Ventricular assist device

Abstract

Apparatus and methods are described that include an impeller (50) including a proximal bushing (64) and a distal bushing (58). Two or more helical elongated 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 elongated elements (52) along the axis about which the helical elongated elements (52) are wound. The impeller (50) includes an impeller over-expansion prevention element (72). The impeller over-expansion prevention element is a single, integrated structure that includes a ring (73) disposed around the axial structure (54) and a plurality of elongated elements (67). Each of the elongated elements (67) extends from the ring to each of the helical elongated elements (52) and is coupled to each of the helical elongated elements (52) to prevent radial expansion of the impeller (50). Other uses are also described.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims priority to U.S. Provisional Patent Application No. 63 / 006,122, entitled "Ventricular Assist Device" by Tuval, filed on April 7, 2020, U.S. Provisional Patent Application No. 63 / 114,136, entitled "Ventricular Assist Device" by Tuval, filed on November 16, 2020, and U.S. Provisional Patent Application No. 63 / 129,983, entitled "Ventricular Assist Device" by Tuval, filed on December 23, 2020.

[0002] Each of the above - referenced U.S. provisional applications is hereby incorporated by reference into this specification.

[0003] Some uses of the present invention generally relate to medical devices. Specifically, some uses of the present invention relate to ventricular assist devices and methods of using the same.

Background Art

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

Summary of the Invention

[0005] According to some uses of the present invention, the blood pump includes an impeller. The impeller includes a proximal bushing and a distal bushing, and two or more helical elongated elements (typically three helical elongated elements) extending from the proximal bushing to the distal bushing. Inside the two or more helical elongated elements, an axial structure (for example, a cylindrical axial structure such as a spring) is arranged along the axis around which the helical elongated elements are wound. A material film is supported between the helical elongated elements and the axial structure, and each of the helical elongated elements to which the material film is attached is configured to define each blade of the impeller. An impeller overexpansion prevention element is arranged inside the impeller. The impeller overexpansion prevention element is a single integrated structure including a ring arranged around the axial structure and a plurality of elongated elements. Each of the elongated elements extends from the ring to each helical elongated element and is coupled to each helical elongated element to prevent radial expansion of the impeller. Typically, the elongated elements are configured not to resist compression and are configured to prevent the impeller from radially expanding by applying tension to the helical elongated elements.

[0006] In some uses, when the material film transitions from one impeller blade to an adjacent blade along at least a portion of the length of the impeller, the material film forms a continuous U-shaped curved surface, and the U-shaped curve of the material film is substantially unbroken in the axial structure. In some uses, when viewed from the distal end of the impeller, the pressure side of each of the blades of the impeller (i.e., the side configured to push blood out during the 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 blades of the impeller changes to be substantially radially directed in the region of the elongated elements within the impeller blade.

[0007] In some applications, the impeller is manufactured by forming a structure having a first bushing and a second bushing at a proximal end and a distal end, respectively, with the first and second bushings being interconnected by at least one elongate element. By at least partially axially compressing the structure, the at least one elongate element expands radially to form at least one helical elongate element. The at least one helical elongate element is coated with a binder, the binder being configured to strengthen the bond between the helical elongate element and the elastomeric layer. The coated helical elongate element is then coated with an elastomeric layer. Subsequently, at least one elastomeric membrane is bonded to the at least one helical elongate element such that the at least one helical elongate element with the elastomeric membrane bonded thereto defines a blade of the impeller. For example, the helical elongate element may be immersed in an elastomeric material for making the elastomeric layer. In some applications, the elastic material constituting 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, and the driven magnets are 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 at least in part in response thereto, a physiological parameter of a subject is determined. For example, at least in part based on fluctuations in the phase difference, a computer processor can determine the difference between the left ventricular pressure of the subject and the aortic pressure of the subject, the left ventricular pressure of the subject, an event in the cardiac cycle of the subject, the afterload of the subject, 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 magnetic flux amplitude measurement, power consumption of the motor, and / or current consumption of the motor. Typically, such measurements are combined with a mathematical model such as a linear regression model and / or a state space model.

[0009] In some applications of the present invention, during operation of a ventricular assist device functioning as a blood pump, the arterial pulsation of a subject is measured 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. Usually, since the blood pump is a continuous flow blood pump rather than a pulsatile blood pump, the flow generated by the blood pump is a non-pulsatile flow. For this reason, as the rotational speed of the impeller increases and the flow rate generated by the blood pump increases, it is common for the arterial pulsation of the subject to decrease. In some applications, the arterial pulsation of the subject when the rotational speed of the impeller changes is measured. Based on the aforementioned measurements, the relationship between the arterial pulsation and the impeller rotational speed and / or the pump flow rate is derived. In some applications, based on the aforementioned relationship, the intrinsic cardiac output of the subject is derived. 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. It is hypothesized that at this value, the blood pump replaces the intrinsic function of the heart, and further, the flow rate generated by the pump at this value gives an approximation of the intrinsic cardiac output of the subject.

[0010] Accordingly, in some applications of the present invention, an apparatus is provided. The apparatus is a blood pump configured to be disposed within the body of a subject, an impeller, proximal bushing and distal bushing, two or more helical elongate elements extending from the proximal bushing to the distal bushing, an axial structure disposed along an axis around which the helical elongate elements are wound, inside the two or more helical elongate elements, a membrane of material supported between the helical elongate elements and the axial structure, wherein each of the helical elongate elements to which the membrane of material is attached defines a respective blade of the impeller, an impeller including an impeller overexpansion prevention element that is a single integrated structure including a ring and a plurality of elongate elements disposed around the axial structure, and a blood pump including. Each elongate element extends from the ring to each of the helical elongate elements and is coupled to each helical elongate element to prevent radial expansion of the impeller.

[0011] In some applications, the impeller includes three helical elongate elements, and the three helical elongate elements to which the membrane of material is attached define three blades of the impeller. Each elongate element extends from the ring to each of the three helical elongate elements such that each elongate element is within each of the three blades of the impeller.

[0012] In some applications, the elongate elements are configured to be non-resistant to compression and are configured to prevent radial expansion of the impeller by applying tension to the helical elongate elements.

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

[0014] In some applications, when viewed from the distal end of the impeller, the pressure side of each of the blades of the impeller 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. In some applications, the pressure side of each of the blades of the impeller changes to be substantially radially directed in the region of the elongate element within the impeller blade.

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

[0016] In some applications, the device further comprises a layer of elastomer disposed between the film of material and the adhesive. In some applications, the layer of elastomer is configured to round the corners of the helical elongate element. In some applications, the film of material is made of an elastomer. In some applications, the elastomer comprises 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 a ring is disposed around the tube.

[0018] Accordingly, in some applications of the present invention, a method is provided. The method is manufacturing 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. By at least partially axially compressing the structure, radially expanding at least one elongated element to form at least one helical elongated element. Coating at least one helical elongated element with an adhesive configured to strengthen the bond between the helical elongated element and the elastomer layer. Coating the coated helical elongated element with an elastomer layer, and Subsequently, bonding an elastomer membrane to at least one helical elongated element such that the at least one helical elongated element to which the elastomer membrane is bonded defines the blade of the impeller. Including manufacturing an impeller thereby.

[0019] In some applications, bonding an elastomer membrane to at least one helical elongated element such that the at least one helical elongated element to which the elastomer membrane is bonded defines the blade of the impeller includes immersing the helical elongated element in an elastomer material for making the elastomer membrane.

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

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

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

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

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

[0025] Furthermore, according to some applications of the present invention, an apparatus is provided. This apparatus is a ventricular assist device comprising an impeller configured to be disposed within the left ventricle of a subject, a motor, at least one drive magnet coupled to the motor and configured to rotate by the motor, At least one driven magnet magnetically coupled to the drive magnet and configured to rotate 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 interest at least in part in response thereto, including a ventricular assist device.

[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 interest 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 the left ventricle of the subject and the aorta of the subject at least in part in response to the magnetic phase difference between the driven magnet and the drive magnet. In some applications, the computer processor is configured to determine the left ventricular pressure of the subject at least in part in response to the magnetic phase difference between the driven magnet and the drive magnet. In some applications, the computer processor is configured to determine an event in the cardiac cycle of the subject at least in part in response to the 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. In 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, a computer processor is configured to receive a signal indicative of current consumption by a motor and to determine a physiological parameter of a subject based at least in part on a combination of the current consumption by the motor and a 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] Furthermore, according to some applications of the present invention, an apparatus is provided. The apparatus includes a ventricular assist device including an impeller disposed within a left ventricle of a subject and configured to pump blood from the left ventricle of the subject to the aorta of the subject, a blood pressure sensor configured to measure the aortic pressure of the subject, a computer processor that derives an arterial pulsation of the subject based on the measured aortic pressure, and a computer processor configured to estimate an intrinsic cardiac output of the subject based at least in part on the arterial pulsation. Including.

[0031] Furthermore, according to some applications of the present invention, an apparatus is provided. The apparatus includes a left ventricular assist device configured to assist the left ventricular function of a subject, an impeller, a frame disposed around the impeller, and a rigid axial shaft extending from a proximal end of the frame to a distal end of the frame, the impeller being 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 being configured to bend relative to each other via the joint. Including a left ventricular assist device.

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

[0033] Furthermore, according to some uses of the present invention, an apparatus is provided. This apparatus is an impeller, comprising a proximal bushing and a distal bushing, a plurality of helical elongated elements, an axial structure disposed along an axis around which the helical elongated elements are wound, inside the helical elongated elements, a membrane of an elastomeric material supported between the helical elongated elements and the axial structure, wherein each of the helical elongated elements to which the membrane of the elastomeric material is attached defines a respective blade of the impeller, and includes an impeller comprising along at least a portion of the length of the impeller, when the membrane of the elastomeric material transitions from one impeller blade to an adjacent blade, the membrane of the elastomer forms a continuous U-shaped bend, and the U-shaped bend of the membrane of the elastomeric material is substantially unbroken in the axial structure.

[0034] In some uses, the axial structure includes a cylindrical axial structure. In some uses, the cylindrical axial structure includes a spring.

[0035] Furthermore, according to some uses of the present invention, a method is provided. This method comprises passing a ventricular assist device, which includes a delivery catheter, a drive cable, and an outer tube surrounding the drive cable, through an arteriotomy via an introducer sheath and inserting it into the vascular system of a subject, removing the introducer sheath while the ventricular assist device remains within the vascular system of the subject, maintaining the sterility of the arteriotomy using a sterile sleeve disposed between the outer tube and the delivery catheter while allowing movement of the outer tube relative to the delivery catheter, and includes

[0036] Furthermore, according to some uses of the present invention, an apparatus is provided. This apparatus A blood pump, 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 a distal end of the impeller to a proximal end of the impeller by rotating the impeller in a given rotational direction, a drive cable configured to extend from the motor unit to the axial shaft and configured to impart a rotational motion from the motor to the impeller by rotation, and including the blood pump, wherein at least a part of the drive cable includes two or more layers, each layer including a plurality of wires, the plurality of wires of each of the two or more layers are arranged in a coiled configuration, and in response to the drive cable rotating in a given rotational direction, the wires of each layer are at least partially wound back, causing a part of the drive cable to shorten axially, the drive cable is maintained in a pre-tensioned state, and the drive cable extends relative to a stationary state even when the impeller is stationary.

[0037] Furthermore, according to some applications of the present invention, an apparatus is provided. The apparatus is a blood pump, 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 a distal end of the impeller to a proximal end of the impeller by rotating the impeller in a counterclockwise direction when viewing 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 impart a rotational motion from the motor to the impeller by rotation, and including the blood pump, wherein at least a part of the drive cable includes two or more layers, each layer including a plurality of wires, and the plurality of wires of each of the two or more layers are arranged in a left-handed layer coiled configuration.

[0038] Furthermore, according to some applications of the present invention, an apparatus is provided. The apparatus is 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 viewing 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 impart a rotational motion from the motor to the impeller by rotation, and includes the blood pump, at least a part of the drive cable includes two or more layers, each layer includes a plurality of wires, and the plurality of wires of each of the two or more layers are arranged in a right-handed layer coil configuration.

[0039] Furthermore, according to some applications of the present invention, an apparatus is provided. The apparatus is 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 given rotational direction, a drive cable configured to extend from the motor unit to the axial shaft and configured to impart a rotational motion from the motor to the impeller by rotation, and includes the blood pump, at least a part of the drive cable includes an inner layer and an outer layer that are coaxial with each other, each layer includes a plurality of wires arranged in a coil 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] Furthermore, according to some uses of the present invention, an apparatus is provided. This apparatus is a blood pump, 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 given rotational direction to pump 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 impart rotational motion from the motor to the impeller by rotation, a drive cable bearing tube configured such that the drive cable rotates inside it, and a part of the drive cable bearing tube includes an inner layer and an outer layer containing mutually different materials, a coiled wire embedded between the inner layer and the outer layer, the coiled wire being configured to maintain a substantially circular cross-section of the drive cable bearing tube even within a region where the drive cable bearing tube is greatly curved, and includes a drive cable bearing tube, and includes a blood pump including the above.

[0041] Generally, in the specification and claims of the present application, when "proximal" and related terms are used with respect to an apparatus or a part thereof, they mean the end of the apparatus or a part thereof, and usually mean a part close to the position where the apparatus is inserted into the subject when the apparatus is inserted into the subject. "Distal" and related terms, when used with respect to an apparatus or a part thereof, mean the end or part of the apparatus, and usually mean a part far from the position where the apparatus is inserted into the subject when the apparatus is inserted into the subject.

[0042] The scope of the present invention includes using the apparatus and method described herein at anatomical locations other than the left ventricle and aorta. Thus, a ventricular assist device and / or a part thereof may be referred to herein (in the specification and claims) as a blood pump.

[0043] The present invention will be more fully understood with reference to the drawings in conjunction with the following detailed description of its embodiments.

Brief Description of the Drawings

[0044]

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Mode for Carrying Out the Invention

[0045] Reference is now made to the schematic diagrams of the ventricular assist device 20 configured such that the distal end is disposed in the target left ventricle 22 according to some applications of the present invention shown in FIGS. 1A, 1B, and 1C. FIG. 1A shows an overview of a ventricular assist device system including a control console 21 and a motor unit 23 (as will be described below, the motor unit is typically a handle that houses a motor). FIG. 1B shows the ventricular assist device inserted into the target left ventricle, and FIG. 1C shows the pump section 27 of the ventricular assist device in more detail. The ventricular assist device includes a pump outlet tube 24 that crosses the target aortic valve 26, with the proximal end 28 of the pump outlet tube disposed in the target aorta 30 and the distal end 32 of the pump outlet tube disposed within the left ventricle 22. Usually, the pump outlet tube 24 is an elongated tube, and the axial length of the pump outlet tube is considerably long compared to the diameter. The scope of the present invention includes using the devices and methods described herein at anatomical locations other than the left ventricle and aorta. Thus, the ventricular assist device and / or a part thereof may be referred to herein (in the specification and claims) as a blood pump.

[0046] In some applications, a ventricular assist device is used to assist the function of the left ventricle of a subject during percutaneous coronary intervention. In such cases, the ventricular assist device is 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, the ventricular assist device is used to assist the function of the left ventricle of a subject for a longer period (e.g., 2 to 20 days, e.g., 4 to 14 days) in patients suffering from cardiogenic shock and may be used in a low cardiac output state (e.g., acute myocardial infarction, myocarditis, cardiomyopathy, post-partum, etc.). In some applications, the ventricular assist device is used to assist the function of the left ventricle of a subject for an even longer period (e.g., several weeks or months), for example, in a "bridge to recovery" treatment. In some such applications, the ventricular assist device is implanted permanently or semi-permanently, and the impeller of the ventricular assist device is powered transcutaneously using, for example, an external antenna that is magnetically coupled to the impeller.

[0047] As shown in FIG. 1B which depicts the step of implanting a ventricular assist device within the left ventricle, typically, the distal end of the ventricular assist device is guided into the left ventricle through a guide wire 10. When inserting the distal end of the device into the left ventricle, a delivery catheter 143 is positioned over the distal end of the device. Once the distal end of the device is positioned within the left ventricle, typically, the delivery catheter is retracted into the aorta and the guide wire is retracted from the subject. By retracting the delivery catheter, typically, the self-expandable component of the distal end of the device assumes a radially unconstrained configuration, as will be described in more detail below. Typically, the ventricular assist device is inserted into the subject to provide acute treatment to the subject. In some applications, upon completion of treatment, 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 of the distal end of the device to assume a radially constrained configuration. Alternatively or additionally, by retracting the distal end of the device into the delivery catheter, the self-expandable component of the distal end of the device assumes a radially constrained configuration.

[0048] In some applications (not shown), the ventricular assist device and / or the delivery catheter 143 includes an ultrasonic transducer at its distal end, and the ventricular assist device advances towards the ventricle of the subject based on ultrasonic guidance.

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

[0050] In some applications, a control console 21 (shown in FIG. 1A), which typically includes a computer processor 25, controls the rotation of the impeller. For example, the computer processor may be disposed within a motor unit 23 (shown in FIG. 1A) and control a motor 74 (such as shown in FIG. 7A) to drive the impeller to rotate through a drive cable 130 (such as shown in FIG. 7A). In some applications, the computer processor is configured to detect a target physiological parameter (such as left ventricular pressure, afterload, rate of change of left ventricular pressure, etc.) and control the rotation of the impeller accordingly, as will be described in more detail below. Typically, the operations performed by the computer processor, as described herein, convert the physical state of a memory, which is a physical article that communicates with the computer processor, to have different magnetic polarities, electrical charges, etc., depending on the technology of the memory used. The computer processor 25 is typically a hardware device programmed with computer program instructions for creating 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 (such as a glucose solution) to pass through a portion of the ventricular assist device 20, for example, to cool a portion of the device and / or to wash debris from a portion of the device. The purge system 29 will be described in more detail below.

[0052] Typically, along the distal section 102 of the pump outlet tube 24, the frame 34 is disposed within the pump outlet tube and around the impeller 50. The frame is typically made of a shape memory alloy such as nitinol. In some applications, the shape memory alloy of the frame is set such that at least a portion of the frame (and thus the distal section 102 of the tube 24) has a cross-sectional shape that is substantially circular, elliptical, or polygonal when no force is applied to the distal section 102 of the tube 24. By having a substantially circular, elliptical, or polygonal cross-sectional shape, the frame is configured to hold the distal portion of the pump outlet tube in an open state. Typically, when the ventricular assist device operates, the distal portion of the pump outlet tube is configured to be disposed within the subject's body such that the distal portion of the pump outlet tube is at least partially disposed within the left ventricle.

[0053] In some applications, the frame is not disposed within the pump outlet tube along the proximal section 106 of the pump outlet tube 24, and thus the pump outlet tube is not supported in an open state by the frame 34. The pump outlet tube 24 is typically made of a blood-impermeable crushable material. For example, the pump outlet tube 24 may include polyurethane, polyester, and / or silicone. Alternatively or additionally, the pump outlet tube is made of polyethylene terephthalate (PET) and / or polyether block amide (e.g., PEBAX®). In some applications (not shown), the pump outlet tube is reinforced with a reinforcing structure, such as a braided reinforcing structure like a braided nitinol tube. Typically, the proximal portion of the pump outlet tube is configured to be disposed 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 tube crosses the subject's aortic valve and reaches the subject's ascending aorta from the subject's left ventricle.

[0054] As described above, the pump outlet tube typically defines one or more blood inlets 108 at the distal end of the pump outlet tube, through which blood flows from the left ventricle into the pump outlet tube when the impeller operates. In some applications, the proximal portion of the pump outlet tube defines one or more blood outlets 109, through which blood flows from the pump outlet tube into the ascending aorta when the impeller operates. Typically, the pump outlet tube defines a plurality of blood outlets 109, for example, two to eight blood outlets (e.g., two to four blood outlets). When the impeller operates, the proximal portion of the pump outlet tube is normally maintained open by the pressure of the blood flow through the pump outlet tube. In some applications, for example, when the impeller malfunctions, the proximal portion of the pump outlet tube is configured to collapse inward in response to the pressure outside the proximal portion of the pump outlet tube exceeding the pressure inside the proximal portion of the pump outlet tube. In this way, the proximal portion of the pump outlet tube functions as a safety valve to prevent retrograde blood flow from the aorta to the left ventricle.

[0055] Referring back to FIG. 1C, in some applications, the frame 34 is shaped such that the frame defines a proximal conical portion 36, a central cylindrical portion 38, and a distal conical portion 40. Typically, in the proximal conical portion, the narrow end of the cone is positioned proximal to the wide end of the cone. Further typically, in the distal conical portion, the narrow end of the cone is positioned distal to the wide end of the cone. In some applications, the pump outlet tube 24 extends to the distal end of the cylindrical portion 38 (or slightly proximal or distal thereto) as shown in FIG. 1C, such that the distal end of the pump outlet tube defines a blood inlet 108 that is oriented in a single axial direction. In some applications, as will be described below with reference to FIGS. 12A-12B, a liner 39 lines at least a portion of the frame 34 within the frame. Depending on the particular application, the liner either partially or completely overlaps the pump outlet tube 24 within the portion of the frame that the liner lines. In such applications, the distal end of the liner defines a blood inlet 108 that is oriented in a single axial direction. In some applications, both the pump outlet tube and the liner terminate in front of the distal end of the cylindrical portion of the frame such that the distal portion of the cylindrical portion of the frame is not covered. This will be described below with reference to FIG. 13.

[0056] Typically, the pump outlet tube 24 includes a conical proximal portion 42 and a cylindrical central portion 44. (Typically, the conical proximal portion 36 is generally disposed within the proximal section 106 described above, and the cylindrical central portion extends from within the proximal section 106 to the distal section 102.) In the proximal conical portion, typically, the narrow end of the cone is positioned proximal to the wide end of the cone. Typically, the 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, as shown in FIG. 1C, the blood outlet is teardrop-shaped. Typically, the combination of the teardrop shape of the blood outlet and the fact that the blood outlet extends at least partially along the proximal conical section of the tube 24 causes the blood to flow out of the blood outlet along streamlines that are 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 tube 24 varies along the length of the central portion of the pump outlet tube such that the central portion of the pump outlet tube has a frustoconical shape. For example, the central portion of the pump outlet tube may flare 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 tube has a diameter of 5-7 mm and at its distal end, the central portion of the pump outlet tube has a diameter of 8-12 mm.

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

[0059] Referring now to FIG. 1D, which is a schematic illustration of the ventricular assist device 20 in some uses of the present invention. The pump outlet tube 24 extends to the end of the distal cone portion 40 of the frame, and the pump outlet tube defines a plurality of lateral blood inlets 108. In such uses, the pump outlet tube typically defines a distal cone portion 46, and the narrow end of this cone is distal to the wide end of the cone. In some such uses, the pump outlet tube defines from two to four lateral blood inlets. Typically, in such uses, each of the blood inlets 108 has an area greater than 20 square millimeters (e.g., greater 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 tube defines more, smaller blood inlets (not shown). For example, more than 10 smaller blood inlets, more than 50 smaller blood inlets, more than 100 smaller blood inlets, or more than 150 smaller blood inlets, e.g., 50-100 smaller blood inlets, 100-150 smaller blood inlets, or 150-200 smaller blood inlets. In some such uses, each of the smaller blood inlets has an area greater than 0.1 square millimeter (e.g., greater than 0.3 millimeter) and / or less than 5 square millimeters (e.g., less than 1 square millimeter), e.g., an area of 0.1-5 square millimeters, 0.2-0.5 square millimeters, or 0.3-1 square millimeter.

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

[0061] Now, refer to FIGS. 1E and 1F, which are schematic views of a ventricular assist device 20 including a braided structure 260 and / or a mesh 282 in a distal region, according to some applications of the present invention. The braided structure and / or the 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 respect to FIG. 20B of Tuval's U.S. Patent Application Publication No. 2019 / 0209758, which is incorporated herein by reference. The mesh 282 is generally similar to the mesh 282 described with respect to FIG. 21D of Tuval's U.S. Patent Application Publication No. 2019 / 0209758, which is incorporated herein by reference.

[0062] Referring to FIG. 1E, in some applications, the braided structure 260 (e.g., braided metal or alloy such as shape memory alloy (e.g., nitinol)) is disposed in the 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 can include a distal tip element 107 (which is typically as described with respect to FIGS. 14 to 16B), and the braided material is disposed around a portion of the device so as to cover a portion of the distal tip element. In some applications, the braided material is disposed on at least a portion of the frame 34. For example, the braided material can surround at least a portion of the frame that extends 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 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, and the mesh 282 is configured to self-expand when the distal tip element 107 is disposed inside the left ventricle of the subject. In some applications, the device includes a distal tip element generally described with reference to FIGS. 14 to 16B, and the mesh is disposed around a portion of the device so as to cover a portion of the distal tip element. In some applications, the mesh is disposed on at least a portion of the frame 34. For example, the mesh can surround at least a portion of the frame that extends 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 disposed to cover the blood inlet 108.

[0064] Typically, the braided structure 260 and / or the mesh 282 three-dimensionally separate one or more blood inlets 108 from the internal structure of the left ventricle. In this way, the braided structure 260 and / or the mesh 282 separate one or more blood inlets 108 from the ventricular septum, chordae tendineae, papillary muscles, trabeculae carneae, and / or the left ventricular apex. As an alternative or in addition to using the braided structure and / or the mesh to separate one or more blood inlets 108 from the internal structure of the left ventricle, the cells of the frame 34 near the blood inlet 108 are configured to define an opening that is smaller than that of other portions of the frame. For example, the cells of the distal conical portion of the frame may define an opening that is smaller than the opening defined by the cells of the proximal conical portion of the frame. Alternatively or additionally, the cells of the distal conical portion of the frame may define an opening that is smaller than the opening defined by the cells of the cylindrical portion of the frame.

[0065] Reference is now made to FIG. 2, a schematic view of a frame 34 that houses an impeller of a ventricular assist device 20 according to some uses of the present invention. As described above, the frame 34 is typically made of a shape memory alloy such as nitinol, and the shape memory alloy of the frame is set to have a shape such that the frame (and thus the tube 24) has a substantially circular, elliptical, or polygonal cross-sectional shape when no force is applied to the pump outlet tube 24 and / or the frame 34. By having a substantially circular, elliptical, or polygonal cross-sectional shape, the frame is configured to hold the distal portion of the tube open.

[0066] Typically, the frame is a stent-like frame that includes struts that define cells. Further typically, the frame is covered by the pump outlet tube 24 and / or the 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 movement of the impeller relative to the frame, a portion of the impeller that defines the maximum span of the impeller is disposed 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 is stretched between the edges of the cells such that the pump outlet tube 24 and / or the liner 39 no longer defines a circular cross-section. In some applications, if this occurs in the region where a portion of the impeller that defines the maximum span of the impeller is disposed, as a result, a non-uniform gap is created between the edges of the impeller blades and the tube 24 (and / or the liner) at the above position during the rotation cycle of the impeller. In some applications, this can lead to an increase in hemolysis compared to when a uniform gap is created between the edges of the impeller blades and the tube 24 (and / or the liner) at the above position during the rotation cycle of the impeller.

[0067] Referring to FIG. 2, in consideration of at least partially the problems described in the above 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 configuration where it is not radially constrained, the maximum cell width CW of each cell within the cylindrical portion of the frame (i.e., the distance measured along the circumference of the cylindrical portion 38 from the inner edge of the strut at the central junction on one side of the cell to the inner edge of the strut at the central junction on the other side of the cell) is less than 2 mm, for example, 1.4 mm - 1.6 mm or 1.6 - 1.8 mm. Since the cells are relatively small, the pump outlet tube 24 (and / or the liner) defines a substantially circular cross-section within the cylindrical portion of the frame.

[0068] Continuing to refer to FIG. 2, starting from the proximal end of the frame (on the left side of the figure), generally, the frame defines (a) a coupling portion 31 where the frame is coupled to the proximal bearing 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, when the frame transitions from the proximal end of the frame towards the center of the frame (e.g., when the frame transitions from the coupling portion 31 and the proximal conical portion 36 to the cylindrical portion 38), the struts 37 of the frame pass through a junction 35 where a single strut branches into two struts in a Y-shape. As will be described in more detail below, generally, the frame 34 is arranged in a configuration that is radially constrained (i.e., crimped) within the delivery catheter 143 by extending axially. Further, generally, the radial narrowing of the frame is transmitted to the impeller, and the impeller is radially constrained by extending axially within the frame. In some applications, the struts of the frame configured in the above manner readily transmit the axial extension from the delivery catheter (or other device configured to crimp the frame) to the frame, which readily transmits the axial extension to the impeller. This is because a pair of struts branching from each junction 35 are configured to approach each other so as to pivot and close about the junction.

[0069] Continuing to refer to FIG. 2, in some applications, the distal strut junction 33 is not circumferentially continuous and is generally configured to be maintained in an open state for placing the impeller within the frame through the distal end of the frame when the frame is coupled to the axial shaft 92 (shown in FIG. 4). Subsequently, as will be described in more detail below with reference to FIGS. 5A - 5B, the distal strut portion is closed around the outside of the distal bearing 118. In some applications, the proximal end of the distal tip element 107 (shown in FIG. 1C) holds the distal strut portion in a closed configuration around the outside of the distal bearing 118.

[0070] Typically, when disposed in a configuration that is not radially constrained, the frame 34 has an overall length greater than 25 mm (e.g., greater than 30 mm) and / or less than 50 mm (e.g., less than 45 mm), e.g., 25 - 50 mm, or 30 - 45 mm. Typically, when disposed in a configuration that is radially constrained (within the delivery catheter 143), the length of the frame increases by 2 - 5 mm. Typically, when disposed in a configuration that is not radially constrained, the length of the cylindrical portion of the frame 34 is greater than 10 mm (e.g., greater than 12 mm) and / or less than 25 mm (e.g., less than 20 mm), 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] Referring now to FIGS. 3A - 3C, which are schematic views of the impeller 50 or a 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 axis spring 54 such that the helix defined by the helical elongate element is coaxial with the central axis spring. (As will be described in detail below herein, typically the central axis spring includes a tube 70 at an intermediate position along its length. Also, as will be described below, the scope of the present application includes using other axial structures instead of a spring. Accordingly, in some places, the present application uses the term "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 axis spring are made of a shape memory material, such as a shape memory alloy like nitinol. Typically, each of the helical elongate element and the central axis spring supports a membrane 56 of material (e.g., an elastomer such as polyurethane and / or silicone) therebetween. In some applications, the membrane of material includes fragments of nitinol embedded therein, e.g., to reinforce the membrane of material. For illustrative purposes, the impeller is shown in FIG. 3A without the membrane of material. FIGS. 3B and 3C are views showing the impeller with a membrane of material supported between the helical elongate element and the spring, respectively.

[0072] Each of the helical elongated elements, together with a membrane extending from the helical elongated element to the spring, defines each impeller blade, the helical elongated element defines the outer edge of the blade, and the axial spring defines the axis of the impeller. Typically, the membrane of material extends along and covers the spring. In some applications, a suture 53 (e.g., a polyester suture as shown in FIGS. 3B and 3C) is wound around the helical elongated element, for example, as described in Schwammenthal U.S. Patent No. 10,864,310, which is incorporated herein by reference. Typically, the suture is configured to facilitate the bond between a membrane of material (usually an elastomer such as polyurethane or silicone) and a helical elongated element (usually a shape memory alloy such as nitinol). In some applications, a suture (e.g., a polyester suture, not shown) is wound around the spring 54. Typically, the suture is configured to facilitate the bond 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] Enlarged views A and B of FIG. 3C show two alternative ways in which a suture is tied around a helical elongated element 52. In some applications, as shown in enlarged view A, the suture is tied around the outer surface of the helical elongated element. Alternatively, as shown in enlarged view B, the helical elongated elements have grooves 45 defined in their outer surfaces and the suture is embedded within the grooves. By embedding the suture within the grooves, the suture typically does not enlarge the outer profile of the impeller, which is defined by the outer surface of the helical elongated element.

[0074] Typically, the proximal ends of spring 54 and the helical elongate element 52 extend from the proximal bushing (i.e., sleeve bearing portion) 64 of the impeller, and the proximal ends of spring 54 and the helical elongate element 52 are disposed at substantially the same position and have a similar radial distance from the longitudinal axis of the impeller. Similarly, typically, the distal ends of spring 54 and the helical elongate element 52 extend from the distal bushing 58 of the impeller, and the distal ends of spring 54 and the helical elongate element 52 are disposed at substantially the same position and have a similar radial distance from the longitudinal axis of the impeller. Typically, spring 54, and the proximal bushing 64 and the distal bushing 58 of the impeller define lumens therethrough, and the impeller is adapted to define a continuous lumen 62 (shown in FIG. 3C) therethrough.

[0075] Next, refer to FIG. 4, which is a schematic view of an impeller 50 disposed inside the frame 34 of the ventricular assist device 20 according to some uses of the present invention. In some uses, as will be described below with reference to FIGS. 12A - 12B, a liner 39 lines at least a portion of the frame 34 inside the frame. According to each use, the liner partially or completely overlaps with the pump outlet tube 24 at a portion of the frame that the liner lines. In some uses, both the pump outlet tube and the liner terminate in front of the distal end of the cylindrical portion 38 of the frame so that the distal end of the cylindrical portion of the frame is not covered. This will be described below with reference to FIG. 13. In some uses, as described with reference to FIG. 1D, the pump outlet tube is continuous to cover the distal conical portion of the frame. In the use shown in FIG. 4, the liner lines the inside of the cylindrical portion of the frame, and the pump outlet tube 24 does not cover the cylindrical portion of the frame. However, the scope of the present application includes applying the devices and methods described with respect to FIG. 4 to any one of the uses described below with reference to FIG. 1D, FIGS. 12A - 12B, or FIG. 13.

[0076] As shown in FIG. 4, usually, even at the position where the span of the impeller is maximum, there is a gap G between the outer edge of the impeller 50 and the lining 39. In some applications, in order for the impeller to efficiently send blood from the target left ventricle to the target aorta, it is desirable that the gap between the outer edge of the blade of the impeller and the lining 39 is relatively small. However, it is desirable that the gap between the outer edge of the blade of the impeller and the inner surface of the frame 34 is maintained 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 the frame 34 are arranged in a configuration where they are not radially constrained, at the position where the span of the impeller is maximum, the gap G between the outer edge of the impeller and the lining 39 is greater than 0.05 mm (for example, greater than 0.1 mm), and / or less than 1 mm (for example, less than 0.4 mm), for example, 0.05 - 1 mm, or 0.1 - 0.4 mm. In some applications, when the impeller is arranged in a configuration where it is not radially constrained, the outer diameter of the impeller at the position where the outer diameter of the impeller is maximum is greater than 7 mm (for example, greater than 8 mm), and / or less than 10 mm (for example, less than 9 mm), for example, 7 - 10 mm, or 8 - 9 mm. In some applications, when the frame 34 is arranged in a configuration where it is not radially constrained, the inner diameter of the frame 34 (measured from the inside of the lining 39 on one side of the frame to the inside of the lining on the opposite side of the frame) is greater than 7.5 mm (for example, greater than 8.5 mm), and / or less than 10.5 mm (for example, less than 9.5 mm), for example, 7.5 - 10.5 mm, or 8.5 - 9.5 mm. In some applications, when the frame is arranged in a configuration where it is not radially constrained, the outer diameter of the frame 34 is greater than 8 mm (for example, greater than 9 mm), and / or less than 13 mm (for example, less than 12 mm), for example, 8 - 13 mm, or 9 - 12 mm.

[0078] Typically, the axial shaft 92 passes through the axis of the impeller 50 via the lumen 62 of the impeller. Further typically, the axial shaft is rigid, for example, a rigid tube. (In some applications, as described with reference to FIGS. 20A through 20C, for example, a portion of the axial shaft is at least partially flexible.) In some applications, the proximal bushing 64 of the impeller is coupled to the shaft 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. The axial shaft itself is radially stabilized via the proximal radial bearing 116 and the distal radial bearing 118. Next, the axial shaft passes through the lumen 62 defined by the impeller to radially stabilize the impeller relative to the inner surface of the frame 34, and a relatively small gap (e.g., the gap as described above) between the outer edge of the blade of the impeller and the inner surface of the frame 34 is maintained even when the impeller rotates.

[0079] Referring again to FIGS. 3A through 3C, in some applications, the impeller includes a plurality of elongate elements 67 that extend radially from the central axial spring 54 to the outer helical elongate element 52. The elongate elements 67 are typically flexible, but are substantially inextensible along the axis defined by the elongate elements 67. Further typically, each of the elongate elements 67 is configured to substantially resist compression. Each elongate element 67 is configured to apply a tension to the helical elongate element 52 that prevents the helical elongate element 52 from moving radially outward, so that the separation distance between the helical elongate element 52 and the central axial spring 54 (in the absence of the elongate elements 67) is greater than the length of the elongate elements 67. For example, the elongate elements 67 can include strings (including polyester and / or another polymer or natural materials including fibers) and / or wires (nitinol wires and / or wires made of another alloy or metal). Thus, the elongate elements prevent the impeller from expanding radially by applying tension to the helical elongate element.

[0080] In some applications, the elongate element 67 maintains the helical elongate element 52 (defining the outer edge of the impeller blade) within a given distance of the axial spring 54. Thus, the elongate element 67 is configured to prevent the outer edge of the impeller from being radially outwardly pushed due to the forces applied to the impeller during rotation of the impeller. In other words, the elongate element 67 acts as an impeller expansion prevention element. The elongate element 67 is thereby configured to maintain a gap between the outer edge of the impeller blade 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 less (e.g., three or less) elongate elements 67 are used in the impeller, and each of the elongate elements 67 is typically doubled (i.e., extends radially from the axial spring 54 to the outer edge of the helical elongate element 52 and then back to the axial spring from the helical elongate element). In some applications, the plurality of elongate elements 67 are formed from a single string or a single wire. Each of the elongate elements 67 extends from the spring to each helical elongate element 52 and then back to the axial spring 54.

[0081] In some applications, the impeller is manufactured as follows. From a tube of a shape memory material such as Nitinol, the proximal bushing 64, the distal bushing 58, and the helical elongate element 52 are cut. The cutting of the tube and the setting of the shape of the shape memory material are typically performed using techniques generally similar to those described in, for example, U.S. Patent No. 10,039,874 to Schwammenthal, such that the helical elongate element and the bushing are defined by the cut and shape-set tube of shape memory material. Typically, the spring 54 is inserted into the cut and shape-set tube so as to extend along at least the length of the tube from the proximal bushing to the distal bushing. In some applications, the spring is inserted into the cut and shape-set tube in an axially compressed state and is configured to be held in a predetermined position relative to the tube by applying a radial force to the proximal and distal bushings. Alternatively or additionally, a portion of the spring is welded to the proximal and distal bushings. In some applications, the spring is cut from a tube of a shape memory material such as Nitinol. In some such applications, the spring is configured such that there is substantially no gap between adjacent turns of the spring when the spring is disposed in a configuration where it is not radially constrained (a configuration in which the spring is typically disposed during operation of the impeller).

[0082] In some applications, after the spring 54 is inserted into the cut and shaped tube, the elongated element 67 as described above is arranged 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 the bushing. Thereafter, a string or wire passes through (a) from the mandrel through the first element of the helical elongated element 52, (b) back from the first element of the helical elongated element 52 to the mandrel, (c) around the mandrel and through the second element of the helical elongated element 52, and (d) back from the second element of the helical elongated element 52 to the mandrel or the like. When the string or wire passes through each of the helical elongated elements 52 from the mandrel 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 elongated elements 52. Usually, each string or wire passes from the helical elongated element around the mandrel and back to the helical elongated element, and the two ends of the string are tied to each other. In some applications, at the longitudinal central position of the spring 54, the spring has a shape that defines the tube 70 as shown (i.e., at this position, the spring does not define a winding), and the string or wire is wound around this tube. In some applications, the string or wire is not wound around the 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). This will be described in detail below with reference to FIG. 3F.

[0083] In some applications, at this stage, to facilitate the bonding between the film of the material (usually an elastomer such as polyurethane or silicone) and the helical elongated element 52 (usually a shape memory alloy such as nitinol) in the next stage of impeller manufacturing, a suture 53 (e.g., a polyester suture) is wound around the helical elongated 52. In some applications, a suture (e.g., a polyester suture, not shown) is wound around the spring 54. Usually, the suture is configured to facilitate the bonding between the film of the material (usually an elastomer such as polyurethane or silicone) and the spring (usually 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 proximal and distal bushings, a helical elongated element, and a cut and shaped tube that defines the spring (and optionally the elongated element and suture). This structure is immersed in the material that defines the membrane 56. In some applications, although the mandrel is not shown in FIG. 3A, the assembled structure is immersed in the material together with a mandrel disposed through the lumen defined by the spring and bushing. Usually, the material forming the membrane is silicone and / or polyurethane (and / or similar elastomers), and the assembled structure is immersed in the material while the material is in an uncured liquid state. Subsequently, the material is cured, for example, by drying to solidify. In some applications, the assembled structure is rotated during the drying of the material. Usually, this facilitates the formation of a film of the material having a substantially uniform thickness within each impeller blade. After the material has dried, the mandrel is typically removed from the lumen defined by the bushing and spring.

[0085] As a result of performing the above-described process, typically, a continuous film of material extending from each of the helical elongated elements to the spring and along the length of the spring so as to define the tube with the spring embedded in the tube is obtained. A portion of the film extending from each of the helical elongated elements to the spring defines an impeller blade. In applications where the impeller includes the elongated element 67, the elongated element is typically embedded within a portion of these films.

[0086] Typically, the elongated element 67 is configured to limit the radial expansion of the impeller blade, as detailed above. In some applications, the span at which the elongated element allows expansion of the impeller blade is set using the following technique. As described in the above paragraph, the two ends of the string or wire within each blade are joined to each other. Typically, when joining the ends of the string or wire in each blade, the span of the impeller blade is set to be smaller than the desired span of the impeller, and there is some slack in the knot where the two ends of the string or wire are joined to each other. Subsequently, by tightening the knot of the ends of the string or wire within each blade, the outer edges of the impeller blade are pulled apart from each other so as to expand the span of the impeller blade. This process is repeated and the span of the impeller blade is measured until the desired span of the impeller blade is achieved. Next, the structure 59 with the string or wire joined is immersed in the elastomer material for making the film 56, and the elastomer material is dried so as to maintain the ends of the string or wire joined to each other at the desired span of the impeller blade.

[0087] Typically, the impeller 50 is inserted into the left ventricle via a catheter while having a radially constrained configuration. In the radially constrained configuration, both the helical elongate element 52 and the central axis spring 54 extend axially and are radially constrained. Typically, the membrane 56 of a material (e.g., silicone and / or polyurethane) changes shape to conform to the shape changes of both the helical elongate element and the central axis spring that support the membrane of the material. Typically, since the spring provides a large surface area to which the inner edge of the membrane attaches, by using the spring to support the inner edge of the membrane, the shape of the membrane can be changed without the membrane breaking or collapsing. In some applications, using a spring to support the inner edge of the membrane can reduce the diameter of the spring itself by axially extending the spring, compared to, for example, using a rigid shaft to support the inner edge of the membrane, such that the diameter at which the impeller can be radially constrained is reduced.

[0088] As described 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 the purpose of inserting the impeller into the ventricle or withdrawing the impeller from the subject, the impeller extends axially by the distal bushing that slides distally along the axial shaft. After the impeller is released within the subject, it assumes a non-radially constrained configuration (the configuration in which the impeller is normally disposed when the impeller operates), as shown in FIGS. 3A through 3C.

[0089] For purposes of illustration, it should be noted that in some of the figures, the impeller 50 is shown without including all of the impeller features shown and described in FIGS. 3A through 3C. For example, some of the figures show impellers that do not include the suture 53 and / or the elongate element 67. The scope of the present application includes using an impeller having any of the features shown and described in FIGS. 3A through 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 an elastomeric material to at least one helical elongated element in such a way that no protrusions occur from the effective edge of the impeller blade. Before immersing in the elastomeric material, the helical elongated element is coated with a binder. Usually, a binder having at least two functional groups configured to bind to the helical elongated element and the elastomeric material respectively is selected. For example, a silane compound such as n-(2-aminoethyl)-3-aminopropyltrimethoxysilane, which contains a first functional group (e.g., (OH)) configured to bind to the helical elongated element (usually made of an alloy such as nitinol), and further contains a second functional group (e.g., (NH2)) configured to bind to the elastomeric material can be used. Usually, the functional groups in the binder are active for a given time period (e.g., about 1 hour or less). Therefore, during this time period, a coating of the elastomeric material is applied around the helical elongated element. Usually, this coating of the elastomeric material is the same elastomeric material as that used for the membrane 56 or a similar elastomeric material. For example, for the membrane 56, a polycarbonate-based thermoplastic polyurethane such as Aromatic Carbothane (trademark) (e.g., Aromatic Carbothane (trademark) 75A) can be used, and the coating can be the same polycarbonate-based thermoplastic polyurethane or a similar polycarbonate-based thermoplastic polyurethane such as Pellethane (registered trademark) (e.g., Pellethane (registered trademark) 90A).

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

[0092] In some applications, after applying a spray to a helical elongated element, the structure 59 is immersed in an elastomer for making the membrane 56, for example as described above. In some applications, the material for making the membrane is an elastomer material having an ultimate elongation of more than 300 percent, for example more than 400 percent. Usually, the material has a relatively small molecular weight. In some applications, the melt flow index of the material (an indirect indicator of molecular weight) is at least 4, for example at least 4.3. In some applications, the tensile strength of the material is more than 6000 psi, for example more than 7000 psi, or more than 7500 psi. In some applications, the material is a thermoplastic polyurethane such as Carbothane (trademark). In some applications, Aromatic Coarbothane (trademark) 75A is used. Usually, in such materials, one or more of the following are combined: no outer diameter loss occurs during the dipping process, fatigue resistance, resistance to deformation by crimping, and small outer shape loss during crimping.

[0093] According to the above description of applying the membrane 56 to the helical elongated element, the scope of the present invention includes any technique of applying an additional layer of the same elastomer material, a different elastomer material, and / or an intervening material to the helical elongated element by spraying, dipping, or another coating method before immersing the helical elongated element in the elastomer material for making the membrane 56. In some applications, the additional layer of the elastomer material is configured to round the corners of the helical elongated element and / or act as a mediator to strengthen the bond between the helical elongated element and the membrane 56 of the material. In some applications, the intervening material (such as silane) is configured to act as a mediator to strengthen the bond between the helical elongated element and the membrane 56 of the material.

[0094] Next, refer to FIGS. 3D and 3E, which are schematic views of an impeller 50 including a single integrated impeller overextension prevention element 72 that defines a plurality of elongated elements 67 according to some uses of the present invention. FIGS. 3D and 3E show the impeller without the material film 56 for illustrative purposes. In some uses, element 72 defines a ring 73 and a plurality of elongated elements 67 that extend radially from this ring. In some uses, instead of wrapping a string and / or wire around spring 54, for example, the ring 73 of element 72 is placed around a tube 70 that is typically disposed at the longitudinal central position of the spring. Then, each end of each elongated element 67 is coupled to each of the helical elongated elements 52. As described above, the elongated elements 67 are typically flexible but not substantially extensible along the axis defined by the elongated elements. More typically, each of the elongated elements 67 is configured to be substantially resistant 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, so that the separation distance between the helical elongated element 52 and the central axis spring 54 (in the absence of the elongated elements 67) is greater than the length of the elongated elements 67. When a force that moves the helical elongated element 52 radially outward (in the absence of the elongated elements 67) acts on the impeller, the impeller overextension prevention element is configured to prevent radial expansion of the impeller. Typically, each elongated element 67 is disposed within each of the impeller blades and is configured to prevent the impeller blades from expanding radially. In some uses, element 72 is made of polyester and / or another polymer, or a natural material including fibers, and / or nitinol (or a similar shape memory alloy).

[0095] It should be noted that the scope of the present invention includes using a single integrated impeller over-expansion prevention element 72 with an impeller having a configuration different from that shown in FIGS. 3D to 3E. For example, the single over-expansion prevention element 72 can be used with an impeller having an axial structure of a configuration different from that of the spring 54. Usually, the axial structure defines a lumen penetrating therethrough, and the impeller is adapted to define a lumen 62 penetrating therethrough.

[0096] Next, reference is made to FIG. 3F, which is a schematic view of an impeller 50 including a fixing element 75 configured to fix an elongate element 67 relative to a tube 70, according to some uses of the present invention. In some uses, the string or wire forming the elongate element 67 is not wound around the tube 70 and does not intersect the longitudinal axis of the impeller. The string or wire is fixed relative to the tube 70 by the fixing element 75. Usually, the string or wire is fixed to the outer surface of the tube 70 at a position on the outer surface of the tube closest to the maximum span of the helical elongate element to which the ends of the string or wire are tied. In some uses, the fixing element includes a ring as shown. In some such uses, the ring defines a small notch (or hole) 80, and the string or wire passes through this notch between the ring and the tube 70.

[0097] Next, refer to FIGS. 3Gi and 3Gii, which are photographs of the impeller 50 according to some uses of the present invention. As shown, in some uses, by manufacturing the impeller using the method described above, the adjacent blades 51 of the impeller 50 are shaped to define a continuous U-shaped surface. As shown by the curve 55 added to FIG. 3Gii, when a film 56 of elastomeric material migrates from one blade to an 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 also substantially unbroken in the spring 54 extending along the axis of the impeller. In some uses, by forming the impeller as described above, the film of material has the above-described curvature. Typically, by defining a continuous U-shaped surface, the impeller blades are configured to provide a smooth streamline along which blood flow passes through the impeller, resulting in increased efficiency of blood infusion by the impeller and / or reduced risk of hemolysis compared to when the adjacent blades do not define a continuous surface (e.g., compared to when the curvature is broken in the spring 54). In some uses, a generally similar impeller having an axial structure (e.g., a cylindrical axial structure) different from that of the spring 54 is used. Usually, the axial structure defines a lumen penetrating therethrough, and the impeller is configured to define a lumen 62 penetrating therethrough. Alternatively, the impeller includes a spring 54 (including the 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 out during operation of the impeller) is convex in the distal region of the impeller, changes to be substantially radially oriented in the region of the elongate element 67, and then is concave in the proximal region of the impeller. (For purposes of illustration, the opposite side of the impeller blade from the pressure side (i.e., the “non-pressure side”) is shown in FIG. 3Gii.) Thus, during use, the blood delivered by the impeller is first delivered by the convex impeller surface and then by the concave impeller surface. In some applications, the elongate element 67 is disposed substantially midway along the length of the impeller blade and is configured to facilitate the transition of the membrane of material from the convex curvature to the concave curvature. Thus, typically, in the region of the elongate element 67 within the impeller blade, the blade is substantially radially oriented. Typically, by defining a concave surface in the proximal region of the impeller, the pressure side of the impeller blade is configured to add flow and / or apply pressure to the blood after blood has flowed and / or pressure has been applied within the distal region of the impeller. Alternatively (not shown), the pressure side of each impeller blade (i.e., the side that pushes blood out during operation of the impeller) is concave in the distal region of the impeller, changes to be substantially radially oriented in the region of the elongate element 67, and then is convex in the proximal region of the impeller.

[0099] Now refer to FIGS. 5A and 5B, which are schematic views of the impeller 50 and the frame 34 of the ventricular assist device 20 in an unconstrained radial state and a constrained radial state, respectively, according to some applications of the present invention. The impeller and the frame are typically arranged in a radially constrained state when the impeller and the frame are inserted into the subject through a catheter, and are arranged in an unconstrained radial state when the impeller operates within the left ventricle of the subject. As described above, typically, the pump outlet tube 24 is disposed on at least a portion of the frame and extends proximally therefrom. However, for purposes of illustration, FIGS. 5A through 5B show the frame and the impeller without the pump outlet tube 24.

[0100] As shown in FIG. 5B, the frame and the impeller are typically maintained in a configuration radially constrained by the delivery catheter 143. Typically, in the radially constrained configuration of the impeller, the overall length of the impeller is greater than 15 mm (e.g., greater than 20 mm) and / or less than 30 mm (e.g., less than 25 mm), for example, 15-30 mm, or 20-25 mm. Further typically, in the configuration where the impeller is not radially constrained, 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), for example, 8-18 mm, or 10-15 mm. Further typically, (as shown in FIG. 5B) when the impeller and the frame 34 are arranged in a configuration radially constrained, 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 described above, typically, the axial shaft 92 passes through the axis of the impeller 50 through the lumen 62 of the impeller (the lumen 62 shown in FIG. 3C). Typically, the proximal bushing 64 of the impeller is coupled to the shaft via a coupling element 65 such that the axial position of the proximal bushing with respect to the shaft is fixed, and the distal bushing 58 of the impeller is slidable with respect to the shaft. The axial shaft itself is radially stabilized via a proximal radial bearing 116 and a distal radial bearing 118.

[0102] Typically, the junction 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 junction 33 is disposed in a groove defined by the outer surface of the distal radial bearing 118, and the groove is shaped to conform to the shape of the distal strut portion. The proximal end of the distal tip element 107 (defining the distal tip portion 120) typically holds the distal strut portion 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 that extends distally from the distal radial bearing. Typically, the extension is configured to reinforce the region of the distal tip element where the distal end of the shaft 92 moves (e.g., the axial shaft receiving tube 126, or a portion thereof, described below).

[0103] As described above, the axial shaft 92 is radially stabilized via the proximal radial bearing 116 and the distal radial bearing 118. Next, as described above, the axial shaft passes through the lumen 62 defined by the impeller to radially stabilize the impeller with respect to the inner surface of the frame 34, and to maintain a relatively small gap (e.g., the gap as described above) between the outer edge of the impeller blades and the inner surface of the frame 34 even when 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, for the purpose of inserting the impeller and the frame into the subject, when the impeller and the frame are crimped (i.e., radially constrained), the distal bushing 58 of the impeller is configured to slide distally along the axial shaft while the impeller extends axially, while the proximal bushing remains in a position axially fixed with respect to the axial shaft. More generally, the impeller changes from a radially constrained configuration to a non-radially constrained configuration, or vice versa, while the distal bushing slides along the axial shaft, while the proximal bushing remains in a position axially fixed with respect to the axial shaft.

[0104] Typically, the impeller itself is not disposed directly within either the radial bearing or the thrust bearing. Rather, bearings 116 and 118 function as radial bearings with respect to 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 rotation of the impeller. In some applications, one or more thrust bearings are disposed outside of the subject (e.g., within motor unit 23 shown in FIGS. 1A, 7A-7Bii), and opposition to the thrust generated by rotation of the impeller is provided only by this one or more thrust bearings disposed outside of the subject. In some applications, mechanical and / or magnetic elements are configured to maintain the impeller within a given range of axial position. For example, a magnet (e.g., magnet 82 described below with reference to FIG. 7A) disposed at the proximal end of drive cable 130 (e.g., outside of the subject) may be configured to impart axial movement 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 views of the ventricular assist device 20 at each stage of the motion cycle of the impeller 50 of the ventricular assist device relative to the frame 34 of the ventricular assist device according to some uses of the present invention. In some uses, as will be described in more detail below with reference to FIGS. 7A through 7Bii, while the impeller rotates to pump blood through the tube 24, the axial shaft 92 (to which the impeller is fixed) is driven to axially move the impeller forward and backward within the frame 34 by the axial shaft moving in an axial back-and-forth motion. Alternatively or additionally, the impeller and the axial shaft are configured to axially move forward and backward within the frame 34 in response to the forces acting on the impeller without being actively driven such that the axial shaft moves in an axial back-and-forth motion. Typically, during the cardiac cycle of a subject, the pressure difference between the left ventricle and the aorta varies from approximately zero during ventricular systole (hereinafter "systole") to a relatively large pressure difference (e.g., 50 to 70 mmHg) during ventricular diastole (hereinafter "diastole"). In some uses, during diastole, the pressure difference for impeller pumping increases (and because the drive cable 130 is stretchable), so the impeller during diastole is pushed distally relative to the frame 34 compared to the position of the impeller relative to the frame 34 during systole. Next, since the impeller is connected to the axial shaft, the axial shaft moves forward. During systole, the impeller (and the axial shaft) returns to the systolic position. In this way, the axial shaft and the impeller are caused to move axially back and forth in a passive manner, i.e., without the need for active driving of the axial shaft and the impeller, and the axial back-and-forth motion of the impeller and the axial shaft occurs. FIG. 6A shows the impeller and the axial shaft disposed in the normal systolic position, and FIG. 6B shows the impeller and the axial shaft disposed in the normal diastolic position.

[0106] In some applications, by moving in an axial back-and-forth motion, a portion of the axial shaft that contacts the proximal bearing portion 116 and the distal bearing portion 118 continuously changes. In some such applications, all other conditions being equal, the frictional force thus applied to the axial shaft by the bearing portions spreads over a wider area of the axial shaft than when the axial shaft does not move relative to the bearing portions, thereby reducing wear of the axial shaft. Alternatively or additionally, by moving in a back-and-forth motion relative to the bearing portions, the axial shaft removes residues such as blood residues at the interface between the axial shaft and the bearing portions.

[0107] In some applications, when the frame 34 and the impeller 50 are configured not to be radially constrained (for example, when the frame and the impeller are installed in the left ventricle), the length of the frame exceeds the length of the impeller by at least 2 mm (for example, at least 4 mm, or at least 8 mm). Usually, the proximal bearing portion 116 and the distal bearing portion 118 each have a length of 2 to 4 mm (for example, 2 to 3 mm). More usually, the impeller and the axial shaft are configured to move axially within the frame in a back-and-forth motion along at least the respective lengths of the proximal and distal bearing portions, or at least twice the respective lengths of the bearing portions. Thus, when the axial shaft moves axially back and forth, the axial shaft is wiped clean on either side of each bearing portion.

[0108] In some applications, the movement range of the impeller is shown in FIGS. 6A and 6B. FIG. 6A shows the most proximal placement of the impeller during the cardiac cycle (usually, the impeller is placed during systole), and FIG. 6B shows the most distal placement of the impeller during the cardiac cycle (usually, the impeller is placed during diastole). As shown in FIG. 6A, in some applications, the proximal end of the impeller is placed at position Ip within the proximal conical section of the frame 34 at its most proximal position. As shown in FIG. 6B, in some applications, the distal end of the impeller is placed at position Id, which is the distal end of the cylindrical section of the frame 34, at its most distal position. For the purposes of this application, the entire section of the frame from Ip to Id usually houses at least a portion of the impeller during at least a portion of the cardiac cycle, so this entire section of the frame may be considered to house the impeller. Usually, during the entire cardiac cycle, the section of the impeller where the span of the impeller is maximized is placed within the cylindrical portion of the frame 34. However, the proximal portion of the impeller is usually placed within the proximal conical section of the frame during at least a portion of the cardiac cycle.

[0109] Refer again to FIGS. 6A and 6B and also refer to FIG. 6C, which is a schematic enlarged view of distal tip element 107 including axial shaft receiving tube 126 and distal tip 120 of ventricular assist device 20 according to some uses of the present invention. Typically, distal tip element 107 is a single integrated element that includes both axial shaft receiving tube 126 and distal tip 120. In some uses, distal tip element 107 is configured to be soft so that the distal tip is configured not to damage the tissue of the subject (e.g., the tissue of the left ventricle) even when in contact with it. For example, distal tip element 107 may be formed of silicone, polyethylene terephthalate (PET), and / or polyether block amide (e.g., PEBAX®). In some uses, the distal tip defines a lumen 122 that penetrates therethrough. In some such uses, when the ventricular assist device is inserted into the left ventricle, for example, guidewire 10 (FIG. 1B) is first inserted into the left ventricle according to known techniques. Next, with the guidewire disposed inside lumen 122, the distal tip of the ventricular assist device is advanced over the guidewire, whereby the distal tip is guided into the left ventricle. In some uses, duckbill valve 390 (or a different type of hemostatic valve) is disposed at the distal end of lumen 122 of distal tip 120.

[0110] Typically, when inserting a ventricular assist device into a subject's ventricle, delivery catheter 143 is disposed over impeller 50 and frame 34 and maintains the impeller and frame in a radially constrained configuration. In some uses, distal tip element 107 extends distally from the delivery catheter when the delivery catheter is inserted into the subject's ventricle. In some uses, at the proximal end of the distal tip element, the distal tip element has a flare portion 124. Flare portion 124 functions as a stopper to prevent the delivery catheter from advancing beyond the flare portion.

[0111] Note that the outer shape of the distal end of FIGS. 6A through 6C (and several other figures) is shown as defining a complete loop where the distal end of the distal tip (where the duckbill valve 390 is disposed) intersects the more proximal portion of the distal tip. Typically, as a result of inserting a guide wire (when inserting a ventricular assist device into the left ventricle), even after removing the guide wire from the distal tip, the distal tip remains partially straight. Typically, the partial straightening of the distal tip occurs when the distal tip is disposed within the left ventricle and there is no external force acting on the distal tip, such that the distal tip does not define a complete loop as shown, for example, in FIGS. 1B, 15D, and 16A. In some applications, a straightening element 270 is used to insert a guide wire into the distal tip, as will be described in more detail below with reference to FIGS. 23A through 23C, for example. Other aspects of the shape of the distal tip will be described in more detail below.

[0112] Next, refer to FIGS. 6D and 6E which are schematic views of the impeller 50 according to some applications of the present invention. The proximal bushing 64 of the impeller is coupled to a coupling element 65 that extends proximally so as to function as a stopper. FIG. 6D shows the impeller during the contraction phase of the impeller's motion cycle, and FIG. 6E shows the impeller during the expansion phase of the motion cycle. Usually, the coupling element extends proximally so as to prevent the central region of the impeller (where the span of the impeller is maximum) from sliding proximally into the proximal conical portion of the frame 34. For example, during the contraction phase of the impeller's motion cycle (shown in FIG. 6D), if the impeller were to slide further proximally beyond a given amount, the proximally extending coupling element would contact the proximal radial bearing portion 116, thereby preventing further proximal movement of the impeller. In some applications, the coupling element extends proximally such that it has an overall length greater than 1.5 mm, for example greater than 4 mm. In some applications (not shown), instead of or in addition to the coupling element extending proximally, a separate stopper element is disposed on the axial shaft in the proximal direction with respect to the coupling element. Usually, the stopper is configured as described above with respect to the proximally extending coupling element. That is, if the impeller were to slide further proximally beyond a given amount, the stopper element would contact the proximal radial bearing portion 116, thereby preventing further proximal movement of the impeller.

[0113] Next, refer to FIG. 7A which is a schematic view of an exploded view of the motor unit 23 of the ventricular assist device 20 according to some applications of the present invention. As shown, the motor unit is typically a handle that houses a motor and is configured to be disposed outside the subject. For this reason, the motor unit may sometimes be referred to instead 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 configured to also control the back-and-forth movement of the axial shaft. Typically, both types of movement are generated by using the motor unit 23. The scope of the present invention includes controlling the back-and-forth movement 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 movement of the axial shaft is synchronized with the subject's cardiac cycle.

[0115] Typically, the motor unit 23 includes a motor 74 configured to impart rotational movement to the impeller 50 via a drive cable 130. As will be described in more detail below, typically, the motor is magnetically coupled to the drive cable. In some applications, the axial movement driver 76 is configured to drive the motor to move in a back-and-forth axial movement as indicated by the double-headed arrow 79. Typically, when the motor magnetically couples to the drive cable, the motor imparts a back-and-forth movement to the drive cable, and then this movement is imparted to the impeller. As described above and below, in some applications, for example, due to periodic changes in the pressure differential for the impeller to pump blood, the drive cable, the impeller, and / or the axial shaft passively receive a back-and-forth axial movement. Typically, in such applications, the motor unit 23 does not include the axial movement 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 adhered to the inner surface of the ring. In some applications, as shown, a spacer 85 is adhered 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 such that the drive magnets and the driven magnet axially overlap. The driven magnet is coupled to a pin 131, and the pin 131 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 adhered to the inner surface of the driven magnet defining the hole. In some applications, the driven magnet is cylindrical and includes a north pole and a south pole, and these poles are mutually divided along the length of the cylinder along a line 83 that bisects the cylinder as shown. In some applications, the driven magnet is housed inside a cylindrical housing 87. Typically, the pin 131 defines a lumen 133, and a guide wire 10 is inserted into the pin through this lumen 133.

[0117] Note that in the application shown in FIG. 7A, the drive magnets are disposed outside the driven magnet. However, the scope of the present application includes making necessary changes and reversing the configuration of the drive magnet and the driven magnet. For example, the proximal end of the drive cable may be coupled to two or more driven magnets disposed around the drive magnet such that the drive magnet and the driven magnets axially overlap.

[0118] As described above, typically, a purge system 29 (shown in FIG. 1A) is used with the ventricular assist device 20. Typically, the motor unit 23 includes an inlet 86 and an outlet 88 for use with the purge system. In some applications, the 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, the magnet 82 and the pin 131 are held in relatively fixed axial positions within the motor unit 23. (In some applications, the magnet 82 has a small degree of freedom of movement axially and / or rotationally relative to other components of the motor unit, such as the drive magnet 77. In some applications, such movement is measurable, as detailed below.) Typically, the proximal end of the drive cable is held in an axially fixed position relative to the pin by being coupled to the pin 131. Typically, the drive cable 130 extends from the pin 131 to the axial shaft 92, thereby at least partially fixing the axial position of the axial shaft and further the impeller 50. In some applications, the drive cable is somewhat stretchable. For example, the drive cable can be made of a stretchable coiled wire, as detailed below. The drive cable typically allows the axial shaft (and further the impeller) to take axial positions within a range (by the drive cable stretching somewhat), but limits the axial movement of the axial shaft and the impeller within a specific range of motion (by the proximal end of the drive cable being held in a relatively fixed axial position and the stretchability of the drive cable being limited).

[0120] Referring now to FIGS. 7Bi and 7Bii, which are schematic views of motor unit 23 for several applications of the present invention. Generally, motor unit 23 is similar to that shown in FIG. 7A, as shown in FIGS. 7Bi and 7Bii, and unless otherwise specified, motor unit 23 shown in FIGS. 7Bi and 7Bii includes components similar to those of motor unit 23 shown in FIG. 7A. In several applications, the motor unit includes a heat sink 90 configured to dissipate heat generated by the motor. Alternatively or additionally, the motor unit includes a ventilation port 93 configured to facilitate dissipation of heat generated by the motor. In several applications, the motor unit includes vibration dampers 94 and 96 configured to dampen 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 several applications, impeller 50 and axial shaft 92 are configured to move axially back and forth within frame 34 in response to forces acting on the impeller without being actively driven such that the axial shaft moves with axial back-and-forth movement. Typically, during the cardiac cycle of interest, the pressure difference between the left ventricle and the aorta varies from nearly zero during systole to a relatively large pressure difference (e.g., 50 - 70 mmHg) during diastole. In several applications, during diastole, the pressure difference for impeller delivery increases (and since the drive cable is stretchable), the impeller during diastole is pushed distally relative to frame 34 compared to the position of the impeller relative to frame 34 during systole. Next, since the impeller is connected to the axial shaft, the axial shaft moves forward. During systole, the impeller (and axial shaft) returns to the systolic position. In this way, in a passive manner, i.e., without the need for active driving of the axial shaft and impeller, axial back-and-forth movement of the axial shaft and impeller occurs to cause axial back-and-forth movement of the axial shaft and impeller.

[0122] Next, refer to FIG. 8A, which is a graph showing the change in the length of the drive cable of the ventricular assist device with respect to the changing pressure gradient of the impeller of the ventricular assist device measured in the experiment. Using the impeller and drive cable described herein, a glycerin-based solution was fed into the chamber. The chamber was set up to reproduce the left ventricle and the aorta, and the solution had properties (such as density and viscosity) similar to blood. The pressure gradient for the delivery by the impeller was pulsatingly varied to represent the pulsation of the pressure gradient for normal delivery when the impeller pumps blood from the left ventricle to the aorta. At the same time, the movement of the drive cable was imaged, and the change in the length of the drive cable was determined by analyzing these images. The graph shown in FIG. 8A shows the measured change in the length of the drive cable as a function of the pressure gradient. As shown in FIG. 8A, as the pressure gradient for the delivery by the impeller increased, the drive cable gradually elongated. As manifested by the results shown in FIG. 8A and as described above, typically, in response to a change in pressure (e.g., the pressure difference between the left ventricle and the aorta) for the delivery of blood by the impeller, the impeller moves back and forth with respect to frame 34. Next, due to the movement of the impeller, the drive cable 130 elongates somewhat.

[0123] In some applications, when the ventricular assist device is operating, the computer processor 25 (FIG. 1A) of the control console 21 is configured to measure an indicator of the pressure applied to the impeller (indicating the pressure difference between the left ventricle and the aorta) by measuring an indicator of the tension of the drive cable 130 and / or the axial movement of the drive cable. In some applications, based on the measured indicators, the computer processor detects events in the cardiac cycle of the subject and determines the left ventricular pressure of the subject and / or determines the afterload of the subject's heart. In some applications, the computer processor controls the rotation of the impeller and / or the axial back-and-forth movement of the corresponding 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) disposed within the motor unit 23, as shown in FIG. 7A. (In some cases, the sensor 84 is referred to as the magnetometer 84.) In some applications, typically, the driven magnet is held in a predetermined position relative to the drive magnet via a magnetic coupling rather than a rigid mechanical coupling, so the axial back-and-forth movement of the impeller causes a measurable back-and-forth movement of the inner driven magnet 82 relative to one or more outer drive magnets 77. It should be noted that the axial movement of the magnet is substantially smaller than the axial movement of the impeller, as the entire movement range of the impeller is not typically 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 in order to determine the pressure against the delivery by the impeller by measuring the axial movement of the drive cable 130. For example, the inner driven magnet 82 may be axially longer than the outer drive magnet 77. Since the inner magnet is longer than the outer magnet, there are magnetic field lines that originate from the inner magnet and do not reach the outer magnet. The magnetic flux generated by these magnetic field lines and measured by the magnetometer changes as the drive cable and the inner magnet move axially. During operation, the motor 74 rotates to generate an AC signal having a frequency typically between 200 Hz and 800 Hz in the magnetometer. Typically, when the tension of the drive cable changes with the cardiac cycle of the subject, a low-frequency envelope having a frequency typically between 0.5 and 2 Hz is generated in the signal measured by the magnetometer. In some applications, a computer processor measures the low-frequency envelope and derives the cardiac cycle of the subject from the measured envelope.

[0125] In some applications, the measurement of the magnetometer is first calibrated so that the change in magnetic flux per unit of pressure with respect to the delivery by the impeller (i.e., the change per unit of the pressure difference between the left ventricle and the aorta, or the change per unit of the pressure gradient) is known. In most subjects, it is known that during systole, the left ventricular pressure is equal to the aortic pressure. Thus, in some applications, the aortic pressure of the subject is measured, and then the left ventricular pressure of the subject at a given time point 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 (assuming that the pressure in the left ventricle is equal to the pressure in the aorta). For example, as detailed below, the aortic pressure of the subject can be measured by measuring the pressure in channel 224 defined by delivery catheter 143. In some applications, alternative or additional physiological parameters are determined using the techniques described above. For example, events in the cardiac cycle of the subject and / or the afterload of the subject can be determined.

[0126] In some applications, techniques generally similar to those described in the above paragraphs are used, but instead of or in addition to utilizing magnetometer measurements, another parameter is measured to determine the left ventricular blood pressure (and / or another physiological parameter, such as an event in the subject's cardiac cycle and / or the subject's afterload) at a given point in time. For example, there is generally a relationship between the amount of power (and / or current) required to power an impeller rotation at a given rotational speed and the pressure differential generated by the impeller. (Note that a portion of the pressure differential generated by the impeller is used to overcome the pressure gradient for pumping by the impeller and to actively pump blood from the left ventricle to the aorta by generating a positive pressure differential between the left ventricle and the aorta. Further, the relationship between the above elements changes over the course of the cardiac cycle.) In some applications, calibration measurements are performed such that the relationship between (a) the motor power (and / or current) consumption required to rotate the impeller at a given rotational speed and (b) the pressure differential 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 point in time is calculated by a computer processor. This calculation is based on (a) the measured aortic pressure, (b) the motor power (and / or current) consumption required to rotate the impeller at a given rotational speed at that time, and (c) a predetermined relationship between the motor power (and / or current) consumption 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 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 afterload can be determined.

[0127] Typically, tube 24 has a known cross-sectional area (when the tube is open for blood flow through the tube). In some applications, the flow through tube 24 generated by the impeller is determined based on the determined pressure difference generated by the impeller and the known cross-sectional area of the tube. In some applications, calibration parameters are incorporated to account for factors such as the flow resistance specific to the ventricular assist device (or a type of ventricular assist device) performing the calculation in order to calculate such a flow rate. 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 the magnetometer 84 configured to measure the magnetic flux density generated by the driven magnet, a second magnetometer 84A (e.g., a second Hall sensor) measures an indicator of the magnetic flux density generated by the drive magnet. In some applications, since the motor directly drives the drive magnet to rotate, the second magnetometer measures the magnetic flux density of the motor representing the magnetic flux density period of the drive magnet. Typically, when the impeller rotates to pump blood, torque is generated on the impeller. More typically, the intensity of the torque depends on various parameters such as, for example, the flow generated by the impeller, the rotational speed of the impeller, and / or the pressure gradient with respect to the delivery by the impeller. In some applications, typically, the driven magnet is held in a predetermined position relative to the drive magnet via a magnetic coupling rather than a rigid mechanical coupling, so the torque generated on the impeller causes a measurable torque on the inner driven magnet 82 relative to the outer drive magnet 77. It should be noted that typically, the torque generated on the impeller is not transmitted along the length of the drive cable, so the torque generated on the driven magnet is substantially smaller than that generated on the impeller. However, typically, the torque generated on the impeller is at least partially transmitted to the driven magnet via the drive cable.

[0129] The torque transmitted to the driven magnet typically causes a phase difference between the signal measured by the magnetometer 84 (which measures the magnetic flux density of the driven magnet) and the signal measured by the second magnetometer 84A (which measures the magnetic flux density of the motor and / or the drive magnet). In some applications, when the torque of the impeller changes, the phase difference between the signal measured by the magnetometer 84 and the signal measured by the second magnetometer 84A changes. In some applications, a computer processor detects the change in the aforementioned phase difference and determines the physiological parameter of interest at least partially in response thereto. For example, at least partially based on the change in the phase difference, the computer processor can determine the difference between the left ventricular pressure and the aortic pressure of the subject, the left ventricular pressure of the subject, an event in the cardiac cycle of the subject, the afterload of the heart of the subject, and / or another physiological parameter. In some applications, instead of the above-described techniques for determining physiological parameters using magnetic flux density measurements and / or power consumption measurements, the techniques described in this paragraph are used. Alternatively, two or more of these techniques are used in combination with each other. For example, it is also possible to determine the physiological parameter of the subject based on a mathematical model incorporating two or more measurements, and / or to confirm the estimation of the physiological parameter of the subject performed using one of these techniques using another one of these techniques.

[0130] Next, refer to FIGS. 8B and 8C, which are graphs demonstrating the correlation between the phase difference signal and the pressure gradient with respect to the delivery by the impeller 50 according to some applications of the present invention.

[0131] The graph shown in FIG. 8B shows the results of an experiment in which blood was pumped against each pressure gradient using the ventricular assist device described herein within a static in vitro system (i.e., the pressure gradient was constant at the time of each measurement). Based on a combination of the phase difference signal, the magnetic flux amplitude signal, and the current consumption by the motor, a linear regression model was used to estimate the pressure gradient for pumping by the impeller. The graph shown in FIG. 8B shows the estimated pressure gradient against the measured pressure gradient. As shown, the linear regression model incorporating the phase difference measurement provides a reliable method for estimating the pressure gradient for pumping by the impeller.

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

[0133] In accordance with the above, and according to some uses of the present invention, a magnetic phase difference between one or more driven magnets and one or more drive magnets is measured, and at least in part in response thereto, a physiological parameter of the subject is determined. For example, at least in part based on a change in the phase difference, a computer processor can determine the difference between the left ventricular pressure of the subject and the aortic pressure of the subject, the left ventricular pressure of the subject, an event in the cardiac cycle of the subject, the afterload of the subject, and / or another physiological parameter. In some uses, the phase difference measurement is combined with one or more additional measurements such as, for example, magnetic flux amplitude measurement, power consumption by the motor, and / or current consumption by the motor, and based on these, the physiological parameter is determined. Usually, such measurements are combined into a mathematical model such as a linear regression model and / or a state space model.

[0134] Next, reference is made to FIGS. 9A through 9G, which are schematic views of each of a motor unit support 170 configured to support a motor unit 23 on a patient's leg 172, according to some uses of the present invention. In some uses, the ventricular assist device is inserted into the patient's body via a femoral connection point 173, and the motor unit support is configured to be disposed on the patient's thigh below the femoral connection point as shown. Usually, 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 disposed on the patient's thigh, and a motor unit dock 178 to which the motor unit docks. Typically, there is a gap 179 between the motor unit dock and the curved base of the motor unit support, and this gap serves to separate the patient's leg from the motor unit, and the gap functions 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. In some applications, the motor unit support is configured to receive a strap 174 used to secure the motor unit support to the patient's leg within the gap. Typically, the strap is stretchable and / or adjustable to fit the patient's leg.

[0136] Typically, the motor unit support includes a coupling element 180 for coupling the motor unit dock to the motor unit (shown, for example, in FIG. 9D). As described above, in some applications, the motor unit includes a vent 93 configured to facilitate dissipation of heat generated by the motor. In some applications, as shown, for example, in FIG. 9E, the coupling element comprises a snap-fit coupling element configured to couple the motor unit dock to the motor unit by snapping onto the vent of the motor unit. In some applications, the motor unit includes vents on both sides so that the motor unit can be coupled to the motor unit dock on either side of the motor unit.

[0137] Next, refer to FIGS. 10A, 10B, and 10C, which are schematic views of the drive cable 130 of the ventricular assist device 20 according to some applications of the present invention. Generally, the rotational movement of the motor is transmitted to the axial shaft via the drive cable. Generally, the drive cable extends from the motor unit 23 (usually disposed outside the subject) to the proximal end of the axial shaft 92 (for example, the connection between the distal end of the drive cable and the proximal end of the axial shaft is shown in the enlarged view on the left side of FIG. 5A). In some applications, the drive cable includes a plurality of wires 134, which are arranged in a coiled configuration to provide sufficient strength and flexibility to the drive cable so that a portion of the cable can be maintained 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 a plurality of coaxial layers of coiled wires. As shown, for example, in FIGS. 10A to 10C, the drive cable includes an outer layer 136 and an inner layer 138, which are coaxial with each other and each may include coiled wires.

[0138] The drive cable is typically disposed within a first outer tube 140 configured to remain stationary while the drive cable undergoes rotational movement and / or axial back-and-forth movement. The first outer tube is configured to act as a bearing tube for the drive cable substantially along the length of the drive cable. For this reason, the first outer tube may be referred to herein as the drive cable bearing tube. The drive cable bearing tube will be described in 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, when inserting the impeller and the frame into the left ventricle, the impeller 50 and the frame 34 are maintained in a radially constrained configuration by the delivery catheter 143. As described above, the delivery catheter is retracted to allow the impeller and the frame to be in a non-radially constrained 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. (FIG. 10A shows the distal end of the delivery catheter disposed within the aortic arch, but 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 the channel shown in FIG. 10A is not to scale for illustrative purposes.) In some such applications, the subject's aortic blood pressure is measured by measuring the pressure of the blood within the channel 224. For example, a pressure sensor 216 (schematically shown in FIG. 1A) can be configured to measure the subject's aortic pressure by being in fluid communication with the channel 224 and measuring the pressure of the blood within the channel 224. Typically, to retract the left ventricular device from the subject, the delivery catheter is advanced over the impeller and the frame to cause the impeller and the frame to be in a radially constrained configuration. The catheter is then retracted from the subject.

[0140] In some applications, the drive cable 130 comprises a plurality of coaxial layers, each layer including a plurality of coiled wires 134. As shown, for example, in FIGS. 10A through 10C, the drive cable includes an outer layer 136 and an inner layer 138, each including coiled wires. Typically, when the direction of rotation of the impeller is such that rotation of the drive cable in this direction causes the coiled wires of the drive cable to be at least partially tensioned, the coiled wires are tensioned (i.e., wound so that the radius of the coil decreases), and thus the impeller advances relative to the frame when rotation is initiated. In some applications, at least a portion of the drive cable is configured such that (a) in response to the impeller rotating in a given direction of rotation to pump blood from the left ventricle to the aorta, and (b) rotation of the drive cable in this direction causes the coiled wires of the drive cable along a portion of the drive cable to be at least partially unwound so that a portion of the drive cable becomes shorter axially (i.e., unwound so that the radius of the coil increases). 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 wires of each layer of the drive cable are configured as left-handed layers. When the impeller rotates in a counterclockwise direction, the coiled wires of each layer of the drive cable are partially unwound by the opposing pressure applied to them, whereby each layer of the drive cable becomes shorter. 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 wires of each layer of the drive cable are configured as right-handed layers.

[0141] Referring again to FIGS. 6A and 6B, which show the range of axial back-and-forth movement of the impeller within frame 34 during the cardiac cycle, according to some uses of the present invention. As described above, FIG. 6A shows the most proximal placement of the impeller during the cardiac cycle (usually where the impeller is placed during systole), and FIG. 6B shows the most distal placement of the impeller during the cardiac cycle (usually where the impeller is placed during diastole). As shown in FIG. 6A, in some uses, at the most proximal position, the proximal end of the impeller is placed at position Ip, which is within the proximal conical section of frame 34. As shown in FIG. 6B, in some uses, at the most distal position, the distal end of the impeller is placed at position Id, which is the distal end of the cylindrical section of frame 34.

[0142] Referring again to FIGS. 10A - 10C and also to the configuration of the drive cable described in connection with these figures, typically, by configuring the drive cable as described above, the length of the frame 34 need not accommodate the distal movement of the impeller that results from the drive cable being tensioned axially as the impeller and drive cable begin to rotate. In some applications, it should be noted that the drive cable does not become shorter because the extent to which the drive cable is wound back and becomes shorter axially is limited by the drive cable bearing tube 140 (and / or for other reasons). Further, in some applications, theoretically the drive cable would become shorter if the impeller rotated in the absence of any fluid, but in practice, when the impeller rotates within the target blood flow, the drive cable does not become shorter. The reason is that when the impeller rotates within the target blood flow, the impeller is pushed distally by the back pressure of the blood being pumped out by the impeller, canceling out the winding back of the drive cable (which would cause the drive cable to become shorter). In some applications, during diastole, the drive cable actually elongates compared to when the impeller is stationary. This is due to the pressure gradient against the pumping by the impeller increasing compared to systole. Typically, even in such applications, since the coil windings are configured as described above, at least during systole, the drive cable is configured not to elongate compared to when the impeller is stationary.

[0143] In some applications, in addition to configuring the direction of the coiled wire in the drive cable as described above, the drive cable is initially held in a pre-loaded (i.e., pre-tensioned) state within the frame 34 and is already extended even before the drive cable and the impeller rotate. That is, even before the drive cable and the impeller begin to rotate, the drive cable is in an extended state compared to the drive cable stationary state (i.e., the state of the drive cable with no external force acting on it). For example, the coupling element 65 (extending in the proximal direction as described above with reference to FIGS. 6D to 6E in some applications) can engage with the proximal bearing portion 116 to hold the drive cable in a pre-loaded state. Usually, (a) the direction of the coiled wire in the drive cable is configured as described above, and / or (b) the drive cable is held in a pre-loaded state within the frame 34, so that when the impeller and the drive cable begin to rotate, even during the ejection phase (e.g., even when the impeller is delivering against a pressure gradient of 50 to 70 mmHg), the drive cable does not extend. In some applications, the drive cable does not extend even during the ejection phase until the impeller rotates at a rotational speed exceeding 6,000 RPM or exceeding 8,000 RPM. In some applications, by configuring the drive cable in this way, even when the impeller is rotating at a speed exceeding 20,000 RPM, the amount by which the drive cable extends during the cardiac cycle is limited to less than 5 mm (usually less than 4 mm). Further, in some applications, by configuring the drive cable in this way, even when the impeller is rotating at a speed exceeding 20,000 RPM, the widest part of the impeller (usually at the center of the length of the impeller) is disposed within the proximal half portion of the frame 34 for more than 50 percent of the cardiac cycle period.

[0144] In some applications, the ventricular assist device is configured such that there is an axial distance between the position of the impeller at its maximum diameter and the blood inlet, even during diastole and even when the impeller is rotating at over 20,000 RPM. For example, the ventricular assist device is configured such that there is an axial distance of over 3 mm (e.g., over 5 mm) between the position of the impeller at its maximum diameter and the blood inlet, even when the impeller is rotating at over 20,000 RPM during diastole. In some such applications, this reduces hemolysis (compared to cases where the axial distance between the position of the impeller at its maximum diameter and the blood inlet is shorter or non - existent), and / or increases the effectiveness of the impeller by reducing turbulent flow, by at least partially aligning the streamline of the blood flowing into the blood inlet with the longitudinal axis of the impeller before it is pumped out by the impeller.

[0145] Typically, the coiled wires in the outer layer 136 of the drive cable are fewer in number than those in the inner layer 138, and each wire is wider than those 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 contains 4 - 8 wires and the inner layer contains 10 - 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 - 0.2 mm, and the diameter of the wires in the inner layer is 0.075 mm - 0.125 mm. Typically, the coiled wires of both layers are made of an alloy. In some applications, the inner diameter of the drive cable (i.e., the diameter of the lumen 132) is 0.4 mm - 0.7 mm. More typically, the outer diameter of the drive cable (defined by the outer layer 138) is 1 mm - 1.2 mm. In some applications, the total length of the drive cable 130 is 1 m long (e.g., 1.1 m long) and / or less than 1.4 m (e.g., less than 1.3 m), e.g., 1 - 1.4 m or 1 - 1.3 m. Typically, the diameters of the lumen 122 and the lumen 133 are generally similar to the diameter of the lumen 132.

[0146] In some applications, the drive cable includes a first (distal) portion and a second (proximal) portion. Typically, the first portion is configured to be disposed in the aortic arch of the subject, and the second portion is disposed along the descending aorta and is typically configured to extend to a motor unit 23 external to the subject. Typically, at a location where the drive cable 130 curves significantly, such as in the aortic arch, it is desirable for the drive cable to be relatively flexible. However, a highly flexible drive cable will generally also have a greater axial stretchability compared to a less flexible drive cable. Thus, in some applications, there is a trade-off between the desire for the drive cable to have sufficient flexibility to conform to the curvature of the aortic arch and the undesirability of the drive cable stretching significantly axially (which can result in the inability to control the axial position of the impeller). In some applications, each portion of the drive cable has a respective level of flexibility. For example, the first portion of the drive cable configured to be disposed in the aortic arch has a first flexibility, the second portion of the drive cable configured to be disposed along the descending aorta has a second flexibility, and the first flexibility can be greater than the second flexibility.

[0147] In some applications, the distal portion of the drive cable is configured to have greater flexibility than the proximal portion by having the coils of wire 134 in the distal portion have different parameters than those used in the proximal portion. In some applications, the distal portion has parameters generally similar to those described above (i.e., with respect to the inner and outer layers). In some applications, the proximal portion of the guide wire includes a single layer of coiled wire. Typically, the number of coiled wires within the proximal portion of the drive cable is less than the number within the outer layer of the distal portion of the drive cable. Typically, the ratio of the number of wires within the outer layer of the distal portion of the drive cable to the number of wires within the proximal portion of the drive cable is from 3:2 to 5:2. In some applications, there are 3 to 6 wires in the proximal portion of the drive cable. Typically, the diameter of the coiled wires within the proximal portion of the drive cable is greater than the diameter of the coiled wires within the outer layer of the distal portion of the drive cable. In some applications, the ratio of the diameter of the wires within the proximal portion to the diameter of the wires within the outer layer of the distal portion is from 3:2 to 5:2. In some applications, the diameter of the wires within the distal portion of the drive cable is from 0.2 mm to 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 each other and are typically as described above.

[0148] Next, refer to FIG. 10D, which is a schematic view of the first outer tube 140 acting 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 of which is typically made of a biocompatible polymer material, and a coil 153 is embedded between the outer layer and the inner layer. In some applications, the outer layer 141 is made of Pebax, the inner layer 144 is made of PTFE and / or polyimide (e.g., a mixture of PTFE and / or polyimide), and the coil is made of an alloy such as stainless steel. Typically, the inner layer includes a material configured to provide a low level of friction and high wear resistance. More typically, the outer layer is configured to provide sufficient flexibility to conform, for example, to the curvature of the aortic arch while giving additional strength to the drive cable bearing tube. Typically, the coil is configured to maintain a substantially circular cross-section of the drive cable bearing tube even within regions where the drive cable bearing tube is highly curved (e.g., within the aortic arch). Typically, in the absence of the coil, the drive cable bearing tube tends to flatten and form an elliptical cross-section within such regions.

[0149] Next, refer to FIGS. 11A, 11B, 11C, 11D, and 11E, which are schematic views of an apparatus and method for purging the drive cable 130, radial bearings 116, 118, and / or impeller bushing 58 of the ventricular assist device 20 according to some applications of the present invention.

[0150] Referring initially to FIG. 11A, typically, the axial shaft and drive cable define a continuous lumen 132 that passes through the interior. In some applications, the left ventricular device is guided to the aorta and left ventricle by placing the axial shaft and cable on 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) disposed at the distal end of the distal tip element 107. The guidewire passes through lumen 122 (of the distal tip) and at that point enters lumen 132 defined by the axial shaft. The guidewire then continues to proceed within lumen 132 until it reaches the proximal end of the drive cable. From the proximal end of the drive cable, the guidewire proceeds within lumen 133 defined by pin 131. Pin 131 is disposed external to the subject even after the distal end of the ventricular assist device 20 has been inserted into the subject's left ventricle. Typically, once the distal end of the ventricular assist device has been disposed within the subject's left ventricle, the guidewire is retracted from the subject by pulling the guidewire from the proximal end of lumen 133. Next, as shown in FIG. 7A, the axial position of the driven magnet 82 (within which pin 131 is disposed) is fixed such that it is disposed between the drive magnets 77. For example, the portion of the motor unit 23 where the driven magnet is disposed may be coupled to the portion of the motor unit where the drive magnets 77 are disposed using a 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 the guidewire into the distal tip element 107. In some applications, by using lumen 132 of the axial shaft and cable as described above, there is no need to provide guidance for an additional guidewire used when inserting the left ventricular assist device 20.

[0151] In some applications, the lumen 132 is further used by the purge system 29 of the ventricular assist device (shown in FIG. 1A). Typically, during rotation of the drive cable, the first and second outer tubes 140, 142 remain stationary. In some applications, the purge system 29 controls the flow of a purge fluid (e.g., a fluid containing glucose or dextrose) via inlets 86 and outlets 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 tube and / or reduce the frictional forces between the rotating drive cable 130 and the stationary outer tube 140 during rotation of the drive cable and / or reduce the frictional forces between the axial shaft 92 and the proximal bearing 116 and / or distal bearing 118.

[0152] Referring again to FIG. 11A, in some applications, the purge fluid is fed between the first and second outer tubes 140, 142. There is an opening 146 in the first outer tube near the proximal bearing. In some applications, the purge fluid is fed through a purge fluid channel 226 defined between the first and second outer tubes. This is described in detail below with reference to FIG. 21. In some applications, the purge fluid flows through the opening 146 between the first outer tube 140 and the drive cable 130 as shown by the purge fluid flow arrow 148 in FIG. 11A. In this way, the interface between the rotating drive cable 130 and the outer tube 140 (acting as a drive cable bearing tube and remaining stationary during rotation of the drive cable) is purged. In some applications, a portion of the purge fluid further flows to the interface between the axial shaft and the proximal bearing 116 as shown by the purge fluid flow arrow 149 in FIG. 11A, thereby purging the interface (and / or reducing the frictional forces at the interface). Also, typically, the purge fluid flow in the direction of arrow 149 prevents blood from flowing into the interface between the axial shaft and the proximal bearing.

[0153] As described above (see FIGS. 10A through 10C), typically, the drive cable includes a plurality of coiled wires. In some applications, the purge fluid enters into the lumen 132 defined by the drive cable through the gaps in the coiled wires. When the purge fluid is disposed within the lumen 132, as indicated by arrow 151 in FIG. 11A, the purge fluid flows in both the proximal and distal directions. The purge fluid flowing in the distal direction typically exits from 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 flowing out of the distal tip by the duckbill valve 390. Accordingly, a portion of the purge fluid typically flows to the interface between the axial shaft and the distal bearing 118, as indicated by the purge fluid flow arrow 154 in FIG. 11A, thereby purging the interface (and / or reducing the frictional force at the interface). Typically, the flow of the purge fluid in the direction of arrow 154 also prevents blood from flowing into the interface between the axial shaft and the distal bearing.

[0154] As described above, when the purge fluid is disposed within the lumen 132, as indicated by arrow 151 in FIG. 11A, the purge fluid flows in both the proximal and distal directions. Referring to FIG. 11B, typically, at the proximal end of the ventricular assist device 20, the purge fluid flows out from the proximal end of the lumen 132 in the direction of arrow 156 and from the proximal end of the lumen 133 defined by the pin 131. In some applications, the purge fluid then flows in the direction of arrow 157 and around the driven magnet 82 so as to reduce the frictional force applied to the driven magnet. In some applications, the purge fluid then flows out from the outlet 88 in the direction of arrow 158. Typically, the purge fluid is then discarded. Alternatively, the purge fluid is sent out of and back into the device through the inlet 86.

[0155] Referring to the above description of the purge procedure commonly used in the ventricular assist device 20, the lumens 122, 132, and 133 (previously used to facilitate insertion of the device on the guide wire 10 as described above) should be noted to be typically used as flow paths for purging fluid during use of the ventricular assist device.

[0156] Next, referring to FIG. 11C, in some applications, the ventricular assist device includes an additional purge fluid inlet 89, which is typically used to deliver purge fluid into the 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 to be able to detect aortic blood pressure through this channel, as described elsewhere in this application. In some applications, rather than continuously delivering fluid into the channel 224, the fluid is delivered into this channel periodically to flush the channel. In some applications, the port 89 and the channel 224 are used for aortic pressure sensing. For example, a pressure sensor 216 (schematically illustrated in FIG. 1A) may be disposed within the channel 224, within the port 89, and / or at another location in fluid communication with the channel 224.

[0157] Referring to FIGS. 11D and 11E, in some applications, the axial shaft 92 includes purge fluid holes 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 the purge fluid hole 194.

[0158] Next, refer to FIGS. 12A and 12B, which are schematic views of the ventricular assist device 20 including a liner 39 that lines the inside of the frame 34 that houses the impeller 50, according to some applications of the present invention. (For purposes of illustration, in FIGS. 12A - 12B, the liner 39 and the pump outlet tube 24 on the side of the device coming out of the page are shown as transparent). In some applications, the liner 39 is disposed inside the frame 34 to provide a smooth inner surface through which blood is pumped by the impeller. Typically, by providing a smooth surface with a coating material, hemolysis caused by pumping blood by the impeller is reduced 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 at least on the inner surface of the cylindrical portion of the frame 34 (the cylindrical portion is shown, for example, in FIGS. 2A through 2C). In some applications, the pump outlet tube 24 also covers the cylindrical portion 38 of the frame outside the frame, and for example, the pump outlet tube 24 and the liner 39 overlap over at least 50 percent of the length of the liner, for example, over the entire length of the cylindrical portion of the frame 34 as shown in FIG. 12A. In some applications, for example, as shown in FIG. 12B, only a portion of the pump outlet tube 24 and the liner 39 overlap. 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 the subject, the impeller is advanced distally within the frame 34 so that there is no longitudinal position where the impeller, the pump outlet tube 24, the frame 34, and the liner 39 all overlap each other, so that the impeller is not disposed within the overlapping area between the pump outlet tube and the liner. As described above, referring to FIG. 1D, in some applications, the pump outlet tube 24 extends to the end of the distal conical portion 40 of the frame, and the pump outlet tube defines a plurality of lateral blood inlets. In some such applications, the cylindrical portion of the frame is lined with the liner 39.

[0160] Typically, in the overlapping area between the liner 39 and the pump outlet tube 24, the liner has a shape that forms a smooth surface (e.g., to reduce hemolysis as described above), and the pump outlet tube 24 has a shape that conforms to the struts of the frame 34 (e.g., as shown in the cross-section of FIG. 12A). Typically, in the overlapping area between the liner 39 and the pump outlet tube 24, the pump outlet tube and the liner are coupled to each other, for example, by vacuum, by an adhesive, and / or using a thermoforming procedure as described below, for example.

[0161] In some applications, the liner 39 and the pump outlet pipe 24 are made of different materials. For example, the liner can be made of polyurethane and the pump outlet pipe can be made of polyether block amide (PEBAX®). Typically, the material used to make the liner has a higher thermoforming temperature than the material used to make the pump outlet pipe. In some applications where the liner and the pump outlet pipe overlap along at least a portion of the frame 34 (e.g., along the cylindrical portion of the frame 34), the pump outlet pipe and the liner are coupled to each other and / or to the frame as follows. First, the liner is placed on a mandrel. Next, the frame is placed on the liner. Next, the pump outlet pipe 24 is placed around the outside of the frame. In some applications, the frame is heated to a temperature that is higher than the thermoforming temperature of the pump outlet pipe 24 but lower than the thermoforming temperature of the liner 39 in order to form the pump outlet pipe 24 to conform to 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 temperature, an outer tube (typically made of silicone) applies a pressure to the pump outlet pipe 24 that pushes the pump outlet pipe 24 radially inward in order to conform the pump outlet pipe to the shape of the struts of the frame as shown in the cross-section of FIG. 12A. In some applications, the combination of the frame, the liner, and the portion of the pump outlet pipe 24 disposed around the frame is then shaped to the desired shape and dimensions using shape setting techniques known in the art.

[0162] In some applications (not shown), the density of the struts of the frame at the distal end of the cylindrical portion of the frame is higher than the density of the struts within other portions of the cylindrical portion of the frame. In some such applications, the high density of the struts of the frame at the distal end of the cylindrical portion of the frame facilitates lining of the frame and / or connection of the pump outlet pipe. In some applications, for example as described with reference to FIG. 13, the lining and / or the pump outlet pipe do not extend to the end of the cylindrical portion of the frame. In some such applications, at the longitudinal position along the cylindrical portion of the frame where the lining and / or the pump outlet pipe terminate, the density of the struts of the frame is higher than at other positions along the cylindrical portion of the frame.

[0163] Next, reference is made to FIG. 13, which is a schematic view of the ventricular assist device 20 in which at least the distal portion 333 of the cylindrical portion 38 of the frame 34 is not covered, according to some applications of the present invention. In some applications, during the axial back-and-forth movement cycle of the impeller, even when the impeller is disposed at the most distal position within the frame 34, the portion of the impeller where the span of the impeller is maximized does not advance beyond a given position within the cylindrical portion of the frame (as described above with reference to FIGS. 10A to 10C). In some applications, the portion of the frame disposed distally beyond this position is not covered by either the pump outlet pipe 24 or the lining 39. (It should be noted that for illustrative purposes, the frame is shown without the lining 39. However, in some applications, the frame is lined with the lining 39. Usually, even in such applications, the distal portion 333 of the cylindrical portion of the frame is not covered by either the pump outlet pipe 24 or the lining 39.)

[0164] In some applications, the uncovered distal portion of the cylindrical portion of the frame functions as a substantial inlet. This is because blood flows from the side of the cylindrical portion of the frame into the cylindrical portion of the frame (as indicated by the blood flow arrows in FIG. 13). In some applications, this reduces hemolysis generated by the impeller pumping blood. Alternatively or additionally, when the pump portion is configured to be radially constrained by not covering a portion of the cylindrical portion of the frame, the diameter of the pump portion 27 can be reduced. For example, in order to reduce the diameter of the pump portion of the ventricular assist device (compared to the case where the widest portion of the impeller overlaps the covered portion of the cylindrical portion of the frame and the widest portion of the impeller overlaps the frame and the covering material), the pump portion can be radially constrained such that the widest portion of the impeller overlaps the uncovered portion of the cylindrical portion of the frame.

[0165] In some applications, the ventricular assist device is configured such that during diastole, there is an axial distance between the position of the impeller having the maximum 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 position of the impeller having the maximum diameter and the blood inlet (as described above with reference to FIGS. 10A to 10C). In some such applications, this reduces hemolysis (compared to the case where the axial distance between the position of the impeller having the maximum diameter and the blood inlet is shorter or non-existent), and / or increases the effectiveness of the impeller by reducing turbulence by at least partially aligning the streamline of the blood flowing into the blood inlet with the longitudinal axis of the impeller before being pumped out by the impeller.

[0166] Reference is now made to FIG. 14, a schematic view (cross-sectional view of the left ventricle) of a ventricular assist device 20 disposed inside the left ventricle 22 of a subject according to some uses of the present invention. (FIG. 14 shows the aortic valve 26 overlapping the cross-section of the left ventricle even though the aortic valve is in a plane different from the plane of the main cross-sectional view for illustrative purposes.) Reference is made to FIGS. 15A - 15D, schematic views of a distal tip element 107 of a ventricular assist device that is at least partially curved so as to define a curvature similar to that of a question mark according to some uses of the present invention, and also to FIGS. 16A and 16B, schematic views of the ventricular assist device of FIGS. 15C - 15D disposed inside the left ventricle of a subject according to some uses of the present invention.

[0167] In some uses, the ventricular assist device is guided by a guide wire inserted toward the apex 342 of the left ventricle. The wall of the left ventricle is composed of the interventricular septum 338 (separating the left ventricle from the right ventricle 340), the posterior wall 336 (from which the papillary muscles 341 project and on which the mitral valve apparatus is disposed), and the free wall 334, and each of these three walls is thought to occupy approximately one-third of the circumference of the left ventricle (shown by the dashed lines dividing the left ventricle in FIG. 14 into thirds). Usually, it is not desirable for the distal tip element (or other parts of the ventricular assist device) to contact the interventricular septum as it may cause arrhythmias. Further usually, it is desirable to maintain a distance between the distal tip element (and other parts of the ventricular assist device) and the posterior wall so as not to interfere with the mitral valve apparatus and to prevent interference of the mitral valve apparatus with the function of the ventricular assist device. Thus, the ventricular assist device is typically guided toward the apex in such a way that the distal tip element contacts the free wall 334 as shown in FIGS. 14 and 16A and 16B when the distal tip element contacts the inner wall of the left ventricle.

[0168] Typically, a ventricular assist device is introduced into a target ventricle via a guidewire as described above. The distal tip 120 defines a lumen 122 such that when the ventricular assist device is introduced into the target ventricle, the distal tip is held in a configuration where the distal tip is straight. In some applications, when the guidewire is removed, the distal tip is configured to assume its curved shape. FIGS. 15A through 15D show the shape of the initially formed distal tip 120. Typically, as a result of the guidewire being inserted through the lumen 122 (thereby causing the distal tip to be temporarily straight), the curvature of the distal tip is less than at least that shown in FIGS. 15A through 15D when installed in the target left ventricle. For example, FIG. 15C shows that the distal tip has 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 target left ventricle in FIG. 16A.

[0169] As described above, the distal tip 120 typically forms part of the distal tip element 107, which also includes the axial shaft receiving tube 126. Typically, the distal tip element 107 is configured such that in an unconstrained configuration (i.e., in the absence of 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 the longitudinal axis 348. The curved portion of the distal tip element 107 curves in a first direction away from the longitudinal axis 348 and, passing through an inflection point, curves in a direction opposite 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 upward out of the plane of the paper and then curves downward out of the plane of the paper. Also, as shown in FIGS. 15C and 15D, within the plane of the paper, the distal tip element first curves downward out of the plane of the paper and then curves upward out of the plane of the paper. Typically, when shaped as shown in FIGS. 15A-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 here that the term "semi-elliptical" is intended to include a semi-circle. Further, note that in some cases, the tip defines not an exact semi-elliptical shape but a bulged shape substantially similar to a semi-elliptical shape.)

[0170] As shown in FIGS. 15A and 15B, in some applications, after passing through the inflection point, the distal tip element continues to curve back across the longitudinal axis 348. FIG. 15A shows an example where the end of the distal tip element does not cross the longitudinal axis again and there is a large gap between the distal end of the distal tip element and the proximal end of the curved portion. FIG. 15B shows an example where the end of the distal tip element crosses the longitudinal axis again 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 FIGS. 15C and 15D (a cross-sectional view and an isometric view of distal tip elements of the same shape, respectively), in some applications, after passing through the inflection point, the tip does not curve such that the distal tip element crosses the longitudinal axis 348, 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, typically, a hemostatic valve (e.g., a duckbill valve 390) is disposed within the distal section of the distal tip portion 120 and is configured to prevent blood inflow into the lumen 122. Typically, the maximum width of the duckbill valve is 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 portion disposed within the most distal 10 mm of the distal tip portion, e.g., within the most distal 5 mm. In some applications, the duckbill valve is oriented in the proximal direction (i.e., the wide inlet of the valve faces the distal end of the distal tip portion and the narrow tip of the valve faces away from the distal end of the distal tip portion 120). Typically, when disposed within the left ventricle of a subject, the curvature of the curved portion of the distal tip element 107 is configured to provide a non-invasive tip to the ventricular assist device 20. Further typically, the distal tip element is configured to space the inlet 108 of the ventricular assist device from the wall of the left ventricle.

[0172] In FIGS. 16A and 16B, first, it should be noted that these figures show cross-sectional views of the left ventricle 22 in which the septum 338 is disposed on the left side of the page and the free wall 334 is disposed on the right side of the page. In these figures, the left atrium 359 and the left atrial appendage 358 are visible 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 the left ventricle shown in FIGS. 16A through 16B (as well as FIGS. 17A-i through 17D) are different from, for example, those shown in FIG. 1B. FIG. 1B is a schematic diagram presented for illustrative purposes and does not accurately depict the scale and orientation of the ventricular assist device with respect to the anatomical structure.

[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 relative to the apex of the subject's left ventricle. Typically, the distal tip element is configured to separate the blood inlet from the septum 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 such that the bulge 351 bulges toward the septum 338. When disposed in this configuration, as the distal tip element 107 is 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 in the direction of the free wall 334 and away from the septum 338 (the direction of the arrow shown in FIG. 16B. Typically, this is due to the proximal straight portion 346 pivoting about the curved portion in the shape of a question mark as shown. In contrast, other shaped tips, when disposed in a similar orientation, can result in the blood inlet being pushed toward the septum. For example, if the distal tip element has a pigtail tip (the tip curves in a single direction of curvature) and the pigtail curve is oriented such that it is on the free wall side of the longitudinal axis of the straight portion of the distal tip element, pushing the tip distally causes the loop of the pigtail curve to tighten, typically causing the blood inlet to face the septum.

[0175] Referring to all of FIGS. 14 through 16B, it should be noted that the scope of the present invention includes the use of a distal tip element having a question mark or tennis racket shape, even in the absence of other features and / or portions of the distal tip element 107 (such as the axial shaft receiving tube 126, etc.) in combination with any ventricular assist device. Further, it should be noted that the curvature of the distal tip portion is typically all within a single plane.

[0176] Next, refer to FIGS. 17Ai and 17Aii, which are schematic views of a ventricular assist device 20 having a balloon 220 disposed on a distal tip element 107 according to some uses of the present invention. The balloon is configured to facilitate movement of the axial shaft 92 relative to the wall of the ventricle.

[0177] As described above, the axial shaft 92 typically passes through the axis of the impeller 50 via the lumen 62 of the impeller. More typically, the axial shaft is rigid, for example, a rigid tube. The axial shaft itself is radially stabilized via the proximal radial bearing 116 and the distal radial bearing 118. Next, the axial shaft passes through the lumen 62 defined by the impeller to radially stabilize the impeller with respect 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. Typically, when the axial shaft bends, the friction between the axial shaft and the distal radial bearing increases. Therefore, it is usually desirable to maintain the axial shaft in a straight configuration. In some applications, the balloon 220 provides freedom of movement of the distal tip element relative to the wall of the left ventricle in such a way that it does not cause significant movement of the proximal end of the distal tip (defining the axial shaft receiving tube). For example, as shown by the arrows near the tip 342 in FIGS. 17Ai and 17Aii, the balloon can rotate relative to the tip without causing significant movement of the axial shaft receiving tube. Thus, even when the balloon moves relative to the tip (as shown by the change from FIG. 17Ai to FIG. 17Aii), the axial shaft remains substantially in a straight configuration. In some applications, a purge fluid is used to inflate the balloon 220. For example, the technique described with respect to FIG. 13D of Tuval's U.S. Patent Application Publication No. 2020 / 0237981, which is incorporated herein by reference, is used.

[0178] Next, refer to FIGS. 17Bi and 17Bii, which are schematic views of the ventricular assist device 20 having a joint 230 configured to facilitate the turning of the distal tip 120 relative to the axial shaft according to some uses of the present invention. As described above, in some uses, the distal tip element 107 includes an axial shaft receiving tube 126 and a distal tip 120. In some uses, the joint 230 enables the distal tip 120 to move relative to the axial shaft receiving tube 126. For example, the joint 230 may be a ball joint, and / or a swivel joint, and / or a cardan joint as shown in the figure. Thus, even when the distal tip moves relative to the apex 342 of the left ventricle (as shown by the change to FIGS. 17Bi and 17Bii), the axial shaft 92 is maintained in a substantially straight configuration. In some such uses, the distal tip 120 has the shape as described above.

[0179] Next, refer to FIG. 17C, which is a schematic view of the ventricular assist device according to some uses of the present invention. The outer tube 140 and / or 142 of the ventricular assist device is set to a shape having a predetermined curvature such that the axial shaft of the ventricular assist device is maintained in a substantially straight configuration when the axial shaft 92 is disposed inside the target left ventricle 22.

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

[0181] Next, refer to FIG. 17D, which is a schematic view of a ventricular assist device 20 having a distal tip 240 configured to be fixed to the tissue of the left ventricular apex 342 according to 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), and is configured to be screwed into the tissue of the apex to fix the distal end of the ventricular assist device to the apex. Typically, fixing the distal tip to the apex reduces movement of the pump portion 27 relative to the internal structure of the left ventricle, thereby reducing the risk of damage to the internal structure of the left ventricle that may be caused by such movement.

[0182] Next, refer to FIGS. 18A, 18B, and 18C, which are schematic views of the distal radial bearing 118 of the ventricular assist device according to each application of the present invention.

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

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

[0185] Referring to FIG. 18C, in some applications, the outer surface 125 of the distal radial bearing portion 118 that abuts against the inner surface of the bearing housing 119 has a convex curved surface. In some applications, the convexly curved outer surface of the bearing portion is configured to allow some movement of the radial bearing portion relative to the bearing housing. In some applications (not shown), the radially inner surface of the bearing housing (which abuts against the outer surface of the bearing portion) has a convex curved surface to allow some movement of the radial bearing portion relative to the bearing housing. In some applications, the proximal radial bearing portion 116 also has a similar configuration, and the outer surface of the bearing portion and / or the radially inner surface of the bearing housing has a convex curved surface. In some such applications, the above-described shape of the bearing portion and / or the bearing housing allows movement of the rigid axial shaft relative to the frame 34 by allowing movement between the radial bearing portion and the bearing housing. In some applications, in this way, the axial shaft is allowed to be slightly misaligned with respect to the longitudinal axis of the frame.

[0186] In some applications, the length of the radial bearing portion allows for axial shaft movement relative to the frame 34 such that the axial shaft is permitted to be slightly misaligned with respect to the longitudinal axis of the frame. For example, the length of each of the proximal and distal radial bearing portions can be less than 2 mm, less than 1.5 mm, or less than 1 mm, such as 0 to 1.5 mm, or 0.5 to 1 mm.

[0187] Now, refer to FIG. 19A, which is a schematic diagram of the ventricular assist device 20 according to some applications of the present invention. The pump outlet tube 24 of this device is configured to curve when blood is pumped out through the pump outlet tube and is rotatable with respect to the distal tip 120 of the ventricular assist device. Also refer to FIG. 19B, which is a schematic diagram of the pump outlet tube 24 of FIG. 19A with other components of the ventricular assist device not present according to some applications. Further, refer to FIG. 19C, which is a schematic diagram of the ventricular assist device 20 of FIGS. 19A to 19B disposed inside the aorta 30 and the left ventricle 22 of a subject according to some applications of the present invention. It should be noted that the diagrams of the aorta and the left ventricle shown in FIG. 19C are different from, for example, those shown in FIG. 1B. FIG. 1B is a schematic diagram presented for illustrative purposes and does not accurately depict the scale and orientation of ventricular assistance with respect to the anatomical structure. Additionally, it should be noted that the diagrams of the aorta and the left ventricle shown in FIG. 19C are different from, for example, those shown in FIGS. 16A to 16B and FIGS. 17Ai to 17D. FIG. 19C shows a cross-sectional view of the left ventricle with the posterior wall 336 disposed on the left side of the paper and the free wall 334 disposed on the right side of the paper.

[0188] As described above, in some applications, the frame 34 is not disposed within the tube along the proximal portion of the pump outlet tube 24, and thus the tube is not supported in an open state by the frame 34. The tube 24 is typically made of a blood-impermeable crushable material. For example, the tube 24 may include polyurethane, polyester, and / or silicone. Alternatively or additionally, the tube is made of polyethylene terephthalate (PET) and / or polyether block amide (PEBAX®). Typically, the proximal portion of the tube is configured to be disposed such that at least a portion of it is within the ascending aorta of the subject. In some applications, as shown in FIG. 1B, the proximal portion of the tube crosses the aortic valve of the subject and reaches the ascending aorta of the subject from the left ventricle of the subject. As described above, the tube typically defines one or more blood inlets 108 at the distal end of the tube, through which blood flows from the left ventricle into the tube when the impeller operates. 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 operates. When the impeller operates, the proximal portion of the tube is typically maintained in an open state by the pressure of the blood flow through the tube.

[0189] In some applications, the pump outlet tube 24 is preformed to curve when the proximal portion of the tube is maintained in an open state by the pressure of the blood flow through the tube when the impeller operates. Typically, when the proximal end of the tube is disposed within the aorta, at least a portion of the tube is disposed within the left ventricle and has a curvature that curves away from the posterior wall of the left ventricle and toward the apex and / or free wall of the left ventricle. Further typically, when the proximal end of the tube is disposed within the aorta, at least a portion of the tube is disposed within the left ventricle and has a curvature that curves away from the interventricular septum of the left ventricle and toward the apex and / or free wall of the left ventricle. In some applications, the curvature of the tube is such that, as shown in FIG. 19C, it maintains a separation between the blood inlet 108 and the posterior wall 336 of the left ventricle, the mitral valve tip 402, and / or the sub-valvular components of the mitral valve (such as chordae tendineae 404, trabeculae carneae, and / or papillary muscles 341).

[0190] Typically, the tube 24 is preformed using blow molding in a curved shape or using a mold after a blow molding process or dipping process. Typically, the distal portion of the tube in which the frame 34, impeller 50 and axial shaft 92 are disposed is maintained in a straight and open configuration by the frame 34. A portion of the tube disposed proximal to the frame 34 and within the left ventricle is typically shaped to define the curvature described above. 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., 90-180 degrees, 90-160 degrees, 120-160 degrees, or 140-150 degrees. In some applications, the curvature of the tube is such that the surface of the tube on the inside of the curve defines a radius of curvature R greater than 10 mm, e.g., greater than 20 mm, and / or less than 200 mm (e.g., 100 mm), e.g., 10-200 mm, or 20-100 mm. (To illustrate the method of measuring the radius of curvature R, a dashed circle including a dashed line across the diameter is shown in FIG. 19B.)

[0191] As will be described with reference to FIGS. 19A through 19C, it should be noted that the pump outlet tube 24 is configured such that (a) when there is no blood flowing through the tube, the tube is typically collapsed by the pressure outside the tube exceeding the pressure inside 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 preformed curved configuration. Further, it should be noted that when the tube 24 assumes its curved configuration, typically, as shown in FIGS. 19A and 19C, a portion of the drive cable 130 disposed within the curve of the tube will also curve. That is, rather than the drive cable (or another element disposed within the tube) curving the tube, typically, the preforming of the tube itself curves the tube and the drive cable. Alternatively, the outer tube 140 and / or 142 (disposed around the drive cable) is shaped to define the curvature, and the outer tube causes the drive cable and the tube 24 to assume a curved shape. In some applications, both the outer tube 140 and / or 142 and the tube 24 are shaped to define a curved shape.

[0192] Reference is now made to FIGS. 19D and 19E, which are schematic views of the pump outlet tube 24 of the ventricular assist device 20 configured to curve as blood is pumped through the tube for several applications of the present invention. FIGS. 19D and 19E show the tube 24 without other components of the ventricular assist device (such as the impeller 50, the frame 34, etc.) for illustrative purposes. FIG. 19E is a schematic view of the ventricular assist device 20 of FIG. 19D disposed within the aorta 30 and left ventricle 22 of a subject for several applications of the present invention. The view of the left ventricle shown in FIG. 19E is similar to that shown in FIG. 19C. In several applications, the inlet 108 and / or the outlet 109 are arranged in a non-axisymmetric configuration around the tube 24. Typically, the tube 24 defines the inlet and / or outlet at a position that curves the tube 24 and / or maintains the curvature of the tube 24 as described with reference to FIGS. 19A - 19C. For example, as shown, the blood inlet hole may be disposed on the side of the tube 24 (or inside the desired curve of the tube) that is inside the curve of the tube. When blood flows into the blood inlet, this causes the pressure in the region above the blood inlet to decrease, and the distal end of the tube 24 is pulled towards this region (shown by arrow 310). Alternatively or additionally, the blood outlet 109 may be disposed on the side of the tube 24 (or inside the desired curve of the tube) that is inside the curve of the tube. When blood exits the blood outlet, the blood impacts the wall of the aorta, which causes the proximal end of the tube 24 to be pushed in the direction of arrow 312, which is the opposite direction.

[0193] As shown with reference to FIGS. 19A through 19C, the curvature of the pump outlet tube is typically such that, as shown in FIG. 19E, it maintains a separation between the blood inlet 108 and the posterior wall 336 of the left ventricle, the mitral valve leaflet 402, and / or the sub-valvular components of the mitral valve (such as the chordae tendineae 404, trabeculae, and / or papillary muscles 341). Typically, when the proximal end of the tube is disposed within the aorta, at least a portion of the tube is disposed within the left ventricle and has a curvature such that it curves away from the posterior wall of the left ventricle and toward the apex and / or free wall of the left ventricle. Further typically, when the proximal end of the tube is disposed within the aorta, at least a portion of the tube is disposed within the left ventricle and has a curvature such that it curves away from the interventricular septum of the left ventricle and toward the apex and / or free wall of the left ventricle.

[0194] In some applications, when implanting a ventricular assist device within the left ventricle, the distal tip is first implanted. As described above, the distal tip is typically implanted in a given orientation with respect to the anatomical structure of the left ventricle. Typically, after implanting the distal tip, the pump outlet tube is implanted. In some cases, since the distal tip may already be implanted in a desired orientation with respect to the anatomical structure of the left ventricle, the curvature of the tube may not be disposed in the desired orientation within the left ventricle. Thus, in some applications, the distal tip is coupled (either directly or indirectly) to the pump outlet tube via a joint 212 that permits rotation of the pump outlet tube with respect to the distal tip of the ventricular assist device, as indicated by arrow 210 in FIGS. 19A through 19E. For example, the joint may be a swivel joint and / or a ball joint (such as ball joint 230 shown in FIGS. 17Bi through 17Bii), and / or a cardan joint (such as joint 232 shown in FIGS. 20A through 20C). In some applications, the joint is disposed within the proximal portion of the distal tip element 107. Alternatively or additionally, the joint is disposed between the distal tip 120 and the axial shaft receiving tube 126 (such as shown in FIGS. 17Bi through 17Bii).

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

[0196] In some applications, the curved element is shaped to have a curvature generally similar to that described in connection with tube 24 with reference to FIGS. 19A through 19E. In some applications, the curvature is such that the angle omega between the longitudinal axis of the curved element at the proximal end of the curved element and the longitudinal axis of the curved element at the distal end of the curved element 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), for example, such that it is 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 curved element on the inside of the curve defines a radius of curvature greater than 10 mm, for example, greater than 20 mm, and / or less than 200 mm (e.g., 100 mm), for example, between 10 and 200 mm, or between 20 and 100 mm. As shown with reference to FIGS. 19A through 19C, the curvature of the tube is generally such that, as shown in FIG. 19C, it maintains a separation between the blood inlet 108 and the posterior wall 336 of the left ventricle, the mitral valve leaflet 402, and / or the sub-valvular components of the mitral valve (such as chordae tendineae 404, trabeculae, and / or papillary muscles 341). Typically, when the proximal end of the tube is disposed within the aorta, at least a portion of the tube is disposed within the left ventricle and has a curvature such that it curves away from the posterior wall of the left ventricle and towards the apex of the left ventricle and / or towards the free wall. Further typically, when the proximal end of the tube is disposed within the aorta, at least a portion of the tube is disposed within the left ventricle and has a curvature such that it curves away from the interventricular septum of the left ventricle and towards the apex of the left ventricle and / or towards the free wall.

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

[0198] Referring to FIGS. 19A - 19F, it should be noted that in some applications, the tube 24, as described above, assumes a curved shape when the outer tube 142 is fixed to the aorta and the distal tip 120 is fixed to the inner wall of the left ventricle (e.g., the free wall around the apex). Further, it should be noted that the curvature of the tubes shown in FIGS. 16A and 16B is less than that shown in FIGS. 19A - 19F, since FIGS. 16A and 16B show different views of the device. In the views shown in FIGS. 16A and 16B, the curvature is typically less prominent than that shown in FIGS. 19A - 19F.

[0199] Next, refer to FIGS. 20A through 20C, which are schematic views of the ventricular assist device 20 according to some uses of the present invention. The axial shaft 92 of this device includes a joint 232 (such as a cardan joint as shown). The joint is typically disposed 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. In FIG. 20A, for purposes of illustration and typically, a portion of the axial shaft 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 through 3C) is visible. Note that a portion of the impeller (such as the membrane 56 and spring 54 of the material are not shown). Alternatively, the joint is disposed at another position along the axial shaft, such as proximal to the impeller or distal to the impeller.

[0200] In some uses, the joint 232 is disposed between the proximal portion 234 of the axial shaft and the distal portion 236 of the axial shaft that are coupled to each other via the joint, and the proximal and distal portions are configured to be able to bend relative to each other via the joint. Typically, due to the joint, the axial shaft can take a shape that conforms to the curvature of the other parts of the left ventricular device and / or the anatomical structure of the subject. In some uses, the joint is configured to conform the axial shaft to the curvature of the frame 34, such that even when the frame 34 is slightly curved, the proximal portion of the axial shaft is coaxially disposed relative to the proximal bearing portion 116, and the distal portion of the axial shaft is coaxially disposed relative to the distal bearing portion 118.

[0201] Figure 21 is a schematic diagram of a ventricular assist device including one or more blood pressure measurement tubes 222 for several applications of the present invention. As described above, typically, a ventricular assist device includes a pump outlet tube 24, and the pump outlet tube 24 crosses the subject's aortic valve such that the proximal end of the tube is disposed within the subject's aorta and the distal end of the tube is disposed within the subject's left ventricle. Typically, a blood pump (usually including an impeller 50) is disposed within the subject's left ventricle within the tube 24 and is configured to pump blood from the left ventricle to the subject's aorta through the tube 24. In some applications, the ventricular blood pressure measurement tube 222 extends at least to the outer surface 213 of the tube 24 such that the opening 214 at the distal end of the blood pressure measurement tube is in direct fluid communication with the patient's blood flow outside the tube 24. Typically, the opening 214 is configured to be proximal to the blood pump (e.g., proximal to the impeller 50) within the subject's left ventricle. A pressure sensor 216 (schematically shown in FIG. 1A) measures the pressure of the blood within the ventricular blood pressure measurement tube. Typically, the pressure sensor measures the blood pressure (i.e., left ventricular blood pressure) of the subject outside the tube 24 by measuring the pressure of the blood within the left ventricular blood pressure measurement tube. Typically, the blood pressure measurement tube 222 extends from outside the subject to the opening 214 at the distal end of the tube, and the pressure sensor 216 is disposed near the proximal end of the tube, e.g., outside the subject. In some applications, a 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 within each left ventricular blood pressure measurement tube, the computer processor 25 determines whether the opening of one of the two or more ventricular blood pressure measurement tubes is blocked. This can occur, for example, due to the opening contacting the wall of the ventricular septum and / or another interventricular portion. Typically, in response to a determination that the opening of one 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 within another of the two or more ventricular blood pressure measurement tubes.

[0203] In some applications, the outer tube 142 defines a groove 215 in a portion of the outer surface of the outer tube configured to be disposed within the tube 24. Typically, when inserting the ventricular assist device into the subject's body, the portion of the ventricular blood pressure measurement tube 222 extending from within the tube 24 to at least the outer surface of the tube 24 is configured to be disposed within this groove so as not to protrude from the outer surface of the outer tube.

[0204] In some applications (not shown), the distal portion of the blood pressure measurement tube 222 is disposed outside the pump outlet tube 24. For example, the blood pressure measurement tube 222 can extend from the outer tube 142 to the proximal end of the pump outlet tube 24 and then be incorporated into the outer surface of the pump outlet tube 24. This is shown, for example, in FIG. 16D of Tuval U.S. Patent No. 10,881,770, which is incorporated herein by reference.

[0205] As described above, in some applications, the drive cable 130 extends from a motor outside the subject to the axial shaft 92 where the impeller 50 is disposed. Typically, the drive cable is disposed inside the first outer tube 140 and the second outer tube 142 as described above. In some applications, as shown in the cross-section of FIG. 21, the proximal portion of the blood pressure measurement tube 222 includes a channel between the first outer tube 140 and the second outer tube 142. In this regard, the blood pressure measurement tube represents a continuous lumen that extends from the pressure sensor 216 to the outside of the pump outlet tube 24 in the left ventricle of the subject, and it should be noted that this is regardless of whether the structure of the lumen changes along the length of the lumen. As described above, typically, a purge fluid is delivered between the outer tube 140 and the outer tube 142, and in some applications, the purge fluid is delivered through the channel 226. Typically, as shown in FIG. 21, the blood pressure measurement tube 222 occupies a portion with a larger 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 tube 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 tube occupies a relatively large proportion of the cross-sectional area defined between the outer tube 140 and the outer tube 142 in order to transmit the blood pressure outside the pump outlet tube 24 in the left ventricle of the subject proximally to the pressure sensor 216.

[0206] Next, refer to FIGS. 22A and 22B, which are schematic views of a sterile sleeve 242 configured to form a seal between the delivery catheter 143 and the outer tube 142 of the ventricular assist device 20 according to some uses of the present invention. In some uses (not shown), the delivery catheter 143 is inserted into a target artery (femoral artery or radial artery) via an introducer sheath (not shown). The introducer sheath is inserted into the arterial incision and typically remains at a predetermined position within the artery throughout the entire operating period of the ventricular assist device. In such a use, a sterile sleeve (substantially similar to that shown in FIGS. 22A to 22B) is usually disposed between the delivery catheter and the introducer sheath to allow movement between the delivery catheter 143 and the introducer sheath (not shown) while maintaining the sterility of the arterial incision.

[0207] In some alternative uses, the ventricular assist device is first inserted into the arterial incision via an introducer sheath, and then the introducer sheath is removed for subsequent operation of the ventricular assist device. For example, the ventricular assist device can be inserted via a peel-away introducer sheath. Thereafter, typically, the delivery catheter comes into direct contact with the arterial incision. Usually, in this case, the diameter of the device disposed within the arterial incision for subsequent procedures is smaller compared to the case where the introducer sheath remains within the arterial incision throughout the entire operating period of the ventricular assist device. For example, the outer diameter of the delivery catheter can be less than 3.3 mm (i.e., 10 French), which is the diameter passing through the incision 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 remains at a predetermined position throughout the entire operating period of the ventricular assist device, the diameter passing through the incision increases because the thickness of the wall of the introducer sheath also has to pass through the incision. For example, this can increase the diameter by 0.3 to 0.6 mm (i.e., 1 to 2 French).

[0208] In some such applications, the delivery catheter is advanced until the distal end of the delivery catheter is positioned at a given location within the target aorta (e.g., within the ascending aorta). Thereafter, the outer tube 142 is advanced relative to the delivery catheter to advance the pump portion 27 of the ventricular assist device relative to the distal end of the delivery catheter. In such an application, the sterile sleeve 242 forms a seal between the delivery catheter 143 of the ventricular assist device 20 and the outer tube 142 and permits movement of the outer tube relative to the delivery catheter while maintaining the sterility of the arteriotomy. In some such applications, the ventricular assist device is provided to the user as a kit including a sterile sleeve 242 disposed at a predetermined location between the outer tube 142 and the delivery catheter 143.

[0209] Refer to FIGS. 23A through 23C, which are schematic views of a tip straightening element 270 used to straighten the distal tip portion 120 of the ventricular assist device 20 when inserting the guide wire 10 for some applications of the present invention. As described above, typically, the ventricular assist device is inserted into the target ventricle via the guide wire 10 and is arranged in a configuration that is radially constrained (i.e., crimped) inside the delivery catheter 143 (e.g., schematically shown in FIG. 1B). Typically, the guide wire is first inserted into the distal end of the distal tip element 107 within the ventricular assist device. In some applications, a tip straightening element 270 is arranged around the distal tip element so as to hold the distal tip element in a straight configuration to facilitate insertion of the guide wire into the distal end of the distal tip element (i.e., into the distal tip portion 120). Typically, the straightening element is a housing that defines a straight lumen 271. As shown, for example, in FIG. 23B, the straightening element is arranged around the distal tip element such that the distal tip element is arranged in a straight configuration within the lumen 271, and the guide wire 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 with the guide wire disposed within the distal tip element. For example, the straightening element can have a cut, a hole, and / or a slit 272 along its length (as shown in the figure) such that the straightening element can be easily removed from the distal tip element, as shown, for example, in FIG. 23C.

[0210] Now, refer to FIGS. 24A, 24B, and 24C, which are graphs showing measurements performed during use of a left ventricular assist device according to some applications of the present invention. The left ventricular assist device described herein was installed inside a pig's heart. While operating the left ventricular assist device at each rotational speed, the arterial pulsation of the pig was measured using an aortic pressure sensor. Based on in vitro tests previously performed with the device, the device was calibrated such that the flow rate generated by the device when the impeller rotates at each rotational speed was known. FIG. 24A shows a plot of arterial pulsation versus the flow rate generated by the device, measured in an experiment performed on a pig (and further using a predetermined correspondence between impeller rotational speed and flow rate). Then, as shown in FIG. 24B, the plot shown in FIG. 24A was fitted to a curve extrapolated with respect to the y-intercept (i.e., where the arterial pulsation is zero). As shown, by extrapolation of the curve, the flow rate when the arterial pulsation is zero was estimated to be 5.6 L / min. In the same pig, a Swan-Ganz catheter was used to measure the cardiac output when the left ventricular assist device was not active. With the Swan-Ganz catheter, the pig's native cardiac output was measured to be 5.2 L / min. That is, it is a value similar to the flow rate at zero arterial pulsation estimated by extrapolation of the flow rate / arterial pulsation curve. When the arterial pulsation is zero, the left ventricular device generally replaces the native function of the heart, and a hypothesis is established that the flow rate generated by the pump at this value gives a reasonable approximation of the native cardiac output of the subject.

[0211] According to the above experimental results, in some applications of the present invention, during the operation of the ventricular assist device, the arterial pulsation of the subject is measured, and parameters are derived from the arterial pulsation of the subject. Usually, when the rotational speed of the impeller increases, the flow rate generated by the blood pump also increases. Usually, since the blood pump is a continuous flow blood pump rather than a pulsatile blood pump, the flow generated by the blood pump is a non-pulsatile flow. Therefore, when the rotational speed of the impeller increases and the flow rate generated by the blood pump increases, it is common for the arterial pulsation of the subject to decrease. In some applications, the arterial pulsation of the subject when the rotational speed of the impeller changes is measured. Based on the above measurements, the relationship between the arterial pulsation and the impeller rotational speed and / or the pump flow rate is derived. In some applications, based on the above relationship, the intrinsic cardiac output of the subject is derived. 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. According to the above results, a hypothesis is established that at this value, the pump replaces the intrinsic function of the heart, and furthermore, the flow rate generated by the pump at this value gives an approximation of the intrinsic cardiac output of the subject.

[0212] With respect to all aspects of the ventricular assist device 20 described with reference to FIGS. 1A through 24C, FIGS. 1A and 1B show the ventricular assist device 20 within the left ventricle of a subject. However, in some applications, the device 20 is placed inside the right ventricle of the subject, across the subject's pulmonary valve, and with the necessary modifications, the techniques described herein are used. It should be noted that in some applications, the components of the device 20 are applicable to different types of blood pumps. For example, aspects 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 aspects may include features of the tube 24 (e.g., the curvature of the tube), the impeller 50, features of the pump section 27, the drive cable 130, etc. Alternatively or additionally, the device 20 and / or a part thereof (e.g., the impeller 50 without the tube 24) is placed within this portion to assist in pumping blood from different parts of the subject. For example, the device 20 and / or a part thereof (e.g., the impeller 50 without the tube 24) can be placed within a blood vessel and used to pump blood through this blood vessel. In some applications, the device 20 and / or a part thereof (e.g., the impeller 50 without the tube 24) is configured to be placed within the subclavian vein or jugular vein at the junction of the vein and lymphatic vessel, and with the necessary modifications, is used to increase the flow of lymph fluid from the lymphatic vessel. The scope of the present invention includes using the devices and methods described herein at anatomical locations other than the left ventricle and aorta, and in this application (the specification and claims), the ventricular assist device and / or a part thereof may be referred to as a blood pump.

[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 application examples (all of which are incorporated herein by reference).

[0214] U.S. Patent Application Publication No. 2020 / 0237981, titled "Distal Tip Element for a Ventricular Assist Device" by Tuval, filed on January 23, 2020, claiming priority below, U.S. Provisional Patent Application No. 62 / 796,138, entitled "Ventricular Assist Device" by Tuval, filed on January 24, 2019, U.S. Provisional Patent Application No. 62 / 851,716, entitled "Ventricular Assist Device" by Tuval, filed on May 3, 2019, U.S. Provisional Patent Application No. 62 / 870,821, entitled "Ventricular Assist Device" by Tuval, filed on July 5, 2019, and U.S. Provisional Patent Application No. 62 / 896,026, entitled "Ventricular Assist Device" by Tuval, filed on September 5, 2019. U.S. Patent No. 10,881,770 by Tuval, which is a continuation application of International Patent Application PCT / IB2019 / 050186, entitled "Ventricular Assist Device" by Tuval, filed on January 10, 2019 (published as WO19 / 138350), claiming priority below: U.S. Provisional Patent Application No. 62 / 615,538, entitled "Ventricular Assist Device" by Sohn, filed on January 10, 2018, U.S. Provisional Patent Application No. 62 / 665,718, entitled "Ventricular Assist Device" by Sohn, filed on May 2, 2018, U.S. Provisional Patent Application No. 62 / 681,868, entitled "Ventricular Assist Device" by Tuval, filed on June 7, 2018, and U.S. Provisional Patent Application No. 62 / 727,605, entitled "Ventricular Assist Device" by Tuval, filed on September 6, 2018. U.S. Patent Application Publication No. 2019 / 0269840 by Tuval, which is the U.S. national stage of International Patent Application PCT / IL2017 / 051273, entitled "Blood Pump" by Tuval, filed on November 21, 2017 (published as WO18 / 096531), claiming priority to U.S. Provisional Patent Application No. 62 / 425,814 by Tuval, filed on November 23, 2016, U.S. Patent Application Publication No. 2019 / 0175806 of Tuval, which is a continuation application of International Patent Application PCT / IL2017 / 051158 (published as WO18 / 078615) entitled "Ventricular Assist Device" filed on October 23, 2017, claiming priority to U.S. Patent Application Publication No. 62 / 412,631 of Tuval filed on October 25, 2016, and U.S. Patent Application Publication No. 62 / 543,540 of Tuval filed on August 10, 2017, U.S. Patent Application Publication No. 2019 / 0239998 of Tuval, which is the U.S. national stage of International Patent Application PCT / IL2017 / 051092 (published as WO18 / 061002) entitled "Vascular Tube" filed on September 28, 2017, claiming priority to U.S. Provisional Patent Application No. 62 / 401,403 of Tuval filed on September 29, 2016, U.S. Patent Application Publication No. 2018 / 0169313 of Schwammenthal, which is the U.S. national stage of International Patent Application PCT / IL2016 / 050525 (published as WO16 / 185473) entitled "Blood Pump" filed on May 18, 2016, claiming priority to U.S. Provisional Patent Application No. 62 / 162,881 of Schwammenthal filed on May 18, 2015, U.S. Patent No. 10,583,231 of Schwammenthal, which is the U.S. national stage of International Patent Application PCT / IL2015 / 050532 (published as WO15 / 177793) entitled "Blood Pump" filed on May 19, 2015, claiming priority to U.S. Provisional Patent Application No. 62 / 000,192 of Schwammenthal filed on May 19, 2014, (a)U.S. Provisional Patent Application No. 61 / 779,803, entitled "Kidney Pump" by Schwammenthal, filed on March 13, 2013, and (b) International Patent Application PCT / IL2014 / 050289, entitled "Kidney Pump" by Schwammenthal, filed on March 13, 2014, claiming priority to U.S. Provisional Patent Application No. 61 / 914,475, entitled "Kidney Pump" by Schwammenthal, filed on December 11, 2013 (published as WO14 / 141284), which is the U.S. national stage of the international patent application, and U.S. Patent No. 10,039,874 by Schwammenthal, U.S. Patent No. 9,764,113, entitled "Curved Catheter" by Tuval, issued on September 19, 2017, claiming priority to U.S. Provisional Patent Application No. 61 / 914,470, entitled "Curved Catheter" by Tuval, filed on December 11, 2013, and, U.S. Patent No. 9,597,205 by Tuval, which is the U.S. national stage of International Patent Application PCT / IL2013 / 050495, entitled "Artificial Kidney Valve" by Tuval, filed on June 6, 2013 (published as WO13 / 183060), claiming priority to U.S. Provisional Patent Application No. 61 / 656,244, entitled "Artificial Kidney Valve" by Tuval, filed on June 6, 2012.

[0215] It will be appreciated by those skilled in the art that the present invention is not limited to what has been specifically illustrated and described above. The scope of the present invention includes both combinations and subcombinations of the various features described above that come to mind when one skilled in the art reads the foregoing description, as well as those variations and modifications thereof that do not exist in the prior art.

Claims

1. An apparatus comprising: a blood pump configured to be disposed within a subject's body, the blood pump comprising: an impeller comprising: a proximal boss and a distal boss; two or more helical elongate elements extending from the proximal boss to the distal boss; an axial structure disposed along an axis about which the helical elongate elements are wound, inside the two or more helical elongate elements; a membrane of material supported between the helical elongate elements and the axial structure, each of the helical elongate elements to which the membrane of material is attached defining a respective blade of the impeller; the impeller; an impeller overexpansion prevention element comprising a single integrated structure including a ring and a plurality of elongate elements disposed around the axial structure; the blood pump; wherein each of the elongate elements extends from the ring to a respective one of the helical elongate elements and is coupled to the respective helical elongate element to prevent radial expansion of the impeller.

2. The apparatus of claim 1, wherein the impeller comprises three helical elongate elements, the three helical elongate elements to which the membrane of material is attached define three blades of the impeller, and each elongate element extends from the ring to a respective one of the three helical elongate elements such that each elongate element is within a respective one of the three blades of the impeller.

3. The apparatus of claim 1, wherein the elongate elements are configured to be substantially resistant to compression and are configured to prevent radial expansion of the impeller by applying tension to the helical elongate elements.

4. The apparatus of claim 1, wherein along at least a portion of the length of the impeller, as the membrane of material transitions from one impeller blade to an adjacent blade, the membrane of material forms a continuous U-shaped surface that is substantially unbroken in the axial structure.

5. The apparatus of claim 4, wherein when viewed from the distal end of the impeller, a pressure side of each of the blades of the impeller configured to pump 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. The pressure side of each of the blades of the impeller configured to extrude blood during operation of the impeller is substantially radially directed in the region of the elongated element within the impeller blade, the apparatus according to claim 5.

7. The helical elongated element is coated with an adhesive configured to strengthen the bond between the helical elongated element and the membrane of the material, the apparatus according to any one of claims 1 to 4.

8. The membrane of the material comprises an elastomeric material, and the adhesive comprises at least two functional groups configured to bind to the helical elongated element and the said elastomeric material respectively, the apparatus according to claim 7.

9. The adhesive comprises a silane compound, the apparatus according to claim 8.

10. The apparatus according to claim 7, further comprising a layer of elastomer disposed between the membrane of the material and the adhesive.

11. The layer of elastomer is configured to round the corners of the helical elongated element, the apparatus according to claim 10.

12. The membrane of the material is made of the elastomer, the apparatus according to claim 10.

13. The elastomer comprises a polycarbonate-based thermoplastic polyurethane, the apparatus according to claim 12.

14. The axial structure comprises a spring, the apparatus according to any one of claims 1 to 4.

15. The spring comprises a tube at an intermediate position along the length of the spring, and the ring is disposed around the tube, the apparatus according to claim 14.

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