Methods and systems for controlling a blood pump

The present invention generally relates to ventricular assist device power monitoring and conservation. In some embodiments, a pump controller may transition the pump to operate in a power-saving operational mode when a power source and/or a power source condition indicate a need to conserve power. In some embodiments, when the power source is an emergency battery and when the emergency battery has powered the pump for an extended period of time, the controller may signal the pump to operate in the power saving-operational mode. In some embodiments, when a low power hazard condition is triggered by signals from one or more external power sources, the controller may signal the pump to transition to the power-saving operational mode if the condition lasts for an extended period of time. In some embodiments, the controller may trigger the power-saving mode when the emergency backup battery is below a voltage threshold.

FIELD OF THE INVENTION

This description relates to generating an artificial pulse, and more specifically to methods and systems for power saving and disabling pulsatility.

BACKGROUND OF THE INVENTION

This application relates generally to mechanical circulatory support systems, and more specifically relates to power management systems and methods for an implantable blood pump.

Ventricular assist devices, known as VADs, are implantable blood pumps used for both short-term (i.e., days, months) and long-term applications (i.e., years or a lifetime) where a patient's heart is incapable of providing adequate circulation, commonly referred to as heart failure or congestive heart failure. According to the American Heart Association, more than five million Americans are living with heart failure, with about 670,000 new cases diagnosed every year. People with heart failure often have shortness of breath and fatigue. Years of living with blocked arteries or high blood pressure can leave your heart too weak to pump enough blood to your body. As symptoms worsen, advanced heart failure develops.

A patient suffering from heart failure, also called congestive heart failure, may use a VAD while the patient awaits a heart transplant or as a long term destination therapy. In another example, a patient may use a VAD while recovering from heart surgery. Thus, a VAD can supplement a weak heart (i.e., partial support) or can effectively replace the natural heart's function. VADs can be implanted in the patient's body and powered by an electrical power source outside the patient's body.

While many advances have been made to supplement and/or replace heart function, further improvements may be desired that improve the duration of VAD operation when powered by portable power sources.

BRIEF SUMMARY OF THE INVENTION

The present invention provides improved systems, methods, and devices which can advantageously sustain VAD operation during low power conditions. Improving the duration of VAD operation during low power has many advantages, such as patient safety, as discussed herein. For example, identifying a mode to conserve power and transitioning from a first operational mode (e.g., pulsatility mode) to a second operation mode (e.g., steady-state) to save on power reserves allows the VAD to continue to operate uninterrupted for longer durations of time while the patient safely secures alternative power sources or recharges existing power sources. Still further, the present invention finds applicability with both external power sources and fully implantable transcutaneous energy transfer systems.

In one general aspect, a continuous flow blood pump can be operated to provide pulsatile blood flow. The motor speed for the pump can be modulated in a repeating cycle that includes a sequence of two or more speed levels. Operation of the pump can produce pressure changes that imitate a rate of pressure change of a natural physiologic pulse.

In another general aspect, pumping blood in a pulsatile manner includes operating a blood pump at a first speed for a first period of time, reducing the speed of the blood pump from the first speed to a second speed, operating the blood pump at the second speed for a second period of time, reducing the speed of the blood pump from the second speed to a third speed, operating the blood pump at the third speed for a third period of time, and increasing the speed of the blood pump from the third speed to the first speed.

Implementations can include one or more of the following features. For example, increasing the speed of the blood pump from the third speed to the first speed includes increasing the speed of the blood pump from the third speed to a fourth speed, operating the blood pump at the fourth speed for a fourth period of time, and increasing the speed of the blood pump from the fourth speed to the first speed. The second period of time is longer than a sum of the first period of time and the third period of time. Operating the blood pump at the first speed, reducing the speed of the blood pump from the first speed to the second speed, operating the blood pump at the second speed, reducing the speed of the blood pump from the second speed to the third speed, operating the blood pump at the third speed, and increasing the speed of the blood pump from the third speed to the first speed comprise a cycle, and pumping blood in a pulsatile manner further includes repeating the cycle. The duration of the second period of time is greater than half of the duration of the cycle. Operating the blood pump at the second speed for the second period of time includes operating the blood pump to produce a blood flow rate that has a predetermined relationship relative to an average blood flow rate for the cycle. Operating the blood pump at the second speed for the second period of time includes operating the blood pump to produce a blood flow substantially the same as the average blood flow rate for the cycle.

One or more of reducing the speed of the blood pump from the first speed to a second speed, reducing the speed of the blood pump from the second speed to a third speed, and increasing the speed of the blood pump from the third speed to the first speed includes one or more of a step-wise reduction in speed and a curvilinear reduction in speed. Operating the blood pump at the second speed includes operating the blood pump at the second speed during at least a portion of a contraction of a ventricle of human heart that is in blood flow communication with the blood pump. Pumping blood in a pulsatile manner also includes determining, based on a relationship between a speed of the blood pump and a power consumption of the blood pump, a synchronization between operating the impeller at the second speed and contraction of a ventricle of a human heart that is in blood flow communication with the blood pump. A generated pulsatile blood flow includes a temporal rate of change of blood pressure that approximates a temporal rate of change of blood pressure of a physiologic pulse. One or more of reducing the speed of the blood pump from the first speed to a second speed, reducing the speed of the blood pump from the second speed to a third speed, and increasing the speed of the blood pump from the third speed to the first speed includes generating a drive signal at a first time to produce a corresponding change in operating speed at a desired time. The second period of time is greater than the first period of time.

In another general aspect, a blood pump controller includes a waveform generator to generate a waveform for operating a blood pump, and a drive waveform transmitter to supply the generated drive waveform to the blood pump. The generated waveform is configured to operate a blood pump at a first speed for a first period of time, reduce the speed of the blood pump from the first speed to a second speed, operate the blood pump at the second speed for a second period of time, reduce the speed of the blood pump from the second speed to a third speed, operate the blood pump at the third speed for a third period of time, and increase the speed of the blood pump from the third speed to the first speed.

Implementations can include one or more of the following features. For example, increasing the speed of the blood pump from the third speed to the first speed includes increasing the speed of the blood pump from the third speed to a fourth speed, operating the blood pump at the fourth speed for a fourth period of time, and increasing the speed of the blood pump from the fourth speed to the first speed. The second period of time is longer than a sum of the first period of time and the third period of time. Operating the blood pump at the first speed, reducing the speed of the blood pump from the first speed to the second speed, operating the blood pump at the second speed, reducing the speed of the blood pump from the second speed to the third speed, operating the blood pump at the third speed, and increasing the speed of the blood pump from the third speed to the first speed comprise a cycle, and wherein the generated waveform is configured to repeat the cycle. The duration of the second period of time is greater than half of the duration of the cycle. Operating the blood pump at the second speed for the second period of time includes operating the blood pump to produce a blood flow rate that has a predetermined relationship relative to an average blood flow rate for the cycle. Operating the blood pump at the second speed for the second period of time includes operating the blood pump to produce a blood flow substantially the same as the average blood flow rate for the cycle.

The generated waveform is configured to change the speed of the blood pump via one or more of a step-wise change in speed and a curvilinear change in speed. The generated waveform operates the blood pump at the second speed during a contraction of a ventricle of a human heart that is in blood flow communication with the blood pump. The blood pump controller further includes a processor configured to determine, based on a relationship between a speed of the blood pump and a power consumption of the blood pump, a synchronization between operating the blood pump at the second speed and a contraction of a ventricle of a human heart that is in blood flow communication with the blood pump. The generated waveform drives the blood pump to generate a temporal rate of change of blood pressure that approximates a temporal rate of change of blood pressure of a physiologic pulse. The generated waveform is further configured to produce a corresponding change in pump operating speed at a desired time. The second period of time is greater than the first period of time.

In another general aspect, producing a pulsatile blood flow having a relatively low pressure portion and a relatively high pressure portion and having a rate of pressure change that mimics a rate of pressure change of a natural physiologic pulse includes operating a continuous flow blood pump to produce a first blood flow rate through the continuous flow blood pump associated with the relatively low pressure portion of the pulsatile blood flow, operating the continuous flow blood pump to produce a second blood flow rate through the continuous flow blood pump associated with the relatively high pressure portion of the pulsatile blood flow, and controlling the continuous flow blood pump to increase a blood flow rate through the continuous flow blood pump from the first flow rate to the second flow rate to produce the rate of pressure change that mimics the rate of pressure change of the natural physiologic pulse.

Implementations can include one or more of the following features. For example, operating the continuous blood flow pump to produce the second blood flow rate can include operating the continuous blood flow pump at a first operating speed, and controlling can include operating the continuous blood flow pump at a second operating speed, the second operating speed being associated with a third blood flow rate, the third blood flow rate being greater than the second blood flow rate. Operating the continuous flow blood pump to produce the second blood flow rate includes operating the continuous flow blood pump to produce the second blood flow rate such that the relatively high pressure portion has a duration that is longer than a duration of the relatively low pressure portion. Repeating a cycle in which the duration of the relatively high pressure portion is greater than half of the duration of the cycle. The cycle includes operating the continuous flow blood pump to produce the first blood flow rate, operating the continuous flow blood pump to produce the second blood flow rate, and controlling the continuous flow blood pump to increase the blood flow rate. Operating the continuous flow blood pump to produce the second blood flow rate includes operating the continuous flow blood pump to produce the second blood flow rate such that the second blood flow rate has a predefined relationship with an average blood flow rate of the pulsatile blood flow. The second blood flow rate is substantially equal to an average blood flow rate of the pulsatile blood flow. Controlling the continuous flow blood pump to increase the blood flow rate includes controlling the continuous flow blood pump to increase the blood flow rate through the continuous flow blood pump from the first flow rate to the second flow rate such that the blood flow rate through the continuous flow blood pump overshoots the second flow rate to produce the rate of pressure change that mimics the rate of pressure change of the natural physiologic pulse.

In many embodiments, a method for controlling an implantable blood pump with a controller is provided. The method may include identifying a status of one or more power sources for the implantable blood pump that is indicative of a need or mode to conserve power. Thereafter, the method may include transmitting a signal to the blood pump from the controller to transition from a pulsatile pumping operation to a constant speed operation. The constant speed operation may consume less power than the pulsatile pumping operation.

Identifying the status of the one or more power sources may include identifying a disconnection between the controller and one or more external power sources or a low power hazard condition status. In some embodiments, identifying the status of the one or more power sources comprises identifying a duration of time in which the controller is disconnected from the external power source or a duration of time in which the pump is operated with the low power hazard condition. The duration of time may be compared to a threshold time period. The signal may be transmitted to the blood pump when the duration of time exceeds the threshold time period. Optionally, the threshold time period may be at least 5 minutes, 10 minutes or more, or the like. In some embodiments the threshold time period is at least 15 minutes.

A low power hazard condition may be identified by monitoring a status of a first cable and a second cable coupled to the controller of the blood pump. The first cable and the second cable may be assigned: a first fault status when: 1) relative state of charge information associated with the respective cable is indicative of a rechargeable battery power source below a first threshold charge, or 2) relative state of charge information associated with the respective cable is indicative of a power module and voltage information is below a first power module threshold voltage; a second fault status when: 1) relative state of charge information associated with the respective cable is indicative of a rechargeable battery power source below a second threshold charge (the second threshold charge being lower than the first threshold charge), or 2) relative state of charge information associated with the respective cable is indicative of a rechargeable battery power source and voltage information is below a battery threshold voltage, or 3) relative state of charge information associated with the respective cable is indicative of a power module and voltage information is below a second power module threshold voltage (the second power module threshold voltage being lower than the first power module threshold voltage); an unknown fault status when relative state of charge of the respective cable is indicative of an unknown power source; a disconnect fault status when voltage information associated with the respective cable is indicative of a disconnected cable; and a third status when the first cable or second cable are not assigned a first fault status, a second fault status, an unknown fault status, or a disconnect fault status.

In some embodiments, the low power hazard condition may be triggered when the first cable is assigned the first fault status, the second fault status, or the unknown fault status, while the second cable is assigned the disconnect fault status, the unknown fault status, or the second fault status.

In further embodiments, the method may further include transmitting a second signal to the blood pump to transition back to the pulsatile pumping operation when the first cable or second cable is assigned the third status or when the first cable and the second cable are assigned the second fault status.

Optionally, the status of the power source may be identified by identifying the power source as an emergency battery which has powered the pump for greater than a threshold time period. The threshold time period may be 5 minutes or more, 10 minutes or more. In some embodiments the time period may be at least 15 minutes.

In some embodiments, the status of the power source may be identified by identifying the power source as an emergency battery which is below a threshold voltage. The threshold voltage may be equal to or less than 10.4 volts, for example.

In other aspects, a method of controlling an implantable blood pump with a controller is provided. The method may include, determining/classifying/categorizing one or more power sources with the controller and identifying an operating condition associated with the determined implantable blood pump power source that is indicative of a need to conserve power. A signal may be transmitted to the implantable blood pump from the controller to transition the implantable blood pump from a first operational mode to a second operational mode when the identified operating condition is indicative of the need to conserve power. The second operational mode may be configured to consume less power than the first operational mode. In some embodiments, the second operational mode may be configured to provide a lower flow rate, a constant speed, or the like.

In some embodiments, the method may determine that the one or more power sources is an emergency battery housed within the controller. The method may make the determination when the controller is disconnected from external power sources.

Optionally, the operating condition associated with the emergency battery that is indicative of the need to conserve power may comprise a voltage of the emergency battery below a threshold voltage or the emergency battery powering the implantable blood pump a duration of time that exceeds a threshold time period. The method may include comparing the identified voltage of the emergency battery with a threshold voltage or comparing the identified duration of time with a threshold time period. The threshold voltage may be 10.4 volts or less for example. Thus, in some embodiments, the blood pump may be transitioned to the second operational mode from the first operational mode when the identified voltage of the emergency battery is less than 10.4 volts. The threshold duration may be 15 minutes, for example. Thus, in some embodiments, the blood pump may be transitioned to the second operational mode from the first operational mode when the emergency battery powers the pump for 15 minutes or more.

Further, methods of the present invention may include determining whether a first cable and a second cable couple one or more external power sources to the controller. This may include steps of monitoring voltage information associated with the first cable and the second cable and comparing the voltage information to a connection threshold. Thereafter, the first and/or second cable may be determined to be connected when the associated voltage information is greater than or equal to the connection threshold. The first or second cable may be determined to be disconnected when the associated voltage information is less than the connection threshold. If it is determined that the cable is disconnected from the controller, a disconnect fault status may be reported to the first or second cable in some embodiments.

In some embodiments, the signal to the blood pump to transition the blood pump from the first operational mode to the second operational mode may be transmitted when the first and second cable are determined to be disconnected from the controller for a time period greater than a threshold time period, (e.g., more than 5 minutes, 10 minutes, or 15 minutes). When the first or second cable are determined to be connected to the controller, the method may include determining whether the connected power source is an external battery or a power module based on relative state of charge information associated with the first and/or second cable.

The methods may include determining that the external power source is a rechargeable battery when the relative state of charge information associated with the first and/or second cable is greater than a minimum battery threshold and less than or equal to a maximum battery threshold. For example, a minimum battery threshold may be 330 mV and the maximum battery threshold may be 4600 mV. The relative state of charge information falling within the range may be indicative of a rechargeable lithium ion battery in some embodiments.

In some embodiments, the external power source may be determined to be a power module when the relative state of charge information associated with the first and/or second cable is greater than a power module threshold. The power module threshold may be 9800 mV, for example.

The method may further include classifying/categorizing the external power source as an unknown power source when the relative state of charge information associated with the first and/or second cable falls outside relative state of charge ranges associated with the external battery and the power module. The method may further include reporting an unknown fault status to the first and/or second cable when the external power source is categorized as an unknown power source.

In some embodiments, the operating condition associated with the blood pump power source that is indicative of a need to conserve power may be identified by monitoring relative state of charge information and the voltage information associated with the first and second cables. Fault statuses associated with the first and/or second cable may be reported based on the relative state of charge information and the voltage information. Fault statutes may be reported by: (1) reporting a first fault status (e.g., a red fault status) to the first and/or second cable when a relative state of charge is less than 1130 mV and greater than or equal to 330 mV; (2) reporting the first fault status (or red fault status) to the first and/or second cable when (a) the external power source is characterized as the rechargeable battery and the voltage is greater than 1000 mV and less than or equal to 13200 mV or when (b) the external power source is characterized as the power module and the voltage is greater than 1000 mV and less than 10400 mV; (3) reporting a second fault status (e.g., a yellow fault status less severe than a red fault status) to the first and/or second cable when the relative state of charge is less than 1930 mV and greater than or equal to 1130 mV; and (4) reporting the second fault status (or yellow fault status) to the first and/or second cable when the external power source is characterized as the power module and the voltage is greater than 10400 mV and less than or equal to 11200 mV; (5) reporting a third status (e.g., a green status or no fault status) to the first and/or second cable when the first and/or second cable is not issued the first fault status, the second fault status, the unknown fault status, or the disconnected fault status.

In some embodiments, the signal to the blood pump to transition the blood pump from the first operational mode to the second operational mode may be transmitted when the pump is operated for an extended period of time in a low power hazard condition. The low power hazard condition may be triggered when the first cable is assigned the first fault status (e.g., red), the second fault status (e.g., yellow), or the unknown fault status while the second cable is assigned the first fault status (red), unknown fault status, or the disconnected fault status. In some embodiments, the signal may be transmitted after the pump operates in such a low power hazard condition for greater than 5 minutes, for greater than 10 minutes, or greater than 15 minutes for example.

Some methods may include transmitting a second signal to the blood pump to transition the blood pump back to the first operational mode when the first cable or second cable is assigned the third status (e.g., green or no fault status) or when the first cable and the second cable are assigned the second fault status (e.g., yellow status).

In some embodiments, the first operational mode may be a pulsatile operational mode and the second operational mode may be a constant speed operational mode. Optionally, the first operational mode and the second operational mode may both be pulsatile operational modes. The second operational mode may consume less power than the first operational mode by operating at a lower flow rate. In some embodiments, the first operational mode and the second operational mode may be a constant speed modes. The second operational mode may consume less power than the first operational mode by operating at a lower flow rate.

In further embodiments an implantable blood pump system is provided. The system may include an implantable blood pump configured to supplement or replace a pumping function of a heart. The system may further include a controller coupled with the implantable blood pump. The controller may be configured to categorize or classify one or more power sources that are powering the implantable blood pump. The controller may further be configured to identify an operating condition associate with the one or more classified power sources that is indicative of a need to conserve power. The controller may also be configured to transmit a signal to the blood pump to transition between a first operational mode and a second operational mode when upon the identification of the power source status that is indicative of the need to conserve power. The second operational mode may be configured to consume less power than the first operational mode.

In some embodiments, the first operational mode may be a pulsatile pumping operation and the second operational mode may be a constant speed operation. The constant speed operation may be configured to consume less power than the pulsatile pumping operation. Alternatively, the first operational mode may comprise a first pulsatile pumping mode and the second operational mode may comprise a second pulsatile pumping mode. The second pulsatile pumping mode may consume less power than the first pulsatile pumping mode. In some embodiments, the first operational mode may comprise a first constant speed mode and the second operational mode may comprise a second constant speed mode—the second constant speed mode may consume less power than the first constant speed mode.

In some embodiments the controller may be configured determine or categorize one or more power sources coupled with the blood pump. The controller may monitor the associated power source based in-part on how the controller categories the operative power source. The controller may be configured to determine when to transition to the second operational mode based on the monitoring of the one or more power sources.

In some embodiments, the controller may be configured to couple to one or more external power sources for powering the blood pump. The controller may further include an emergency battery for powering the blood pump when the controller is disconnected from the external power source. The controller may be configured to transmit the signal to transition the blood pump from the first operational mode to the second operational mode when the controller determines that the emergency battery is powering the blood pump for greater than a threshold duration of time. The threshold duration of time may be greater than 5 minutes in some embodiments, (e.g., 10 minutes, 15 minutes, or the like).

The controller may also be configured to couple to one or more external power sources for powering the blood pump and while also including an emergency battery for powering the blood pump when the controller is disconnected from the external power source. The controller may transmit signals to the blood pump to transition from the first operational mode to the second operational mode when the power monitor determines that the emergency battery is below a threshold voltage. The threshold voltage may be less than 12.0 volts in some embodiments, (e.g., 11.0 volts, 10.4 volts, or the like).

In some embodiments, the controller may be configured to couple to one or more external power sources by a first cable and a second cable. The controller may be configured to classify the one or more power source or determine the power sources coupled thereto. In some embodiments, the controller includes a power monitor module that may be configured to classify/describe the one or more coupled power sources and to monitor the operational status of the power source based on the categorizations of the power source. In some embodiments, the controller may be configured to monitor the status of the power source based on voltage information and relative state of charge information associated with the first cable and the second cable. In some embodiments a system may include an analog to digital driver unit configured to gather voltage information and relative state of charge information associated with the first cable and the second cable.

The controller may be configured to report disconnect fault statuses to the first and/or second cable when voltage information associated with the first and/or second cable is below a connection threshold. In some embodiments, the controller may be configured to characterize the power source as a battery, a power module, or an unknown power source, and to report unknown fault statuses to the associated first and/or second cable when the relative state of charge information is indicative of an unknown power source.

The controller may further be configured to monitor the status of the battery or the power module by issuing fault statuses to the first and/or second cable depending on relative state of charge information and voltage information associated with the first and/or second cable. A controller may be configure to trigger or indicate a low power hazard condition based on the fault statuses issued to the first and/or second cable.

Optionally, the controller may be configured to transmit the signal to the blood pump to transition from the first operational mode to the second operational mode when the system operates with low power hazard condition and/or detects disconnection of the external power source from the controller for greater than a threshold duration of time. In some embodiments, the threshold duration of time may be a time period greater than 5 minutes or greater than 10 minutes, for example. In some embodiments, the controller may transmit the signal after operating with a low power hazard condition and/or disconnected condition for 15 minutes or more.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is an illustration of a mechanical circulatory support system10implanted in a patient's body12. The mechanical circulatory support system10comprises a implantable blood pump14, ventricular cuff16, outflow cannula18, system controller20, and power sources22. The implantable blood pump14may comprise a VAD that is attached to an apex of the left ventricle, as illustrated, or the right ventricle, or both ventricles of the heart24. The VAD may comprise a centrifugal (as shown) or axial flow pump as described in further detail herein that is capable of pumping the entire output delivered to the left ventricle from the pulmonary circulation (i.e., up to 10 liters per minute). Related blood pumps applicable to the present invention are described in greater detail below and in U.S. Pat. Nos. 5,695,471, 6,071,093, 6,116,862, 6,186,665, 6,234,772, 6,264,635, 6,688,861, 7,699,586, 7,976,271, 7,997,854, 8,007,254, 8,152,493, 8,652,024, and 8,668,473 and U.S. Patent Publication Nos. 2007/0078293, 2008/0021394, 2009/0203957, 2012/0046514, 2012/0095281, 2013/0096364, 2013/0170970, 2013/0121821, and 2013/0225909, all of which are incorporated herein by reference for all purposes in their entirety. With reference toFIGS. 1 and 2, the blood pump14may be attached to the heart24via the ventricular cuff16which is sewn to the heart24and coupled to the blood pump14. The other end of the blood pump14connects to the ascending aorta via the outflow cannula18so that the VAD effectively diverts blood from the weakened ventricle and propels it to the aorta for circulation to the rest of the patient's vascular system.

FIG. 1illustrates the mechanical circulatory support system10during battery22powered operation. A driveline26which exits through the patient's abdomen28, connects the implanted blood pump14to the system controller20, which monitors system10operation. Related controller systems applicable to the present invention are described in greater detail below and in U.S. Pat. Nos. 5,888,242, 6,991,595, 8,323,174, 8,449,444, 8,506,471, 8,597,350, and 8,657,733 and U.S. Patent Publication Nos. 2005/0071001 and 2013/0314047, all of which are incorporated herein by reference for all purposes in their entirety. The system may be powered by either one, two, or more batteries22. It will be appreciated that although the system controller20and power source22are illustrated outside/external to the patient body, the driveline26, system controller20and/or power source22may be partially or fully implantable within the patient, as separate components or integrated with the blood bump14. Examples of such modifications are further described in U.S. Pat. No. 8,562,508 and U.S. Patent Publication No. 2013/0127253, all of which are incorporated herein by reference for all purposes in their entirety.

With reference toFIGS. 3 to 5, a left ventricular assist blood pump100having a circular shaped housing110is implanted in a patient's body with a first face111of the housing110positioned against the patient's heart H and a second face113of the housing110facing away from the heart H. The first face111of the housing110includes an inlet cannula112extending into the left ventricle LV of the heart H. The second face113of the housing110has a chamfered edge114to avoid irritating other tissue that may come into contact with the blood pump100, such as the patient's diaphragm. To construct the illustrated shape of the puck-shaped housing110in a compact form, a stator120and electronics130of the pump100are positioned on the inflow side of the housing toward first face111, and a rotor140of the pump100is positioned along the second face113. This positioning of the stator120, electronics130, and rotor140permits the edge114to be chamfered along the contour of the rotor140, as illustrated in at leastFIGS. 2-4, for example.

Referring toFIG. 4, the blood pump100includes a dividing wall115within the housing110defining a blood flow conduit103. The blood flow conduit103extends from an inlet opening101of the inlet cannula112through the stator120to an outlet opening105defined by the housing110. The rotor140is positioned within the blood flow conduit103. The stator120is disposed circumferentially about a first portion140aof the rotor140, for example about a permanent magnet141. The stator120is also positioned relative to the rotor140such that, in use, blood flows within the blood flow conduit103through the stator120before reaching the rotor140. The permanent magnet141has a permanent magnetic north pole N and a permanent magnetic south pole S for combined active and passive magnetic levitation of the rotor140and for rotation of the rotor140. The rotor140also has a second portion140bthat includes impeller blades143. The impeller blades143are located within a volute107of the blood flow conduit such that the impeller blades143are located proximate to the second face113of the housing110.

The puck-shaped housing110further includes a peripheral wall116that extends between the first face111and a removable cap118. As illustrated, the peripheral wall116is formed as a hollow circular cylinder having a width W between opposing portions of the peripheral wall116. The housing110also has a thickness T between the first face111and the second face113that 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 approximately 2 inches, and the thickness T can be approximately 1 inch.

The peripheral wall116encloses an internal compartment117that surrounds the dividing wall115and the blood flow conduit103, with the stator120and the electronics130disposed in the internal compartment117about the dividing wall115. The removable cap118includes the second face113, the chamfered edge114, and defines the outlet opening105. The cap118can be threadedly engaged with the peripheral wall116to seal the cap118in engagement with the peripheral wall116. The cap118includes an inner surface118aof the cap118that defines the volute107that is in fluid communication with the outlet opening105.

Within the internal compartment117, the electronics130are positioned adjacent to the first face111and the stator120is positioned adjacent to the electronics130on an opposite side of the electronics130from the first face111. The electronics130include circuit boards131and various components carried on the circuit boards131to control the operation of the pump100(e.g., magnetic levitation and/or drive of the rotor) by controlling the electrical supply to the stator120. The housing110is configured to receive the circuit boards131within the internal compartment117generally parallel to the first face111for efficient use of the space within the internal compartment117. The circuit boards also extend radially-inward towards the dividing wall115and radially-outward towards the peripheral wall116. For example, the internal compartment117is generally sized no larger than necessary to accommodate the circuit boards131, and space for heat dissipation, material expansion, potting materials, and/or other elements used in installing the circuit boards131. Thus, the external shape of the housing110proximate the first face111generally fits the shape of the circuits boards131closely to provide external dimensions that are not much greater than the dimensions of the circuit boards131.

With continued reference toFIGS. 4 and 5, the stator120includes a back iron121and pole pieces123a-123farranged at intervals around the dividing wall115. The back iron121extends around the dividing wall115and is formed as a generally flat disc of a ferromagnetic material, such as steel, in order to conduct magnetic flux. The back iron121is arranged beside the control electronics130and provides a base for the pole pieces123a-123f.

Each of the pole piece123a-123fis L-shaped and has a drive coil125for generating an electromagnetic field to rotate the rotor140. For example, the pole piece123ahas a first leg124athat contacts the back iron121and extends from the back iron121towards the second face113. The pole piece123amay also have a second leg124bthat extends from the first leg124athrough an opening of a circuit board131towards the dividing wall115proximate the location of the permanent magnet141of the rotor140. In an aspect, each of the second legs124bof the pole pieces123a-123fis sticking through an opening of the circuit board131. In an aspect, each of the first legs124aof the pole pieces123a-123fis sticking through an opening of the circuit board131. In an aspect, the openings of the circuit board are enclosing the first legs124aof the pole pieces123a-123f.

In a general aspect, the implantable blood pump100may include a Hall sensor that may provide an output voltage, which is directly proportional to a strength of a magnetic field that is located in between at least one of the pole pieces123a-123fand the permanent magnet141, and the output voltage may provide feedback to the control electronics130of the pump100to determine if the rotor140and/or the permanent magnet141is not at its intended position for the operation of the pump100. For example, a position of the rotor140and/or the permanent magnet141may be adjusted, e.g. the rotor140or the permanent magnet141may be pushed or pulled towards a center of the blood flow conduit103or towards a center of the stator120.

Each of the pole pieces123a-123falso has a levitation coil127for generating an electromagnetic field to control the radial position of the rotor140. Each of the drive coils125and the levitation coils127includes multiple windings of a conductor around the pole pieces123a-123f. Particularly, each of the drive coils125is wound around two adjacent ones of the pole pieces123, such as pole pieces123dand123e, and each levitation coil127is wound around a single pole piece. The drive coils125and the levitation coils127are wound around the first legs of the pole pieces123, and magnetic flux generated by passing electrical current though the coils125and127during use is conducted through the first legs and the second legs of the pole pieces123and the back iron121. The drive coils125and the levitation coils127of the stator120are arranged in opposing pairs and are controlled to drive the rotor and to radially levitate the rotor140by generating electromagnetic fields that interact with the permanent magnetic poles S and N of the permanent magnet141. Because the stator120includes both the drive coils125and the levitation coils127, only a single stator is needed to levitate the rotor140using only passive and active magnetic forces. The permanent magnet141in this configuration has only one magnetic moment and is formed from a monolithic permanent magnetic body141. For example, the stator120can be controlled as discussed in U.S. Pat. No. 6,351,048, the entire contents of which are incorporated herein by reference for all purposes. The control electronics130and the stator120receive electrical power from a remote power supply via a cable119(FIG. 3). Further related patents, namely U.S. Pat. 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 for all purposes in their entirety.

The rotor140is arranged within the housing110such that its permanent magnet141is located upstream of impeller blades in a location closer to the inlet opening101. The permanent magnet141is received within the blood flow conduit103proximate the second legs124bof the pole pieces123to provide the passive axial centering force though interaction of the permanent magnet141and ferromagnetic material of the pole pieces123. The permanent magnet141of the rotor140and the dividing wall115form a gap108between the permanent magnet141and the dividing wall115when the rotor140is centered within the dividing wall115. The gap108may be from about 0.2 millimeters to about 2 millimeters. For example, the gap108is approximately 1 millimeter. The north permanent magnetic pole N and the south permanent magnetic pole S of the permanent magnet141provide a permanent magnetic attractive force between the rotor140and the stator120that acts as a passive axial centering force that tends to maintain the rotor140generally centered within the stator120and tends to resist the rotor140from moving towards the first face111or towards the second face113. When the gap108is smaller, the magnetic attractive force between the permanent magnet141and the stator120is greater, and the gap108is sized to allow the permanent magnet141to provide the passive magnetic axial centering force having a magnitude that is adequate to limit the rotor140from contacting the dividing wall115or the inner surface118aof the cap118. The rotor140also includes a shroud145that covers the ends of the impeller blades143facing the second face113that assists in directing blood flow into the volute107. The shroud145and the inner surface118aof the cap118form a gap109between the shroud145and the inner surface118awhen the rotor140is levitated by the stator120. The gap109is from about 0.2 millimeters to about 2 millimeters. For example, the gap109is approximately 1 millimeter.

As blood flows through the blood flow conduit103, blood flows through a central aperture141aformed through the permanent magnet141. Blood also flows through the gap108between the rotor140and the dividing wall115and through the gap109between the shroud145and the inner surface108aof the cap118. The gaps108and109are large enough to allow adequate blood flow to limit clot formation that may occur if the blood is allowed to become stagnant. The gaps108and109are also large enough to limit pressure forces on the blood cells such that the blood is not damaged when flowing through the pump100. As a result of the size of the gaps108and109limiting pressure forces on the blood cells, the gaps108and109are too large to provide a meaningful hydrodynamic suspension effect. That is to say, the blood does not act as a bearing within the gaps108and109, and the rotor is only magnetically-levitated. In various embodiments, the gaps108and109are sized and dimensioned so the blood flowing through the gaps forms a film that provides a hydrodynamic suspension effect. In this manner, the rotor can be suspended by magnetic forces, hydrodynamic forces, or both.

Because the rotor140is radially suspended by active control of the levitation coils127as discussed above, and because the rotor140is axially suspended by passive interaction of the permanent magnet141and the stator120, no rotor levitation components are needed proximate the second face113. The incorporation of all the components for rotor levitation in the stator120(i.e., the levitation coils127and the pole pieces123) allows the cap118to be contoured to the shape of the impeller blades143and the volute107. Additionally, incorporation of all the rotor levitation components in the stator120eliminates the need for electrical connectors extending from the compartment117to the cap118, which allows the cap to be easily installed and/or removed and eliminates potential sources of pump failure.

In use, the drive coils125of the stator120generates electromagnetic fields through the pole pieces123that selectively attract and repel the magnetic north pole N and the magnetic south pole S of the rotor140to cause the rotor140to rotate within stator120. For example, the Hall sensor may sense a current position of the rotor140and/or the permanent magnet141, wherein the output voltage of the Hall sensor may be used to selectively attract and repel the magnetic north pole N and the magnetic south pole S of the rotor140to cause the rotor140to rotate within stator120. As the rotor140rotates, the impeller blades143force blood into the volute107such that blood is forced out of the outlet opening105. Additionally, the rotor draws blood into pump100through the inlet opening101. As blood is drawn into the blood pump by rotation of the impeller blades143of the rotor140, the blood flows through the inlet opening101and flows through the control electronics130and the stator120toward the rotor140. Blood flows through the aperture141aof the permanent magnet141and between the impeller blades143, the shroud145, and the permanent magnet141, and into the volute107. Blood also flows around the rotor140, through the gap108and through the gap109between the shroud145and the inner surface118aof the cap118. The blood exits the volute107through the outlet opening105, which may be coupled to an outflow cannula.

FIG. 6is a schematic diagram of an overall communication architecture of the mechanical support system ofFIG. 1. A driveline couples the implanted blood pump100to the system controller20, which monitors system operation via various software applications. The blood pump100itself also includes several software applications that are executable by the on board electronics130(e.g., processors) for various functions, such as to control radial levitation and/or drive of the rotor of the pump100during operation. The system controller20may in turn be coupled to batteries22or a power module30that connect to an AC electrical outlet. The system controller20may also include an emergency backup battery (EBB) to power the system (e.g., when the batteries22are depleted) and a membrane overlay, including Bluetooth capabilities for wireless data communication. An external computer having a system monitor32that is configurable by an operator, such as clinician or patient, may further be coupled to the circulatory support system for configuring the system controller20, implanted blood pump100, and/or patient parameters, updating software on the system controller20and/or implanted blood pump100, monitoring system operation, and/or as a conduit for system inputs or outputs.

In addition to producing blood flow at a desired rate, a pulsatile blood flow pattern may be desired. A pulsatile blood flow pattern includes time periods of relatively high blood flow rates and blood pressures and time periods of relatively low blood flow rates and blood pressures. Such a pulsatile blood flow pattern may be desired to augment or replace a weakened pulse in patients, especially those whose native cardiac output is small compared to the volume flow rate of the blood pump. Additionally, a pulsatile blood flow pattern may be desired to produce a physiologic response similar to that of a native pulsatile blood flow pattern and/or blood pulse pressure from a healthy heart. This physiologic response may be markedly different than the response of a blood pump operating at a constant speed. While non-pulsatile circulation can lead to certain physiologic, metabolic, and vasomotor changes, the clinical relevance of pulsatility for VADs is unclear. Nevertheless, it is hypothesized that pulsatile circulation may reduce blood stasis in the ventricles, help exercise the aortic valve, improve washing on the distal side of atherosclerotic lesions, increase coronary and/or end organ perfusion, reduce the risk of ventricular suction, reduce the propensity for maladies related to reduced pulsatility, such as arteriovenous malformations, and increase myocardial recovery. Further, it is expected that these phenomena do not require mimicking a native pulse waveform in its entirety. Rather, such may be accomplished with the techniques and waveforms described herein.

Importantly, various characteristics of the artificial pulse may differ substantially from those of a physiologic pulse even while producing a response in the body that is similar to that caused by the physiologic pulse. Although with the multitude of potential clinical advantages there may be different aspects of a native pulse that mediate physiologic response, it is generally understood that the dominant source of dissipated energy that characterizes a meaningful pulse is the pressure wave generated at the start of cardiac systole. Accordingly, the artificial pulse described herein can include a relatively brief perturbation of a nature designed to produce such dissipated energy.

In some implementations, an artificial pulse cycle includes a perturbation period that simulates the pulse pressure that occurs at the leading edge of systole of a physiologic pulse. The perturbation period can include, for example, a period during which the blood pump100is operated at a low speed, followed immediately by a period during which the blood pump100is operated at a higher speed. The artificial pulse cycle can also include a period longer than the perturbation period during which the pump100is operated at an intermediate speed, for example, a speed maintained between the speeds realized during the perturbation period.

Operating the pump at the intermediate speed can contribute to a high operating efficiency. The efficiency achieved can be greater than, for example, the efficiency of a pump that only alternates between equal periods of operation at a high speed and at a low speed. Typically, a continuous flow pump operates with highest efficiency near the middle of its rotational speed range. Therefore, it can be advantageous to operate such a pump at or near a mid-range speed for at least a portion of an artificial pulse cycle.

Some of the parameters that affect physiologic phenomena include pulse pressure and the rate of blood pressure change (dp/dt). For the blood pump100, for example, pulse pressure and time variation in blood pressure are affected by the angular velocity of the rotor140. Thus, the blood pump100can be selectively controlled to produce a pulsatile blood flow pattern, including a desired pulse pressure and/or a desired rate of pressure change, by producing a pump speed pattern that includes a time period of relatively high rotor rotation speeds and a time period of relatively low rotor rotation speeds. In some implementations, the pulse pressure produced by the blood pump100or produced by the blood pump100and the patient's heart H in combination can be approximately 10 mmHg or more, such as from approximately 20 mmHg to approximately 40 mmHg.

For example, the blood pump100can be operated to produce a pump speed pattern200, illustrated inFIG. 7. The pump speed pattern200includes a first portion210with high pump speed producing a relatively high blood pressure, and a second portion220with low pump speed producing a relatively low blood pressure. Additionally, the pulsatile blood flow pattern can include a transition between the first portion210and the second portion220that produces a desired rate of pressure change in the patient's circulatory system, such as a rate of pressure change that simulates a natural physiologic pulse and that produces desired physiological effects associated with rate of pressure change. In some implementations, the rate of pressure change produced by the transition is, for example, between 500 to 1000 mmHg per second.

The first portion210and/or the second portion220of the pump speed pattern200can include multiple segments. In some implementations, the segments each have predetermined durations. As also shown inFIG. 7, the first high speed portion210of the pump speed pattern200includes a first segment210aand a second segment210b. In the first segment210a, the rotor140is rotated at a first rotation speed ω1 for a first period of time from a time T0to a time T1. At the time T1, the rotation speed of the rotor140is rapidly decreased from the first rotation speed ω1 to a second rotation speed ω2, producing a stepped transition. The rotor140is rotated at the second rotation speed ω2 for a second period of time from the time T1to a time T2during a second segment210bof the first portion210of the pump speed pattern200. At the time T2, the rotation speed of the rotor140is decreased to a third rotation speed ω3 for a third period of time from the time T2to a time T4during the second portion220of the pump speed pattern200. This speed decrease may be as rapid as the aforementioned speed increase, or more gradual to mimic pressure changes during native diastole.

In the pump speed pattern200, the second rotation speed ω2 is a target high blood flow pump speed, and the first rotation speed ω1 is a desired overshoot pump speed that is selected to increase the rate of change of the blood pressure during the first period. The first period of time from the time T0to the time T1, during which the blood pump100is operated at the first rotation speed ω1, is shorter than the second period of time from the time T1to the time T2, during which the blood pump100is operated at the second rotation speed ω2. The first period of time can be from approximately 0.01 seconds to approximately 1 second. In some implementations, the first period of time is approximately 0.05 seconds in duration. In some implementations, the first period of time can be approximately equal to, or greater than the second period of time.

Additionally, the duration of the first period can be selected to produce a desired pulse pressure, i.e., the difference between blood pressure before the speed change time T1and during the time T1, and can be selected independently of the duration of the second period of time. The first portion210, including the first and second time periods from the time T0to the time T2, is longer than the second portion220. In some implementations, the first and second time periods from the time T0to the time T2can be shorter than, longer than, or substantially the same duration as the second portion220. For example, to increase the duration of pumping at the higher flow rate relative to pumping at the lower rate while still benefiting from the occasional pulse, it may be advantageous for the first portion210to be longer than the second portion220. If desired, the speed of the blood pump100is increased to the first rotation speed ω1 and the pump speed pattern200can be repeated. The pump speed pattern200can be repeated on a continuous or discontinuous basis, and the increase of rotation speed of the rotor140is also sufficiently rapid to produce a desired rate of pressure change.

The concept of overshooting the rotation speed ω2 with a greater speed, such as rotation speed ω1, is based upon partly decoupling pulse pressure, i.e. the difference between the blood pressures before and after the speed change, from the volume flow rate at the higher speed. Thus. target pulse pressures and volume flow rates can be attained at various flow conditions. Ideal values will vary with particular pump design and requirements.

As shown inFIG. 7, the period210bcan be longer than the period210a. The period21210bcan also be longer than the portion220. In some implementations, the duration of the period210bis more than half of the duration of the pump speed pattern200. For example, the duration of the period210bcan be 60%, 70%, 80% or more of the duration of the pump speed pattern200. As an alternative, depending on patient needs and pump characteristics, the duration of the period210bcan be 50% or less of the duration of the pump speed pattern200, for example, 40%, 30%, 20% or less.

Operating the pump at the rotation speed ω2 during the period210bcan contribute to a high hydraulic efficiency during the pump speed pattern200. During the pump speed pattern200, the pulse pressure generated in a patient's body is generally correlated to the change in pump rotation speed, for example, the magnitude of the speed change between the speeds ω3 and ω1 at time T4. Therefore, to simulate a pressure change that occurs at the beginning of systole of a physiologic pulse, a significant speed differential between the rotation speeds ω3 and ω1 is generally desired. The speed differential can be, for example, 1000 rpm, 2000 rpm, or more depending on the characteristics of the blood pump100. Due to the magnitude of the speed differential, one or both of the speeds ω3 to ω1 may occur outside the range of highest operating efficiency of the blood pump100.

The rotation speed ω2 can be a speed that results in a high hydraulic efficiency of the blood pump100, for example, a speed near the middle of the operating range of the blood pump100. During the pump speed pattern200, the blood pump100can operate at the speed ω2 that results in high efficiency for a significant portion of the pump speed pattern200, contributing to a high efficiency. As described above, the blood pump100can operate at the speed ω2 for more than half of the duration at the pump speed pattern200. Thus the blood pump100can operate in a highly efficient manner for the majority of the pump speed pattern200and can also produce a pressure change that simulates the beginning of systole of a physiologic heart. Accordingly, some implementations of the pump speed pattern200can provide a higher efficiency than control modes that attempt to mimic all aspects of a native cardiac cycle.

The length of the period210brelative to the length of the pump speed pattern200can vary based on the frequency of the artificial pulse. The duration of the period210aand of the portion220, by contrast, can be independent of the pulse rate. To produce the desired physiological response, a minimum duration for the period210aand the portion220can be selected, for example, 0.125 seconds. The period210bcan fill the remainder of the pump speed pattern200.

As an example, the pump speed pattern200can have a duration of one second, for a frequency of 60 cycles per minute. Given that the period210aand the portion220have a combined duration of 0.125 seconds, the period210bcan have a duration of 0.750 seconds, or 75% of the pump speed pattern200. As another example, when the pump speed pattern200has a duration of two seconds (and thus a frequency of 30 cycles per minute), the duration of the period210bcan be 1.75 seconds, which is 87.5% of the duration of the pump speed pattern200.

In some implementations, the rotation speed ω2 is selected such that the operation of the blood pump100at the rotation speed ω2 produces a flow rate that has a predetermined relationship relative to the average flow rate during the pump speed pattern200. The flow rate during the portion210bcan be within a predefined range of the average flow rate, for example, within 30% or within 10% of the average flow rate. The flow rate during the portion210bcan be substantially equal to the average flow rate.

Selecting the rotation speed ω2 to produce a flow rate that is substantially equal to the average flow rate can facilitate a transition between a pulsatile control mode and another control mode, such as a continuous flow control mode. In some implementations, the blood pump100operates at a particular constant speed for the greater part of the pump speed pattern200. Operation at the constant speed can occur during, for example, the period210b. By adjusting the speeds ω1 and ω3 and duration of the period210aand of the portion220, the average pump volume flow rate can be tuned to substantially match an average pump volume flow rate that would be realized in a different optional setting. Consequently, a clinician or patient can switch from an artificial pulse mode to another control mode in a manner that causes only a small difference or no difference in average volume flow rate. This can provide a clinical advantage when the artificial pulse is a selectable option among at least one alternative, for example, a constant speed option.

As an example, a speed set by a clinician for a constant speed mode can also be utilized for a constant speed portion of an artificial pulse mode. The speed can be selected by the clinician to produce a desired volume flow rate through the blood pump100during the constant speed mode (e.g., during continuous flow or non-pulsatile operation of the blood pump100). In the artificial pulse mode, the same selected speed can be used as, for example, the rotation speed ω2 during the period210bof the pump speed pattern200. The speeds ω1, ω3 and the duration of the period210aand the portion220are calculated or chosen to approximately balance the volume flow rate for the pump speed pattern200. For example, the reduced flow rate during the portion220can offset the increased flow rate during the portion210a. As a result, the net volume flow rate during the pump speed pattern200can substantially match the volume flow rate during the constant speed mode. Thus in either the constant speed mode or the artificial pulse mode, the volume flow rate can be approximately the same, permitting the clinician to switch from one mode to another without affecting the volume flow rate. This can help avoid potentially dangerous conditions that could occur if switching from one mode to another resulted in sudden changes in flow rate. for example, a sudden decrease in volume flow rate could cause acutely insufficient perfusion for the patient, and a sudden increase in volume flow rate could cause ventricular suction and arrhythmia.

As mentioned above, the second portion210of the pump speed pattern200can also include multiple segments. For example, as shown inFIG. 8, a pump speed pattern300includes a first portion310that has a first segment310aand a second segment310band the pump speed pattern300includes a second portion320that has a first segment320aand a second segment320b. During the first segment310a, from the time T0to the time T1, the blood pump100is operated at the first rotation speed ω1. At the time T1, the speed of the blood pump100is reduced to the second rotation speed ω2, and the blood pump100is operated at the second rotation speed ω2 for the second period of time from the time T1to the time T2. At the time T2, the speed of the blood pump100is reduced from the second speed ω2 to the third rotation speed ω3. The blood pump100is operated at the third rotation speed ω3 for a third period of time from the time T2to a time T3during a first segment320aof the second portion320of the pump speed pattern300. At the time T3, the speed of the blood pump100is increased from the third rotation speed ω3 to a fourth rotation speed ω4, and the blood pump100is operated at the fourth rotation speed ω4 during a fourth period of time from the time T3to the time T4during a second segment320bof the second portion320of the pump speed pattern300. If desired, the speed of the blood pump100is increased to the first rotation speed ω1 and the pump speed pattern300can be repeated. The pump speed pattern300can be repeated on a continuous or discontinuous basis, and the increase of rotation speed of the rotor140is also sufficiently rapid to produce a desired rate of pressure change.

Similar to the concept of overshooting ω2 in pattern200, the concept of overshooting the rotation speed ω4 with a lower rotation speed, such as the rotation speed ω3, is also based upon decoupling pulse pressure from the volume flow rate at the lower rotation speed ω4. Thus, the pump speed pattern300more completely decouples target pulse pressures and volume flow rates than the pump speed pattern200, and ideal values can be attained, or more closely approximated, at various flow conditions.

While a single overshoot pump speed for a transition between pump speeds are illustrated and described with reference toFIGS. 7 and 8, multiple overshoot pump speeds for one or more transitions can be used. For example,FIG. 9illustrates a pump speed pattern400that includes multiple overshoot pump speeds for each transition. The pump speed pattern400includes a first portion410having a first segment410aand a second segment410b, and that includes a second portion420having a first segment420aand a second segment420h. The first segment410aof the first portion410of the pump speed pattern400includes a first step431during which the blood pump100is operated at the first rotation speed ω1 to overshoot the target pump speed ω2 and a second transition step433during which time the blood pump100is operated at a fifth speed ω5 to transition from the first rotation speed ω1 to the second rotation speed ω2. Similarly, the first segment420aof the second portion420includes a first step441during which the blood pump100is operated at the third rotation speed ω3 and a second segment443during which the blood pump100is operated at a sixth speed ω6 to transition between the third speed ω3 and the fourth rotation speed ω4. If desired, the speed of the blood pump100is increased to the first rotation speed ω1 and the pump speed pattern400can be repeated. The pump speed pattern400can be repeated on a continuous or discontinuous basis, and the increase of rotation speed of the rotor140is also sufficiently rapid to produce a desired rate of pressure change.

The concept of creating multiple stepwise rotation speed changes is based upon producing the physiologic response that is similar to that produced during human cardiac systole and diastole. This is distinct from mimicking the nature of a native pulse waveform in its entirety. As described above, greater hydraulic efficiency can often be achieved by avoiding imitation of the physiologic pressure waveform over the pulse cycle. It was previously mentioned that an artificial pulse offers a multitude of potential clinical advantages. For some or all of these potential clinical advantages, the benefit of closely matching the energy dissipated during a healthy native pulse varies. To the extent that close matching facilitates achieving these potential clinical advantages, the additional complexity of pattern400may be warranted.

In contrast to the stepped or discontinuous transitions discussed above with respect toFIGS. 7-9, smooth or continuous transitions may be used in place of, or in combination with, stepped transitions between different pump operation speeds. For example, smooth transitions are illustrated in the pump speed pattern500ofFIG. 10. The pump speed pattern500includes a first portion510and a second portion520. The first portion510includes a first segment510aduring which the speed of the pump100is decreased gradually, at a strategically-selected rate, from the first rotation speed ω1 to the second rotation speed ω2 from the time T0to the time T1. The selected rate of pump speed decrease can be, for example, a particular linear rate or a particular non-linear rate. During the second segment510bof the first portion510, from the time T1to the rime T2, the blood pump100is operated at the second rotation speed ω2. Similarly, the second portion520includes a first segment520aduring which the speed of the blood pump100is increased gradually, at a strategically-selected rate, from the third rotation speed ω3 to the fourth rotation speed ω4 from the time T2to the time T3. During the second segment520bof the second portion520, from the time T3to the time T4, the blood pump100is operated at the fourth rotation speed ω4. If desired, at time T4, there is a step increase in the rotation speed of the rotor140can be rapidly increased to the first rotation speed ω1, and the pump speed pattern500is repeated.

The concept of creating multiple speed changes at a strategically-selected rate is based upon producing the physiologic response that is similar to that produced during human cardiac systole and diastole. For example, if very accurate matching of energy dissipation during a human pulse is necessary, the additional complexity of pattern500may be warranted.

The pump speed pattern500illustrates the difference between stepped transitions discussed above with respect to pump speed patterns200-400, produced by rapidly changing the rotation speed of the rotor140, and the gradual transitions of the first segment510aof the first portion510and the first segment520aof the second portion520of the pump speed pattern500. Such gradual transitions can be included, for example, to mimic pressure changes exhibited during native diastole, as may be achieved by the gradual transition of the first segment510aof the first portion510of the pump speed pattern500. In some implementations, one or more of the rotation speed decreases of a pump speed pattern can be gradual transitions. For example, a pump speed pattern can include a gradual decrease in rotation speed from the first rotation speed ml to the third rotation speed ω3 and a stepped transition from the third pump speed ω3 back to the first rotation speed ω1. Various combinations of stepped and gradual transitions can be included in a pump speed pattern to produce a desired arterial pressure wave form, or other desired physiologic effect. Additionally, the type of transition between rotation speeds can affect power consumption of the blood pump100, and the pump speed pattern can be selected based, at least in part, on power consumption considerations.

For all the pump speed patterns discussed it should be appreciated that although rotor speed is the technological parameter utilized to impart an artificial pulse, any physiologic effect is related to the consequential pressure and flow patterns, including pulse pressure, the maximum time variation in rate of blood pressure change (dp/dt), and the like. Rotor speed is not intrinsically physiologically meaningful. The human vascular system naturally dampens the native pulse produced by the heart, and it will do the same for an artificial pulse produced as described. The invention describes a utilitarian combination of factors that result in a physiological meaningful pulse. Thus, the pump speed patterns200-500described above are exemplary combinations of parameters that result in a physiologically meaningful pulse.

In use, the pump speed patterns200-500can be generated by a controller that is configured to generate an electrical drive signal to operate the blood pump100. For example, the controller can include a computer system600, shown inFIG. 11, that outputs an electrical current to operate the blood pump100. In order to produce the pump speed pattern200described above, the controller outputs a first electrical current from the time T0to the time T1. At the time T1, the controller reduces the output electrical current to a second current that is lower than the first electrical current, and outputs the second electrical current from the time T1to the time T2. At the time T2, the controller reduces the output electrical current from the second current to a third current, and outputs the third electrical current from the time T2to the time T4.

The computer system600includes one or more processors610, memory modules620, storage devices630, and input/output devices640connected by a system bus650. The input/output devices640are operable to communicate signals to, and/or receive signals from, one or more peripheral devices660. For example, a peripheral device660can be used to store computer executable instructions on the memory modules620and/or the storage devices630that are operable, when executed by the processors to cause the controller to generate a waveform to control the operation of the pump100and produce a pump speed pattern, such as the pump speed patterns200-500.

Additionally, the controller can include a sensor that provides a signal that indicates activity of the heart H. For example, the controller can include a sensor that provides a signal indicative of power consumption of the blood pump100. The signal can be used to determine when the left ventricle LV contracts. For example, the power consumption of the blood pump100may, for a given operating speed, increase as the left ventricle LV contracts. Based on the determined heart activity, the controller can adjust the generated control waveform. For example, the controller can automatically adjust the timing and duration of the first portion210and the second portion220of the pump speed pattern200such that the first portion210approximately coincides with a contraction of the left ventricle LV. The pump100is controlled such that the time T0approximately coincides with a beginning of a contraction of the left ventricle LV and the time T2approximately coincides with an end of the contraction of the left ventricle LV. The time T4approximately coincides with a beginning of a subsequent contraction of the left ventricle LV. Thus, the durations of the various portions and/or segments of the pump speed patterns described above can be changed individually or collectively for one or more repetitions of the pump speed patterns. Using these techniques, the controller can synchronize the pulsatile operation of the blood pump100with the natural physiologic pulse of the heart H.

Alternatively, the controller can generate the control waveform independently of the activity of the heart H and/or to operate in opposition to the activity of the heart H, such as where the first portion210occurs during left ventricular relaxation. Similarly, the controller can generate a control waveform that includes a distinctly non-physiologic pulse rate, such as fewer than 40 high-pressure periods per minute, and the waveform can be generated independently of native heart function. In some examples, the blood pump100can be operated to produce distinctly physiologic pulse rates, such as between 50 and 110 high-pressure periods per minute, and can be controlled dependently or independently of heart function.

A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the claimed invention. For example, the pump speed patterns described above can be used with various types of blood pumps, including axial flow blood pumps and centrifugal flow blood pumps. Similarly, the rotors of blood pumps used to produce pulsatile blood flow patterns as described above may be electromagnetically-suspended, hydraulically-suspended, mechanically-suspended, or combinations thereof. The rotors may also partially be passively magnetically-suspended. However, the effect of an artificial pulse may most accurately be simulated by a pump in which the rotor is electromagnetically suspended, with or without partial passive magnetic suspension, because in general, other things being equal, electromagnetic suspension yields a high degree of responsiveness of the rotor to speed change inputs. For example, mechanical hearings associated with mechanical suspension and/or very narrow rotor clearance gaps associated with hydraulic suspension hinder rapid acceleration of the rotor compared to similar pumps that employ electromagnetic suspension. Additionally, while the pump speed patterns described above have been described with regard to a measure of angular velocity, the pump speed patterns can be produced with regard to one or more different measures of pump speeds. Additionally, there may be a delay between a change in drive signal generated by the controller and a change in operating speed of the blood pump. Thus, the controller can be operated such that changes in the output drive signal are effected at a time to produce a corresponding change in pump operating speed at a desired time, such as a time that approximately coincides with selected activity of the heart.

In some implementations, the pump speed patterns200-500can include additional portions or segments during which the blood pump is operated at other speeds. For example, at desired times, the blood pump can be operated to produce a pump speed pattern that produces a desired physiologic effect, such as opening or dosing the aortic valve. Such operation of the blood pump can interrupt a generally continuous repetition of a selected one or more of the pump speed patterns described above, or others, including an indefinite period of constant speed, and a selected pump speed pattern can be resumed after the desired physiologic effect has been produced. The pump speed patterns200-500can also include different portions or segments. For example, the second segment210bof the first portion210of the pump speed pattern200can include multiple pump speeds. Similarly, the transitions between pump speeds, such as the reduction in pump speed from the first rotation speed ω1 to the second rotation speed ω2, can include constant, variable, exponential, combinations thereof, or other rate of speed change over time such that the transition, such as the first segment510aof the first portion510of the pump speed pattern500, is linear, curvilinear, parabolic, logarithmic, sinusoidal, stepped, or combinations thereof.

In some implementations, one or more of the pump speed changes in the pump speed patterns200-500can be monotonic. A transition from one speed to another may occur gradually over a period of time, yet change directly from one speed to another. For example, to decrease a pump speed from a first rotational speed to a second rotational speed, the controller can reduce the pump speed without causing an intervening period of increasing pump speed. Similarly, the transition from the first rotational speed to the second rotational speed can occur without operating the pump above the first rotational speed during the transition.

Additionally, a blood pump can be operated according to a pump speed pattern that is selected according to a pump power consumption rate associated with the pump speed pattern, a pump efficiency associated with the pump speed pattern, a blood flow rate associated with the pump speed pattern, and/or a rate of blood pressure change associated with the pump speed pattern. For example, in a first mode, the controller can be operated to produce a pump speed pattern that produces a desired rate of blood pressure change. When a low power condition is detected, the controller can be switched to a power-saving mode to produce a pump speed pattern that has a low power consumption rate, even if the desired rate of pressure change is not produced in the power-saving mode.

FIG. 12illustrates an exemplary method1000for conserving power according to some embodiments of the present invention. Method1000may start at step1002where the implantable blood pump is operated in a first flow mode. One or more power source types may be determined1004that are delivering power to the pump. The method1000may further include monitoring the one or more power sources based on the one or more power source types1006. A power condition that is indicative of a mode to conserve power may be identified1008. When the power condition is indicative of a mode to conserve power1008, a signal may be transmitted to the pump to transition the pump from the first flow mode to a second flow mode that consumes less power1010. The pump may then be operated at the second flow mode1012. Thereafter, the method1000may include identifying an end to the power condition that is indicative of a mode to conserve power1014. After identifying an end to the power condition that is indicative of a mode to conserve power1014, a signal may be transmitted to the pump to transition the pump from the second flow mode to the first flow mode1016. The pump may then be operated in the first flow mode1002.

The method1000can advantageously sustain VAD operation during low power conditions. Improving the duration of VAD operation during low power has many advantages, such as patient safety, as discussed herein. For example, the method may allow the VAD to continue to operate uninterrupted for longer durations of time while the patient safely secures alternative power sources or recharges existing power sources. Still further, the present invention finds applicability with both external power sources and fully implantable transcutaneous energy transfer systems.

In some embodiments, the first flow mode may be a pulsatile flow mode described above or a variation thereof. For example, the first flow mode may comprise a baseline speed, a transition to a slower speed, then a transition to a speed faster than baseline, and then a return to the baseline speed. In some embodiments, the first flow mode may have an adjustable a base rate, an overshoot, and a diastole. In other embodiments the first flow mode may be a non-pulsatile flow mode. Optionally, the first flow mode may be a continuous speed or constant speed flow mode. The first flow mode may be set by a practitioner depending on the needs of the user or may be a default operational mode for a pump.

In some embodiments, the method1000may determine or classify the one or more power source types that are delivering power to the pump1002. In some embodiments, an implanted blood pump100may receive power from a plurality of power sources. As described above, a controller20may connect to one or more power sources via a first power cable and a second power cable. For example, some embodiments of a blood pump100may be connected to and receive power from a first external rechargeable battery22via the first cable and a second external rechargeable battery22connected via the second cable. The rechargeable batteries may be lithium ion batteries, for example. Further, in some embodiments, a controller20may house a lower capacity rechargeable battery for use in emergency situations, such as when the first and second cables are disconnected from the controller20, or higher capacity rechargeable battery for pro-longed periods of use. The controller20battery may be an emergency backup battery (EBB). Optionally, the blood pump100may also be connected to a power module30and may receive power directly from an electrically coupled electrical outlet (e.g., AC outlet) coupled with the power module30and/or from an EBB housed within the power module30. The power module30may couple to the controller20via the first and second cables in some embodiments.

In some embodiments, the controller20may include a power monitor module for periodically checking the voltages of one or more attached cables to gather RSOC status information of the one or more attached cables and/or to determine the type of power source connected thereto. In some embodiments, the controller20may be configured to determine the type of power source delivering power through the one or more cables and the voltage being supplied therefrom1004. For example, an analog to digital converter (ADC) may be configured to provide power source information. Optionally a digital to analog converter (DAC) may be provided to verify that the ADC is functioning properly. Further, in some embodiments, an EBB driver may be configured to provide EBB information. A power monitor may be coupled to the ADC and/or EBB driver and be configured to monitor information from the ADC and/or an EBB driver to monitor status of the power supplies of the blood pump.

In some embodiments, RSOC information may be used to identify the type of power source1004. For example, if the relative state of charge (RSOC) through the first and second cables is greater than 9800 mV, the power monitor may be configured to determine that the power source is a coupled power module30. When the relative state of charge is greater than or equal to 330 mV and less than or equal to 4600 mV, the power monitor may be configured to determine that the power source for the blood pump100is one or more coupled lithium ion batteries22. When relative state of charge is less than 330 mV or greater than 4600 mV and less than or equal to 9800 mV, the power monitor may identify the power source as unknown. In some embodiments, the power monitor may be further configured to monitor the power status for one or more cables (e.g., the first cable and second cable) attached to the controller via the information from the ADC and/or EBB driver. For example, in some embodiments, when the RSOC information from the associated cables are indicative of disconnected cables, the controller20may determine that the system is disconnected from external power sources and that an EBB is powering the pump.

The method may further include monitoring the one or more power sources based on the one or more power source types1006. For example, the power monitor may periodically analyze information gathered from the ADC driver unit and may provide power related information to other units in the system. For example, the relative state of charge (RSOC) battery levels may be detected and used to determine power sources, power levels, and the average pump power draw level. This information may then be output via a system monitor display or visual indicators (e.g., as power gauge LEDs, or the like) for use by a user or practitioner. Additionally, a power monitor may be configured to analyze readings and report fault conditions to a fault handler as appropriate.

The power monitor may also monitor the one or more power sources by gathering non-RSOC information from the one or more attached cables. Based on this information, the power monitor may be configured to monitor the one or more power sources1006by setting and clearing faults related to the voltage levels on each power cable. For example, a power monitor may be configured to handle the following faults: cable disconnected fault, RSOC red fault, RSOC yellow fault, unknown fault, voltage red fault, and voltage yellow fault for the one or more attached cables. The red faults have higher priority over the yellow faults and the voltage faults may have priority over the RSOC faults. In some embodiments, the disconnected fault may have the highest priority and the unknown fault may have a second highest priority.

Accordingly, in some embodiments where the power monitor is configured to set and clear faults related to voltage levels on two power cables, a first power cable and a second power cable, the power monitor may handle the following faults: first cable disconnected fault; second cable disconnected fault; first cable RSOC red fault; second cable RSOC red fault; first cable RSOC yellow fault; second cable RSOC yellow fault; first cable unknown fault; second cable unknown fault; first cable voltage red fault; second cable voltage red fault; first cable voltage yellow fault; and second cable voltage yellow fault.

A power monitor may assign a cable a green status when the power monitor does not assign a yellow, red, unknown, or disconnected status to the cable.

In some embodiments, for example, a power monitor may assign a disconnected fault to a cable when the ADC returns a voltage less than or equal to 1000 mV. Additionally, a cable unknown fault may be reported when ADC returns an RSOC less than 330 mV or greater than 4600 mV and less than or equal to 9800 mV. RSOC yellow faults may be triggered for a connected cable when the RSOC is less than 1930 mV and greater than or equal to 1130 mV. RSOC red faults may be triggered for a connected cable when the relative state of charge is less than 1130 mV. When powered by a power module30, voltage yellow faults may be triggered for a connected cable when voltage is greater than 10400 mV and less than or equal to 11200 mV and voltage red faults may be triggered for a connected cable when voltage is greater than 1000 mV and less than or equal to 10400 mV. When powered by lithium ion battery22, voltage red faults may be triggered for a connected cable when voltage is greater than 1000 mV and less than or equal to 13200 mV.

FIG. 13illustrates a graphical description700of exemplary power monitoring rules for a power monitor. The power monitor may first determine whether a cable is disconnected710. When ADC driver returns voltage less than or equal to a disconnect voltage (e.g., 1000 mV in the illustrated embodiment), the power monitor may report a cable disconnect fault for the respective cable711. When the ADC driver returns voltage greater than the disconnect voltage (e.g., 1000 mV), the power monitor may determine that the cable is connected712. Once the power monitor determines that the cable is connected, the power monitor may be configured to determine the power source720.

When the ADC driver returns an RSOC greater than or equal to a minimum battery threshold (e.g., 330 mV in the illustrated embodiment) and lower than a maximum battery threshold (e.g., 4600 mV in the illustrated embodiment), the power monitor may be configured to determine that the power source is a battery730(e.g., a rechargeable lithium ion battery, or the like). When the RSOC is greater than a minimum power module threshold (e.g., 9800 mV in the illustrated embodiment), the power monitor may be configured to determine that the power source is a power module740. When the RSOC is less than the minimum battery threshold (e.g., 330 mV) or greater than the maximum battery threshold (e.g., 4600 mV) but less than or equal to the minimum power module threshold (e.g., 9800 mV), the power monitor may be configured to determine that the power source is unknown750and report a cable unknown fault751.

When the power monitor determines that the power source is a battery730, the power monitor may be configured to monitor a charge and/or voltage of the battery. When the voltage is less than or equal to a voltage red fault threshold (e.g., 13200 mV in the illustrated example for an exemplary lithium ion battery), the power monitor may be configured to report a voltage red fault status for the power cable731. When a voltage is greater than or equal to a normal voltage threshold (e.g., 14000 mV in the illustrated example for an exemplary lithium ion battery), the power monitor may be configured to then analyze for RSOC faults of the battery732.

For example, as illustrated inFIG. 13, when the RSOC is less than or equal to a RSOC yellow fault threshold (e.g., 1930 mV in the illustrated embodiment for a lithium ion battery), the power monitor may report a RSOC yellow fault733. When the RSOC is less than RSOC red fault threshold (e.g., 1130 mV in the illustrated embodiment for a lithium ion battery), the power monitor may report a RSOC red fault734. When the RSOC is greater than the RSOC yellow fault threshold (e.g., 1930 mV), the power monitor may determine that the battery is operating normally and may report a power level (e.g., 1-4)735to a user via a system monitor, LED power indicators, or the like.

When the power monitor determines that the power source is a power module740, the power monitor may be configured to monitor a voltage level of the power monitor. When the voltage is less than or equal to a yellow voltage fault threshold (e.g., 11200 mV in the illustrated embodiment), the power monitor may report a yellow voltage fault741. When the voltage is less than or equal to a red voltage fault threshold (e.g., 10400 mV in the illustrated embodiment), the power monitor may report a red voltage fault742. When the voltage is greater than the yellow voltage fault threshold, the power monitor may determine that the power monitor is operating normally and may report a power level (e.g., 1-4)743to a user via a system monitor, LED power indicators, or the like.

The power monitor may report one fault per cable each time the monitor executes. Faults may remain until a lower priority fault (or no fault) occurs. For example, when going from voltage red fault to disconnected, the red alarm may remain set, but when going from disconnected to voltage red, the disconnect fault may be cleared.

FIG. 14illustrates a chart describing exemplary alarms for various situations depending on the status of a first cable (e.g., black cable status) and a second cable (e.g., white cable status). As illustrated, a low power hazard condition is triggered when the power monitor reports an unknown, red, or yellow fault for one cable and reports a disconnected, unknown, or red fault for the other cable. When the power monitor reports cable disconnected faults for both cables (white and black), a “no external power” condition is triggered. When one of the cables is green (i.e., not reported as disconnected, unknown, red, or yellow), the system may be configured to trigger at most a low power advisory no matter the status of the other cable. Further, a low power advisory may be issued when the power monitor reports a yellow fault for both cables. When both cables have a green status, no alarms are issued.

The controller20may be configured to monitor the status of the system to identify a power condition that is indicative of a mode to conserve power1008. For example, a power-saving mode may be initiated when the power monitor detects a low power hazard condition and/or a “no external power” condition that persists for an extended duration of time. The extended duration of time may be preset and may be more than 5 minutes, 10 minutes, 15 minutes, 20 minutes or more. The no external power condition may be triggered when the power monitor sets a disconnected fault for each cable. For example, when the controller couples to power sources (e.g., a first battery and a second battery) via a first power cable and a second power cable, the no external power condition may be triggered when the first power cable and the second power cable are disconnected or otherwise assigned a disconnected fault. In such circumstances, a pump100may still be powered by an EBB housed within a controller20. However, due to the relatively short battery life of the EBB, it may be preferable to alert the user and to initiate a power saving mode when a low power hazard condition and/or a no external power condition persists for an extended period of time (e.g., 15 minutes).

The low power hazard condition may be triggered a number of ways as illustrated inFIG. 14. For example, in embodiments where a controller20couples to a power source via a first cable and a second cable, a low power hazard condition may be triggered when 1) the status of the first cable is assigned a disconnected, unknown, or red fault (e.g., RSOC red, voltage red) by a power monitor; and 2) the status of the second cable is issued a yellow (RSOC yellow, voltage yellow), red (RSOC red, voltage red), or unknown fault by the power monitor.

In some embodiments, the power-saving mode may be entered when a low power hazard alarm condition or a no external power alarm condition has persisted for the extended duration, individually or cumulatively. For example, when the extended duration for entering the power saving mode is fifteen minutes, the power saving mode may be entered when a low power hazard condition has persisted for seven minutes and a no external power alarm condition persists for eight minutes thereafter. Accordingly, the power saving mode may be initiated after a low power hazard condition persists for an extended duration of time, after a no external power condition persists for an extend duration of time, or after a combined low power hazard condition and a no external power condition for an extended duration of time.

Additionally, the power-saving mode may be initiated when the controller20is powered by an emergency backup battery (EBB) and the bus voltage of the EBB falls below a threshold value, (e.g., 10.4 v or the like). This power-saving mode trigger may be advantageous when the pump has been powered by the EBB for an extended period and may benefit from recharging time prior to exiting a power-saving mode.

When the power-saving mode is entered, the controller20may be configured to send a command to the VAD100to transition from a pulsed mode to a constant or uniform speed mode within a time period from the initiation of power-save mode1010. The time period may be five seconds in some embodiments. Preferably, the controller may be configured to send the transition command within two seconds from the initiation of the power-saving mode. Optionally, when there is no external power, the controller may be configured to send a command to the VAD to transition from a pulsed mode to a constant speed mode within one second of entering the power-saving mode.

In some implementations, a physician or a user may input a low speed limit for the VAD100or a low speed limit may be a default value for the device. The controller20may be configured to send a command to the VAD100to ramp the speed down to the low speed limit when entering the power-saving mode. In some embodiments, the controller20may command the VAD to ramp the speed down to the low speed limit at 50 rpm/15 seconds.

FIG. 15illustrates an exemplary constant speed mode800for operating an implantable blood pump during a power-saving condition. The constant speed mode800may operate the implantable blood pump a constant rotational speed ω throughout the operation of the constant speed mode800. In the exemplary constant speed mode800, the constant rotational speed ω is illustrated as rotational speed ωLSL, which corresponds to the rotational speed at the default or previously entered lower speed limit for the user. While illustrated as operating at a constant low speed limit ωLSL, it should be understood that other constant speed modes may be operated at other rotational speeds. It will further be appreciated that in continuous speed mode, the blood pump operational rate is more uniform or steady-state, but may still change over time as suitable in view of changing operational scenarios.

Further, while the above power saving mode is discussed with reference to a controller20sending signals to a VAD100for transitioning from a pulsatile mode to a constant speed mode, it should be understood that other transitions are possible. For example, a controller20may be configured to command an VAD100from a first pulsatile mode to a second pulsatile mode when power-saving mode is triggered. The second pulsatile flow mode may consume less power than the first pulsatile mode by, for example, pumping at a lower speed. For example, in some embodiments, a pump may transition to the second pulsatile flow mode from a first pulsatile flow mode by adjusting a base rate speed, an overshoot speed, and/or a diastole speed of the first pulsatile flow mode of the pump. Alternatively, in some embodiments, a controller20may be configured to command a VAD100to transition from a first constant speed to a second constant speed mode when power-saving mode is triggered. The second constant speed mode may consume less power than the first constant speed mode by providing continuous speed at a lower speed, for example.

When in the power-save mode, and when one or more power-saving mode triggers end (e.g., external power connection)1014, the controller20may then send a signal to the VAD100to resume operation according to the prior operational mode1016. For example, in some embodiments, when the VAD100is operating in a power-saving mode and the controller20detects a connection to an external power source such as a charged external battery, AC outlet, or the like, the controller20may exit power-saving mode and send a signal to the VAD100to change speed to the previous operating mode. In some embodiments, the controller20may command the VAD100to transition from a power-saving continuous flow mode to a normal continuous speed mode or a pulsatile speed mode when one or more of the power-saving triggering conditions ceases. The normal continuous speed mode or the pulsatile flow mode may be the prior operational mode. Optionally, the controller20may command the VAD100to transition from a power-saving pulsatile flow mode to a normal pulsatile flow mode which may be the prior operational mode prior to the controller entering the power-saving mode.

As mentioned above, in some implementations, the blood pump100can be used to assist a patient's heart during a transition period, such as during a recovery from illness and/or surgery or other treatment. In other implementations, the blood pump100can be used to partially or completely replace the function of the patient's heart on a generally permanent basis, such as where the patient's aortic valve is surgically scaled.

The subject matter and the functional operations described in this specification can be implemented in digital electronic circuitry, in tangibly-embodied computer software or firmware, in computer hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. The subject matter described in this specification can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a tangible non transitory program carrier for execution by, or to control the operation of, data processing apparatus. The program carrier can be a computer storage medium for example, a machine-readable storage device, a machine-readable storage substrate, a random or serial access memory device, or a combination of one or more of them, as described further below. Alternatively or in addition, the program instructions can be encoded on an artificially generated propagated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus for execution by a data processing apparatus.

Computers suitable for the execution of a computer program can include, by way of example, general or special purpose microprocessors or both, or any other kind of central processing unit. Generally, a central processing unit will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processing unit for performing or executing instructions and one or more memory devices for storing instructions and data. A computer can also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a pump, a pump controller, or a portable storage device, e.g., a universal serial bus (USB) flash drive or other removable storage module, to name a few.