FIELD OF EMBODIMENTS OF THE INVENTION

Some applications of the present invention generally relate to medical apparatus. Specifically, some applications of the present invention relate to a ventricular assist device and methods of use thereof.

BACKGROUND

Ventricular assist devices are mechanical circulatory support devices designed to assist and unload cardiac chambers in order to maintain or augment cardiac output. They are used in patients suffering from a failing heart and in patients at risk for deterioration of cardiac function during percutaneous coronary interventions. Most commonly a left-ventricular assist device is applied to a defective heart in order to assist left-ventricular functioning. In some cases, a right-ventricular assist device is used in order to assist right-ventricular functioning. Such assist devices are either designed to be permanently implanted or mounted on a catheter for temporary placement.

SUMMARY OF EMBODIMENTS

In accordance with some applications of the present invention, a ventricular assist device includes an impeller disposed upon an axial shaft, with a frame disposed around the impeller. The ventricular assist device typically includes a tube, which traverses the subject's aortic valve, such that a proximal end of the tube is disposed in the subject's aorta and a distal end of the tube is disposed within the subject's left ventricle. The impeller, the axial shaft and the frame are disposed within a distal portion of the tube inside the subject's left ventricle. Typically, the impeller is configured to pump blood from the left ventricle into the aorta by rotating. The tube typically defines one or more blood inlet openings at the distal end of the tube, via which blood flows into the tube from the left ventricle, during operation of the impeller. For some applications, the proximal portion of the tube defines one or more blood outlet openings, via which blood flows from the tube into the ascending aorta, during operation of the impeller.

For some applications, the impeller includes proximal and distal bushings, and the frame includes proximal and distal bearings. The axial shaft typically passes through the proximal and distal bearings of the frame and the proximal and distal bushings of the impeller. For some applications, (a) the proximal bushing of the impeller is coupled to the axial shaft, such that the proximal bushing is held in an axially-fixed position with respect to the axial shaft, and (b) the distal bushing of the impeller is not coupled to the axial shaft, such that the distal bushing is not held in an axially-fixed position with respect to the axial shaft. Typically, the impeller defines a radially-constrained configuration in which the impeller is introduced into the subject's body and a non-radially-constrained configuration in which the impeller is configured to pump blood within the subject's body. For some applications, the impeller changes from its radially-constrained configuration to its non-radially-constrained configuration by the distal bushing sliding over the axial shaft.

Typically, the axial shaft is not held in an axially-fixed position with respect to the proximal and distal bearings. Further typically, the ventricular assist device (and/or a blood pump portion thereof) does not include any thrust bearing configured to be disposed within the subject's body. For some applications, the ventricular assist device includes one or more thrust bearings that are disposed outside the subject's body, and opposition to thrust generated by the rotation of the impeller is provided solely by the one or more thrust bearings disposed outside the subject's body.

For some applications, a motor drives the impeller to pump blood from the left ventricle to the aorta, by rotating the impeller, and the impeller is configured to undergo axial motion with respect to the frame, in response to the pressure difference between the left ventricle and the aorta changing. For some applications, a computer processor measures an indication of the axial motion of the impeller. For some applications, the computer processor derives the subject's cardiac cycle, the pressure difference between the left ventricle and the aorta, and/or left-ventricular pressure of the subject, based upon the measured indication of the axial motion of the impeller. For some applications, the computer processor changes a rate of rotation of the impeller, at least partially based upon the sensor signal. For example, the computer processor may determine left-ventricular pressure of the subject, at least partially based upon the sensor signal, and may change a rate of rotation of the impeller, at least partially based upon the determined left-ventricular pressure. For some applications, the computer processor reduces the rate of rotation of the impeller, in response to determining that the subject's left-ventricular pressure has decreased. For some applications, the impeller is coupled to a magnet such that axial motion of the impeller causes the magnet to undergo axial motion, and the computer processor measures the indication of the axial motion of the impeller by measuring magnetic flux generated by the magnet.

Typically, a drive cable extends from outside the subject's body to the axial shaft, and is configured to impart rotational motion from the motor to the impeller by rotating, such that the impeller pumps blood from the left ventricle to the aorta by rotating a given direction. For some applications, at least a portion of the drive cable includes a plurality of wires disposed in a coiled configuration that is such that, in response to the drive cable rotating in the given direction of rotation, the plurality of wires disposed in the coiled configuration at least partially unwind, such that the portion of the drive cable shortens axially. For some applications, an outer tube is disposed around the drive cable, and frictional forces between the outer tube and the drive cable are such as to typically generate debris. Alternatively or additionally, a fluid (e.g., a purging fluid) is disposed between the outer tube and the drive cable. For some such applications, at least a portion of the drive cable is configured such that the plurality of wires disposed in the coiled configuration are configured to pump the debris and/or the fluid toward the proximal end of the drive cable.

For some applications, the drive cable includes a first portion configured to be disposed at least partially within an aortic arch of the subject, and a second portion configured to be disposed at least partially within a descending aorta of the subject, and the flexibility of the first portion is greater than the flexibility of the second portion. For example, the first portion of the drive cable may include a first number of wires disposed in a coiled configuration, and the second portion of the drive cable may include a second number of wires disposed in a coiled configuration, and the first number is lower than the second number. For example, the first portion of the drive cable may include between 4 and 8 wires disposed in a coiled configuration, and the second portion of the drive cable may include between 8 and 12 wires disposed in a coiled configuration.

For some applications, the impeller includes at least one helical elongate element (and typically, three helical elongate elements), and a spring that is disposed inside of the helical elongate element, and along an axis around which the helical elongate element winds. Typically, a film of material (e.g., silicone) is supported between the helical elongate element and the spring. For some applications, at least one elongate element (e.g., a string or a wire) extends from the spring to the helical elongate element and is configured to maintain the helical elongate element within a given distance from the spring.

As described hereinabove, for some applications, a frame is disposed around the impeller. For some applications, the ventricular assist device includes a stator that includes a plurality of curved projections that are coupled to a proximal end of the frame. Typically, the curvature of the curved projections opposes the direction of rotation of the impeller. For some applications, the curvature of the curved projections is such that, from distal ends of the curved projections to proximal ends of the curved projections, the curved projections become progressively closer to being parallel with the longitudinal axis of the frame. Typically, the curved projections comprise a plurality of curved struts that are integral with the frame, and a flexible material (e.g., silicone) that extends from the curved struts. For some applications, the flexible material is shaped to define a lumen therethrough.

As described hereinabove, typically the impeller is disposed within a tube (which is sometimes referred to herein as a “blood-pump tube”) that extends from the subject's left ventricle to the subject's aorta. For some applications, at least one blood-pressure-measurement tube, which defines an opening at its distal end, extends to at least an outer surface of the blood-pump tube, such that the opening at the distal end of the blood-pressure-measurement tube is in direct fluid communication with the subject's bloodstream outside the blood-pump tube. A pressure sensor measures pressure of blood within the blood-pressure-measurement tube. For some applications, the blood-pressure-measurement tube is configured to pass along an outer surface of the blood-pump tube from the proximal end of the blood-pump tube until the opening at the distal end of the blood-pressure-measurement tube. Typically, the blood-pressure-measurement tube is a left-ventricular blood-pressure measurement tube that is configured to extend to the outer surface of the blood-pump tube at a location along the blood-pump tube that is configured to be within the subject's left ventricle proximal to the impeller, and the pressure sensor is configured to measure left-ventricular pressure of the subject by measuring pressure of blood within the left-ventricular blood-pressure-measurement tube.

Typically, the blood-pump tube defines one or more blood inlet openings within the distal portion of the blood-pump tube, and one or more blood outlet openings within a proximal portion of the blood-pump tube. For some applications, the ventricular assist device includes a radially-expandable atraumatic distal tip portion configured to be disposed within the subject's left ventricle distally with respect to the one or more blood inlet openings. The distal tip portion is typically configured to be inserted into the left ventricle in a radially-constrained configuration, and to assume a non-radially-constrained configuration within the subject's left ventricle in which at least a radially-expandable portion of the distal tip portion is radially expanded relative to the radially-constrained configuration of the distal tip portion. Typically, in its non-radially-constrained configuration, the radially-expandable portion of the distal tip portion separates the one or more blood inlet openings from inner structures of the left ventricle, such as the interventricular septum, chordae tendineae, papillary muscles, and/or the apex of the left ventricle. Further typically, in its non-radially-constrained configuration, the radially-expandable portion of the distal tip portion separates the one or more blood inlet openings from the inner structures of the left ventricle in three dimensions. For some applications, in its non-radially-constrained configuration, the radially-expandable portion of the distal tip portion directs blood flow from the left ventricle into the one or more blood inlet openings.

For some applications, in the radially-constrained configuration of the distal tip portion, a distal region of the distal tip portion is configured to be least semi-rigid, and is shaped to radially converge along a longitudinal direction toward a distal end of the distal tip portion. Typically, the ventricular assist device is configured to be inserted into the subject's body via a puncture in the subject's body. For some applications, during the insertion of the ventricular assist device, the distal region of the distal tip portion is configured to act as a dilator by dilating the puncture.

In general, in the specification and in the claims of the present application, the term “proximal” and related terms, when used with reference to a device or a portion thereof, should be interpreted to mean an end of the device or the portion thereof that, when inserted into a subject's body, is typically closer to a location through which the device is inserted into the subject's body. The term “distal” and related terms, when used with reference to a device or a portion thereof, should be interpreted to mean an end of the device or the portion thereof that, when inserted into a subject's body, is typically further from the location through which the device is inserted into the subject's body.

The scope of the present invention includes using the apparatus and methods described herein in anatomical locations other than the left ventricle and the aorta. Therefore, the ventricular assist device and/or portions thereof are sometimes referred to herein (in the specification and the claims) as a blood pump.

There is therefore provided, in accordance with some applications of the present invention, apparatus including:a blood pump configured to be placed inside a body of subject, the blood pump including:an impeller including proximal and distal bushings;a frame configured to be disposed around the impeller, the frame including proximal and distal bearings;an axial shaft configured to pass through the proximal and distal bearings of the frame and the proximal and distal bushings of the impeller,the proximal bushing of the impeller being coupled to the axial shaft, such that the proximal bushing is held in an axially-fixed position with respect to the axial shaft, andthe distal bushing of the impeller not being coupled to the axial shaft, such that the distal bushing is not held in an axially-fixed position with respect to the axial shaft, andthe impeller defining a radially-constrained configuration in which the impeller is introduced into the subject's body and a non-radially-constrained configuration in which the impeller is configured to pump blood within the subject's body, the impeller being configured to change from its radially-constrained configuration to its non-radially constrained configuration by the distal bushing sliding over the axial shaft.

In some applications, the impeller is configured to be placed inside a left ventricle of the subject, and to pump blood from the subject's left ventricle to an aorta of the subject. In some applications, the impeller is configured to be placed inside a right ventricle of the subject, and to pump blood from the subject's right ventricle to a pulmonary artery of the subject. In some applications, the impeller is configured to be placed inside a blood vessel of the subject. In some applications, the impeller is configured to be placed inside a cardiac chamber of the subject.

In some applications, the impeller includes:at least one helical elongate element that extends from the proximal bushing to the distal bushing;a spring that is disposed inside of the helical elongate element, and along an axis around which the helical elongate element winds;a film of material supported between the helical elongate element and the spring; andat least one flexible elongate element extending from the spring to the helical elongate element and configured to maintain the helical elongate element within a given distance from the spring, the at least one flexible elongate element being selected from the group consisting of: a string and a wire.

In some applications, the apparatus further includes a delivery catheter,the delivery catheter is configured to maintain the impeller in its radially-constrained configuration during introduction of the impeller into the subject's body,upon the impeller being released from the delivery catheter, the impeller is configured to self-expand to thereby cause the distal bushing to slide over the axial shaft proximally, such that the impeller assumes its non-radially-constrained configuration, andin order to retract the impeller from the subject's body, the delivery catheter is configured to cause the impeller to assume its radially-constrained configuration by a distal end of the delivery catheter and the impeller being moved with respect to one another such that the distal end of the delivery catheter causes the distal bushing to slide over the axial shaft distally.

There is further provided, in accordance with some applications of the present invention, apparatus including:a ventricular assist device including:an impeller configured to be placed inside a left ventricle of a subject;a frame configured to be disposed around the impeller; anda motor configured to drive the impeller to pump blood from the left ventricle to an aorta of the subject, by rotating the impeller,the impeller being configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the left ventricle and the aorta.

In some applications:the impeller includes proximal and distal bushings;the frame includes proximal and distal bearings; andthe ventricular assist device further includes an axial shaft configured to pass through the proximal and distal bearings defined by the frame and the proximal and distal bushings of the impeller, the axial shaft:being coupled to at least one of the proximal and distal bushings of the impeller, such that the at least one bushing is held in an axially-fixed position with respect to the axial shaft, andnot being held in an axially-fixed position with respect to the proximal and distal bearings.

In some applications, the ventricular assist device does not include any thrust bearing configured to be disposed within a body of the subject.

In some applications, the ventricular assist device further includes one or more thrust bearings configured to be disposed outside a body of the subject, and wherein opposition to thrust generated by the rotation of the impeller is provided solely by the one or more thrust bearings disposed outside the subject's body.

In some applications,the motor is configured to drive the impeller to pump blood from the subject's left ventricle to the subject's aorta, by rotating the impeller in a given direction of rotation; andthe ventricular assist device further includes:an axial shaft, the impeller being disposed on the axial shaft; anda drive cable configured to extend from outside a body of the subject to the axial shaft, the drive cable being configured to impart rotational motion from the motor to the impeller by rotating, at least a portion of the drive cable including a plurality of wires disposed in a coiled configuration that is such that, in response to the drive cable rotating in the given direction of rotation, the plurality of wires disposed in the coiled configuration at least partially unwind, such that the portion of the drive cable shortens axially.

In some applications, the apparatus further includes:a sensor configured to detect an indication of axial motion of the impeller, and to generate a sensor signal in response thereto; anda computer processor configured to receive the sensor signal and to generate an output in response thereto.

In some applications, the computer processor is configured to generate an output indicating a cardiac cycle of the subject, in response to receiving the sensor signal. In some applications, the computer processor is configured to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal. In some applications, the computer processor is configured to change a rate of rotation of the impeller, at least partially based upon the sensor signal.

In some applications, the computer processor is configured:to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal, andto change a rate of rotation of the impeller, at least partially based upon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce the rate of rotation of the impeller, in response to determining that the subject's left-ventricular pressure has decreased.

In some applications, the apparatus further includes:a magnet, the impeller being coupled to the magnet such that axial motion of the impeller causes the magnet to undergo axial motion;a sensor configured to detect magnetic flux generated by the magnet, and to generate a sensor signal in response thereto; anda computer processor configured to receive the sensor signal and to generate an output in response thereto.

In some applications, the computer processor is configured to generate an output indicating a cardiac cycle of the subject, in response to receiving the sensor signal. In some applications, the computer processor is configured to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal. In some applications, the computer processor is configured to change a rate of rotation of the impeller, at least partially based upon the sensor signal.

In some applications, the computer processor is configured:to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal, andto change a rate of rotation of the impeller, at least partially based upon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce the rate of rotation of the impeller, in response to determining that the subject's left-ventricular pressure has decreased.

In some applications:the impeller includes proximal and distal bushings;the frame includes proximal and distal bearings;the ventricular assist device further includes an axial shaft configured to pass throughthe proximal and distal bearings of the frame and the proximal and distal bushings of the impeller;the impeller is coupled to the axial shaft such that the impeller causes the axial shaft to undergo axial back-and-forth motion with respect to the proximal and distal bearings of the frame.

In some applications, the axial shaft is configured to clean interfaces between the axial shaft and the proximal and distal bearings of the frame, by undergoing the axial back-and-forth motion with respect to the proximal and distal bearings of the frame. In some applications, the axial shaft is configured to reduce a build-up of heat at interfaces between the axial shaft and the proximal and distal bearings of the frame, by undergoing the axial back-and-forth motion with respect to the proximal and distal bearings of the frame, relative to if the axial shaft did not undergo the axial back-and-forth motion with respect to the proximal and distal bearings of the frame.

There is further provided, in accordance with some applications of the present invention, apparatus including:a blood pump including:an impeller including proximal and distal bushings, and configured to pump blood through the subject's body;a frame configured to be disposed around the impeller, the frame including proximal and distal bearings;an axial shaft configured to pass through the proximal and distal bearings of the frame and the proximal and distal bushings of the impeller, the axial shaft:being coupled to at least one of the proximal and distal bushings of the impeller, such that the at least one bushing is held in an axially-fixed position with respect to the axial shaft, andnot being held in an axially-fixed position with respect to the proximal and distal bearings.

In some applications, the blood pump does not include any thrust bearing configured to be disposed within the subject's body. In some applications, wherein the blood pump further includes one or more thrust bearings configured to be disposed outside the subject's body, and wherein opposition to thrust generated by the rotation of the impeller is provided solely by the one or more thrust bearings disposed outside the subject's body.

In some applications, the apparatus further includes:a sensor configured to detect an indication of axial motion of the impeller, and to generate a sensor signal in response thereto; anda computer processor configured to receive the sensor signal and to generate an output in response thereto.

In some applications, the computer processor is configured to generate an output indicating a cardiac cycle of the subject, in response to receiving the sensor signal. In some applications, the computer processor is configured to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal. In some applications, the computer processor is configured to change a rate of rotation of the impeller, at least partially based upon the sensor signal.

In some applications, the computer processor is configured:to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal, andto change a rate of rotation of the impeller, at least partially based upon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce the rate of rotation of the impeller, in response to determining that the subject's left-ventricular pressure has decreased.

In some applications, the apparatus further includes:a magnet, the impeller being coupled to the magnet such that axial motion of the impeller causes the magnet to undergo axial motion;a sensor configured to detect magnetic flux generated by the magnet, and to generate a sensor signal in response thereto; anda computer processor configured to receive the sensor signal and to generate an output in response thereto.

In some applications, the computer processor is configured to generate an output indicating a cardiac cycle of the subject, in response to receiving the sensor signal. In some applications, the computer processor is configured to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal. In some applications, the computer processor is configured to change a rate of rotation of the impeller, at least partially based upon the sensor signal.

In some applications, the computer processor is configured:to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal, andto change a rate of rotation of the impeller, at least partially based upon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce the rate of rotation of the impeller, in response to determining that the subject's left-ventricular pressure has decreased.

In some applications, the impeller is configured to pump blood from a first location within the subject's body to a second location within the subject's body, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the first location and the second location. In some applications, the impeller is configured to pump blood from a left ventricle of the subject to an aorta of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the left ventricle and the aorta. In some applications, the impeller is configured to pump blood from a right ventricle of the subject to a pulmonary artery of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the right ventricle and the pulmonary artery. In some applications, the impeller is configured to pump blood from a right atrium of the subject to a right ventricle of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the right atrium and the right ventricle. In some applications, the impeller is configured to pump blood from a vena cava of the subject to a right ventricle of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the vena cava and the right ventricle. In some applications, the impeller is configured to pump blood from a right atrium of the subject to a pulmonary artery of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the right atrium and the pulmonary artery. In some applications, the impeller is configured to pump blood from a vena cava of the subject to a pulmonary artery of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the vena cava and the pulmonary artery.

In some applications, the apparatus further includes:a motor configured to drive the impeller to pump blood through the subject's body, by rotating the impeller in a given direction of rotation; anda drive cable configured to extend from outside a body of the subject to the axial shaft, the drive cable being configured to impart rotational motion from the motor to the impeller by rotating, at least a portion of the drive cable including a plurality of wires disposed in a coiled configuration that is such that, in response to the drive cable rotating in the given direction of rotation, the plurality of wires disposed in the coiled configuration at least partially unwind, such that the portion of the drive cable shortens axially.

In some applications, the impeller is coupled to the axial shaft such that the impeller causes the axial shaft to undergo axial back-and-forth motion with respect to the proximal and distal bearings of the frame. In some applications, the axial shaft is configured to clean interfaces between the axial shaft and the proximal and distal bearings of the frame, by undergoing the axial back-and-forth motion with respect to the proximal and distal bearings of the frame. In some applications, the axial shaft is configured to reduce a build-up of heat at interfaces between the axial shaft and the proximal and distal bearings of the frame, by undergoing the axial back-and-forth motion with respect to the proximal and distal bearings of the frame, relative to if the axial shaft did not undergo the axial back-and-forth motion with respect to the proximal and distal bearings of the frame.

There is further provided, in accordance with some applications of the present invention, apparatus including:a blood pump including:an impeller configured to be placed inside a body of a subject, and configured to pump blood through the subject's body;a frame configured to be disposed around the impeller,the blood pump not including any thrust bearing configured to be disposed within the subject's body.

In some applications, the blood pump further includes one or more thrust bearings configured to be disposed outside the subject's body, and opposition to thrust generated by the rotation of the impeller is provided solely by the one or more thrust bearings disposed outside the subject's body.

In some applications, the apparatus further includes:a sensor configured to detect an indication of axial motion of the impeller, and to generate a sensor signal in response thereto; anda computer processor configured to receive the sensor signal and to generate an output in response thereto.

In some applications, the computer processor is configured to generate an output indicating a cardiac cycle of the subject, in response to receiving the sensor signal. In some applications, the computer processor is configured to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal. In some applications, the computer processor is configured to change a rate of rotation of the impeller, at least partially based upon the sensor signal.

In some applications, the computer processor is configured:to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal, andto change a rate of rotation of the impeller, at least partially based upon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce the rate of rotation of the impeller, in response to determining that the subject's left-ventricular pressure has decreased.

In some applications, the apparatus further includes:a magnet, the impeller being coupled to the magnet such that axial motion of the impeller causes the magnet to undergo axial motion;a sensor configured to detect magnetic flux generated by the magnet, and to generate a sensor signal in response thereto; anda computer processor configured to receive the sensor signal and to generate an output in response thereto.

In some applications, the computer processor is configured to generate an output indicating a cardiac cycle of the subject, in response to receiving the sensor signal. In some applications, the computer processor is configured to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal. In some applications, the computer processor is configured to change a rate of rotation of the impeller, at least partially based upon the sensor signal.

In some applications, the computer processor is configured:to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal, andto change a rate of rotation of the impeller, at least partially based upon the determined left-ventricular pressure.

In some applications, the computer processor is configured to reduce the rate of rotation of the impeller, in response to determining that the subject's left-ventricular pressure has decreased.

In some applications, the impeller is configured to pump blood from a first location within the subject's body to a second location within the subject's body, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the first location and the second location. In some applications, the impeller is configured to pump blood from a left ventricle of the subject to an aorta of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the left ventricle and the aorta. In some applications, the impeller is configured to pump blood from a right ventricle of the subject to a pulmonary artery of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the right ventricle and the pulmonary artery. In some applications, the impeller is configured to pump blood from a right atrium of the subject to a right ventricle of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the right atrium and the right ventricle. In some applications, the impeller is configured to pump blood from a vena cava of the subject to a right ventricle of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the vena cava and the right ventricle. In some applications, the impeller is configured to pump blood from a right atrium of the subject to a pulmonary artery of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the right atrium and the pulmonary artery. In some applications, the impeller is configured to pump blood from a vena cava of the subject to a pulmonary artery of the subject, and the impeller is configured to undergo axial back-and-forth motion with respect to the frame, in response to cyclical changes in a pressure difference between the vena cava and the pulmonary artery.

In some applications, the apparatus further includes:a motor configured to drive the impeller to pump blood through the subject's body, by rotating the impeller in a given direction of rotation;an axial shaft, the impeller being coupled to the axial shaft; anda drive cable configured to extend from outside a body of the subject to the axial shaft, the drive cable being configured to impart rotational motion from the motor to the impeller by rotating, at least a portion of the drive cable including a plurality of wires disposed in a coiled configuration that is such that, in response to the drive cable rotating in the given direction of rotation, the plurality of wires disposed in the coiled configuration at least partially unwind, such that the portion of the drive cable shortens axially.

In some applications:the impeller includes proximal and distal bushings;the frame includes proximal and distal bearings;the apparatus further includes an axial shaft that:passes through the proximal and distal bearings defined by the frame and the proximal and distal bushings of the impeller,is coupled to at least one of the proximal and distal bushings of the impeller, such that the at least one bushing is held in an axially-fixed position with respect to the axial shaft,is not held in an axially-fixed position with respect to the proximal and distal bearings,such that the impeller causes the axial shaft to undergo axial back-and-forth motion with respect to the proximal and distal bearings of the frame.

In some applications, the axial shaft is configured to clean interfaces between the axial shaft and the proximal and distal bearings of the frame, by undergoing the axial back-and-forth motion with respect to the proximal and distal bearings of the frame. In some applications, the axial shaft is configured to reduce a build-up of heat at interfaces between the axial shaft and the proximal and distal bearings of the frame, by undergoing the axial back-and-forth motion with respect to the proximal and distal bearings of the frame, relative to if the axial shaft did not undergo the axial back-and-forth motion with respect to the proximal and distal bearings of the frame.

There is further provided, in accordance with some applications of the present invention, the following inventive concepts:Inventive concept 1. Apparatus comprising:an impeller comprising:at least one helical elongate element;a spring that is disposed inside of the helical elongate element, and along an axis around which the helical elongate element winds;a film of material supported between the helical elongate element and the spring; andat least one flexible elongate element extending from the spring to the helical elongate element and configured to maintain the helical elongate element within a given distance from the spring, the at least one flexible elongate element being selected from the group consisting of: a string and a wire.Inventive concept 2. The apparatus according to inventive concept 1, wherein the impeller is configured such that in a non-radially-constrained configuration of the impeller, an outer diameter of the impeller at a location at which the outer diameter is at its maximum is less than 8 mmInventive concept 3. The apparatus according to inventive concept 1, wherein the at least one helical elongate element comprises a plurality of helical elongate elements, and wherein the at least one flexible elongate element extends from the spring to each of the helical elongate elements.Inventive concept 4. The apparatus according to any one of inventive concepts 1-3, wherein the impeller is configured to pump blood through a body of a subject.Inventive concept 5. The apparatus according to inventive concept 4, wherein the impeller is configured to be placed in a blood vessel of the subject.Inventive concept 6. The apparatus according to inventive concept 4, wherein the impeller is configured to be placed in a cardiac chamber of the subject.Inventive concept 7. The apparatus according to inventive concept 4, wherein the impeller is configured to pump blood from a left ventricle of a subject to an aorta of the subject.Inventive concept 8. The apparatus according to inventive concept 4, wherein the impeller is configured to pump blood from a right ventricle of a subject to a pulmonary artery of the subject.Inventive concept 9. A method comprising:placing into a body of a subject an impeller that includes:at least one helical elongate element;a spring that is disposed inside of the helical elongate element, and along an axis around which the helical elongate element winds;a film of material supported between the helical elongate element and the spring; andat least one flexible elongate element extending from the spring to the helical elongate element selected from the group consisting of: a string and a wire; andpumping blood through the subject's body by rotating the impeller, the flexible elongate element maintaining the helical elongate element within a given distance from the spring, during the rotation of the impeller.Inventive concept 10. Apparatus comprising:a blood pump comprising:an impeller configured to be placed inside a cardiac chamber of a subject;a frame configured to be disposed around the impeller; anda motor configured to drive the impeller to pump blood from the cardiac chamber to a blood vessel of the subject, by rotating the impeller,the impeller being configured to undergo axial motion with respect to the frame, in response to cyclical changes in a pressure difference between the cardiac chamber and the blood vessel.Inventive concept 11. A method comprising:placing an impeller of a blood pump inside a cardiac chamber of a subject, with a frame disposed around the impeller; anddriving the impeller to pump blood from the cardiac chamber to a blood vessel of the subject, by rotating the impeller,placement of the impeller inside the cardiac chamber being such that the impeller is allowed to undergo axial motion with respect to the frame, in response to cyclical changes in a pressure difference between the cardiac chamber and the blood vessel.Inventive concept 12. Apparatus comprising:a blood pump comprising:an impeller configured to be placed inside a first blood vessel of a subject;a frame configured to be disposed around the impeller; anda motor configured to drive the impeller to pump blood from the first blood vessel to a second blood vessel of the subject, by rotating the impeller,the impeller being configured to undergo axial motion with respect to the frame, in response to cyclical changes in a pressure difference between the first blood vessel and the second blood vessel.Inventive concept 13. A method comprising:placing an impeller of a blood pump inside a first blood vessel of a subject, with a frame disposed around the impeller; anddriving the impeller to pump blood from the first blood vessel to a second blood vessel of the subject, by rotating the impeller,placement of the impeller inside the first blood vessel being such that the impeller is allowed to undergo axial motion with respect to the frame, in response to cyclical changes in a pressure difference between the cardiac chamber and the blood vessel.Inventive concept 14. Apparatus comprising:a blood pump comprising:an impeller configured to be placed inside a body of a subject, and configured to rotate such as to pump blood through the subject's body;a frame configured to be disposed around the impeller; andone or more thrust bearings configured to be disposed outside the subject's body, wherein opposition to thrust generated by the rotation of the impeller is provided solely by the one or more thrust bearings disposed outside the subject's body.Inventive concept 15. A method comprising:placing an impeller of a blood pump inside a body of a subject, with a frame disposed around the impeller; anddriving the impeller to pump blood through the subject's body, by rotating the impeller, opposition to thrust generated by the rotation of the impeller being provided solely by one or more thrust bearings disposed outside the subject's body.Inventive concept 16. Apparatus comprising:a blood-pump tube;a blood pump configured to be disposed within the blood-pump tube, and to pump blood through the blood-pump tube;at least one blood-pressure-measurement tube that defines an opening at a distal end thereof, and that is configured to extend to at least an outer surface of the blood-pump tube, such that the opening at the distal end of the blood-pressure-measurement tube is in direct fluid communication with a bloodstream of the subject outside the blood-pump tube; andat least one pressure sensor configured to measure pressure of the bloodstream of the subject outside the blood-pump tube by measuring pressure of blood within the blood-pressure-measurement tube.Inventive concept 17. The apparatus according to inventive concept 16, wherein the blood pump comprises an impeller that is configured to pump blood through the blood-pump tube, by rotating.Inventive concept 18. The apparatus according to inventive concept 16, wherein the blood-pressure-measurement tube is configured to pass along an outer surface of the blood-pump tube from the proximal end of the blood-pump tube until the opening at the distal end of the blood-pressure-measurement tube.Inventive concept 19. The apparatus according to inventive concept 16, further comprising at least one computer processor that is configured to receive an indication of the blood pressure measured within the blood-pressure-measurement tube and to control the pumping of blood by the blood pump in response to the blood pressure measured within the blood-pump tube.Inventive concept 20. The apparatus according to any one of inventive concepts 16-19, wherein the at least one blood-pressure measurement tube comprises at least one left-ventricular blood-pressure measurement tube that is configured to extend to the outer surface of the blood-pump tube at a location along the tube that is configured to be within the subject's left ventricle proximal to the blood pump, and wherein the pressure sensor is configured to measure left-ventricular pressure of the subject by measuring pressure of blood within the left-ventricular blood-pressure-measurement tube.Inventive concept 21. The apparatus according to inventive concept 20, wherein the at least one blood-pressure measurement tube comprises two or more left-ventricular blood-pressure measurement tubes that are configured to extend to the outer surface of the blood-pump tube at locations along the blood-pump tube that are configured to be within the subject's left ventricle proximal to the blood pump, and wherein the at least one pressure sensor is configured to measure left-ventricular pressure of the subject by measuring pressure of blood within at least one of the left-ventricular blood-pressure-measurement tubes.Inventive concept 22. The apparatus according to inventive concept 21,wherein the at least one pressure sensor is configured to measure pressure of blood within each of the two or more left-ventricular blood-pressure-measurement tubes,the apparatus further comprising at least one computer processor that is configured:to receive an indication of the blood pressure measured within each of the two or more left-ventricular blood-pressure-measurement tubes,in response thereto, to determine that the opening of one of the two or more left-ventricular blood-pressure-measurement tubes is occluded, andin response thereto, to determine left-ventricular pressure of the subject, based upon the blood pressure measured within a different one of the two or more left-ventricular blood-pressure-measurement tubes.Inventive concept 23. The apparatus according to inventive concept 20, wherein the at least one blood-pressure measurement tube further comprises at least one aortic blood-pressure measurement tube that is configured to extend to the outer surface of the blood-pump tube at a location along the blood-pump tube that is configured to be within the subject's aorta, and wherein the pressure sensor is configured to measure aortic pressure of the subject by measuring pressure of blood within the aortic blood-pressure-measurement tube.Inventive concept 24. The apparatus according to inventive concept 23, wherein the at least one aortic blood-pressure measurement tube comprises two or more aortic blood-pressure measurement tubes that are configured to extend to the outer surface of the blood-pump tube at locations along the blood-pump tube that are configured to be within the subject's aorta, and wherein the at least one pressure sensor is configured to measure aortic pressure of the subject by measuring pressure of blood within at least one of the aortic blood-pressure-measurement tubes.Inventive concept 25. The apparatus according to any one of inventive concepts 16-19, wherein the at least one blood-pressure measurement tube comprises at least one aortic blood-pressure measurement tube that is configured to extend to the outer surface of the blood-pump tube at a location along the blood-pump tube that is configured to be within the subject's aorta, and wherein the pressure sensor is configured to measure aortic pressure of the subject by measuring pressure of blood within the aortic blood-pressure-measurement tube.Inventive concept 26. The apparatus according to inventive concept 25, wherein the at least one aortic blood-pressure measurement tube comprises two or more aortic blood-pressure measurement tubes that are configured to extend to the outer surface of the blood-pump tube at locations along the blood-pump tube that are configured to be within the subject's aorta, and wherein the at least one pressure sensor is configured to measure aortic pressure of the subject by measuring pressure of blood within at least one of the aortic blood-pressure-measurement tubes.Inventive concept 27. The apparatus according to inventive concept 26,wherein the at least one pressure sensor is configured to measure pressure of blood within each of the two or more aortic blood-pressure-measurement tubes,the apparatus further comprising at least one computer processor that is configured:to receive an indication of the blood pressure measured within each of the two or more aortic blood-pressure-measurement tubes,in response thereto, to determine that the opening of one of the two or more aortic blood-pressure-measurement tubes is occluded, andin response thereto, to determine aortic pressure of the subject, based upon the blood pressure measured within a different one of the two or more aortic blood-pressure-measurement tubes.Inventive concept 28. The apparatus according to any one of inventive concepts 16-19, wherein the blood-pressure-measurement tube is configured to extend from outside a body of the subject to the opening at the distal end, and wherein the at least one pressure sensor is configured to be disposed outside the subject's body.Inventive concept 29. The apparatus according to inventive concept 28, wherein the blood pump comprises an impeller disposed upon an axial shaft, the impeller being configured to pump blood from the left ventricle to the aorta by rotating, wherein the apparatus further comprises:a motor disposed outside the subject's body, and configured to drive the impeller to rotate;a drive cable extending from outside the subject's body to the axial shaft, and configured to impart rotational motion from the motor to the impeller, by rotating; andan outer tube configured to extend from outside the subject's body to within the blood-pump tube,wherein the drive cable and the blood-pressure-measurement tube are configured to be disposed within the outer tube.Inventive concept 30. The apparatus according to inventive concept 29,wherein the at least one blood-pressure measurement tube comprises at least one left-ventricular blood-pressure measurement tube that is configured to extend to the outer surface of the blood-pump tube at a location along the blood-pump tube that is configured to be within the subject's left ventricle proximal to the blood pump, and wherein the at least one pressure sensor is configured to measure left-ventricular pressure of the subject by measuring pressure of blood within the left-ventricular blood-pressure-measurement tube;the apparatus further comprising an aortic blood-pressure-measurement tube that defines an opening at a distal end thereof, and that is configured to extend from outside the subject's body to an outer surface of the outer tube within an aorta of the subject, such that the opening at the distal end of the blood-pressure-measurement tube is in direct fluid communication with an aortic bloodstream of the subject;wherein the at least one pressure sensor is further configured to measure aortic pressure of the subject by measuring pressure of blood within the aortic blood-pressure-measurement tube.Inventive concept 31. The apparatus according to inventive concept 29,wherein the at least one blood-pressure measurement tube comprises at least one left-ventricular blood-pressure measurement tube that is configured to extend to the outer surface of the blood-pump tube at a location along the blood-pump tube that is configured to be within the subject's left ventricle proximal to the blood pump, and wherein the at least one pressure sensor is configured to measure left-ventricular pressure of the subject by measuring pressure of blood within the left-ventricular blood-pressure-measurement tube;the apparatus further comprising an aortic blood-pressure-measurement tube that defines an opening at a distal end thereof, and that is configured to extend from outside the subject's body to a portion of an outer surface of the outer tube that is disposed within the blood-pump tube, such that the opening at the distal end of the blood-pressure-measurement tube is in direct fluid communication with an aortic bloodstream of the subject;wherein the at least one pressure sensor is further configured to measure aortic pressure of the subject by measuring pressure of blood within the aortic blood-pressure-measurement tube.Inventive concept 32. The apparatus according to inventive concept 29, wherein the outer tube defines a groove in a portion of an outer surface of the outer tube that is configured to be disposed within the blood-pump tube, and wherein, during insertion of the ventricular assist device into the subject's body, a portion of the blood-pressure-measurement tube that is configured to extend from within the blood-pump tube to the outer surface of the blood-pump tube is configured to be disposed within the groove, such that the portion of the blood-pressure-measurement tube does not protrude from the outer surface of the outer tube.Inventive concept 33. The apparatus according to inventive concept 28, wherein a diameter of the blood-pressure-measurement tube at least within a distal portion of the blood-pressure-measurement tube is less than 0.5 mmInventive concept 34. The apparatus according to inventive concept 33, wherein the diameter of the blood-pressure-measurement tube at least within the distal portion of the blood-pressure-measurement tube is more than 0.2 mmInventive concept 35. A method comprising:placing into a body of a subject:a blood-pump tube,a blood pump disposed within the blood-pump tube, andat least one blood-pressure-measurement tube that defines an opening at a distal end thereof, and that extends to at least an outer surface of the blood-pump tube, such that the opening at the distal end of the blood-pressure-measurement tube is in direct fluid communication with a bloodstream of the subject outside the blood-pump tube;pumping blood through the blood-pump tube, using the blood pump; andmeasuring pressure of the bloodstream of the subject outside the blood-pump tube by measuring pressure of blood within the blood-pressure-measurement tube.Inventive concept 36. Apparatus comprising:a blood pump comprising:a tube;an impeller configured to be disposed within the tube and configured to rotate, such as to pump blood through the tube;a frame disposed around the impeller; anda stator configured to reduce rotational flow components from blood flow generated by rotation of the impeller, the stator comprising:a plurality of struts that are integral with the frame and that are curved; anda flexible material coupled to the curved struts such as to form a plurality of curved projections.Inventive concept 37. The apparatus according to inventive concept 36, wherein the curvature of the curved projections opposes the direction of rotation of the impeller.Inventive concept 38. The apparatus according to inventive concept 36, wherein the curvature of the curved projections is such that, from distal ends of the curved projections to proximal ends of the curved projections, the curved projections become progressively closer to being parallel with a longitudinal axis of the frame.Inventive concept 39. The apparatus according to inventive concept 36, wherein the flexible material is shaped to define a lumen therethrough.Inventive concept 40. A method comprising:placing a blood pump into a subject's body, the blood pump including:a tube,an impeller configured to be disposed within the tube,a frame disposed around the impeller, anda stator that includes a plurality of struts that are integral with the frame and that are curved, and a flexible material coupled to the curved struts such as to form a plurality of curved projections; andpumping blood through the tube using the impeller, the stator reducing rotational flow components from blood flow generated by rotation of the impeller.Inventive concept 41. Apparatus comprising:a ventricular assist device comprising:an axial shaft;an impeller disposed on the axial shaft and configured to be placed in a left ventricle of a subject;a motor configured to be disposed outside a body of the subject, and configured to drive the impeller to pump blood from the left ventricle to an aorta of the subject by rotating the impeller;a drive cable configured to extend from outside the subject's body to the axial shaft, the drive cable being configured to impart rotational motion from the motor to the impeller by rotating, the drive cable comprising a first portion configured to be disposed at least partially within an aortic arch of the subject, and a second portion configured to be disposed at least partially within a descending aorta of the subject,the first portion of the drive cable comprising a first number of wires disposed in a coiled configuration, and the second portion of the drive cable comprising a second number of wires disposed in a coiled configuration, the first number being lower than the second number.Inventive concept 42. The apparatus according to inventive concept 41, wherein a length of the first portion of the drive cable is between 20 cm and 40 cm.Inventive concept 43. The apparatus according to inventive concept 41, wherein a length of the second portion of the drive cable is between 60 cm and 100 cm.Inventive concept 44. The apparatus according to inventive concept 41, wherein the first portion of the drive cable comprises between 4 and 8 wires disposed in the coiled configuration, and the second portion of the drive cable comprises between 8 and 12 wires disposed in the coiled configuration.Inventive concept 45. Apparatus comprising:a blood pump comprising:an axial shaft;an impeller disposed on the axial shaft;a motor configured to be disposed outside a body of the subject, and configured to drive the impeller to pump blood through the subject's body by rotating the impeller;a drive cable configured to extend from outside the subject's body to the axial shaft, the drive cable being configured to impart rotational motion from the motor to the impeller by rotating, the drive cable comprising a first portion configured to be disposed at least partially within a curved portion of vasculature of the subject, and a second portion configured to be disposed at least partially within a straight portion of vasculature of the subject,the first portion of the drive cable comprising a first number of wires disposed in a coiled configuration, and the second portion of the drive cable comprising a second number of wires disposed in a coiled configuration, the first number being lower than the second number.Inventive concept 46. Apparatus comprising:a blood pump comprising:an axial shaft;an impeller disposed on the axial shaft;a motor configured to be disposed outside a body of the subject, and 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 direction of rotation;a drive cable configured to extend from outside the subject's body to the axial shaft, the drive cable being configured to impart rotational motion from the motor to the impeller by rotating,at least a portion of the drive cable comprising a plurality of wires disposed in a coiled configuration that is such that, in response to the drive cable rotating in the given direction of rotation, the plurality of wires disposed in the coiled configuration at least partially unwind, such that the portion of the drive cable shortens axially.Inventive concept 47. The apparatus according to inventive concept 46, wherein the impeller is configured to pump blood from a first location to a second location, and wherein the impeller is configured to undergo axial back-and-forth motion, in response to cyclical changes in a pressure difference between the first location and the second location.Inventive concept 48. A method comprising:placing a blood pump into a body of a subject, the blood pump including:an axial shaft,an impeller disposed on the axial shaft, anda drive cable extending from outside the subject's body to the axial shaft; anddriving the impeller to pump blood from a distal end of the impeller to a proximal end of the impeller by imparting rotational motion the impeller via the drive cable, at least a portion of the drive cable comprising a plurality of wires disposed in a coiled configuration that is such that, in response to the drive cable rotating in the given direction of rotation, the plurality of wires disposed in the coiled configuration at least partially unwind, such that the portion of the drive cable shortens axially.Inventive concept 49. Apparatus comprising:a blood pump comprising:an axial shaft;an impeller disposed on the axial shaft;a motor configured to be disposed outside a body of the subject, and configured to drive the impeller to pump blood in a proximal direction by rotating the impeller in a given direction of rotation;a drive cable configured to extend a proximal end of the drive cable disposed outside the subject's body to a distal end of the drive cable, which is coupled to the axial shaft, the drive cable being configured to impart rotational motion from the motor to the impeller by rotating;an outer tube disposed around the drive cable; andfluid disposed between the outer tube and the drive cable,at least a portion of the drive cable comprising a plurality of wires disposed in a coiled configuration that is such that in response to the drive cable rotating in the given direction of rotation, the plurality of wires are configured to pump the fluid toward the proximal end of the drive cable.Inventive concept 50. A method comprising:placing a blood pump into a body of a subject, the blood pump including:an axial shaft,an impeller disposed on the axial shaft,a drive cable extending from outside the subject's body to the axial shaft,an outer tube disposed around the drive cable, anda fluid disposed between the drive cable and the outer tube; anddriving the impeller to pump blood from a distal end of the impeller to a proximal end of the impeller by imparting rotational motion the impeller via the drive cable, at least a portion of the drive cable comprising a plurality of wires disposed in a coiled configuration that is such that, in response to the drive cable rotating in the given direction of rotation, the plurality of wires are configured to pump the fluid toward the proximal end of the drive cable.Inventive concept 51. Apparatus comprising:a blood pump comprising:an impeller;a motor configured to drive the impeller to pump blood by rotating the impeller, the impeller being configured to undergo axial motion, in response to changes in a pressure difference against which the impeller is pumping the blood;a magnet, the impeller being coupled to the magnet such that axial motion of the impeller causes the magnet to undergo axial motion;a sensor configured to detect magnetic flux generated by the magnet, and to generate a sensor signal in response thereto; anda computer processor configured to receive the sensor signal and to generate an output in response thereto.Inventive concept 52. The apparatus according to inventive concept 51, wherein the computer processor is configured to generate an output indicating a cardiac cycle of the subject, in response to receiving the sensor signal.Inventive concept 53. The apparatus according to inventive concept 51, wherein the computer processor is configured to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal.Inventive concept 54. The apparatus according to any one of inventive concepts 51-53, wherein the computer processor is configured to change a rate of rotation of the impeller, at least partially based upon the sensor signal.Inventive concept 55. The apparatus according to inventive concept 54, wherein the computer processor is configured:to determine left-ventricular pressure of the subject, at least partially based upon the sensor signal, and

to change a rate of rotation of the impeller, at least partially based upon the determined left-ventricular pressure.Inventive concept 56. The apparatus according to inventive concept 55, wherein the computer processor is configured to reduce the rate of rotation of the impeller, in response to determining that the subject's left-ventricular pressure has decreased.Inventive concept 57. Apparatus comprising:a blood pump comprising:an impeller;a motor configured to drive the impeller to pump blood by rotating the impeller, the impeller being configured to undergo axial motion, in response to changes in a pressure difference against which the impeller is pumping the blood;a sensor configured to detect an indication of the axial motion of the impeller, and to generate a sensor signal in response thereto; anda computer processor configured to receive the sensor signal and to generate an output in response thereto.Inventive concept 58. A method comprising:placing a blood pump inside a body of a subject, the blood pump including an impeller;driving the impeller to pump blood by rotating the impeller, the impeller being configured to undergo axial motion, in response to changes in a pressure difference against which the impeller is pumping the blood;detecting an indication of the axial motion of the impeller, and generating a sensor signal in response thereto; andreceiving the sensor signal, and generating an output in response thereto.Inventive concept 59. Apparatus comprising:a blood pump comprising:an impeller;a frame,the impeller and the frame being configured to be inserted into a body of a subject, such that, within the subject's body, the frame is disposed aroundthe impeller; anda computer processor configured to drive a motor unit to, simultaneously, (a) drive the impeller to pump blood through the subject's body, by driving the impeller to rotate, and (b) drive the impeller to move axially within the frame in a back-and-forth motion.Inventive concept 60. A method comprising:placing, into a body of a subject, a blood pump that includes an impeller and a frame, such that the frame is disposed around the impeller; andsimultaneously:driving the impeller to pump blood through the subject's body, by driving the impeller to rotate; anddriving the impeller to move axially within the frame in a back-and-forth motion.Inventive concept 61. Apparatus comprising:a blood pump comprising:an axial shaft;an impeller disposed on the axial shaft and configured to be placed in a left ventricle of a subject;a motor configured to be disposed outside a body of the subject, and configured to drive the impeller to rotate;a drive cable configured to extend from outside of the subject's body to the axial shaft, via an aortic arch of the subject, the drive cable being configured to impart rotational motion from the motor to the impeller, by rotating;a tube, within which the drive cable is configured to be disposed during rotation of the drive cable, the tube being configured to remain stationary during rotation of the drive cable; anda plurality of ball bearings configured to be disposed between the drive cable and the tube, such as to reduce friction between the drive cable and the tube during movement of the drive cable with respect to the tube.Inventive concept 62. The apparatus according to inventive concept 61, wherein the ball bearings are configured to be disposed between the drive cable and the tube, at least at portions of the drive cable and the tube that are configured to be disposed within the subject's aortic arch, during the rotation of the impeller.Inventive concept 63. Apparatus comprising:a blood pump comprising:an axial shaft;an impeller disposed on the axial shaft and configured to be placed inside abody of a subject;a motor configured to be disposed outside the subject's body;a drive cable configured to extend from outside the subject's body to the axial shaft;exactly two driving magnets disposed in a driving magnet housing, which is coupled to the motor; anda driven magnet coupled to the drive cable and disposed between the driving magnets such there is axial overlap between the driving magnets and the driven magnets, the driven magnet defining a single North pole and a single South pole that are divided along an axial length of the driven magnet, the motor being configured to impart rotational motion to the impeller by rotating the drive cable by rotating the driven magnet, by rotating the driving magnet housing.Inventive concept 64. A method comprising:placing, into a subject's body, a blood pump that includes:an axial shaft,an impeller disposed on the axial shaft, anda drive cable extending from outside the subject's body to the axial shaft; and driving the impeller to rotate by:using a motor to rotate exactly two driving magnets disposed in a driving magnet housing, which is coupled to the motor,the driving magnets being configured to thereby drive a driven magnet to rotate, the driven magnet being coupled to the drive cable and disposed between the driving magnets such there is axial overlap between the driving magnets and the driven magnets, the driven magnet defining a single North pole and a single South pole that are divided along an axial length of the driven magnet.Inventive concept 65. Apparatus comprising:a blood pump comprising:an axial shaft;an impeller disposed on the axial shaft and configured to be placed inside a body of a subject;a motor configured to be disposed outside the subject's body;a drive cable configured to extend from outside the subject's body to the axial shaft;exactly two driven magnets disposed in a driven magnet housing, which is coupled to the drive cable; anda drive magnet coupled to the motor and disposed between the driven magnets such there is axial overlap between the driven magnets and the driving magnet, the driving magnet defining a single North pole and a single South pole that are divided along an axial length of the driving magnet, the motor being configured to impart rotational motion to the impeller by rotating the drive cable, by rotating the driven magnets, by rotating the driving magnet.Inventive concept 66. A method comprising:placing, into a subject's body, a blood pump that includes:an axial shaft,an impeller disposed on the axial shaft, anda drive cable extending from outside the subject's body to the axial shaft; and driving the impeller to rotate by:using a motor to rotate a drive magnet coupled to the motor, the drive magnet defining a single North pole and a single South pole that are divided along an axial length of the driving magnet,the driving magnet being configured to thereby drive driven magnets to rotate, the driven magnets comprising exactly two driven magnets disposed in a driven magnet housing, the driven magnet housing being coupled to the drive cable and being disposed around the drive magnet.Inventive concept 67. Apparatus comprising:a blood pump comprising:an axial shaft;an impeller disposed on the axial shaft and configured to be placed inside a body of a subject;a motor configured to be disposed outside the subject's body, and configured to drive the impeller to pump blood by rotating the impeller in a given direction of rotation;a drive cable configured to extend from outside the subject's body to the axial shaft, the drive cable being configured to impart rotational motion from the motor to the impeller by rotating, and the drive cable comprising a plurality of wires that are disposed in a coiled configuration and that are coupled to the axial shaft, the axial shaft defining grooves at an interface between the drive cable andthe axial shaft, the grooves being configured such that stress generated by the wires at the interface is spread over radii of the grooves.Inventive concept 68. Apparatus comprising:a blood pump comprising:an axial shaft;an impeller disposed on the axial shaft and configured to be placed inside a body of a subject;a motor configured to be disposed outside the subject's body, and configured to drive the impeller to pump blood by rotating the impeller in a given direction of rotation;a drive cable configured to extend from outside the subject's body to the axial shaft, the drive cable being configured to impart rotational motion from the motor to the impeller by rotating, and the drive cable comprising a plurality of wires that are disposed in a coiled configuration and that are coupled to the axial shaft,the coiled wires being shaped such that as the coiled wires approach an interface between the drive cable and the axial shaft, a pitch of the wires is increased, such that stress at locations at which the wires of the drive cable are coupled to the axial shaft is reduced, relative to if the pitch of the wires were not increased.Inventive concept 69. Apparatus comprising:a blood pump comprising:an axial shaft;an impeller disposed on the axial shaft and configured to be placed inside a body of a subject;a motor configured to be disposed outside the subject's body, and configured to drive the impeller to pump blood by rotating the impeller in a given direction of rotation;a drive cable configured to extend from outside the subject's body to the axial shaft, the drive cable being configured to impart rotational motion from the motor to the impeller by rotating,the drive cable comprising first and second portions, the first portion of the drive cable comprising a first number of wires disposed in a coiled configuration, and the second portion of the drive cable comprising a second number of wires disposed in a coiled configuration, the first number being lower than the second number; andan interface component, the first and second portions of the drive cable being coupled to each other via the interface component,the interface component defining grooves at an interface between at least one of the drive cable portions and the interface component, the grooves being configured such that stress generated by the wires at the interface is spread over radii of the grooves.Inventive concept 70. Apparatus comprising:a blood pump comprising:an axial shaft;an impeller disposed on the axial shaft and configured to be placed inside a body of a subject;a motor configured to be disposed outside the subject's body, and configured to drive the impeller to pump blood by rotating the impeller in a given direction of rotation;a drive cable configured to extend from outside the subject's body to the axial shaft, the drive cable being configured to impart rotational motion from the motor to the impeller by rotating, the drive cable comprising first and second portions, the first portion of the drive cable comprising a first number of wires disposed in a coiled configuration, and the second portion of the drive cable comprising a second number of wires disposed in a coiled configuration, the first number being lower than the second number; andan interface component, the first and second portions of the drive cable being coupled to each other via the interface component,the coiled wires of at least one of the portions of the drive cable being shaped such that, as the coiled wires approach the interface component, a pitch of the wires is increased, such that stress at locations at which the wires are coupled to the interface component is reduced relative to if the pitch of the wires were not increased.Inventive concept 71. Apparatus comprising:a ventricular assist device comprising:a tube configured to traverse an aortic valve of a subject, such that a proximal portion of the tube is disposed within an aorta of the subject and a distal portion of the tube is disposed within a left ventricle of the subject, the tube defining one or more blood inlet openings within the distal portion of the tube, and one or more blood outlet openings within the proximal portion of the tube;a blood pump configured to be disposed within the tube, and to pump blood from the left ventricle into the tube through the one or more blood inlet openings, and out of the tube into the aorta through the one or more blood outlet openings; anda radially-expandable atraumatic distal tip portion configured to be disposed within the subject's left ventricle distally with respect to the one or more blood inlet openings, the distal tip portion being configured to be inserted into the left ventricle in a radially-constrained configuration, and to assume a non-radially-constrained configuration within the subject's left ventricle in which at least a radially-expandable portion of the distal tip portion is radially expanded relative to the radially-constrained configuration of the distal tip portion.Inventive concept 72. The apparatus according to inventive concept 71, wherein the distal tip portion comprises a braided shape-memory alloy that is at least partially covered with a blood impermeable material.Inventive concept 73. The apparatus according to inventive concept 71, wherein the distal tip portion is configured such that, in the non-radially-constrained configuration of the distal tip portion, the radially-expandable portion of the distal tip portion separates the one or more blood inlet openings from an interventricular septum within the left ventricle.Inventive concept 74. The apparatus according to inventive concept 71, wherein the distal tip portion is configured such that, in the non-radially-constrained configuration of the distal tip portion, the radially-expandable portion of the distal tip portion separates the one or more blood inlet openings from chordae tendineae within the left ventricle.Inventive concept 75. The apparatus according to inventive concept 71, wherein the distal tip portion is configured such that, in the non-radially-constrained configuration of the distal tip portion, the radially-expandable portion of the distal tip portion separates the one or more blood inlet openings from papillary muscles within the left ventricle.Inventive concept 76. The apparatus according to inventive concept 71, wherein the distal tip portion is configured such that, in the non-radially-constrained configuration of the distal tip portion, the radially-expandable portion of the distal tip portion separates the one or more blood inlet openings from an apex of the left ventricle.Inventive concept 77. The apparatus according to inventive concept 71, wherein the distal tip portion is configured such that, in the non-radially-constrained configuration of the distal tip portion, the radially-expandable portion of the distal tip portion separates the one or more blood inlet openings from inner structures of the left ventricle in three dimensions.Inventive concept 78. The apparatus according to inventive concept 71, wherein the distal tip portion is configured such that, in the non-radially-constrained configuration of the distal tip portion, the radially-expandable portion of the distal tip portion directs blood flow from the left ventricle into the one or more blood inlet openings.Inventive concept 79. The apparatus according to any one of inventive concepts 71-78, wherein:in the radially-constrained configuration of the distal tip portion, a distal region of the distal tip portion is configured to be least semi-rigid, and is shaped to radially converge along a longitudinal direction toward a distal end of the distal tip portion;the ventricular assist device is configured to be inserted into the subject's body via a puncture, in the subject's body, andduring the insertion of the ventricular assist device the distal region of the distal tip portion is configured to act as a dilator by dilating the puncture.Inventive concept 80. The apparatus according to any one of inventive concepts 71-78, wherein the distal tip portion is configured such that in the non-radially-constrained configuration of the distal tip portion, a distal end of the distal tip portion is enveloped within the radially-expandable portion of the distal tip portion.Inventive concept 81. The apparatus according to inventive concept 80, wherein the distal tip portion is configured to prevent the distal end of the distal tip portion becoming entangled with chordae tendineae of the left ventricle by the distal end of the distal tip portion being enveloped within the radially expanded portion of the distal tip.Inventive concept 82. The apparatus according to inventive concept 80, wherein the distal tip portion is configured to prevent the distal end of the distal tip portion causing trauma to an internal structure of the left ventricle by the distal end of the distal tip portion being enveloped within the radially-expandable portion of the distal tip portion.Inventive concept 83. The apparatus according to inventive concept 80, wherein the distal end of the distal tip portion is configured to be enveloped within the radially-expandable portion of the distal tip portion, by the distal end of the distal tip portion inverting.Inventive concept 84. The apparatus according to inventive concept 80, wherein the distal end of the distal tip portion is configured to be enveloped within the radially-expandable portion of the distal tip portion, by the distal end of the distal tip portion being retracted proximally, such that the distal end is disposed within the radially-expandable portion of the distal tip portion.Inventive concept 85. Apparatus comprising:a ventricular assist device configured to be inserted into a subject's body via a puncture, the ventricular assist device comprising:a tube configured to traverse an aortic valve of a subject, such that a proximal portion of the tube is disposed within an aorta of the subject and a distal portion of the tube is disposed within a left ventricle of the subject, the tube defining one or more blood inlet openings within the distal portion of the tube, and one or more blood outlet openings within the proximal portion of the tube;a blood pump configured to be disposed within the tube, and to pump blood from the left ventricle into the tube through the one or more blood inlet openings, and out of the tube into the aorta through the one or more blood outlet openings; anda distal tip portion configured:to have a radially-constrained configuration in which a distal region of the distal tip portion is at least partially rigid, and is shaped to radially converge along a longitudinal direction toward a distal end of the distal tip portion, the distal region being configured to act as a dilator by dilating the puncture, during insertion of the ventricular assist device into the subject's body, andto have a non-radially-constrained configuration that the distal tip region is configured to assume within the subject's left ventricle in which the radially-expandable portion of the distal tip portion is configured to be atraumatic and to separate the one or more blood inlet openings from internal structures of the subject's left ventricle.Inventive concept 86. A method comprising:operating a blood pump, the blood pump including:an axial shaft,an impeller disposed on the axial shaft and disposed in a left ventricle of a subject;a motor disposed outside a body of the subject, and configured to drive the impeller to rotate,a drive cable extending from outside the subject's body to the axial shaft via an aortic arch of the subject, and configured to impart rotational motion from the motor to the impeller, by rotating, anda tube, within which the drive cable is disposed, the tube being configured to remain stationary during rotation of the drive cable; andwhile operating the blood pump, pumping fluid into a space between the drive cable and the tube, such that the fluid fills the space between the drive cable and the tube, but without releasing the fluid into a bloodstream of the subject.Inventive concept 87. A method comprising:operating a blood pump, the blood pump including:an axial shaft,an impeller disposed on the axial shaft and disposed in a left ventricle of a subject,a motor disposed outside a body of the subject, and configured to drive the impeller to rotate,a drive cable extending from outside the subject's body to the axial shaft via an aortic arch of the subject, and configured to impart rotational motion from the motor to the impeller, by rotating, anda tube, within which the drive cable is disposed, the tube being configured to remain stationary during rotation of the drive cable;prior to operating the blood pump, pumping fluid into a space between the drive cable and the tube, such that the fluid fills the space between the drive cable and the tube, but without releasing the fluid into a bloodstream of the subject; andleaving the fluid within the space between the drive cable and the tube, during the operation of the blood pump.Inventive concept 88. Apparatus comprising:a left-ventricular assist device configured to assist left-ventricular functioning of a subject, the left ventricular assist device comprising:a tube configured to traverse an aortic valve of the subject, such that a proximal portion of the tube is at least partially disposed within an ascending aorta of the subject and a distal portion of the tube is disposed at least partially a left ventricle of the subject;a frame disposed within the distal portion of the tube, the frame being configured to hold a distal portion of the tube in an open state,the frame not being disposed within the proximal portion of the tube, and the proximal portion of the tube thereby being configured to collapse inwardly in response to pressure outside of the proximal portion of the tube exceeding pressure inside the proximal portion of the tube;a pump disposed within the frame and configured to pump blood through the tube from the subject's left ventricle to the subject's aorta, such that, the proximal portion of the tube is maintained in an open state when blood pressure generated within the proximal portion of the tube by the blood pump exceeds aortic pressure of the subject outside the proximal portion of the tube; anda plurality of elongate commissure elements that are disposed within the proximal portion of the tube, such that, when the proximal portion of the tube collapses inwardly, respective portions of a circumference of the tube form cusps that contact each other.Inventive concept 89. The apparatus according to inventive concept 88, further comprising a computer processor that is configured to control pumping of blood through the tube by the blood pump, such that blood pressure generated by the blood pump within the tube exceeds systolic aortic pressure of the subject, and is less than diastolic aortic pressure of the subject.Inventive concept 90. The apparatus according to inventive concept 88, further comprising a pressure sensor configured to measure aortic blood pressure of the subject, and wherein the computer processor is configured to receive an indication of the measured aortic blood pressure, and to control pumping of blood through the tube by the blood pump responsively to the measured aortic blood pressure.Inventive concept 91. The apparatus according to inventive concept 88, further comprising a pressure sensor configured to measure left-ventricular blood pressure of the subject, and wherein the computer processor is configured to receive an indication of the measured left-ventricular blood pressure, and to control pumping of blood through the tube by the blood pump responsively to the measured left-ventricular blood pressure.Inventive concept 92. Apparatus, for use with a delivery device, the apparatus comprising:an impeller;a frame disposed around the impeller,the impeller and the frame being configured to be inserted into a blood vessel of a subject via the delivery device, while disposed in radially-constrained configurations thereof, and to assume non-radially-constrained configuration by being released from the delivery device; anda coupling element comprising a first portion disposed upon the impeller, and a second portion disposed on the frame and configured to engage with the first portion, the coupling element being configured to facilitate radial constriction of the impeller by holding an end of the impeller such that the impeller can be axially elongated, without radially constricting the frame.Inventive concept 93. Apparatus comprising:a blood-pump tube;an impeller configured to be disposed within the blood-pump tube, and to pump blood from a first location to a second location by pumping blood through the blood-pump tube:a motor disposed outside the subject's body, and configured to drive the impeller to rotate;a drive cable extending from outside the subject's body to the axial shaft, and configured to impart rotational motion from the motor to the impeller, by rotating;an outer tube disposed around the drive cable configured to extend from outside the subject's body to within the blood-pump tube, the outer tube defining first and second openings on a portion of the outer tube disposed within the blood-pump tube; anda flow obstacle disposed over the first opening, such that the first opening is configured to function as a stagnation pressure tap, and the second opening is configured to function as a static pressure tap;at least one pressure sensor configured to measure pressure within the stagnation pressure tap and pressure within the static pressure tap; anda computer processor configured to determine flow through the blood-pump tube, at least partially based upon the pressure measured within the stagnation pressure tap and the pressure measured within the static pressure tap.Inventive concept 94. A method comprising:inserting a blood pump into a body of subject, the blood pump including:an impeller that includes proximal and distal bushings,a frame disposed around the impeller, the frame including proximal and distal bearings, andan axial shaft that passes through the proximal and distal bearings of the frame and the proximal and distal bushings of the impeller, the proximal bushing of the impeller being coupled to the axial shaft, such that the proximal bushing is held in an axially-fixed position with respect to the axial shaft, and the distal bushing of the impeller not being coupled to the axial shaft, such that the distal bushing is not held in an axially-fixed position with respect to the axial shaft,the impeller being maintained in a radially-constrained configuration by a delivery catheter while the impeller is inserted into the subject's body;when the impeller is disposed within the subject's body, causing the impeller to change from its radially-constrained configuration to a non-radially-constrained configuration by allowing the distal bushing to slide over the axial shaft, by releasing the impeller from the catheter; andpumping blood through the subject's body using the impeller, while the impeller is disposed in its non-radially-constrained configuration.Inventive concept 95. A method comprising:placing an impeller of a ventricular assist device inside a left ventricle of a subject, with a frame disposed around the impeller; anddriving the impeller to pump blood from the left ventricle to an aorta of the subject, by rotating the impeller,placement of the impeller inside the left ventricle being such that the impeller is allowed to undergo axial motion with respect to the frame, in response to cyclical changes in a pressure difference between the left ventricle and the aorta.Inventive concept 96. A method comprising:placing a blood pump inside a body of a subject the blood pump including:an impeller with a frame disposed around the impeller, the impeller including proximal and distal bushings, and the frame including proximal and distal bearings, andan axial shaft that passes through the proximal and distal bearings of the frame and the proximal and distal bushings of the impeller, the axial shaft being coupled to at least one of the proximal and distal bushings of the impeller, such that the at least one bushing is held in an axially-fixed position with respect to the axial shaft, and not being held in an axially-fixed position with respect to the proximal and distal bearings; andpumping blood through the subject's body, using the impeller.Inventive concept 97. A method comprising:placing an impeller of a blood pump inside a body of a subject, with a frame disposed around the impeller; anddriving the impeller to pump blood through the subject's body, without using any thrust bearing disposed within the subject's body to provide opposition to thrust generated by the rotation of the impeller.

The present invention will be more fully understood from the following detailed description of embodiments thereof, taken together with the drawings, in which:

