Patent Description:
Ventricular assist devices, known as VADs, are implantable blood pumps used for both short-term (i.e., days, months) and long-term (i.e., years or a lifetime) applications where a patient's heart is incapable of providing adequate circulation, commonly referred to as heart failure or congestive heart failure. A patient suffering from heart failure may use a VAD while awaiting 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 inside or outside the patient's body.

<CIT> discloses an example of a prior art ventricular assist device.

A controller can be used to control operation of the implanted VAD. The controller can be operatively connected to the VAD via a wired, wireless, and/or mechanical connection, which can be used to supply the VAD with operating power (e.g., electrical and/or mechanical power) and control signals to control the operation of the VAD.

At least some VADs utilize pressure feedback from one or more pressure sensors to control operation of the VAD. Some VADs, for example, use a pressure sensor located in the left ventricle of a patient's heart to measure pressure and monitor a patient's cardiac cycle for control of the VAD. Other VADs include a pressure sensor connected to or located within a fluid conduit that connects the VAD to a patient's heart, such as an inflow or outflow conduit.

The location of pressure sensors used in previous VADs has several drawbacks that have prevented wide-spread adoption. For example, implanting a pressure sensor in the ventricle of a patient's heart requires separate steps or procedures from the VAD implant procedure, and also requires separate power lines and/or communication pathways to be run between the pressure sensor and the VAD, increasing the burden of surgical placement. Additionally, pressure sensors located within the ventricle of a patient's heart or within a fluid conduit can be susceptible to tissue overgrowth that can cause sensor drift and/or accuracy deficiencies. Further, pressure sensors located within the ventricle of a patient's heart or within a fluid conduit can lack sufficient mechanical stability, making the pressure sensors susceptible to positional drift, mechanical strain, and resulting measurement inaccuracies.

Accordingly, a need exists for improved VADs that use pressure sensors to monitor a patient's cardiac cycle and/or control operation of the VAD.

The present disclosure is directed to an implantable blood pump assembly that includes a housing defining an inlet, an outlet, a flow path extending from the inlet to the outlet, and an internal compartment separated from the flow path. The blood pump assembly further includes a rotor positioned within the flow path and operable to pump blood from the inlet to the outlet, a stator positioned within the internal compartment and operable to drive the rotor, and an inlet conduit connected to the housing inlet and having a downstream end that has a reduced cross-sectional area that produces a localized region of high velocity blood flow. The blood pump assembly further includes at least one pressure sensor positioned between the inlet and the outlet and configured to detect a pressure of blood flowing through the flow path. The pressure sensor is located adjacent the downstream end of the inlet conduit.

The present disclosure is further directed to a method of assembling a blood pump assembly. The method includes providing a blood pump housing that defines an inlet, an outlet, a flow path extending from the inlet to the outlet, and an internal compartment, positioning a rotor within the flow path such that the rotor is operable to pump blood from the inlet to the outlet, positioning a stator within the internal compartment such that the stator is operable to drive the rotor, and connecting a downstream end of an inlet conduit to the housing inlet. The downstream end of the inlet conduit has a reduced cross-sectional area that produces a localized region of high velocity blood flow. The method further includes positioning at least one pressure sensor between the inlet and the outlet, and adjacent to the downstream end of the inlet conduit such that the at least one pressure sensor is configured to detect a pressure of blood flowing through the flow path.

The present disclosure is directed to implantable blood pump assemblies that include one or more pressure sensors for detecting a blood pressure within a ventricle of a patient's heart. Embodiments of the implantable blood pump assemblies disclosed herein include one or more pressure sensors located within a housing of the blood pump assembly adjacent to a localized region of high velocity blood flow. The position of the pressure sensors in the implantable blood pump assemblies disclosed herein facilitates improved blood pressure measurements. By locating pressure sensors adjacent to or within a localized region of high velocity blood flow, tissue overgrowth on the pressure sensors is minimized or reduced. Additionally, pressure sensors that are located within the housing of a blood pump assembly can be physically protected by the pump housing and can be securely connected to the pump housing, which reduces or limits positional drift and mechanical stress variations on the pressure sensors.

Further, pressure sensors that are located within the housing of a blood pump assembly can be directly connected to an on-board controller of the blood pump assembly for receiving electrical power directly from the controller and for sending pressure measurement signals directly to the controller. Such a direct connection between the pressure sensor and the controller simplifies the implant procedure by eliminating the need to run separate power or communication lines to the pressure sensor, and also improves performance of the blood pump by reducing signal noise in pressure measurements.

Referring now to the drawings, <FIG> is an illustration of a mechanical circulatory support system <NUM> implanted in a patient's body <NUM>. The mechanical circulatory support system <NUM> includes an implantable blood pump assembly <NUM> that includes a blood pump <NUM>, a ventricular cuff <NUM>, and an outflow cannula <NUM>. The mechanical circulatory support system <NUM> also includes an external system controller <NUM> and one or more power sources <NUM>.

The blood pump assembly <NUM> can be implemented as or can include a ventricular assist device (VAD) that is attached to an apex of the left ventricle, as illustrated, or the right ventricle, or both ventricles of the heart <NUM>. The blood pump assembly <NUM> can be attached to the heart <NUM> via the ventricular cuff <NUM> which is sewn to the heart <NUM> and coupled to the blood pump assembly <NUM>. The other end of the blood pump assembly <NUM> connects to the ascending or descending aorta via the outflow cannula <NUM> so that the blood pump assembly <NUM> effectively diverts blood from the weakened ventricle and propels it to the aorta for circulation to the rest of the patient's vascular system. The VAD can include 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 <NUM> liters per minute).

<FIG> illustrates the mechanical circulatory support system <NUM> during battery powered operation. A communication line <NUM> connects the implanted blood pump assembly <NUM> to the external system controller <NUM>, which monitors system <NUM> operation. In the illustrated embodiment, the communication line <NUM> is shown as a driveline that exits through the patient's abdomen <NUM>, although it should be understood that the blood pump assembly <NUM> may be connected to the external system controller <NUM> via any suitable communication line, including wired and/or wireless communication. The system can be powered by either one, two, or more batteries <NUM>. It will be appreciated that although the system controller <NUM> and power source <NUM> are illustrated outside/external to the patient body, the communication line <NUM>, system controller <NUM> and/or power source <NUM> can be partially or fully implantable within the patient, as separate components or integrated with the blood pump assembly <NUM>.

<FIG> is an illustration of an implantable blood pump assembly <NUM> suitable for use in the mechanical circulatory support system <NUM> of <FIG>, where the blood pump assembly <NUM> is shown in an operational position implanted in a patient's body. <FIG> is a schematic cross-sectional view of the blood pump assembly <NUM> of <FIG>. In the illustrated embodiment, the blood pump assembly <NUM> is a left ventricular assist blood pump assembly connected to the left ventricle LV of the heart H.

The blood pump assembly <NUM> includes a blood pump <NUM> including a circular shaped housing <NUM> having a first outer face or wall <NUM> and a second outer face or wall <NUM>. The blood pump assembly <NUM> further includes an inlet cannula <NUM> (generally, an inlet conduit) that, in the illustrated embodiment, extends from the first outer wall <NUM> of the pump housing <NUM>. When the blood pump assembly <NUM> is implanted into a patient's body, as shown in <FIG>, the first outer wall <NUM> of the housing <NUM> is positioned against the patient's heart H, and the second outer wall <NUM> of the housing <NUM> faces away from the heart H. The inlet cannula <NUM> extends into the left ventricle LV of the heart H to connect the blood pump assembly <NUM> to the heart H. The second outer wall <NUM> of the housing <NUM> has a chamfered edge <NUM> to avoid irritating other tissue that may come into contact with the blood pump assembly <NUM>, such as the patient's diaphragm.

The blood pump assembly <NUM> further includes a stator <NUM>, a rotor <NUM>, an on-board controller <NUM>, and a pressure sensor assembly <NUM> (<FIG>), all of which are enclosed within the pump housing <NUM>. In the illustrated embodiment, the stator <NUM> and the on-board controller <NUM> are positioned on the inflow side of the pump housing <NUM> toward the first outer wall <NUM>, and the rotor <NUM> is positioned along the second outer wall <NUM>. In other embodiments, the stator <NUM>, the rotor <NUM>, and the on-board controller <NUM> may be positioned at any suitable location within the pump housing <NUM> that enables the blood pump assembly <NUM> to function as described herein. Power is supplied to operational components of the blood pump assembly <NUM> (e.g., the stator <NUM> and the on-board controller <NUM>) from a remote power supply via a power supply cable <NUM>.

With additional reference to <FIG>, the pump housing <NUM> defines an inlet <NUM> for receiving blood from a ventricle of a heart (e.g., left ventricle LV), an outlet <NUM> for retuming blood to a circulatory system, and a flow path <NUM> extending from the inlet <NUM> to the outlet <NUM>. The pump housing <NUM> further defines an internal compartment <NUM> separated from the flow path <NUM>, for example, by one or more dividing walls <NUM>.

The pump housing <NUM> also includes an intermediate wall <NUM> located between the first outer wall <NUM> and the second outer wall <NUM>, and a peripheral wall <NUM> that extends between the first outer wall <NUM> and the intermediate wall <NUM>. Together, the first outer wall <NUM>, the dividing wall <NUM>, the intermediate wall <NUM>, and the peripheral wall <NUM> define the internal compartment <NUM> in which the stator <NUM> and the on-board controller <NUM> are enclosed.

In the illustrated embodiment, the pump housing <NUM> also includes a cap <NUM> removably attached to the pump housing <NUM> along the intermediate wall <NUM>. The cap <NUM> is threadably connected to the pump housing <NUM> in the illustrated embodiment, although in other embodiments the cap <NUM> may be connected to the pump housing <NUM> using any suitable connection means that enables the blood pump assembly <NUM> to function as described herein. In some embodiments, for example, the cap <NUM> is non-removably connected to the pump housing <NUM>, for example, by welding. The removable cap <NUM> includes the second outer wall <NUM>, the chamfered edge <NUM>, and defines the outlet <NUM>. The cap <NUM> also defines a volute <NUM> that is in fluid communication with the outlet <NUM>, and a rotor chamber <NUM> in which the rotor <NUM> is positioned. The cap <NUM> can be attached to the pump housing <NUM> using any suitable connection structure. For example, the cap <NUM> can be engaged via threads with the peripheral wall <NUM> to seal the cap <NUM> in engagement with the peripheral wall <NUM>.

The rotor <NUM> is positioned within the blood flow path <NUM>, specifically, within the rotor chamber <NUM>, and is operable to rotate in response to an electromagnetic field generated by the stator <NUM> to pump blood from the inlet <NUM> to the outlet <NUM>. The rotor defines a central aperture <NUM> through which blood flows during operation of the blood pump <NUM>. The rotor <NUM> includes impeller blades <NUM> located within the volute <NUM> of the blood flow path <NUM>, and a shroud <NUM> that covers the ends of the impeller blades <NUM> facing the second outer wall <NUM> to assist in directing blood flow into the volute <NUM>.

In the illustrated embodiment, the rotor <NUM> includes a permanent magnet <NUM> that defines the central aperture <NUM>. The permanent magnet <NUM> has a permanent magnetic north pole N and a permanent magnetic south pole S for combined active and passive magnetic levitation of the rotor <NUM> and for rotation of the rotor <NUM>. In operation, the stator <NUM> is controlled to drive (i.e., rotate) the rotor and to radially levitate the rotor <NUM> by generating electromagnetic fields that interact with the permanent magnetic poles S and N of the permanent magnet <NUM>.

Any suitable stator <NUM> can be employed to rotate the rotor <NUM>. The stator <NUM> generally includes a plurality of winding structures that generate suitable electromagnetic fields that interact with the rotor <NUM> to cause rotor <NUM> to rotate and levitate. In the illustrated embodiment, the stator <NUM> includes a plurality of pole pieces <NUM> arranged circumferentially at intervals around the dividing wall <NUM>. The example blood pump assembly <NUM> includes six pole pieces <NUM>, two of which are visible in <FIG>. In other embodiments, the blood pump assembly <NUM> can include more than or less than six pole pieces, such as four pole pieces, eight pole pieces, or any other suitable number of pole pieces that enables the blood pump assembly <NUM> to function as described herein. In the illustrated embodiment, each of the pole pieces <NUM> includes a drive coil <NUM> for generating an electromagnetic field to rotate the rotor <NUM>, and a levitation coil <NUM> for generating an electromagnetic field to control the radial position of the rotor <NUM>.

Each of the drive coils <NUM> and the levitation coils <NUM> includes multiple windings of a conductor wound around the pole pieces <NUM>. The drive coils <NUM> and the levitation coils <NUM> of the stator <NUM> are arranged in opposing pairs and are controlled to drive the rotor and to radially levitate the rotor <NUM> by generating electromagnetic fields that interact with the permanent magnetic poles S and N of the permanent magnet <NUM>. Suitable methods for generating electromagnetic fields to rotate and radially levitate the rotor <NUM> are described, for example, in <CIT>, the entire contents of which are incorporated herein by reference for all purposes. Although the drive coil <NUM> and levitation coil <NUM> are shown as separate coils in the illustrated embodiment, it should be understood that the drive coil <NUM> and levitation coil <NUM> may be implemented as a single coil configured to generate electromagnetic fields for both rotating and radially levitating the rotor <NUM>.

The inlet cannula <NUM> is attached to the pump housing <NUM> at the inlet <NUM>. As shown in <FIG>, the pump housing <NUM> includes an inlet cannula receiving portion <NUM> that includes suitable connecting structure for connecting the inlet cannula <NUM> to the pump housing <NUM>. In the illustrated embodiment, the pump housing <NUM> includes an internally threaded sleeve <NUM> that threadably engages external threads <NUM> on a downstream end <NUM> of the inlet cannula <NUM> to connect the inlet cannula <NUM> to the pump housing <NUM>.

The inlet cannula <NUM> defines an inlet flow path <NUM> that supplies blood to the inlet <NUM> of the pump housing <NUM>. As shown in <FIG>, in the illustrated embodiment, the inlet cannula <NUM> extends into the blood flow path <NUM> defined by the pump housing <NUM> such that the inlet flow path <NUM> partially overlaps with the blood flow path <NUM>.

The downstream end <NUM> of the inlet cannula <NUM> has a reduced cross-sectional area (e.g., relative to an upstream end of the inlet cannula <NUM>) that produces a localized region of high velocity blood flow through the inlet flow path <NUM> and the blood flow path <NUM>. Specifically, the cross-sectional area of the inlet flow path <NUM> gradually and continuously decreases towards the downstream end <NUM> of the inlet cannula <NUM> such that blood flowing through the inlet cannula <NUM> at a constant flow rate will experience an increase in velocity as it flows through the downstream end <NUM> of the inlet cannula <NUM>. Consequently, during operation of the blood pump assembly <NUM>, the reduced-cross-sectional area of the downstream end <NUM> produces a localized region of high velocity blood flow that flows through the inlet <NUM> and through the blood flow path <NUM>.

The pressure sensor assembly <NUM> includes one or more pressure sensors <NUM> configured to detect a pressure of blood flowing through the blood flow path <NUM>. In the illustrated embodiment, the pressure sensor assembly <NUM> includes two pressure sensors <NUM>, although the pressure sensor assembly <NUM> can include more than or less than two pressure sensors <NUM> in other embodiments. The pressure sensors <NUM> are located adjacent the downstream end <NUM> of the inlet cannula <NUM>, at the interface between the inlet cannula <NUM> and the pump housing <NUM>. More specifically, the pressure sensors <NUM> are located between an outlet <NUM> of the inlet cannula <NUM> and an inlet <NUM> to the rotor chamber <NUM>.

As shown in <FIG> and <FIG>, in the illustrated embodiment, each pressure sensor <NUM> includes a sensing element <NUM> and a deflectable membrane <NUM> positioned between the sensing element <NUM> and the blood flow path <NUM>. Pressure sensing elements suitable for use in the pressure sensors <NUM> include, for example and without limitation, capacitive pressure sensing elements and piezo-resistive pressure sensing elements. Suitable materials from which the deflectable membrane <NUM> can be constructed include, for example and without limitation, glass.

In the illustrated embodiment, the pressure sensor assembly <NUM> includes a housing <NUM> that includes an enclosure <NUM> and a sleeve <NUM> extending upstream from the enclosure <NUM>. The pressure sensors <NUM> are connected to the sensor assembly housing <NUM> and are positioned within the sensor assembly housing <NUM> (specifically, within the enclosure <NUM>) diametrically opposite one another. The sleeve <NUM> receives the downstream end <NUM> of the inlet cannula <NUM> such that the downstream end <NUM> of the inlet cannula <NUM> is positioned within the sleeve <NUM> when the blood pump assembly <NUM> is assembled. Further, in this embodiment, the sleeve <NUM> defines the dividing wall <NUM> (<FIG>) of the pump housing <NUM>.

The sensor assembly housing <NUM> (specifically, the enclosure <NUM> and the sleeve <NUM>) defines a flow path <NUM> that is concentric with the downstream end <NUM> of the inlet cannula <NUM> and the blood flow path <NUM> when the blood pump assembly <NUM> is assembled. The enclosure <NUM> of the sensor assembly housing <NUM> has two windows <NUM> (<FIG>) defined therein along a radial inner surface <NUM> of the enclosure <NUM>. Each of the windows <NUM> is defined in the enclosure <NUM> at a location that corresponds to the location of one of the pressure sensors <NUM> such that each of the pressure sensors <NUM> can detect the pressure of fluid flow through the flow path <NUM> and the blood flow path <NUM> via the windows <NUM>.

The sensor assembly housing <NUM> further includes a flexible annular membrane <NUM> positioned within the flow path <NUM> along the radial inner surface <NUM>. The flexible membrane <NUM> covers or occludes windows <NUM>, and provides a smooth, inner surface along the flow path <NUM> to prevent or inhibit turbulent blood flow. The pressure of fluid flowing through the flow path <NUM> is transmitted to pressure sensors <NUM> through the flexible membrane <NUM>. Suitable materials from which the flexible membrane <NUM> can be constructed include, for example and without limitation, soft polymeric materials, such as silicone.

The pressure sensors <NUM> are connected to the on-board controller <NUM> by suitable electrical conduits for receiving electrical power therefrom and sending pressure measurement signals thereto. In the illustrated embodiment, each of the pressure sensors <NUM> is directly connected to the on-board controller <NUM> by a plurality of pin connectors <NUM> that extend from one of the pressure sensors <NUM>, out of the enclosure <NUM>, and to the on-board controller <NUM>. In other words, each of the pressure sensors <NUM> is connected to the on-board controller <NUM> via a suitable electrical conduit without intervening controllers, signal processing components, or similar equipment. The pressure sensors <NUM> are connected to the on-board controller <NUM> by four pin connectors <NUM> in the illustrated embodiment. In other embodiments, the pressure sensors <NUM> can be connected to the on-board controller <NUM> by more than or less than four pin-connectors.

In some embodiments, a portion <NUM> of the internal compartment <NUM> (shown in <FIG>) is hermetically sealed from the intemal cavity defined by the enclosure <NUM> to inhibit fluid (e.g., blood) ingress into the portion of the internal compartment <NUM> in which electronics (e.g., stator <NUM> and on-board controller <NUM>) are housed. In the illustrated embodiment, for example, the sensor assembly housing <NUM> forms a seal against the pump housing <NUM> to hermetically seal the portion <NUM> of the internal compartment <NUM> (shown in <FIG>) in which electronics are housed from the internal cavity defined by the enclosure <NUM>.

The location of pressure sensors <NUM> facilitates accurate measurement of pressure within the left ventricle of the heart. For example, by locating the pressure sensors <NUM> adjacent the downstream end <NUM> of the inlet cannula <NUM>, which is connected to the left ventricle, the pressure detected by the pressure sensors <NUM> within the blood flow path <NUM> provides an accurate pressure measurement for determining the pressure within the left ventricle of the heart. The pressure measurements detected by the pressure sensors <NUM> can be used to determine the pressure waveform of the left ventricle (i.e., pressure in the left ventricle over time), which, in turn, can be used to identify a number of clinically relevant cardiac events or characteristics. For example, the pressure waveform of the left ventricle can be used to determine the left ventricular filling pressure, or preload (Frank-Starling), which is a primary physiologic mechanism to regulate cardiac output. Increasing left ventricular preload causes an increase in stroke volume and stretch-dependent contractility. As described further herein, the left ventricular pressure waveform can also be used to identify heart rate, left ventricular contractility (i.e., maximum systolic dP/dt), end-systolic left ventricular pressure, end-diastolic left ventricular pressure, atrial kick pressure, maximum left ventricular filling pressure, average left ventricular filling pressure, left ventricular relaxation (i.e., minimum systolic dP/dt), and valve openings and closures. The same cardiac events or characteristics can be determined for the right ventricle in right ventricle assist devices or bi-ventricle assist devices. In some embodiments, a correction factor is applied to the pressure measured by the pressure sensors <NUM> (e.g., using on-board controller <NUM>) to assess true ventricle pressure. The correction factor may account for "nozzle" effects due to fluid accelerating as the cross-section changes in the inlet cannula <NUM>. The correction factor can be based, for example, on flow (estimated using the rotor drive current) and Bernoulli's equation, and additional terms (e.g., experimentally determined coefficients) based on known fluid dynamic principles and equations.

The location of the pressure sensors <NUM> facilitates measuring left ventricular pressure with improved accuracy. For example, previous ventricular assist devices included pressure sensors at locations that were susceptible to tissue overgrowth that resulted in sensor drift and/or accuracy deficiencies. By locating pressure sensors <NUM> adjacent the downstream end <NUM> of the inlet cannula <NUM>, the pressure sensors <NUM> are located adjacent the localized region of high velocity blood flow produced by the reduced cross-sectional area of the inlet cannula <NUM>, thereby minimizing or limiting tissue overgrowth on the pressure sensors <NUM>. Additionally, in the illustrated embodiment, the pressure sensors <NUM> are located within the internal compartment <NUM> of the pump housing <NUM>, and are secured to the pump housing <NUM>. The pressure sensors <NUM> are therefore physically protected by the pump housing <NUM> and have a secure structural connection, which reduces or limits positional drift and mechanical stress variations on the pressure sensors <NUM>.

Further, in the illustrated embodiment, the location of the pressure sensors <NUM> permits the pressure sensors <NUM> to be directly connected to the on-board controller <NUM> for receiving electrical power directly from the on-board controller <NUM>, and for sending pressure measurement signals directly to the on-board controller <NUM>. The direct connection between the pressure sensor <NUM> and on-board controller <NUM> simplifies the implant procedure by eliminating the need to run separate power or communication lines to the pressure sensor <NUM>, and also improves performance of the blood pump <NUM> by reducing signal noise in pressure measurements, thereby providing more accurate pressure measurements.

The on-board controller <NUM> is operatively connected to the stator <NUM>, and is configured to control operation of the pump <NUM> by controlling the supply of electrical current to the stator <NUM> and thereby control rotation of the rotor <NUM>. Additionally, the on-board controller <NUM> is connected to the pressure sensors <NUM>, and is configured to receive pressure measurements from the pressure sensors <NUM>, determine or calculate cardiac events or characteristics based on the pressure measurements detected by the pressure sensors <NUM>, and control operation of the pump <NUM> (e.g., rotation of the rotor <NUM>) based on the pressure measurements detected by the pressure sensors <NUM> and/or the determined cardiac events or characteristics. In particular, the on-board controller <NUM> is configured to perform closed-loop speed control of the pump rotor <NUM> based on the pressure measurements received from the pressure sensors <NUM> and/or the determined cardiac events or characteristics. The on-board controller <NUM> can be configured to control the rotor <NUM> in continuous flow operation and/or pulsatile flow operation.

In some embodiments, for example, the on-board controller <NUM> is configured to control operation of the pump <NUM> to achieve a desired or preset pressure set point of blood in the left ventricle. The on-board controller <NUM> can periodically or continuously query the pressure sensors <NUM> to measure the pressure of blood flowing through the pump <NUM>, and compare the detected pressure with the pressure set point. If the detected blood pressure is different from the pressure set point, the on-board controller <NUM> can adjust the speed of the rotor <NUM> (e.g., by controlling the supply of electrical current to the stator <NUM>) to achieve the pressure set point. In some embodiments, the on-board controller <NUM> is configured to determine if the difference between the measured pressure and the pressure set point exceeds a threshold difference before adjusting the speed of the rotor <NUM>.

The pressure set point can be established by user input, for example, from a patient or a clinician, and can be stored in a memory device of the on-board controller <NUM>. The pressure set point can be a fixed (i.e., time invariable) pressure set point, or the pressure set point can be a time variable set point. For example, the pressure set point can vary according to different phases of the cardiac cycle. That is, the pressure set point can be defined by a pressure profile that defines a desired or target pressure set point at different times or phases of the cardiac cycle.

In some embodiments, the pressure set point is a minimum left ventricle pressure set point. That is, the on-board controller <NUM> adjusts the speed of the rotor <NUM> to achieve a minimum left ventricle pressure that is equal to the target pressure set point. The minimum left ventricle pressure is typically referred to as "filling pressure," and is one of the primary indicators of the body's demand for total cardiac output. In other embodiments, the pressure set point is based on an amplitude of the left ventricle pressure waveform (i.e., the difference between the maximum left ventricle pressure and the minimum left ventricle pressure). The amplitude of the left ventricle pressure waveform is affected by the contractility of the left ventricle, and is less susceptible to long term drift as compared to other pressure sensor-based measurements.

Further, in some embodiments, the pressure set point may be adjusted in real time based on pressure measurements received from the pressure sensors <NUM> and/or the determined cardiac events or characteristics. For example, in some embodiments, the on-board controller <NUM> is configured to increase or decrease the pressure set point based on the maximum slope of the measured ventricle pressure waveform (dP/dt). The maximum dP/dt is related to the contractility of the left ventricle, and can be used to adjust the pressure set point, and the resulting rotor speed, to achieve a desired left ventricle unloading. For example, the on-board controller <NUM> may be configured to increase the pressure set point and/or the rotor speed based on the determined maximum dP/dt to increase left ventricle unloading. Further, in some embodiments, the on-board controller <NUM> is configured to increase or decrease the pressure set point based on a determined heart rate of a patient. For example, an increased heart rate is indicative of increased need for cardiac output (e.g., from exercise), and the on-board controller <NUM> can be configured to increase the pressure set point by a corresponding amount. Additionally or alternatively, the on-board controller <NUM> may be configured to increase or decrease the pressure set point based on feedback received from an accelerometer included in the blood pump assembly <NUM>. For example, the on-board controller <NUM> may determine that a user of the blood pump assembly <NUM> is exercising or engaged in rigorous activity based on feedback from an accelerometer, and increase the pressure set point or speed of the rotor accordingly.

Additionally, in some embodiments, the on-board controller <NUM> is configured to determine a target rotor speed based on a multi-variable algorithm or function that takes into account one or more of the measured pressure of the ventricle and the determined cardiac characteristics or events. In some embodiments, for example, the on-board controller <NUM> is configured to determine a target rotor speed based on a statistically weighted function with one or more of the following variables: heart rate, minimum ventricle pressure, ventricle pressure amplitude, and maximum dP/dt.

Additionally, in some embodiments, the on-board controller <NUM> is configured to control the speed of the rotor <NUM> according to a speed profile that defines a time-variable speed set point of the rotor <NUM>. In such embodiments, the on-board controller <NUM> can be configured to modulate the speed of the rotor <NUM> to different speed set points within a single cardiac cycle of a patient's heart. This type of rotor speed control, also known as "synchronized pulsing", may be implemented by the on-board controller <NUM> in any suitable manner that enables the blood pump assembly <NUM> to function as described herein. In some embodiments, for example, the on-board controller <NUM> can be configured to increase the speed of the rotor <NUM> during systole (known as "co-pulsation"), or decrease the speed of the rotor <NUM> during systole (known as "counter-pulsation"). In yet other embodiments, the on-board controller <NUM> can be configured to increase the speed of the rotor <NUM> over a first period of time during systole, and decrease the speed of the rotor <NUM> over a second period of time during systole. Additionally, synchronized pulsing of the rotor may be implemented by the on-board controller <NUM> at varying intervals. For example, the on-board controller <NUM> can be configured to modulate the speed of the rotor <NUM> to different speed set points within a single cardiac cycle of a patient's heart, or across more than one cardiac cycle of a patient's heart (for example, across two cardiac cycles).

In other embodiments, the on-board controller <NUM> is configured to control the speed of the rotor <NUM> according to a fixed (i.e., time invariable) speed set point. In such embodiments, the on-board controller <NUM> can be configured to control the speed of the rotor <NUM> to achieve an average speed equal to the speed set point. Rotor speed profiles and/or set points can be established by user input, for example, from a patient or a clinician, and can be stored in a memory device of the on-board controller <NUM>.

The on-board controller <NUM> can also be configured to calculate or determine physiological characteristics of a patient based on pressure data collected by the pressure sensors <NUM>. <FIG> is an example plot of data that may be collected and output by the pressure sensors <NUM> during operation of the blood pump assembly <NUM>. The example plot illustrates the left ventricle pressure waveform (i.e., pressure vs. time) over a period of about <NUM> seconds. Based on the data collected by the pressure sensors <NUM>, the on-board controller <NUM> can calculate or determine various cardiac events or characteristics using known techniques and methods. In some embodiments, for example, the on-board controller <NUM> is configured to determine one or more of the following based on pressure data collected by the pressure sensors <NUM>: heart rate, ventricular filling pressure or minimum pressure, maximum systolic pressure, pressure amplitude (i.e., the difference between maximum pressure and minimum pressure), average pressure, end systolic pressure, end diastolic pressure, atrial kick pressure, contractility (i.e., maximum systolic dP/dt), and relaxation (i.e., minimum systolic dP/dt). For example, the on-board controller <NUM> may be programmed to determine the heart rate of a patient by applying a fast Fourier transform to the pressure data collected by the pressure sensors <NUM>, and/or by calculating a time interval between cardiac cycle detection points evident from the pressure waveform (e.g., beginning of systole, end of systole, beginning of diastole, and/or end of diastole).

The on-board controller <NUM> may also be programmed to determine ventricular filling pressure or minimum pressure, maximum pressure or maximum systolic pressure, pressure amplitude (i.e., the difference between maximum pressure and minimum pressure), average pressure, contractility (i.e., maximum systolic dP/dt), relaxation (i.e., minimum systolic dP/dt), end systolic pressure, end diastolic pressure, and atrial kick pressure by applying mathematical operations to the pressure data collected by the pressure sensors <NUM>. For example, the on-board controller <NUM> may be configured to determine the ventricular filling pressure or minimum pressure by identifying a local minimum pressure value on the pressure waveform within a single phase of the cardiac cycle. An example ventricular filling pressure value is identified at point <NUM> in <FIG>. Additionally, the on-board controller <NUM> may be configured to determine maximum systolic pressure by identifying a local maximum pressure value on the pressure waveform within a single phase of the cardiac cycle. An example maximum systolic pressure value is identified at point <NUM> in <FIG>. The on-board controller <NUM> may be further configured to determine the pressure amplitude <NUM> within a single cardiac phase of the pressure waveform by determining the difference between the maximum pressure <NUM> and the minimum pressure <NUM>. The on-board controller <NUM> may be further configured to determine contractility by determining the maximum slope <NUM> of the pressure waveform within the systolic phase of a single cardiac cycle. The on-board controller <NUM> may also be configured to determine relaxation by determining the minimum slope <NUM> of the pressure waveform within the systolic phase of a single cardiac cycle. The on-board controller <NUM> may also be configured to determine end-systolic pressure and end-diastolic pressure by identifying pressure values along the pressure waveform at the end of the systolic and diastolic phases, respectively, of the cardiac cycle. The on-board controller <NUM> may also be configured to identify atrial kick pressure by identifying the pressure value at a localized maximum value on the pressure waveform within the diastolic phase of a single cardiac cycle (i.e., between the end of systole of a first cardiac cycle, and the beginning of systole of a second cardiac cycle). The on-board controller <NUM> may be configured to determine or identify the various phases of the cardiac cycle (e.g., systole and diastole) for the pressure waveform based on, for example, minimum pressure values, maximum pressure values, maximum slope values, and minimum slope values. For example, the on-board controller <NUM> may be configured to determine that a certain portion of the pressure waveform corresponds to the systolic phase of the cardiac cycle by determining or identifying a region on the pressure waveform between the maximum slope and the minimum slope.

As noted above, one or more of the determined cardiac events or characteristics may be used by the on-board controller <NUM> to perform closed-loop speed control of the pump rotor <NUM>. For example, an increase in heart rate, minimum ventricle pressure, or ventricle pressure amplitude generally indicates an increased need for cardiac output. Accordingly, in some embodiments, the on-board controller <NUM> is configured to adjust the speed of the rotor <NUM> by a corresponding amount when pressure data from pressure sensors <NUM> indicate an increase in heart rate, minimum ventricle pressure, and/or ventricle pressure amplitude.

Additionally, in some embodiments, one or more of the determined cardiac events or characteristics can be used to examine and/or evaluate physiologic cardiac function. For example, the left ventricle pressure amplitude (i.e., the difference between maximum pressure and minimum pressure) is a combined indicator of both filling pressure and heart contractility. The minimum dP/dt can be used to evaluate the relaxation speed of the ventricle and to identify possible fibrosis or electrical conduction issues. The maximum dP/dt can be used to evaluate the systolic elastance curve of the ventricle, which is a direct measure of left ventricle functional performance. This may be used, for example, to detect left ventricle recovery, and to adjust the target pressure and/or rotor speed set points stored in on-board controller <NUM> accordingly.

The on-board controller <NUM> can include one or more modules or devices that are enclosed within pump housing <NUM>. The on-board controller <NUM> can generally include any suitable computer and/or other processing unit, including any suitable combination of computers, processing units and/or the like that may be communicatively coupled to one another (e.g., on-board controller <NUM> can form all or part of a controller network). Thus, on-board controller <NUM> can include one or more processor(s) and associated memory device(s) configured to perform a variety of computer-implemented functions (e.g., performing the methods, steps, calculations and/or the like disclosed herein). As used herein, the term "processor" refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate array (FPGA), and other programmable circuits. Additionally, the memory device(s) of on-board controller <NUM> may generally include memory element(s) including, but not limited to, non-transitory computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s) can generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure the on-board controller <NUM> to perform various functions including, but not limited to, controlling the supply of electrical current to the stator <NUM>, determining the pressure and/or pressure waveform within the left ventricle of a patient's heart, determining or calculating cardiac events or characteristics based on the pressure measurements detected by the pressure sensors <NUM>, such as heart rate, contractility, end-systolic pressure, end-diastolic pressure, atrial kick pressure, left ventricular contractility, max left ventricular pressure, and left ventricular relaxation, adjusting the speed of the rotor <NUM> based on the pressure detected by the pressure sensors <NUM> and/or one or more of the determined cardiac events or characteristics, outputting pressure measurement data to an external controller (e.g., external system controller <NUM>), and various other suitable computer-implemented functions.

In the illustrated embodiment, the on-board controller <NUM> is implemented as one or more circuit boards <NUM> and various components carried on the circuit boards (e.g., processors and memory devices) to control operation of the pump <NUM> by controlling the electrical supply to the stator <NUM>.

<FIG> is a schematic view of an embodiment of the on-board controller <NUM>, which includes the circuit boards <NUM>, one or more processors <NUM>, and a memory device <NUM> operatively coupled to the one or more processors <NUM>. The memory device <NUM> can include any suitable forms of memory, for example, a read only memory (ROM) <NUM> and a random access memory (RAM) <NUM>. The ROM <NUM> can be used to store basic instructional sets for the operation of the one or more processors <NUM>. The RAM <NUM>, or any other suitable memory device such as long term, short term, volatile, nonvolatile, or other suitable storage medium, can be used to store patient specific parameters that are used by the on-board controller <NUM> to control patient specific operational aspects of the blood pump assembly <NUM>, as well as related software modules.

A communication line (e.g., communication line <NUM>) couples the blood pump assembly <NUM> and on-board controller <NUM> to the external system controller <NUM>, which monitors system operation via various software applications. As noted above, the blood pump assembly <NUM> itself also includes several software applications that are executable by the on-board controller <NUM> for various functions, such as to control radial levitation and/or drive of the rotor <NUM> of the pump assembly <NUM> during operation. The external system controller <NUM> can in turn be coupled to batteries <NUM> or a power module (not shown) that connects to an AC electrical outlet. The external system controller <NUM> can also include an emergency backup battery (EBB) to power the system (e.g., when the batteries <NUM> are depleted) and a membrane overlay, including Bluetooth capabilities for wireless data communication. An external computer that is configurable by an operator, such as clinician or patient, can further be coupled to the circulatory support system <NUM> for configuring the external system controller <NUM>, the implanted blood pump assembly <NUM>, and/or patient specific parameters, updating software on the external system controller <NUM> and/or the implanted blood pump assembly <NUM>, monitoring system operation, and/or as a conduit for system inputs or outputs.

Pressure data collected by pressure sensors <NUM> can be output to the external system controller <NUM> for additional processing. In some embodiments, for example, the external system controller <NUM> includes an atmospheric pressure sensor <NUM> (<FIG>) for detecting an ambient pressure to facilitate determining a gauge pressure of blood flowing through the blood pump assembly <NUM>. In such embodiments, the external system controller <NUM> can be configured to determine a gauge pressure of blood flow within the left ventricle of a patient's heart based on the pressure measurement data collected by the pressure sensors <NUM> and the ambient pressure data collected by the atmospheric pressure sensor <NUM>. Additionally or alternatively, the on-board controller <NUM> can be configured to receive ambient pressure data from the external system controller <NUM>, and determine a gauge pressure of blood flow within the left ventricle of a patient's heart. Further, the on-board controller <NUM> can be configured to control operation of the pump <NUM> (e.g., rotation of the rotor <NUM>) based on the determined gauge pressure.

<FIG> is a partially exploded view of the blood pump assembly <NUM> shown in <FIG>, and <FIG> is a flow diagram illustrating one embodiment of a method <NUM> for assembling a blood pump assembly, such as the blood pump assembly <NUM> shown in <FIG>. In the illustrated embodiment, the method <NUM> includes providing <NUM> a blood pump housing (e.g., blood pump housing <NUM>) that defines an inlet, an outlet, a flow path extending from the inlet to the outlet, and an internal compartment separated from the flow path. The method <NUM> further includes positioning <NUM> a rotor (e.g., rotor <NUM>) within the flow path such that the rotor is operable to pump blood from the inlet to the outlet, and positioning <NUM> a stator (e.g., stator <NUM>) within the internal compartment such that the stator is operable to drive the rotor. The method <NUM> further includes connecting <NUM> a downstream end of an inlet conduit (e.g., inlet cannula <NUM>) to the housing inlet. The downstream end of the inlet conduit has a reduced cross-sectional area that produces a localized region of high velocity blood flow. The method <NUM> further includes positioning <NUM> at least one pressure sensor (e.g., pressure sensor <NUM>) between the inlet and the outlet, and adjacent to the downstream end of the inlet conduit such that the at least one pressure sensor is configured to detect a pressure of blood flowing through the flow path.

In some embodiments, the step of positioning <NUM> at least one pressure sensor within the internal compartment of the housing includes connecting a sensor assembly (e.g., pressure sensor assembly <NUM>) to the housing, where the sensor assembly includes a housing, and the at least one pressure sensor is positioned within the sensor assembly housing. In such embodiments, the sensor assembly housing can include a sleeve that extends upstream from the sensor assembly housing, and the step of connecting <NUM> a downstream end of an inlet conduit to the housing inlet includes positioning the downstream end of the inlet conduit within the sleeve.

In some embodiments, the method <NUM> further includes positioning a controller (e.g., on-board controller <NUM>) within the internal compartment, and connecting the controller to the at least one pressure sensor. In such embodiments, the controller can be configured to control a rotational speed of the rotor based on the pressure detected by the at least one pressure sensor. Further, in such embodiments, the method can further include directly connecting the at least one pressure sensor to the controller (e.g., via one or more pin connectors <NUM>).

Although certain steps of the example method are numbered, such numbering does not indicate that the steps must be performed in the order listed. Thus, particular steps need not be performed in the exact order they are presented, unless the description thereof specifically require such order. The steps may be performed in the order listed, or in another suitable order.

As described herein, the implantable blood pump assemblies of the present disclosure provide several advantages over previous VAD designs. For example, embodiments of the implantable blood pump assemblies disclosed herein include one or more pressure sensors located on or within a housing of the blood pump assembly and/or adjacent to or within a localized region of high velocity blood flow. By locating pressure sensors adjacent to or within a localized region of high velocity blood flow, tissue overgrowth on the pressure sensors is minimized or reduced. Additionally, pressure sensors that are located one or within the housing of a blood pump assembly can be physically protected by the pump housing and can be securely connected to the pump housing, which reduces or limits positional drift and mechanical stress variations on the pressure sensors. Further, pressure sensors that are located on or within the housing of a blood pump assembly can be directly connected to an on-board controller of the blood pump assembly for receiving electrical power directly from the controller and for sending pressure measurement signals directly to the controller. Such a direct connection between the pressure sensor and the controller simplifies the implant procedure by eliminating the need to run separate power or communication lines to the pressure sensor, and also improves performance of the blood pump by reducing signal noise in pressure measurements.

Claim 1:
An implantable blood pump assembly (<NUM>, <NUM>) comprising:
a housing (<NUM>) defining an inlet (<NUM>), an outlet (<NUM>), a flow path (<NUM>) extending from the inlet (<NUM>) to the outlet (<NUM>), and an internal compartment (<NUM>) separated from the flow path (<NUM>);
a rotor (<NUM>) positioned within the flow path (<NUM>) and operable to pump blood from the inlet (<NUM>) to the outlet (<NUM>);
a stator (<NUM>) positioned within the internal compartment (<NUM>) and operable to drive the rotor (<NUM>);
an inlet conduit (<NUM>) connected to the housing inlet (<NUM>), the inlet conduit (<NUM>) having a downstream end (<NUM>) having a reduced cross-sectional area that produces a localized region of high velocity blood flow; and
characterized by at least one pressure sensor (<NUM>) positioned between the inlet (<NUM>) and the outlet (<NUM>) and configured to detect a pressure of blood flowing through the flow path (<NUM>), wherein the at least one pressure sensor (<NUM>) is located adjacent the downstream end (<NUM>) of the inlet conduit (<NUM>).