Patent Description:
Implantable blood pumps used as mechanical circulatory support devices include a pumping mechanism to move blood from the heart to the rest of the body. The pumping mechanism may be a centrifugal flow pump, such as the HVAD® Pump manufactured by HeartWare, Inc. in Miami Lakes, Fla. The HVAD® Pump is further discussed in <CIT>, the disclosure of which is hereby incorporated herein in the entirety. In operation, the blood pump draws blood from a source, such as the right ventricle, left ventricle, right atrium, or left atrium of a patient's heart and impels the blood into an artery, such as the patient's ascending aorta or peripheral artery.

Known blood pumps, such as the HVAD® pump, typically include an impeller positioned within a pump housing to impel blood through the housing from an inflow end to an outflow end. The HVAD® pump includes dual stators, one located upstream of the impeller and one located downstream from the impeller, configured to rotate the impeller to impel the blood. A control system typically controls operation of a power source or power supply in communication with the stators to drive the impeller at a set rotational speed and thus provide a constant pumping action.

When the blood pump is off, and/or operation of the impeller is temporarily suspended, it is desirable to start or resume operation of the pump as quickly and efficiently as possible to provide assistance to a patient's heart. However, starting the impeller may be difficult, particularly when the impeller is at rest against the housing of the pump. At least one known method of starting a blood pump includes a ramp phase, a commutation phase, and a speed phase in which a pump speed is locked for a time period followed by a speed increase. Another known method of starting a blood pump includes the use of only a single stator when a fault is detected in a second stator which increases the difficulty of a successful startup Relevant prior art is disclosed in documents <CIT>, <CIT> and <CIT>.

The present disclosure advantageously provides a method and system for starting a blood pump.

A control circuit for an implantable blood pump according to the present invention comprises the technical features as defined in independent claim <NUM>.

In one aspect, the present disclosure provides a method of starting an implantable blood pump. The method includes gradually increasing a motor speed from an inactive state to a first speed during a first- time period. A predetermined maximum voltage is applied during the gradual increase in the motor speed. The gradual increase in motor speed is transitioned to a closed loop speed control to achieve an operating speed, the operating speed being greater than the first speed.

In another aspect, the method further includes bypassing a commutation phase.

In another aspect, the method further includes maintaining a voltage below a predetermined maximum voltage threshold.

In another aspect, a transition of the motor speed from the inactive state to the operating speed occurs over a startup time duration of less than <NUM> seconds.

In another aspect, the method further includes displacing an impeller of the blood pump from a starting position in which the impeller is in contact with a disk to an operating position in which the impeller is displaced away from the disk.

In another aspect, the method further includes generating a non-linear frequency ramp when gradually increasing the motor speed from the inactive state to the first speed.

In another aspect, the method further includes applying a predetermined maximum voltage to a plurality of coils of a stator disposed within the implantable blood pump when gradually increasing the motor speed from the inactive state to the first speed.

In another aspect, the inactive state includes a speed of zero and the first speed being between <NUM> to <NUM> RPM.

In another aspect, the first-time period is between <NUM> to <NUM> seconds and the second-time period is less than one second.

In one aspect, a method of starting an implantable blood pump including a first stator and a second stator includes detecting an electrical fault in one of a group consisting of the first stator and the second stator. A startup of the first stator and the second stator is commenced in response to the electrical fault.

In another aspect, the method further includes operating the first stator in at least three phases and the second stator in a set of two phases when detecting the electrical fault in the second stator.

In another aspect, the method further includes using the first stator for measuring back electromotive force.

In another aspect, the first stator and the second stator each include a set of three motor windings.

In another aspect, the method further includes increasing an axial force and a radial torque relative to a predetermined amount to displace an impeller from a disk within the implantable blood pump.

In another aspect, the method further includes alternating a phase angle of the first stator.

In one aspect, a method of starting an implantable blood pump includes performing a plurality of motor startup attempts including applying a first voltage less than a predetermined maximum voltage to a plurality of stators. In response to a failure of the plurality of motor startup attempts, an additional startup attempt is performed including applying the predetermined maximum voltage to the plurality of stators.

In another aspect, the plurality of motor startup attempts includes a set of two startup attempts.

In another aspect, the method further includes detecting whether a motor startup has occurred after each of the plurality of motor startup attempts.

In another aspect, the method further includes gradually increasing a motor speed from an inactive state to an operating speed.

In another aspect, the predetermined maximum voltage is between <NUM>-14V.

Before describing in detail exemplary embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to starting a blood pump. Accordingly, the system and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

Referring now to the drawings in which like reference designators refer to like elements there is shown in <FIG> an exemplary blood pump constructed in accordance with the principles of the present application and designated generally "<NUM>. " The general arrangement of the blood pump components may be the same or similar to the HVAD® Pump described in <CIT> and <CIT>.

For example, the blood pump <NUM> may include a housing <NUM> having a chamber <NUM>, an inflow cannula <NUM>, and a major longitudinal axis <NUM> extending therethrough. An enclosed flow path extends along the axis <NUM> from an upstream to a downstream direction, as indicated by the arrows U and D, respectively. A generally disc-shaped ferromagnetic impeller <NUM> is mounted within the chamber <NUM> between a first ceramic disk <NUM> and a second ceramic disk <NUM> for rotation about the axis <NUM>.

The blood pump <NUM> may be arranged so that the impeller <NUM> is levitated within the housing <NUM> by contactless bearings, such as magnetic bearings, hydrodynamic bearings or a combination of the two. For example, the blood pump <NUM> may include a first stator <NUM> and a second stator <NUM> disposed within the housing <NUM>. The first stator <NUM> may be located proximate the first ceramic disk <NUM> and the second stator <NUM> may be located proximate the second ceramic disk <NUM>. In operation, a voltage may be applied to one or more coils of the first stator <NUM> and/or the second stator <NUM> to rotate the impeller <NUM> to impel the blood. An electrical connector <NUM> may supply the voltage to the coils from, as shown in <FIG>, a power supply <NUM> such as an external AC power supply, external battery, implanted battery, or any combination thereof, coupled to or stored within a controller <NUM>.

With reference to <FIG> and <FIG>, the first stator <NUM> and the second stator <NUM> may operate in combination or independent of each other and may each form a portion of a sensorless three-phase brushless direct-current ("BLDC") motor <NUM>. In one configuration, the coils of the first stator <NUM> and the second stator <NUM> are in the form of three motor windings controlled by a different respective phase U, V, W, of a power input for three-phase motor control. The BLDC motor includes an inverter circuit to convert a DC input to the three-phase output. Alternatively, the blood pump <NUM> may receive an alternating current (AC) three-phase input. Examples of three-phase motor control methods and devices are provided in commonly owned and co-pending <CIT>, and <CIT>.

<FIG> shows an example control circuit <NUM> coupled to the blood pump <NUM> including hardware and software for monitoring and controlling startup and subsequent operation of one or both of the stators <NUM> and <NUM> according to the routines of the present disclosure. The control circuit <NUM> includes a processor <NUM>, a memory <NUM>, and an interface <NUM> for interfacing with the motor <NUM>. The memory <NUM> stores information accessible by the processor <NUM>, including instructions <NUM> that may be executed by the processor <NUM>. The memory <NUM> also includes data <NUM> that may be retrieved, manipulated or stored by the processor <NUM>. Further details associated with the control circuit <NUM> are provided in commonly owned and co-pending <CIT>.

The instructions <NUM> stored in the memory <NUM> may include one or more instruction sets or modules, for performing certain operations in accordance with the present disclosure. One such module may be a motor control module <NUM> for controlling operation of the motor <NUM> (e.g., increasing or decreasing current supplied to the motor). The instructions may also include one or more motor monitor modules <NUM> for monitoring operation of the motor <NUM>. Examples of motor control and monitoring modules may be found in any of the commonly owned and co-pending <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

Referring now to <FIG>, a startup routine <NUM> may be executed by the control circuit <NUM> of <FIG>, or by a similarly capable control circuit coupled to the controller <NUM>. The startup routine <NUM> generates a relatively higher amount of initial torque than that which may be produced during one or more alternative startup routines. As such, the startup routine <NUM> may be activated after a failure of another startup routine and thus may be referred to as a secondary startup routine. The startup routines disclosed herein are configured to displace the impeller <NUM> from a starting position at rest, in which the impeller <NUM> is in contact with the first disk <NUM> and/or the second disk <NUM>, to an operating position in which the impeller <NUM> is suspended within the housing <NUM> to impel the blood.

In one configuration, the startup routine <NUM> begins at step <NUM> with the control circuit <NUM> instructing the motor <NUM> to gradually increase a motor speed during a ramp phase from an inactive state, including a speed of zero when the impeller <NUM> is at rest, to an operating speed. During the speed increase, at step <NUM>, the control circuit <NUM> applies a predetermined maximum voltage, creating high torque to overcome friction or coagulated blood that may hinder the movement of the impeller <NUM>. At step <NUM>, the control circuit <NUM> transitions or switches from the gradual increase in motor speed to a closed-loop speed control to achieve the operating speed in which the blood pump operates in a normal mode. The closed-loop speed control may be performed by the control circuit <NUM> of the controller (<FIG>). For example, the motor speed may be maintained by adjusting a voltage according to a speed difference produced by the torque.

In response to the predetermined maximum voltage still applied, the transition to closed-loop control may cause an overshoot in the motor speed in which the motor speed increases from a first speed to an overshoot speed greater than the operating speed. In other words, rather than a control loop increasing from the inactive state directly to the operating speed, an overshoot of the operating speed may inadvertently occur. This overshoot may be minimized by appropriate tuning of the closed-loop speed-control parameters.

With reference to <FIG>, a speed waveform "SP" is depicted in a solid line illustrating the gradual increase in motor speed from an initial speed <NUM> of zero in the inactive state to the first speed <NUM>. The first speed <NUM> may be between <NUM> to <NUM> RPM, such as <NUM> RPM, or as otherwise preprogrammed in accordance with the pump parameters. The term "gradual" includes the speed change occurring within a first-time period <NUM>, such as <NUM> to <NUM> seconds. During the first-time period <NUM>, the speed waveform is produced as a non-linear frequency ramp. The control circuit <NUM> may include a timer or timing mechanism configured to control the changes in timing of the motor speed.

In one configuration, the predetermined maximum voltage is applied during the ramp phase of the startup routine <NUM>. The predetermined maximum voltage has a corresponding torque output that is relatively high in comparison to the amount of torque existing in other phases of the motor startup. For example, as depicted using a voltage/current waveform "VC" represented in a solid line, the voltage is increased from zero to the predetermined maximum voltage during the first-time period <NUM> beginning with initial activation. The predetermined maximum voltage may be between <NUM> to 14V and the first-time period <NUM> may be under one second. The controller <NUM> may be programmed to maintain the voltage below a predetermined maximum voltage threshold, such as 14V, or as otherwise designated. The increase in the motor speed may result in a speed phase that directly follows the ramp phase, thereby bypassing a commutation phase. In other words, the startup routine <NUM> is executed without incrementally ramping the motor voltage and searching for or measuring back electromotive force, i.e., "BEMF" or "Back-EMF," signals indicating impeller motion or positioning, as is commonly found during the commutation phase. The speed phase may include the overshoot and may occur during a second-time period <NUM> less than the first-time period <NUM>, such as less than one second, for example between <NUM> to <NUM> seconds. In other words, the motor speed increases at a faster rate in the speed phase when compared to the speed increase in the ramp phase. Ordinary operation of the motor <NUM> may commence when the motor <NUM> reaches the operating speed <NUM>, such as between <NUM> to <NUM> RPM. Overall, the ramp and speed phases, including the motor speed transition from the initial speed of zero to the operating speed <NUM>, occur over a startup time duration that is less than <NUM> seconds, such as between <NUM>-<NUM> seconds.

With reference to <FIG>, the control circuit <NUM> or a similarly capable control circuit coupled to the controller <NUM>, performs a startup routine <NUM> including detecting an electrical fault in the first stator <NUM> or the second stator <NUM>. The startup routine <NUM> may be referred to as a <NUM>-wire start. For example, in one configuration, the startup routine <NUM> begins at step <NUM> with detecting the electrical fault, for example, in the second stator <NUM>, such as using the control circuit <NUM>. At step <NUM>, startup of the first stator <NUM> and the second stator <NUM> are commenced, such as by applying a voltage thereto from the power supply, in response to the electrical fault condition. In other words, despite the presence of the electrical fault condition, both stators are started. At step <NUM>, closed-loop control of the motor may be commenced including the non-faulty stator being used for monitoring BEMF. In another configuration, the electrical fault may be detected after startup is completed, such as when the stators are running at the operating speed in the normal operative mode. Detection of the electrical fault in the second stator <NUM> is provided for illustrative purposes only as the electrical fault condition may exist in either stator.

With reference to <FIG>, further details associated with the startup routine <NUM> are depicted including the power supply <NUM> and the controller <NUM> being in communication with the first stator <NUM> having the three motor windings <NUM> and the second stator <NUM> having the three motor windings <NUM> on opposing sides of the impeller <NUM>. The controller <NUM> commences startup of the first stator <NUM> by driving the three motor windings <NUM> using voltage and current from the power supply <NUM> such that the first stator <NUM> operates in the three phases, e.g., U, V, W. Commencing startup of the first stator <NUM> generates a predetermined amount of axial force and radial torque for rotating and suspending the impeller <NUM>.

Before the first stator <NUM> and the second stator <NUM> are started, as mentioned above, the controller <NUM> may detect the electrical fault condition, such as a continuity loss <NUM> in one or more of the motor windings <NUM> of the second stator <NUM>. Despite the electrical fault condition, the controller <NUM> may commence the startup of the second stator <NUM> such that the second stator <NUM> operates in a set of two phases, thereby providing a five-wire start between the combined stators <NUM>, <NUM>. Commencing startup of the second stator <NUM>, even in the presence of the electrical fault condition, generates a greater amount of axial force and radial torque than that which is generated using only a single stator to increase the likelihood of a successful startup. The successful startup includes the impeller <NUM> being rotated and suspended within the housing <NUM> to impel the blood in a normal operative mode. In situations in which the electrical fault is detected in either stator after startup is completed, the first stator <NUM> and the second stator <NUM> may be configured to continue operating in the normal operative mode at the operating speed despite the presence of the electrical fault condition.

The two operating phases of the second stator <NUM>, or faulty stator, may vary in accordance with the location of the continuity loss <NUM> with respect to the coils in an effort to rotate and suspend the impeller <NUM>. In other words, the phase angle of the first stator <NUM> and/or the second stator <NUM> with respect to the housing <NUM> may be altered depending upon the location of the faulty stator within the housing <NUM>, e.g., proximate the first disk <NUM> or the second disk <NUM>, and the location of the electrical fault condition. For example, the control circuit <NUM> may alter the wire phase of the first stator <NUM> and/or the second stator <NUM> to alter the phase angle and vary the torque in an effort to rotate the impeller <NUM>.

Referring now to <FIG>, the control circuit <NUM> or a similarly capable control circuit coupled to the controller <NUM>, performs a startup routine <NUM> in which a first voltage is applied to the stators <NUM>, <NUM>, that is less than a predetermined maximum voltage. In one configuration, the predetermined maximum voltage is the predetermined maximum voltage that is below the predetermined maximum voltage threshold discussed above with respect to the startup routine <NUM>. As such, the startup routine <NUM> attempts the motor startup using an amount of torque less than the amount of torque initially generated during the startup routine <NUM> in an attempt to decrease the risk of harm to the patient that may occur with the higher amount of torque. Accordingly, the startup routine <NUM> may be referred to as a primary startup routine with the startup routine <NUM> being the secondary startup routine.

In one configuration, the startup routine <NUM> begins at step <NUM> with a first motor startup attempt including applying a first voltage to both stators <NUM>, <NUM>, such as from the power supply <NUM>. If unsuccessful, the control circuit <NUM> executes a second startup attempt in the manner described with respect to the first startup attempt. In one configuration, two startup attempts are performed with an interval of <NUM> to <NUM> seconds therebetween; however, other configurations may include a single startup attempt and/or more than two startup attempts with a shorter or longer interval therebetween.

At step <NUM>, after each motor startup attempt, the control circuit <NUM> detects whether the motor <NUM> was successfully started. In response to a failure of the motor startup attempts, at step <NUM>, the control circuit <NUM> performs an additional startup attempt using the startup routine <NUM>. In other words, the additional startup attempt includes applying the predetermined maximum voltage, which is greater than the first voltage, to the stators <NUM>, <NUM>, and implementing the speed ramp of the startup routine <NUM>.

For example, with reference to <FIG>, the first and second motor startup attempts include applying the first voltage, depicted using the voltage current waveform "VC2," to the first stator <NUM> and/or the second stator <NUM> during a first-time period. In one configuration, the first voltage is between <NUM> to 12V and the first-time period includes the first stator <NUM> and the second stator <NUM> being in the inactive state. The first voltage and the predetermined maximum voltage may be stored in the memory of the controller <NUM>.

If the startup attempt is successful, during the ramp phase, the first voltage may increase from zero to a range below the predetermined maximum voltage threshold in less than one second. In addition, the motor speed, depicted using a speed waveform "SP2" shown in a solid line, will undergo stepwise changes during the ramp phase, a commutation phase, and a speed phase that may exceed a startup duration of more than <NUM> seconds. Whether or not the startup is successful may be determined through one or more methods, such as the control circuit <NUM> attempting to search for and/or measure the BEMF signals indicating the motion or positioning of the impeller <NUM>.

If the startup attempts, such as the two startup attempts, are not successful in starting the motor <NUM> and displacing the impeller <NUM> from the disks <NUM>, <NUM>, the additional startup attempt is performed. In one configuration, the additional startup attempt is the startup routine <NUM> which includes applying the predetermined maximum voltage, such as 14V, to the first stator <NUM> and/or the second stator <NUM> from the inactive state and transitioning the motor speed from the ramp phase directly to the speed phase to the exclusion of the commutation phase. In other configurations, an alternative amount of voltage may be used during another type of startup routine.

Claim 1:
A control circuit (<NUM>) for an implantable blood pump (<NUM>), the control circuit (<NUM>) being coupled to the implantable blood pump (<NUM>) and having processing circuity including one or more processors (<NUM>),
the control circuit being characterized by
the one or more processors (<NUM>) being configured to:
gradually increase a motor speed from an inactive state to a first speed (<NUM>) during a first- time period (<NUM>);
apply a predetermined maximum voltage during the gradual increase in the motor speed; and
transition from the gradual increase in motor speed to a closed loop speed control to achieve an operating speed (<NUM>), the operating speed (<NUM>) being greater than the first speed (<NUM>).