Ventricular assist device

Abstract

To improve the performance of a ventricular assist device.SOLUTION: Apparatus and methods are described including an impeller (50) that includes a proximal bushing (64) and a distal bushing (58). Two or more helical elongate elements (52) extend from the proximal bushing (64) to the distal bushing (58). An axial structure (54) is disposed inside the two or more helical elongate elements (52), and along an axis around which the helical elongate elements (52) are wound. The impeller (50) includes an impeller-overexpansion-prevention element (72). The impeller-overexpansion-prevention element is a single integrated structure that includes a ring (73) disposed around the axial structure (54), and a plurality of elongate elements (67). Each of the elongate elements (67) extends from the ring to a respective helical elongate element (52) and is coupled to each helical elongate element (52) so as to prevent radial expansion of the impeller (50). Other applications are also described.SELECTED DRAWING: Figure 3E

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application is U.S. Provisional Patent Application No. 63 / 006,122, entitled "Ventricular Assist Device," filed April 7, 2020, to Tuval; U.S. Provisional Patent Application No. 63 / 114,136, entitled "Ventricular Assist Device," to Tuval, filed November 16, 2020; and Priority is claimed to U.S. Provisional Patent Application No. 63 / 129,983, filed December 23, 2020, to 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, left ventricular assist devices are applied to failing hearts to assist left ventricular function. In some cases, right ventricular assist devices are used to assist right ventricular function. Such 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 present invention, a blood pump includes an impeller. The impeller includes a proximal bushing, a distal bushing, and two or more helical elongated elements (typically three helical elongated elements) extending from the proximal bushing to the distal bushing. An axial structure (e.g., a cylindrical axial structure such as a spring) is disposed inside the two or more helical elongated elements along an axis around which the helical elongated elements are wound. A film of material is supported between the helical elongated elements and the axial structure, and each of the helical elongated elements to which the film of material is connected defines a blade of the impeller. An impeller over-expansion prevention element is disposed within the impeller. The impeller over-expansion prevention element is a single integrated structure including a ring disposed around the axial structure and a plurality of elongated elements. Each of the elongated elements extends from the ring to each of the helical elongated elements and is coupled to each of the helical elongated elements to prevent radial expansion of the impeller. Typically, the elongate element is configured to not resist compression and is configured to prevent radial expansion of the impeller by applying tension to the helical elongate element.

[0006] In some applications, along at least a portion of the length of the impeller, the film of material forms a continuous U-shaped curve as it transitions from one impeller blade to an adjacent blade, and the U-shaped curvature of the film of material is substantially uninterrupted in its axial configuration. In some applications, when viewed from the distal end of the impeller, the pressure side of each of the impeller blades (i.e., the side configured to push blood during operation of the impeller) is convex in the distal region of the impeller and concave in the proximal region of the impeller. Typically, the pressure side of each of the impeller blades changes to be substantially radially oriented in the region of the elongated element within the impeller blade.

[0007] In some applications, an impeller is manufactured by forming a structure having a first bushing and a second bushing at a proximal end and a distal end, the first and second bushings being interconnected by at least one elongated element. At least partially compressing the structure axially causes the at least one elongated element to radially expand to form at least one helical elongated element. The at least one helical elongated element is coated with a bonding agent, the bonding agent configured to strengthen the bond between the helical elongated element and an elastomeric layer. The coated helical elongated element is then coated with an elastomeric layer. An elastomeric membrane is then bonded to the at least one helical elongated element, such that the at least one helical elongated element with the bonded elastomeric membrane defines a blade of the impeller. For example, the helical elongated element may be dipped in an elastomeric material to create the elastomeric layer. In some applications, the elastic material comprising the elastomeric membrane has an ultimate elongation of greater than 300 percent, a melt flow index of at least 4, and / or a tensile strength of greater than 6000 psi.

[0008] In some applications, the impeller is driven to rotate by one or more drive magnets (which are coupled to a motor) that drive one or more driven magnets to rotate, the driven magnets being coupled to the impeller via a drive cable. According to some applications of the present invention, a magnetic phase difference between one or more driven magnets and one or more drive magnets is measured and a physiological parameter of the subject is determined, at least in part, accordingly. For example, based at least in part on variations in the phase difference, a computer processor can determine the difference between the subject's left ventricular pressure and the subject's aortic pressure, the subject's left ventricular pressure, an event in the subject's cardiac cycle, the subject's cardiac afterload, and / or another physiological parameter. In some applications, the physiological parameter is determined based on combining the phase difference measurement with one or more additional measurements, such as a magnetic flux amplitude measurement, a motor power consumption, and / or a motor current consumption. Typically, such measurements are combined in a mathematical model, such as a linear regression model and / or a state-space model.

[0009] In some applications of the present invention, a subject's arterial pulsation is measured during operation of a ventricular assist device functioning as a blood pump, and parameters are derived from the subject's arterial pulsation. Typically, as the rotational speed of the impeller increases, the flow rate generated by the blood pump also increases. Because blood pumps are typically continuous-flow blood pumps rather than pulsatile blood pumps, the flow rate generated by the blood pump is non-pulsatile. Therefore, as the rotational speed of the impeller increases and the flow rate generated by the blood pump increases, the subject's arterial pulsation typically decreases. In some applications, the subject's arterial pulsation is measured as the rotational speed of the impeller changes. Based on these measurements, a relationship between the arterial pulsation and the impeller rotational speed and / or the pump flow rate is derived. In some applications, the subject's intrinsic cardiac output is derived based on this relationship. In some such applications, the relationship between the subject's arterial pulsation and the pump flow rate is extrapolated to determine what the pump flow rate will be when the subject's arterial pulsation reaches zero. It is hypothesized that at this value, the blood pump replaces the intrinsic function of the heart, and further, that the flow rate generated by the pump at this value approximates the subject's intrinsic cardiac output.

[0010] Thus, according to some applications of the present invention, there is provided an apparatus comprising: 1. A blood pump configured to be placed inside a subject's body, comprising: An impeller, a proximal bushing and a distal bushing; two or more helical elongated elements extending from the proximal bushing to the distal bushing; an axial structure disposed inside the two or more helical elongated elements along an axis around which the helical elongated elements are wound; a film of material supported between the helical elongate element and the axial structure, such that each helical elongate element with an associated film of material defines a respective blade of the impeller; an impeller including an impeller over-expansion prevention element that is a single integrated structure including a ring and a plurality of elongated elements disposed about the axial structure; Each of the elongated elements extends from a ring to each helical elongated element and is coupled to each helical elongated element to prevent radial expansion of the impeller.

[0011] In some applications, the impeller includes three helical elongated elements with a film of material attached thereto to define three blades of the impeller, each elongated element extending from the ring to each of the three helical elongated elements such that each elongated element is within each of the three blades of the impeller.

[0012] In some applications, the elongated element is configured to not resist compression, and the elongated element is configured to prevent radial expansion of the impeller by applying tension to the helical elongated element.

[0013] In some applications, along at least a portion of the length of the impeller, as the film of material transitions from one impeller blade to an adjacent blade, the film of material forms a continuous U-shaped curved surface, and the U-shaped curvature of the film of material is substantially uninterrupted in its axial configuration.

[0014] In some applications, when viewed from the distal end of the impeller, the pressure side of each of the impeller blades configured to propel blood during operation of the impeller is convex in a distal region of the impeller and concave in a proximal region of the impeller, hi some applications, the pressure side of each of the impeller blades changes to be substantially radially oriented in the region of the elongated element within the impeller blade.

[0015] In some applications, the helical elongate element is coated with a bonding agent configured to enhance bonding between the helical elongate element and the film of material. In some applications, the film of material includes an elastomeric material, and the bonding agent includes at least two functional groups configured to bond to the helical elongate element and the elastomeric material, respectively. In some applications, the bonding agent includes a silane compound.

[0016] In some applications, the device further includes a layer of elastomer disposed between the film of material and the binder. In some applications, the layer of elastomer is configured to round corners of the helical elongate element. In some applications, the film of material is made of an elastomer. In some applications, the elastomer includes a polycarbonate-based thermoplastic polyurethane.

[0017] In some applications, the axial structure includes a spring. In some applications, the spring includes a tube at an intermediate position along the length of the spring, and the ring is disposed around the tube.

[0018] Thus, according to some applications of the present invention, a method is provided, the method comprising: Manufacture an impeller, forming a structure having a first bushing and a second bushing at a proximal end and a distal end, the first and second bushings being interconnected by at least one elongated element; at least partially compressing the structure axially to radially expand the at least one elongated element to form at least one helical elongated element; coating at least one helical elongate element with a bonding agent configured to enhance bonding between the helical elongate element and the elastomeric layer; coating the coated helical elongate element with an elastomer layer; and thereafter, bonding an elastomeric membrane to the at least one helical elongate element such that the at least one helical elongate element with the elastomeric membrane bonded thereto defines an impeller blade; The method includes manufacturing an impeller by

[0019] In some applications, bonding an elastomeric membrane to the at least one helical elongate element such that the at least one helical elongate element with the elastomeric membrane bonded thereto defines an impeller blade includes immersing the helical elongate element in an elastomeric material that creates the elastomeric membrane.

[0020] In some applications, the elastomeric membrane comprises an elastic material having an ultimate elongation of greater than 300 percent. In some applications, the elastomeric membrane comprises an elastic material having a melt flow index of at least 4. In some applications, the elastomeric membrane comprises an elastic material having a tensile strength of greater than 6000 psi.

[0021] In some applications, coating the at least one helical elongate element with a bonding agent includes coating the at least one helical elongate element with a silane compound containing a first functional group configured to bond with the helical elongate element and a second functional group configured to bond with the elastomer layer.

[0022] In some applications, the elastomeric layer is made of a given elastomeric material and the elastomeric membrane is made of the given elastomeric material, hi some applications, the elastomeric layer is made of a first elastomeric material and the elastomeric membrane is made of a second elastomeric material that is different from the first elastomeric material.

[0023] In some applications, coating the coated helical elongate element with an elastomer layer includes spraying the elastomer onto the coated helical elongate element. In some applications, coating the coated helical elongate element with an elastomer layer includes at least partially rounding corners of the coated helical elongate element.

[0024] In some applications, coating the coated helical elongate element with an elastomeric layer includes coating the coated helical elongate element with an elastomeric layer within a given time period of coating the at least one helical elongate element with a binder. In some applications, coating the coated helical elongate element with an elastomeric layer further includes spraying additional elastomeric material onto the coated helical elongate element after coating the coated helical elongate element with an elastomeric layer within a given time period of coating the at least one helical elongate element with a binder.

[0025] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: 1. A ventricular assist device comprising: an impeller configured to be positioned within the left ventricle of a subject; A motor; at least one drive magnet coupled to the motor and configured to be rotated by the motor; at least one driven magnet magnetically coupled to the drive magnet and configured to be rotated by the drive magnet; a drive cable extending from the driven magnet and configured to impart rotational motion from the driven magnet to the impeller; a sensor set configured to detect a magnetic phase difference between the driven magnet and the drive magnet; a computer processor configured to receive the detected magnetic phase difference and determine a physiological parameter of the subject at least in part in response thereto; and ventricular assist devices including:

[0026] In some applications, the sensor set is further configured to measure a magnetic flux amplitude signal, and the computer processor is configured to determine a physiological parameter of the subject based at least in part on a combination of the magnetic flux amplitude signal and the detected magnetic phase difference.

[0027] In some applications, the computer processor is configured to determine a pressure difference between a left ventricle of the subject and an aorta of the subject in response at least in part to a magnetic phase difference between the driven magnet and the drive magnet. In some applications, the computer processor is configured to determine a left ventricular pressure of the subject in response at least in part to a magnetic phase difference between the driven magnet and the drive magnet. In some applications, the computer processor is configured to determine an event in a cardiac cycle of the subject in response at least in part to a magnetic phase difference between the driven magnet and the drive magnet.

[0028] In some applications, the sensor set includes a first magnetometer configured to measure the magnetic phase of the driven magnet and a second magnetometer configured to measure the magnetic phase of the driven magnet, hi some applications, the second magnetometer is configured to measure the magnetic phase of the driven magnet by measuring the magnetic phase of the motor.

[0029] In some applications, the computer processor is configured to receive a signal indicative of current consumption by the motor and to determine a physiological parameter of the subject based at least in part on a combination of the current consumption by the motor and the detected magnetic phase difference. In some applications, the sensor set is further configured to measure a magnetic flux amplitude signal and the computer processor is configured to determine a physiological parameter of the subject based at least in part on a combination of the current consumption by the motor, the magnetic flux amplitude signal and the detected magnetic phase difference.

[0030] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: a ventricular assist device including an impeller configured to be positioned within a left ventricle of the subject and to pump blood from the left ventricle of the subject to an aorta of the subject; a blood pressure sensor configured to measure aortic pressure of the subject; 1. A computer processor comprising: deriving an arterial pulse of the subject based on the measured aortic pressure; a computer processor configured to estimate a subject's intrinsic cardiac output based at least in part on arterial pulsation; Includes.

[0031] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: 1. A left ventricular assist device configured to assist left ventricular function in a subject, comprising: The impeller and a frame disposed around the impeller; a rigid axial shaft extending from a proximal end of the frame to a distal end of the frame, the impeller coupled to the rigid axial shaft, the rigid axial shaft including a proximal portion and a distal portion coupled to each other via a joint, the proximal portion and the distal portion configured to bend relative to each other via the joint.

[0032] In some applications, the frame length is greater than 25 mm.

[0033] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: An impeller, a proximal bushing and a distal bushing; a plurality of spiral elongated elements; an axial structure disposed inside the helical elongated element along the axis about which the helical elongated element is wound; a membrane of elastomeric material supported between the helical elongate element and the axial structure, such that each helical elongate element to which the membrane of elastomeric material is attached defines a respective blade of the impeller; an impeller including Along at least a portion of the length of the impeller, as the film of elastomeric material transitions from one impeller blade to an adjacent blade, the film of elastomeric material forms a continuous U-shaped curvature, and the U-shaped curvature of the film of elastomeric material is substantially uninterrupted in its axial configuration.

[0034] In some applications, the axial structure comprises a cylindrical axial structure. In some applications, the cylindrical axial structure comprises a spring.

[0035] Further, in accordance with some applications of the present invention, a method is provided, the method comprising: inserting a ventricular assist device including a delivery catheter, a drive cable, and an outer tube surrounding the drive cable through the introducer sheath, through the arteriotomy, and into the vasculature of the subject; removing the introducer sheath while the ventricular assist device remains within the subject's vasculature; maintaining sterility of the arteriotomy while allowing movement of the outer tube relative to the delivery catheter with a sterile sleeve disposed between the outer tube and the delivery catheter; Includes.

[0036] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: 1. A blood pump comprising: an axial shaft; an impeller disposed on the axial shaft; a motor unit including a motor configured to rotate the impeller in a given rotational direction, thereby driving the impeller to pump blood from a distal end of the impeller to a proximal end of the impeller; a drive cable configured to extend from the motor unit to the axial shaft and configured to rotate to impart rotational motion from the motor to the impeller; a blood pump including At least a portion of the drive cable includes two or more layers, each layer including a plurality of wires; the plurality of wires in each of the two or more layers are arranged in a coiled configuration, and in response to rotation of the drive cable in a given rotational direction, the wires in each layer at least partially unwind, axially shortening a portion of the drive cable; The drive cable is maintained in a pre-tensioned state so that even when the impeller is stationary, the drive cable is stretched relative to the stationary state.

[0037] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: 1. A blood pump comprising: an axial shaft; an impeller disposed on the axial shaft; a motor unit including a motor configured to drive the impeller by rotating the impeller in a counterclockwise direction when viewed from the proximal end of the impeller to the distal end of the impeller, thereby pumping blood from the distal end of the impeller to the proximal end of the impeller; a drive cable configured to extend from the motor unit to the axial shaft and configured to rotate to impart rotational motion from the motor to the impeller; a blood pump including At least a portion of the drive cable includes two or more layers, each layer including a plurality of wires; The plurality of wires in each of the two or more layers are arranged in a left-handed layer coil configuration.

[0038] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: 1. A blood pump comprising: an axial shaft; an impeller disposed on the axial shaft; a motor unit including a motor configured to drive the impeller to pump blood from the distal end of the impeller to the proximal end of the impeller by rotating the impeller in a clockwise direction when viewed from the proximal end of the impeller to the distal end of the impeller; a drive cable configured to extend from the motor unit to the axial shaft and configured to rotate to impart rotational motion from the motor to the impeller; a blood pump including At least a portion of the drive cable includes two or more layers, each layer including a plurality of wires; The plurality of wires in each of the two or more layers are arranged in a right-handed layer coil configuration.

[0039] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: 1. A blood pump comprising: an axial shaft; an impeller disposed on the axial shaft; a motor unit including a motor configured to rotate the impeller in a given rotational direction, thereby driving the impeller to pump blood from a distal end of the impeller to a proximal end of the impeller; a drive cable configured to extend from the motor unit to the axial shaft and configured to rotate to impart rotational motion from the motor to the impeller; a blood pump including At least a portion of the drive cable includes inner and outer layers that are coaxial with one another, each layer including a plurality of wires arranged in a coiled configuration; The ratio of the number of wires in the outer layer to the number of wires in the inner layer is 2:3 to 2:5, and the ratio of the diameter of the wires in the outer layer to the diameter of the wires in the inner layer is 3:2 to 5:2.

[0040] Further, in accordance with some applications of the present invention, there is provided an apparatus comprising: 1. A blood pump comprising: an axial shaft; an impeller disposed on the axial shaft; a motor unit including a motor configured to rotate the impeller in a given rotational direction, thereby driving the impeller to pump blood from a distal end of the impeller to a proximal end of the impeller; a drive cable configured to extend from the motor unit to the axial shaft and configured to rotate to impart rotational motion from the motor to the impeller; a drive cable bearing tube configured to rotate within the drive cable, a portion of the drive cable bearing tube comprising: an inner layer and an outer layer comprising different materials; a coiled wire embedded between the inner and outer layers, the coiled wire configured to maintain a substantially circular cross section of the drive cable bearing tube even in areas where the drive cable bearing tube is significantly curved; and a drive cable bearing tube including: The blood pump includes:

[0041] Generally, in the specification and claims of this application, "proximal" and related terms, when used with respect to a device or portion thereof, refer to an end or portion of the device, and are generally interpreted to mean a portion that is closer to the location where the device would 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, refer to an end or portion of the device, and are generally interpreted to mean a portion that is further from the location where the device would be inserted into a subject when the device is inserted into the subject.

[0042] 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 aorta, and therefore, ventricular assist devices and / or portions thereof may be referred to herein (in the specification and claims) as blood pumps.

[0043] 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 explanation of the drawings]

[0044] [Figure 1A] 1 is a schematic illustration 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 illustration 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 illustration 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 1D] 1 is a schematic illustration 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 1E] 1 is a schematic diagram of a ventricular assist device including a braided structure and / or mesh in a distal region, in accordance with some applications of the present invention, the braided structure and / or mesh configured to separate the blood inlet of the ventricular assist device from the internal structure of the ventricle. [Figure 1F] 1 is a schematic diagram of a ventricular assist device including a braided structure and / or mesh in a distal region, in accordance with some applications of the present invention, the braided structure and / or mesh configured to separate the blood inlet of the ventricular assist device from the internal structure of the ventricle. [Figure 2] 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 3F] 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 3Gi] 1 is a photograph of an impeller of a ventricular assist device, according to some applications of the present invention. [Figure 3Gii] 1 is a photograph of an impeller of a ventricular assist device, according to some applications of the present invention. [Figure 4] 1 is a schematic diagram of an impeller positioned within a frame of a ventricular assist device, in accordance with some applications of the present invention. [Figure 5A] 1 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 6A] 1A-1C are schematic diagrams of a ventricular assist device at different stages of a motion cycle of an impeller relative to a frame of the ventricular assist device, in accordance with some applications of the present invention. [Figure 6B] 1A-1C are schematic diagrams of a ventricular assist device at different stages of a motion cycle of an impeller relative to a frame of the ventricular assist device, in accordance with some applications of the present invention. [Figure 6C] 1 is a schematic diagram of a distal tip element including an axial shaft receiving tube and a distal tip of a ventricular assist device, according to some applications of the present invention. [Figure 6D] 10 is a schematic diagram of a coupling element for coupling an impella bushing that extends proximally and functions as a stopper, according to some applications of the present invention. FIG. [Figure 6E] 10 is a schematic diagram of a coupling element for coupling an impella bushing that extends proximally and functions as a stopper, according to some applications of the present invention. FIG. [Figure 7A]1 is a schematic diagram of a motor unit of a ventricular assist device, in accordance with some applications of the present invention. [Figure 7Bi] 1 is a schematic diagram of a motor unit of a ventricular assist device, in accordance with some applications of the present invention. [Figure 7Bii] 1 is a schematic diagram of a motor unit of a ventricular assist device, in accordance with some applications of the present invention. [Figure 8A] 1 is a graph showing experimentally measured changes in the length of a drive cable of a ventricular assist device with varying pressure gradients across the blood pump impeller. [Figure 8B] 1 is a graph showing experimentally measured changes in magnetic phase measurements performed on a blood pump in response to varying pressure gradients across the blood pump's impeller. [Figure 8C] 1 is a graph showing experimentally measured changes in magnetic phase measurements performed on a blood pump in response to varying pressure gradients across the blood pump's impeller. [Figure 9A] 1 is a schematic diagram of a motor unit support configured to support a motor unit on a patient's leg, according to some applications of the present invention. FIG. [Figure 9B] 1 is a schematic diagram of a motor unit support configured to support a motor unit on a patient's leg, according to some applications of the present invention. FIG. [Figure 9C] 1 is a schematic diagram of a motor unit support configured to support a motor unit on a patient's leg, according to some applications of the present invention. FIG. [Figure 9D] 1 is a schematic diagram of a motor unit support configured to support a motor unit on a patient's leg, according to some applications of the present invention. FIG. [Figure 9E] 1 is a schematic diagram of a motor unit support configured to support a motor unit on a patient's leg, according to some applications of the present invention. FIG. [Figure 9F] 1 is a schematic diagram of a motor unit support configured to support a motor unit on a patient's leg, according to some applications of the present invention. FIG. [Figure 9G]1 is a schematic diagram of a motor unit support configured to support a motor unit on a patient's leg, according to some applications of the present invention. FIG. [Figure 10A] 1 is a schematic diagram of a drive cable for a ventricular assist device, in accordance with some applications of the present invention. [Figure 10B] 1 is a schematic diagram of a drive cable for a ventricular assist device, in accordance with some applications of the present invention. [Figure 10C] 1 is a schematic diagram of a drive cable for a ventricular assist device, in accordance with some applications of the present invention. [Figure 10D] 1 is a schematic diagram of a drive cable bearing tube according to some applications of the present invention. [Figure 11A] 1 is a schematic diagram of an apparatus and method for purging a drive cable, radial bearing, and / or impella bushing of a ventricular assist device, according to some applications of the present invention. [Figure 11B] 1 is a schematic diagram of an apparatus and method for purging a drive cable, radial bearing, and / or impella bushing of a ventricular assist device, according to some applications of the present invention. [Figure 11C] 1 is a schematic diagram of an apparatus and method for purging a drive cable, radial bearing, and / or impella bushing of a ventricular assist device, according to some applications of the present invention. [Figure 11D] 1 is a schematic diagram of an apparatus and method for purging a drive cable, radial bearing, and / or impella bushing of a ventricular assist device, according to some applications of the present invention. [Figure 11E] 1 is a schematic diagram of an apparatus and method for purging a drive cable, radial bearing, and / or impella bushing of a ventricular assist device, according to some applications of the present invention. [Figure 12A] 1 is a schematic diagram of a ventricular assist device including a liner inside the frame that houses the impeller, in accordance with some applications of the present invention. [Figure 12B] 1 is a schematic diagram of a ventricular assist device including a liner inside the frame that houses the impeller, in accordance with some applications of the present invention. [Figure 13]1 is a schematic diagram of a ventricular assist device having a frame that houses an impeller and defines a cylindrical portion that is uncovered at least at its distal end, in accordance with some applications of the present invention. [Figure 14] 1 is a schematic illustration of a ventricular assist device positioned inside the left ventricle of a subject, including a cross-sectional view of the left ventricle, in accordance with some applications of the present invention. [Figure 15A] 1 is a schematic illustration of a distal tip element of a ventricular assist device at least partially curved to define a question mark or tennis racket shape, in accordance with some applications of the present invention. [Figure 15B] 1 is a schematic illustration of a distal tip element of a ventricular assist device at least partially curved to define a question mark or tennis racket shape, in accordance with some applications of the present invention. [Figure 15C] 1 is a schematic illustration of a distal tip element of a ventricular assist device at least partially curved to define a question mark or tennis racket shape, in accordance with some applications of the present invention. [Figure 15D] 1 is a schematic illustration of a distal tip element of a ventricular assist device at least partially curved to define a question mark or tennis racket shape, in accordance with some applications of the present invention. [Figure 16A] 15D positioned inside the left ventricle of a subject, in accordance with some applications of the present invention. [Figure 16B] 15D positioned inside the left ventricle of a subject, in accordance with some applications of the present invention. [Figure 17Ai] 1 is a schematic illustration of a ventricular assist device having a balloon disposed on its distal tip, the balloon configured to facilitate movement of the axial shaft against the wall of the ventricle, in accordance with some applications of the present invention. [Figure 17Aii] 1 is a schematic illustration of a ventricular assist device having a balloon disposed on its distal tip, the balloon configured to facilitate movement of the axial shaft against the wall of the ventricle, in accordance with some applications of the present invention. [Figure 17Bi]1 is a schematic diagram of a ventricular assist device having a joint configured to facilitate pivoting of the distal tip relative to the axial shaft, in accordance with some applications of the present invention. [Figure 17Bii] 1 is a schematic diagram of a ventricular assist device having a joint configured to facilitate pivoting of the distal tip relative to the axial shaft, in accordance with some applications of the present invention. [Figure 17C] 1 is a schematic diagram of a ventricular assist device according to some applications of the present invention, wherein the outer tube of the ventricular assist device is configured with a predetermined curvature to maintain the axial shaft of the ventricular assist device in a substantially straight configuration when the axial shaft is positioned within the left ventricle of a subject. [Figure 17D] FIG. 1 is a schematic diagram of a ventricular assist device having a distal tip configured to be anchored to tissue at the left ventricular apex. [Figure 18A] 1A-1C are schematic diagrams of a distal radial bearing of a ventricular assist device according to respective applications of the present invention. [Figure 18B] 1A-1C are schematic diagrams of a distal radial bearing of a ventricular assist device according to respective applications of the present invention. [Figure 18C] 1A-1C are schematic diagrams of a distal radial bearing of a ventricular assist device according to respective applications of the present invention. [Figure 19A] 1 is a schematic diagram of a ventricular assist device including a pump outlet tube configured to bend as blood is pumped through the pump outlet tube and rotatable relative to the distal tip of the ventricular assist device, according to some applications of the present invention. [Figure 19B] 1 is a schematic diagram of a ventricular assist device including a pump outlet tube configured to bend as blood is pumped through the pump outlet tube and rotatable relative to the distal tip of the ventricular assist device, according to some applications of the present invention. [Figure 19C] 1 is a schematic diagram of a ventricular assist device including a pump outlet tube configured to bend as blood is pumped through the pump outlet tube and rotatable relative to the distal tip of the ventricular assist device, according to some applications of the present invention. [Figure 19D]1 is a schematic diagram of a ventricular assist device including a pump outlet tube configured to bend as blood is pumped through the pump outlet tube and rotatable relative to the distal tip of the ventricular assist device, according to some applications of the present invention. [Figure 19E] 1 is a schematic diagram of a ventricular assist device including a pump outlet tube configured to bend as blood is pumped through the pump outlet tube and rotatable relative to the distal tip of the ventricular assist device, according to some applications of the present invention. [Figure 19F] 1 is a schematic illustration of a ventricular assist device including a curved element, according to some applications of the present invention, the curved element being made of a shape memory material, configured to impart a predetermined curvature to a portion of the ventricular assist device, and rotatable relative to the distal tip of the ventricular assist device. [Figure 20A] 1 is a schematic diagram of a ventricular assist device including an axial shaft including a joint, such as a Cardan joint, in accordance with some applications of the present invention. [Figure 20B] 1 is a schematic diagram of a ventricular assist device including an axial shaft including a joint, such as a Cardan joint, in accordance with some applications of the present invention. [Figure 20C] 1 is a schematic diagram of a ventricular assist device including an axial shaft including a joint, such as a Cardan joint, in accordance with some applications of the present invention. [Figure 21] 1 is a schematic diagram of a ventricular assist device including one or more blood pressure measurement tubes, in accordance with some applications of the present invention. [Figure 22A] 1 is a schematic illustration of a sterile sleeve configured to form a seal between a delivery catheter and an outer tube of a ventricular assist device, in accordance with some applications of the present invention. [Figure 22B] 1 is a schematic illustration of a sterile sleeve configured to form a seal between a delivery catheter and an outer tube of a ventricular assist device, in accordance with some applications of the present invention. [Figure 23A] 1 is a schematic diagram of a tip straightener used to straighten the distal tip of a ventricular assist device during guidewire insertion, according to some applications of the present invention. FIG. [Figure 23B]1 is a schematic diagram of a tip straightener used to straighten the distal tip of a ventricular assist device during guidewire insertion, according to some applications of the present invention. FIG. [Figure 23C] 1 is a schematic diagram of a tip straightener used to straighten the distal tip of a ventricular assist device during guidewire insertion, according to some applications of the present invention. FIG. [Figure 24A] 1 is a graph illustrating measurements performed during use of a left ventricular assist device, in accordance with some applications of the present invention. [Figure 24B] 1 is a graph illustrating measurements performed during use of a left ventricular assist device, in accordance with some applications of the present invention. [Figure 24C] 1 is a graph illustrating measurements performed during use of a left ventricular assist device, in accordance with some applications of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0045] Reference is now made to FIGS. 1A, 1B, and 1C, which are schematic illustrations of a ventricular assist device 20 configured for placement at its distal end in a subject's left ventricle 22, in accordance with some applications of the present invention. FIG. 1A shows an overview of a ventricular assist device system, including a control console 21 and a motor unit 23 (the motor unit is typically a handle housing a motor, as described below). FIG. 1B shows the ventricular assist device inserted into a subject's left ventricle, and FIG. 1C shows a pump portion 27 of the ventricular assist device in greater detail. The ventricular assist device includes a pump outlet tubing 24 that traverses a subject's aortic valve 26, such that a proximal end 28 of the pump outlet tubing is positioned in the subject's aorta 30 and a distal end 32 of the pump outlet tubing is positioned within the left ventricle 22. Typically, the pump outlet tubing 24 is an elongated tube, with the axial length of the pump outlet tubing being significantly 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 aorta. Thus, the ventricular assist device and / or portions thereof may be referred to herein (in the specification and claims) as a blood pump.

[0046] In some applications, ventricular assist devices are used to support the function of a subject's left ventricle during percutaneous coronary intervention. In such cases, ventricular assist devices are typically used for up to 10 hours (e.g., up to 6 hours) during a period when there is a risk of developing hemodynamic instability (e.g., during or immediately after percutaneous coronary intervention). Alternatively or additionally, ventricular assist devices are used to support the function of a 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 support the function of a 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 magnetically coupled to the impeller.

[0047] As shown in FIG. 1B , which illustrates the steps of placing a ventricular assist device in the left ventricle, the distal end of the ventricular assist device is typically guided into the left ventricle over a guidewire 10. 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, the delivery catheter is typically retracted into the aorta and the guidewire is retracted from the subject. Retracting the delivery catheter typically causes the self-expandable component at the distal end of the device to assume a radially unconstrained configuration, as described in more detail below. Typically, ventricular assist devices are inserted into a subject to provide acute therapy to the subject. In some applications, once therapy is complete, to withdraw the left ventricular device from the subject, the delivery catheter is advanced beyond the distal end of the device, causing the self-expandable component 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, causing the self-expandable component at the distal end of the device to assume a radially constrained configuration.

[0048] 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.

[0049] 1C, which illustrates the pump portion 27 of the ventricular assist device 20 in greater detail. Typically, the impeller 50 is disposed within the distal section 102 of the pump outlet tubing 24 and is configured to rotate to pump blood from the left ventricle into the aorta. Typically, the pump outlet tubing defines one or more blood inlets 108 at the distal end 32 of the pump outlet tubing, through which blood flows from the left ventricle into the pump outlet tubing as the impeller operates. In some applications, the proximal section 106 of the pump outlet tubing defines one or more blood outlets 109 through which blood flows from the pump outlet tubing into the ascending aorta as the impeller operates.

[0050] In some applications, a control console 21 (shown in FIG. 1A), typically including a computer processor 25, controls the rotation of the impeller. For example, the computer processor may control a motor 74 (shown in FIG. 7A, for example) disposed in a motor unit 23 (shown in FIG. 1A) that drives the impeller to rotate via a drive cable 130 (shown in FIG. 7A, for example). In some applications, the computer processor is configured to detect physiological parameters of interest (such as left ventricular pressure, cardiac afterload, or rate of change of left ventricular pressure) and control the rotation of the impeller accordingly, as described in more detail below. Typically, the operations performed by the computer processor described herein transform the physical state of memory, which is an actual physical item in communication with the computer processor, to have different magnetic polarities, charges, etc., depending on the memory technology 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.

[0051] 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 and / or to flush debris from portions of the device. The purge system 29 is described in more detail below.

[0052] Typically, a frame 34 is positioned within the pump outlet tubing around the impeller 50, along the distal section 102 of the pump outlet tubing 24. 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 at least a portion of the frame (and thus the distal section 102 of the tubing 24) has a generally circular, elliptical, or polygonal cross-sectional shape when no force is applied to the distal section 102 of the tubing 24. 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, when the ventricular assist device is operating, the distal portion of the pump outlet tubing has a configuration that is positioned within the subject's body such that the distal portion of the pump outlet tubing is at least partially positioned within the left ventricle.

[0053] In some applications, the frame is not disposed within the pump outlet tubing along the proximal section 106 of the pump outlet tubing 24, and therefore the pump outlet tubing is not supported open by the frame 34. The pump outlet tubing 24 is typically made of a blood-impermeable, collapsible material. For example, the pump outlet tubing 24 may include polyurethane, polyester, and / or silicone. Alternatively or additionally, the pump outlet tubing is made of polyethylene terephthalate (PET) and / or polyether block amide (e.g., PEBAX®). In some applications (not shown), the pump outlet tubing is reinforced with a reinforcing structure, for example, a braided reinforcing structure such as a braided nitinol tubing. Typically, the proximal portion of the pump outlet tubing has a configuration that is positioned such that at least a portion of it is disposed within the subject's ascending aorta. In some applications, as shown in FIG. 1B, the proximal portion of the pump outlet tubing traverses the subject's aortic valve and passes from the subject's left ventricle to the subject's ascending aorta.

[0054] As described above, the pump outlet tubing typically defines one or more blood inlets 108 at the distal end of the pump outlet tubing, through which blood flows from the left ventricle into the pump outlet tubing when the impeller operates. In some applications, the proximal portion of the pump outlet tubing defines one or more blood outlets 109, through which blood flows from the pump outlet tubing to the ascending aorta when the impeller operates. Typically, the pump outlet tubing defines multiple blood outlets 109, e.g., two to eight blood outlets (e.g., two to four blood outlets). When the impeller operates, the pressure of the blood flow through the pump outlet tubing typically keeps the proximal portion of the pump outlet tubing open. In some applications, for example, in the event of an impeller malfunction, the proximal portion of the pump outlet tubing is configured to collapse inward in response to pressure outside the proximal portion of the pump outlet tubing exceeding pressure inside the proximal portion of the pump outlet tubing. 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.

[0055] Referring again to FIG. 1C , in some applications, the frame 34 is shaped so that it defines a proximal conical section 36, a central cylindrical section 38, and a distal conical section 40. Typically, in the proximal conical section, the narrow end of the cone is located proximal to the wide end of the cone. Furthermore, typically, in the distal conical section, the narrow end of the cone is located distal to the wide end of the cone. In some applications, the pump outlet tubing 24 extends to the distal end of the cylindrical section 38 (or slightly proximal or distal thereto), as shown in FIG. 1C , such that the distal end of the pump outlet tubing defines a single axially directed blood inlet 108. In some applications, a liner 39 lines the frame within at least a portion of the frame 34, as described below with reference to FIGS. 12A-12B . Depending on the application, the liner may partially or completely overlap the pump outlet tubing 24 in the portion of the frame it lines. In such applications, the distal end of the liner defines a single axially directed blood inlet 108. In some applications, both the pump outlet tube and the liner terminate short of the distal end of the barrel of the frame, leaving the distal portion of the barrel of the frame uncovered, as described below with reference to FIG.

[0056] Typically, the pump outlet tube 24 includes a conical proximal portion 42 and a cylindrical central portion 44. (Typically, the conical proximal portion 42 is disposed entirely within the aforementioned proximal section 106, and the cylindrical central portion extends from within the proximal section 106 to the distal section 102.) In the proximal conical portion, the narrow end of the cone is typically located 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 portion 42 of the pump outlet tube 24. In some such applications, the blood outlet is teardrop-shaped, as shown in FIG. 1C. The teardrop-shaped feature of the blood outlet, combined with the blood outlet's extension at least partially along the proximal conical section of the tube 24, typically 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.

[0057] In some applications (not shown), the diameter of the pump outlet tubing 24 varies along the length of the central portion of the pump outlet tubing such that the central portion of the pump outlet tubing has a frusto-conical shape. For example, the central portion of the pump outlet tubing may widen from its proximal end to its distal end, or may narrow from its proximal end to its distal end. In some applications, at its proximal end, the central portion of the pump outlet tubing has a diameter of 5-7 mm, and at its distal end, the central portion of the pump outlet tubing has a diameter of 8-12 mm.

[0058] Referring again to FIG. 1C, the ventricular assist device typically includes a distal tip element 107 positioned distally relative to the frame 34 and including an axial shaft receiving tube 126 and a distal tip 120, both of which are described in further detail below.

[0059] Reference is now made to Figure 1D, which is a schematic illustration of a ventricular assist device 20 according to some applications of the present invention. The pump outlet tube 24 extends to the end of the distal cone 40 of the frame, the pump outlet tube defining a plurality of lateral blood inlets 108. In such applications, the pump outlet tube typically defines a distal cone 46, the narrow end of which is distal to the wide end of the cone. In some such applications, the pump outlet tube defines two to four lateral blood inlets. Typically, in such applications, each of the blood inlets 108 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., an area of ​​20-60 square millimeters or 30-50 square millimeters. Alternatively or additionally, the outlet conduit defines many more, smaller blood inlets (not shown), e.g., more than 10 small blood inlets, more than 50 small blood inlets, more than 100 small blood inlets, or more than 150 small blood inlets, e.g., 50 to 100 small blood inlets, 100 to 150 small blood inlets, or 150 to 200 small blood inlets. In some such applications, each of the small blood inlets defines an area of ​​more than 0.1 square millimeter (e.g., more than 0.3 millimeter) and / or less than 5 square millimeters (e.g., less than 1 square millimeter), e.g., 0.1 to 5 square millimeters, 0.2 to 0.5 square millimeters, or 0.3 to 1 square millimeter.

[0060] Typically, the distal conical portion 46 of the pump outlet tube is configured to reduce the risk of structures from the left ventricle (such as chordae tendineae, trabeculae, and / or papillary muscles) penetrating the frame and being damaged by the impeller and / or the axial shaft to which the impeller is attached, and / or damaging the left ventricular assist device. Accordingly, in some applications, the small blood inlet is shaped to have a width (or span) in at least one direction of less than 1 mm, e.g., 0.1-1 mm or 0.3-0.8 mm. By defining such a small width (or span), structures from the left ventricle (such as chordae tendineae, trabeculae, and / or papillary muscles) are typically prevented from penetrating the frame. In some applications, the small blood inlet defines a generally rectangular (or elliptical) shape. In some such applications, the ratio of the length to width of the small blood inlet is between 1.1:1 and 4:1, e.g., between 3:2 and 5:2. In some applications, the small blood inlet is configured to (a) prevent structures from the left ventricle (such as chordae tendineae, trabeculae, and / or papillary muscles) from entering the frame, while (b) providing a relatively high porosity to the portion of the pump outlet tubing that defines the small blood inlet. Typically, the portion of the pump outlet tubing that defines the small blood inlet has a porosity greater than 40 percent, e.g., greater than 50 percent (porosity is defined as the percentage of the area of ​​this portion that is porous to blood flow).

[0061] Reference is now made to Figures 1E and 1F, which are schematic illustrations of a ventricular assist device 20 including a braided structure 260 and / or mesh 282 in a distal region, in accordance with some applications of the present invention. The braided structure and / or mesh are configured to separate the blood inlet of the ventricular assist device from the internal structure of the ventricle. The braided structure 260 is generally similar to the braided structure 260 described with reference to Figure 20B of U.S. Patent Application Publication No. 2019 / 0209758 to Tuval, which is incorporated herein by reference. The mesh 282 is generally similar to the mesh 282 described with reference to Figure 21D of U.S. Patent Application Publication No. 2019 / 0209758 to Tuval, which is incorporated herein by reference.

[0062] Referring to FIG. 1E, in some applications, a braided structure 260 (e.g., a braided metal or alloy, such as a shape memory alloy (e.g., Nitinol)) is disposed in a distal region of the device. For example, the braided material may be disposed at the distal end of the device. Alternatively or additionally, the device may include a distal tip element 107 (typically as described with respect to FIGS. 14-16B), with the braided material disposed around a portion of the device to cover a portion of the distal tip element. In some applications, the braided material is disposed over at least a portion of the frame 34. For example, the braided material may surround at least a portion of the frame extending distally from a longitudinal position along the frame where the blood outflow tube 24 and / or the liner 39 terminate to the distal end of the frame. In some applications, the braided structure is disposed to cover the blood inlet 108.

[0063] As shown in FIG. 1F , in some applications, the outer surface of the distal tip element 107 includes a radially expandable mesh 282 configured to self-expand when the distal tip element 107 is positioned within the left ventricle of a subject. In some applications, the device includes a distal tip element generally as described with reference to FIGS. 14 through 16B , with the mesh positioned around a portion of the device to cover a portion of the distal tip element. In some applications, the mesh is positioned over at least a portion of the frame 34. For example, the mesh can surround at least a portion of the frame extending distally from a longitudinal position along the frame where the blood outflow tube 24 terminates and / or the liner 39 terminates to the distal end of the frame. In some applications, the mesh is positioned to cover the blood inlet 108.

[0064] Typically, the braided structure 260 and / or mesh 282 separate one or more blood inlets 108 from the interior structures of the left ventricle in three dimensions. In this manner, the braided structure 260 and / or mesh 282 separate one or more blood inlets 108 from the interventricular septum, chordae tendineae, papillary muscles, trabeculae, and / or the left ventricular apex. As an alternative or in addition to separating one or more blood inlets 108 from the interior structures of the left ventricle using a braided structure and / or mesh, cells of the frame 34 near the blood inlets 108 are configured to define smaller openings than those in other portions of the frame. For example, cells in the distal conical portion of the frame may define smaller openings than cells in the proximal conical portion of the frame. Alternatively or additionally, cells in the distal conical portion of the frame may define smaller openings than cells in the cylindrical portion of the frame.

[0065] Reference is now made to Figure 2, which is a schematic illustration of a frame 34 housing the impeller of a ventricular assist device 20, in accordance with some applications of the present invention. As mentioned above, the frame 34 is typically made of a shape memory alloy, such as Nitinol, that has a set shape such that the frame (and therefore 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 and / or the frame 34. By having a generally circular, elliptical, or polygonal cross-sectional shape, the frame is configured to hold open the distal portion of the tube.

[0066] Typically, the frame is a stent-like frame that includes struts that define cells. The frame is further typically covered by the pump outlet tube 24 and / or a liner 39, described below with reference to FIGS. 12A-12B. As described below, in some applications, the impeller 50 moves axially back and forth relative to the frame 34. Typically, during the impeller's movement relative to the frame, a portion of the impeller that defines its maximum span is located within the cylindrical portion 38 of the frame 34. In some cases, if the cells of the cylindrical portion 38 of the frame 34 are too large, the pump outlet tube 24 and / or the liner 39 may be stretched between the edges of the cells, causing the pump outlet tube 24 and / or the liner 39 to no longer 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, the result will be a non-constant clearance between the edges of the impeller blades and the tube 24 (and / or lining) at that location over the course of the impeller's rotational cycle, which in some applications can lead to increased hemolysis compared to a consistent clearance between the edges of the impeller blades and the tube 24 (and / or lining) at that location over the course of the impeller's rotational cycle.

[0067] Referring to FIG. 2 , and at least partially addressing the issues discussed in the preceding paragraph, within the 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, each cell within the cylindrical portion of the frame has a maximum cell width CW (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) of 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 pump outlet tube 24 (and / or liner) defines a substantially circular cross-section within the cylindrical portion of the frame.

[0068] 2 , beginning with the proximal end of the frame (on the left side of the figure), the frame typically defines (a) a junction 31 where the frame mates with the proximal bearing portion 116 (shown in FIG. 4 ) of the ventricular assist device, (b) a proximal conical portion 36, (c) a cylindrical portion 38, (d) a distal conical portion 40, and (e) a distal 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 through junction 31 and proximal conical portion 36 to cylindrical portion 38), 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 within the delivery catheter 143 in a radially constrained (i.e., crimped) configuration by axial extension. Additionally, typically, the radial narrowing of the frame is transmitted to the impeller, which is radially constrained by axial expansion within the frame. In some applications, the struts of a frame configured in the above manner readily transmit axial expansion from a delivery catheter (or other device configured to crimp the frame) to the frame, which in turn readily transmits axial expansion to the impeller. This is because a pair of struts branching from each junction 35 are configured to converge toward each other as they pivot about the junction to close.

[0069] 2, in some applications, the distal strut joints 33 are not circumferentially continuous and are typically configured to be held open when the frame is coupled to the axial shaft 92 (shown in FIG. 4) to position the impeller within the frame via the distal end of the frame. The distal strut sections are then closed around the outside of the distal bearing section 118, as described in more detail below with reference to FIGS. 5A-5B. In some applications, the proximal end of the distal tip element 107 (shown in FIG. 1C) holds the distal strut sections in a closed configuration around the outside of the distal bearing section 118.

[0070] Typically, when deployed in a radially unconstrained configuration, 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), e.g., 25-50 mm, or 30-45 mm. Typically, when deployed in a radially constrained configuration (within 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 cylindrical portion of 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), e.g., 10-25 mm, or 12-20 mm. In some applications, the ratio of the length of the cylindrical portion of the frame to the overall length of the frame is greater than 1:4 and / or less than 1:2, e.g., between 1:4 and 1:2.

[0071] Reference is now made to FIGS. 3A-3C, which are schematic illustrations of an impeller 50 or portion thereof, according to some applications of the present invention. Typically, the impeller includes at least one outer helical elongate element 52 wound around a central axial spring 54 such that the helix defined by the helical elongate element is coaxial with the central axial spring. (As discussed in more detail herein below, the central axial spring typically includes a tube 70 at an intermediate location along its length. Also, as discussed below, the scope of this application includes the use of other axial structures in place of a spring. Accordingly, in some places, this application refers to "axial structure 54.") Typically, the impeller includes two or more helical elongate elements (e.g., the three helical elongate elements shown in FIGS. 3A-3C). In some applications, the helical elongate element and the central axial spring are made of a shape memory material, e.g., a shape memory alloy such as Nitinol. Typically, the helical elongate element and central axial spring each support a membrane 56 of material (e.g., an elastomer such as polyurethane, and / or silicone) therebetween. In some applications, the membrane of material includes, for example, pieces of nitinol embedded therein to strengthen the membrane of material. For illustrative purposes, the impeller is shown in FIG. 3A without the membrane of material. FIGS. 3B and 3C respectively show an impeller with a membrane of material supported between the helical elongate element and the spring.

[0072] Each helical elongate element, together with a membrane extending from the helical elongate element to the spring, defines a respective impeller blade, with the helical elongate element defining the outer edge of the blade and the axial spring defining 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 shown in FIGS. 3B and 3C) is wound around the helical elongate element, as described, for example, in U.S. Pat. No. 10,864,310 to Schwammenthal, which is incorporated herein by reference. 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 a membrane of material (usually an elastomer such as polyurethane or silicone) and a spring (usually a shape memory alloy such as nitinol).

[0073] Enlargements A and B of Figure 3C show two alternative ways in which the sutures may be tied around the helical elongate element 52. In some applications, as shown in enlargement A, the sutures may be tied around the outer surface of the helical elongate element. Alternatively, as shown in enlargement B, the helical elongate elements may have grooves 45 defined in their outer surface and the sutures may be embedded within the grooves. By embedding the sutures within the grooves, the sutures generally do not expand the outer profile of the impeller, which is defined by the outer surface of the helical elongate element.

[0074] 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 approximately co-located and have a similar radial distance from the longitudinal axis of the impeller. Similarly, the distal ends of the spring 54 and the helical elongate element 52 typically 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 approximately co-located and have a similar radial distance from the longitudinal axis of the impeller. Typically, the spring 54 and the proximal and distal bushings 64 and 58 of the impeller define lumens therethrough, such that the impeller defines a continuous lumen 62 (shown in FIG. 3C ) therethrough.

[0075] Reference is now made to FIG. 4, which is a schematic illustration of an impeller 50 disposed inside the frame 34 of a ventricular assist device 20, according to some applications of the present invention. In some applications, a liner 39 lines the frame within at least a portion of the frame 34, as described below with reference to FIGS. 12A-12B. Depending on the application, the liner partially or completely overlaps the pump outlet tubing 24 in the portion of the frame it lines. In some applications, both the pump outlet tubing and the liner terminate short of the distal end of the cylindrical portion 38 of the frame, leaving the distal end of the cylindrical portion of the frame uncovered, as described below with reference to FIG. 13. In some applications, the pump outlet tubing continues over the distal conical portion of the frame, as described with reference to FIG. 1D. In the application shown in FIG. 4, the liner lines the inside of the cylindrical portion of the frame, and the pump outlet tubing 24 does not cover the cylindrical portion of the frame. However, the scope of this application includes applying the apparatus and method described with respect to FIG. 4 to any one of the applications described below with reference to FIG. 1D, 12A-12B or 13.

[0076] 4, there is typically a gap G between the outer edge of the impeller 50 and the liner 39, even at the maximum span of the impeller. In some applications, it is desirable for the gap between the outer edge of the impeller blades and the liner 39 to be relatively small so that the impeller efficiently pumps blood from the subject's left ventricle to the subject's aorta. However, it is desirable for the gap between the outer edge of the impeller blades and the inner surface of the frame 34 to remain substantially constant throughout the rotation of the impeller within the frame 34, for example, to reduce the risk of hemolysis.

[0077] In some applications, when both the impeller and frame 34 are arranged in a radially unconstrained configuration, the gap G between the outer edge of the impeller and the lining 39 at the location where the impeller's span 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), for example, 0.05 to 1 mm, or 0.1 to 0.4 mm. In some applications, when the impeller is arranged in a radially unconstrained configuration, 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), for example, 7 to 10 mm, or 8 to 9 mm. In some applications, when the frame 34 is positioned 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), for example, between 7.5 and 10.5 mm, or between 8.5 and 9.5 mm. In some applications, when the frame is positioned 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), for example, between 8 and 13 mm, or between 9 and 12 mm.

[0078] 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, a portion of the axial shaft is at least partially flexible, as described with reference to, e.g., FIGS. 20A-20C .) In some applications, the impeller's 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's distal bushing 58 is slidable relative to the shaft. The axial shaft itself is radially stabilized via the proximal and distal radial bearings 116, 118. The axial shaft then passes through the lumen 62 defined by the impeller, radially stabilizing the impeller relative to the inner surface of the frame 34, maintaining even relatively small clearances (e.g., those described above) between the outer edges of the impeller's blades and the inner surface of the frame 34 as the impeller rotates.

[0079] 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 67 are typically flexible but substantially inextensible along the axis defined by the elongated elements 67. More typically, each of the elongated elements 67 is configured to provide substantially no resistance to compression. Each elongated element 67 is configured to apply tension to the helical elongated element 52, preventing the helical elongated element 52 from moving radially outward, such that the separation between the helical elongated element 52 and the central axial spring 54 (in the absence of the elongated element 67) is greater than the length of the elongated element 67. For example, the elongated elements 67 may include string (such as polyester and / or another polymer or natural material, including fiber) and / or wire (such as nitinol wire and / or wire made of another alloy or metal). In this manner, the elongated element prevents the impeller from expanding radially by applying tension to the helical elongated element.

[0080] 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 54. In this manner, the elongated elements 67 are configured to prevent the outer edges of the impeller from being forced radially outward due to forces applied to the impeller during rotation of the impeller. In other words, the elongated elements 67 act as impeller expansion prevention elements. The elongated elements 67 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 an impeller, and each of the elongated elements 67 is usually double (i.e., extending radially from the central axial spring 54 to the outer edge of the helical elongated element 52, and then back from the helical elongated element to the central axial spring). In some applications, the elongated elements 67 are formed from a single string or wire. Each of the elongated elements 67 extends from the spring to a respective helical elongated element 52 and then back to the central axial spring 54.

[0081] In some applications, the impeller is manufactured as follows: The proximal bushing 64, the distal bushing 58, and the helical elongate element 52 are cut from a tube of shape-memory material, such as Nitinol. The tube is cut and the shape-memory material is set, typically using techniques generally similar to those described in U.S. Pat. No. 10,039,874 to Schwammenthal, such that the cut and set tube of shape-memory material defines the helical elongate element and bushing. Typically, a spring 54 is inserted into the cut and set tube, extending along the length of the tube from at least the proximal bushing to the distal bushing. In some applications, the spring is inserted into the cut and set tube in an axially compressed state and configured to be held in place relative to the tube by applying radial forces to the proximal and distal bushings. Alternatively or additionally, portions of the spring are welded to the proximal and distal bushings. In some applications, the spring is cut from a tube of shape-memory material, such as Nitinol. In some such applications, the spring is configured so that when placed in a radially unconstrained configuration (the configuration in which the spring is typically placed during operation of the impeller), there are substantially no gaps between adjacent windings of the spring.

[0082] In some applications, after the spring 54 is inserted into the cut and shaped tube, an elongated element 67, as described above, is positioned to extend between the spring and one or more helical elongated elements 52 as follows: A mandrel (e.g., a polyetheretherketone (PEEK) and / or polytetrafluoroethylene (PTFE) mandrel) is inserted through the lumen defined by the spring and bushing. The string or wire then passes (a) from the mandrel through a first one of the helical elongated elements 52, (b) from the first one of the helical elongated elements 52 back to the mandrel, (c) around the mandrel and through a second one of the helical elongated elements 52, (d) from the second one of the helical elongated elements 52 back to the mandrel, and so on. As the string or wire passes from the mandrel through each of the helical elongated elements 52 and back again, the ends of the string or wire are joined, for example, by tying them together. In some applications, a separate string or wire is used for each of the helical elongate elements 52. Typically, each string or wire passes from the helical elongate element, around a mandrel, and back to the helical elongate element, with the two ends of the string tied together. In some applications, at the longitudinal center of the spring 54, the spring is shaped to define a tube 70 as shown (i.e., at this position, the spring does not define any windings), and the string or wire is wound around this tube. In some applications, the string or wire is not wound around a tube and does not intersect the longitudinal axis of the impeller. In this case, the string or wire is fixed to the tube 70 via a fixing element 75 (such as a ring), as described in more detail below with reference to FIG. 3F.

[0083] In some applications, a suture 53 (e.g., polyester suture) is wrapped around the helical elongate element 52 at this stage to facilitate bonding between the membrane of material (typically an elastomer such as polyurethane or silicone) and the helical elongate element 52 (typically a shape memory alloy such as Nitinol) in the next stage of impeller manufacturing. In some applications, a suture (e.g., polyester suture, not shown) is wrapped 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) in the next stage of impeller manufacturing.

[0084] Typically, at this stage, the structure 59 shown in FIG. 3A is assembled. This structure includes cut and shaped tubes that define the proximal and distal bushings, the helical elongate element, and the spring (and elongate element and suture, if necessary). This structure is dipped into a material that defines the membrane 56. In some applications, the assembled structure is dipped into the material with the mandrel placed through the lumen defined by the spring and bushing, although a mandrel is not shown in FIG. 3A. Typically, the material forming the membrane is silicone and / or polyurethane (and / or similar elastomer), and the assembled structure is dipped into the material while the material is in an uncured liquid state. The material is then cured, e.g., by drying, to solidify. In some applications, the assembled structure is rotated while the material dries. Typically, this facilitates the formation of a membrane of material having a substantially uniform thickness within each impeller blade. After the material is dried, the mandrel is typically removed from the lumen defined by the bushing and spring.

[0085] The result of the above process typically is a continuous film of material extending from each of the helical elongate elements to the spring and along the length of the spring so as to define a tube when the spring is embedded in the tube. The portions of the film extending from each of the helical elongate elements to the spring define impeller blades. In applications where the impeller includes elongate elements 67, the elongate elements are typically embedded within portions of these films.

[0086] Typically, the elongated elements 67 are configured to limit the radial expansion of the impeller blades, as detailed above. In some applications, the span over which the elongated elements allow the impeller blades to expand is set using the following technique. As described in the paragraph above, the two ends of the string or wire within each blade are tied together. Typically, the ends of the string or wire within each blade are tied together so that the span of the impeller blades is set to be smaller than the desired span of the impeller and so that there is some slack in the knot where the two ends of the string or wire are tied together. The knots at the ends of the string or wire within each blade are then tightened, thereby pulling the outer edges of the impeller blades apart to increase the span of the impeller blades. This process is repeated, and the span of the impeller blades is measured, until the desired span of the impeller blades is achieved. The knotted string or wire structure 59 is then dipped into an elastomeric material that creates the membrane 56, and the elastomeric material is allowed to dry, maintaining the ends of the string or wire knotted together at the desired span of the impeller blades.

[0087] Typically, the impeller 50 is inserted transcatheterically into the left ventricle while in a radially constrained configuration. In the radially constrained configuration, both the helical elongate element 52 and the central axial spring 54 are axially elongated and radially constrained. A membrane 56, typically of a material (e.g., silicone and / or polyurethane), changes shape to match the shape changes of the helical elongate element and the central axial spring, both of which support the membrane. Using a spring to support the membrane's inner edge typically allows the membrane to change shape without breaking or collapsing, since the spring provides a large surface area to which the membrane's inner edge bonds. In some applications, using a spring to support the membrane's inner edge reduces the diameter of the spring itself by axially stretching it, thereby reducing the diameter to which the impeller can be radially constrained, compared to, for example, using a rigid shaft to support the membrane's inner edge.

[0088] 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, when the impeller is radially constrained for purposes of inserting the impeller into a cardiac chamber or withdrawing the impeller from a subject, the impeller is axially extended by the distal bushing sliding distally along the axial shaft. After release within the subject, the impeller assumes a radially unconstrained configuration (the configuration in which the impeller is normally positioned when operating), as shown in Figures 3A-3C.

[0089] It should be noted that for illustrative purposes, in some figures, impeller 50 is shown without all of the impeller features shown and described in Figures 3A-3C. For example, some figures show the impeller without suture 53 and / or elongated element 67. The scope of the present application includes the use of an impeller having any of the features shown and described in Figures 3A-3C in combination with any of the devices and methods described herein.

[0090] In some applications, the following technique is used to enhance the bonding of the elastomeric material to at least one helical elongated element in a manner that does not result in protrusion from the effective edge of the impeller blade. The helical elongated element is coated with a bonding agent before being immersed in the elastomeric material. Typically, a bonding agent is selected that has at least two functional groups configured to bond with the helical elongated element and the elastomeric material, respectively. For example, a silane compound, such as n-(2-aminoethyl)-3-aminopropyltrimethoxysilane, may be used that contains a first functional group (e.g., (OH)) configured to bond with the helical elongated element (usually made of an alloy such as Nitinol) and a second functional group (e.g., (NH)) configured to bond with the elastomeric material. Typically, the functional groups in the bonding agent are active for a given period of time (e.g., about one hour or less). During this period, a coating of elastomeric material is then applied around the helical elongated element. Typically, this elastomeric coating is the same or a similar elastomeric material as used for membrane 56. For example, membrane 56 can be made of a polycarbonate-based thermoplastic polyurethane such as Aromatic Carbothane™ (e.g., Aromatic Carbothane™ 75A), and the coating can be the same polycarbonate-based thermoplastic polyurethane or a similar polycarbonate-based thermoplastic polyurethane such as Pellethane™ (e.g., Pellethane™ 90A).

[0091] In some applications, after applying the coating to the helical elongate element, another layer of elastomeric material is sprayed onto the coated helical elongate element. Typically, the sprayed elastomeric material is the same or a similar elastomeric material used for the membrane 56. For example, the membrane 56 can be made of a polycarbonate-based thermoplastic polyurethane such as Aromatic Carbothane™ (e.g., Aromatic Carbothane™ 75A), and the sprayed material can be the same or a similar polycarbonate-based thermoplastic polyurethane such as Pellethane™ (e.g., Pellethane™ 90A). In some applications, applying the spray to the helical elongate element rounds the corners of the helical elongate element. Typically, when the helical elongate element has a cross-section with rounded corners, the elastomeric material forms a layer with a substantially uniform thickness at the interface with the helical elongate element. In some applications, the step of applying a coating of elastomeric material as described in the previous paragraph at least partially rounds the corners of the helical elongate element.

[0092] In some applications, after the helical elongate element is spray-applied, the structure 59 is dipped into an elastomer from which the membrane 56 is made, for example, as described above. In some applications, the material from which the membrane is made is an elastomeric material having an ultimate elongation greater than 300 percent, e.g., greater than 400 percent. Typically, the material has a relatively low molecular weight. In some applications, the material has a melt flow index (an indirect indicator of molecular weight) of at least 4, e.g., at least 4.3. In some applications, the material has a tensile strength greater than 6000 psi, e.g., greater than 7000 psi, or greater than 7500 psi. In some applications, the material is a thermoplastic polyurethane, such as Carbothane™. In some applications, Aromatic Coarbothane™ 75A is used. Typically, such materials combine one or more of the following: no outer diameter loss during the dipping process, fatigue resistance, resistance to deformation due to crimping, and low outer diameter loss during crimping.

[0093] In accordance with the above description of applying film 56 to the helical elongate element, the scope of the present invention includes any technique for applying an additional layer of the same elastomeric material, a different elastomeric material, and / or an intervening material to the helical elongate element by spraying, dipping, or another coating method prior to immersing the helical elongate element in the elastomeric material from which film 56 is created. In some applications, the additional layer of elastomeric material is configured to round the corners of the helical elongate element and / or act as a mediator to strengthen the bond between the helical elongate element and film 56 of material. In some applications, the intervening material (e.g., a silane) is configured to act as a mediator to strengthen the bond between the helical elongate element and film 56 of material.

[0094] Reference is now made to FIGS. 3D and 3E, which are schematic illustrations 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. For illustrative purposes, FIGS. 3D and 3E show the impeller without the web of material 56. 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 string and / or wire around the spring 54, the ring 73 of elements 72 is positioned around the spring, for example, by placing it around a tube 70, which is typically located at the longitudinal center of the spring. Each end of the elongated element 67 is then coupled to each of the helical elongated elements 52. As noted above, the elongated elements 67 are typically flexible but not substantially extensible along the axis defined by the elongated element. Furthermore, each of the elongated elements 67 is typically configured to provide substantially no resistance to compression. Each elongated element 67 is configured to apply a tension to the helical elongated element 52 that prevents the helical elongated element 52 from moving radially outward, such that the separation between the helical elongated element 52 and the central axial spring 54 (in the absence of the elongated element 67) is greater than the length of the elongated element 67. The impeller over-expansion prevention element is configured to prevent radial expansion of the impeller when a force acting on the impeller to move the helical elongated element 52 radially outward (in the absence of the elongated element 67) is acting on the impeller. Typically, each elongated element 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).

[0095] It should be noted that the scope of the present invention includes the use of a single integrated impeller anti-overexpansion element 72 with impellers having configurations different from those shown in Figures 3D-3E. For example, a single anti-overexpansion element 72 may be used with an impeller having an axial structure configured differently than spring 54. Typically, the axial structure defines a lumen therethrough, and the impeller defines lumen 62 therethrough.

[0096] Reference is now made to FIG. 3F, which is a schematic illustration of impeller 50 including a securing element 75 configured to secure elongated element 67 relative to tube 70, in accordance with some applications of the present invention. In some applications, the string or wire comprising elongated element 67 is not wound around tube 70 and does not intersect the longitudinal axis of the impeller. The string or wire is secured relative to tube 70 by securing element 75. Typically, the string or wire is secured to the outer surface of tube 70 at a location on the outer surface of the tube closest to the maximum span of the helical elongated element to which the ends of the string or wire are tied. In some applications, the securing element includes a ring, as shown. In some such applications, the ring defines a small notch (or hole) 80 through which the string or wire passes between the ring and tube 70.

[0097] Reference is now made to Figures 3Gi and 3Gii, which are photographs of an impeller 50 according to some applications of the present invention. As shown, in some applications, by fabricating the impeller using the methods described above, adjacent blades 51 of the impeller 50 are shaped to define a continuous U-shaped curve. As shown by the added curve 55 in Figure 3Gii, when the film of elastomeric material 56 transitions from one blade to the adjacent blade along at least a portion of the length of the impeller, the film forms a continuous U-shaped curve. It should be noted that the curvature of the film of material is substantially uninterrupted even at the spring 54 extending along the axis of the impeller. In some applications, by fabricating the impeller as described above, the film of material has this curvature. Typically, by defining a continuous U-shaped curve, the impeller blades are configured to provide smooth flow lines along which blood flows through the impeller, increasing the efficiency of blood injection by the impeller and / or reducing the risk of hemolysis compared to when adjacent blades do not define a continuous curve (e.g., when the curve is broken at spring 54). In some applications, a generally similar impeller is used with an axial structure configured differently from spring 54 (e.g., a cylindrical axial structure). Typically, the axial structure defines a lumen therethrough, with the impeller defining lumen 62 therethrough. Alternatively, the impeller includes spring 54 (including tube 70) as the axial structure, as shown.

[0098] When viewed from the distal end of the impeller, the pressure side of each impeller blade (i.e., the side that pushes blood during operation of the impeller) is convex in the distal region of the impeller, transitions to a substantially radial orientation in the region of the elongated elements 67, and then is concave in the proximal region of the impeller. (For illustrative purposes, FIG. 3Gii shows the opposite side of the impeller blade from the pressure side (i.e., the "non-pressure side").) Thus, during use, blood pumped by the impeller is first pumped by the convex impeller surface and then by the concave impeller surface. In some applications, the elongated elements 67 are positioned approximately midway along the length of the impeller blade and are configured to facilitate a transition of the film of material from a convex curvature to a concave curvature. For this reason, typically, the impeller blades are substantially radially oriented in the region of the elongated elements 67. Typically, the pressure side of the impeller blade is configured to provide additional flow and / or pressure to blood after it has flowed and / or pressured into the distal region of the impeller by defining a concave surface at the proximal region of the impeller. Alternatively (not shown), the pressure side of each impeller blade (i.e., the side that pushes blood during operation of the impeller) may be concave at the distal region of the impeller, transition to a substantially radial orientation in the region of the elongated elements 67, and then convex at the proximal region of the impeller.

[0099] 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. As noted above, the pump outlet tubing 24 is typically positioned over at least a portion of the frame and extends proximally therefrom. However, for purposes of illustration, Figures 5A-5B show the frame and impeller without the pump outlet tubing 24.

[0100] As shown in FIG. 5B, the frame and impeller are typically maintained in a radially constrained configuration by a 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), e.g., 15-30 mm, or 20-25 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), e.g., 8-18 mm, or 10-15 mm. More typically, when the impeller and frame 34 are arranged in a radially constrained configuration (as shown in FIG. 5B), the impeller has an outer diameter of less than 2 mm (e.g., less than 1.6 mm) and the frame has an outer diameter of less than 2.5 mm (e.g., less than 2.1 mm).

[0101] As mentioned above, the axial shaft 92 typically passes through the axis of the impeller 50 via the impeller lumen 62 (lumen 62 shown in FIG. 3C). Typically, the impeller's 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's distal bushing 58 is slidable relative to the shaft. The axial shaft itself is radially stabilized via proximal and distal radial bearings 116, 118.

[0102] Typically, the joint 31 of the frame 34 is coupled to the proximal radial bearing 116, for example, via a snap-fit ​​connection and / or via welding. Typically, at the distal end of the frame 34, the distal strut joint 33 is disposed in a groove defined by the outer surface of the distal radial bearing 118, which is shaped to match the shape of the distal strut. The proximal end of the distal tip element 107 (defining the distal tip 120) typically holds the distal strut in a closed configuration around the outside of the distal radial bearing 118, as shown. In some applications, the device includes a distal extension 121 extending distally from the distal radial bearing. Typically, the extension is configured to reinforce the area of ​​the distal tip element through which the distal end of the shaft 92 travels (e.g., the axial shaft receiving tube 126, described below, or a portion thereof).

[0103] As mentioned above, the axial shaft 92 is radially stabilized via the proximal radial bearing 116 and the distal radial bearing 118. As mentioned above, the axial shaft then passes through the lumen 62 defined by the impeller, radially stabilizing the impeller against the inner surface of the frame 34, maintaining even a relatively small clearance (e.g., the clearance described above) between the outer edges of the impeller blades and the inner surface of the frame 34 as the impeller rotates. In some applications, the axial shaft 92 is made of stainless steel, and the proximal bearing 116 and / or the distal bearing 118 are made of hardened steel. Typically, when the impeller and frame are crimped (i.e., radially constrained) for insertion into a subject, the distal bushing 58 of the impeller is configured to slide distally along the axial shaft, allowing the impeller to extend axially while the proximal bushing remains in an axially fixed position relative to the axial shaft. More generally, the impeller changes from a radially constrained configuration to a radially unconstrained configuration, or vice versa, by the distal bushing sliding on the axial shaft, while the proximal bushing remains in an axially fixed position relative to the axial shaft.

[0104] Typically, the impeller itself is not directly disposed within either a radial or thrust bearing. Rather, bearings 116 and 118 function as radial bearings for the axial shaft. Typically, pump section 27 (and more generally ventricular assist device 20) is configured to be disposed within a subject and does not include any thrust bearings configured to oppose the thrust generated by the rotation of the impeller. In some applications, one or more thrust bearings are disposed outside the subject (e.g., within motor unit 23 shown in FIGS. 1A, 7A-7Bii), and opposition to the thrust generated by the rotation of the impeller is provided solely by the one or more thrust bearings disposed outside the subject. 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 FIG. 7A) located at the proximal end of drive cable 130 (e.g., outside the subject) may be configured to impart axial motion to the impeller and / or to maintain the impeller within a given range of axial position.

[0105] Reference is now made to FIGS. 6A and 6B, which are schematic illustrations of ventricular assist device 20 at various stages in the motion cycle of ventricular assist device impeller 50 relative to ventricular assist device frame 34, in accordance with some applications of the present invention. In some applications, as described in more detail below with reference to FIGS. 7A through 7Bii, axial shaft 92 (to which the impeller is fixed) is driven to move the impeller axially back and forth within frame 34 by moving the axial shaft in a back and forth axial motion, while the impeller rotates to pump blood through tube 24. Alternatively or additionally, the impeller and axial shaft are configured to move axially back and forth within frame 34 in response to forces acting on the impeller, without the axial shaft being actively driven to move in a back and forth axial motion. Typically, over the course of a subject's cardiac cycle, the pressure differential between the left ventricle and the aorta varies from near zero during ventricular systole (hereinafter "systole") to a relatively large pressure differential (e.g., 50-70 mmHg) during ventricular diastole (hereinafter "diastole"). In some applications, the greater pressure differential for impeller delivery during diastole (and the extensibility of the drive cable 130) pushes the impeller distally relative to the frame 34 during diastole compared to the position of the impeller relative to the frame 34 during systole. The impeller's connection to the axial shaft then causes the axial shaft to move forward. During systole, the impeller (and axial shaft) returns to its systolic position. Thus, the axial back-and-forth movement of the impeller and axial shaft occurs passively, i.e., without the need for active actuation of the axial shaft and impeller to cause the axial back-and-forth movement of the axial shaft and impeller. Figure 6A shows the impeller and axial shaft positioned in a normal systolic position, and Figure 6B shows the impeller and axial shaft positioned in a normal diastolic position.

[0106] In some applications, by moving in an axial back-and-forth motion, the portion of the axial shaft in contact with the proximal and distal bearings 116, 118 continuously changes. In some such applications, other things being equal, the frictional force exerted on the axial shaft by the bearings in this manner is spread over a wider area of ​​the axial shaft than if the axial shaft were not moving 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, from the interface between the axial shaft and the bearings.

[0107] In some applications, when the frame 34 and impeller 50 are radially unconstrained (e.g., when the frame and impeller are located within the left ventricle), the length of the frame exceeds the length of the impeller by at least 2 mm (e.g., at least 4 mm, or at least 8 mm). Typically, the proximal bearing 116 and the distal bearing 118 each have a length of 2-4 mm (e.g., 2-3 mm). Furthermore, typically, the impeller and axial shaft are configured to move axially within the frame in a back-and-forth motion along at least the length of each of the proximal and distal bearings, or along at least twice the length of each bearing. Thus, as the axial shaft moves back and forth, it is wiped clean on either side of each bearing.

[0108] In some applications, the range of motion of the impeller is shown in Figures 6A and 6B, where Figure 6A shows the impeller's most proximal position during the cardiac cycle (typically during systole) and Figure 6B shows the impeller's most distal position during the cardiac cycle (typically during diastole). As shown in Figure 6A, in some applications, the proximal end of the impeller is located at its most proximal position, position Ip, within the proximal conical section of frame 34. As shown in Figure 6B, in some applications, the distal end of the impeller is located at its most distal position, position Id, which is the distal end of the cylindrical section of frame 34. For purposes of this application, the entire section of the frame from Ip to Id may be considered to house the impeller, as this entire section of the frame typically houses at least a portion of the impeller during at least a portion of the cardiac cycle. Typically, during the course of the entire cardiac cycle, the section of the impeller that has the greatest span of the impeller is located within the cylindrical portion of the frame 34. However, the proximal portion of the impeller is typically located within the proximal conical section of the frame during at least a portion of the cardiac cycle.

[0109] Referring again to FIGS. 6A and 6B, see also FIG. 6C, which is an enlarged schematic illustration of a distal tip element 107 including an axial shaft receiving tube 126 and a distal tip 120 of a ventricular assist device 20, according to some applications of the present invention. Typically, the distal tip element 107 is a single, integrated element including both the axial shaft receiving tube 126 and the distal tip 120. In some applications, the distal tip element 107 is configured to be flexible so that the distal tip does not traumatize target tissue (e.g., tissue of the left ventricle) upon contact with the tissue. For example, the distal tip element 107 may be formed from 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 a ventricular assist device is inserted into the left ventricle, for example, a guidewire 10 (FIG. 1B) is first inserted into the left ventricle 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 inside lumen 122. In some applications, a duckbill valve 390 (or a different type of hemostatic valve) is positioned at the distal end of lumen 122 of distal tip 120.

[0110] Typically, during insertion of the ventricular assist device into a subject's ventricle, a delivery catheter 143 is positioned over the impeller 50 and frame 34 to maintain the impeller and frame in their radially constrained configuration. In some applications, a distal tip element 107 extends distally from the delivery catheter during insertion of the delivery catheter into a subject's ventricle. In some applications, at the proximal end of the distal tip element, the distal tip element has a flared portion 124. The flared portion 124 acts as a stop, preventing the delivery catheter from being advanced beyond the flared portion.

[0111] It should be noted that the distal end profile in Figures 6A-6C (and in some other figures) is shown as defining a complete loop where the distal end of the distal tip (where the duckbill valve 390 is located) intersects with a more proximal portion of the distal tip. Typically, as a result of guidewire insertion (such as during insertion of a ventricular assist device into the left ventricle), the distal tip remains partially straight, even after the guidewire is removed from the distal tip. Partial straightening of the distal tip typically occurs when the distal tip is positioned within the left ventricle, and in the absence of external forces acting on the distal tip, the distal tip does not define a complete loop, as shown, for example, in Figures 1B, 15D, and 16A. In some applications, a straightening element 270 is used to insert a guidewire into the distal tip, as described in more detail below, for example, with reference to Figures 23A-23C. Other aspects of the distal tip shape are described in more detail below.

[0112] Reference is now made to FIGS. 6D and 6E, which are schematic illustrations of impeller 50 according to some applications of the present invention. The impeller's proximal bushing 64 is coupled to a proximally extending coupling element 65 to function as a stop. FIG. 6D shows the impeller during the systolic phase of its motion cycle, and FIG. 6E shows the impeller during the diastolic phase of its motion cycle. Typically, the coupling element extends proximally to prevent the central region of the impeller (where the impeller's span is greatest) from sliding proximally into the proximal cone of frame 34. For example, during the systolic phase of the impeller's motion cycle (shown in FIG. 6D), if the impeller slides proximally beyond a given amount, the proximally extending coupling element contacts proximal radial bearing 116, thereby preventing further proximal movement of the impeller. In some applications, the coupling element extends proximally to have an overall length greater than 1.5 mm, e.g., greater than 4 mm. In some applications (not shown), instead of or in addition to a proximally extending coupling element, a separate stop element is disposed on the axial shaft proximally relative to the coupling element. Typically, the stop is configured as described above with respect to the proximally extending 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 movement of the impeller.

[0113] Reference is now made to Figure 7A, which is a schematic illustration of an exploded view of the motor unit 23 of the ventricular assist device 20, in accordance with some applications of the present invention. As shown, the motor unit is typically a handle that houses a motor and is configured to be placed external to the subject. For this reason, the motor unit may alternatively be referred to as a handle unit.

[0114] In some applications, the computer processor 25 of the control console 21 (FIG. 1A) that controls the rotation of the impeller 50 is also configured to control the back and forth motion of the axial shaft. Typically, 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.

[0115] 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, the motor is typically 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 due, for example, 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.

[0116] In some applications, the magnetic coupling of the motor to the drive cable is as shown in FIG. 7A. As shown in FIG. 7A, at least one or more drive magnets 77 (e.g., two drive magnets 77) are 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, as shown, a spacer 85 is bonded to the inner surface of the ring 81 between the two drive magnets. At least one driven magnet 82 is disposed between the drive magnets so that the drive magnet and the driven magnet axially overlap. The driven magnet is coupled to a pin 131, which extends beyond the distal end of the driven magnet 82 and is coupled to the 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, which 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 lumen 133 through which guidewire 10 is inserted into the pin.

[0117] Note that in the application shown in Figure 7A, the drive magnet is positioned outside the driven magnet. However, the scope of this application includes, mutatis mutandis, reversing the configuration of the drive and driven magnets. For example, the proximal end of the drive cable may be coupled to two or more driven magnets positioned around the drive magnet such that the drive magnets and driven magnets axially overlap.

[0118] 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 delivered to the ventricular assist device via the inlet 86 and discharged from the ventricular assist device via the outlet 88. Additional aspects of the purge system are described below.

[0119] Typically, magnet 82 and pin 131 are held in a relatively fixed axial position within motor unit 23. (In some applications, magnet 82 has a small degree of freedom of movement axially and / or rotationally relative to other components of the motor unit, such as drive magnet 77. In some applications, such movement is measurable, as described in more detail below.) Typically, the proximal end of the drive cable is coupled to pin 131, thereby holding it in a fixed axial position relative to the pin. Typically, drive cable 130 extends from pin 131 to axial shaft 92, thereby at least partially fixing the axial position of the axial shaft, and therefore impeller 50. In some applications, the drive cable is somewhat stretchable. For example, the drive cable may be made of a stretchable coiled wire, as described in more detail below. 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 slightly stretchable), but restricts 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 a relatively fixed axial position and the drive cable's limited elasticity).

[0120] Reference is now made to FIGS. 7Bi and 7Bii, which are schematic illustrations of a motor unit 23 according to some applications of the present invention. Generally, the motor unit 23, as shown in FIGS. 7Bi and 7Bii, is similar to that shown in FIG. 7A, and unless otherwise noted, the motor unit 23 shown in FIGS. 7Bi and 7Bii includes similar components to the motor unit 23 shown in FIG. 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 opening 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 movement of components of the ventricular assist device.

[0121] As described 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 axial shaft being actively driven to move in an axial back and forth motion. Typically, over the course of a subject's cardiac cycle, the pressure differential between the left ventricle and the aorta varies from near zero during systole to a relatively large pressure differential (e.g., 50-70 mmHg) during diastole. In some applications, because the pressure differential for impeller delivery is greater during diastole (and because the drive cable is stretchable), the impeller is pushed distally relative to the frame 34 during diastole, compared to its position relative to the frame 34 during systole. The impeller's connection to the axial shaft then causes the axial shaft to move forward. During systole, the impeller (and axial shaft) return to its systolic position. In this manner, axial back and forth movement of the impeller and axial shaft occurs in a passive manner, i.e., without the need for active driving of the axial shaft and impeller to cause the axial shaft and impeller to move back and forth.

[0122] Reference is now made to FIG. 8A, which is a graph showing experimentally measured changes in the length of a ventricular assist device's drive cable against varying pressure gradients from the device's impeller. Using the impeller and drive cable described herein, a glycerin-based solution was pumped into a chamber. The chamber was configured to replicate the left ventricle and aorta, and the solution had similar properties (e.g., density and viscosity) to blood. The pressure gradient relative to the impeller's pumping motion was varied pulsatilely to represent the pulsating pressure gradient relative to normal pumping as the impeller pumps blood from the left ventricle to the aorta. Simultaneously, images of the drive cable's movement were captured, and the change in drive cable length was determined by analyzing these images. The graph shown in FIG. 8A shows the measured change in drive cable length as a function of pressure gradient. As shown in FIG. 8A, as the pressure gradient relative to the impeller's pumping motion increased, the drive cable gradually stretched. 8A and as discussed above, the impeller typically moves back and forth relative to the frame 34 in response to changes in pressure against which the impeller pumps blood (e.g., the pressure difference between the left ventricle and the aorta). The movement of the impeller, in turn, causes some elongation of the drive cable 130.

[0123] In some applications, as the ventricular assist device operates, the computer processor 25 of the control console 21 (FIG. 1A) is configured to measure an indicator of the tension in the drive cable 130 and / or an indicator of the pressure applied to the impeller (indicative of the pressure difference between the left ventricle and the aorta) by measuring the axial movement of the drive cable. In some applications, based on the measured indicators, the computer processor detects events 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.

[0124] 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 within the motor unit 23, as shown in FIG. 7A . (Sometimes, the sensor 84 is referred to as a magnetometer 84.) In some applications, the driven magnet is typically held in place relative to the drive magnet via a magnetic coupling rather than a rigid mechanical coupling, so that axial back-and-forth movement of the impeller causes measurable back-and-forth movement of the inner driven magnet 82 relative to the outer drive magnet(s) 77. Note that the axial movement of the magnets is typically substantially smaller than the axial movement of the impeller, because the full range of motion of the impeller is not transmitted along the length of the drive cable. In some applications, the magnetometer measures the change in the magnetic field generated by one of the magnets to measure the axial movement of the drive cable 130 and, in turn, determine the pressure on the impeller pumping. For example, the inner driven magnet 82 may be axially longer than the outer drive magnet 77. Because the inner magnet is longer than the outer magnet, some magnetic field lines emanate from the inner magnet but do not reach the outer magnet. These field lines generate magnetic flux, measured by the magnetometer, that changes as the drive cable and inner magnet move axially. During operation, the motor 74 rotates, generating an AC signal at the magnetometer, typically having a frequency between 200 Hz and 800 Hz. Changes in drive cable tension, typically due to the subject's cardiac cycle, typically produce a low-frequency envelope in the signal measured by the magnetometer, typically having a frequency between 0.5 and 2 Hz. In some applications, a computer processor measures the low-frequency envelope and derives the subject's cardiac cycle from the measured envelope.

[0125] In some applications, the magnetometer measurements are first calibrated so that the change in magnetic flux per unit change in pressure relative to impeller pumping (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, during systole, the left ventricular pressure is equal to the aortic pressure. Therefore, in some applications, the subject's aortic pressure is measured, and then the subject's left ventricular pressure at a given time is calculated by a computer processor. This calculation is 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 (when left ventricular pressure is assumed to be equal to aortic pressure). For example, as described in more detail below, the subject's aortic pressure can be measured by measuring the pressure within the channel 224 defined by the delivery catheter 143. In some applications, the techniques described above 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.

[0126] 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, another parameter is measured to determine left ventricular blood pressure (and / or another physiological parameter, such as an event 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 impeller rotation at a given rotational speed and the pressure differential generated by the impeller. (It should be noted that a portion of the pressure difference generated by the impeller is used to overcome the pressure gradient against which the impeller pumps, and also to actively pump blood from the left ventricle to the aorta by creating a positive pressure difference between the left ventricle and the aorta. Furthermore, the relationship between the above factors changes over the course of the cardiac cycle.) In some applications, calibration measurements are 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 by a computer processor. This calculation is 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 differential generated by the impeller. In some applications, the above-described 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 change in the rotational speed of the impeller is taken into account in the above-described calculation. In some applications, the above-described 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.

[0127] Typically, the tube 24 has a known cross-sectional area (when the tube is open for blood flow therethrough). In some applications, the flow 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 in the ventricular assist device (or type of ventricular assist device) performing the calculation. In some applications, a ventricular pressure-volume loop is derived based on the determined ventricular pressure.

[0128] Referring again to FIG. 7A , in some applications, in addition to 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 motor directly drives the drive magnet to rotate, so the second magnetometer measures the motor's magnetic flux density, which 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 impeller's rotational speed, and / or the pressure gradient against which the impeller pumps. In some applications, the driven magnet is typically held in place relative to the drive magnet via a magnetic coupling rather than a rigid mechanical coupling, so that the torque generated on the impeller produces a measurable torque on the inner driven magnet 82 relative to the outer drive magnet 77. It should be noted that the torque generated on the driven magnet is substantially less than that generated on the impeller because the torque generated on the impeller is typically not transmitted along the length of the drive cable, however, the torque generated on the impeller is typically transmitted at least partially to the driven magnet via the drive cable.

[0129] Torque transmitted to the driven magnet typically induces 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 drive magnet). In some applications, changes in the torque of the impeller cause a change in 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 change in this phase difference and determines a physiological parameter of the subject, at least in part, accordingly. For example, based at least in part on the change in phase difference, the computer processor can determine the difference between the subject's left ventricular pressure and the subject's aortic pressure, the subject's left ventricular pressure, an event in the subject's cardiac cycle, the subject's cardiac afterload, and / or another physiological parameter. In some applications, the techniques described in this paragraph are used in place of the above-described techniques for determining physiological parameters using magnetic flux density measurements and / or power consumption measurements. Alternatively, two or more of these techniques are used in combination with each other. For example, it is possible to determine a physiological parameter of a subject based on a mathematical model incorporating two or more measurements, and / or to use one of these techniques to confirm an estimate of a physiological parameter of a subject made using another of these techniques.

[0130] Reference is now made to Figures 8B and 8C, which are graphs demonstrating the correlation between the phase difference signal and the pressure gradient for delivery by impeller 50, in accordance with some applications of the present invention.

[0131] The graph shown in FIG. 8B illustrates the results of an experiment in which the ventricular assist device described herein pumped blood against various pressure gradients 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 relative to impeller pumping based on a combination of the phase difference signal, the magnetic flux amplitude signal, and the current consumption by the motor. The graph shown in FIG. 8B illustrates the estimated pressure gradient relative to the measured pressure gradient. As shown, the linear regression model incorporating the phase difference measurement provides a reliable method for estimating the pressure gradient relative to impeller pumping.

[0132] The graph shown in FIG. 8C illustrates experimental results in which the ventricular assist device described herein pumped blood against various pressure gradients in a pulsatile in vitro system (i.e., the pressure gradient varied pulsatilely). A space state model was used to estimate the pressure gradient relative to impeller pumping based on a combination of the phase difference signal, the magnetic flux amplitude signal, and the current consumption by the motor. The graph shown in FIG. 8C illustrates the estimated pressure gradient relative to the measured pressure gradient. As shown, the space state model incorporating the phase difference measurement provides a reliable method for estimating the pressure gradient relative to impeller pumping.

[0133] In accordance with the above, and in accordance with some applications of the present invention, a magnetic phase difference between one or more driven magnets and one or more driving 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 changes in the phase difference, a computer processor can determine the difference between the subject's left ventricular pressure and the subject's aortic pressure, the subject's left ventricular pressure, an event in the subject's cardiac cycle, the subject's cardiac afterload, and / or another physiological parameter. In some applications, the phase difference measurement is combined with one or more additional measurements, such as a magnetic flux amplitude measurement, power consumption by the motor, and / or current consumption by the motor, to determine the physiological parameter. Typically, such measurements are combined with a mathematical model, such as a linear regression model and / or a space state model.

[0134] 9A-9G, which are schematic illustrations of various views of a motor unit support 170 configured to support a motor unit 23 on a patient's leg 172, in accordance with some applications of the present invention. In some applications, the ventricular assist device is inserted into the patient via a femoral connection point 173, and the motor unit support is configured to be positioned on the patient's upper thigh below the femoral connection point, as shown. Typically, the motor unit support is configured to at least partially isolate the patient's leg from vibrations and / or heat generated by the motor unit during operation of the motor unit.

[0135] In some applications, the motor unit support includes a curved base 176 configured to be placed on the patient's upper thigh and a motor unit dock 178 to which the motor unit docks. A gap 179 typically exists between the motor unit dock and the curved base of the motor unit support, separating the patient's leg from the motor unit and serving to at least partially isolate the patient's leg from vibrations and / or heat generated by the motor unit during operation. In some applications, the motor unit support is configured to receive a strap 174 within the gap, which is used to secure the motor unit support to the patient's leg. The strap is typically stretchable and / or adjustable to fit the patient's leg.

[0136] Typically, the motor unit support includes coupling elements 180 for coupling the motor unit dock to the motor unit (e.g., as shown in FIG. 9D ). As mentioned above, in some applications, the motor unit includes ventilation openings 93 configured to facilitate dissipation of heat generated by the motor. In some applications, for example, as shown in FIG. 9E , the coupling elements comprise snap-fit ​​coupling elements configured to couple the motor unit dock to the motor unit by snapping into the ventilation openings of the motor unit. In some applications, the motor unit includes ventilation openings on both sides so that either side of the motor unit can be coupled to the motor unit dock.

[0137] 10A, 10B, and 10C, which are schematic illustrations of a drive cable 130 of a ventricular assist device 20 according to some applications of the present invention. Typically, 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 external to the subject) to the proximal end of the axial shaft 92 (e.g., the close-up on the left side of FIG. 5A shows the connection between the distal end of the drive cable and the proximal end of the axial shaft). 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 (i.e., the portion corresponding to arrow 145 in FIG. 10A) while 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 10A-10C, the drive cable includes an outer layer 136 and an inner layer 138, which are coaxial with one another and each may include a coiled wire.

[0138] The drive cable is typically disposed within a first outer tube 140 configured to remain stationary as the drive cable undergoes rotational and / or axial back-and-forth movement. The first outer tube is configured to essentially act as a bearing tube for the drive cable along its length. For this reason, the first outer tube may be referred to herein as the drive cable bearing tube. Drive cable bearing tubes are described in more detail below with reference to FIG. 10D . 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 material that is more flexible than the material of the drive cable bearing tube (e.g., nylon and / or polyether block amide) and is typically thicker than the drive cable bearing tube.

[0139] Typically, during insertion of the impeller and frame into the left ventricle, the impeller 50 and frame 34 are maintained in a radially constrained configuration by the delivery catheter 143. 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. 10A , the delivery catheter remains within the subject's aorta during operation of the left ventricular device, and the outer tube 142 is disposed within the delivery catheter. (Although FIG. 10A shows the distal end of the delivery catheter disposed within the aortic arch, in some applications, the distal end of the delivery catheter is disposed within 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. (It should be noted that, for illustrative purposes, the channel shown in FIG. 10A is not to scale.) In some such applications, the subject's aortic blood pressure is measured by measuring the pressure of blood within the channel 224. For example, pressure sensor 216 (shown schematically 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 within channel 224. Typically, to retract the left ventricular device from the subject, a delivery catheter is advanced over the impeller and frame so that the impeller and frame are in a radially constrained configuration. The catheter is then retracted from the subject.

[0140] In some applications, the drive cable 130 is comprised of multiple coaxial layers, each layer including multiple coiled wires 134. For example, as shown in FIGS. 10A-10C , the drive cable includes an outer layer 136 and an inner layer 138, each including a coiled wire. Typically, if the impeller rotates in a direction such that rotation of the drive cable in this direction at least partially tightens the coiled wires of the drive cable, the impeller advances relative to the frame upon initiation of rotation due to the coiled wires tightening (i.e., winding to a smaller coil radius) and therefore stretching axially. In some applications, at least a portion of the drive cable is configured such that (a) in response to the impeller rotating in a predetermined rotational direction to pump blood from the left ventricle to the aorta, (b) rotation of the drive cable in this direction at least partially unwinds the coiled wires of the drive cable along a portion of the drive cable, thereby axially shortening the portion of the drive cable (i.e., unwinding to a larger coil radius). In some applications, the impeller is configured to rotate in a counterclockwise direction when viewed from the proximal end to the distal end of the impeller, and the coiled wire in each layer of the drive cable is configured as a left-handed layer. As the impeller rotates in the counterclockwise direction, opposing pressure is exerted on the coiled wire in each layer of the drive cable, causing them to partially unwind, thereby shortening each layer of the drive cable. Alternatively, the impeller is configured to rotate in a clockwise direction when viewed from the proximal end to the distal end of the impeller, and the coiled wire in each layer of the drive cable is configured as a right-handed layer.

[0141] Reference is again made to Figures 6A and 6B, which illustrate the range of axial back-and-forth motion of the impeller within frame 34 during a cardiac cycle, according to some applications of the present invention. As noted above, Figure 6A illustrates the most proximal position of the impeller during a cardiac cycle (typically during systole), and Figure 6B illustrates the most distal position of the impeller during a cardiac cycle (typically during diastole). As shown in Figure 6A, in some applications, the most proximal position will have the proximal end of the impeller positioned at position Ip, which is within the proximal conical section of frame 34. As shown in Figure 6B, in some applications, the most distal position will have the distal end of the impeller positioned at position Id, which is at the distal end of the cylindrical section of frame 34.

[0142] 10A-10C and the drive cable configurations described in conjunction with those figures, typically, by configuring the drive cables as described above, the length of the frame 34 does not need to accommodate distal movement of the impeller caused by axial elongation as the drive cable tightens when the impeller and drive cable begin to rotate. It should be noted that in some applications, the drive cable will not shorten because the extent to which the drive cable unwinds and shortens axially is limited by the drive cable bearing tube 140 (and / or for other reasons). Furthermore, in some applications, although theoretically the drive cable would shorten if the impeller were to rotate in the absence of any fluid, in practice the drive cable will not shorten when the impeller rotates within the subject's blood flow. This is because, as the impeller rotates within the subject's blood flow, the counter pressure of the blood being pumped by the impeller will push the impeller distally, thereby offsetting the unwinding of the drive cable (which would shorten the drive cable). In some applications, the drive cable actually elongates during diastole compared to when the impeller is stationary because the pressure gradient against which the impeller pumps is greater than during systole. Typically, even in such applications, the coil windings are configured as described above so that the drive cable does not elongate, at least during systole, compared to when the impeller is stationary.

[0143] In some applications, in addition to configuring the coiled wire orientation within the drive cable as described above, the drive cable may initially be held in a preloaded (i.e., pretensioned) state within frame 34, such that the drive cable and impeller are already stretched before they begin to rotate. That is, even before the drive cable and impeller begin to rotate, the drive cable is in a stretched state relative to its resting state (i.e., the state of the drive cable when no external forces are acting on it). For example, coupling element 65 (which in some applications extends proximally as described above with reference to FIGS. 6D-6E ) may engage proximal bearing 116 to hold the drive cable in a preloaded state. Typically, due to (a) the configuration of the coiled wire orientation within the drive cable as described above and / or (b) the drive cable being held in a preloaded state within frame 34, the drive cable will not stretch when the impeller and drive cable begin to rotate, even during diastole (e.g., when the impeller is pumping against a pressure gradient of 50-70 mmHg). In some applications, the drive cable does not stretch, even during diastole, until the impeller is rotating at speeds greater than 6,000 RPM or greater than 8,000 RPM. In some applications, this drive cable configuration limits the amount of stretch of the drive cable over the course of a cardiac cycle to less than 5 mm (typically less than 4 mm), even when the impeller is rotating at speeds greater than 20,000 RPM. Furthermore, in some applications, this drive cable configuration ensures that the widest portion of the impeller (typically in the middle of its length) is located within the proximal half of the frame 34 for more than 50 percent of the cardiac cycle, even when the impeller is rotating at speeds greater than 20,000 RPM.

[0144] In some applications, the ventricular assist device is configured such that, during diastole, even when the impeller is rotating at greater than 20,000 RPM, there is an axial distance between the impeller at its maximum diameter and the blood inlet. For example, the ventricular assist device is configured such that, during diastole, even when the impeller is rotating at greater than 20,000 RPM, there is an axial distance of more than 3 mm (e.g., more than 5 mm) between the impeller at its maximum diameter and the blood inlet. In some such applications, this reduces hemolysis (compared to a shorter or no axial distance between the impeller at its maximum diameter and the blood inlet) and / or increases the effectiveness of the impeller by reducing turbulence by at least partially aligning the flow lines of blood entering the blood inlet with the longitudinal axis of the impeller before it is pumped by the impeller.

[0145] Typically, the coiled wires in the outer layer 136 of the drive cable are fewer in number than in the inner layer 138, and each wire is wider than the wires in the inner layer. For example, the ratio of the number of wires in the outer layer to the number of wires in the inner layer can be 2:3 to 2:5. In some applications, the outer layer includes 4 to 8 wires, and the inner layer includes 10 to 14 wires. In some applications, the ratio of the diameter of the wires in the outer layer to the diameter of the wires in the inner layer is 3:2 to 5:2. In some applications, the diameter of the wires in the outer layer is 0.15 mm to 0.2 mm, and the diameter of the wires in the outer layer is 0.075 mm to 0.125 mm. Typically, the coiled wires in both layers are made of alloy. In some applications, the inner diameter of the drive cable (i.e., the diameter of the lumen 132) is 0.4 mm to 0.7 mm. More typically, the outer diameter of the drive cable (defined by the outer layer 138) is 1 mm to 1.2 mm. In some applications, the overall length of drive cable 130 is less than 1 meter (e.g., 1.1 meters) and / or less than 1.4 meters (e.g., less than 1.3 meters), such as between 1 and 1.4 meters, or between 1 and 1.3 meters. Typically, the diameters of lumens 122 and 133 are generally similar to the diameter of lumen 132.

[0146] In some applications, the drive cable includes a first (distal) section and a second (proximal) section. Typically, the first section is configured to be positioned in the aortic arch of the subject, and the second section is configured to be positioned along the descending aorta, typically extending to the motor unit 23 outside the subject. Typically, in locations where the drive cable 130 experiences a significant curvature, such as the aortic arch, it is desirable for the drive cable to be relatively flexible. However, a more flexible drive cable typically also exhibits greater axial stretch than a less flexible drive cable. Thus, in some applications, there is a trade-off between the desirability of the drive cable having sufficient flexibility to conform to the curvature of the aortic arch and the undesirability of the drive cable experiencing significant axial stretch (which may result in a loss of control over the axial position of the impeller). In some applications, each section of the drive cable has a respective level of flexibility. For example, a first portion of the drive cable configured to be placed in the aortic arch can have a first flexibility, and a second portion of the drive cable configured to be placed in the descending aorta can have a second flexibility, where the first flexibility is greater than the second flexibility.

[0147] In some applications, the coils of wire 134 in the distal portion of the drive cable have different parameters than those used in the proximal portion, thereby configuring the distal portion to have greater flexibility than the proximal portion. In some applications, the distal portion has generally similar parameters (i.e., with respect to the inner and outer layers) to those described above. In some applications, the proximal portion of the guidewire includes a single layer of coiled wire. Typically, there are fewer coiled wires in the proximal portion of the drive cable than in the outer layer of the distal portion of the drive cable. Typically, the ratio of the number of wires in the outer layer of the distal portion of the drive cable to the number of wires in the proximal portion of the drive cable is between 3:2 and 5:2. In some applications, there are between 3 and 6 wires in the proximal portion of the drive cable. Typically, the diameter of the coiled wires in the proximal portion of the drive cable is larger than the diameter of the coiled wires in the outer layer of the distal portion of the drive cable. In some applications, the ratio of the diameter of the wires in the proximal portion of the drive cable to the diameter of the wires in the outer layer of the distal portion of the drive cable is between 3:2 and 5:2. In some applications, the diameter of the wire in the distal portion of the drive cable is between 0.2 mm and 0.35 mm. Typically, the inner and outer diameters of both the distal and proximal portions of the drive cable are similar (or identical) to one another, typically as described above.

[0148] Reference is now made to FIG. 10D , which is a schematic diagram of a first outer tube 140 serving 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, with 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 blend 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 levels of friction and high wear resistance. More typically, the outer layer is configured to provide additional strength to the drive cable bearing tube while providing sufficient flexibility to conform to the curvature of, for example, the aortic arch. Typically, the coil is configured to maintain the substantially circular cross-section of the drive cable bearing tube, even in areas where the drive cable bearing tube is highly curved (e.g., within the aortic arch). Typically, without the coil, the drive cable bearing tube tends to flatten in such areas to form an oval cross section.

[0149] Reference is now made to Figures 11A, 11B, 11C, 11D, and 11E, which are schematic illustrations of apparatus and methods for purging the drive cable 130, radial bearings 116, 118, and / or impella bushing 58 of a ventricular assist device 20, in accordance with some applications of the present invention.

[0150] Referring initially to FIG. 11A , the axial shaft and drive cable typically define a continuous lumen 132 therethrough. In some applications, the left ventricular device is guided into the aorta and left ventricle by placing the axial shaft and cable over guidewire 10 (as described above) and disposing the guidewire within lumen 132. Typically, the guidewire is inserted through a duckbill valve 390 (or other hemostatic valve) located at the distal end of the distal tip of distal tip element 107. The guidewire passes through lumen 122 (at the distal tip), at which point it enters lumen 132 defined by the axial shaft. The guidewire then continues through lumen 132 to the proximal end of the drive cable. From the proximal end of the drive cable, the guidewire advances through lumen 133 defined by pin 131, which remains external to the subject after the distal end of ventricular assist device 20 has been inserted into the subject's left ventricle. Typically, once the distal end of the ventricular assist device is positioned within the subject's left ventricle, the guidewire is retracted from the subject's body by pulling it from the proximal end of lumen 133. Next, as shown in FIG. 7A , the axial position of driven magnet 82 (with pin 131 disposed therein) is fixed so that it is positioned between drive magnets 77. For example, the portion of motor unit 23 in which the driven magnet is disposed may be coupled to the portion of motor unit 23 in which drive magnet 77 is disposed using click-lock element 150 (shown in FIG. 11B ). In some applications, techniques such as those described below with reference to FIGS. 23A-23C are used to insert a guidewire into distal tip element 107. In some applications, by using axial shaft and cable lumen 132 as described above, it is not necessary to provide an additional guidewire guide for use in inserting left ventricular assist device 20.

[0151] In some applications, lumen 132 is further used by a purge system 29 (shown in FIG. 1A ) of the ventricular assist device. Typically, first and second outer tubes 140, 142 remain stationary during drive cable rotation. In some applications, purge system 29 controls the flow of a purge fluid (e.g., a fluid containing glucose or dextrose) via inlet 86 and outlet 88 (shown in FIGS. 7A through 7Bii, 11B, and 11C ). The fluid is configured to remove air from the space between the drive cable and the outer tubes, and / or reduce frictional forces between drive cable 130 (which rotates) and outer tube 140 (which remains stationary during drive cable rotation), and / or reduce frictional forces between axial shaft 92 and proximal bearing 116 and / or distal bearing 118.

[0152] Referring again to FIG. 11A , in some applications, purge fluid is pumped between the first and second outer tubes 140, 142. An opening 146 is located in the first outer tube near the proximal bearing. In some applications, purge fluid is pumped through a purge fluid channel 226 defined between the first and second outer tubes, as described in more detail below with reference to FIG. 21 . In some applications, purge fluid flows between the first outer tube 140 and the drive cable 130 through the opening 146, as indicated by purge fluid flow arrows 148 in FIG. 11A . In this manner, the interface between the drive cable 130 (which rotates) and the outer tube 140 (which acts as a drive cable bearing tube and remains stationary during drive cable rotation) is purged. In some applications, a portion of the purge fluid also flows to the interface between the axial shaft and the proximal bearing 116, as indicated by purge fluid flow arrows 149 in FIG. 11A , thereby purging the interface (and / or reducing frictional forces at the interface). Also, purge fluid flow generally in the direction of arrow 149 prevents blood from entering the interface between the axial shaft and the proximal bearing.

[0153] As mentioned above (see FIGS. 10A-10C ), the drive cable typically includes multiple coiled wires. In some applications, purge fluid enters the lumen 132 defined by the drive cable through gaps in the coiled wires. Once the purge fluid is disposed within the lumen 132, it flows in both a proximal and distal direction, as indicated by arrow 151 in FIG. 11A . Distal-flowing purge fluid typically exits the distal end of the lumen 132 and flows toward the lumen 122 defined by the distal tip, as indicated by arrow 152 in FIG. 11A . At the end of the distal tip, the purge fluid is typically prevented from exiting the distal tip by a duckbill valve 390. Thus, a portion of the purge fluid typically flows to the interface between the axial shaft and the distal bearing 118, thereby purging the interface (and / or reducing frictional forces at the interface), as shown by purge fluid flow arrow 154 in Figure 11A. The flow of purge fluid in the direction of arrow 154 also typically prevents blood from entering the interface between the axial shaft and the distal bearing.

[0154] As mentioned above, once purging fluid is placed within lumen 132, it flows in both proximal and distal directions, as indicated by arrow 151 in FIG. 11A. Referring to FIG. 11B, typically at the proximal end of ventricular assist device 20, purging fluid flows out the proximal end of lumen 132 in the direction of arrow 156 and out the proximal end of lumen 133 defined by pin 131. In some applications, purging fluid then flows in the direction of arrow 157 and around driven magnet 82 to reduce frictional forces on the driven magnet. In some applications, purging fluid then flows out outlet 88 in the direction of arrow 158. Typically, the purging fluid is then discarded. Alternatively, the purging fluid is pumped back into the device via inlet 86.

[0155] Referring to the above description of the purging procedures typically used with ventricular assist device 20, it should be noted that lumens 122, 132, and 133 (previously used to facilitate insertion of the device over guidewire 10, as discussed above) are typically used as flow paths for purging fluid during use of the ventricular assist device.

[0156] 11C, in some applications, the ventricular assist device includes an additional purge fluid inlet 89, which is typically used to deliver purge fluid into a channel 224 between the delivery catheter 143 and the outer tube 142. In some applications, the purge fluid is delivered into this channel at a pressure low enough that aortic blood pressure can be sensed through this channel, as described elsewhere herein. In some applications, rather than continuously delivering fluid into channel 224, fluid is delivered into the channel periodically to flush the channel. In some applications, port 89 and channel 224 are used for aortic pressure sensing. For example, a pressure sensor 216 (shown schematically in FIG. 1A) may be located in channel 224, in port 89, and / or at another location in fluid communication with channel 224.

[0157] 11D and 11E , in some applications, the axial shaft 92 includes a purge fluid hole configured to allow purge fluid to flow out of the lumen 132 defined by the axial shaft 92. In some applications, the axial shaft defines a purge fluid hole 190 near the distal bushing 58 of the impeller 50. As described above, in some applications, the distal bushing is configured to be slidable relative to the axial shaft. In some such applications, the interface between the distal bushing and the axial shaft is purged by purge fluid flowing out of the purge fluid hole 190. In some applications, the axial shaft defines a hole 192 near the distal radial bearing 118. In some such applications, the interface between the distal radial bearing and the axial shaft is purged by purge fluid flowing out of the purge fluid hole 192. In some applications, the axial shaft defines a hole 194 near the proximal radial bearing 116. In some such applications, the interface between the distal radial bearing and the axial shaft is purged by purge fluid flowing out of purge fluid holes 194 .

[0158] Reference is now made to FIGS. 12A and 12B, which are schematic illustrations of a ventricular assist device 20 including a liner 39 lining the inside of a frame 34 that houses an impeller 50, according to some applications of the present invention. (For illustrative purposes, the liner 39 and pump outlet tubing 24 on the side of the device facing out of the page are shown as transparent in FIGS. 12A-12B.) In some applications, the liner 39 is disposed on the inside of the frame 34 to provide a smooth inner surface through which blood is pumped by the impeller. Typically, the smooth surface provided by the coating material reduces hemolysis caused by blood pumped by the impeller 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®).

[0159] Typically, the liner is disposed on at least the inner surface of the cylindrical portion of the frame 34 (the cylindrical portion is shown, for example, in FIGS. 2A-2C). In some applications, the pump outlet tube 24 also covers the cylindrical portion 38 of the frame 34 on the outside of the frame, e.g., the pump outlet tube 24 and the liner 39 overlap over at least 50 percent of the length of the liner, e.g., the entire length of the cylindrical portion of the frame 34 as shown in FIG. 12A. In some applications, the pump outlet tube 24 and the liner 39 only partially overlap, e.g., as shown in FIG. 12B. 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 inserting the ventricular assist device 20 into a subject, the impeller is advanced distally within the frame 34 so 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 positioned within the overlap area between the pump outlet tube and the liner. 1D, in some applications, the pump outlet tube 24 extends to the end of the distal conical portion 40 of the frame, the pump outlet tube defining a plurality of lateral blood inlets. In some such applications, the cylindrical portion of the frame is lined with a liner 39.

[0160] Typically, in the overlap area between the liner 39 and the pump outlet tube 24, the liner 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. 12A ). Typically, in the overlap area between the liner 39 and the pump outlet tube 24, the pump outlet tube and the liner are bonded to one another, for example, by vacuum, by adhesive, and / or using a thermoforming procedure, for example, as described below.

[0161] 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, 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 where the liner and pump outlet tube overlap along at least a portion of the frame 34 (e.g., along the cylindrical portion of the frame 34), the pump outlet tube and liner are bonded to each other and / or the frame as follows: First, the liner is placed on a mandrel. Then, the frame is placed on the liner. Next, the pump outlet tube 24 is placed around the outside of the frame. In some applications, the frame is heated to a temperature higher than the thermoforming temperature of the pump outlet tube 24 but lower than the thermoforming temperature of the liner 39 to shape the pump outlet tube 24 to match the struts of the frame 34 without deforming the liner. Typically, the frame is heated from the inside of the frame using a mandrel. Typically, while the frame is being heated to the above temperatures, an outer tube (typically made of silicone) applies pressure to the pump outlet tube 24, pushing it radially inward to conform to the shape of the struts of the frame, as shown in cross section in Figure 12A. In some applications, the combination of the frame, liner, and portion of the pump outlet tube 24 positioned around the frame is then set to the desired shape and dimensions using setting techniques known in the art.

[0162] In some applications (not shown), the density of the frame struts at the distal end of the frame cylindrical portion is higher than the density of the struts in other portions of the frame cylindrical portion. In some such applications, the higher density of the frame struts at the distal end of the frame cylindrical portion facilitates coupling of the liner and / or pump outlet tubing to the frame. In some applications, the liner and / or pump outlet tubing do not extend to the end of the frame cylindrical portion, as described with reference to FIG. 13, for example. In some such applications, the density of the frame struts is higher at the longitudinal location along the frame cylindrical portion where the liner and / or pump outlet tubing terminates, compared to other locations along the frame cylindrical portion.

[0163] Reference is now made to FIG. 13, which is a schematic illustration of a ventricular assist device 20 in which at least a distal portion 333 of the cylindrical portion 38 of the frame 34 is uncovered, according to some applications of the present invention. In some applications, during the impeller's axial back-and-forth motion cycle, even when the impeller is positioned at its most distal position within the frame 34, the portion of the impeller at its maximum span does not advance beyond a given position within the cylindrical portion of the frame (e.g., as described above with reference to FIGS. 10A-10C). In some applications, the portion of the frame located distally beyond this position is uncovered by either the pump outlet tube 24 or the liner 39. (Note that for illustrative purposes, the frame is shown without the liner 39; however, in some applications, the frame is lined with the liner 39. Typically, even in such applications, the distal portion 333 of the cylindrical portion of the frame is uncovered by either the pump outlet tube 24 or the liner 39.)

[0164] In some applications, the uncovered distal portion of the cylindrical frame portion functions as a substantial enlarged inlet because blood flows from the sides of the cylindrical frame portion into the cylindrical frame portion (as shown by the blood flow arrows in FIG. 13 ). In some applications, this reduces hemolysis caused by the impeller pumping blood. Alternatively, or additionally, by leaving a portion of the cylindrical frame portion uncovered, the diameter of the pump portion 27 can be reduced if the pump portion is configured to be radially constrained. For example, to reduce the diameter of the pump portion of a ventricular assist device (compared to when the widest portion of the impeller overlaps the covered portion of the cylindrical frame portion and the widest portion of the impeller overlaps the frame and the covering material), the pump portion can be radially constrained so that the widest portion of the impeller overlaps the uncovered portion of the cylindrical frame portion.

[0165] In some applications, the ventricular assist device is configured such that, during diastole, there is an axial distance between the impeller at its largest diameter and the blood inlet. For example, the ventricular assist device is configured such that, during diastole, there is an axial distance of more than 3 mm (e.g., more than 5 mm) between the impeller at its largest diameter and the blood inlet (e.g., as described above with reference to Figures 10A-10C). In some such applications, this reduces hemolysis (compared to a shorter or no axial distance between the impeller at its largest diameter and the blood inlet) and / or increases the effectiveness of the impeller by reducing turbulence by at least partially aligning the flow lines of blood entering the blood inlet with the longitudinal axis of the impeller before it is pumped by the impeller.

[0166] Reference is now made to Figure 14, which is a schematic illustration (a transverse cross-section of the left ventricle) of a ventricular assist device 20 positioned inside a subject's left ventricle 22, in accordance with some applications of the present invention. (Figure 14 shows, for purposes of illustration, an aortic valve 26 superimposed on the transverse cross-section of the left ventricle, even though the aortic valve is in a plane different from the plane of the main cross-section.) Reference is now made to Figures 15A-15D, which are schematic illustrations of a distal tip element 107 of a ventricular assist device that is at least partially curved to define a curvature similar to that of a question mark, in accordance with some applications of the present invention, and to Figures 16A-16B, which are schematic illustrations of the ventricular assist device of Figures 15C-15D positioned inside a subject's left ventricle, in accordance with some applications of the present invention.

[0167] In some applications, the ventricular assist device is guided by a guidewire inserted toward the apex 342 of the left ventricle. The walls of the left ventricle are considered to be comprised of a septal wall 338 (separating the left ventricle from the right ventricle 340), a posterior wall 336 (from which papillary muscles 341 project and upon which the mitral valve apparatus is positioned), and a free wall 334, with each of these three walls accounting for approximately one-third of the circumference of the left ventricle (indicated by the dashed line trisecting the left ventricle in FIG. 14 ). It is typically undesirable for the distal tip element (or other parts of the ventricular assist device) to contact the septal wall, as this could result in arrhythmias. Furthermore, it is typically desirable to maintain a distance between the distal tip element (and other parts of the ventricular assist device) and the posterior wall to avoid interference with the mitral valve apparatus and to prevent the mitral valve apparatus from interfering with the function of the ventricular assist device. Thus, the ventricular assist device is typically guided toward the apex in such a manner that when the distal tip element contacts the inner wall of the left ventricle, it contacts the free wall 334, as shown in Figures 14 and 16A and 16B.

[0168] Typically, a ventricular assist device is introduced into a subject's ventricle via a guidewire, as described above. 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. In some applications, the distal tip is configured to assume its curved shape when the guidewire is removed. Note that FIGS. 15A through 15D show the initial shape of distal tip 120. Typically, as a result of a guidewire being inserted through lumen 122 (which temporarily straightens the distal tip), the curvature of the distal tip will be less than that shown in at least FIGS. 15A through 15D once placed within the subject's left ventricle. For example, FIG. 15C shows the distal tip having a curvature such that the curved portion of the distal tip forms a complete loop. However, the distal tip of FIG. 15C does not form a complete loop within the subject's left ventricle in FIG. 16A.

[0169] As described above, the distal tip 120 typically forms part of a distal tip element 107 that also includes the axial shaft receiving tube 126. Typically, the distal tip element 107 is configured such that, in an unconstrained configuration (i.e., with no forces acting on the distal tip), the distal tip element is at least partially curved. In some applications, within a given plane, the distal tip element 107 has a proximal straight portion 346 (at least a portion of which typically includes the axial shaft receiving tube 126). The proximal straight portion of the distal tip element 107 defines a longitudinal axis 348. The curved portion of the distal tip element 107 curves in a first direction away from the longitudinal axis 348, passes through an inflection point, and curves in an opposite direction relative to the longitudinal axis 348. For example, as shown in FIGS. 15A and 15B , within the plane of the paper, the distal tip element first curves toward the top of the paper and then curves toward the bottom of the paper. Also, as shown in FIGS. 15C and 15D, within the plane of the paper, the distal tip element first curves toward the bottom of the paper and then curves toward the top of the paper. Typically, when shaped as shown in FIGS. 15A through 15D, the distal tip element defines an overall curvature similar to that of a question mark or a tennis racket, defining a bulge 351 on one side of the longitudinal axis of the straight proximal straight portion of the distal tip element. In some applications, the bulge has a generally semi-elliptical shape. (Note that the term "semi-ellipse" herein includes a semicircle. Further, note that in some cases, the tip does not define an exact semi-ellipse, but rather a bulged shape substantially similar to a semi-ellipse.)

[0170] As shown in Figures 15A and 15B, in some applications, the distal tip element continues to curve back across the longitudinal axis 348 after passing through the inflection point. Figure 15A shows an example where the end of the distal tip element does not again intersect the longitudinal axis, and there is a large gap between the distal end of the distal tip element and the proximal end of the curved portion. Figure 15B shows an example where the end of the distal tip element again intersects the longitudinal axis, and there is a small gap between the distal end of the distal tip element and the proximal end of the curved portion. As shown in Figures 15C and 15D (cross-sectional and isometric views, respectively, of the same shaped distal tip element), in some applications, the tip does not curve so that the distal tip element intersects the longitudinal axis 348 after passing through the inflection point, and all of the curvature of the curved portion of the distal tip element occurs on one side of the longitudinal axis 348.

[0171] Referring to FIG. 15C , a hemostatic valve (e.g., duckbill valve 390) is typically disposed within the distal section of distal tip 120 and configured to prevent blood inflow into lumen 122. Typically, the duckbill valve has a maximum width of less than 3 mm, e.g., less than 2 mm. Typically, the entire duckbill valve is disposed within the distal section of the distal tip, located within the most distal 10 mm, e.g., within the most distal 5 mm, of the distal tip. In some applications, the duckbill valve faces proximally (i.e., the wide inlet of the valve points toward the distal end of the distal tip, and the narrow tip of the valve points away from the distal end of distal tip 120). Typically, the curvature of the curved portion of distal tip element 107 is configured to provide an atraumatic tip for ventricular assist device 20 when placed within a subject's left ventricle. Further, typically, the distal tip element is configured to space ventricular assist device inlet 108 from the wall of the left ventricle.

[0172] 16A and 16B, it should first be noted that these figures show cross-sectional views of the left ventricle 22 with the septal wall 338 located on the left side of the page and the free wall 334 located on the right side of the page. In these views, the left atrium 359 and left atrial appendage 358 are viewed above the left ventricle, and the right ventricle 340 is seen on the left side of the left ventricle. It should be noted that the views of the aorta and left ventricle shown in FIGS. 16A-16B (and FIGS. 17A-17D) differ from those shown in, for example, FIG. 1B. FIG. 1B is a schematic view presented for illustrative purposes and does not accurately depict the scale and orientation of the ventricular assist device relative to the anatomy.

[0173] In some applications, the distal tip element 107 is configured to separate the blood inlet from the posterior wall of the subject's left ventricle when the distal tip element is positioned against the apex of the subject's left ventricle. Typically, the distal tip element is configured to separate the blood inlet from the septal wall of the subject's left ventricle when the distal tip element contacts the apex of the subject's left ventricle.

[0174] Typically, the distal tip element 107 is inserted into the left ventricle so that the bulge 351 bulges toward the septal wall 338 . When positioned in this configuration, in response to the distal tip element 107 being pushed against the apex (e.g., due to the physician advancing the device or in response to movement of the left ventricle), the blood inlet 108 is typically pushed toward the free wall 334 and away from the septal wall 338 (in the direction of the arrow shown in FIG. 16B . Typically, this is due to the proximal straight portion 346 pivoting about the question-mark shaped curve, as shown. In contrast, tips of other shapes, when positioned in a similar orientation, may result in the blood inlet being pushed toward the septal wall. For example, if the distal tip element has a pigtail tip (the tip curves in a single direction of curvature) and is oriented so that the pigtail curve is on the free wall side of the longitudinal axis of the straight portion of the distal tip element, pushing the tip distally will typically force the blood inlet toward the septal wall due to the tightening of the loop in the pigtail curve.

[0175] 14 through 16B, it should be noted that the scope of the present invention includes the use of the question mark or tennis racket shaped distal tip element in combination with any ventricular assist device, even in the absence of other features and / or portions of the distal tip element 107, such as the axial shaft receiving tube 126. It should also be noted that typically, the curvature of the distal tip will all lie in a single plane.

[0176] 17Ai and 17Aii, which are schematic illustrations of a ventricular assist device 20 having a balloon 220 disposed on the distal tip element 107, in accordance with some applications of the present invention. The balloon is configured to facilitate movement of the axial shaft 92 against the wall of the ventricle.

[0177] As mentioned above, the axial shaft 92 typically 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. The axial shaft itself is radially stabilized via the proximal and distal radial bearings 116, 118. The axial shaft then passes through the lumen 62 defined by the impeller, radially stabilizing the impeller relative to the inner surface of the frame 34. In some applications, the axial shaft extends into the axial-shaft receiving tube 126 of the distal tip element 107. Bending the axial shaft typically increases friction between the axial shaft and the distal radial bearing. Therefore, it is typically desirable to maintain the axial shaft in a straight configuration. In some applications, the balloon 220 allows the distal end of the distal tip element freedom of movement relative to the wall of the left ventricle in a manner that does not cause significant movement of the proximal end of the distal tip (which defines the axial-shaft receiving tube). For example, as shown by the arrows near the apex 342 in Figures 17Ai and 17Aii, the balloon can rotate relative to the apex without causing significant movement of the axial shaft-receiving tube. Thus, even if the balloon moves relative to the apex (as shown in the transition from Figure 17Ai to Figure 17Aii), the axial shaft remains in a substantially straight configuration. In some applications, a purge fluid is used to inflate the balloon 220, for example, as described with respect to Figure 13D of U.S. Patent Application Publication No. 2020 / 0237981 to Tuval, which is incorporated herein by reference.

[0178] Reference is now made to FIGS. 17Bi and 17Bii, which are schematic illustrations of a ventricular assist device 20 having a joint 230 configured to facilitate pivoting of the distal tip 120 relative to the axial shaft, according to some applications of the present invention. As described above, in some applications, the distal tip element 107 includes an axial shaft receiving tube 126 and a distal tip 120. In some applications, the joint 230 allows the distal tip 120 to move relative to the axial shaft receiving tube 126. For example, the joint 230 may be a ball-and-socket joint, as shown, and / or a swivel joint, and / or a Cardan joint. As such, the axial shaft 92 remains in a substantially straight configuration even when the distal tip moves relative to the apex 342 of the left ventricle (as shown by the transitions in FIGS. 17Bi and 17Bii). In some such applications, the distal tip 120 has a shape as described above.

[0179] 17C, which is a schematic illustration of a ventricular assist device according to some applications of the present invention. The outer tube 140 and / or 142 of the ventricular assist device is configured with a predetermined curvature to maintain the axial shaft 92 of the ventricular assist device in a substantially straight configuration when the axial shaft is positioned within the left ventricle 22 of a subject.

[0180] As described above with reference to FIGS. 10A-10C, in some applications, the drive cable 130 is disposed within a first outer tube 140, which is configured to act as a drive cable bearing tube, remaining stationary during rotational and / or back-and-forth axial movement of the drive cable. The first outer tube is configured to act as a bearing along the length of the drive cable. In some applications, the first outer tube 140 is disposed within a second outer tube 142. In some applications, at least one of the first and second outer tubes is shaped such that the portion of the outer tube disposed within the aortic arch has a predetermined radius of curvature RC greater than 18 mm and / or less than 32 mm (e.g., less than 24 mm), e.g., a predetermined radius of curvature RC between 18 and 32 mm or between 18 and 24 mm. In some applications, defining such a radius of curvature causes the axial shaft to enter the left ventricle at an angle such that the axial shaft assumes a substantially straight configuration when the distal tip of the ventricular assist device is positioned near the apex 342.

[0181] 17D, which is a schematic illustration of a ventricular assist device 20 having a distal tip 240 configured to be anchored to tissue at the left ventricular apex 342, in accordance with some applications of the present invention. In some applications, the distal tip 240 is a screw-type element (e.g., a corkscrew-type element as shown) configured to be screwed into tissue at the apex to secure the distal end of the ventricular assist device to the apex. Securing the distal tip to the apex typically reduces movement of the pump portion 27 relative to internal structures of the left ventricle, thereby reducing the risk of damage to the internal structures of the left ventricle that such movement may cause.

[0182] Reference is now made to Figures 18A, 18B, and 18C, which are schematic illustrations of a distal radial bearing 118 of a ventricular assist device, in accordance with respective applications of the present invention.

[0183] 18A , in some applications, the radial bearing is disposed within a bearing housing 119. In some such applications, the radial bearing and the bearing housing are made of different materials. For example, the radial bearing may be made of a first material having a relatively high hardness, such as a ceramic, and the bearing housing may be made of a second material, such as a metal or alloy, that is relatively easy to form into a desired shape (e.g., stainless steel, cobalt chrome, and / or nitinol). In some such applications, the proximal radial bearing 116 is also disposed within the bearing housing, and the proximal radial bearing and the bearing housing are made of different materials (in a manner generally similar to that described with respect to the distal radial bearing 118). As noted above, in some such applications, the ventricular assist device includes a distal extension 121 configured to strengthen the region of the distal tip element where the distal end of the shaft 92 enters (e.g., the axial shaft receiving tube 126, described below, or a portion thereof). In applications where the distal radial bearing 118 is disposed within the bearing housing 119, the distal extension 121 typically comprises an extension from the bearing housing 119 rather than from the distal radial bearing itself. As noted above, the distal strut joint 33 typically resides at the distal end of the frame 34 within a groove defined by the outer surface of the distal radial bearing 118. This groove is shaped to match the shape of the distal strut. In some applications, the outer surface of the bearing housing (rather than the bearing) is shaped to define such a groove (these grooves are shown at 127 in FIGS. 18A and 18B ).

[0184] 18B , in some applications, a layer of material 123 is disposed between the radial bearing 118 and the bearing housing 119. In some applications, the material is configured to allow some movement of the radial bearing relative to the bearing housing and / or to cushion such movement. For example, the layer of material may include an elastomeric material layer. In some applications, the proximal radial bearing 116 has a similar configuration, with the material (e.g., an elastomeric material) disposed between the radial bearing and the bearing housing being configured to allow some movement of the radial bearing relative to the bearing housing. In some such applications, the layer of material allows some movement of the rigid axial shaft relative to the frame 34 by allowing movement between the radial bearing and the bearing housing. In some applications, the axial shaft 92 may thus be allowed to be slightly misaligned with respect to the longitudinal axis of the frame.

[0185] 18C, in some applications, the outer surface 125 of the distal radial bearing 118, which abuts the inner surface of the bearing housing 119, has a convex curve. In some applications, the convexly curved outer surface of the bearing is configured to allow some movement of the radial bearing relative to the bearing housing. In some applications (not shown), the inner radial surface of the bearing housing (which abuts the outer surface of the bearing) has a convex curve to allow some movement of the radial bearing relative to the bearing housing. In some applications, the proximal radial bearing 116 has a similar configuration, with the outer surface of the bearing and / or the inner radial surface of the bearing housing having a convex curve. In some such applications, the above-described shapes of the bearing and / or bearing housing allow movement between the radial bearing and the bearing housing, thereby allowing movement of the rigid axial shaft relative to the frame 34. In some applications, the axial shaft is thus allowed to be slightly misaligned with respect to the longitudinal axis of the frame.

[0186] In some applications, the length of the radial bearings is such that they allow movement of the rigid axial shaft relative to the frame 34, allowing for slight misalignment of the axial shaft relative to the longitudinal axis of the frame. For example, the length of each of the proximal and distal radial bearings can be less than 2 mm, less than 1.5, or less than 1 mm, such as 0-1.5 mm, or 0.5-1 mm.

[0187] Reference is now made to FIG. 19A, which is a schematic illustration of a ventricular assist device 20 according to some applications of the present invention. The pump outlet tubing 24 of this device is configured to curve as blood is pumped through the pump outlet tubing and is rotatable relative to the distal tip 120 of the ventricular assist device. Reference is also made to FIG. 19B, which is a schematic illustration of the pump outlet tubing 24 of FIG. 19A without the other components of the ventricular assist device present, according to some applications. Reference is also made to FIG. 19C, which is a schematic illustration of the ventricular assist device 20 of FIGS. 19A-19B positioned within the aorta 30 and left ventricle 22 of a subject, according to some applications of the present invention. It should be noted that the view of the aorta and left ventricle shown in FIG. 19C is different from that shown in, for example, FIG. 1B. FIG. 1B is a schematic illustration presented for illustrative purposes and does not accurately depict the scale and orientation of the ventricular assist device relative to the anatomy. Additionally, it should be noted that the view of the aorta and left ventricle shown in Figure 19C is different from those shown in, for example, Figures 16A-16B and 17Ai-17D. Figure 19C shows a cross-sectional view of the left ventricle with the posterior wall 336 located on the left side of the page and the free wall 334 located on the right side of the page.

[0188] As mentioned above, in some applications, the frame 34 is not disposed within the pump outlet tubing 24 along its proximal portion, and therefore the tubing is not supported open by the frame 34. The tubing 24 is typically made of a blood-impermeable, collapsible material. For example, the tubing 24 may include polyurethane, polyester, and / or silicone. Alternatively or additionally, the tubing is made of polyethylene terephthalate (PET) and / or polyether block amide (PEBAX®). Typically, the proximal portion of the tubing is configured to be positioned at least partially within the subject's ascending aorta. In some applications, as shown in FIG. 1B , the proximal portion of the tubing traverses the subject's aortic valve and reaches the subject's ascending aorta from the subject's left ventricle. As mentioned above, the tubing typically defines one or more blood inlets 108 at its distal end, through which blood enters the tubing from the left ventricle when the impeller is actuated. In some applications, the proximal portion of the tube defines one or more blood outlets 109 through which blood flows from the tube into the ascending aorta when the impeller is actuated. When the impeller is actuated, the pressure of blood flowing through the tube typically keeps the proximal portion of the tube open.

[0189] In some applications, the pump outlet tube 24 is pre-shaped so that when the pressure of blood flow through the tube maintains the proximal portion of the tube open during impeller operation, the tube curves. Typically, when the proximal end of the tube is positioned within the aorta, at least a portion of the tube is positioned within the left ventricle and curves away from the posterior wall of the left ventricle toward the apex and / or free wall of the left ventricle. Furthermore, typically, when the proximal end of the tube is positioned within the aorta, at least a portion of the tube is positioned within the left ventricle and curves away from the septal wall of the left ventricle toward the apex and / or free wall of the left ventricle. In some applications, the curvature of the tube is adapted to maintain separation between the blood inlet 108 and the posterior wall 336 of the left ventricle, the mitral valve leaflets 402, and / or subvalvular components of the mitral valve (such as the chordae tendineae 404, trabeculae, and / or papillary muscles 341), as shown in FIG. 19C .

[0190] Typically, tube 24 is pre-formed using blow molding in a curved mold or using a molding die after the blow molding or dipping process. Typically, the distal portion of the tube, where frame 34, impeller 50, and axial shaft 92 are disposed, is maintained in a straight and open configuration by frame 34. The portion of the tube proximal to frame 34 and disposed within the left ventricle is typically shaped to define the above-described curvature. In some applications, the curvature is such that the angle gamma between the longitudinal axis of the tube at the proximal end of the tube and the longitudinal axis of the tube at the distal end of the tube is greater than 90 degrees (e.g., greater than 120 degrees or greater than 140 degrees) and / or less than 180 degrees (e.g., less than 160 degrees or less than 150 degrees), e.g., between 90 and 180 degrees, between 90 and 160 degrees, between 120 and 160 degrees, or between 140 and 150 degrees. In some applications, the curvature of the tube is such that the surface of the tube inside the bend defines a radius of curvature R of more than 10 mm, e.g., more than 20 mm, and / or less than 200 mm (e.g., 100 mm), e.g., 10 to 200 mm, or 20 to 100 mm. (A dashed circle with a dashed line across its diameter is shown in FIG. 19B to show how the radius of curvature R is measured.)

[0191] As described with reference to FIGS. 19A-19C, it should be noted that pump outlet tube 24 is configured such that (a) the tube typically collapses when pressure outside the tube exceeds pressure inside the tube in the absence of blood flowing through the tube, and (b) when blood flows through the tube at a sufficient velocity such that the pressure inside the tube exceeds the pressure outside the tube, the tube assumes a pre-formed, curved configuration. Furthermore, it should be noted that when tube 24 assumes its curved configuration, the portion of drive cable 130 positioned within the curved portion of the tube typically also becomes curved, as shown in FIGS. 19A and 19C. That is, rather than the drive cable (or another element positioned within the tube) causing the tube to curve, a pre-formation of the tube itself typically causes the tube and drive cable to curve. Alternatively, outer tube 140 and / or 142 (disposed around the drive cable) may be shaped to define the curve, and the outer tube causes the drive cable and tube 24 to assume the curved shape. In some applications, both outer tube 140 and / or 142 and tube 24 are shaped to define the curved shape.

[0192] Reference is now made to FIGS. 19D and 19E, which are schematic illustrations of a pump outlet tube 24 of a ventricular assist device 20 configured to curve as blood is pumped through the tube, according to some applications of the present invention. For illustrative purposes, FIGS. 19D and 19E show the tube 24 without other components of the ventricular assist device (e.g., impeller 50, frame 34, etc.). FIG. 19E is a schematic illustration of the ventricular assist device 20 of FIG. 19D positioned within the aorta 30 and left ventricle 22 of a subject, according to some applications of the present invention. The view of the left ventricle shown in FIG. 19E is similar to that shown in FIG. 19C. In some applications, the inlet 108 and / or outlet 109 are positioned in a non-axisymmetric configuration about the tube 24. Typically, the tube 24 defines the inlet and / or outlet at locations that curve the tube 24 and / or maintain the curvature of the tube 24, as described with reference to FIGS. 19A-19C. For example, as shown, the blood inlet may be located on the side of the tube 24 inside the tube's curvature (or inside the desired tube curvature). As blood enters the blood inlet, this reduces the pressure in the area above the blood inlet, pulling the distal end of the tube 24 toward this area (indicated by arrow 310). Alternatively or additionally, the blood outlet 109 may be located on the side of the tube 24 inside the tube's curvature (or inside the desired tube curvature). As the blood exits the blood outlet, it impacts the aortic wall, which pushes the proximal end of the tube 24 in the opposite direction, indicated by arrow 312.

[0193] 19A-19C, the curvature of the pump outlet tubing is typically such that it maintains separation between the blood inlet 108 and the posterior wall 336 of the left ventricle, the mitral valve leaflets 402, and / or the subvalvular components of the mitral valve (such as the chordae tendineae 404, trabeculae, and / or papillary muscles 341), as shown in FIG. 19E. Typically, when the proximal end of the tubing is positioned within the aorta, at least a portion of the tubing is positioned within the left ventricle and curves away from the posterior wall of the left ventricle toward the apex and / or free wall of the left ventricle. Furthermore, when the proximal end of the tubing is positioned within the aorta, at least a portion of the tubing is positioned within the left ventricle and curves away from the septal wall of the left ventricle toward the apex and / or free wall of the left ventricle.

[0194] In some applications, when placing a ventricular assist device in the left ventricle, the distal tip is placed first. As described above, the distal tip is typically placed in a given orientation relative to the left ventricular anatomy. Typically, the pump outlet tubing is placed after the distal tip is placed. In some cases, the distal tip is already placed in a desired orientation relative to the left ventricular anatomy, so the curved portion of the tubing is not positioned in a desired orientation within the left ventricle. Thus, in some applications, the distal tip is coupled (directly or indirectly) to the pump outlet tubing via a fitting 212 that allows rotation of the pump outlet tubing relative to the distal tip of the ventricular assist device, as indicated by arrow 210 in FIGS. 19A-19E. For example, the fitting may be a swivel and / or ball-and-socket joint (e.g., similar to ball-and-socket joint 230 shown in FIGS. 17Bi-17Bii) and / or a Cardan joint (e.g., similar to fitting 232 shown in FIGS. 20A-20C). In some applications, the coupling is disposed within the proximal portion of the distal tip element 107. Alternatively or additionally, the coupling is disposed between the distal tip 120 and the axial shaft receiving tube 126 (e.g., as shown in Figures 17Bi-17Bii).

[0195] Reference is now made to FIG. 19F, which is a schematic illustration of a ventricular assist device 20 including a curved element 218 configured to impart a predetermined curvature to the tube 24, in accordance with some applications of the present invention. In some applications, as an alternative to or in addition to a tube 24 shaped to define a curvature itself (e.g., as described with reference to FIGS. 19A-19E), the ventricular assist device includes a curved element 218. Typically, the curved element is made of a shape-memory material, e.g., a shape-memory alloy such as Nitinol. In some applications, the curved element is formed from a Nitinol tube cut to define holes or slits, thereby allowing the tube to be pre-formed into a desired curved shape. For example, the Nitinol element may be a Nitinol "hypotube" (i.e., a Nitinol tube with micro-engineered features along its length), as is well known in the art. Typically, the curved element 218 is disposed around the drive cable 130 along a longitudinal section of the drive cable proximal (e.g., immediately adjacent) to the proximal radial bearing 116. In some applications, a curved element is used in place of outer tube 142 along this longitudinal section of the drive cable.

[0196] In some applications, the curved elements are shaped to have a curvature generally similar to that described with reference to Figures 19A-19E in connection with tube 24. In some applications, the curvature is such that the angle omega between the longitudinal axis of the curved element at its proximal end and the longitudinal axis of the curved element at its distal end is greater than 90 degrees (e.g., greater than 120 degrees or greater than 140 degrees) and / or less than 180 degrees (e.g., less than 160 degrees or less than 150 degrees), e.g., between 90 and 180 degrees, 90 and 160 degrees, 120 and 160 degrees, or 140 and 150 degrees. In some applications, the curvature of the tube is such that the surface of the curved element on the inside of the curvature defines a radius of curvature greater than 10 mm, e.g., greater than 20 mm, and / or less than 200 mm (e.g., 100 mm), e.g., between 10 and 200 mm, or between 20 and 100 mm. 19A-19C, the curvature of the tube is typically such that it maintains separation between the blood inlet 108 and the posterior wall 336 of the left ventricle, the mitral valve leaflets 402, and / or subvalvular components of the mitral valve (such as the chordae tendineae 404, trabeculae, and / or papillary muscles 341), as shown in FIG. 19C. Typically, when the proximal end of the tube is positioned within the aorta, at least a portion of the tube is positioned within the left ventricle and curves away from the posterior wall of the left ventricle toward the apex and / or free wall of the left ventricle. Furthermore, when the proximal end of the tube is positioned within the aorta, at least a portion of the tube is positioned within the left ventricle and curves away from the septal wall of the left ventricle toward the apex and / or free wall of the left ventricle.

[0197] In some applications, when placing a ventricular assist device in the left ventricle, the distal tip is placed first. As described above, the distal tip is typically placed in a given orientation relative to the left ventricular anatomy. Typically, the curved element 218 is placed after the distal tip is placed. In some cases, the curved element 218 is not positioned in a desired orientation within the left ventricle because the distal tip is already placed in a desired orientation relative to the left ventricular anatomy. Thus, in some applications, the distal tip is coupled (directly or indirectly) to the curved element 218 via a joint 212 that allows rotation of the pump outlet tubing relative to the distal tip of the ventricular assist device, as shown by arrow 210 in FIGS. 19A-19E. For example, the joint may be a swivel joint and / or a ball-and-socket joint (e.g., similar to ball-and-socket joint 230 shown in FIGS. 17Bi-17Bii), and / or a Cardan joint (e.g., similar to joint 232 shown in FIGS. 20A-20C). In some applications, the coupling is disposed within the proximal portion of the distal tip element 107. Alternatively or additionally, the coupling is disposed between the distal tip 120 and the axial shaft receiving tube 126 (e.g., as shown in Figures 17Bi-17Bii).

[0198] 19A-19F, it should be noted that in some applications, tube 24 will assume a curved shape due to outer tube 142 being anchored to the aorta and distal tip 120 being anchored to the interior wall of the left ventricle (e.g., the free wall around the apex), as described above. It should also be noted that the curvature of the tube shown in Figures 16A and 16B is less than that shown in Figures 19A-19F because Figures 16A and 16B show different views of the device. In the views shown in Figures 16A and 16B, the curvature is generally less pronounced than in the views shown in Figures 19A-19F.

[0199] Reference is now made to FIGS. 20A-20C, which are schematic illustrations of a ventricular assist device 20 according to some applications of the present invention. The axial shaft 92 of this device includes a coupling 232 (such as a Cardan coupling, as shown). The coupling is typically located within a portion of the axial shaft configured to be disposed between the proximal bushing 64 and the distal bushing 58 of the impeller, as shown. It should be noted that in FIG. 20A, for purposes of illustration and to allow visualization of the portion of the axial shaft that is typically disposed between the proximal bushing 64 and the distal bushing 58 of the impeller within the lumen 62 defined by the impeller (the lumen 62 is shown, for example, in FIGS. 3A-3C), portions of the impeller (such as the membrane of material 56 and spring 54) are not shown. Alternatively, the coupling may be located at another location along the axial shaft, such as proximal to the impeller or distal to the impeller.

[0200] In some applications, the joint 232 is disposed between the proximal axial shaft portion 234 and the distal axial shaft portion 236, which are coupled to one another via the joint, allowing the proximal and distal portions to bend relative to one another via the joint. Typically, the joint allows the axial shaft to assume a shape that matches the curvature of the rest of the left ventricular device and / or the target anatomy. In some applications, the joint is configured to conform the axial shaft to the curvature of the frame 34, such that the proximal portion of the axial shaft remains coaxial with the proximal bearing 116 and the distal portion of the axial shaft remains coaxial with the distal bearing 118, even when the frame 34 is slightly curved.

[0201] FIG. 21 is a schematic diagram of a ventricular assist device including one or more blood pressure measurement tubes 222, according to some applications of the present invention. As described above, a ventricular assist device typically includes a pump outlet tube 24 that traverses a subject's aortic valve such that a proximal end of the tube is positioned within the subject's aorta and a distal end of the tube is positioned within the subject's left ventricle. A blood pump (typically including an impeller 50) is typically positioned within the subject's left ventricle within tube 24 and configured to pump blood from the left ventricle to the subject's aorta via tube 24. In some applications, ventricular blood pressure measurement tube 222 extends to at least an outer surface 213 of 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 tube 24. Typically, opening 214 is configured to be proximal to the blood pump (e.g., proximal to 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, the pressure sensor measures the subject's blood pressure outside tube 24 (i.e., left ventricular blood pressure) by measuring the pressure of blood in the left ventricular blood pressure measurement tube. Typically, blood pressure measurement tube 222 extends from outside the subject's body to 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.

[0202] In some applications, the ventricular assist device includes two or more such ventricular blood pressure measurement tubes 222, as shown, for example, in FIG. 21 . In some applications, based on the blood pressure measured in each of the left ventricular blood pressure measurement tubes, the computer processor 25 determines whether the opening of one of the two or more ventricular blood pressure measurement tubes is blocked. This may occur, for example, due to the opening contacting the interventricular septal wall and / or another interventricular portion. Typically, in response to determining that one opening of the two or more ventricular blood pressure measurement tubes is blocked, the computer processor determines the subject's left ventricular pressure based on the blood pressure measured in another of the two or more ventricular blood pressure measurement tubes.

[0203] 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 a subject, the portion of ventricular blood pressure measurement tube 222 that extends from within tube 24 to at least the outer surface of tube 24 is configured to be disposed within this groove so as not to protrude beyond the outer surface of the outer tube.

[0204] In some applications (not shown), the distal portion of the blood pressure measurement tubing 222 is positioned 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 integrated into the exterior 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.

[0205] As mentioned above, in some applications, the drive cable 130 extends from a motor external to 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, as shown in cross section in FIG. 21 , the proximal portion of the blood pressure measurement tubing 222 includes a channel between the first outer tube 140 and the second outer tube 142. In this regard, it should be understood that the blood pressure measurement tubing represents a continuous lumen extending from the pressure sensor 216 to the outside of the pump outlet tubing 24 within the subject's left ventricle, regardless of whether the lumen's structure varies along its length. As described above, a purge fluid is typically delivered between the outer tube 140 and the outer tube 142, and in some applications, the purge fluid is delivered via the channel 226. 21 , the blood pressure measurement tubing 222 typically occupies a larger portion 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 portion of the cross-sectional area defined between the outer tube 140 and the outer tube 142 to transmit blood pressure outside the pump outlet tubing 24 in the subject's left ventricle proximally to the pressure sensor 216.

[0206] Reference is now made to FIGS. 22A and 22B, which are schematic illustrations of a sterile sleeve 242 configured to form a seal between a delivery catheter 143 and the outer tube 142 of a ventricular assist device 20, according to some applications of the present invention. In some applications (not shown), the delivery catheter 143 is inserted into a subject's artery (such as the femoral or radial artery) via an introducer sheath (not shown). The introducer sheath is inserted into an incision in the artery and typically remains in place within the artery throughout the entire operation of the ventricular assist device. In such applications, a sterile sleeve (generally similar to that shown in FIGS. 22A-22B) is typically placed between the delivery catheter and the introducer sheath (not shown) to allow movement between the delivery catheter 143 and the introducer sheath (not shown) while maintaining sterility of the arteriotomy.

[0207] In some alternative applications, the ventricular assist device is first inserted into the arteriotomy through an introducer sheath, which is then removed for subsequent operation of the ventricular assist device. For example, the ventricular assist device can be inserted through a tear-away introducer sheath. The delivery catheter then typically makes direct contact with the arteriotomy. In this case, the diameter of the device placed within the arteriotomy for subsequent procedures is typically smaller than if the introducer sheath remained within the arteriotomy for the entire duration of ventricular assist device operation. For example, the outer diameter of the delivery catheter can be less than 3.3 mm (i.e., 10 French), which is the diameter that will fit through the arteriotomy after the introducer sheath is removed. The inner diameter of the delivery catheter is typically less than 3 mm (i.e., 9 French), and can be, for example, 2.7 mm (i.e., 8 French). In contrast, if the introducer sheath is to remain in place for the entire duration of the ventricular assist device, the diameter through the incision will increase because the thickness of the introducer sheath wall must also be passed through the incision. For example, this may increase the diameter by 0.3-0.6 mm (i.e., 1-2 French).

[0208] In some such applications, the delivery catheter is advanced until the distal end of the delivery catheter is positioned at a predetermined location within the subject's aorta (e.g., within the ascending aorta). The pump portion 27 of the ventricular assist device is then advanced relative to the distal end of the delivery catheter by advancing the outer tube 142 relative to the delivery catheter. In such applications, the sterile sleeve 242 forms a seal between the delivery catheter 143 and the outer tube 142 of the ventricular assist device 20, allowing movement of the outer tube relative to the delivery catheter while maintaining sterility of the arteriotomy. In some such applications, the ventricular assist device is provided to the user as a kit including the sterile sleeve 242 positioned in a predetermined location between the outer tube 142 and the delivery catheter 143.

[0209] Reference is now made to FIGS. 23A-23C, which are schematic illustrations of a tip straightening element 270 used to straighten the distal tip 120 of a ventricular assist device 20 during insertion of a guidewire 10, according to some applications of the present invention. As discussed above, the ventricular assist device is typically inserted into a subject's ventricle over a guidewire 10 and disposed in a radially constrained (i.e., crimped) configuration within a delivery catheter 143 (e.g., as shown schematically in FIG. 1B ). Typically, a guidewire is first inserted into the distal end of a distal tip element 107 within the ventricular assist device. In some applications, a tip straightening element 270 is disposed about the distal tip element to hold the distal tip element in a straight configuration to facilitate insertion of a guidewire into the distal end of the distal tip element (i.e., into the distal tip 120). Typically, the straightening element is a housing defining a straight lumen 271. For example, as shown in FIG. 23B, the straightening element is disposed about the distal tip element such that the distal tip element is disposed in a straight configuration within the lumen 271, and a guidewire is inserted into the distal end of the distal tip element (i.e., into the distal tip portion 120). In some applications, the straightening element is configured to be detachable from the distal tip element while the guidewire is disposed within the distal tip element. For example, the straightening element can be scored, perforated, and / or have slits 272 (as shown) along its length to facilitate removal of the straightening element from the distal tip element, as shown in FIG. 23C.

[0210] Reference is now made to FIGS. 24A, 24B, and 24C, which are graphs illustrating measurements performed during use of a left ventricular assist device according to some applications of the present invention. A left ventricular assist device described herein was placed inside a pig's heart. The pig's arterial pulse was measured using an intra-aortic pressure sensor while the left ventricular assist device was operated at various rotational speeds. Based on in vitro testing previously performed on the device, the device was calibrated so that the flow rate generated by the device was known when the impeller rotated at each rotational speed. FIG. 24A shows a plot of arterial pulse versus flow rate generated by the device, as measured in an experiment performed on the pig (and using a predetermined correspondence between impeller rotational speed and flow rate). The plot shown in FIG. 24A was then fitted to a curve extrapolated to the y-intercept (i.e., where arterial pulse is zero), as shown in FIG. 24B. As shown, the extrapolation of the curve estimated the flow rate at zero arterial pulse to be 5.6 L / min. In the same pig, cardiac output was measured with a Swan-Ganz catheter when the left ventricular assist device was inactive. The Swan-Ganz catheter measured the pig's intrinsic cardiac output to be 5.2 L / min, a value similar to the flow rate at zero arterial pulsation estimated by extrapolation of the flow / arterial pulsation curve. It is hypothesized that when arterial pulsation is zero, the left ventricular apparatus largely replaces the heart's intrinsic function, and that the flow rate generated by the pump at this value provides a reasonable approximation of the subject's intrinsic cardiac output.

[0211] According to the above experimental results, in some applications of the present invention, the arterial pulsation of a subject is measured during operation of a ventricular assist device, and parameters are derived from the arterial pulsation of the subject. Typically, as the rotational speed of the impeller increases, the flow rate generated by the blood pump also increases. Because blood pumps are typically continuous-flow blood pumps rather than pulsatile blood pumps, the flow rate generated by the blood pump is non-pulsatile. Therefore, as the rotational speed of the impeller increases and the flow rate generated by the blood pump increases, the arterial pulsation of the subject typically decreases. In some applications, the arterial pulsation of the subject is measured as the rotational speed of the impeller changes. Based on the measurements, a relationship between the arterial pulsation and the impeller rotational speed and / or the pump flow rate is derived. In some applications, the intrinsic cardiac output of the subject is derived based on the relationship. In some such applications, the relationship between the arterial pulsation of the subject and the pump flow rate is extrapolated to determine what the pump flow rate will be when the arterial pulsation of the subject reaches zero. In accordance with the results above, it is hypothesized that at this value the pump replaces the intrinsic function of the heart and further that the flow rate generated by the pump at this value provides an approximation of the subject's intrinsic cardiac output.

[0212] With respect to all embodiments of ventricular assist device 20 described with reference to FIGS. 1A through 24C, it should be noted that while FIGS. 1A and 1B depict ventricular assist device 20 within a subject's left ventricle, in some applications, device 20 may be positioned within a subject's right ventricle across the subject's pulmonary valve, and the techniques described herein may be used, mutatis mutandis. In some applications, components of device 20 may be 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 tube 24 (e.g., tube curvature), impeller 50, features of pump portion 27, drive cable 130, etc. Alternatively or additionally, device 20 and / or portions thereof (e.g., impeller 50 without tube 24) may be positioned within a different portion of a subject's body to assist in pumping blood from that 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 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 the vein and lymphatic vessel, and used, mutatis mutandis, to augment lymphatic flow from the lymphatic vessel. The scope of the present invention includes use of the devices and methods described herein in anatomical locations other than the left ventricle and aorta, and ventricular assist devices and / or portions thereof may be referred to herein (and in the claims) as blood pumps.

[0213] 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:

[0214] U.S. Patent Application Publication No. 2020 / 0237981, entitled "Distal Tip Element for Ventricular Assist Device," filed January 23, 2020, to Tuval, which claims priority to: U.S. Provisional Patent Application No. 62 / 796,138, entitled "Ventricular Assist Device," to Tuval, filed January 24, 2019; U.S. Provisional Patent Application No. 62 / 851,716, entitled "Ventricular Assist Device," filed May 3, 2019, to Tuval; 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, to Tuval, entitled "Ventricular Assist Device." Tuval's U.S. Patent No. 10,881,770, which is a continuation of Tuval's International Patent Application No. PCT / IB2019 / 050186 (published as WO19 / 138350), entitled "Ventricular Assist Device," filed January 10, 2019, which claims priority to: U.S. Provisional Patent Application No. 62 / 615,538, entitled "Ventricular Assist Device," to Sohn, filed January 10, 2018; U.S. Provisional Patent Application No. 62 / 665,718, entitled "Ventricular Assist Device," filed May 2, 2018, to Sohn; U.S. Provisional Patent Application No. 62 / 681,868, entitled "Ventricular Assist Device," to Tuval, filed June 7, 2018; and U.S. Provisional Patent Application No. 62 / 727,605, filed September 6, 2018, to Tuval, entitled "Ventricular Assist Device." 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 October 23, 2017, which claims priority to Tuval's U.S. Patent Application Publication No. 62 / 412,631, filed October 25, 2016, and Tuval's U.S. Patent Application Publication No. 62 / 543,540, filed 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 No. 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" to Schwammenthal, filed May 18, 2016, which claims priority to U.S. Provisional Patent Application No. 62 / 162,881 entitled "Blood Pump" to Schwammenthal, filed May 18, 2015; Schwammenthal, U.S. Patent No. 10,583,231, which is the U.S. national stage of International Patent Application 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 PCT / IL2014 / 050289 (published as WO14 / 141284), entitled "Kidney Pump," filed March 13, 2014, which claims priority to (a) 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; U.S. Patent 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 U.S. Patent No. 9,597,205 to Tuval, which is the U.S. national stage 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.

[0215] Those skilled in the art will recognize that the present invention is not limited to what has been particularly shown and described above. The scope of the present invention includes both combinations and subcombinations of the various features described above, as well as variations and modifications thereof that would occur to one skilled in the art upon reading the foregoing description.

Claims

1. 1. An apparatus comprising:

1. A blood pump configured to be placed inside a subject's body, comprising: An impeller, a proximal bushing and a distal bushing; two or more helical elongated elements extending from the proximal bushing to the distal bushing; an axial structure disposed inside the two or more helical elongate elements along an axis about which the helical elongate elements are wound; a film of material supported between the helical elongate element and the axial structure, such that each of the helical elongate elements to which the film of material is coupled defines a respective blade of the impeller; and an impeller comprising: an impeller over-expansion prevention element that is a single integrated structure including a ring and a plurality of elongated elements disposed around the axial structure; a blood pump comprising: each of the elongated elements extends from the ring to a respective helical elongated element and is coupled to the respective helical elongated element to prevent radial expansion of the impeller.

2. 2. The apparatus of claim 1, wherein the impeller comprises three helical elongated elements, the three helical elongated elements having the film of material bonded thereto defining three blades of the impeller, each elongated element extending from the ring to each of the three helical elongated elements such that each elongated element is within each of the three blades of the impeller.

3. 2. The apparatus of claim 1, wherein the elongated element is configured to be substantially non-resistant to compression, and the elongated element is configured to prevent radial expansion of the impeller by applying tension to the helical elongated element.

4. 2. The apparatus of claim 1, wherein along at least a portion of the length of the impeller, the film of material forms a continuous U-shaped curve as it transitions from one impeller blade to an adjacent blade, and the U-shaped curvature of the film of material is substantially uninterrupted in the axial configuration.

5. 5. The device of claim 1, wherein, when viewed from the distal end of the impeller, the pressure side of each of the blades of the impeller configured to push the blood during operation of the impeller is convex in a distal region of the impeller and concave in a proximal region of the impeller.

6. 6. The apparatus of claim 1, wherein the pressure side of each of the blades of the impeller is oriented substantially radially in the region of the elongated element within the impeller blade.

7. 5. The device of claim 1, wherein the helical elongate element is coated with a bonding agent configured to enhance bonding between the helical elongate element and the film of material.

8. 8. The device of claim 7, wherein the film of material comprises an elastomeric material, and the binding agent comprises at least two functional groups configured to bind to the helical elongate element and the elastomeric material, respectively.

9. The apparatus of claim 8 , wherein the bonding agent comprises a silane compound.

10. The device of claim 7 further comprising a layer of elastomer disposed between the film of material and the binder.

11. The device of claim 10 , wherein the layer of elastomer is configured to round corners of the helical elongate element.

12. The device of claim 10 , wherein the membrane of material is made of the elastomer.

13. The device of claim 12 , wherein the elastomer comprises a polycarbonate-based thermoplastic polyurethane.

14. The apparatus of claim 1 , wherein the axial structure includes a spring.

15. 15. The device of claim 14, wherein the spring includes a tube at an intermediate location along the length of the spring, and the ring is disposed around the tube.

16. Manufacture an impeller, forming a structure having a first bushing and a second bushing at a proximal end and a distal end, the first and second bushings being interconnected by at least one elongated element; at least partially compressing the structure axially to radially expand the at least one elongated element to form at least one helical elongated element; coating the at least one helical elongate element with a bonding agent configured to enhance bonding between the helical elongate element and an elastomeric layer; coating the coated helical elongate element with the elastomeric layer; and thereafter, coupling an elastomeric membrane to the at least one helical elongate element such that the at least one helical elongate element with the elastomeric membrane coupled thereto defines a blade of the impeller; and manufacturing the impeller by

17. 17. The method of claim 16, wherein bonding the elastomeric membrane to the at least one helical elongate element such that the at least one helical elongate element having the elastomeric membrane bonded thereto defines a blade of the impeller comprises dipping the helical elongate element into an elastomeric material that creates the elastomeric membrane.

18. 18. The method of claim 16 or claim 17, wherein the elastomeric membrane comprises a resilient material having an ultimate elongation of greater than 300 percent.

19. 19. The method of any one of claims 16 to 18, wherein the elastomeric membrane comprises a resilient material having a melt flow index of at least 4.

20. 20. The method of any one of claims 16 to 19, wherein the elastomeric membrane comprises a resilient material having a tensile strength greater than 6000 psi.

21. 21. The method of any one of claims 16 to 20, wherein coating the at least one helical elongate element with the binder comprises coating the at least one helical elongate element with a silane compound containing a first functional group configured to bond with the helical elongate element and a second functional group configured to bond with the elastomeric layer.

22. 22. The method of any one of claims 16 to 21, wherein the elastomeric layer is made of a given elastomeric material and the elastomeric membrane is made of the given elastomeric material.

23. 22. The method of any one of claims 16 to 21, wherein the elastomeric layer is made of a first elastomeric material and the elastomeric membrane is made of a second elastomeric material different from the first elastomeric material.

24. 24. The method of any one of claims 16 to 23, wherein coating the coated helical elongate element with the elastomer layer comprises spraying the coated helical elongate element with an elastomer.

25. 25. The method of any one of claims 16 to 24, wherein coating the coated helical elongate element with the elastomeric layer comprises at least partially rounding corners of the coated helical elongate element.

26. 26. The method of any one of claims 16 to 25, wherein coating the coated helical elongate element with the elastomer layer comprises coating the coated helical elongate element with the elastomer layer within a given time period of coating the at least one helical elongate element with the binder.

27. 27. The method of claim 26, wherein coating the coated helical elongate element with the elastomeric layer further comprises spraying additional elastomeric material onto the coated helical elongate element after coating the coated helical elongate element with the elastomeric layer within the given time period of coating the at least one helical elongate element with the binder.

28. 1. A ventricular assist device comprising: an impeller configured to be positioned within the left ventricle of a subject; A motor; a drive magnet coupled to the motor and configured to be rotated by the motor; a driven magnet magnetically coupled to the drive magnet and configured to be rotated by the drive magnet; a drive cable extending from the driven magnet and configured to impart rotational motion from the driven magnet to the impeller; a sensor set configured to detect a magnetic phase difference between the driven magnet and the drive magnet; a computer processor configured to receive the detected magnetic phase difference and to determine a physiological parameter of the subject at least in part in response thereto; 1. An apparatus comprising a ventricular assist device comprising:

29. 30. The apparatus of claim 28, wherein the sensor set is further configured to measure a magnetic flux amplitude signal, and wherein the computer processor is configured to determine the physiological parameter of the subject based at least in part on a combination of the magnetic flux amplitude signal and the detected magnetic phase difference.

30. 30. The apparatus of claim 28, wherein the computer processor is configured to determine a pressure difference between the subject's left ventricle and the subject's aorta in response at least in part to the magnetic phase difference between the driven magnet and the driving magnet.

31. 30. The apparatus of claim 28, wherein the computer processor is configured to determine left ventricular pressure of the subject at least in part in response to the magnetic phase difference between the driven magnet and the driving magnet.

32. 30. The apparatus of claim 28, wherein the computer processor is configured to determine an event in the subject's cardiac cycle at least in part in response to the magnetic phase difference between the driven magnet and the driving magnet.

33. 33. The apparatus of any one of claims 28 to 32, wherein the sensor set includes a first magnetometer configured to measure a magnetic phase of the driven magnet and a second magnetometer configured to measure a magnetic phase of the driven magnet.

34. 34. The apparatus of claim 33, wherein the second magnetometer is configured to measure the magnetic phase of the driven magnet by measuring the magnetic phase of the motor.

35. 33. The apparatus of any one of claims 28 to 32, wherein the computer processor is configured to receive a signal indicative of current consumption by the motor, and to determine the physiological parameter of the subject based at least in part on a combination of the current consumption by the motor and the detected magnetic phase difference.

36. 36. The apparatus of claim 35, wherein the sensor set is further configured to measure a magnetic flux amplitude signal, and wherein the computer processor is configured to determine the physiological parameter of the subject based at least in part on a combination of the current consumption by the motor, the magnetic flux amplitude signal, and the detected magnetic phase difference.

37. a ventricular assist device including an impeller configured to be positioned within a left ventricle of a subject and to pump blood from the left ventricle of the subject to an aorta of the subject; a blood pressure sensor configured to measure an aortic pressure of the subject; 1. A computer processor comprising: deriving an arterial pulse of the subject based on the measured aortic pressure; a computer processor configured to estimate an intrinsic cardiac output of the subject based at least in part on the arterial pulsation; An apparatus comprising:

38. 1. A left ventricular assist device configured to assist left ventricular function in a subject, comprising: The impeller and a frame disposed around the impeller; a rigid axial shaft extending from a proximal end of the frame to a distal end of the frame, the impeller coupled to the rigid axial shaft, the rigid axial shaft including a proximal portion and a distal portion coupled to one another via a joint, the proximal portion and the distal portion configured to flex relative to one another via the joint.

39. 39. The device of claim 38, wherein the length of the frame is greater than 25 mm.

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