Ventricular assist device

Abstract

Apparatus and methods are described that include a ventricular assist device (20). An impeller (50) is disposed within a left ventricle of a subject and defines a lumen (62) therein. A frame (34) is disposed about the impeller, with a proximal bearing portion (116) disposed at a proximal end of the frame and a distal bearing portion (118) disposed at a distal end of the frame. An axial shaft (92) passes through the proximal bearing portion (116), the lumen (62) defined by the impeller, and the distal bearing portion (118). A motion dampening spring (68) is disposed about the axial shaft (92) between the distal end of the impeller (50) and the distal bearing portion (118) and configured to dampen axial motion occurring in the impeller (50). Other applications are also described.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) The present application, U.S. Provisional Patent Application No. 63 / 254,321, entitled "Ventricular Assist Device," by Tuval, filed on October 11, 2021; and Priority is claimed to U.S. Provisional Patent Application No. 63 / 317,199, filed March 7, 2022, by Tuval, entitled "Ventricular Assist Device."

[0002] Each of the above-referenced US provisional applications is incorporated herein by reference.

[0003] Some applications of the present invention relate generally to medical devices, and more particularly to ventricular assist devices and methods of use thereof. [Background technology]

[0004] A ventricular assist device is a mechanical circulatory assist device designed to assist and unload the ventricles to maintain or enhance cardiac output. These devices are used in patients suffering from heart failure and in patients at risk of compromised cardiac function during percutaneous coronary intervention. Most commonly, a left ventricular assist device is applied to a failing heart to assist left ventricular function. In some cases, a right ventricular assist device is used to assist right ventricular function. Such ventricular assist devices are designed to be permanently implanted or attached to a catheter for temporary placement. Summary of the Invention

[0005] According to some applications of the invention, the ventricular assist device includes a motion dampening spring. As described in more detail below, typically, during operation of the ventricular assist device, i.e., when the impeller of the ventricular assist device rotates, the impeller of the ventricular assist device moves back and forth in an axial direction. In some applications, as the impeller moves back and forth in an axial direction, the motion dampening spring is configured to act as a shock absorber to provide motion dampening. As the impeller moves distally from a systolic position to a diastolic position, the motion dampening spring is further compressed. In some applications, the impeller is configured to be radially restrained (i.e., crimped) by stretching axially, and the motion dampening spring is configured to compress to correspond to the axial stretch of the impeller.

[0006] In some applications, the motion buffer spring is coupled to an elastomeric material (such as polyurethane and / or silicone) such that the elastomeric material covers at least a portion of the axial shaft of the ventricular assist device between the distal end of the impeller and the distal radial bearing. In some applications, coupling the elastomeric material to the spring reduces the risk of spring-induced thrombosis and / or hemolysis compared to when the spring is not coupled to the elastomeric material. It is noted that the scope of the present disclosure includes providing a motion buffer spring in the absence of an elastomeric material, which may be desirable in some cases. In some applications, the spring is coated with an elastomeric material, which extends between adjacent windings of the spring. Alternatively, the spring is embedded within the elastomeric material. Typically, the elastomeric material is coupled to the motion buffer spring such that it changes shape (e.g., by stretching and compressing) to match the shape changes occurring in the motion buffer spring (e.g., when the motion buffer spring is stretched and compressed). More typically, the elastomeric material is configured to undergo the above-mentioned shape changes without breaking, crumbling, or creasing upon compression of the spring.

[0007] In some applications, a proximal motion damping spring is disposed proximal to the impeller. In some such applications, the proximal motion damping spring is disposed around the axial shaft between the proximal end of the impeller and the proximal bearing. In some applications, the pump head includes both a proximal motion damping spring (disposed proximal to the impeller) and a distal motion damping spring disposed distal to the impeller, such that axial motion of the impeller in the distal or proximal direction is damped by the motion damping springs.

[0008] In some applications, the ventricular assist device includes a distal thrust bearing configured to prevent axial movement of the axial shaft of the device in response to (and typically prevents axial movement of) the impeller in response to changes in the pressure gradient against which the impeller is pumping. In some applications, the thrust bearing is disposed within a frame of the device. Typically, the thrust bearing is coupled to the frame via a connecting strut that extends radially inward from the frame to the thrust bearing. Typically, to manufacture the frame, the frame is cut from a tube of a shape memory alloy, such as Nitinol. In some applications, the frame does not need to be bonded to one another (e.g., by adhesive, welding, etc.) because the connecting struts are cut from the cut tube such that the frame and connecting struts form a single, integral element. In some applications, the frame and connecting struts are cut from a single piece of material such that they form a single, integral element. In some applications, the connecting struts and the thrust bearing itself are cut from the tube from which the frame was cut, such that the frame, connecting struts, and thrust bearing form a single, integral element, and there is no need to bond them to one another (e.g., by adhesive, welding, etc.). Generally, in some applications, the frame, connecting struts, and thrust bearing itself are cut from a single piece of material, such that they form a single, integral element.

[0009] In some applications, a spring generally similar to the motion damping spring described above is used in combination with a thrust bearing (or a thrust bearing of a different design located distal to the impeller). In some applications, the spring helps stabilize the impeller (e.g., the distal end of the impeller) relative to the thrust bearing after the impeller expands radially. Thus, the spring functions as an impeller stabilization spring. In some applications, the impeller is configured to be radially constrained (i.e., compressed) by axial extension, and the spring is configured to compress to accommodate the axial extension of the impeller. Typically, when the impeller is in a radially constrained configuration during insertion of the pump head into the left ventricle, the impeller extends axially such that the distal end of the impeller is located distally in the frame and the impeller stabilization spring is compressed to accommodate the movement of the distal end of the impeller. Typically, the impeller stabilization spring is located around the axial shaft between the distal end of the impeller and the thrust bearing.

[0010] Thus, according to some applications of the present invention, there is provided an apparatus comprising: 1. A ventricular assist device comprising: an impeller configured to be disposed within a left ventricle of a subject and defining a lumen therein; a frame configured to be disposed about the impeller; a proximal bearing portion disposed at a proximal end of the frame and a distal bearing portion disposed at a distal end of the frame; an axial shaft extending through the proximal bearing, the lumen defined by the impeller, and the distal bearing; a motion damping spring disposed around the axial shaft between a distal end of the impeller and the distal bearing portion, the motion damping spring configured to damp axial motion occurring in the impeller; The present invention relates to a ventricular assist device comprising:

[0011] In some applications, the impeller is configured to move axially back and forth while rotating, and the motion dampening spring is configured to provide dampening against the axial back and forth motion.

[0012] In some applications, the impeller is configured to be radially restrained by axial expansion, and the motion dampening spring is configured to compress to accommodate the axial expansion of the impeller.

[0013] In some applications, a motion dampening spring is coupled to a distal end of the impeller.

[0014] In some applications, the ventricular assist device further includes a proximal motion damping spring disposed about the axial shaft between the proximal end of the impeller and the proximal bearing portion, the motion damping spring configured to dampen axial motion of the impeller in the proximal direction.

[0015] In some applications, the motion dampening spring is coupled to the distal bearing. In some applications, the device further includes a distal bearing housing disposed about the distal bearing, the motion dampening spring being coupled to the distal bearing via the distal bearing housing.

[0016] In some applications, the apparatus further includes an elastomeric material coupled to the motion damping spring such that at least a portion of the axial shaft between the distal end of the impeller and the distal bearing portion is covered with the elastomeric material. In some applications, the motion damping spring is coated with the elastomeric material. In some applications, the motion damping spring is embedded within the elastomeric material. In some applications, the elastomeric material includes at least one of silicone and polyurethane.

[0017] In some applications, the ventricular assist device includes a purge system configured to deliver a purge fluid into a lumen defined by the axial shaft, such that at least a portion of the purge fluid flows proximally through an interface between the axial shaft and the elastomeric material.

[0018] In some applications, the elastomeric material is coupled to the motion dampening spring such that it changes shape to match the shape change occurring in the motion dampening spring. In some applications, the elastomeric material is configured to change shape without breaking or collapsing. In some applications, the elastomeric material is configured to prevent the motion dampening spring from wrinkling as a result of being compressed.

[0019] In some applications, the ventricular assist device further includes a pump outlet tube configured to traverse the subject's aortic valve, such that a proximal portion of the pump outlet tube is disposed within the subject's aorta and a distal portion of the pump outlet tube is disposed within the subject's left ventricle, the distal portion of the pump outlet tube extending to a distal end of the frame and defining one or more lateral blood inlets configured to allow blood flow from the subject's left ventricle into the pump outlet tube.

[0020] In some applications, the porosity of the distal portion of the pump outlet tubing that defines the blood inlets is lower in a proximal region of the distal portion of the pump outlet tubing than in a distal region of the distal portion of the pump outlet tubing distal to the proximal region. In some applications, the distal portion of the pump outlet tubing has a porosity of greater than 40 percent. In some applications, the distal portion of the pump outlet tubing defines greater than 10 blood inlets sized to (a) allow blood flow from the subject's left ventricle into the tubing and (b) prevent structures from the subject's left ventricle from entering the frame. In some applications, the distal portion of the pump outlet tubing defines greater than 50 blood inlets sized to (a) allow blood flow from the subject's left ventricle into the tubing and (b) prevent structures from the subject's left ventricle from entering the frame.

[0021] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: a pump outlet tube configured to traverse an aortic valve of the subject, such that a proximal end of the pump outlet tube is disposed within the aorta of the subject and a distal end of the pump outlet tube is disposed within a left ventricle of the subject; an impeller disposed within the left ventricle and within the pump outlet tube and configured to pump blood through the pump outlet tube; a frame disposed about the impeller and defining a cylindrical portion and a proximal conical portion disposed proximally relative to the cylindrical portion, the proximal conical portion extending in width from a proximal end of the frame to the cylindrical portion of the frame; at least one optical fiber, a proximal end of the optical fiber configured to be placed outside the subject's body and a distal portion of the optical fiber coupled to the proximal cone of the frame such that the distal end of the optical fiber extends outside of the pump outlet tubing and is configured to be placed outside of the pump outlet tubing in direct fluid communication with the subject's left ventricular blood flow; Includes.

[0022] In some applications, the device further includes a light source and a light detector disposed at the proximal end of the optical fiber and configured to detect blood pressure at the distal end of the optical fiber by directing light through the optical fiber and detecting reflected light.

[0023] In some applications, the device further includes a computer processor configured to receive blood pressure detected at the distal end of the optical fiber and to control pumping of blood by the impeller in response to the blood pressure detected at the distal end of the optical fiber.

[0024] In some applications, the device further includes a computer processor configured to receive the blood pressure detected at the distal end of the optical fiber, and the computer processor configured to derive at least one physiological parameter of the subject based at least in part on the blood pressure detected at the distal end of the optical fiber, wherein the at least one physiological parameter of the subject is selected from the group consisting of intrinsic cardiac output, total cardiac output, arterial compliance, and peripheral resistance.

[0025] In some applications, the pump outlet tubing defines one or more blood inlets through which blood is pumped into the pump outlet tubing, and the distal end of the optical fiber is configured to be in direct fluid communication with the subject's left ventricular blood flow at a location proximal to a proximal-most portion of the one or more blood inlets.

[0026] In some applications, the distal end of the fiber is exposed to blood having a pressure that reflects the blood pressure in the left ventricle itself and is not affected by pressure fluctuations generated near one or more blood inlets as a result of fluid flow dynamics occurring at the one or more blood inlets.

[0027] In some applications, the distal end of the optical fiber is configured to be in direct fluid communication with the left ventricular blood flow of the subject at a location at least 1 cm proximal to the proximal-most portion of the one or more blood inlets.

[0028] In some applications, the at least one optical fiber includes two or more optical fibers, and the device further includes a computer processor configured to receive the blood pressure detected at a distal end of each of the optical fibers and to thereby determine whether a distal end of one of the optical fibers is not exposed to left ventricular blood flow. In some applications, in response to determining that a distal end of one of the optical fibers is not exposed to left ventricular blood flow, the computer processor determines a left ventricular pressure of the subject based on the blood pressure measured using different ones of the two or more optical fibers.

[0029] Further, in accordance with some applications of the present invention, there is provided a method for determining the intrinsic cardiac output of a subject undergoing treatment with a percutaneous left ventricular assist device, the method comprising: pumping blood from a left ventricle of the subject to an aorta of the subject using a percutaneous left ventricular assist device; sensing one or more pressure-related and / or flow-related parameters using a percutaneous left ventricular assist device; Varying a rate at which blood is pumped by the percutaneous left ventricular assist device during one or more vascular parameter determination periods; applying a mathematical model representing the dynamic vasculature of the subject to each rate of pumping of the percutaneous ventricular assist device; estimating a vascular parameter of the subject based on the difference between the applied mathematical models when the percutaneous ventricular assist device is pumping blood at each rate and the pressure-related parameter and / or the flow-related parameter; estimating an intrinsic cardiac output of the subject based on the pressure-related and / or flow-related parameters and the estimated vascular parameters of the subject; Includes.

[0030] Further, in accordance with some applications of the present invention, there is provided an apparatus for determining an intrinsic cardiac output of a subject, the apparatus comprising: a percutaneous left ventricular assist device configured to pump blood from a left ventricle of a subject to an aorta of the subject; at least one computer processor, Sensing one or more pressure-related and / or flow-related parameters using a percutaneous left ventricular assist device; varying a rate at which blood is pumped by the percutaneous left ventricular assist device during one or more vascular parameter determination periods; applying a mathematical model representing the dynamic vasculature of the subject to each rate of pumping of the percutaneous left ventricular assist device; estimating a vascular parameter of the subject based on the difference between the applied mathematical models when the percutaneous left ventricular assist device is pumping blood at each rate and the pressure-related parameter and / or the flow-related parameter; estimating an intrinsic cardiac output of the subject based on the pressure-related and / or flow-related parameters and the estimated vascular parameters of the subject; at least one computer processor configured to Includes.

[0031] In some applications, the computer processor is configured to generate an output indicative of the subject's intrinsic cardiac output.

[0032] In some applications, the computer processor is configured to apply a mathematical model representing the dynamic vasculature of the subject by applying a Windkessel model of the aorta.

[0033] In some applications, the computer processor is configured to estimate the subject's vascular parameter by estimating one or more of the subject's aortic compliance, characteristic impedance, and peripheral resistance.

[0034] In some applications, the computer processor is configured to detect one or more pressure-related and / or flow-related parameters by detecting an aortic pressure of the subject. In some applications, the computer processor is further configured to detect one or more pressure-related and / or flow-related parameters by detecting an aortic flow of the subject by detecting flow through the percutaneous left ventricular assist device.

[0035] In some applications, the percutaneous left ventricular assist device includes a pump outlet tube having a known cross-sectional area and a pump, and the computer processor is configured to detect flow through the percutaneous left ventricular assist device by calculating flow through the pump outlet tube based on the known cross-sectional area of ​​the pump outlet tube of the percutaneous left ventricular assist device and a pressure differential generated by the pump of the percutaneous left ventricular assist device.

[0036] In some applications, The percutaneous left ventricular assist device includes a motor; The pump of the percutaneous left ventricular assist device includes an impeller configured to be rotated by a motor to pump blood; The computer processor is configured to determine the pressure differential generated by the pump of the percutaneous left ventricular assist device by measuring the power consumption by the motor as it rotates the impeller at a given rotational speed, using a predetermined relationship between the power consumption by the motor required to rotate the impeller at the rotational speed and the pressure differential generated by the impeller.

[0037] According to some applications, the computer processor is configured to determine a pressure differential generated by a pump of the percutaneous left ventricular assist device by measuring left ventricular and aortic pressures of the subject.

[0038] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: 1. A ventricular assist device comprising: An axial shaft; an impeller disposed on the axial shaft and configured to pump blood; A frame disposed around the impeller; a distal thrust bearing disposed within the frame, the distal end of the axial shaft being configured to engage the distal thrust bearing to prevent axial movement of the axial shaft in response to variations in a pressure gradient across which the impeller pumps blood; a plurality of connecting struts extending radially inwardly from the frame to the thrust bearing portion and coupling the thrust bearing portion to the frame, the frame and the connecting struts being formed as a single integral element; The present invention relates to a ventricular assist device comprising:

[0039] In some applications, the frame, connecting struts, and thrust bearing are all formed as a single, integral element.

[0040] In some applications, the ventricular assist device further includes an impeller stabilization spring disposed about the axial shaft between the distal end of the impeller and the thrust bearing, the impeller stabilization spring configured to stabilize the distal end of the impeller. In some applications, the impeller is configured to be radially constrained by stretching axially, and the impeller stabilization spring configured to compress to accommodate the axial stretch of the impeller. In some applications, the impeller stabilization spring is coupled to the distal end of the impeller.

[0041] For some applications, the ventricular assist device further includes a proximal bearing and a proximal impeller stabilization spring disposed about the axial shaft between the proximal end of the impeller and the proximal bearing.

[0042] In some applications, the impeller stabilization spring is coupled to the thrust bearing.

[0043] In some applications, the device further includes an elastomeric material coupled to the impeller stabilization spring such that at least a portion of the axial shaft between the distal end of the impeller and the thrust bearing is covered by the elastomeric material. In some applications, the impeller stabilization spring is coated with the elastomeric material. In some applications, the impeller stabilization spring is embedded within the elastomeric material. In some applications, the elastomeric material includes at least one of silicone and polyurethane. In some applications, the ventricular assist device includes a purge system configured to direct a purge fluid into a lumen defined by the axial shaft such that at least a portion of the purge fluid flows proximally through an interface between the axial shaft and the elastomeric material.

[0044] In some applications, the elastomeric material is coupled to the impeller stabilizer spring such that the elastomeric material changes shape to match the shape change occurring in the impeller stabilizer spring. In some applications, the elastomeric material is configured to change shape without breaking or crumbling. In some applications, the elastomeric material is configured to prevent the impeller stabilizer spring from wrinkling as a result of being compressed.

[0045] In some applications, the ventricular assist device further includes a pump outlet tube configured to traverse the subject's aortic valve, such that a proximal portion of the pump outlet tube is disposed within the subject's aorta and a distal portion of the pump outlet tube is disposed within the subject's left ventricle, the distal portion of the pump outlet tube extending to a distal end of the frame and defining one or more lateral blood inlets configured to allow blood flow from the subject's left ventricle into the pump outlet tube.

[0046] In some applications, the porosity of the distal portion of the pump outlet tubing that defines the blood inlet is lower in a proximal region of the distal portion of the pump outlet tubing than in a distal region of the distal portion of the pump outlet tubing distal to the proximal region.

[0047] In some applications, the distal portion of the pump outlet tubing has a porosity of greater than 40 percent. In some applications, the distal portion of the pump outlet tubing defines greater than 10 blood inlets sized to (a) allow blood flow from the subject's left ventricle into the tubing and (b) prevent structures from the subject's left ventricle from entering the frame. In some applications, the distal portion of the pump outlet tubing defines greater than 50 blood inlets sized to (a) allow blood flow from the subject's left ventricle into the tubing and (b) prevent structures from the subject's left ventricle from entering the frame.

[0048] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: 1. A ventricular assist device comprising: An axial shaft; an impeller disposed on the axial shaft and configured to pump blood; A frame disposed around the impeller; a distal thrust bearing, a distal end of the axial shaft configured to engage the distal thrust bearing to prevent axial movement of the axial shaft in response to variations in a pressure gradient across which the impeller pumps blood; an impeller stabilization spring disposed about the axial shaft between the distal end of the impeller and the thrust bearing, the impeller stabilization spring configured to stabilize the distal end of the impeller; The present invention relates to a ventricular assist device comprising:

[0049] In some applications, the impeller is configured to be radially constrained by axial expansion, and the impeller stabilization spring is configured to compress to accommodate the axial expansion of the impeller.

[0050] In some applications, an impeller stabilizing spring is coupled to a distal end of the impeller.

[0051] For some applications, the ventricular assist device further includes a proximal bearing and a proximal impeller stabilization spring disposed about the axial shaft between the proximal end of the impeller and the proximal bearing.

[0052] In some applications, the impeller stabilization spring is coupled to the thrust bearing.

[0053] In some applications, the apparatus further includes an elastomeric material coupled to the impeller stabilization spring such that at least a portion of the axial shaft between the distal end of the impeller and the thrust bearing is covered by the elastomeric material. In some applications, the impeller stabilization spring is coated with the elastomeric material. In some applications, the impeller stabilization spring is embedded within the elastomeric material. In some applications, the elastomeric material includes at least one of silicone and polyurethane.

[0054] In some applications, the ventricular assist device includes a purge system configured to deliver a purge fluid into a lumen defined by the axial shaft, such that at least a portion of the purge fluid flows proximally through an interface between the axial shaft and the elastomeric material.

[0055] In some applications, the elastomeric material is coupled to the impeller stabilizer spring such that the elastomeric material changes shape to match the shape change occurring in the impeller stabilizer spring. In some applications, the elastomeric material is configured to change shape without breaking or crumbling. In some applications, the elastomeric material is configured to prevent the impeller stabilizer spring from wrinkling as a result of being compressed.

[0056] Further, in accordance with some applications of the present invention, there is provided an apparatus for use with a percutaneous ventricular assist device including a self-expanding pump head, the percutaneous ventricular assist device being configured to be delivered to a left ventricle of a subject using a delivery catheter while the pump head is disposed in a radially constrained configuration within the delivery catheter. 1. A package for a ventricular assist device, comprising: a package shaped to define a pump head chamber within which the pump head is packaged in a radially unconstrained configuration; a catheter fixture reversibly coupled to the package and shaped to define a hole, the catheter fixture configured to couple to the package with the distal end of the delivery catheter disposed within the hole to thereby secure the distal end of the delivery catheter within the hole; and wherein the package is configured to be radially constrained by the pump head being retracted into the distal end of the delivery catheter while the distal end of the delivery catheter is secured within the bore.

[0057] In some applications, the pump head chamber is configured to be filled with solution before the pump head is retracted into the distal end of the delivery catheter. In some applications, the catheter fixation device is configured to secure the distal end of the delivery catheter to a downwardly sloping surface such that the distal end of the catheter is in a downwardly sloping orientation. In some applications, the slope of the surface is configured to reduce the likelihood of air bubbles entering the distal end of the delivery catheter when the pump head is retracted into the distal end of the delivery catheter compared to when the distal end of the catheter is secured to a horizontal surface.

[0058] In general, in the specification and claims of this application, "proximal" and related terms, when used with respect to a device or portion thereof, are to be interpreted as meaning the end of the device or portion thereof that is closer to the location where the device would normally be inserted into a subject when the device is inserted into the subject. "Distal" and related terms, when used with respect to a device or portion thereof, are to be interpreted as meaning the end of the device or portion thereof that is farther from the location where the device would normally be inserted into a subject when the device is inserted into the subject.

[0059] The present invention will be more fully understood with reference to the drawings in conjunction with the following detailed description of the embodiments thereof. [Brief description of the drawings]

[0060] [Figure 1A] 1 is a schematic diagram of a ventricular assist device configured with a distal end for placement in the left ventricle of a subject, in accordance with some applications of the present invention. [Figure 1B] 1 is a schematic diagram of a ventricular assist device configured with a distal end for placement in the left ventricle of a subject, in accordance with some applications of the present invention. [Figure 1C] 1 is a schematic diagram of a ventricular assist device configured with a distal end for placement in the left ventricle of a subject, in accordance with some applications of the present invention. [Diagram 2] FIG. 1 is a schematic diagram of a frame housing an impeller of a ventricular assist device, according to some applications of the present invention. [Figure 3A] 1 is a schematic diagram of an impeller or portion thereof of a ventricular assist device, according to some applications of the present invention. [Figure 3B] 1 is a schematic diagram of an impeller or portion thereof of a ventricular assist device, according to some applications of the present invention. [Figure 3C] 1 is a schematic diagram of an impeller or portion thereof of a ventricular assist device, according to some applications of the present invention. [Figure 3D] 1 is a schematic diagram of an impeller or portion thereof of a ventricular assist device, according to some applications of the present invention. [Figure 3E] 1 is a schematic diagram of an impeller or portion thereof of a ventricular assist device, according to some applications of the present invention. [Figure 4] FIG. 1 is a schematic diagram of an impeller disposed within a frame of a ventricular assist device, in accordance with some applications of the present invention. [Figure 5A] FIG. 2 is a schematic diagram of an impeller and frame of a ventricular assist device in a radially unconstrained state, in accordance with some applications of the present invention. [Figure 5B] 1 is a schematic diagram of an impeller and frame of a ventricular assist device in a radially constrained state, in accordance with some applications of the present invention. [Figure 5C] FIG. 2 is an enlarged schematic view of the proximal end of a frame of a ventricular assist device, according to some applications of the present invention. [Figure 6A] 1A-1C are schematic diagrams of a ventricular assist device at various stages in the motion cycle of its impeller relative to its frame, in accordance with some applications of the present invention. [Figure 6B] 1A-1C are schematic diagrams of a ventricular assist device at various stages in the motion cycle of its impeller relative to its frame, in accordance with some applications of the present invention. [Figure 6C] FIG. 1 is a schematic diagram of a ventricular assist device including a motion dampening spring, in accordance with some applications of the present invention. [Figure 6D] FIG. 1 is a schematic diagram of a ventricular assist device including a motion dampening spring, in accordance with some applications of the present invention. [Figure 7A] FIG. 1 is a schematic diagram of a motor unit of a ventricular assist device according to some applications of the present invention. [Figure 7B] FIG. 1 is a schematic diagram of a motor unit of a ventricular assist device according to some applications of the present invention. [Figure 7C] FIG. 1 is a schematic diagram of a motor unit of a ventricular assist device according to some applications of the present invention. [Figure 8A] 1 is a graph showing the variation in length of a drive cable of a ventricular assist device as a pressure gradient across a blood pump impeller is varied, as measured in experiments conducted in accordance with several applications of the present invention. [Figure 8B] 1 is a graph showing the variation of magnetic phase measurements made on a blood pump as the pressure gradient across the blood pump's impeller varies, as measured in experiments performed in accordance with some applications of the present invention. [Figure 8C] 1 is a graph showing the variation of magnetic phase measurements made on a blood pump as the pressure gradient across the blood pump's impeller varies, as measured in experiments performed in accordance with some applications of the present invention. [Figure 9A] 1 is a schematic diagram of a ventricular assist device including one or more blood pressure measuring tubes and / or fibers, according to some applications of the present invention. [Figure 9B] 1 is a schematic diagram of a ventricular assist device including one or more blood pressure measuring tubes and / or fibers, according to some applications of the present invention. [Figure 10A] FIG. 1 is a schematic diagram of a ventricular assist device including a lining on the inside of the frame that houses the impeller, in accordance with some applications of the present invention. [Figure 10B] FIG. 1 is a schematic diagram of a ventricular assist device including a lining on the inside of the frame that houses the impeller, in accordance with some applications of the present invention. [Figure 11A] 1 is a schematic diagram of a pump outlet tube defining a blood inlet at a distal end, according to some applications of the present invention. FIG. [Figure 11B] 1 is a schematic diagram of a pump outlet tube defining a blood inlet at a distal end, according to some applications of the present invention. FIG. [Figure 11C] 1 is a schematic diagram of a pump outlet tube defining a blood inlet at a distal end, according to some applications of the present invention. FIG. [Figure 11D]1 is a schematic diagram of a pump outlet tube defining a blood inlet at a distal end, according to some applications of the present invention. FIG. [Figure 11E] 1 is a schematic diagram of a pump outlet tube defining a blood inlet at a distal end, according to some applications of the present invention. FIG. [Figure 12A] FIG. 1 is a schematic diagram of a drive cable for a ventricular assist device, in accordance with some applications of the present invention. [Figure 12B] FIG. 1 is a schematic diagram of a drive cable for a ventricular assist device, in accordance with some applications of the present invention. [Figure 12C] FIG. 1 is a schematic diagram of a drive cable for a ventricular assist device, in accordance with some applications of the present invention. [Figure 12D] 1 is a schematic diagram of a drive cable bearing tube according to some applications of the present invention. [Figure 13] 1 is a schematic diagram of a ventricular assist device having a guidewire disposed within a guidewire lumen, in accordance with some applications of the present invention. [Figure 14A] FIG. 1 is a schematic diagram of a two-state guidewire, in accordance with some applications of the present invention. [Figure 14B] FIG. 1 is a schematic diagram of a two-state guidewire, in accordance with some applications of the present invention. [Figure 15] FIG. 1 is a schematic diagram of a ventricular assist device with a distal thrust bearing, in accordance with some applications of the present invention. [Figure 16A] FIG. 1 is a schematic diagram of a package for packaging a ventricular assist device, according to some applications of the present invention. [Figure 16B] FIG. 1 is a schematic diagram of a package for packaging a ventricular assist device, according to some applications of the present invention. [Figure 16C] FIG. 1 is a schematic diagram of a package for packaging a ventricular assist device, according to some applications of the present invention. [Figure 16D] FIG. 1 is a schematic diagram of a package for packaging a ventricular assist device, according to some applications of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0061] Reference is now made to Figures 1A, 1B, and 1C, which are schematic diagrams of a ventricular assist device 20 configured with a distal end positioned in a subject's left ventricle 22, in accordance with some applications of the present invention. Figure 1A shows an overview of a ventricular assist device system including a control console 21 and a motor unit 23. Figure 1B shows the ventricular assist device inserted into a subject's left ventricle, and Figure 1C shows a pump head portion 27 of the ventricular assist device in greater detail. The ventricular assist device includes a pump outlet tube 24 that traverses a subject's aortic valve 26, such that a proximal end 28 of the pump outlet tube is positioned in the subject's aorta 30, and a distal end 32 of the pump outlet tube is positioned within the left ventricle 22. Typically, the pump outlet tube 24 (sometimes referred to herein as the "blood pump tube") is an elongated tube, with the axial length of the pump outlet tube being substantially longer than its diameter. The scope of the present invention includes the use of the devices and methods described herein in anatomical locations other than the left ventricle and the aorta. Thus, the ventricular assist device and / or portions thereof may be referred to herein (in the specification and claims) as a blood pump.

[0062] In some applications, ventricular assist devices are used to assist the function of the subject's left ventricle during percutaneous coronary intervention. In such cases, ventricular assist devices are typically used for up to 6 hours (e.g., up to 10 hours) during a period of risk of developing hemodynamic instability (e.g., during or immediately after percutaneous coronary intervention). Alternatively or additionally, ventricular assist devices are used to assist the function of the subject's left ventricle for longer periods (e.g., 2-20 days, e.g., 4-14 days) in patients suffering from cardiogenic shock and in low cardiac output conditions (e.g., acute myocardial infarction, myocarditis, cardiomyopathy, postpartum, etc.). In some applications, ventricular assist devices are used to assist the function of the subject's left ventricle for even longer periods (e.g., weeks or months), for example in "bridge to recovery" therapy. In some such applications, the ventricular assist device is permanently or semi-permanently implanted and the impeller of the ventricular assist device is powered percutaneously, for example, using an external antenna that is magnetically coupled to the impeller.

[0063] As shown in FIG. 1B, which shows the steps of deployment of a ventricular assist device in the left ventricle, typically the distal end of the ventricular assist device is guided through the guidewire 10 into the left ventricle. During insertion of the distal end of the device into the left ventricle, a delivery catheter 143 is placed over the distal end of the device. Once the distal end of the device is positioned in the left ventricle, typically the delivery catheter is retracted into the aorta and the guidewire is retracted from the subject. Retracting the delivery catheter typically causes the self-expandable components at the distal end of the device to assume a radially unconstrained configuration, as described in more detail below. Typically, the ventricular assist device is inserted into the subject to provide acute therapy to the subject. In some applications, once therapy is over, to withdraw the left ventricular device from the subject, the delivery catheter is advanced over the distal end of the device to cause the self-expandable components at the distal end of the device to assume a radially constrained configuration. Alternatively or additionally, the distal end of the device is retracted into the delivery catheter to cause the self-expandable components at the distal end of the device to assume a radially constrained configuration.

[0064] In some applications (not shown), the ventricular assist device and / or delivery catheter 143 includes an ultrasound transducer at its distal end, and the ventricular assist device is advanced toward the target ventricle under ultrasound guidance.

[0065] Reference is now made to FIG. 1C, which illustrates in greater detail the pump head portion 27 of the ventricular assist device 20 according to some applications of the present invention. Typically, the impeller 50 is disposed within the distal portion 102 of the pump outlet tube 24 and is configured to rotate to pump blood from the left ventricle into the aorta. Typically, the pump outlet tube defines one or more blood inlets 108 at a distal end of the pump outlet tube through which blood flows from the left ventricle into the pump outlet tube during operation of the impeller. As shown in FIG. 1C, in some applications, the pump outlet tube defines a single axially oriented blood inlet. Alternatively, the pump outlet tube defines multiple lateral blood inlets (e.g., as shown in FIG. 1B), as described in more detail below. In some applications, the proximal portion 106 of the pump outlet tube defines one or more blood inlets 109 through which blood flows from the pump outlet tube into the ascending aorta during operation of the impeller.

[0066] In some applications, a control console 21 (shown in FIG. 1A), which typically includes a computer processor 25, drives the impeller to rotate. For example, the computer processor may control a motor 74 (shown in FIG. 7A), which is disposed in a motor unit 23 (shown in FIG. 1A) and drives the impeller to rotate through a drive cable 130 (shown in FIG. 12A). In some applications, the computer processor is configured to detect physiological parameters of interest (such as left ventricular pressure, cardiac afterload, rate of change of left ventricular pressure, etc.) and control the rotation of the impeller accordingly, as described in more detail below. Typically, the operations performed by the computer processor, as described herein, transform the physical state of a memory, which is an actual physical item in communication with the computer processor, to have a different magnetic polarity, charge, etc., depending on the technology of the memory used. The computer processor 25 is typically a hardware device programmed with computer program instructions to create a special purpose computer. For example, when programmed to execute the techniques described herein, the computer processor 25 typically functions as a special purpose ventricular assist computer processor and / or a special purpose blood pump computer processor.

[0067] In some applications, a purge system 29 (shown in FIG. 1A ) drives a fluid (e.g., a glucose solution) through portions of the ventricular assist device 20, for example, to cool portions of the device, to lubricate interfaces between rotating parts and stationary bearings, and / or to flush debris from portions of the device.

[0068] Typically, a frame 34 is disposed along the distal portion 102 of the pump outlet tubing 24 and around the impeller 50 within the pump outlet tubing. The frame is typically made of a shape memory alloy, such as Nitinol. In some applications, the shape memory alloy of the frame has a set shape such that, in the absence of any force being applied to the distal portion 102 of the tubing 24, at least a portion of the frame (and thus the distal portion 102 of the tubing 24) has a generally circular, elliptical, or polygonal cross-sectional shape. By having a generally circular, elliptical, or polygonal cross-sectional shape, the frame is configured to hold the distal portion of the pump outlet tubing open. Typically, during operation of the ventricular assist device, the distal portion of the pump outlet tubing is configured to be disposed within the subject such that it is at least partially disposed within the left ventricle.

[0069] In some applications, the frame is not disposed within the pump outlet tube along the proximal portion 106 of the pump outlet tube 24, and thus the pump outlet tube is not supported open by the frame 34. The pump outlet tube 24 is typically made of a blood impermeable, crushable material. For example, the pump outlet tube 24 may include polyurethane, polyester, and / or silicone. Alternatively or additionally, the pump outlet tube is made of polyethylene terephthalate (PET) and / or polyether block amide (e.g., PEBAX®). In some applications (not shown), the pump outlet tube is reinforced with a reinforcing structure, for example, a braided reinforcing structure, such as a braided nitinol tube. Typically, the proximal portion of the pump outlet tube has a configuration that is disposed such that at least a portion of it is placed within the ascending aorta of the subject. In some applications, as shown in FIG. 1B, the proximal portion of the pump outlet tube traverses the aortic valve of the subject and reaches the ascending aorta of the subject from the left ventricle of the subject.

[0070] As described above, the pump outlet tube typically defines one or more blood inlets 108 at a distal end thereof through which blood flows from the left ventricle into the pump outlet tube during operation of the impeller. In some applications, a proximal portion of the pump outlet tube defines one or more blood outlets 109 through which blood flows from the pump outlet tube into the ascending aorta during operation of the impeller. Typically, the pump outlet tube defines a plurality of blood outlets 109, e.g., between two and eight blood outlets (e.g., between two and four blood outlets). During operation of the impeller, the proximal portion of the pump outlet tube is typically maintained open by pressure of blood flow through the pump outlet tube. In some applications, the proximal portion of the pump outlet tube is configured to collapse inward in response to pressure outside the proximal portion of the pump outlet tube exceeding pressure inside the proximal portion of the pump outlet tube, e.g., in the event of an impeller malfunction. In this way, the proximal portion of the pump outlet tubing acts as a safety valve, preventing retrograde blood flow from the aorta into the left ventricle.

[0071] Referring again to FIG. 1C, in some applications, the frame 34 is shaped to define a proximal cone 36, a central cylindrical portion 38, and a distal cone 40. Typically, the proximal cone faces proximally, i.e., the narrow end of the cone is oriented proximally relative to the wide end of the cone. More typically, the distal cone faces distally, i.e., the narrow end of the cone is oriented distally relative to the wide end of the cone. In some applications, a lining 39 lines the frame within at least a portion of the frame 34 (e.g., along all or a portion of the central cylindrical portion of the frame). While FIG. 1C shows an embodiment of the pump head that does not include the lining 39, some figures show an embodiment of the pump head that does include the lining 39. Depending on the respective application, the lining partially or completely overlaps the pump outlet tube 24 in the portion of the frame that it lines. This is described in more detail below with reference to FIGS. 10A-10B.

[0072] Typically, the pump outlet tube 24 includes a conical proximal section 42 and a cylindrical central section 44. Typically, the proximal conical section faces proximally, i.e., is oriented such that the narrow end of the cone is proximal to the wide end of the cone. Typically, a blood outlet 109 is defined by the pump outlet tube 24 such that it extends at least partially along the proximal conical section of the tube 24. In some such applications, the blood outlet is teardrop shaped, as shown in FIG. 1C. Typically, the teardrop shaped feature of the blood outlet, combined with the blood outlet extending at least partially along the proximal conical section of the tube 24, causes blood to exit the blood outlet along a flow line that is substantially parallel to the longitudinal axis of the tube 24 at the location of the blood outlet.

[0073] In some applications (not shown), the diameter of the pump outlet tube 24 varies along the length of the central portion of the pump outlet tube such that the central portion of the pump outlet tube has a frusto-conical shape. For example, the central portion of the pump outlet tube may widen from its proximal end to its distal end, or may narrow from its proximal end to its distal end. In some applications, the central portion of the pump outlet tube has a diameter of 5-7 mm at the proximal end and a diameter of 8-12 mm at the distal end.

[0074] Referring again to FIG. 1C, the ventricular assist device typically includes a distal tip element 107 disposed distally relative to the frame 34, including an axial shaft receiving tube 126 and a distal tip 120. Typically, the axial shaft receiving tube is configured to receive a distal portion of the axial shaft 92 of the pump head during back and forth movement of the axial shaft (as described in more detail below) and / or during delivery of the ventricular assist device. (Typically, during delivery of the ventricular assist device, the frame is maintained in a radially constrained configuration, so that the orientation of the axial shaft relative to the frame is in a different position than the orientation relative to the frame during operation of the ventricular assist device.) Typically, as shown, for example, in FIG. 1C, the distal tip 120 is configured to assume a curved shape when deployed within the left ventricle of a subject. In some applications, the curvature of the distal tip is configured to provide an atraumatic tip for the ventricular assist device 20. Alternatively or additionally, the distal tip element is configured to space the blood inlet 108 of the ventricular assist device from the wall of the left ventricle.

[0075] As shown in the close-up of FIG. 1B, in some applications, the pump outlet tube 24 extends to the end of the distal cone 40 of the frame, and the pump outlet tube defines a plurality of lateral blood inlets 108, as described in more detail below. In such applications, the pump outlet tube typically defines a distally facing distal cone, i.e., a distal cone oriented such that the narrow end of the cone is distal to the wide end of the cone. In some such applications (not shown), the pump outlet tube defines between two and four lateral blood inlets (e.g., four lateral blood inlets as shown). Typically, in such applications, each of the blood inlets defines an area of ​​more than 20 square millimeters (e.g., more than 30 square millimeters) and / or less than 60 square millimeters (e.g., less than 50 square millimeters), e.g., between 20 and 60 square millimeters or between 30 and 50 square millimeters. Alternatively or additionally, the outlet tube defines more, smaller blood inlets, e.g., more than 10 blood inlets, more than 50 blood inlets, more than 200 blood inlets, or more than 400 blood inlets, e.g., 50-100 blood inlets, 100-400 blood inlets, or 400-600 blood inlets. In some such applications, each of the blood inlets defines an area of ​​more than 0.05 square millimeters (e.g., more than 0.1 millimeters) and / or less than 3 square millimeters (e.g., less than 1 square millimeter), e.g., 0.05-3 square millimeters, or 0.1-1 square millimeters. Alternatively, each of the blood inlets defines an area of ​​more than 0.1 square millimeters (e.g., more than 0.3 millimeters) and / or less than 5 square millimeters (e.g., less than 1 square millimeter), e.g., 0.1-5 square millimeters, or 0.3-1 square millimeters. Such applications are further described below, for example with reference to Figures 11A through 11E.In general, the scope of the present disclosure includes combining a pump outlet tube defining a single axial blood inlet 108 as shown in FIG. 1C (as well as FIGS. 9A-9B, 10A-10B, and 16A-16C) with a pump outlet tube defining multiple lateral blood inlets 108 as shown in FIG. 1B (as well as FIGS. 4, 5A-5B, 6A-6D, 11A-11E, and 13), in combination with other features of the ventricular assist device described herein, mutatis mutandis.

[0076] Reference is now made to Figure 2, which is a schematic diagram of a frame 34 housing the impeller of the ventricular assist device 20, in accordance with some applications of the present invention. The frame 34 is typically made of a shape memory alloy, such as Nitinol, that has a set shape such that the central portion of the frame (and thus the tube 24) has a generally circular, elliptical, or polygonal cross-sectional shape in the absence of any force being applied to the pump outlet tube 24. By having a generally circular, elliptical, or polygonal cross-sectional shape, the frame is configured to hold open the distal portion of the tube.

[0077] Typically, the frame is a stent-like frame including struts that define the cells. More typically, the frame is covered by the pump outlet tube 24 and / or covered by a liner 39, described below with reference to Figures 10A-10B. As described below, in some applications, the impeller 50 moves axially back and forth relative to the frame 34. Typically, during the course of the impeller's movement relative to the frame, the location of a portion of the impeller that defines the maximum span of the impeller is located within the central cylindrical portion 38 of the frame 34. In some cases, if the cells of the central cylindrical portion 38 of the frame 34 are too large, the pump outlet tube 24 and / or the liner 39 will be stretched between the edges of the cells, such that the pump outlet tube 24 and / or the liner 39 will not define a circular cross section. In some applications, if this occurs in the region where the portion of the impeller that defines the maximum span of the impeller is located, this results in a substantially non-constant gap between the edges of the impeller blades and the tube 24 (and / or lining) at said location over the course of the impeller's rotational cycle, which in some applications can lead to increased hemolysis compared to a substantially constant gap between the edges of the impeller blades and the tube 24 (and / or lining) at said location over the course of the impeller's rotational cycle.

[0078] 2, and at least in part in consideration of the problems described in the paragraph above, within a central cylindrical portion 38 of the frame 34, the frame defines a number of relatively small cells. Typically, when the frame is arranged in a radially unconstrained configuration, the maximum cell width CW of each cell within the cylindrical portion of the frame (i.e., the distance measured around the circumference of the cylindrical portion 38 from the inner edge of the strut at the central junction on one side of the cell to the inner edge of the strut at the central junction on the other side of the cell) is less than 2 mm, e.g., 1.4 mm to 1.6 mm or 1.6 mm to 1.8 mm. Because the cells are relatively small, the lining 39 defines a substantially circular cross-section within the cylindrical portion of the frame.

[0079] 2, beginning with the distal end of the frame (on the right side of the figure), the frame typically defines (a) a junction 31 where the frame is coupled to the distal bearing housing 118H (shown in FIG. 5A) of the ventricular assist device, (b) a distal conical section 40, (c) a central cylindrical section 38, (d) a proximal conical section 36, and (e) a proximal strut junction 33. As shown, as the frame transitions from the proximal end of the frame toward the center of the frame (e.g., as the frame transitions from the proximal strut junction 33 through the proximal conical section 36 to the central cylindrical section 38), the struts 37 of the frame pass through junction 35 where a single strut bifurcates into two struts in a Y-shape. As described in more detail below, the frame 34 is typically positioned in a radially constrained (i.e., crimped) configuration within the delivery catheter 143 by extending axially. Furthermore, typically, the frame transmits radial narrowing to the impeller, which is radially constrained by axial stretching within the frame. In some applications, the struts of a frame configured as described above easily transmit axial stretching from a delivery catheter (or other device configured to crimp the frame) to the frame, and then to the impeller, because the pairs of struts branching off from each junction 35 are configured to pivot at the junction and move closer together.

[0080] 2, during assembly of the ventricular assist device, the distal coupling 31 is first coupled to the distal bearing housing 118H (shown in FIG. 5A) via, for example, a snap-fit ​​mechanism. In some applications, the proximal strut joint 33 is still held open at this stage in order to place the impeller in the frame via the proximal end of the frame. Typically, the struts of the frame 34 shown in FIG. 2 are used in applications where the pump outlet tube extends to the distal end of the frame 34 (e.g., as shown in FIG. 1B). In such cases, the distal end of the frame is covered by the pump outlet tube 24, so that the impeller cannot be inserted via the distal end of the frame. During assembly of the ventricular assist device, after the impeller is inserted via the proximal end of the frame, the proximal strut joint is closed. In some applications, the proximal strut joint is closed around the outside of the proximal bearing housing 116H (shown in FIG. 5A), as will be described in more detail below with reference to FIGS. 5A-5B. Typically, a fixation element 117 (eg, a ring as shown in FIG. 5A) holds the strut joints in a closed configuration around the outside of the proximal bearing housing 116H.

[0081] Typically, when deployed in a radially unconstrained configuration, the frame 34 has an overall length greater than 25 mm (e.g., greater than 30 mm) and / or less than 50 mm (e.g., less than 45 mm), such as 25-50 mm or 30-45 mm. Typically, when deployed in a radially constrained configuration (within the delivery catheter 143), the length of the frame increases by 2-5 mm. Typically, when deployed in a radially unconstrained configuration, the length of the central cylindrical portion of the frame 34 is greater than 10 mm (e.g., greater than 12 mm) and / or less than 25 mm (e.g., less than 20 mm), such as 10-25 mm or 12-20 mm. In some applications, the ratio of the length of the central cylindrical portion of the frame to the overall length of the frame is greater than 1:4 and / or less than 1:2, such as 1:4 to 1:2.

[0082] Reference is now made to Figures 3A to 3E, which are schematic illustrations of an impeller 50 or a portion thereof, according to some applications of the present invention. Typically, the impeller includes at least one outer helical elongated element 52 wound around a central axial spring 54 such that the helix defined by the helical elongated elements is coaxial with the central axial spring. Usually, the impeller includes more than one helical elongated element (e.g., three helical elongated elements as shown in Figures 3A to 3C). In some applications, the helical elongated element and the central axial spring are made of a shape memory material, e.g., a shape memory alloy such as Nitinol. Usually, each of the helical elongated element and the central axial spring supports a membrane 56 of material (e.g., an elastomer such as polyurethane and / or silicone) between them. In some applications, the membrane of material includes pieces of Nitinol embedded therein, e.g., to strengthen the membrane of material. For illustrative purposes, the impeller is shown in Figure 3A without the membrane of material. Figures 3B and 3C respectively show an impeller with material supported between a helical elongate element and a spring, and Figures 3D and 3E show an impeller similar to that shown in Figures 3B and 3C, but with some features of the impeller that differ from those shown in Figures 3B and 3C, as will be described in more detail below.

[0083] Each of the helical elongate elements defines a respective impeller blade with a membrane extending from the helical elongate element to the spring. The helical elongate element defines the outer edge of the blade and the axial spring defines the axis of the impeller. Typically, a membrane of material extends along and covers the spring. In some applications, a suture 53 (e.g., polyester suture as shown in Figures 3A-3C) is wound around the helical elongate element. Typically, the suture is configured to facilitate bonding between the membrane of material (typically an elastomer such as polyurethane or silicone) and the helical elongate element (typically a shape memory alloy such as Nitinol). In some applications, a suture (e.g., polyester suture, not shown) is wound around the spring 54. Typically, the suture is configured to facilitate bonding between the membrane of material (typically an elastomer such as polyurethane or silicone) and the spring (typically a shape memory alloy such as Nitinol).

[0084] Typically, the proximal ends of the spring 54 and the helical elongate element 52 extend from a proximal bushing (i.e., sleeve bearing) 64 of the impeller such that the proximal ends of the spring 54 and the helical elongate element 52 are disposed at similar radial distances from the longitudinal axis of the impeller. Similarly, typically, the distal ends of the spring 54 and the helical elongate element 52 extend from a distal bushing 58 of the impeller such that the distal ends of the spring 54 and the helical elongate element 52 are disposed at similar radial distances from the longitudinal axis of the impeller. The helical elongate elements typically rise gradually from the proximal bushing, reach a maximum span, and then gradually drop toward the distal bushing. Typically, the helical elongate elements are symmetrical along their length such that the ascending portion of their length is symmetrical to the descending portion of their length. Typically, the impeller defines a lumen 62 therethrough (shown in FIG. 3C). This lumen typically passes through and is defined by the spring 54 and the proximal and distal bushings 64 and 58 of the impeller.

[0085] Reference is now made to Figure 4, which is a schematic diagram of an impeller 50 disposed inside a frame 34 of a ventricular assist device 20, according to some applications of the present invention. In some applications, a lining 39 lines the frame within at least a portion of the frame 34 (e.g., along all or part of the central cylindrical portion 38 of the frame). Depending on the application, the lining partially or completely overlaps the pump outlet tube 24 in the portion of the frame that it lines, as will be described in more detail below with reference to Figures 9A-9B.

[0086] As shown in FIG. 4, there is typically a gap G between the outer edge of the impeller 50 and the lining 39, even at the position where the impeller spans at its maximum. In some applications, it is desirable for the gap to be relatively small between the outer edge of the impeller blades and the lining 39 so that the impeller can efficiently pump blood from the subject's left ventricle to the subject's aorta. (Note that because of the relatively small gap between the outer edge of the impeller 50 and the lining 39, even at the position where the impeller spans at its maximum, and because of the shape of the impeller, the impeller functions as an axial-flow impeller, pumping blood axially from the distal end of the pump outlet tube 24 to the proximal end of the pump outlet tube.) It is also desirable for the gap between the outer edge of the impeller blades and the inner surface of the frame 34 to be maintained throughout the rotation of the impeller within the frame 34, for example to reduce the risk of hemolysis.

[0087] In some applications, when both the impeller 50 and the frame 34 are arranged in a radially unconstrained configuration, and prior to operation of the impeller, the gap G between the outer edge of the impeller and the lining 39 at the location where the span of the impeller is greatest is greater than 0.05 mm (e.g., greater than 0.1 mm) and / or less than 1 mm (e.g., less than 0.4 mm), such as between 0.05 and 1 mm, or between 0.1 and 0.4 mm. In some applications, when the impeller is arranged in a radially unconstrained configuration, and prior to operation of the impeller, the outer diameter of the impeller at the location where the outer diameter of the impeller is greatest is greater than 7 mm (e.g., greater than 8 mm) and / or less than 10 mm (e.g., less than 9 mm), such as between 7 and 10 mm, or between 8 and 9 mm. In some applications, when the frame 34 is arranged in a radially unconstrained configuration, the inner diameter of the frame 34 (as measured from the inside of the liner 39 on one side of the frame to the inside of the liner on the opposite side of the frame) is greater than 7.5 mm (e.g., greater than 8.5 mm) and / or less than 10.5 mm (e.g., less than 9.5 mm), such as between 7.5 and 10.5 mm, or between 8.5 and 9.5 mm. In some applications, when the frame is arranged in a radially unconstrained configuration, the outer diameter of the frame 34 is greater than 8 mm (e.g., greater than 9 mm) and / or less than 13 mm (e.g., less than 12 mm), such as between 8 and 13 mm, or between 9 and 12 mm.

[0088] Typically, the axial shaft 92 passes through the axis of the impeller 50 via the impeller lumen 62. More typically, the axial shaft is rigid, e.g., a rigid tube. In some applications, the impeller proximal bushing 64 is coupled to the shaft such that the axial position of the proximal bushing relative to the shaft is fixed, and the impeller distal bushing 58 is slidable relative to the shaft. For example, the proximal bushing can be coupled, e.g., via a snap-fit ​​mechanism, to a coupling element 65 (shown in FIG. 4 ) disposed on the axial shaft. (Alternatively, the impeller distal bushing 58 is coupled to the shaft such that the axial position of the distal bushing relative to the shaft is fixed, and the impeller proximal bushing 64 is slidable relative to the shaft.) The axial shaft itself is radially stabilized via proximal and distal radial bearings 116 and 118. The axial shaft then passes through a lumen 62 defined by the impeller, radially stabilizing the impeller against the inner surface of the frame 34 so that even a relatively small gap (such as that described above) between the outer edges of the impeller blades and the inner surface of the frame 34 is maintained during rotation of the impeller.

[0089] 3A-3C, in some applications, the impeller includes a plurality of elongated elements 67 extending radially from the central axial spring 54 to the outer helical elongated element 52. The elongated elements are typically flexible, but substantially inextensible along the axis they define. More typically, each of the elongated elements is configured to exert no force on the helical elongated element except when a force is acting on the impeller to move the helical elongated element radially outward, and the separation distance between the helical elongated element and the central axial spring (in the absence of the elongated element) is greater than the length of the elongated element. For example, the elongated elements 67 may include a string (such as polyester, and / or another polymer, or natural material including fibers) and / or a wire (such as a nitinol wire, and / or a wire made of another alloy or metal).

[0090] In some applications, the elongated elements 67 maintain the helical elongated elements 52 (which define the outer edges of the impeller blades) within a given distance relative to the central axial spring. In this manner, the elongated elements are configured to prevent the outer edges of the impeller from being forced radially outward due to forces on the impeller during rotation of the impeller. The elongated elements are thereby configured to maintain a gap between the outer edges of the impeller blades and the inner surface of the frame 34 during rotation of the impeller. Typically, two or more (e.g., three or more) and / or seven or fewer (e.g., three or fewer) elongated elements 67 are used in the impeller, and each of the elongated elements is usually doubled (i.e., extending radially from the central axial spring 54 to the outer helical elongated element 52, then back from the helical elongated element to the central axial spring). In some applications, the multiple elongated elements are formed from a single string or wire. Each of the elongated elements extends from a spring into a respective helical elongated element and then returns to the spring.

[0091] Reference is now made to Figures 3D and 3E, which are schematic diagrams of an impeller 50 including a single integral impeller over-expansion prevention element 72 defining a plurality of elongated elements 67, according to some applications of the present invention. In some applications, the impeller over-expansion prevention element 72 (defining a plurality of elongated elements 67) is used as an alternative to the elongated element 67 shown in Figures 3A-3C. In some applications, the element 72 defines a ring 73 and a plurality of elongated elements 67 extending radially from the ring. In some applications, rather than wrapping the string and / or wire around the spring 54, the ring 73 of elements 72 is placed around the spring, for example, by placing it around a tube 70, which is typically located at a longitudinal center position of the spring. Each end of the elongated element 67 is then coupled to each of the helical elongated elements 52. As mentioned above, the elongated element 67 is typically flexible, but not substantially extensible along the axis defined by the elongated element. More typically, each of the elongated elements 67 is configured to provide substantially no resistance to compression. Each of the elongated elements 67 is configured to apply tension to the helical elongated element 52 preventing the helical elongated element 52 from moving radially outward, such that (in the absence of the elongated element 67) the separation distance between the helical elongated element 52 and the central axial spring 54 is greater than the length of the elongated element 67. When a force is acting on the impeller to move the helical elongated element 52 radially outward (in the absence of the elongated element 67), the impeller over-expansion prevention element is configured to prevent radial expansion of the impeller. Typically, each of the elongated elements 67 is disposed within each of the impeller blades and configured to prevent the impeller blades from expanding radially. In some applications, the elements 72 are made of polyester, and / or another polymer, or natural material including fiber, and / or Nitinol (or a similar shape memory alloy).

[0092] It is noted that the scope of the present invention includes the use of a single integral impeller anti-overexpansion element 72 with impellers having configurations different from those shown in Figures 3D-3E. For example, a single integral anti-overexpansion element 72 may be used with impellers having axial structures configured differently than spring 54. Typically, the impeller defines a lumen 62 therethrough, with the axial structures defining a lumen therethrough.

[0093] In some applications, the material from which the membrane is made is an elastomer with an ultimate elongation of more than 300 percent, such as more than 400 percent. Typically, the material has a relatively low molecular weight. In some applications, the melt flow index (which is an indirect indicator of molecular weight) of the material is at least 4, such as at least 4.3. In some applications, the ultimate tensile strength of the material is more than 6000 psi, such as more than 7000 psi, or more than 7500 psi. In some applications, the material is a polycarbonate-based thermoplastic polyurethane, such as Carbothane™. In some applications, Aromatic Coarbothane™ (e.g. Aromatic Coarbothane™ 75A) is used. Typically, such materials combine one or more of the following properties: no outer diameter loss during the dipping process, fatigue resistance, resistance to deformation due to crimping, and low outer diameter loss during crimping. The material is then cured to solidify, such as by drying.

[0094] Typically, the impeller 50 is inserted transcatheterically into the left ventricle in a radially constrained configuration. In the radially constrained configuration, both the helical elongate element 52 and the central axial spring 54 are axially stretched and radially constrained. Typically, a membrane of material (e.g., silicone and / or polyurethane) 56 changes shape to match the shape change of the helical elongate element and axial support spring that support the membrane of material. Typically, using a spring to support the inner edge of the membrane allows the membrane to change shape without breaking or collapsing because the spring provides a large surface area for the inner edge of the membrane to bond to. In some applications, for example, using a spring to support the inner edge of the membrane reduces the diameter of the spring itself by axially stretching it, thereby reducing the diameter to which the impeller can be radially constrained, as compared to using a rigid shaft to support the inner edge of the membrane.

[0095] As mentioned above, in some applications, the proximal bushing 64 of the impeller 50 is coupled to the axial shaft 92 such that the axial position of the proximal bushing relative to the shaft is fixed, and the distal bushing 58 of the impeller is slidable relative to the shaft. In some applications, the proximal bushing can be coupled to a coupling element 65 (shown in FIG. 4 ) disposed on the axial shaft, for example, via a snap-fit ​​mechanism. In some applications, the impeller extends axially when the impeller is radially constrained for inserting the impeller into a ventricle or for withdrawing the impeller from a subject, with the distal bushing sliding distally along the axial shaft. Alternatively (not shown), the distal bushing 58 of the impeller is coupled to the shaft such that the axial position of the distal bushing relative to the shaft is fixed, and the proximal bushing 64 of the impeller is slidable relative to the shaft. In some such applications, when the impeller is radially constrained for purposes of inserting it into a cardiac ventricle or withdrawing it from a subject, the proximal bushing slides proximally along the axial shaft, causing the impeller to extend axially. After being released within the subject, the impeller assumes a radially unconstrained configuration (the configuration in which the impeller is normally positioned during operation) as shown in Figures 3A-3E.

[0096] Reference is now made to Figures 5A and 5B, which are schematic illustrations of the impeller 50 and frame 34 of the ventricular assist device 20 in a radially unconstrained and radially constrained state, respectively, in accordance with some applications of the present invention. The impeller and frame are typically positioned in a radially constrained state during transcatheter insertion of the impeller and frame into a subject, and in a radially unconstrained state during operation of the impeller within the subject's left ventricle. Reference is also made to Figure 5C, which is an enlarged schematic illustration of the proximal end of the frame of the ventricular assist device, in accordance with some applications of the present invention.

[0097] As shown in FIG. 5B, the frame and impeller are typically maintained in a radially constrained configuration by the delivery catheter 143. Typically, in the radially constrained configuration of the impeller, the overall length of the impeller is greater than 15 mm (e.g., greater than 20 mm) and / or less than 30 mm (e.g., less than 25 mm), such as between 15 and 30 mm or between 20 and 25 mm. More typically, in the radially unconstrained configuration of the impeller, the length of the impeller is greater than 8 mm (e.g., greater than 10 mm) and / or less than 18 mm (e.g., less than 15 mm), such as between 8 and 18 mm or between 10 and 15 mm. More typically, when the impeller and frame 34 are arranged in a radially constrained configuration (as shown in FIG. 5B), the outer diameter of the impeller is less than 2 mm (e.g., less than 1.6 mm) and the outer diameter of the frame is less than 2.5 mm (e.g., less than 2.1 mm).

[0098] As mentioned above, the axial shaft 92 typically passes through the axis of the impeller 50 via the impeller lumen 62. Typically, the impeller proximal bushing 64 is coupled to the shaft via a coupling element 65 such that the axial position of the proximal bushing relative to the shaft is fixed, and the impeller distal bushing 58 is slidable relative to the shaft. (Alternatively, the impeller distal bushing 58 is coupled to the shaft such that the axial position of the distal bushing relative to the shaft is fixed, and the impeller proximal bushing 64 is slidable relative to the shaft.) The axial shaft itself is radially stabilized via a proximal radial bearing 116 and a distal radial bearing 118. Typically, a proximal bearing housing 116H is disposed around and houses the proximal bearing, and a distal bearing housing 118H is disposed around and houses the distal bearing. In some such applications, the radial bearings and the bearing housings are made of different materials. For example, the radial bearing portion may be made of a first material having a relatively high hardness, such as a ceramic (e.g., zirconia), and the bearing housing may be made of a second material, such as a metal or alloy, that can be formed into a desired shape (e.g., stainless steel, cobalt chrome, and / or nitinol).

[0099] In some applications, the axial shaft 92 is made of a metal or alloy such as stainless steel. In some such applications, the axial shaft is covered with a ceramic sleeve 240 (e.g., a zirconia sleeve) along the areas of the axial shaft that contact either the proximal or distal bearings 116, 118 during operation of the ventricular assist device. Thus, the radial interfaces between the axial shaft and the proximal and distal bearings are ceramic-ceramic interfaces. As described in more detail herein, typically, the impeller and the axial shaft are configured to undergo axial back-and-forth motion during operation of the ventricular assist device. Thus, in some applications, at locations along the axial shaft corresponding to the proximal and distal bearings, the axial shaft is covered with a ceramic sleeve along a length of more than 5 mm, e.g., more than 7 mm. Thus, the areas of the axial shaft that contact the radial bearings during the axial back-and-forth motion of the axial shaft are covered with a ceramic sleeve.

[0100] In some applications, along the portion of the axial shaft covered by the ceramic sleeve, as shown in cross section in Figure 5C, the shaft is shaped (e.g., by milling, molding, or a different shaping process) to define one or more grooves or depressions 95. Alternatively or additionally (not shown), the inner surface of the ceramic sleeve is shaped to define one or more grooves or depressions. In some such applications, to bond the sleeve to the axial shaft, an adhesive is injected into the grooves or depressions, which then spreads from the grooves or depressions to the interface between the axial shaft and the sleeve.

[0101] In some applications, the proximal bearing housing 116H and the distal bearing housing 118H perform additional functions. Referring first to the proximal bearing housing, as described above, in some applications, the proximal strut joint 33 of the frame 34 is closed around the outside of the proximal bearing housing. In some applications, the outer surface of the proximal bearing housing defines a groove shaped to receive the proximal strut joint. For example, as shown, the proximal strut joint has a wide head, and the outer surface of the proximal bearing housing defines a groove shaped to match the wide head of the proximal strut joint. Typically, a fixation element 117 (typically comprising a ring) holds the strut joint in a closed configuration around the outside of the proximal bearing housing 116H. In some applications, additional portions of the ventricular assist device are coupled to the proximal bearing housing. In some applications, a drive cable 130 extends from outside the subject to the axial shaft 92 and is coupled to the axial shaft. Typically, the drive cable rotates within a first outer tube 140. The first outer tube 140 serves as a drive cable bearing tube and extends from the exterior of the subject to the proximal bearing housing. In some applications, the first outer tube is disposed within the second outer tube 142. The second outer tube 142 also extends from the exterior of the subject to the proximal bearing housing. In some applications, the first outer tube 140 and / or the second outer tube 142 are bonded (e.g., with an adhesive) to the proximal bearing housing. For example, the first outer tube 140 can be bonded to an inner surface of the proximal bearing housing and the second outer tube 142 can be bonded to an outer surface of the proximal bearing housing.

[0102] Referring now to the distal bearing housing 118H, in some applications, the distal coupling 31 of the frame 34 is coupled to an outer surface of the distal bearing housing 118H, for example, via a snap-fit ​​mechanism. For example, the outer surface of the proximal-most portion 119 of the distal bearing housing may include a snap-fit ​​mechanism to which the distal coupling 31 of the frame 34 is coupled. In some applications, as shown in FIG. 5A, the distal bearing 118 is disposed within the proximal-most portion 119 of the distal bearing housing. As mentioned above, in some applications, the pump outlet tube 24 extends to the distal end of the frame 34 and defines the lateral blood inlet 108. In some such applications, a coupling 41 (e.g., a tubular coupling) extends distally from the pump outlet tube and is coupled to the distal bearing housing to secure the distal end of the pump outlet tube. In some applications, the intermediate portion 123 of the distal bearing housing defines a ridged or threaded outer surface to which the pump outlet tubing coupling 41 is bonded (e.g., with an adhesive). In some applications, the outer surface is ridged to enhance the bond between the distal bearing housing and the pump outlet tubing coupling 41. In some applications, the outer surface is threaded to enhance the bond between the distal bearing housing and the pump outlet tubing coupling 41 and to facilitate application of an adhesive between the outer surface and the pump outlet tubing coupling 41, as described in more detail below with reference to FIG. 12B. In some applications, the distal portion 121 of the distal bearing housing is configured to reinforce the area of ​​the distal tip element 107 into which the distal end of the shaft 92 is inserted (e.g., the axial shaft receiving tube 126 or a portion thereof). Typically, the distal tip element 107 is bonded (e.g., with an adhesive) to the outer surface of the distal portion 121 of the distal bearing housing. In some applications, at least a portion of the outer surface of the distal portion 121 of the distal bearing housing is formed with elongated ridges and / or threads to enhance the connection between the distal tip element 107 and the distal bearing housing.

[0103] As mentioned above, the axial shaft 92 is radially stabilized via the proximal radial bearing 116 and the distal radial bearing 118. In turn, as mentioned above, the axial shaft passes through the lumen 62 defined by the impeller, radially stabilizing the impeller against the inner surface of the frame 34 and the lining 39, so that even a relatively small gap (such as that described above) between the outer edge of the impeller blades and the lining 39 is maintained during rotation of the impeller. Typically, the impeller itself is not located directly within either the radial or thrust bearings. Rather, the bearings 116 and 118 function as radial bearings for the axial shaft. Typically, the pump head 27 (and more generally the ventricular assist device 20) does not include a thrust bearing configured to be disposed within a subject and to counter the thrust generated by the rotation of the impeller. In some applications, one or more thrust bearings are located outside the object (e.g., in motor unit 23 shown in Figures 1A and 7A-7C), and opposition to thrust generated by rotation of the impeller is provided solely by the one or more thrust bearings located outside the object. In some applications, mechanical and / or magnetic elements are configured to maintain the impeller within a given range of axial positions. For example, a magnet (e.g., magnet 82 described below with reference to Figure 7A) located at a proximal end of the drive cable (e.g., outside the object) can be configured to impart axial motion to the impeller and / or maintain the impeller within a given range of axial positions.

[0104] Reference is now made to Figures 6A and 6B, which are schematic illustrations of the ventricular assist device 20 at various stages of a motion cycle of the ventricular assist device's impeller 50 relative to the ventricular assist device's frame 34, according to some applications of the present invention. In some applications, while the impeller rotates to pump blood through the tube 24, the axial shaft 92 (to which the impeller is fixed) is driven to move in an axial back and forth motion, thereby moving the impeller axially back and forth within the frame 34, as will be described in more detail below with reference to Figure 7A. Alternatively or additionally, the impeller and axial shaft are configured to move axially back and forth within the frame 34 in response to forces acting on the impeller, without the need to actively drive the axial shaft to move in an axial back and forth motion. Typically, over the course of a subject's cardiac cycle, the pressure difference between the left ventricle and the aorta varies from approximately zero during ventricular systole (hereinafter "systole") to a relatively large pressure difference (e.g., 50-70 mmHg) during ventricular diastole (hereinafter "diastole"). In some applications, due to the greater pressure differential for impeller delivery during diastole (and due to the stretchability of the drive cable 130), the impeller during diastole is pushed distally relative to the frame 34 compared to the position of the impeller relative to the frame 34 during systole. Since the impeller is connected to the axial shaft, the axial shaft then moves forward. During systole, the impeller (and axial shaft) returns to its systolic position. In this manner, the axial back and forth motion of the impeller and axial shaft is generated passively, i.e., without the need for active actuation of the axial shaft and impeller to produce this motion. Figures 6A and 6B show the impeller and axial shaft disposed at various positions within the frame 34 during the axial back and forth motion cycle described above.

[0105] In some applications, by moving in an axial back and forth motion, the portion of the axial shaft that is in contact with the proximal and distal bearings 116, 118 constantly changes. In some such applications, other things being equal, the frictional force exerted by the bearings on the axial shaft in this manner is spread over a larger area of ​​the axial shaft than if the axial shaft did not move relative to the bearings, thereby reducing wear on the axial shaft. Alternatively or additionally, by moving in a back and forth motion relative to the bearings, the axial shaft clears residue, such as blood residue, at the interface between the axial shaft and the bearings.

[0106] In some applications, at the impeller's most proximal position during the motion cycle, the proximal end of the impeller is disposed in the proximal cone section of the frame 34, as shown in FIG. 6A. In some applications, at the impeller's most distal position during the motion cycle, the distal end of the impeller is disposed in the distal end of the cylindrical section of the frame 34. Alternatively, at the impeller's most distal position during the motion cycle, the distal end of the impeller is disposed proximal to the distal end of the cylindrical section of the frame 34, as shown in FIG. 6B. Typically, during the course of the entire cardiac cycle, the section of the impeller that has the greatest span of the impeller is disposed within the cylindrical portion of the frame 34. However, the proximal portion of the impeller is typically disposed within the proximal cone section of the frame during at least a portion of the cardiac cycle.

[0107] Referring again to Figures 6A and 6B, the distal tip element 107 is typically a single integrated element including both the axial shaft receiving tube 126 and the distal tip 120. Typically, the axial shaft receiving tube is configured to receive the distal portion of the pump head axial shaft 92 during axial back and forth movement of the axial shaft (described in more detail below) and / or during delivery of the ventricular assist device. (Typically, during delivery of the ventricular assist device, the frame is maintained in a radially constrained configuration, so that the orientation of the axial shaft relative to the frame is in a different position than the orientation relative to the frame during operation of the ventricular assist device.) In some applications, the distal tip 120 is configured to be soft so that it does not injure the target tissue (e.g., tissue of the left ventricle) even when it contacts the tissue. For example, the distal tip 120 or the entire distal tip element can be made of silicone, polyethylene terephthalate (PET), and / or polyether block amide (e.g., PEBAX®). In some applications, the distal tip defines a lumen 122 therethrough. In some such applications, when the ventricular assist device is inserted into the left ventricle, the guidewire 10 (FIG. 1B) is first inserted into the left ventricle, for example, according to known techniques. The distal tip of the ventricular assist device is then guided into the left ventricle by advancing the distal tip over the guidewire with the guidewire positioned within lumen 122. In some applications, a duckbill valve 390 (or a different type of hemostatic valve) is disposed at the distal end of lumen 122 of the distal tip 120.

[0108] Typically, a delivery catheter 143 is placed over the impeller 50 and frame 34 to maintain the impeller and frame in a radially constrained configuration when the ventricular assist device is inserted into the subject's ventricle. In some applications, as shown in FIG. 1B, the distal tip element 107 extends distally from the delivery catheter when the delivery catheter is inserted into the subject's ventricle. In some applications, near the proximal end of the distal tip element, the distal tip element has a protrusion 110. Referring to FIG. 5B (showing the pump head portion disposed within the delivery catheter 143), in some applications, when the ventricular assist device is inserted into the subject's ventricle, the delivery catheter extends proximal to the protrusion such that the delivery catheter and the protrusion form a smooth continuous surface. The distal side of the protrusion 110 is tapered so that the vasculature is exposed to a tapered diameter change but not to an edge caused by an abrupt change in diameter at the interface between the delivery catheter and the distal tip element.

[0109] In some applications, the distal tip element 107 defines an overall curvature similar to that of a question mark or tennis racquet, defining a straight proximal portion and a bulge on one side of a longitudinal axis of the straight proximal portion. Typically, as described above, the ventricular assist device is introduced into the subject's ventricle over a guidewire. The distal tip 120 defines a lumen 122 such that the distal tip is maintained in a straight configuration during introduction of the ventricular assist device into the subject's ventricle (e.g., as shown in the left frame of FIG. 1B). In some applications, the distal tip is configured to assume a curved shape when the guidewire is removed.

[0110] 6A-6B, in some applications, the axial shaft receiving tube 126 extends proximally from the distal tip 120 of the distal tip element 107. As described above, the axial shaft typically undergoes axial back and forth motion during operation of the impeller 50. The axial shaft receiving tube 126 defines a lumen 127 configured to receive the axial shaft when the axial shaft extends beyond the distal bearing portion 118. In some applications, the axial shaft receiving tube defines a stopper 128 at a distal end configured to prevent the axial shaft from advancing beyond the stopper. In some applications, the stopper includes a rigid component inserted (e.g., embedded) into the distal end of the shaft receiving tube. Alternatively (not shown), the stopper includes a shoulder between the lumen 127 of the axial shaft receiving tube and the lumen 122 of the distal tip 120.

[0111] Typically, during normal operation of the impeller, even when the drive cable 130 (shown in FIG. 5A ) is maximally extended (e.g., during diastole), the axial shaft does not contact the stopper 128. However, when the delivery catheter is advanced over the impeller 50 and frame 34 during retraction of the ventricular assist device 20 from the subject's ventricle, the stopper 128 is configured to prevent the axial shaft from protruding into the tip. In some cases, when the delivery catheter is advanced over the frame and impeller, there is a risk that the drive cable will break. In such a case, if the stopper 128 were not present, the axial shaft could protrude into the tip. Even if the drive cable were to break, the stopper 128 prevents this from happening.

[0112] It should be noted that at the proximal end of the frame 34, the proximal radial bearing 116 also functions as a stop by preventing the coupling element 65 and / or the proximal bushing 64 of the impeller 50 from moving beyond the proximal radial bearing. Typically, the coupling element 65 and the proximal bushing 64 do not contact the proximal radial bearing 116 during normal operation of the impeller. However, the proximal radial bearing 116 is configured to prevent the coupling element 65 and / or the proximal bushing 64 of the impeller 50 from moving proximally from within the frame, for example, when the impeller and frame are held in a radially constrained (i.e., crimped) configuration within the delivery catheter 143. Typically, the coupling element and / or the proximal bushing extends proximally to prevent the central region of the impeller (where the span of the impeller is greatest) from sliding proximally into the proximal cone of the frame 34. For example, during the systole phase of the impeller's motion cycle (as shown in FIG. 6A ), if the impeller slides further proximally beyond a given amount, the coupling element contacts the proximal radial bearing 116, thereby preventing further proximal motion of the impeller. In some applications, the coupling element and / or the proximal bushing extends proximally to have an overall length of more than 1.5 mm, such as an overall length of more than 4 mm. In some applications (not shown), another stop element is located on the axial shaft proximal to the coupling element and / or the proximal bushing 64. Typically, the stop is configured as described for the coupling element. That is, if the impeller slides further proximally beyond a given amount, the stop element contacts the proximal radial bearing 116, thereby preventing further proximal motion of the impeller.

[0113] Typically, during operation of the ventricular assist device and throughout the impeller's axial back and forth cycle, the impeller is located relatively close to the distal tip. For example, throughout the impeller's axial back and forth cycle, the distance of the impeller to the distal tip can be within the most distal 50 percent of tube 24, such as within the most distal 30 percent (or the most distal 20 percent).

[0114] Reference is now made to Figures 6C and 6D, which are schematic illustrations of a ventricular assist device including a motion dampening spring 68, according to some applications of the present invention. As will be described in more detail below, typically, during operation of the ventricular assist device (i.e., when the impeller is rotating), the impeller moves back and forth axially. In some applications, as the impeller moves back and forth axially, the motion dampening spring is configured to act as a shock absorber to provide motion dampening. Figure 6C illustrates the impeller during the systolic phase of its motion cycle, and Figure 6D illustrates the impeller during the diastolic phase of its motion cycle. As shown, as the impeller moves distally from the systolic position to the diastolic position, the motion dampening spring is further compressed. In some applications, the impeller is configured to be radially constrained (i.e., crimped) by stretching axially, and the motion dampening spring is configured to compress to correspond to the axial stretch of the impeller. Typically, when the impeller is in a radially constrained configuration, upon insertion of the pump head into the left ventricle, the impeller expands axially such that the distal end of the impeller is positioned further distally within the frame 34 and the spring is further compressed relative to the impeller and spring configuration shown in FIG. 6D.

[0115] Typically, the motion damping spring is disposed about the axial shaft 92 between the distal end of the impeller (e.g., the impeller distal bushing 58) and the distal bearing 118. In some applications, the motion damping spring is coupled to the distal bearing 118 or the distal bearing housing 118H and extends proximally on the axial shaft 92 from the distal bearing or the distal bearing housing 118H. Typically, in such cases, the motion damping spring is configured to remain rotationally stationary as the impeller rotates, and the impeller rotates relative to the motion damping spring. Alternatively or additionally, the motion damping spring is coupled to the distal end of the impeller (e.g., the impeller distal bushing 58) and / or extends distally on the axial shaft 92 from the distal end of the impeller (e.g., the impeller distal bushing 58). In some such applications, the motion damping spring is configured to rotate with the impeller. Alternatively, the motion damping spring extends from a radial bearing disposed about the distal end of the impeller (e.g., the impeller's distal bushing 58) such that as the impeller rotates, the motion damping spring remains rotationally stationary while the impeller rotates relative to the motion damping spring.

[0116] In some applications, the motion damping spring is coupled to an elastomeric material 69 (such as polyurethane and / or silicone) such that the elastomeric material covers at least a portion of the axial shaft 92 between the distal end of the impeller and the distal radial bearing. In some applications, coupling an elastomeric material to the spring reduces the risk of the spring causing thrombus and / or hemolysis compared to when the spring is not coupled to an elastomeric material. It is noted that the scope of the present disclosure includes providing a motion damping spring in the absence of an elastomeric material, which may be desirable in some cases.

[0117] 6C and 6D show the spring coated with an elastomeric material that extends between adjacent windings of the spring. Alternatively, the spring is embedded in the elastomeric material. Typically, the elastomeric material is generally similar to the elastomeric material used for the material of the membrane 56 in the impeller 50. More typically, the manner in which the elastomeric material is bonded to the motion damper spring is generally similar to that described above with respect to bonding the elastomeric material membrane to the impeller spring. Typically, the elastomeric material is bonded to the motion damper spring such that it changes shape (e.g., by stretching and compressing) to match the shape changes that occur in the motion damper spring (e.g., when the motion damper spring is stretched and compressed). More typically, the elastomeric material is configured to change shape as described above without breaking or collapsing and without creasing when the spring is compressed.

[0118] As mentioned above, a purge fluid is typically pumped between the outer tube 140 and the outer tube 142. Typically, within the pump head, a portion of the purge fluid flows within a lumen defined in the axial shaft 92 and then exits the axial shaft near the distal bearing 118 to purge the interface between the axial shaft and the distal bearing. In some applications, the purge system is configured such that the purge fluid flows proximally from the distal bearing along the interface between the axial shaft and the elastomeric material. In this manner, the interface between the axial shaft and the elastomeric material is purged and / or lubricated.

[0119] In some applications (not shown), a proximal motion damping spring is disposed proximal to the impeller. In some such applications, the proximal motion damping spring is disposed around the axial shaft 92 between the proximal end of the impeller (e.g., the impeller's proximal bushing 64) and the proximal bearing 116. In some applications, the proximal motion damping spring is coupled to the proximal bearing 116 or the proximal bearing housing 116H and extends distally on the axial shaft 92 from the proximal bearing or the proximal bearing housing. Typically, in such cases, the proximal motion damping spring remains rotationally stationary as the impeller rotates, and the impeller is configured to rotate relative to the motion damping spring. Alternatively or additionally, the proximal motion damping spring is coupled to the proximal end of the impeller (e.g., the impeller's proximal bushing 64) and / or extends distally on the axial shaft 92 from the proximal end of the impeller (e.g., the impeller's proximal bushing 64). In some such applications, the motion damping spring is configured to rotate with the impeller, or the motion damping spring extends from a radial bearing disposed about a proximal end of the impeller (e.g., impeller proximal bushing 64) such that as the impeller rotates, the motion damping spring remains rotationally stationary while the impeller rotates relative to the motion damping spring.

[0120] In some applications, the pump head includes both a proximal motion damping spring (located proximal to the impeller) and a distal motion damping spring located distal to the impeller, such that axial movement of the impeller in the distal or proximal direction is damped by these motion damping springs.

[0121] Reference is now made to FIG. 7A, which is a schematic illustration of an exploded view of the motor unit 23 of the ventricular assist device 20, according to some applications of the present invention. In some applications, the computer processor 25 of the control console 21 (FIG. 1A), which controls the rotation of the impeller 50, is also configured to control the back and forth motion of the axial shaft. In some applications, both types of motion are generated using the motor unit 23. The scope of the present invention includes controlling the back and forth motion at any frequency. In some applications, an indicator of the subject's cardiac cycle is detected (e.g., by detecting the subject's ECG) and the back and forth motion of the axial shaft is synchronized to the subject's cardiac cycle.

[0122] Typically, the motor unit 23 includes a motor 74 configured to impart rotational motion to the impeller 50 via a drive cable 130. As described in more detail below, typically, the motor is magnetically coupled to the drive cable. In some applications, an axial motion driver 76 is configured to drive the motor to move in an axial back and forth motion, as indicated by double-headed arrow 79. Typically, the motor is magnetically coupled to the drive cable, such that the motor imparts back and forth motion to the drive cable, which in turn imparts this motion to the impeller. As described above and below, in some applications, the drive cable, impeller, and / or axial shaft passively undergo axial back and forth motion, for example, due to cyclic changes in the pressure gradient against which the impeller pumps blood. Typically, in such applications, the motor unit 23 does not include an axial motion driver 76.

[0123] In some applications, the magnetic coupling of the motor to the drive cable is as shown in FIG. 7A. As shown in FIG. 7A, a drive magnet set 77 is coupled to the motor via a drive magnet housing 78. In some applications, the drive magnet housing includes a ring 81 (e.g., a steel ring) and the drive magnets are bonded to the inner surface of the ring. In some applications, a spacer 85 is bonded to the inner surface of the ring 81 between the two drive magnets as shown. A driven magnet 82 is positioned between the drive magnets such that the drive magnet and the driven magnet axially overlap. The driven magnet is coupled to a pin 131 that extends beyond the distal end of the driven magnet 82 and is coupled to a proximal end of the drive cable 130. For example, the driven magnet can be cylindrical and define a hole therethrough, and the pin 131 can be bonded to the inner surface of the driven magnet that defines the hole. In some applications, the driven magnet is cylindrical and includes a north pole and a south pole that are separated from one another along the length of the cylinder along a line 83 that bisects the cylinder as shown. In some applications, the driven magnet is housed within a cylindrical housing 87. Typically, pin 131 defines a guidewire lumen 133.

[0124] It is noted that in the application shown in Figure 7A, the drive magnet is disposed outside the driven magnet. However, the scope of the present application includes, mutatis mutandis, reversing the configuration of the drive magnet and driven magnet. For example, the proximal end of the drive cable may be coupled to two or more driven magnets disposed about the drive magnet such that the drive magnets axially overlap.

[0125] As mentioned above, a purge system 29 (shown in FIG. 1A) is typically used in conjunction with the ventricular assist device 20. The motor unit 23 typically includes an inlet 86 and an outlet 88 for use with the purge system. In some applications, purge fluid is continuously or periodically pumped into the ventricular assist device via inlet 86 and pumped out of the ventricular assist device via outlet 88.

[0126] Typically, the magnet 82 and pin 131 are held in an axially fixed position within the motor unit 23. Typically, the proximal end of the drive cable is coupled to and held in an axially fixed position by the pin 131. Typically, the drive cable 130 extends from the pin 131 to the axial shaft 92, thereby at least partially fixing the axial position of the axial shaft, and thus the impeller 50. In some applications, the drive cable is somewhat stretchable. For example, the drive cable may be made of a stretchable coiled wire. The drive cable typically allows the axial shaft (and thus the impeller) to assume a range of axial positions (by virtue of the drive cable being stretchable somewhat), but limits the axial movement of the axial shaft and impeller to a particular range of motion (by virtue of the drive cable's proximal end being held in an axially fixed position and the drive cable's limited stretchability).

[0127] As mentioned above, in some applications, the impeller 50 and axial shaft 92 are configured to move axially back and forth within the frame 34 in response to forces acting on the impeller, without the need to actively drive the axial shaft to move in a back and forth axial motion. Typically, over the course of a subject's cardiac cycle, the pressure difference between the left ventricle and the aorta varies from near zero during systole to a relatively large pressure difference during diastole (e.g., 50-70 mmHg). In some applications, because of the large pressure difference for impeller delivery during diastole (and because the drive cable is stretchable), the impeller is pushed distally relative to the frame 34 during diastole, compared to the position of the impeller relative to the frame 34 during systole. The axial shaft then moves forward due to the impeller being connected to the axial shaft. During systole, the impeller (and axial shaft) return to the systolic position. In this manner, the axial back and forth motion of the impeller and axial shaft is passively generated, i.e., generated without the need to actively drive the axial shaft and impeller to produce this motion.

[0128] Reference is now made to Figures 7B and 7C, which are schematic diagrams of the motor unit 23 according to some applications of the present invention. In general, the motor unit 23 shown in Figures 7B and 7C is similar to that shown in Figure 7A, and unless otherwise noted, the motor unit 23 shown in Figures 7B and 7C includes similar components as the motor unit 23 shown in Figure 7A. In some applications, the motor unit includes a heat sink 90 configured to dissipate heat generated by the motor. Alternatively or additionally, the motor unit includes a ventilation port 93 configured to facilitate dissipation of heat generated by the motor. In some applications, the motor unit includes vibration damping portions 94 and 96 configured to damp vibrations of the motor unit caused by rotational and / or axial back and forth movements of components of the ventricular assist device.

[0129] Reference is now made to FIG. 8A, which is a graph showing the experimentally measured variation in the length of the drive cable of a ventricular assist device as the pressure gradient through which the impeller of the ventricular assist device varies. Using the impeller and drive cable described herein, a glycerin-based solution having similar properties to blood (such as density and viscosity) was pumped through a chamber designed to replicate the left ventricle and aorta. The pressure gradient through which the impeller pumped was varied in a pulsatile manner that represents the pulsation of the pressure gradient through which the impeller normally pumps blood from the left ventricle to the aorta. At the same time, the movement of the drive cable was imaged and the change in the length of the drive cable was determined by analysis of the images. The graph shown in FIG. 8A shows the measured change in the length of the drive cable as a function of the pressure gradient. As shown in FIG. 8A, as the pressure gradient through which the impeller pumped increased, the drive cable became increasingly stretched. 8A represents, and as discussed above, the impeller typically moves back and forth relative to frame 34 in response to changes in the pressure gradient against which it is pumping (e.g., the pressure difference between the left ventricle and the aorta). The movement of the impeller then causes drive cable 130 to stretch more or less.

[0130] In some applications, during operation of the ventricular assist device, the computer processor 25 of the control console 21 (FIG. 1A) is configured to measure an indication of the tension in the drive cable 130 and / or an indication of the pressure exerted on the impeller (which is indicative of the pressure difference between the left ventricle and the aorta) by measuring an indication of the tension in the drive cable 130 and / or the axial movement of the drive cable. In some applications, based on the measured indications, the computer processor detects an event in the subject's cardiac cycle, determines the subject's left ventricular pressure, and / or determines the subject's cardiac afterload. In some applications, the computer processor controls the rotation of the impeller and / or the corresponding back and forth axial movement of the axial shaft.

[0131] Referring again to FIG. 7A, in some applications, the ventricular assist device 20 includes a sensor 84. For example, the sensor may include a magnetometer (e.g., a Hall sensor) located in the motor unit 23 as shown in FIG. 7A. (Sometimes, the sensor 84 is referred to as a magnetometer 84.) In some applications, the axial back and forth motion of the impeller generates a measurable back and forth motion of the inner driven magnet 82 relative to the outer driving magnet(s) 77 because the driven magnet is held in place relative to the driving magnet by a magnetic coupling, not a rigid mechanical coupling. Note that the axial motion of the magnet is typically substantially less than the axial motion of the impeller because the full range of motion of the impeller is not transmitted along the length of the drive cable (which is typically somewhat extensible). In some applications, the magnetometer measures the change in the magnetic field generated by one of the magnets to measure the axial motion of the drive cable 130 and, in turn, determine the pressure at which the impeller pumps. For example, the inner driven magnet 82 may be axially longer than the outer driving magnet 77. Because the inner magnet is longer than the outer magnet, there are magnetic field lines that do not extend from the inner magnet to the outer magnet. As the drive cable moves axially and then the inner magnet moves axially, the magnetic flux generated by these field lines varies as measured by the magnetometer. In operation, the motor 74 rotates and generates an AC signal at the magnetometer, typically having a frequency of 200 Hz to 800 Hz. Typically, as the tension in the drive cable changes with the subject's cardiac cycle, this generates a low frequency envelope in the signal measured by the magnetometer, typically having a frequency of 0.5 to 2 Hz. In some applications, a computer processor measures the low frequency envelope and derives the subject's cardiac cycle from the measured envelope.

[0132] In some applications, the magnetometer measurement is first calibrated so that the change in magnetic flux per unit change in pressure at which the impeller pumps (i.e., per unit change in pressure difference between the left ventricle and the aorta, or per unit change in pressure gradient) is known. It is known that in most subjects, the left ventricular pressure is equal to the aortic pressure during systole. Thus, in some applications, the subject's aortic pressure is measured and then the subject's left ventricular pressure at a given time is calculated. This calculation is performed by a computer processor based on (a) the measured aortic pressure and (b) the difference between the magnetic flux measured by the magnetometer at that time and the magnetic flux measured by the magnetometer during systole (where the pressure in the left ventricle is assumed to be equal to the pressure in the aorta). For example, the subject's aortic pressure may be measured by measuring the pressure in the channel 224 defined by the delivery catheter 143, as described in more detail below. In some applications, the techniques described above may be used to determine alternative or additional physiological parameters. For example, events in the subject's cardiac cycle and / or the subject's cardiac afterload may be determined.

[0133] In some applications, techniques generally similar to those described in the paragraph above are used, but instead of or in addition to utilizing magnetometer measurements, different parameters are measured to determine left ventricular blood pressure (and / or different physiological parameters, such as events in the subject's cardiac cycle and / or the subject's cardiac afterload) at a given time. For example, there is typically a relationship between the amount of power (and / or current) required to power an impeller rotation at a given rotational speed and the pressure differential that the impeller generates. (Note that part of the pressure difference generated by the impeller is used to overcome the pressure gradient against which the impeller is pumping, and part of the pressure difference generated by the impeller is used to actively pump blood from the left ventricle to the aorta by generating a positive pressure difference between the left ventricle and the aorta. Furthermore, the relationship between the above factors typically varies over the course of the cardiac cycle.) In some applications, a calibration measurement is performed so that the relationship between (a) the power (and / or current) consumption by the motor required to rotate the impeller at a given rotational speed and (b) the pressure difference generated by the impeller is known. In some applications, the subject's aortic pressure is measured and then the subject's left ventricular pressure at a given time is calculated. This calculation is performed by a computer processor based on (a) the measured aortic pressure, (b) the power (and / or current) consumption by the motor required to rotate the impeller at a given rotational speed at that time, and (c) a predetermined relationship between the power (and / or current) consumption by the motor required to rotate the impeller at a given rotational speed and the pressure difference generated by the impeller. In some applications, the above techniques are performed while maintaining the rotational speed of the impeller at a constant speed. Alternatively or additionally, the rotational speed of the impeller is varied and the variation in the rotational speed of the impeller is taken into account in the above calculation. In some applications, the above techniques are used to determine alternative or additional physiological parameters. For example, events in the subject's cardiac cycle and / or the subject's cardiac afterload can be determined.

[0134] Typically, the tube 24 has a known cross-sectional area (when the tube is open for blood flow therethrough). In some applications, the flow rate through the tube 24 generated by the impeller is determined based on the determined pressure differential generated by the impeller and the known cross-sectional area of ​​the tube. In some applications, such flow rate calculations incorporate calibration parameters to account for factors such as flow resistance inherent to the ventricular assist device (or type of ventricular assist device) for which the calculation is performed. In some applications, a ventricular pressure-volume loop is derived based on the determined ventricular pressure.

[0135] Referring again to FIG. 7A, in some applications, in addition to the magnetometer 84 configured to measure the magnetic flux density generated by the driven magnet, a second magnetometer 84A (e.g., a second Hall sensor) measures an indication of the magnetic flux density generated by the drive magnet. In some applications, the second magnetometer measures the magnetic flux density of the motor. The motor directly drives the drive magnet to rotate, so the magnetic flux density of the motor is indicative of the magnetic flux density period of the drive magnet. Typically, as the impeller rotates to pump blood, a torque is generated on the impeller. More typically, the magnitude of the torque depends on various parameters, such as the flow generated by the impeller, the rotational speed of the impeller, and / or the pressure gradient through which the impeller is pumping. In some applications, the torque generated on the impeller generates a measurable torque on the inner driven magnet 82 relative to the outer drive magnet 77. This is because the driven magnet is held in place relative to the drive magnet by a magnetic coupling rather than a rigid mechanical coupling. Typically, the torque generated at the driven magnet is substantially less than that generated at the impeller because the torque generated at the impeller is not transmitted along the length of the drive cable, however, typically the torque generated at the impeller is at least partially transmitted to the driven magnet via the drive cable.

[0136] The torque transmitted to the driven magnet typically generates a phase difference between the signal measured by magnetometer 84 (which measures the magnetic flux density of the driven magnet) and the signal measured by second magnetometer 84A (which measures the magnetic flux density of the motor and / or the driving magnet). In some applications, as the torque of the impeller varies, this varies the phase difference between the signal measured by magnetometer 84 and the signal measured by second magnetometer 84A. In some applications, a computer processor detects the variation in the phase difference and determines a physiological parameter of the subject at least in part accordingly. For example, based at least in part on the variation in the phase difference, the computer processor can determine a difference between the subject's left ventricular pressure and the subject's aortic pressure, the subject's left ventricular pressure, events in the subject's cardiac cycle, the subject's cardiac afterload, and / or different physiological parameters. In some applications, the techniques described in this paragraph are used as an alternative to the above-mentioned techniques that use magnetic flux density measurements and / or power consumption measurements to determine a physiological parameter. Alternatively, two or more of these techniques are used in combination with each other. For example, a physiological parameter of the subject may be determined based on a mathematical model incorporating two or more measurements, and / or one of these techniques may be used to validate an estimation of a physiological parameter of the subject made using another of the techniques.

[0137] Reference is now made to Figures 8B and 8C, which are graphs demonstrating the correlation between the phase difference signal and the pressure gradient through which impeller 50 pumps, in accordance with some applications of the present invention.

[0138] The graph shown in FIG. 8B shows the results of an experiment in which the ventricular assist device described herein was used to pump blood against each pressure gradient in a static in vitro system (i.e., the pressure gradient was constant when each measurement was taken). A linear regression model was used to estimate the pressure gradient at which the impeller pumped based on a combination of the phase difference signal, the flux amplitude signal, and the current consumed by the motor. The graph shown in FIG. 8B shows the estimated pressure gradient versus the measured pressure gradient. As shown, the linear regression model incorporating the phase difference measurement provides a reliable method for estimating the pressure gradient at which the impeller pumps.

[0139] The graph shown in FIG. 8C shows the results of an experiment in which the ventricular assist device described herein was used to pump blood against each pressure gradient in a pulsed in vitro system (i.e., the pressure gradient was varied in a pulsatile manner). A space state model was used to estimate the pressure gradient at which the impeller would pump based on a combination of the phase difference signal, the flux amplitude signal, and the current consumed by the motor. The graph shown in FIG. 8C shows the estimated pressure gradient superimposed on the measured pressure gradient. As shown, the space state model incorporating the phase difference measurement provides a reliable method for estimating the pressure gradient at which the impeller would pump.

[0140] In accordance with the above, and in accordance with some applications of the present invention, a magnetic phase difference between one or more non-driven magnets and one or more driven magnets is measured, and a physiological parameter of the subject is determined at least in part in response thereto. For example, based at least in part on the variation of the phase difference, a computer processor can determine a difference between the subject's left ventricular pressure and the subject's aortic pressure, the subject's left ventricular pressure, events in the subject's cardiac cycle, the subject's cardiac afterload, and / or different physiological parameters. In some applications, the physiological parameter is determined based on the phase difference measurement in combination with one or more additional measurements, such as, for example, a magnetic flux amplitude measurement, the power consumed by the motor, and / or the current consumed by the motor. Typically, such measurements are combined into a mathematical model, such as a linear regression model and / or a space state model.

[0141] Reference is now made to Figures 9A and 9B, which are schematic illustrations of a ventricular assist device including one or more blood pressure measuring tubes 222 and / or fibers 228, in accordance with some applications of the present invention.

[0142] 9A is a schematic diagram of a ventricular assist device including one or more blood pressure measurement tubes 222, according to some applications of the invention. As described above, the ventricular assist device typically includes a pump outlet tube 24 that traverses the subject's aortic valve such that a proximal end of the tube is disposed within the subject's aorta and a distal end of the tube is disposed within the subject's left ventricle. Typically, a blood pump (typically including an impeller 50) is disposed within the tube 24 within the subject's left ventricle and configured to pump blood from the left ventricle through the tube 24 to the subject's aorta. In some applications, the ventricular blood pressure measurement tube 222 is configured to extend to at least the outer surface 213 of the tube 24 such that an opening 214 at the distal end of the blood pressure measurement tube is in direct fluid communication with the patient's blood flow outside the tube 24. Typically, the opening 214 is configured to be proximal to the blood pump (e.g., proximal to the impeller 50) within the subject's left ventricle. Pressure sensor 216 (shown diagrammatically in FIG. 1A) measures the pressure of blood in the ventricular blood pressure measurement tube. Typically, by measuring the pressure of blood in the left ventricular blood pressure measurement tube, the pressure sensor measures the subject's blood pressure outside tube 24 (i.e., left ventricular blood pressure). Typically, blood pressure measurement tube 222 extends from outside the subject's body to an opening 214 at the distal end of the tube, and pressure sensor 216 is positioned near the proximal end of the tube, e.g., outside the subject's body. In some applications, computer processor 25 (FIG. 1A) receives an indication of the measured blood pressure and controls the pumping of blood by the impeller in response to the measured blood pressure.

[0143] In some applications, the ventricular assist device includes two or more such ventricular blood pressure measurement tubes 222, as shown, for example, in FIG. 9A. In some applications, based on the blood pressure measured within each of the left ventricular blood pressure measurement tubes, the computer processor 25 determines whether an opening of one of the two or more ventricular blood pressure measurement tubes is blocked. This may occur, for example, by the opening contacting the wall of the interventricular septum and / or a portion within a different ventricle. Typically, in response to determining that an opening of one of the two or more ventricular blood pressure measurement tubes is blocked, the computer processor determines the left ventricular pressure of the subject based on the blood pressure measured within a different one of the two or more ventricular blood pressure measurement tubes.

[0144] In some applications, outer tube 142 defines a groove 215 in a portion of its outer surface that is configured to be disposed within tube 24. Typically, when the ventricular assist device is inserted into the subject's body, the portion of ventricular blood pressure measurement tubing 222 that extends from within tube 24 to at least the outer surface of tube 24 is configured to be disposed within the groove such that this portion of the ventricular blood pressure measurement tubing does not protrude beyond the outer surface of the outer tube.

[0145] In some applications (not shown), the distal portion of the blood pressure measurement tubing 222 is disposed outside of the pump outlet tubing 24. For example, the blood pressure measurement tubing 222 can extend from the outer tube 142 to the proximal end of the pump outlet tubing 24 and then be assembled to the exterior surface of the pump outlet tubing 24. This is shown, for example, in Figure 16D of U.S. Patent No. 10,881,770 to Tuval, which is incorporated herein by reference.

[0146] As mentioned above, in some applications, the drive cable 130 extends from the motor outside the subject to the axial shaft 92 on which the impeller 50 is disposed. Typically, the drive cable is disposed within the first outer tube 140 and the second outer tube 142, as described above. In some applications, the proximal portion of the blood pressure measurement tube 222 includes a channel between the first outer tube 140 and the second outer tube 142, as shown in the cross-sectional view of FIG. 9A. It should be understood that in this regard, the blood pressure measurement tube represents a continuous lumen extending from the pressure sensor 216 to the outside of the pump outlet tube 24 in the left ventricle of the subject, regardless of whether the structure of the lumen changes along its length. As described above, typically, a purge fluid is also delivered between the outer tube 140 and the outer tube 142, and in some applications, the purge fluid is delivered via the channel 226. Typically, as shown in FIGURE 9A, the blood pressure measurement tubing 222 occupies a larger proportion of the cross-sectional area defined between the outer tube 140 and the outer tube 142 than the purge fluid channel 226. For example, the ratio of (a) the cross-sectional area defined between the outer tube 140 and the outer tube 142 occupied by the blood pressure measurement tubing to (b) the cross-sectional area defined between the outer tube 140 and the outer tube 142 occupied by the purge fluid channel 226 is typically greater than 3:2, greater than 3:1, or greater than 5:1. In some applications, the blood pressure measurement tubing occupies a relatively large proportion of the cross-sectional area defined between the outer tube 140 and the outer tube 142 to communicate blood pressure outside the pump outlet tubing 24 within the subject's left ventricle proximally to the pressure sensor 216.

[0147] 9B, in some applications, the optical fiber 228 is configured to extend to at least the outer surface 213 of the tube 24 such that a distal end 230 of the optical fiber is directly exposed to the patient's blood stream outside of the tube 24. Typically, the optical fiber extends from a proximal end of the fiber (e.g., within the motor unit 23) that is external to the subject to the distal end 230. More typically, a light source and a light detector (not shown) are disposed at the proximal end of the optical fiber and configured to detect blood pressure at the distal end of the optical fiber by directing light through the optical fiber and detecting reflected light.

[0148] Typically, distal end 230 of optical fiber 228 is configured to be proximal to a blood pump (e.g., proximal to impeller 50) within the subject's left ventricle. Typically, the pressure sensor measures the subject's blood pressure outside tube 24 (i.e., left ventricular blood pressure) by measuring the pressure of blood at distal end 230 of optical fiber 228. In some applications, computer processor 25 (FIG. 1A) receives an indication of the measured blood pressure and controls the pumping of blood by the impeller in response to the measured blood pressure.

[0149] In some applications, the ventricular assist device includes two or more such optical fibers 228, for example as shown in FIG. 9B. In some applications, based on the blood pressure measured using each of the optical fibers, the computer processor 25 determines whether the distal end of one of the optical fibers is not exposed to left ventricular blood flow. This may occur, for example, by the distal end of one of the optical fibers contacting the wall of the interventricular septum and / or a portion within a different ventricle. Typically, in response to determining that the distal end of one of the optical fibers is not exposed to left ventricular blood flow, the computer processor determines the left ventricular pressure of the subject based on the blood pressure measured using different ones of the two or more optical fibers 228.

[0150] In some applications, the optical fiber is disposed within the outer tube 142 along the length thereof. Typically, at the distal end of the outer tube, the optical fiber is coupled to the proximal cone 36 of the frame 34 such that the optical fiber extends radially to the outer surface of the pump outlet tube 24. For example, as shown in FIG. 9B, the optical fiber can be sutured or tied to the proximal cone of the frame 34 using a coupling element 232 (e.g., a thread). In some applications (not shown), the distal portion of the optical fiber 228 is disposed outside the pump outlet tube 24. For example (not shown), the optical fiber 228 can extend from the outer tube 142 to the proximal end of the pump outlet tube 24 and then be coupled to the outer surface of the pump outlet tube 24.

[0151] With reference to both the blood pressure measuring tube 222 and the optical fiber 228, it should be noted that the distal end of this tube or fiber is typically in direct fluid communication with the subject's left ventricular blood flow at a location proximal to the most proximal portion of the blood inlet(s) 108 (e.g., at least 1 cm or at least 1.5 cm proximal to the most proximal portion of the blood inlet(s) 108). Thus, the pressure of the blood exposed to the distal end of the tube or fiber typically reflects the blood pressure of the left ventricle itself and is not affected by pressure fluctuations generated near the blood inlet as a result of fluid flow dynamics occurring at the blood inlet.

[0152] In accordance with the techniques described above, the computer processor 25 is typically configured to determine parameters related to pressure and flow in the left ventricle of the subject, for example using any one of the techniques described herein for determining flow through a ventricular assist device in combination with any one of the techniques described herein for determining left ventricular pressure. In some applications, using the parameters described above, the computer processor is configured to estimate the subject's intrinsic cardiac output (i.e., stroke volume), total cardiac output, arterial compliance, and / or peripheral resistance. In some applications, the parameters described above are determined using a mathematical model that represents the aorta and / or left ventricle as a dynamic vasculature.

[0153] For example, according to the Windkessel model of the aorta, the relationship between flow and pressure within the aorta can be described by the following equation:

[0154]

number

[0155] where p(t) and Q(t) are the instantaneous arterial pressure and flow rate, respectively, and the variables C and Z C , R are the aortic compliance, characteristic impedance, and peripheral resistance, respectively.

[0156] During operation of the ventricular assist device 20, Equation 1 can be rewritten as follows:

[0157]

number

[0158] where n, p represent the contributions of the native heart function and the ventricular assist device function to flow and aortic pressure, respectively.

[0159] In some applications, in a first step, the vascular parameters of interest (C, Z C , R). To do this, the speed at which the impeller is rotated is varied during one or more vascular parameter determination periods. Typically, the one or more vascular parameter determination periods last for a small number of cardiac cycles (e.g., 1-10 or 2-6 cardiac cycles) or only during the diastole of a small number of cardiac cycles (e.g., 1-10 or 2-6 cardiac cycles). During the one or more vascular parameter determination periods, the parameter of interest is assumed to remain substantially unchanged. (Alternatively, changes in the vascular parameter of interest caused by changes in the speed at which the impeller is rotated are accounted for using a mathematical model that models such changes.)

[0160] For two operating conditions of the ventricular assist device (i.e., when the impeller is operating at a normal operating speed and when the impeller is rotating at a speed that is varied during one or more vascular parameter determination periods), Equation 2 can be rewritten as Equations 3 and 4. The notations 1 and 2 in the subscripts represent the first and second operating conditions.

[0161]

number

[0162] By subtracting Equation 4 from Equation 3, the effect of the ventricular assist device on the vasculature can be characterized as in Equation 5.

[0163]

number

[0164] According to the above-mentioned technique, the computer processor 25 is typically configured to determine the parameters related to the pressure and flow of the left ventricle of the subject, for example, using any one of the techniques described herein for determining flow through the ventricular assist device in combination with any one of the techniques described herein for determining left ventricular pressure. Thus, only the vascular parameters (aortic compliance, characteristic impedance, and peripheral resistance) are unknown. Typically, the known values ​​of the parameters related to the pressure and flow of the left ventricle of the subject are used to estimate the vascular parameters (aortic compliance, characteristic impedance, and peripheral resistance) of the subject, for example, by using a model identification technique (such as linear regression).

[0165] In some applications, after estimating the subject's vascular parameters, parameters related to the subject's left ventricular pressure and flow (which are typically determined in real time using the sensors described herein), as well as the subject's vascular parameters (which are determined by varying the speed at which the impeller rotates as described above), are used to estimate total cardiac output and the subject's intrinsic cardiac output based on Equation 3.

[0166] In some applications, techniques generally similar to those described above are used, but with a different mathematical model representing the subject's dynamic vasculature (e.g., the subject's aorta and / or the subject's left ventricle) to determine, for example, vascular parameters, intrinsic cardiac output, and / or alternative or additional physiological parameters. Typically, the mathematical model is of the same type as the Windkessel model, in that it considers the shape of the aortic waveform in terms of the interaction between stroke volume and aortic compliance.

[0167] In general, the scope of the present application includes a method, comprising: a) determining one or more pressure-related and / or flow-related parameters (e.g., aortic pressure in the subject, left ventricular pressure in the subject, and / or flow through a ventricular assist device) using one or more of the sensing devices and methods described herein; b) varying the speed at which the impeller rotates during one or more vascular parameter determination periods; c) applying a mathematical model representing the subject's dynamic vascular system (e.g., the subject's aorta and / or the subject's left ventricle) to two operating conditions of the ventricular assist device (i.e., when the impeller is operating at a normal operating speed and when the impeller is rotating at a speed that is varied during one or more vascular parameter determination periods); d) estimating vascular parameters of interest (e.g., aortic compliance, characteristic impedance, and peripheral resistance) based on the difference between the mathematical models at each of the two operating conditions of the ventricular assist device and the known pressure-related and / or flow-related parameters; e) Estimating the subject's intrinsic cardiac output and / or additional cardiac parameters based on the known pressure-related and / or flow-related parameters and the subject's estimated vascular parameters (e.g., aortic compliance, characteristic impedance, and peripheral resistance).

[0168] More generally, the above steps can be summarized as follows: a) pumping blood from the subject's left ventricle to the subject's aorta using a percutaneous left ventricular assist device; b) sensing one or more pressure-related and / or flow-related parameters using a percutaneous left ventricular assist device (e.g., using the devices and methods for sensing described herein); c) varying the rate at which blood is pumped by the percutaneous left ventricular assist device during one or more vascular parameter determination periods and applying a mathematical model representing the dynamic vasculature of the subject when the percutaneous left ventricular assist device is pumping blood at each rate; d) estimating vascular parameters of interest based on the difference between the applied mathematical models when the percutaneous left ventricular assist device is pumping blood at each rate and based on the pressure-related parameters and / or the flow-related parameters; e) estimating the subject's intrinsic cardiac output and / or additional cardiac parameters based on the pressure-related and / or flow-related parameters and the estimated vascular parameters of the subject.

[0169] The above steps are typically repeated as many times as necessary during operation of the ventricular assist device.

[0170] Reference is now made to Figures 10A and 10B, which are schematic illustrations of a ventricular assist device 20 including a liner 39 lining the inside of a frame 34 housing an impeller 50, according to some applications of the present invention. In some applications, the liner 39 is disposed on the inside of the frame 34 to provide a smooth inner surface (e.g., a smooth inner surface having a substantially circular cross-sectional shape) over which blood is pumped by the impeller. By providing a smooth surface, the coating material typically reduces hemolysis caused by pumping of blood by the impeller, as compared to when blood is pumped between the impeller and the struts of the frame 34. In some applications, the liner includes polyurethane, polyester, and / or silicone. Alternatively or additionally, the liner includes polyethylene terephthalate (PET) and / or polyether block amide (e.g., PEBAX®).

[0171] Typically, the liner is disposed on at least a portion of the inner surface of the central cylindrical portion 38 of the frame 34. In some applications, the pump outlet tube 24 also covers the central cylindrical portion 38 of the frame 34 on the outside of the frame, such that the pump outlet tube 24 and the liner 39 overlap over at least 50 percent of the length of the liner, such as the entire length of the cylindrical portion of the frame 34 as shown in FIG. 10A. In some applications, the pump outlet tube 24 and the liner 39 only overlap partially, such as shown in FIG. 10B. For example, the pump outlet tube 24 overlaps the liner over less than 50 percent (e.g., less than 25 percent) of the length of the liner. In some such applications, when the ventricular assist device 20 is inserted into a subject, the impeller is advanced distally within the frame 34 such that there is no longitudinal position where the impeller, pump outlet tube 24, frame 34, and liner 39 all overlap one another such that the impeller is not disposed within the overlap area of ​​the pump outlet tube and the liner. As shown in Figures 10A and 10B, in some applications, the distal end of the pump outlet tube and / or liner defines a single axially oriented blood inlet 108. Alternatively, the liner is disposed on at least a portion of the inner surface of the central cylindrical portion 38 of the frame 34, and the pump outlet tube extends to the distal end of the frame to define multiple lateral blood inlets 108. Such applications are described in more detail below, for example with reference to Figures 11A-11E.

[0172] Typically, in the overlap area of ​​the lining 39 and the pump outlet tube 24, the lining is shaped to provide a smooth surface (e.g., to reduce hemolysis, as discussed above), and the pump outlet tube 24 is shaped to match the struts of the frame 34 (e.g., as shown in cross section in FIG. 10A). More typically, the lining has a substantially circular cross section (e.g., due to the relatively small cells in the central cylindrical portion of the frame, as discussed above with reference to FIG. 2). In some applications, in the overlap area of ​​the lining 39 and the pump outlet tube 24, the pump outlet tube and the lining are bonded to one another, for example, by vacuum, by adhesive, and / or using a thermoforming procedure.

[0173] In some applications, the liner 39 and the pump outlet tube 24 are made of different materials. For example, the liner can be made of polyurethane and the pump outlet tube can be made of polyether block amide (PEBAX®). Typically, in such applications, the material from which the liner is made has a higher thermoforming temperature than the material from which the pump outlet tube is made. Alternatively, the liner 39 and the pump outlet tube 24 are made of the same material. For example, both the liner and the pump outlet tube can be made of polyurethane or polyether block amide (PEBAX®).

[0174] In some applications, the pump outlet tube and the liner are bonded to each other and / or to the frame as follows: In some applications, the liner is bonded directly to the inner surface of the frame, and then the pump outlet tube is bonded to the outside of the frame. Note that by directly bonding the liner to the inner surface of the frame (rather than simply bonding the liner to the pump outlet tube, thereby sandwiching the frame between the liner and the pump outlet tube), air bubbles, folds, and other interruptions to the surface smoothness provided by the liner are typically avoided. In some applications, the bond between the liner and the inner surface of the frame is strengthened using techniques similar to those described above for strengthening the bond between the elastomeric membrane of the impeller and the helical elongated element. In some applications, the frame is first treated to strengthen the bond between the liner and the inner surface of the frame. In some applications, the treatment of the frame includes subjecting the frame (e.g., to the inner surface of the frame) to a plasma treatment, immersing the frame in a bonding agent (e.g., a silane solution) having at least two functional groups configured to bond to each of the materials from which the frame and the liner are made, and / or immersing the frame in a solution containing the material from which the liner is made (e.g., a polyurethane solution). In some applications, the liner is made of an elastomeric material (e.g., polyurethane) and the bonding agent is a silane solution, such as a solution of n-(2-aminoethyl)-3-aminopropyltrimethoxysilane, that contains a first functional group (e.g., (OH)) configured to bond with the frame (typically made of an alloy such as Nitinol) and a second functional group (e.g., (NH)) configured to bond with the elastomeric material.

[0175] In some applications, the central cylindrical portion of the frame is then sprayed with a solution (e.g., a polyurethane solution) containing the material from which the liner will be made. Once the inner surface of the frame has been treated, the liner is bonded to the inner surface of the central cylindrical portion of the frame (e.g., to the inner surface of the central cylindrical portion of the frame). Typically, the liner (having the shape of a tube) is placed on a mandrel, the frame is placed over the liner, and pressure is applied by a heat shrink process. More typically, the assembly of the liner and frame is heated in an oven.

[0176] After bonding the liner to the frame, a portion of the pump outlet tube 24 is placed around the outside of the frame. As mentioned above, in some applications, the liner 39 and the pump outlet tube 24 are made of different materials. For example, the liner may be made of polyurethane and the pump outlet tube may be made of polyether block amide (PEBAX®). Typically, in such applications, the material from which the liner is made has a higher thermoforming temperature than the material from which the pump outlet tube is made. In some applications, the frame is heated to a temperature above the thermoforming temperature of the pump outlet tube 24 but below the thermoforming temperature of the liner 39 to shape the pump outlet tube 24 to match the struts of the frame 34 without distorting the liner.

[0177] Typically, the frame is heated from inside the frame using a mandrel. Typically, while the frame is heated to the above-mentioned temperature, an outer tube (typically made of silicone) applies pressure to the pump outlet tube 24 to push it radially inward to conform to the shape of the struts of the frame, as shown in the cross-sectional view of FIG. 10A. In some applications, the mandrel that is placed inside the lining to heat the lining at this stage is shorter than the length of the lining. The mandrel is typically placed inside the lining such that a margin remains outside the mandrel at each end of the lining. Typically, the lining acts as a shield to protect the pump outlet tube from overheating and being damaged by the heating of the mandrel. Placing the lining over the mandrel as described above prevents the mandrel from coming into direct contact with the frame and / or the pump outlet tube. In some applications, the combination of the frame, the lining, and the portion of the pump outlet tube 24 placed around the frame is then shape-set to the desired shape and dimensions using shape-setting techniques known in the art.

[0178] Reference is now made to Figures 11A-11C, which are schematic illustrations of pump outlet tube 24, or a portion thereof, configured to define a lateral blood inlet 108 at a distal end, according to some applications of the present invention. In some applications, the pump outlet tube extends substantially to the distal end of the distal cone 40 of the frame 34. In such applications, the pump outlet tube typically defines a distally facing distal cone 46, i.e., a distal cone 46 oriented such that the narrow end of the cone is distal to the wide end of the cone. Typically, the pump outlet tube includes a coupling 41 (e.g., a tubular coupling as shown) extending distally from the pump outlet tube. As discussed above, the coupling is coupled to the distal bearing housing to secure the distal end of the pump outlet tube.

[0179] In some applications (not shown), the pump outlet tube defines two to four lateral blood inlets. Typically, in such applications, the blood inlets each define an area of ​​more than 20 square millimeters (e.g., more than 30 square millimeters) and / or less than 60 square millimeters (e.g., less than 50 square millimeters), e.g., 20-60 square millimeters or 30-50 square millimeters. Alternatively or additionally, the outlet tube defines more, smaller blood inlets 108. For example, more than 10 blood inlets, more than 50 blood inlets, more than 100 blood inlets, or more than 150 blood inlets, e.g., 50-100 blood inlets, 100-150 blood inlets, or 150-200 blood inlets. In some applications, the blood inlet is sized to (a) allow blood flow from the subject's left ventricle into the tube, and (b) prevent structures from the subject's left ventricle from entering the frame. Typically, in such applications, the distal cone 46 of the pump outlet tube 24 is configured to reduce the risk of structures from the left ventricle (such as chordae tendineae, trabeculae, and / or papillary muscles) entering the frame 34 and being damaged by the impeller and / or axial shaft, and / or damaging the left ventricular assist device. Thus, in some applications, the blood inlet is shaped such that the width (or span) of the inlet in at least one direction is less than 1 mm, e.g., 0.1-1 mm or 0.3-0.8 mm. By defining such a small width (or span), typically, structures from the left ventricle (such as chordae tendineae, trabeculae, and / or papillary muscles) are prevented from entering the frame 34. In some such applications, each of the blood inlets defines an area of ​​more than 0.05 square millimeters (e.g., more than 0.1 square millimeters) and / or less than 3 square millimeters (e.g., less than 1 square millimeter), e.g., an area of ​​between 0.05 and 3 square millimeters or between 0.1 and 1 square millimeters. Alternatively, each of the blood inlets defines an area of ​​more than 0.1 square millimeters (e.g., more than 0.3 square millimeters) and / or less than 5 square millimeters (e.g., less than 1 square millimeter), e.g., an area of ​​between 0.1 and 5 square millimeters or between 0.3 and 1 square millimeters.

[0180] Typically, the portion of the pump outlet tube that defines the blood inlet has a porosity of more than 40 percent, such as more than 50 percent, or even more than 60 percent (porosity being defined as the percentage of the area of ​​this portion that is permeable to blood flow). Thus, on the one hand, the blood inlet is relatively small (to prevent structures from the left ventricle from penetrating the frame), but on the other hand, the porosity of the portion of the pump outlet tube that defines the blood inlet is relatively high, to allow sufficient blood flow into the pump outlet tube.

[0181] In some applications, each blood inlet has a circular or polygonal shape. In some applications, as shown in Figures 11A-11D, each blood inlet has a hexagonal shape. Typically, openings having a hexagonal shape are used to allow the portion of the pump outlet tube that defines the blood inlets to have a relatively high porosity (e.g., as described above) while still providing sufficient material between the blood inlets in the portion of the pump outlet tube that defines the blood inlets to prevent tearing and / or stretching of the material. As shown in Figure 11B, in some applications, the width W of the gap between adjacent hexagonal (or other polygonal) holes is greater than 0.01 mm (e.g., greater than 0.04 mm) and / or less than 0.1 mm (e.g., less than 0.08 mm), e.g., 0.01-0.1 mm or 0.04-0.08 mm. In some applications, the distance D between each opposite side of the hexagon (or other type of polygon) is greater than 0.2 mm (e.g., greater than 0.4 mm) and / or less than 0.8 mm (e.g., less than 0.6 mm), e.g., 0.2-0.8 mm or 0.4-0.6 mm. As shown in FIG. 11B, typically each polygon encircles a circle (such that structures that cannot pass through a circle cannot pass through the polygon). Typically, the diameter of the circle enclosed by the polygon is equal to the distance D, e.g., greater than 0.2 mm (e.g., greater than 0.4 mm) and / or less than 0.8 mm (e.g., less than 0.6 mm), e.g., 0.2-0.8 mm or 0.4-0.6 mm.

[0182] FIG. 11D shows a portion of the distal cone 46 of the pump outlet tube 24 according to some applications of the invention. In the view shown in FIG. 11D, the portion is flattened out for illustration purposes. As shown in FIG. 11D, in some applications, the width W1 of the gap between the hexagonal (or other type of polygonal) holes in the proximal region 46P of the distal cone 46 of the pump outlet tube 24 is greater than the width W of the gap between the hexagonal (or other type of polygonal) holes in the distal region 46D of the distal cone 46 of the pump outlet tube. In some applications, the ratio of the width of the gap between adjacent blood inlets in the proximal region of the distal part of the pump outlet tube to the width of the gap between adjacent blood inlets in the distal region of the distal part of the pump outlet tube is greater than 3:2, for example, between 3:2 and 5:2. Typically, in such applications, the distance D1 between each opposing side of the hexagon (or other type of polygon) in the proximal region 46P of the distal cone 46 of the pump outlet tubing 24 is less than the distance D between each opposing side of the hexagon (or other type of polygon) in the distal region 46D of the distal cone 46 of the pump outlet tubing. (As noted above, typically, the distances D and D1 also represent the diameter of a circle enclosed by a polygon of the respective size.) In some applications, the ratio of the diameter of a circle enclosed by each blood inlet in the distal region of the distal portion of the pump outlet tubing to the diameter of a circle enclosed by each blood inlet in the proximal region of the distal portion of the pump outlet tubing is greater than 7:6, e.g., between 7:6 and 4:3. More typically, in the distal region 46D, the distal cone of the pump outlet tubing 24 has a higher porosity than in the proximal region 46P of the distal cone 46 of the pump outlet tubing. For example, the ratio of porosity in distal region 46D to porosity in proximal region 46P is greater than 4:3, or greater than 3:2. In some applications, the length that the proximal region extends is greater than 0.5 mm and / or less than 2 mm (e.g., less than 1.5 mm), such as between 0.5 and 2 mm or between 0.5 and 1.5 mm. In some applications, the total length of the distal cone is greater than 6 mm and / or less than 12 mm (e.g., less than 10 mm), such as between 6 and 12 mm or between 6 and 10 mm.

[0183] As described above with reference to Figures 9A-9B, the pump outlet tube is typically bonded to the frame 34 by heating. In some applications, the blood inlet holes have wider gaps and / or smaller blood inlet holes and / or less porosity in the proximal region 46P of the distal cone 46 of the pump outlet tube 24 than in the distal region 46D. This is to prevent and / or reduce damage (e.g., tearing, thinning, and / or stretching) that may occur to the material defining the blood inlet holes during the heating process described above. In some applications, differences in the size of the gaps between the blood inlets in the distal region 46D and the proximal region 46P and / or the size and / or porosity of the blood inlets themselves are reduced or eliminated as a result of using the heating process described above.

[0184] Typically, the gap width W between the hexagonal (or other type of polygonal) holes in the distal region 46D of the distal cone 46 of the pump outlet tube, and the distance D between each opposite side of the hexagon (or other type of polygonal) holes in the distal region 46D of the distal cone 46 of the pump outlet tube, are as described above. In some applications, the gap width W1 between adjacent hexagonal (or other type of polygonal) holes in the proximal region 46P of the distal cone 46 of the pump outlet tube 24 is greater than 0.05 mm (e.g., greater than 0.07 mm) and / or less than 0.2 mm (e.g., less than 0.15 mm), e.g., between 0.05 and 0.2 mm or between 0.07 and 0.15 mm. In some applications, the distance D1 between each opposing side of the hexagon (or other type of polygon) within the proximal region 46P of the distal cone 46 of the pump outlet tube 24 is greater than 0.1 mm (e.g., greater than 0.3 mm) and / or less than 0.6 mm (e.g., less than 0.5 mm), for example, between 0.1 and 0.6 mm or between 0.3 and 0.5 mm.

[0185] The scope of the present disclosure includes having lateral blood inlets of non-uniform size and / or shape (e.g., circular, rectangular, polygonal, and / or hexagonal lateral blood inlets) arranged in any arrangement along the distal cone 46 of the pump outlet tube. Similarly, the scope of the present disclosure includes the distal cone 46 of the pump outlet tube defining lateral blood inlets arranged to have varying non-uniform porosity in different regions of the distal cone. In some applications, the shape and / or size of the lateral blood inlets and / or the porosity of the distal cone vary to accommodate different blood flow dynamics in different regions of the distal cone. Alternatively or additionally, the shape and / or size of the lateral blood inlets and / or the porosity of the distal cone vary to accommodate changes in shape along the length of the distal cone.

[0186] Reference is now made to FIG. 11E, which is an enlarged schematic diagram of the interface between the distal end of the pump outlet tube 24 and the distal tip element 107. Typically, the pump outlet tube includes a coupling 41 (e.g., a tubular coupling as shown) extending distally from the pump outlet tube. As discussed above, the coupling is coupled to the distal bearing housing 118H to secure the distal end of the pump outlet tube. As further discussed above, typically, the pump outlet tube is coupled to the outside of the central cylindrical portion of the frame. In some applications, the distal cone 46 of the pump outlet tube is not itself coupled to the distal cone 40 of the frame. By coupling the coupling 41 to the distal bearing housing 118H and coupling the pump outlet tube to the outside of the central cylindrical portion of the frame, the distal cone 46 of the pump outlet tube is held in place relative to the distal cone 40 of the frame. Alternatively, the distal cone 46 of the pump outlet tube is directly coupled (e.g., by heat shrinking) to the distal cone 40 of the frame.

[0187] As described above, in some applications, the coupling 41 is coupled to the outer surface of the portion 123 of the distal bearing housing 118H. In some applications, the coupling 41 defines a hole 111 (near the distal end of the coupling), as shown in FIG. 11E. In some applications, the adhesive is applied between the coupling 41 and the outer surface of the portion 123 of the distal bearing housing 118H through the hole. In some applications, the outer surface of the portion 123 of the distal bearing housing 118H is threaded. Typically, the threaded outer surface allows the adhesive to spread gradually and evenly between the coupling 41 and the outer surface of the portion 123 of the distal bearing housing 118H. More typically, the coupling is transparent so that the spreading of the adhesive can be seen through the coupling. Thus, in some applications, the application of the adhesive is terminated once the adhesive has sufficiently spread between the coupling 41 and the outer surface of the portion 123 of the distal bearing housing 118H (once the outer surface of the portion 123 is covered with adhesive).

[0188] Reference is now made to Figures 12A, 12B, and 12C, which are schematic illustrations of a drive cable 130 of a ventricular assist device 20 according to some applications of the present invention. Typically, the rotational motion of the motor is transmitted to the axial shaft via a drive cable. Typically, the drive cable extends from the motor unit 23, which is typically located outside the subject, to the proximal end of the axial shaft 92 (the connection between the distal end of the drive cable and the proximal end of the axial shaft is shown, for example, in one of the close-ups of Figure 5A). In some applications, the drive cable includes multiple wires 134 arranged in a coiled configuration to provide the drive cable with sufficient strength and flexibility to maintain a portion of the cable within the aortic arch as the cable rotates and moves in an axial back and forth motion. In some applications, the drive cable includes multiple coaxial layers of coiled wires. For example, as shown in Figures 12A-12C, the drive cable includes an outer layer 136 and an inner layer 138, which are mutually coaxial and each include a coiled wire.

[0189] The drive cable is typically disposed within a first outer tube 140 configured to remain stationary while the drive cable undergoes rotational and / or back and forth axial movement. The first outer tube is configured to effectively act as a drive cable bearing tube along the length of the drive cable. For this reason, the first outer tube is also referred to herein as a drive cable bearing tube. Drive cable bearing tubes are described in more detail below with reference to FIG. 12D. In some applications, the drive cable bearing tube is disposed within a second outer tube 142. The second outer tube 142 is typically made of a more flexible material (e.g., nylon and / or polyether block amide) than the drive cable bearing tube and is typically thicker than the drive cable bearing tube.

[0190] Typically, the impeller 50 and frame 34 are maintained in a radially constrained configuration by the delivery catheter 143 when the impeller and frame are inserted into the left ventricle. As described above, the delivery catheter is retracted to place the impeller and frame in a radially unconstrained configuration. In some applications, as shown in FIG. 12A, the delivery catheter remains in the subject's aorta and the outer tube 142 is disposed within the delivery catheter during operation of the left ventricular device. (Although FIG. 12A shows the distal end of the delivery catheter disposed in the aortic arch, in some applications the distal end of the delivery catheter is disposed in the descending aorta during operation of the left ventricular device.) In some applications, a channel 224 is defined between the delivery catheter 143 and the outer tube 142 during operation of the left ventricular device. (Note that for illustrative purposes, the channel as shown in FIG. 12A is not to scale.) In some such applications, the aortic blood pressure of the subject is measured by measuring the pressure of blood in the channel 224. For example, pressure sensor 216 (shown diagrammatically in FIG. 1A) may be in fluid communication with channel 224 and configured to measure the subject's aortic pressure by measuring the pressure of blood in channel 224. Typically, to retract the left ventricular device from the subject, a delivery catheter is advanced over the impeller and frame such that the impeller and frame assume a radially constrained configuration. The catheter is then withdrawn from the subject.

[0191] Reference is now made to FIG. 12D, which is a schematic diagram of a first outer tube 140 that functions as a drive cable bearing tube according to some applications of the present invention. In some applications, the drive cable bearing tube includes an outer layer 141 and an inner layer 144, each typically made of a biocompatible polymeric material, and a coil 153 embedded between the outer and inner layers. In some applications, the outer layer 141 is made of Pebax, the inner layer 144 is made of PTFE and / or polyimide (e.g., a mixture of PTFE and / or polyimide), and the coil is made of an alloy such as stainless steel. Typically, the inner layer includes a material configured to provide low friction and high wear resistance. More typically, the outer layer is configured to provide additional strength to the drive cable bearing tube, while still providing the drive cable bearing tube with sufficient flexibility to be able to conform to the curvature of, for example, the aortic arch. Typically, the coil is configured to maintain a substantially circular cross-section of the drive cable bearing tube, even in areas where the drive cable bearing tube is highly curved (e.g., in the aortic arch). Typically, in the absence of a coil, the drive cable bearing tube will tend to flatten in such areas forming an elliptical cross section.

[0192] Reference is now made to Figure 13, which is a schematic illustration of a ventricular assist device with guidewire 10 disposed within guidewire lumen 122, according to some applications of the present invention. In some such embodiments, when inserting the ventricular assist device into the left ventricle, guidewire 10 is first inserted into the left ventricle, for example according to known techniques. With the guidewire disposed within lumen 122, the distal tip of the ventricular assist device is then advanced over the guidewire such that the distal tip is guided into the left ventricle. In some applications, a duckbill valve 390 (or a different type of hemostasis valve) is disposed at the distal end of lumen 122 of distal tip 120.

[0193] Reference is now made to Figures 14A and 14B, which are schematic illustrations of a guidewire 10 configured to have two states, in accordance with some applications of the present invention. As described with reference to Figure 13, typically, the distal end of a ventricular assist device is guided over the guidewire 10 into the left ventricle. Typically, it is desirable for the tip of the guidewire to be flexible to avoid damage to the subject's vasculature and / or left ventricle when advancing the guidewire through the subject's vasculature and when the tip of the guidewire is positioned within the subject's left ventricle.

[0194] After guiding the distal end of the ventricular assist device into the left ventricle, the delivery catheter is retracted, typically causing the impeller 50 and frame 34 of the ventricular assist device to assume a radially unconstrained configuration, thereby deploying the impeller and frame. Typically, at this stage, the tip of the guidewire is retracted proximally through the distal tip 120 and proximally from the pump section. In some cases, after retracting the guidewire as described above, it may be desirable to reinsert the guidewire through the distal tip 120 and out of the duckbill valve 160 located near the distal end of the distal tip. For example, this may be desirable if the pump section has moved out of position and needs to be repositioned within the left ventricle. However, if the tip of the guidewire is flexible (as described above), it is not possible to advance the tip of the guidewire through the narrow tip of the proximally facing duckbill valve 160. Thus, in some applications, the guidewire is configured such that the tip can define two states: a flexible state and a rigid state.

[0195] In some applications, the guidewire 10 includes an outer coil 250 and an inner stiffening wire 252. When the distal end of the guidewire must be in a flexible state, the inner stiffening wire is retracted from the distal end of the guidewire so that there is no stiffening wire disposed within the distal portion of the outer coil. In some applications, the guidewire is releasably fixed in this state to prevent the distal end of the guidewire from becoming rigid and damaging the vasculature and / or left ventricle of the subject. For example, as shown in FIG. 14A, in some applications, one or more fixation elements 254 extend radially from the proximal portion of the stiffening wire and protrude between the windings of the outer coil to prevent the stiffening wire from advancing. In some applications, the proximal end 256 of the outer coil has a larger gap between the coil windings than the more distal portion of the outer coil, so that the fixation elements protrude between the windings of the outer coil at the proximal end. In some applications, to convert the distal end of the guidewire to a rigid state, the fixation element 254 is pushed radially inwardly into the outer coil and the stiffening wire is advanced distally so that it is also disposed within the outer coil at the distal end of the guidewire. In some applications, the fixation element remains disposed within the outer coil as the stiffening wire is advanced distally because the portion of the outer coil where the fixation element is then disposed has windings that are sufficiently close to one another to prevent the fixation element from protruding between the windings.

[0196] Reference is now made to FIG. 15, which is a schematic diagram of a ventricular assist device 20 including a distal thrust bearing 260, according to some applications of the invention. Typically, the bearing 260 functions as both a distal radial bearing and a distal thrust bearing. The top view of the ventricular device shown in FIG. 15 shows the device in a radially constrained (i.e., crimped) configuration, and the bottom view shows the device in a radially unconstrained configuration, with the arrows indicating movement of parts of the device between the two configurations. Some applications of the invention have been described above as directed to a ventricular assist device that does not include a thrust bearing disposed within a subject, and that is configured to allow axial back and forth movement of the impeller 50 and axial shaft 92. In some alternative embodiments, the ventricular assist device includes a thrust bearing configured to prevent axial movement of the axial shaft 92 in response to (and typically prevents axial movement of) the impeller in response to (and typically prevents axial movement of) the impeller in response to) variations in the pressure gradient against which the impeller pumps.

[0197] In some applications, the thrust bearing 260 is disposed within the frame 34 as shown. For example, the thrust bearing may be disposed within a cylindrical portion of the frame or within a distal conical portion of the frame. In some applications, at the distal end of the axial shaft, the axial shaft defines a widened portion 262 configured to engage the thrust bearing and prevent axial movement of the axial shaft (and thereby the impeller). (Furthermore, the widened portion of the axial shaft is radially constrained by the bearing 260 such that the bearing also functions as a distal radial bearing.) Typically, the thrust bearing is coupled to the frame via a connecting strut 264 that extends radially inward from the frame to the thrust bearing. Typically, to manufacture the frame 34, the frame is cut from a tube of a shape memory alloy, such as Nitinol. In some applications, the connecting struts 264 are cut from the tube from which the frame is cut such that the frame and connecting struts form a single, integral element, and there is no need to bond them to each other (e.g., by adhesive, welding, etc.). Generally, in some applications, the frame and connecting struts are cut from a single piece of material to form a single, integral element. In some applications, the connecting struts 264 and the thrust bearing 260 themselves are cut from the tube from which the frame is cut such that the frame, connecting struts, and thrust bearing form a single, integral element, and there is no need to bond them to each other (e.g., by adhesive, welding, etc.). Generally, in some applications, the frame, connecting struts, and thrust bearing 260 themselves are cut from a single piece of material to form a single, integral element.

[0198] In some applications, a spring generally similar to the motion damping spring 68 (shown in FIGS. 6C-6D) is used in combination with the thrust bearing 260 (or a thrust bearing of a different design located distal to the impeller). In some applications, the spring helps stabilize the impeller (e.g., the distal end of the impeller) relative to the thrust bearing after the impeller expands radially. Thus, the spring functions as an impeller stabilization spring. In some applications, the impeller is configured to be radially constrained (i.e., compressed) by axial expansion, and the spring is configured to compress to accommodate the axial expansion of the impeller. Typically, when the impeller is in a radially constrained configuration during insertion of the pump head into the left ventricle, the impeller expands axially such that the distal end of the impeller is located distally within the frame 34 and the impeller stabilization spring is compressed to accommodate the movement of the distal end of the impeller.

[0199] Typically, the impeller stabilization spring is disposed about the axial shaft 92 between a distal end of the impeller (e.g., the impeller distal bushing 58) and the thrust bearing 260. In some applications, the impeller stabilization spring is coupled to the thrust bearing 260 and extends proximally on the axial shaft 92 from the thrust bearing 260. Typically, in such cases, the impeller stabilization spring is configured to remain rotationally stationary as the impeller rotates, and the impeller rotates relative to the impeller stabilization spring. Alternatively or additionally, the impeller stabilization spring is coupled to a distal end of the impeller (e.g., the impeller distal bushing 58) and / or extends distally on the axial shaft 92 from the distal end of the impeller (e.g., the impeller distal bushing 58). In some such applications, the impeller stabilization spring is configured to rotate with the impeller. Alternatively, the impeller stabilization spring extends from a radial bearing disposed about the distal end of the impeller (e.g., the impeller distal bushing 58) such that the impeller stabilization spring remains rotationally stationary as the impeller rotates, and the impeller is configured to rotate relative to the impeller stabilization spring. In some applications, the impeller stabilization spring is coupled to (e.g., coated with or embedded within) an elastomeric material 69 (also shown in Figures 6C-6D), with the elastomeric material / spring combination typically being formed and functioning generally similarly as described above with reference to the motion damping spring 68.

[0200] In some applications, an impeller stabilization spring is disposed about the axial shaft proximal to the impeller, e.g., as described above with reference to Figures 6C-6D. In some applications, an impeller stabilization spring is disposed about the axial shaft both proximal and distal to the impeller. In some applications, the combination of proximal and distal impeller stabilization springs disposed about the axial shaft functions to hold the impeller in place axially and / or limit axial movement of the impeller when the pump head is expanded.

[0201] In some applications, the thrust bearing 260 is used in combination with a pump outlet tube 24 configured as shown in and described with reference to Figures 11A-11E. The pump outlet tube defines a lateral blood inlet 108 at its distal end. As described above, in some applications, the blood inlet is sized to (a) allow blood flow from the subject's left ventricle into the tube, and (b) prevent structures from the subject's left ventricle from entering the frame. Typically, in such applications, the distal cone 46 of the pump outlet tube 24 is configured to reduce the risk that structures from the left ventricle (such as chordae tendineae, trabeculae, and / or papillary muscles) will enter the frame 34 and be damaged by the impeller and / or axial shaft, and / or cause damage to the left ventricular assist device. In such applications, the dimensions and other characteristics of the pump outlet tube and blood inlet are typically generally as described with reference to Figures 11A-11E.

[0202] When the thrust bearing 260 is disposed within the frame 34, as shown in FIG. 15, the axial shaft 92 does not extend to the distal end of the frame 34. In a radially unconstrained configuration of the frame, as shown in FIG. 5, for example, the distal end of the axial shaft is disposed within the cylindrical portion of the frame, which is typically proximal to the blood inlet of the ventricular assist device. In some such applications, even if left ventricular structures (such as chordae tendineae, trabeculae, and / or papillary muscles) enter the frame via the blood inlet, the axial shaft terminating proximally to the blood inlet reduces or prevents damage to the axial shaft or other portions of the ventricular assist device. In some such applications, even if left ventricular structures (such as chordae tendineae, trabeculae, and / or papillary muscles) enter the frame via the blood inlet, the axial shaft terminating proximally to the blood inlet reduces or prevents damage to such structures.

[0203] Reference is now made to Figures 16A, 16B, 16C, and 16D, which are schematic illustrations of a package 270 for packaging a ventricular assist device 20, according to some applications of the present invention. Typically, the package 270 is packaged within a sealed outer wrapping 272 to enhance sterility of the package. The package 270 is typically shaped to define a pump head chamber 274 within which the pump head (e.g., impeller 50 and frame 34) of the ventricular assist device is packaged. In some applications, a catheter fixture 276 is reversibly coupled to the package 270. The catheter fixture is shaped to define a hole 278. As part of the process of packaging the ventricular assist device within the package 270, the catheter fixture is coupled to the package with the distal end of the delivery catheter 143 disposed within the hole, thereby securing the distal end of the delivery catheter within the hole. In some applications, the pump head chamber defines a vertical projection 280 around which distal tip 120 is positioned to secure the distal end of the pump head within the pump head chamber.

[0204] In some applications, to unpack and prepare the ventricular assist device for use, the top cover 271 of the package is removed to expose the pump head chamber 274. In some applications, the pump head chamber is then filled with a solution 282, such as saline, as shown in FIG. 16B. The pump head is then retracted into the distal end of the delivery catheter 143 to radially constrain the pump head, as shown in the transition from FIG. 16B to FIG. 16D. In some applications, the catheter fixture is configured to secure the distal end of the delivery catheter to the downwardly sloping surface 284 such that the distal end of the catheter is in a downwardly sloping orientation. This typically reduces the likelihood of air bubbles being introduced into the distal end of the delivery catheter as the pump head is retracted into the distal end of the delivery catheter, as compared to when the distal end of the catheter is positioned in a horizontal orientation.

[0205] With respect to all the embodiments of the ventricular assist device 20 described with reference to Figures 1A-15, it should be noted that although Figures 1A and 1B show the ventricular assist device 20 in the left ventricle of a subject, in some applications the ventricular assist device 20 is placed in the right ventricle of a subject across the pulmonary valve of the subject and the techniques described herein are used mutatis mutandis. In some applications, the components of the device 20 are applicable to different types of blood pumps. For example, embodiments of the present invention may be applicable to pumps used to pump blood from the vena cava and / or right atrium to the right ventricle, from the vena cava and / or right atrium to the pulmonary artery, and / or from the renal vein to the vena cava. Such embodiments may include features of the tube 24 (e.g., tube curvature), the impeller 50, features of the pump head 27, the drive cable 130, etc. Alternatively or additionally, the device 20 and / or portions thereof (e.g., the impeller 50 without the tube 24) are placed in different portions of a subject's body to assist in pumping blood from this portion. For example, device 20 and / or portions thereof (e.g., impeller 50 without tube 24) may be placed within a blood vessel and used to pump blood through the blood vessel. In some applications, device 20 and / or portions thereof (e.g., impeller 50 without tube 24) may be configured for placement within a subclavian or jugular vein at the junction of a vein with a lymphatic vessel and used, mutatis mutandis, to increase lymphatic flow from the lymphatic vessel to a vein. Because the scope of the invention includes use of the devices and methods described herein in anatomical locations other than the left ventricle and aorta, the ventricular assist device and / or portions thereof may be referred to herein (and in the claims) as a blood pump.

[0206] The scope of the present invention includes combining any of the devices and methods described herein with any of the devices and methods described in one or more of the following applications, all of which are incorporated herein by reference: International Patent Application PCT / IB2022 / 051990, entitled "Ventricular Assist Device," filed March 7, 2022, by Tuval, which claims priority to: U.S. Provisional Patent Application No. 63 / 158,708, entitled "Ventricular Assist Device," filed on March 9, 2021, by Tuval; and U.S. Provisional Patent Application No. 63 / 254,321, filed on October 11, 2021, by Tuval, entitled "Ventricular Assist Device." International patent application PCT / IB2021 / 052590, entitled "Centrifugal Mixed-Flow Impeller for Use in a Blood Pump," filed March 29, 2021 (published as WO21 / 198881), to Zipory, which claims priority to U.S. Patent No. 63 / 003,955, entitled "Ventricular Assist Device," filed April 2, 2020. U.S. Patent Application Publication No. 17 / 609,589, entitled "Ventricular Assist Device" to Tuval, which is the U.S. national stage of PCT application PCT / IB2021 / 052857 (published as WO21 / 205346), filed April 6, 2021: U.S. Provisional Patent Application No. 63 / 006,122, entitled “Ventricular Assist Device,” by Tuval, filed April 7, 2020; U.S. Provisional Patent Application No. 63 / 114,136, entitled "Ventricular Assist Device," to Tuval, filed November 16, 2020; and U.S. Provisional Patent Application No. 63 / 129,983, filed December 23, 2020, by Tuval, entitled “Ventricular Assist Device.” U.S. Patent Application Publication No. 2020 / 0237981, entitled "Distal Tip Element for Ventricular Assist Device," filed on January 23, 2020, to Tuval, which claims priority to: U.S. Provisional Patent Application No. 62 / 796,138, entitled “Ventricular Assist Device,” by Tuval, filed on January 24, 2019; U.S. Provisional Patent Application No. 62 / 851,716, entitled “Ventricular Assist Device,” by Tuval, filed May 23, 2019; U.S. Provisional Patent Application No. 62 / 870,821, entitled "Ventricular Assist Device," filed July 5, 2019, to Tuval; and U.S. Provisional Patent Application No. 62 / 896,026, filed September 5, 2019, by Tuval, entitled “Ventricular Assist Device.”

[0207] U.S. Patent Application Publication No. 2019 / 0209758 to Tuval, which is a continuation of International Patent Application No. PCT / IB2019 / 050186 (published as WO19 / 138350), entitled "Ventricular Assist Device," filed on January 10, 2019, which claims priority to: U.S. Provisional Patent Application No. 62 / 615,538, entitled “Ventricular Assist Device,” to Sohn, filed on January 10, 2018; U.S. Provisional Patent Application No. 62 / 665,718, entitled “Ventricular Assist Device,” to Sohn, filed May 2, 2018; U.S. Provisional Patent Application No. 62 / 681,868, entitled "Ventricular Assist Device," filed June 7, 2018, to Tuval; and U.S. Provisional Patent Application No. 62 / 727,605, entitled “Ventricular Assist Device,” by Tuval, filed September 6, 2018; Tuval's U.S. Patent Application Publication No. 2019 / 0269840, which is the U.S. national stage of Tuval's International Patent Application No. PCT / IL2017 / 051273 (published as WO18 / 096531), entitled "Blood Pump", filed November 21, 2017, which claims priority to Tuval's U.S. Provisional Patent Application No. 62 / 425,814, filed November 23, 2016; Tuval's U.S. Patent Application Publication No. 2019 / 0175806, which is a continuation of Tuval's International Patent Application No. PCT / IL2017 / 051158 (published as WO18 / 078615), entitled "Ventricular Assist Device," filed on October 23, 2017, which claims priority to Tuval's U.S. Patent Application Publication No. 62 / 412,631, filed on October 25, 2016, and Tuval's U.S. Patent Application Publication No. 62 / 543,540, filed on August 10, 2017; Tuval's U.S. Patent Application Publication No. 2019 / 0239998, which is the U.S. national stage of Tuval's International Patent Application PCT / IL2017 / 051092 (published as WO18 / 061002), entitled "Vascular Tube," filed September 28, 2017, which claims priority to Tuval's U.S. Provisional Patent Application No. 62 / 401,403, filed September 29, 2016; U.S. Patent Application Publication No. 2018 / 0169313 to Schwammenthal, which is the U.S. national stage of International Patent Application No. PCT / IL2016 / 050525 (published as WO16 / 185473), entitled "Blood Pump," filed May 18, 2016, which claims priority to U.S. Provisional Patent Application No. 62 / 162,881, entitled "Blood Pump," filed May 18, 2015, to Schwammenthal; U.S. Patent Application Publication No. 2017 / 0100527 to Schwammenthal, which is the U.S. national stage of International Patent Application No. PCT / IL2015 / 050532 (published as WO15 / 177793), entitled "Blood Pump," filed May 19, 2015, which claims priority to U.S. Provisional Patent Application No. 62 / 000,192, entitled "Blood Pump," filed May 19, 2014, to Schwammenthal; No. 10,039,874 to Schwammenthal, which is the U.S. national stage of International Patent Application No. PCT / IL2014 / 050289 (published as WO14 / 141284), entitled "Kidney Pump," filed March 13, 2014, which claims priority to U.S. Provisional Patent Application No. 61 / 779,803, entitled "Kidney Pump," filed March 13, 2013, and (b) U.S. Provisional Patent Application No. 61 / 914,475, entitled "Kidney Pump," filed December 11, 2013, to Schwammenthal; No. 9,764,113, entitled "Curved Catheter," issued to Tuval on September 19, 2017, which claims priority to U.S. Provisional Patent Application No. 61 / 914,470, entitled "Curved Catheter," filed on December 11, 2013; and No. 9,597,205 to Tuval, which is a U.S. national phase of International Patent Application No. PCT / IL2013 / 050495 (published as WO13 / 183060), entitled "Prosthetic Kidney Valve," filed June 6, 2013, which claims priority to U.S. Provisional Patent Application No. 61 / 656,244, entitled "Prosthetic Kidney Valve," filed June 6, 2012, to Tuval.

[0208] It will be appreciated by those skilled in the art that the present invention is not limited to what has been particularly shown and described above, and the scope of the present invention includes both combinations and subcombinations of the various features described above that would occur to one skilled in the art upon reading the foregoing description, as well as variations and modifications thereof that are not present in the prior art.

Claims

1. 1. A ventricular assist device comprising: an impeller configured to be positioned within a left ventricle of a subject and defining a lumen therein; a frame configured to be disposed around the impeller; a proximal bearing portion disposed at a proximal end of the frame and a distal bearing portion disposed at a distal end of the frame; an axial shaft extending through the proximal bearing, the lumen defined by the impeller, and the distal bearing; a motion damping spring disposed around the axial shaft between a distal end of the impeller and the distal bearing portion, the motion damping spring configured to damp axial motion of the impeller; 1. An apparatus comprising a ventricular assist device comprising:

2. 2. The apparatus of claim 1, wherein the impeller is configured to move axially back and forth while rotating, and the motion damping spring is configured to provide damping against the axial back and forth motion.

3. 2. The apparatus of claim 1, wherein the impeller is configured to be radially constrained by axial expansion, and the motion damper spring is configured to compress to correspond to the axial expansion of the impeller.

4. The device of claim 1 , wherein the motion damping spring is coupled to a distal end of the impeller.

5. 10. The device of claim 1, wherein the ventricular assist device further comprises a proximal motion damping spring disposed around the axial shaft between the proximal end of the impeller and the proximal bearing portion, the motion damping spring configured to damp axial motion of the impeller in a proximal direction.

6. 6. The device of claim 1, wherein the motion damping spring is coupled to the distal bearing portion.

7. The device of claim 6 , further comprising a distal bearing housing disposed around the distal bearing, the motion damping spring being coupled to the distal bearing via the distal bearing housing.

8. 6. The device of claim 1, further comprising an elastomeric material coupled to the motion damping spring, such that at least a portion of the axial shaft between the distal end of the impeller and the distal bearing portion is covered by a combination of the motion damping spring and the elastomeric material.

9. The device of claim 8 , wherein the motion damping spring is coated with the elastomeric material.

10. The device of claim 8 , wherein the motion damping spring is embedded within the elastomeric material.

11. The device of claim 8 , wherein the elastomeric material comprises at least one of silicone and polyurethane.

12. The ventricular assist device delivers a purge fluid into a lumen defined by the axial shaft.

9. The device of claim 8, further comprising a purge system configured to pump fluid through the axial shaft and the combination of the motion damping spring and the elastomeric material such that at least a portion of the purge fluid flows proximally through an interface between the axial shaft and the combination of the motion damping spring and the elastomeric material.

13. 9. The device of claim 8, wherein the elastomeric material is coupled to the motion damper spring such that the elastomeric material changes shape to match changes in shape occurring in the motion damper spring.

14. The device of claim 13 , wherein the elastomeric material is configured to undergo the change in shape without breaking or disintegrating.

15. 14. The device of claim 13, wherein the elastomeric material is configured to prevent the motion damper spring from creasing as a result of being compressed.

16. 6. The apparatus of claim 1, wherein the ventricular assist device further comprises a pump outlet tube configured to traverse the subject's aortic valve, a proximal portion of the pump outlet tube being positioned within the subject's aorta and a distal portion of the pump outlet tube being positioned within the subject's left ventricle, the distal portion of the pump outlet tube extending to the distal end of the frame and defining one or more lateral blood inlets configured to allow blood flow from the subject's left ventricle into the pump outlet tube.

17. 17. The device of claim 16, wherein the porosity of the distal portion of the pump outlet tubing defining the blood inlet is lower in a proximal region of the distal portion of the pump outlet tubing than in a distal region of the distal portion of the pump outlet tubing distal to the proximal region.

18. 17. The device of claim 16, wherein the distal portion of the pump outlet tube has a porosity greater than 40 percent.

19. 17. The device of claim 16, wherein the distal portion of the pump outlet tube defines more than 10 blood inlet openings sized to (a) allow blood flow from the subject's left ventricle into the tube and (b) prevent structures from the subject's left ventricle from entering the frame.

20. 20. The device of claim 19, wherein the distal portion of the pump outlet tube defines more than 50 blood inlet openings sized to (a) allow blood flow from the subject's left ventricle into the tube and (b) prevent structures from the subject's left ventricle from entering the frame.

21. 1. A ventricular assist device comprising: an axial shaft; an impeller disposed on the axial shaft and configured to pump blood; a frame disposed around the impeller; a distal thrust bearing, the distal end of the axial shaft configured to engage the distal thrust bearing to prevent axial movement of the axial shaft in response to variations in the pressure gradient across which the impeller pumps blood; and an impeller stabilization spring disposed about the axial shaft between a distal end of the impeller and the thrust bearing, the impeller stabilization spring configured to stabilize the distal end of the impeller; 1. An apparatus comprising a ventricular assist device comprising:

22. 22. The apparatus of claim 21, wherein the impeller is configured to be radially constrained by axial expansion, and the impeller stabilization spring is configured to compress to accommodate the axial expansion of the impeller.

23. 22. The apparatus of claim 21, wherein the impeller stabilization spring is coupled to a distal end of the impeller.

24. 22. The apparatus of claim 21, wherein the ventricular assist device further comprises a proximal bearing and a proximal impeller stabilization spring disposed about the axial shaft between the proximal end of the impeller and the proximal bearing.

25. 22. The apparatus of claim 21, wherein the impeller stabilization spring is coupled to the thrust bearing.

26. 26. The apparatus of any one of claims 21 to 25, further comprising an elastomeric material coupled to the impeller stabilization spring, such that at least a portion of the axial shaft between the distal end of the impeller and the thrust bearing portion is covered by a combination of the impeller stabilization spring and the elastomeric material.

27. 27. The apparatus of claim 26, wherein the impeller stabilization spring is coated with the elastomeric material.

28. 27. The apparatus of claim 26, wherein the impeller stabilization spring is embedded within the elastomeric material.

29. 27. The device of claim 26, wherein the elastomeric material comprises at least one of silicone and polyurethane.

30. 27. The apparatus of claim 26, wherein the ventricular assist device comprises a purge system configured to direct a purge fluid into a lumen defined by the axial shaft, such that at least a portion of the purge fluid flows proximally through an interface between the axial shaft and the combination of the impeller stabilization spring and the elastomeric material.

31. 27. The apparatus of claim 26, wherein the elastomeric material is coupled to the impeller stabilizer spring such that the elastomeric material changes shape to match changes in shape occurring in the impeller stabilizer spring.

32. 32. The device of claim 31, wherein the elastomeric material is configured to undergo the change in shape without breaking or disintegrating.

33. 32. The apparatus of claim 31, wherein the elastomeric material is configured to prevent the impeller stabilization spring from wrinkling as a result of being compressed.

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