood flow rate through the blood pump being less than a target minimum blood flow rate. In response to determining that continuing to control the rotational speed of the blood pump according to the first-segment operating mode during the second segment would result in a blood flow rate through the blood pump being less than the target minimum blood flow rate, the controller controls the rotational speed of the blood pump during the second segment such that the blood flow rate through the blood pump approaches the target minimum blood flow rate.

[0009] Any suitable controller can be used in this method to control the rotational speed of the continuous-flow blood pump during ventricular diastole. For example, in some embodiments, the controller includes a speed controller integrated with the blood pump. In other embodiments, the controller is located in a separate implantable unit or in a non-implantable external control unit.

[0010] In methods for controlling the rotational speed of a continuous-flow blood pump during ventricular diastole, the controller may use any suitable method to monitor the blood flow rate through the pump. For example, in some embodiments, the controller may monitor the blood flow rate through the pump via pump electronics, which may be integrated with the pump, located in a separate implantable unit, and / or located in a non-implantable external control unit.

[0011] In many embodiments of the method, the target minimum blood flow rate can be any suitable blood flow rate through the blood pump during ventricular diastole in the patient. For example, in many embodiments of the method, the target minimum blood flow rate is in the range of approximately 0.0 L / min to 2.0 L / min. In some embodiments of the method, the target minimum blood flow rate is in the range of 0.5 L / min to 1.5 L / min. In some embodiments of the method, the target minimum blood flow rate is in the range of 0.8 L / min to 1.2 L / min. In another embodiment, the blood pump is controlled to act as a one-way valve during diastole, wherein the net diastolic blood flow is 0.0 L / min or close to 0.0 L / min.

[0012] In many embodiments of the method, the controller compares the current blood flow rate through the blood pump with a target minimum blood flow rate to determine whether to continue controlling the operation of the blood pump according to the first operating mode, or to switch to controlling the rotational rate of the blood pump to pump blood through the blood pump at the target minimum blood flow rate. For example, in some embodiments of the method, determining whether continuing to control the rotational rate of the blood pump according to the first operating mode during the second segment of the cardiac cycle would result in a blood flow rate through the blood pump being less than the target minimum blood flow rate includes determining the relative difference between the current blood flow rate through the blood pump and the target minimum blood flow rate. In some embodiments of the method, determining whether continuing to control the rotational rate of the blood pump according to the first operating mode during the second segment of the cardiac cycle would result in a blood flow rate through the blood pump being less than the target minimum blood flow rate further includes determining the current rate of change of the blood flow rate through the blood pump.

[0013] This method can be practiced in conjunction with any suitable first-stage operating mode of the blood pump. For example, in some embodiments of the method, the rotational rate of the blood pump in the first-stage operating mode is constant. In some embodiments of the method, the rotational rate of the blood pump in the first-stage operating mode is varied to generate periodic pulsating blood flow. In some embodiments of the method, the periodic pulsating blood flow is synchronized with the patient's cardiac cycle. In some embodiments of the method, the periodic pulsating blood flow is synchronized with the patient's cardiac cycle based on monitored blood flow through the blood pump. In some embodiments of the method, the rotational rate of the blood pump in the first stage is controlled by a controller to generate blood pressure pulses during ventricular systole.

[0014] In many embodiments, the method further includes switching back to controlling the blood pump operation according to the first-segment operating mode at an appropriate point in the cardiac cycle. For example, in many embodiments of the method, the controller detects the end of the second segment by detecting when the blood pump rotation rate for pumping blood at a target minimum blood flow rate decreases to or below the blood pump rotation rate according to the first-segment operating mode of the blood pump. In response to detecting the end of the second segment, the controller switches back to controlling the rotation rate according to the first-segment operating mode of the blood pump.

[0015] In many embodiments of the method, the first operating mode provides a level of circulatory support during ventricular systole suitable for exercising the patient's semilunar valves and / or for attempting to wean the patient off the ventricular assist device. Accordingly, in many embodiments of the method, the rotational rate of the blood pump in the first operating mode results in the opening and closing of the patient's semilunar valves during ventricular systole. When attempting to wean the patient off the ventricular assist device, the target minimum blood flow rate can be selected to prevent large retrograde flow rates through the blood pump. For example, when attempting to wean the patient off the ventricular assist device, the target minimum blood flow rate can be in the range of about 0.0 L / min to 0.5 L / min. In some embodiments of the method, the target minimum blood flow rate when attempting to wean the patient off the ventricular assist device can be 0.0 L / min.

[0016] Any suitable method can be used by the controller to monitor the blood flow rate through the blood pump. For example, in some embodiments of the method, the controller monitors the blood flow rate through the blood pump by estimating the blood flow rate based on the rotational speed of the blood pump and operating parameters indicating the power consumption of the blood pump. In some embodiments of the method, the controller monitors the blood flow rate through the blood pump by estimating the blood flow rate based on the rotational speed of the blood pump and operating parameters indicating the pressure difference across the blood pump.

[0017] In some embodiments of the method, the controller updates the target minimum blood flow rate based on the patient's activity level. For example, in some embodiments, the method includes measuring patient physiological parameters indicating the patient's activity level via sensors. In some embodiments, the controller updates the target minimum blood flow rate based on the patient's physiological parameters.

[0018] In many embodiments of this method, the rotational rate of the blood pump in the first segment can be selectively switched between being controlled by the controller according to a first operating mode and being controlled by the controller via a second operating mode in the first segment, and vice versa. Any suitable criteria and / or clinician input can be used to select when to control the rotational rate of the blood pump in the first segment via either the first or second operating mode.

[0019] On the other hand, the mechanical circulatory support system includes a continuous flow blood pump and a controller. The continuous flow blood pump is implanted in fluid communication with the patient's ventricles and arteries to assist blood flow from the ventricles to the arteries. The controller is operatively connected to the blood pump. The controller is operable to control the rotational speed of the blood pump to pump blood from the ventricles to the arteries. The rotational rate of the blood pump is controlled according to a first-stage operating mode of the blood pump within a first stage. The controller is operable to monitor the blood flow velocity through the blood pump. Based on the monitored blood flow velocity through the blood pump, the controller determines whether continuing to control the rotational rate of the blood pump according to the first-stage operating mode within a second stage of the cardiac cycle will result in the blood flow velocity through the blood pump being less than a target minimum blood flow velocity. In response to determining that continuing to control the rotational rate of the blood pump according to the first-stage operating mode within the second stage will result in the blood flow velocity through the blood pump being less than the target minimum blood flow velocity, the controller controls the rotational speed of the blood pump within the second stage such that the blood flow velocity through the blood pump approaches the target minimum blood flow velocity.

[0020] In many embodiments of this system, the target minimum blood flow rate can be any suitable blood flow rate through the blood pump during ventricular diastole in a patient. For example, in many embodiments of this system, the target minimum blood flow rate is in the range of approximately 0 L / min to 2.0 L / min. In some embodiments of this system, the target minimum blood flow rate is in the range of 0.5 L / min to 1.5 L / min. In some embodiments of this system, the target minimum blood flow rate is in the range of 0.8 L / min to 1.2 L / min. In another embodiment, the blood pump is controlled to act as a one-way valve during diastole, where the net diastolic blood flow is or close to 0.0 L / min.

[0021] In many embodiments of the system, the controller compares the current blood flow rate of the blood pump with a target minimum blood flow rate to determine whether to continue controlling the operation of the blood pump according to the first operating mode, or to switch to controlling the rotational rate of the blood pump to pump blood through the blood pump at the target minimum blood flow rate. For example, in some embodiments of the system, determining whether continuing to control the rotational rate of the blood pump according to the first operating mode during the second segment of the cardiac cycle would result in a blood flow rate through the blood pump being less than the target minimum blood flow rate includes determining the relative difference between the current blood flow rate through the blood pump and the target minimum blood flow rate. In some embodiments of the system, determining whether continuing to control the rotational rate of the blood pump according to the first operating mode during the second segment of the cardiac cycle would result in a blood flow rate through the blood pump being less than the target minimum blood flow rate further includes determining the rate of change of the blood flow rate through the blood pump.

[0022] In many embodiments of this system, any suitable first-stage operating mode of the blood pump can be used. For example, in some embodiments of the system, the rotational rate of the blood pump in the first-stage operating mode is constant. In some embodiments of the system, the rotational rate of the blood pump in the first-stage operating mode is varied to generate periodic pulsating blood flow. In some embodiments of the system, the periodic pulsating blood flow is synchronized with the patient's cardiac cycle. In some embodiments of the system, the periodic pulsating blood flow is synchronized with the patient's cardiac cycle based on monitored blood flow through the blood pump. In some embodiments of the system, the rotational rate of the blood pump in the first stage is controlled by a controller to generate blood pressure pulses during ventricular systole.

[0023] In many embodiments of the system, the controller switches back to controlling the blood pump operation according to the first-segment operating mode at appropriate points in the cardiac cycle. For example, in many embodiments of the system, the controller detects the end of the second segment by detecting when the blood pump rotation rate for pumping blood at a target minimum blood flow rate decreases to or below the blood pump rotation rate according to the first-segment operating mode. In response to detecting the end of the second segment, the controller switches back to controlling the rotation rate according to the first-segment operating mode of the blood pump.

[0024] In many embodiments of the system, the first operating mode provides a level of circulatory support during ventricular systole suitable for exercising the patient's semilunar valves and / or for attempting to wean the patient off the ventricular assist device. Accordingly, in many embodiments of the system, the rotational rate of the blood pump in the first operating mode results in the opening and closing of the patient's semilunar valves during ventricular systole. When attempting to wean the patient off the ventricular assist device, a target minimum blood flow rate can be selected to prevent large retrograde flow rates through the blood pump. For example, the target blood flow rate may be in the range of about 0.0 L / min to 0.5 L / min when attempting to wean the patient off the ventricular assist device. In some embodiments of the system, the target minimum blood flow rate may be 0.0 L / min when attempting to wean the patient off the ventricular assist device.

[0025] In many embodiments of this system, the controller may use suitable methods to monitor the blood flow rate through the blood pump. For example, in some embodiments of the system, the controller estimates the blood flow rate based on the rotational speed of the blood pump and operating parameters indicating the power consumption of the blood pump. In some embodiments of the system, the controller estimates the blood flow rate based on the rotational speed of the blood pump and operating parameters indicating the pressure difference across the blood pump.

[0026] In some embodiments of the system, the controller updates the target minimum blood flow rate based on the patient's activity level. For example, in some embodiments, the system includes a sensor that measures patient physiological parameters indicative of the patient's activity level. In some embodiments of the system, the controller updates the target minimum blood flow rate based on patient physiological parameters. In some embodiments of the system, the sensor includes a heart rate sensor. In some embodiments of the system, the sensor includes an accelerometer.

[0027] To gain a more complete understanding of the nature and advantages of this invention, reference should be made to the following detailed descriptions and accompanying drawings. Attached Figure Description

[0028] Figure 1 This is an illustration of a mechanical circulatory support system according to many embodiments, which includes a ventricular assist device (VAD) implanted in the patient.

[0029] Figure 2 yes Figure 1 An exploded view of the implanted components of the circulatory support system.

[0030] Figure 3 yes Figure 1 An illustration of a VAD that is attached to the patient's heart to enhance the blood pumping action of the patient's left ventricle.

[0031] Figure 4 yes Figure 3 A cross-sectional view of the VAD.

[0032] Figure 5 yes Figure 3 An illustration of an embodiment of the control unit of the VAD.

[0033] Figure 6 According to many embodiments Figure 5 The heart-side view of the control unit shows the triaxial accelerometer included in the control unit.

[0034] Figure 7 yes Figure 1 A schematic diagram of the control system architecture of the mechanical support system according to an embodiment.

[0035] Figure 8 It is a graph showing the left ventricular pressure, left atrial pressure, and aortic pressure during one cardiac cycle.

[0036] Figure 9 It is a graph showing the blood flow velocity through the blood pump of the left ventricular assist device during one cardiac cycle.

[0037] Figure 10 A typical head-flow curve for a centrifugal blood pump is shown.

[0038] Figure 11 The diagram illustrates adjusting the rotational speed of a blood pump according to an embodiment to prevent the flow rate through the blood pump from dropping below a target minimum blood flow rate during ventricular diastole.

[0039] Figure 12 It is a graph of the blood flow velocity through the blood pump of the left ventricular assist device during a cardiac cycle according to an embodiment, wherein the speed of the blood pump is adjusted during ventricular diastole to prevent the flow velocity through the blood pump from falling below a target minimum blood flow velocity.

[0040] Figure 13 It is a graph of blood flow velocity through the blood pump of the left ventricular assist device during a cardiac cycle according to an embodiment, wherein the speed of the blood pump is adjusted during ventricular diastole to prevent retrograde flow through the blood pump.

[0041] Figure 14 This is a simplified block diagram of a method for operating a blood pump in a first operating mode and switching to control the blood pump to maintain a target minimum blood flow rate through the blood pump during ventricular diastole, according to an embodiment.

[0042] Figure 15 This is a simplified block diagram of a method for controlling a blood pump to maintain a target minimum blood flow rate through the blood pump during ventricular diastole, according to an embodiment.

[0043] Figure 16 This is a graph showing the variation of the target minimum blood flow rate through the blood pump according to the patient's activity level, based on an embodiment. Detailed Implementation

[0044] In the following description, various embodiments of the invention will be described. Specific configurations and details are set forth for illustrative purposes to provide a thorough understanding of the embodiments. However, it will also be apparent to those skilled in the art that the invention may be practiced without these specific details. Furthermore, well-known features may be omitted or simplified so as not to obscure the described embodiments.

[0045] Methods for controlling the rotational speed of a blood pump and related mechanical circulatory support systems adjust the pump's rotational speed based on the blood flow rate during ventricular diastole to prevent the flow rate through the pump from falling below a target minimum flow rate. In the case of continuous-flow pumps (such as those used in many ventricular assist devices (VADs), the blood flow rate through the pump depends on the pump's rotational speed and the pressure differential across the pump. For example, for a left ventricular assist device (LVAD), the pressure differential across the pump is approximately equal to the aortic pressure minus the left ventricular pressure. In many cases, physicians use echocardiography and pump performance parameters (such as estimated flow) to set the VAD's rotational speed. However, once a patient is discharged, a single, set-it-and-forget-it speed setting may not be optimal for the patient because volumetric status may change, the natural heart shape may change, and physiological pressures may change. The methods and systems described herein employ an adaptive approach, where the pump's rotational speed is adjusted to maintain optimal diastolic flow.

[0046] The methods and systems described herein can be implemented using any suitable continuous flow pump. For example, a particularly suitable type of blood pump includes a magnetically levitated rotor / impeller. In many cases, blood pumps including magnetically levitated rotors / impellers are capable of the rotational speed regulation described herein, which can occur once per cardiac cycle during ventricular diastole. By regulating the rotational speed of the blood pump during ventricular diastole, the sensitivity of the continuous flow blood pump (e.g., centrifugal LVAD) to changes in the pressure differential across the pump can be reduced, thereby preventing excessively low blood flow rates through the pump during ventricular diastole.

[0047] With good accuracy in flow rate estimation, the rotational speed of the blood pump can be adjusted to maintain optimal or desired flow during ventricular diastole and / or ventricular systole. During ventricular diastole, the aortic valve closes, and the pressure gradient across the blood pump is maximized. If the rotational speed of the blood pump remains constant, the blood flow velocity through the pump will reach its minimum during ventricular diastole. Physicians will typically set the rotational speed of the blood pump low enough to ensure that the blood flow velocity through the pump is low enough to avoid ventricular aspiration events. Once the blood flow velocity through the pump is already low enough to avoid aspiration events, any subsequent increase in the patient's blood pressure will further reduce the blood flow velocity through the pump during ventricular diastole. The methods and systems described in this article adjust the rotational speed of the blood pump to ensure adequate ventricular unload during a wide range of blood pressure variations.

[0048] The methods and systems described herein can be implemented in any suitable operational scenario. For example, the methods and systems described herein can be used during normal operational scenarios to increase the effectiveness of the blood pump. As another example, the methods and systems can be used in conjunction with attempts to wean a patient off the VAD to enable device removal. In many cases, attempts to wean a patient off the VAD involve temporarily reducing the rotational speed of the blood pump to temporarily increase the load on the patient's natural heart. However, a reduction in the blood pump speed can, in many cases, result in retrograde flow through the blood pump during ventricular diastole, which does not imply the complete absence of the device. Therefore, the methods and systems described herein can be employed during attempts to wean a patient off the VAD, in which the rotational speed of the VAD is adjusted such that the blood flow velocity through the blood pump during ventricular diastole approaches zero (i.e., no diastolic unloading and no retrograde flow).

[0049] Mechanical circulation auxiliary system

[0050] Referring now to the accompanying drawings, in which the same reference numerals denote the same parts throughout several views. Figure 1 This is an illustration of a mechanical circulatory support system 10, which includes a ventricular assist device (VAD) 14 implanted in the patient's body 12. The mechanical circulatory support system 10 includes the VAD 14, a ventricular cuff 16, an outflow cannula 18, an external system controller 20, and a power supply 22. The VAD 14 can be attached to the tip of the left ventricle, as shown, or to the right ventricle, or separate VADs can be attached to each of the ventricles of the heart 24. The VAD 14 can be able to pump the entire blood flow delivered from the pulmonary circulation to the left ventricle (i.e., up to 10 liters per minute). The relevant blood pumps applicable to the present invention are described in more detail below and in the following U.S. patents: No. 5,695,471, No. 6,071,093, No. 6,116,862, No. 6,186,665, No. 6,234,772, No. 6,264,635, No. 6,688,861, No. 7,699,586, No. 7,976,271, No. 7,997,854, and No. 8,007,254. U.S. Patent Nos. 8,152,493, 8,419,609, 8,652,024, 8,668,473, 8,852,072, 8,864,643, 8,882,744, 9,068,572, 9,091,271, 9,265,870, and 9,382,908, all of which are U.S. Patents and Patents, all of which are incorporated herein by reference in their entirety for all purposes. References Figure 1 and Figure 2The VAD 14 can be attached to the heart 24 via a ventricular cuff 16, which can be sutured to the heart 24 and coupled to the VAD 14. In the illustrated embodiment, the output of the VAD 14 is connected to the ascending aorta via an outflow cannula 18, allowing the VAD 14 to effectively transfer blood from the left ventricle and push it into the aorta for circulation through the rest of the patient's vascular system.

[0051] Figure 1 A mechanical circulatory support system 10 is shown during operation powered by battery 22. A drive system 26 passing through the patient's abdomen 28 connects the VAD 14 to an external system controller 20, which monitors the operation of system 10. Relevant controllers applicable to the invention are described in more detail below and in the following patents: U.S. Patent Nos. 5,888,242, 6,991,595, 8,323,174, 8,449,444, 8,506,471, 8,597,350, and 8,657,733, EP 1812094, and U.S. Patent Publications Nos. 2005 / 0071001 and 2013 / 0314047, all of which are incorporated herein by reference in their entirety for all purposes. System 10 may be powered by one, two, or more batteries 22. It should be understood that although the system controller 20 and power supply 22 are shown as being external to / outside the patient's body 12, the drive system 26, system controller 20, and / or power supply 22 may be partially or completely implanted within the patient's body 12, as separate components or integrated with the VAD 14. Examples of such modifications are further described in U.S. Patent Nos. 8,562,508 and 9,079,043, all of which are incorporated herein by reference in their entirety for all purposes.

[0052] refer to Figure 3 and Figure 4The VAD 14 has a circular housing 110 and is shown implanted in a patient 12, with a first face 111 of the housing 110 positioned against the patient's heart 24 and a second face 113 facing away from the heart 24. The first face 111 of the housing 110 includes an inlet cannula 112 extending into the left ventricle (LV) of the heart 24. The second face 113 of the housing 110 has a chamfered edge 114 to avoid irritating other tissues that may come into contact with the VAD 14, such as the patient's septum. To construct the disc-shaped housing 110 in a compact form, the stator 120 and electronics 130 of the VAD 14 are positioned on the inflow side of the housing facing the first face 111, and the rotor 140 of the VAD 14 is positioned along the second face 113. This positioning of the stator 120, electronics 130, and rotor 140 allows the edge 114 to be chamfered along the profile of the rotor 140, for example, as at least in Figure 3 and Figure 4 As shown in the image.

[0053] Reference Figure 4 VAD 14 includes a partition wall 115 within housing 110, defining a blood flow conduit 103. The blood flow conduit 103 extends from an inlet opening 101 of inlet sleeve 112 through stator 120 to an outlet opening 105 defined by housing 110. Rotor 140 is positioned within the blood flow conduit 103. Stator 120 is circumferentially disposed around a first portion 140a of rotor 140 (e.g., around permanent magnet 141). Stator 120 is also positioned relative to rotor 140 such that, in use, blood flows through stator 120 within blood flow conduit 103 before reaching rotor 140. Permanent magnet 141 has a permanent magnetic north pole (N) and a permanent magnetic south pole (S) for combined active and passive magnetic levitation of rotor 140 and for rotation of rotor 140. Rotor 140 also has a second portion 140b, which includes impeller blades 143. The impeller blade 143 is positioned within the volute 107 of the blood flow conduit, such that the impeller blade 143 is positioned close to the second surface 113 of the housing 110.

[0054] The disc-shaped housing 110 further includes a circumferential wall 116 extending between the first face 111 and the removable cover 118. As shown, the circumferential wall 116 is formed as a hollow cylinder having a width W between opposing portions of the circumferential wall 116. The housing 110 also has a thickness T between the first face 111 and the second face 113 that is less than the width W. The thickness T is from about 0.5 inches to about 1.5 inches, and the width W is from about 1 inch to about 4 inches. For example, the width W can be about 2 inches, and the thickness T can be about 1 inch.

[0055] A circumferential wall 116 encloses an internal compartment 117 surrounding a partition wall 115 and a blood flow conduit 103, wherein a stator 120 and electronics 130 are disposed within the internal compartment 117 surrounding the partition wall 115. A removable cover 118 includes a second surface 113, a chamfered edge 114, and defines an outlet opening 105. The cover 118 can be threadedly engaged with the circumferential wall 116 to seal the cover 118 in engagement with the circumferential wall 116. The cover 118 includes an inner surface 118a that defines a volute 107 in fluid communication with the outlet opening 105.

[0056] Within the internal compartment 117, electronics 130 is positioned adjacent to the first surface 111, and stator 120 is positioned adjacent to electronics 130 on the side opposite to the first surface 111. Electronics 130 includes a circuit board 131 and various components carried on the circuit board 131 for controlling the operation of VAD 14 (e.g., magnetic levitation and / or rotor drive) by controlling the power supply to stator 120. Housing 110 is configured to house the circuit board 131 within the internal compartment 117, generally parallel to the first surface 111, to efficiently utilize the space within the internal compartment 117. The circuit board also extends radially inward toward partition wall 115 and radially outward toward circumferential wall 116. For example, the size of the internal compartment 117 is generally designed not to exceed the space required to house the circuit board 131, as well as space for heat dissipation, material expansion, potting material, and / or mounting other components of the circuit board 131. Therefore, the external shape of the housing 110 near the first surface 111 generally closely conforms to the shape of the circuit board 131 to provide an external dimension that is not much larger than the size of the circuit board 131.

[0057] Continue to refer to Figure 4 The stator 120 includes a back iron 121 and pole pieces 123a-123f, which are spaced apart and arranged around a partition wall 115. The back iron 121 extends around the partition wall 115 and is formed as a generally flat disk of a ferromagnetic material such as steel to conduct magnetic flux. The back iron 121 is arranged next to the control electronics 130 and provides a base for the pole pieces 123a-123f.

[0058] Each of the pole pieces 123a-123f is L-shaped and has a drive coil 125 for generating an electromagnetic field to rotate the rotor 140. For example, pole piece 123a has a first leg 124a that contacts the back iron 121 and extends from the back iron 121 toward the second surface 113. Pole piece 123a may also have a second leg 124b that extends from the first leg 124a through an opening in the circuit board 131 toward a partition wall 115 near the permanent magnet 141 of the rotor 140. In one aspect, each of the second legs 124b of pole pieces 123a-123f is inserted through an opening in the circuit board 131. In another aspect, each of the first legs 124a of pole pieces 123a-123f is inserted through an opening in the circuit board 131. In another aspect, the opening in the circuit board encloses the first legs 124a of pole pieces 123a-123f.

[0059] In a general sense, VAD 14 may include one or more Hall sensors that can provide an output voltage proportional to the magnetic field strength between at least one of the poles 123a-123f and the permanent magnet 141, and the output voltage can provide feedback to the control electronics 130 of VAD 14 to determine whether the rotor 140 and / or the permanent magnet 141 is not in its intended position for operation of VAD 14. For example, the position of the rotor 140 and / or the permanent magnet 141 can be adjusted, for example, by pushing or pulling the rotor 140 or the permanent magnet 141 toward the center of the blood flow conduit 103 or toward the center of the stator 120.

[0060] Each of pole pieces 123a-123f also has a levitation coil 127 for generating an electromagnetic field to control the radial position of rotor 140. Each of drive coils 125 and levitation coils 127 includes multiple windings around the conductors of pole pieces 123a-123f. Specifically, each of drive coils 125 is wound around two adjacent pole pieces (such as pole pieces 123d and 123e) of pole piece 123, and each levitation coil 127 is wound around a single pole piece. Drive coils 125 and levitation coils 127 are wound around a first leg of pole piece 123, and during use, the magnetic flux generated by allowing current to flow through coils 125 and 127 is conducted through the first and second legs of pole piece 123 and the back iron 121. The drive coil 125 and levitation coil 127 of stator 120 are arranged in a pair and controlled to drive the rotor and levitate the rotor 140 radially by generating an electromagnetic field that interacts with the permanent magnet poles S and N of permanent magnet 141. Because stator 120 includes both drive coil 125 and levitation coil 127, only a single stator is needed to levitate the rotor 140 using only passive and active magnetic forces. In this configuration, permanent magnet 141 has only one magnetic moment and is formed as a monolithic permanent magnet 141. For example, stator 120 can be controlled as discussed in U.S. Patent No. 6,351,048, the entire contents of which are incorporated herein by reference for all purposes. Control electronics 130 and stator 120 are connected via cable 119 ( Figure 3 Receiving electrical power from a remote power source. Other relevant patents, namely U.S. Patents Nos. 5,708,346, 6,053,705, 6,100,618, 6,222,290, 6,249,067, 6,278,251, 6,351,048, 6,355,998, 6,634,224, 6,879,074, and 7,112,903, all of which are incorporated herein by reference in their entirety for all purposes.

[0061] Rotor 140 is arranged within housing 110 such that its permanent magnet 141 is located upstream of the impeller blades and closer to inlet opening 101. Permanent magnet 141 is housed within blood flow conduit 103 near the second leg 124b of pole piece 123 to provide a passive axial centering force through the interaction of the permanent magnet 141 with the ferromagnetic material of pole piece 123. When rotor 140 is centered within partition wall 115, a gap 108 is formed between permanent magnet 141 and partition wall 115. Gap 108 can range from approximately 0.2 mm to approximately 2 mm. For example, gap 108 can be approximately 1 mm. The north permanent magnet N and south permanent magnet S of permanent magnet 141 provide permanent magnetic attraction between rotor 140 and stator 120. This permanent magnetic attraction serves as a passive axial alignment force, which tends to keep rotor 140 substantially centered within stator 120 and tends to resist movement of rotor 140 toward first face 111 or toward second face 113. When gap 108 is small, the magnetic attraction between permanent magnet 141 and stator 120 is large, and the size of gap 108 is designed to allow permanent magnet 141 to provide a passive magnetic axial alignment force of sufficient magnitude to limit rotor 140 contact with the inner surface 118a of partition wall 115 or cover 118. Rotor 140 also includes a shroud 145 that covers the end of impeller blade 143 facing second face 113, which helps guide blood flow into volute 107. When the rotor 140 is suspended by the stator 120, the inner surfaces 118a of the shroud 145 and the cover 118 form a gap 109 between the shroud 145 and the inner surface 118a. The gap 109 can be from about 0.2 mm to about 2 mm. For example, the gap 109 can be about 1 mm.

[0062] As blood flows through the blood flow conduit 103, it passes through a central aperture 141a formed by the permanent magnet 141. Blood also flows through a gap 108 between the rotor 140 and the partition wall 115, and through a gap 109 between the shroud 145 and the inner surface 108a of the cover 118. Gap 108 and 109 are large enough to allow sufficient blood flow to limit clot formation, which could occur if blood is allowed to stagnate. Gap 108 and 109 are also large enough to limit the pressure acting on the blood cells so that the blood is not damaged when flowing through the VAD 14. Because the size of gap 108 and 109 limits the pressure acting on the blood cells, gap 108 and 109 are too large to provide meaningful hydrodynamic levitation. That is, the blood does not act as a bearing within gap 108 and 109, and the rotor is only magnetically levitated. In various embodiments, the size and dimensions of gap 108 and 109 are designed such that the blood flowing through the gap forms a membrane that provides hydrodynamic levitation. In this way, the rotor can be suspended by magnetic force, hydrodynamic force, or both.

[0063] Since the rotor 140 is radially levitated by active control of the levitation coil 127 as discussed above, and axially levitated by the passive interaction between the rotor 140 and the stator 120, no rotor levitation component generated by a magnetic field is required near the second surface 113. The incorporation of all components for rotor levitation (i.e., the levitation coil 127 and pole piece 123) into the stator 120 allows the profile of the cover 118 to be designed to resemble the shape of the impeller plate 143 and the volute 107. Additionally, the incorporation of all rotor levitation components into the stator 120 eliminates the need for electrical connectors extending from the compartment 117 to the cover 118, allowing for easy installation and / or removal of the cover and eliminating potential sources of pump failure.

[0064] In operation, the drive coil 125 of the stator 120 generates an electromagnetic field through pole pieces 123. This electromagnetic field selectively attracts and repels the magnetic north pole (N) and magnetic south pole (S) of the rotor 140, causing the rotor 140 to rotate within the stator 120. For example, one or more Hall sensors can sense the current position of the rotor 140 and / or the permanent magnet 141, wherein the output voltage of one or more Hall sensors can be used to selectively attract and repel the magnetic north pole (N) and magnetic south pole (S) of the rotor 140, causing the rotor 140 to rotate within the stator 120. As the rotor 140 rotates, the impeller blades 143 force blood into the volute 107, causing the blood to be forced out from the outlet opening 105. Additionally, the rotor draws blood into the VAD 14 through the inlet opening 101. As blood is drawn into the blood pump by the rotation of the impeller blades 143 of the rotor 140, the blood flows through the inlet opening 101 and through the control electronics 130 and the stator 120 toward the rotor 140. Blood flows through the orifice 141a of the permanent magnet 141 and between the impeller blade 143, the shroud 145, and the permanent magnet 141, entering the volute 107. Blood also flows around the rotor 140, through gap 108, and through gap 109 between the shroud 145 and the inner surface 118a of the cover 118. Blood exits the volute 107 through outlet opening 105, which can be coupled to an outlet sleeve.

[0065] Figure 5A Hall sensor assembly 200 for a VAD 14 according to various embodiments is shown. The Hall sensor assembly 200 includes a printed circuit board (PCB) 202 and six individual Hall effect sensors 208 supported by the PCB 202. The Hall effect sensors 208 are configured to transduce the position of the rotor 140 of the VAD 14. In the illustrated embodiment, the Hall effect sensors 208 are supported orthogonally upright relative to the PCB 202, and the longest edges of each of the Hall effect sensors 208 are aligned to have orthogonal components relative to the surface of the PCB 202. Each of the Hall effect sensors 208 generates an output voltage that is directly proportional to the strength of the magnetic field located between at least one of the pole pieces 123a-123f and the permanent magnet 141. The voltage output by each of the Hall effect sensors 208 is received by control electronics 130, which processes the sensor output voltage to determine the position and orientation of the rotor 140. The determined position and orientation of rotor 140 are used to determine whether rotor 140 is not in the intended position for operation of VAD 14. For example, the position of rotor 140 and / or permanent magnet 141 can be adjusted, for example, by pushing or pulling rotor 140 or permanent magnet 141 toward the center of blood flow conduit 103 or toward the center of stator 120. The determined position of rotor 140 can also be used to determine rotor eccentricity or target rotor eccentricity (which can be used as described in U.S. Patent No. 9,901,666, the entire contents of which are incorporated herein by reference in their entirety for all purposes) to estimate the flow rate of blood pumped by VAD 14.

[0066] Figure 6 This is a frontal view of a control electronics 130 according to many embodiments, showing an accelerometer 210 included within the control electronics 130. In many embodiments, the accelerometer 210 is a triaxial accelerometer that measures the acceleration experienced by the control electronics 130 (and therefore by the VAD 14) along three orthogonal axes (i.e., X-axis 212, Y-axis 214, and Z-axis 216). In the illustrated embodiment, the X-axis 212 and Y-axis 214 are each oriented orthogonal to the rotation axis of the rotor 140, and the Z-axis 216 is parallel to the rotation axis of the rotor 140.

[0067] Figure 7 This is a schematic diagram of the control system architecture of the mechanical support system 10. The drive system 26 couples the embedded VAD 14 to an external system controller 20, which monitors system operation via various software applications.

[0068] VAD 14 includes control electronics 130, Hall effect sensor assembly 200, motor stator 120, and rotor / impeller 140. In the illustrated embodiment, the control electronics include a processor 218, a storage device 220 (which may include read-only memory and / or random access memory), an accelerometer 210, a motor control unit 222, and a communication unit 224. In some embodiments, storage device 220 stores one or more software applications executable by processor 218 for various functions. For example, one or more software applications may implement control of motor control unit 222 to achieve radial levitation and rotational drive of rotor 140 during operation. In some embodiments, as described herein, one or more programs implement processing of outputs from accelerometer 210 and / or operating parameters of VAD 14 (e.g., drive current, rotational speed, flow rate, pressure difference across impeller) to detect and / or measure patient physiological events and / or activities (e.g., patient orientation, patient activity level, cardiac wall motion, heart sounds, heart rate, respiratory rate, diaphragm contraction, cardiac cycle timing). As described herein, one or more programs can implement control of the motor control unit 222 to synchronize changes in the output of the VAD 14 with the patient's cardiac cycle timing. For example, the output of the VAD 14 can be increased for a period of time during ventricular systole to increase blood pumping via ventricular systole, thereby reducing the associated load on the ventricles. One or more programs can implement control of the motor control unit 222 to change the output of the VAD 14 based on the patient's activity level. For example, in many embodiments, the output of the VAD 14 increases in response to increased patient activity and decreases in response to decreased patient activity. One or more programs can also be used to process the output from the accelerometer 210 and / or the operating parameters of the VAD 14 to generate patient monitoring data and / or VAD monitoring data as described herein. The communication unit 224 provides wired and / or wireless communication between the VAD 14 and the external system controller 20. In some embodiments, the motor control unit 222 is included in the VAD 14. In some embodiments, the motor control unit 222 is included in the external system controller 20.

[0069] The external system controller 20 may then be coupled to the battery 22 or to an AC power module 30 connected to an AC outlet. The external system controller 20 may include a processor 226, a storage device 228 (which may include read-only memory and / or random access memory), an emergency backup battery (EBB) for powering the system (e.g., when battery 22 is depleted), one or more display units 230, one or more input / output devices 232, and a communication unit 234, which may have Bluetooth functionality for wireless data transmission. An external computer with a system monitor 32 (which may be operated by a clinician or patient) may be further coupled to the circulatory support system 10 for: configuring the external system controller 20, the implanted VAD 14, and / or patient-specific parameters; updating the software on the external system controller 20 and / or the implanted VAD 14; monitoring system operation; and / or acting as a conduit for system input or output.

[0070] In some embodiments, storage device 228 stores one or more software applications executable by processor 226 for various functions. For example, one or more software applications may implement control of motor control unit 222 to achieve radial levitation and rotational drive of rotor 140 during operation. In some embodiments, as described herein, one or more programs implement processing of outputs from accelerometer 210 and / or operating parameters of VAD 14 (e.g., drive current, rotational speed, flow rate, pressure difference across the impeller) to detect and / or measure patient physiological events and / or activities (e.g., patient orientation, patient activity level, cardiac wall motion, heart sounds, heart rate, respiratory rate, diaphragm contraction, cardiac cycle timing). As described herein, one or more programs may implement control of motor control unit 222 to synchronize changes in the output of VAD 14 with the patient's cardiac cycle timing. For example, the output of VAD 14 may be increased for a period of time during ventricular systole to increase blood pumping via ventricular systole, thereby reducing the associated load on the ventricles. One or more programs may implement control of motor control unit 222 to change the output of VAD 14 based on the patient's activity level. For example, in many embodiments, the output of VAD 14 increases in response to increased patient activity and decreases in response to decreased patient activity. One or more programs may also be used to process the output from accelerometer 210 and / or operating parameters of VAD 14 to generate patient monitoring data and / or VAD monitoring data as described herein. Communication unit 234 provides wired and / or wireless communication between external system controller 20 and VAD 14 and / or system monitor 32.

[0071] Pumping blood flow rate during ventricular diastole

[0072] Figure 8 This is a graph showing the left ventricular pressure (302), left atrial pressure (304), and aortic pressure (306) during one cardiac cycle. At the beginning of the cardiac cycle, the atrioventricular (AV) valves open, and blood flows from the left and right atria into the left and right ventricles, respectively. During ventricular systole, the ventricular contraction closes the AV valves and increases ventricular pressure. During left ventricular systole, the left ventricular pressure (302) increases to a level slightly higher than the aortic pressure (306), causing the aortic valve to open spontaneously. The sustained contraction of the left ventricle ejects blood from the left ventricle through the aortic valve into the aorta. This ejection of blood into the aorta raises the aortic pressure (306), which is slightly lower than the left ventricular pressure (302) at the initial portion of the blood ejection from the left ventricle, but slightly higher than the left ventricular pressure (302) at the terminal portion of the blood ejection from the left ventricle. At the end of the ejection of blood from the left ventricle into the aorta, the aortic valve naturally closes in response to a left ventricular pressure of 302 being slightly less than an aortic pressure of 306. Subsequent relaxation of the left ventricle causes a significant decrease in left ventricular pressure of 302 to a level slightly less than left atrial pressure of 304, thereby causing the left AV valve to open.

[0073] The blood flow rate via the pump of a ventricular assist device typically varies throughout the patient's cardiac cycle in response to changes in the pressure differential across the pump during that cycle. For example, Figure 9 This is a graph showing an example blood flow rate 308 through the blood pump of a left ventricular assist device during a patient's cardiac cycle. The blood flow rate 308 shown is for constant rotational speed operation of the blood pump. Figure 9 Blood flow velocity 308 and Figure 8 Alignment with the cardiac cycle to better reflect changes in blood flow velocity 308 with Figure 8 The pressure gradients shown are correlated. At the beginning of the cardiac cycle, blood flow velocity 308 is relatively low due to the relatively large difference between aortic pressure 306 and left ventricular pressure 302. During the initial portion of ventricular systole, the increase in left ventricular pressure 302 reduces the difference between aortic pressure 306 and left ventricular pressure 302, resulting in a corresponding increase in blood flow velocity 308 due to the decrease in the pressure gradient across the pump. During the ejection of blood from the left ventricle into the aorta, blood flow velocity 308 gradually decreases as aortic pressure 306 gradually increases relative to left ventricular pressure 302. After the natural aortic valve closes, blood flow velocity 308 significantly decreases in response to the increased pressure gradient across the pump due to the decrease in ventricular pressure 302. After the AV valve opens, blood flow velocity 308 gradually increases in response to the gradually decreasing pressure gradient across the pump, primarily due to the gradual decrease in aortic pressure 306.

[0074] The rotational speed of the continuous-flow blood pump in a VAD is typically limited during ventricular diastole to avoid aspiration events, in which blood is drawn from the ventricles at an excessively high rate. Correspondingly, physicians will usually set the pump's rotational speed low enough to ensure that the blood flow through the pump is low enough to avoid causing ventricular aspiration events.

[0075] Once the blood flow rate through the pump is already low enough to avoid aspiration, any subsequent increase in the patient's blood pressure will further reduce the blood flow rate through the pump during ventricular diastole. Continuous flow pumps are particularly sensitive to increases in the pressure differential across the pump at the upper limit of the pump's differential capacity. For example, Figure 10 Typical head-flow profiles for a centrifugal blood pump operating at a constant rotational speed are shown. At low differential pressures, the flow rate 310 through the pump is higher. At the upper limit of the pump's differential pressure capacity, the flow rate 310 through the pump is zero. At low flow rates 310, relatively small changes in the differential pressure across the pump result in relatively large changes in flow rate 310. As described herein, when used in a VAD and operated at a constant rotational speed, the centrifugal blood pump speed is set such that the flow rate 310 is sufficiently low during ventricular diastole to avoid aspiration events. However, operating the centrifugal blood pump at a constant speed selected to produce a relatively low flow rate during ventricular diastole can result in relatively large changes in flow rate 310 during ventricular diastole in response to relatively small changes in the patient's blood pressure.

[0076] Adjusting the blood pump rotation speed to control the pump flow rate during ventricular diastole.

[0077] Variations in the ventricular diastolic flow velocity 310 can lead to inappropriate flow through the blood pump. For example, a significant decrease in a patient's blood pressure (relative to the patient's blood pressure corresponding to the set rotational speed of the blood pump during ventricular diastole) can result in an excessively high flow velocity 310 through the blood pump, which can cause aspiration events. On the other hand, a significant increase in a patient's blood pressure can result in an excessively low flow velocity 310 through the blood pump, which is insufficient to unload the ventricle before ventricular contraction. Furthermore, especially when the blood pump operates at a lower rotational speed than normal to provide reduced support during attempts to wean the patient off the VAD, a significant increase in the patient's blood pressure can cause retrograde flow through the blood pump, thus actually adding an unnatural extra burden to the patient's heart during attempts to wean the patient off the VAD.

[0078] In many embodiments, the rotational speed of the blood pump in the VAD is adjusted during ventricular diastole to prevent inappropriate flow rates through the blood pump during ventricular diastole. Any suitable method can be used to monitor the blood flow rate through the blood pump. For example, the blood flow rate through the blood pump can be monitored by estimating the blood flow rate using known methods based on the drive current supplied to the blood pump, the rotational speed of the blood pump rotor, the blood pressure at the blood pump inlet side, and / or the blood at the blood pump outlet side. Inlet-side pressure sensors and / or outlet-side pressure sensors can be used to measure inlet-side blood pressure and / or outlet-side blood pressure. The blood flow rate can be estimated based on the drive current supplied to the blood pump, the rotational speed of the blood pump rotor, and the pressure difference across the blood pump. Any suitable method can be used to estimate or measure the pressure difference across the blood pump. For example, the pressure difference and / or blood flow rate across the blood pump can be estimated and / or measured as described in U.S. Patent Publication No. 2017-0021070, the entire contents of which are incorporated herein by reference for all purposes. Figure 11The diagram illustrates adjusting the rotational speed of the blood pump to prevent the flow rate 312 through the pump from falling below a target minimum blood flow rate 314 during ventricular diastole. In the illustrated embodiment, the blood pump operates at a constant speed 316 during ventricular systole. The flow rate 312 through the pump decreases as the pressure differential across the pump increases after the natural aortic valve closes. With the pump operating at a constant speed 316 throughout ventricular diastole, if the patient's blood pressure is significantly higher than the blood pressure corresponding to the selection of the constant speed 316, the flow rate 312 may fall below the target minimum blood flow rate 314. Furthermore, particularly when the constant speed 316 is selected to provide reduced support to the patient during attempts to wean them off the VAD, the flow rate 312 through the pump may become negative even during ventricular diastole in the absence of adjustment to the pump's rotational speed. In the illustrated embodiment, the blood flow rate 312 through the blood pump is monitored, and when the flow rate 312 decreases below the initial flow rate 318, the rotational speed of the blood pump is increased such that the flow rate 312 changes from the initial flow rate 318 to the target minimum flow rate 314 within a suitable transition period. In the illustrated embodiment, the rotational speed of the blood pump is increased from a constant speed 316 through a rotational speed 320 to a rotational speed 322. The initial flow rate 318 can be selected to provide a suitable transition period, taking into account the rate at which the rotational speed of the blood pump can be increased. After the transition period, the rotational speed of the blood pump can then be adjusted so that the flow rate 312 through the blood pump is maintained at the target minimum blood flow rate 314 within an appropriate portion of ventricular diastole. For example, in some embodiments, the rotational speed of the blood pump is adjusted whenever the rotational speed of the flow rate 312, which is equal to the target minimum blood flow rate 314, is greater than the constant speed 316 at which the blood pump operates during ventricular systole. In such an embodiment, when the rotational speed for a flow rate 312 equal to the target minimum flow rate becomes less than the constant speed 316, the rotational speed of the blood pump can be restored to the constant speed 316.

[0079] Figure 12This is a graph illustrating the blood flow velocity 312 of the blood pump of the left ventricular assist device during a cardiac cycle according to an embodiment, wherein the rotational speed of the blood pump is adjusted during ventricular diastole to prevent the flow velocity through the blood pump from falling below a target minimum blood flow velocity 314. During the first segment of the cardiac cycle, the rotational speed of the blood pump is controlled according to a first-segment operating mode (e.g., constant speed mode, pulsatile mode, disengagement mode), and during the second segment of the cardiac cycle during ventricular diastole, the rotational speed of the blood pump is adjusted to prevent the flow velocity through the blood pump from falling below the target minimum blood flow velocity 314. In the illustrated embodiment, the blood flow velocity 312 approaches its maximum during the ejection of blood from the left ventricle into the aorta due to the corresponding low pressure differential across the blood pump. After the natural aortic valve is closed, the flow velocity 312 decreases in response to a corresponding increase in the relative pressure between the left ventricular pressure 302 and the aortic pressure 306. By monitoring the flow velocity 312, the rotational speed of the blood pump can be increased when the flow velocity 312 decreases to an initial flow velocity 318. By increasing the rotational speed of the blood pump, the rate of decrease in flow rate 312 is reduced to zero during the transition period 324. After the transition period 324, the rotational speed of the blood pump is adjusted to maintain flow rate 312 at a target minimum blood flow rate 314 for an appropriate portion of the cardiac cycle. In many embodiments, the rotational speed used to maintain flow rate 312 at the target minimum blood flow rate is reduced at the recovery point 326 to the blood pump rotational speed according to the first stage operating mode of the blood pump. The adjustment of the blood pump rotational speed can be terminated, and control of the blood pump rotational speed can be restored to control according to the first stage operating mode of the blood pump at the recovery point 326. To illustrate the effect of adjusting the blood pump rotational speed on the flow rate 312 through the blood pump, Figure 12 This illustrates a flow rate of 312 nm that would occur if the blood pump's rotational speed were controlled according to the first-stage operating mode throughout the cardiac cycle. The flow rate of 312 nm increases at recovery point 326 to return to the target minimum blood flow rate of 314.

[0080] Figure 13This is a graph of the blood flow velocity 312 through the blood pump of the left ventricular assist device during a cardiac cycle according to an embodiment, wherein the speed of the blood pump is adjusted during diastole to prevent retrograde flow through the blood pump. During the illustrated cardiac cycle, the rotational speed of the blood pump is controlled according to a disengaged first-segment operating mode during the first segment of the cardiac cycle, and the rotational speed of the blood pump is adjusted during ventricular diastole in the second segment of the cardiac cycle to prevent retrograde flow through the blood pump. The disengaged first-segment operating mode provides limited circulatory support to increase the percentage of the total blood pumping workload performed by the patient's heart. The disengaged first-segment operating mode can employ any suitable basic first-segment operating mode, such as a constant-speed mode or a pulsatile mode. In many cases, the rotational speed of the blood pump in the disengaged first-segment operating mode is lower than the rotational speed of the blood pump in the first-segment operating mode for a higher support level, resulting in a lower blood flow velocity 312 through the blood pump during ventricular diastole compared to the blood flow velocity through the blood pump for the first-segment operating mode for a higher support level. During the illustrated cardiac cycle, as blood is ejected from the left ventricle into the aorta, the blood flow velocity 312 approaches its maximum due to the corresponding low pressure differential across the pump. After the natural aortic valve closes, the flow velocity 312 decreases in response to the corresponding increase in the relative pressure between the left ventricular pressure 302 and the aortic pressure 306. By monitoring the flow velocity 312, the pump rotation speed can be increased once the flow velocity 312 decreases to an initial flow velocity 318. By increasing the pump rotation speed, the rate of decrease in flow velocity 312 reaches zero during the transition period 324. After the transition period 324, the pump rotation speed is adjusted to maintain the flow velocity 312 at a target minimum blood flow velocity suitable for weaning the patient off the VAD during ventricular diastole. In the illustrated embodiment, the pump rotation speed is adjusted such that the flow velocity 312 is zero during the second segment of the cardiac cycle. In many embodiments, the rotational speed used to maintain the flow rate 312 at zero is reduced at recovery point 326 to the blood pump rotational speed according to the blood pump's disengagement from the first stage operating mode. The adjustment of the blood pump rotational speed can be terminated, and control of the blood pump rotational speed can be restored at recovery point 326 to be controlled according to the blood pump's disengagement from the first stage operating mode. To illustrate the effect of adjusting the blood pump rotational speed on the flow rate 312 through the blood pump, Figure 13 This illustrates the flow rate of 312 nm (which is retrograde) that would occur if the blood pump's rotational speed were controlled according to the disengagement phase 1 operating mode throughout the cardiac cycle. The flow rate of 312 nm increases back to zero at recovery point 326.

[0081] The initial flow rate 318 can be determined by adding any suitable initial flow rate offset to the applicable target minimum blood flow rate 314. For example, a suitable initial flow rate offset can be selected based on the rate at which the blood flow rate 312 is decreasing after the corresponding semilunar valve closes. For a faster rate of decrease in blood flow rate 312, a larger initial flow rate offset can be used to counteract the faster rate of decrease in blood flow rate 312. Similarly, for a slower rate of decrease in blood flow rate 312, a smaller initial flow rate offset can be used. The suitable initial rate offset can be stored in memory in a lookup table based on the observed rate of decrease in blood flow rate 312. Alternatively, the blood pump can be programmed to determine an appropriate adjustment of the blood pump's rotation rate to prevent the observed decrease in blood flow rate 212 to the target blood flow rate. For example, the blood pump can be equipped with machine learning capabilities to control the adjustment of the blood pump's rotation speed to produce an appropriate transition from the decreasing blood flow rate 312 to the target blood flow rate.

[0082] Figure 14This is a simplified block diagram of method 400 according to an embodiment, which is used to operate a blood pump in a first-segment operating mode during a first segment of the cardiac cycle and switch to controlling the blood pump during a second segment of the same cardiac cycle to maintain a target minimum blood flow rate through the blood pump during ventricular diastole. Any suitable mechanical circulatory support system (such as the system described herein) can be used to practice method 400. The method 400 described herein begins in the first segment of the cardiac cycle. The method includes: controlling the rotational speed of the blood pump according to the first-segment operating mode during the first segment of the cardiac cycle (action 402). Any suitable first-segment operating mode can be used, including but not limited to a constant speed mode, a pulsating mode, and a disengagement mode. Method 400 includes: measuring or estimating the blood flow rate 312 through the blood pump (action 404). In action 406, the measured or estimated blood flow rate 312 is stored in a storage device (such as in a first-in-first-out buffer) for monitoring the rate of change of the blood flow rate 312. In action 408, the controller processes the current blood flow rate 312 and its current rate of change to determine whether continuing operation of the blood pump in the first operating mode will cause the blood flow rate 312 to drop below the target minimum blood flow rate 314. If continuing operation in the first operating mode will not cause the blood flow rate 312 to drop below the target minimum blood flow rate 314, the rotation of the blood pump continues to be controlled according to the first operating mode, and actions 402, 404, 406, and 408 are repeated until the controller determines, based on the current blood flow rate 312 and its current rate of change, that continuing operation in the first operating mode will cause the blood flow rate 312 to drop below the target minimum blood flow rate 314. For example, when the current blood flow rate 312 decreases and the current blood flow rate 312 is at or near the initial flow rate 318, the controller can switch from controlling the rotation of the blood pump according to the first operating mode to controlling the rotation of the blood pump as described herein, so that the blood flow rate 312 is converted to the target minimum blood flow rate 314 and then maintained at the target minimum blood flow rate 314 for the duration of the second stage (action 410).

[0083] Figure 15This is a simplified block diagram of a method 450 for controlling the rotation of a blood pump during the second segment of a cardiac cycle according to an embodiment. Method 450 begins by controlling the blood pump to operate at its current rotational speed (action 452). The controller then measures or estimates the current pump blood flow rate 312 (action 454). In action 456, the measured or estimated blood flow rate 312 is stored in a storage device (e.g., in a first-in-first-out buffer) for calculating the rate of change of the current blood flow rate 312. The controller calculates the difference between the current blood flow rate 312 and a target minimum blood flow rate 314 (action 458). The controller also calculates the rate of change of the current blood flow rate 312 (action 460). Based on the calculated difference between the current blood flow rate 312 and the target minimum blood flow rate 314 and the rate of change of the current blood flow rate 312, the controller updates the current rotational rate for the next time segment (action 462). For example, for each suitable combination of the difference between the current blood flow rate 312 and the target minimum blood flow rate 314 and the current rate of change of the current blood flow rate, a suitable rotation rate increment can be stored in a lookup table such that when the current rotation rate is updated incrementally for the next time period, the blood flow rate 312 will converge to the target minimum blood flow rate 312 and remain at the target minimum blood flow rate 312 for the remaining duration of the second segment of the cardiac cycle. In action 464, the controller checks whether the current rotation rate of the next time period is less than the blood pump rotation rate according to the first segment operation mode. If the current rotation rate of the next time period is less than the blood pump rotation rate according to the first segment operation mode, the controller resumes controlling the rotation of the blood pump according to the first segment operation mode according to method 400 (action 466). If the current rotation rate of the next time period is not less than the blood pump rotation rate according to the first segment operation mode, actions 452, 454, 456, 458, 462, and 464 are repeated until the controller detects the end of the second segment of the cardiac cycle in action 464.

[0084] Any suitable flow rate can be used as the target minimum blood flow rate. For example, as described herein, when the first-stage operating mode provides substantial level circulatory support to the patient, the target minimum blood flow rate can be any suitable rate in the range of approximately 0 L / min to 2.0 L / min. When the first-stage operating mode is out of operating mode, the target minimum blood flow rate can be any suitable rate in the range of approximately 0.0 L / min to 0.5 L / min. The target minimum blood flow rate can also be selected based on the patient's level of activity. For example, Figure 16 The diagram illustrates the variation of the target minimum blood flow rate through the blood pump according to an embodiment, based on the patient's activity level. The controller can use any suitable method (such as measuring heart rate and / or measuring the patient's acceleration level) to measure the patient's activity level. The measured patient activity level can then be used to select an appropriate blood flow rate for the target minimum blood flow rate 314.

[0085] Preferred embodiments of the invention are described herein, including the best modes known to the inventors for carrying out the invention. Variations of these preferred embodiments will become apparent to those skilled in the art upon reading the prior description. For example, the target minimum blood flow rate may be a target range of blood flow rates, and the rotational rate of the blood flow pump may be adjusted during ventricular diastole to maintain the blood flow rate 312 within the target range of blood flow rates. The inventors expect those skilled in the art to employ these variations as appropriate, and the inventors intend for the invention to be practiced in forms other than those specifically described herein. Correspondingly, the invention includes all modifications and equivalents to the subject matter set forth in the appended claims, as permitted by applicable regulations. Furthermore, any combination of the foregoing elements in all possible variations is covered by the invention unless otherwise stated herein or clearly contradicted by the context.

[0086] In the context of describing the invention (especially in the context of the following claims), the terms “a,” “an,” and “the,” and similar designations are intended to cover both the singular and plural, unless otherwise stated herein or obviously contradicted by the context. The terms “comprising,” “having,” “including,” and “covering” should be interpreted as open-ended terms (i.e., meaning “including, but not limited to”), unless otherwise noted. The term “connected” should be interpreted as being partially or wholly included, attached to, or combined, even in the presence of some intermediary. The recitation of value ranges herein is intended only as a shorthand method for individually referring to each individual value falling within that range, unless otherwise stated herein, and each individual value is incorporated into this specification as if it were separately recited herein. All methods described herein may be performed in any suitable order, unless otherwise stated herein or obviously contradicted by the context. The use of any and all examples or exemplary language (e.g., “such as”) provided herein is intended only to better illustrate embodiments of the invention and does not constitute a limitation on the scope of the invention, unless otherwise required. The language in this specification should not be construed as indicating that any unclaimed element is necessary for practicing the invention.

[0087] All references cited in this document (including publications, patent applications and patents) are incorporated herein by reference as if each reference were individually and specifically indicated to be incorporated by reference and to be presented in its entirety in this document.

[0088] Examples of embodiments of this disclosure can be described from the perspective of the following terms:

[0089] Clause 1. A method for controlling the rotational speed of a continuous-flow blood pump of a ventricular assist device to control the blood flow rate through the pump during ventricular diastole, the method comprising: pumping blood from the patient's ventricle to the patient's artery via the ventricular assist device during a first segment of the patient's cardiac cycle; wherein the rotational rate of the pump during the first segment is controlled by a controller according to a first-segment operating mode of the pump; the controller monitors the blood flow rate through the pump; the controller determines, based on the monitored blood flow rate through the pump, whether continuing to control the rotational rate of the pump according to the first-segment operating mode during a second segment of the cardiac cycle would result in the blood flow rate through the pump being less than the target minimum blood flow rate; and in response to determining that continuing to control the rotational rate of the pump according to the first-segment operating mode during the second segment would result in the blood flow rate through the pump being less than the target minimum blood flow rate, the controller controls the rotational speed of the pump during the second segment such that the blood flow rate through the pump approaches the target minimum blood flow rate.

[0090] Clause 2. The method of Clause 1, wherein the target minimum blood flow rate is in the range of about 0 liters / minute to 2.0 liters / minute.

[0091] Clause 3. The method of Clause 1, wherein the target minimum blood flow rate is in the range of 0.5 liters / minute to 1.5 liters / minute.

[0092] Clause 4. The method of Clause 1, wherein determining whether continuing to control the rotational rate of the blood pump according to the operating mode of the first segment during the second segment of the cardiac cycle will result in the blood flow velocity through the blood pump being less than the target minimum blood flow velocity includes: determining the relative difference between the current blood flow velocity through the blood pump and the target minimum blood flow velocity.

[0093] Clause 5. The method of Clause 4, wherein determining whether continuing to control the rotational rate of the blood pump according to the operating mode of the first segment during the second segment of the cardiac cycle will result in the blood flow velocity through the blood pump being less than the target minimum blood flow velocity includes: determining the current rate of change of the blood flow velocity through the blood pump.

[0094] Clause 6. The method of any one of Clauses 1 to 5, wherein the rotational rate of the blood pump is constant in the first operating mode.

[0095] Clause 7. The method of any one of Clauses 1 to 5, wherein the rotational rate of the blood pump in the first operating mode is altered to generate periodic pulsatile blood flow.

[0096] Clause 8. The method of Clause 7, wherein the periodic pulsatile blood flow is synchronized with the patient’s cardiac cycle.

[0097] Clause 9. The method of Clause 8, wherein periodic pulsatile blood flow is synchronized with the patient’s cardiac cycle based on the monitored blood flow through the blood pump.

[0098] Clause 10. The method of Clause 8, wherein the rotational rate of the blood pump is controlled by a controller in the first segment to generate a blood pressure pulse during ventricular systole.

[0099] Clause 11. The method of any one of Clauses 1 to 5 further comprises: the controller detecting the end of the second segment by detecting when the blood pump rotation rate for pumping blood at a target minimum blood flow rate decreases to or below the blood pump rotation rate according to the first segment operating mode of the blood pump; and in response to detecting the end of the second segment, controlling the rotation rate according to the first segment operating mode of the blood pump.

[0100] Clause 12. The method of any one of Clauses 1, 4 and 5, wherein the rotational rate of the blood pump in the first operating mode causes the opening and closing of the semilunar valves of the patient during ventricular systole.

[0101] Clause 13. The method of Clause 12, wherein the target minimum blood flow rate is in the range of about 0.0 liters / minute to 0.5 liters / minute.

[0102] Clause 14. The method of Clause 13, wherein the target minimum blood flow rate is 0.0 liters / minute.

[0103] Clause 15. The method of any one of Clauses 1 to 5, wherein the controller monitors the blood flow rate through the blood pump by: estimating the blood flow rate based on the rotational rate of the blood pump and operating parameters indicating the power consumption of the blood pump.

[0104] Clause 16. The method of any one of Clauses 1 to 5, wherein the controller monitors the blood flow velocity through the blood pump by estimating the blood flow velocity based on the rotational rate of the blood pump and operating parameters indicating the pressure difference across the blood pump.

[0105] Clause 17. The method of any one of Clauses 1 to 5 further includes: measuring patient physiological parameters indicating the patient's activity level via sensors; and updating the target minimum blood flow rate by the controller based on the patient physiological parameters.

[0106] Clause 18. A mechanical circulatory support system comprising: a continuous flow blood pump implantable in fluid communication with a patient's ventricles and arteries to assist blood flow from the ventricles to the arteries; and a controller operatively connected to the blood pump and operable to: control the rotational speed of the blood pump during a first segment of the patient's cardiac cycle to pump blood from the ventricles to the arteries, the rotational speed of the blood pump during the first segment being controlled according to a first segment operating mode of the blood pump; monitor the blood flow velocity through the blood pump; determine, based on the monitored blood flow velocity through the blood pump: whether continuing to control the rotational speed of the blood pump according to the first segment operating mode during a second segment of the cardiac cycle would result in the blood flow velocity through the blood pump being less than a target minimum blood flow velocity; and in response to determining that continuing to control the rotational speed of the blood pump according to the first segment operating mode during the second segment would result in the blood flow velocity through the blood pump being less than the target minimum blood flow velocity, controlling the rotational speed of the blood pump during the second segment such that the blood flow velocity through the blood pump approaches the target minimum blood flow velocity.

[0107] Clause 19. Mechanical circulatory support system of Clause 18, wherein the target minimum blood flow rate is in the range of about 0 liters / minute to 2.0 liters / minute.

[0108] Clause 20. Mechanical circulatory support system of Clause 18, wherein the target minimum blood flow rate is in the range of 0.5 liters / minute to 1.5 liters / minute.

[0109] Clause 21. The mechanical circulatory support system of Clause 18, wherein the determination of whether continuing to control the rotational rate of the blood pump according to the first-segment operating mode during the second segment of the cardiac cycle will result in the blood flow velocity through the blood pump being less than the target minimum blood flow velocity includes: determining the relative difference between the current blood flow velocity through the blood pump and the target minimum blood flow velocity.

[0110] Clause 22. Clause 21's mechanical circulatory support system, wherein the determination of whether continuing to control the rotational rate of the blood pump according to the first-segment operating mode during the second segment of the cardiac cycle would result in the blood flow velocity through the blood pump being less than the target minimum blood flow velocity includes: determining the current rate of change of the blood flow velocity through the blood pump.

[0111] Clause 23. A mechanical circulatory support system of any one of Clauses 18 to 22, wherein the rotational rate of the blood pump is constant in the first operating mode.

[0112] Clause 24. A mechanical circulatory support system of any one of Clauses 18 to 22, wherein the rotational rate of the blood pump in a first operating mode is altered to generate periodic pulsatile blood flow.

[0113] Clause 25. Clause 24 Mechanical circulatory support system, wherein periodic pulsatile blood flow is synchronized with the patient’s cardiac cycle.

[0114] Clause 26. Clause 25 Mechanical circulatory support system, wherein periodic pulsatile blood flow is synchronized with the patient’s cardiac cycle based on monitored blood flow through the blood pump.

[0115] Clause 27. Clause 25 Mechanical circulatory support system, wherein the rotational rate of the blood pump is altered in the first segment to generate a blood pressure pulse during ventricular systole.

[0116] Clause 28. A mechanical circulatory support system of any one of Clauses 18 to 22, wherein the controller is further operable to detect the end of the second stage by detecting when the blood pump rotation rate for pumping blood at a target minimum blood flow rate decreases to or below the blood pump rotation rate according to the first stage operating mode of the blood pump; and in response to detecting the end of the second stage,

[0117] 212318F1 1PWCN

[0118] The rotation rate is controlled according to the first stage of the blood pump's operation mode.

[0119] Clause 29. A mechanical circulatory support system of any of Clauses 18, 21 and 22, wherein the rotational rate of the blood pump in a first operating mode causes the opening and closing of the semilunar valves of the patient during ventricular systole.

[0120] The mechanical circulatory support system of Clause 30 and Clause 29, wherein the target minimum blood flow rate is in the range of about 0.0 liters / minute to 0.5 liters / minute.

[0121] Clause 31. Mechanical circulatory support system of Clause 30, wherein the target minimum blood flow rate is 0.0 liters / minute.

[0122] Clause 32. A mechanical circulatory support system of any one of Clauses 18 to 22, wherein the controller estimates the blood flow rate based on the rotational rate of the blood pump and operating parameters indicating the power consumption of the blood pump.

[0123] Clause 33. A mechanical circulatory support system of any one of Clauses 18 to 22, wherein the controller estimates the blood flow rate based on the rotational rate of the blood pump and operating parameters indicating the pressure difference across the blood pump.

[0124] Clause 34. A mechanical circulatory support system of any one of Clauses 18 to 22, further comprising a sensor that measures a patient physiological parameter indicating the patient’s level of activity, and wherein a controller updates a target minimum blood flow rate based on the patient physiological parameter.

[0125] Clause 35. Clause 34 Mechanical circulatory support system, wherein the sensors include a heart rate sensor.

[0126] Clause 36. Clause 34 Mechanical cycle assist system, wherein the sensors include accelerometers.

Claims

1. A mechanical circulation auxiliary system, comprising: A continuous flow blood pump, which can be implanted in fluid communication with a patient's ventricles and arteries to assist blood flow from the ventricles to the arteries; as well as A controller, operatively connected to the blood pump and operable to: The rotational speed of the blood pump is controlled according to the first operating mode to pump blood from the ventricle to the artery; Monitor the blood flow rate through the blood pump; The detection measures the reduction of blood flow velocity through the blood pump to the initial blood flow velocity or to a level lower than the initial blood flow velocity during ventricular diastole. as well as In response to detecting that the blood flow rate through the blood pump during ventricular diastole has decreased to or below the initial blood flow rate, the rotational rate of the blood pump is increased relative to the rotational rate of the blood pump according to the first operating mode to prevent the blood flow rate through the blood pump during ventricular diastole from decreasing below a target minimum blood flow rate.

2. The mechanical circulation auxiliary system as described in claim 1, characterized in that, The first operating mode is a disengagement mode, which provides reduced circulatory support to the patient during an attempt to wean the patient off the mechanical circulatory support system.

3. The mechanical circulation auxiliary system as described in claim 2, characterized in that, The target minimum blood flow rate is in the range of 0.0 liters / minute to 0.5 liters / minute.

4. The mechanical circulation auxiliary system as described in claim 3, characterized in that, The target minimum blood flow rate is 0.0 liters per minute.

5. The mechanical circulatory support system of claim 1, further comprising a sensor that measures patient physiological parameters indicating the patient's activity level, and wherein the controller adjusts the blood flow output of the blood pump in the first operating mode based on the patient's activity level.

6. The mechanical circulation auxiliary system as described in claim 5, characterized in that, The controller is configured to: The blood flow output of the blood pump is increased in response to an increase in the patient's activity level; and The blood flow output of the blood pump is reduced in response to a decrease in the patient's activity level.

7. The mechanical circulation auxiliary system as described in claim 5, characterized in that, The controller is configured to update the target minimum blood flow rate based on the patient's activity level.

8. The mechanical circulation auxiliary system as described in claim 7, characterized in that, The controller is configured to: The target minimum blood flow rate is increased in response to an increase in the patient's activity level; and The target minimum blood flow rate is reduced in response to a decrease in the patient's activity level.

9. The mechanical circulation auxiliary system as described in claim 5, characterized in that, The sensor includes a heart rate sensor.

10. The mechanical circulation auxiliary system as described in claim 5, characterized in that, The sensor includes an accelerometer.

11. The mechanical circulation auxiliary system as described in claim 1, characterized in that, The target minimum blood flow rate is in the range of 0 liters / minute to 2.0 liters / minute.

12. The mechanical circulation auxiliary system as described in claim 10, characterized in that, The target minimum blood flow rate is in the range of 0.5 liters / minute to 1.5 liters / minute.

13. The mechanical circulation auxiliary system as described in claim 1, characterized in that, The rotational rate of the blood pump in the first operating mode causes the opening and closing of the patient's semilunar valves during ventricular systole.

14. The mechanical circulation auxiliary system as described in claim 1, characterized in that, The controller estimates the blood flow rate based on the rotational rate of the blood pump and operating parameters that indicate the power consumption of the blood pump.

15. The mechanical circulation auxiliary system as described in claim 1, characterized in that, The controller estimates the blood flow rate based on the rotational rate of the blood pump and operating parameters indicating the pressure difference across the blood pump.

16. The mechanical circulation auxiliary system as described in claim 1, characterized in that, The rotational rate of the blood pump in the first operating mode is constant.

17. The mechanical circulation auxiliary system as described in claim 1, characterized in that, The rotational rate of the blood pump in the first operating mode is altered to generate periodic pulsating blood flow.

18. The mechanical circulation auxiliary system as described in claim 17, characterized in that, The periodic pulsating blood flow is synchronized with the patient's cardiac cycle.

19. The mechanical circulation auxiliary system as described in claim 18, characterized in that, The periodic pulsatile blood flow is synchronized with the patient's cardiac cycle based on the monitored blood flow through the blood pump.

20. The mechanical circulation auxiliary system as described in claim 18, characterized in that, The rotational rate of the blood pump in the first operating mode is altered to generate a blood pressure pulse during ventricular contraction.

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