Patent Application
20130041460
The following information is provided to assist the reader to understand the technology described below and certain environments in which such technology can be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the technology or the background thereof. The disclosure of all references cited herein are incorporated by reference.
Heart failure, or the inability of the heart to pump sufficient blood for the body's needs, results in very poor quality of life, huge costs to society, and hundreds of thousands of yearly deaths. Heart failure is caused by an abnormally low cardiac output. Cardiac output is the outflow of blood from the heart and can be measured in liters of blood flow per minute or LPM. Cardiac output for a normal man at rest or during light activity is approximately 5 liters per minute. Severe heart failure exists when the cardiac output is between approximately 2.5 to 3.5 liters per minute. For an average man in heart failure having a heart rate of 80 beats per minute, the average amount of blood that is pumped with each heartbeat (sometimes referred to as stroke volume) might, for example, be 37 milliliters or ml. If the same man was not in heart failure, his heart might, for example, pump 62 milliliters with each heartbeat. An effective treatment for such heart failure would be to increase the low, 37 ml stroke volume up to the normal, 62 ml stroke volume.
The main pumping chamber of the heart or left ventricle or LV includes an inlet mitral valve and an outlet aortic valve. During left ventricular contraction or systole, the inlet valve closes as blood is pushed through the aortic valve into the aorta or main artery to the body. When the LV is resting during diastole, LV pressure may be between 2 and 20 mm of Hg pressure. This diastolic pressure is termed the LV preload. The preload will be in the higher end of its pressure range during heart failure. During active LV contraction or systole, the LV must eject its blood against the pressure in the aorta. Aortic pressure is typically between 70 and 140 mm Hg Pressure. This aortic pressure is termed the after-load. It is well known that, if the after-load is reduced in heart failure, the LV stroke volume will naturally increase and this increase is one reason that afterload-reducing drugs such as ACE-inhibitors help heart failure patients.
Blood pumps which lower the aortic pressure after-load can be desirable because such pumps allow the failing LV to eject more blood with less effort. However, no commercially available afterload reducing devices have thus far been shown to be practical for extended support of the failing LV. Instead, all long term (that is, months to years), commercially available heart assist devices, whether rotary turbine pumps or collapsing chamber pumps, go around or bypass the failing LV, pumping blood from the LV apex through the pump into the aorta. By doing so, those pumps act in parallel to the LV and compete with the LV in their pumping action. This pumping competition has several negative complications including right heart failure, fusion of the aortic valve over time and the risk of collapsing the LV. Collapsing chamber pumps are physically large and thus cannot be implanted in some small patients. Rotary turbine pumps are smaller, but have other limiting complications. For example, rotary turbine pumps induce high levels of shear stress in the blood elements and also may reduce the normal pulsatility of the blood entering the aorta. High shear stress on the blood cells promotes blood clotting which can lead to strokes and heart attacks. Physicians try to reduce this blood clotting by giving the patients anticoagulants, which, in turn, puts the patients at risk of excessive bleeding. These clotting and bleeding complications are substantial limitations to broader use of rotary turbine assist pumps.
For short-term heart assist (that is, hours to days), counterpulsation devices such as intraaortic balloon pumps or IABPs provide an afterload-reducing type of cardiac assist. See U.S. Pat. Nos. 4,733,652 and 3,692,018. The main benefit of such devices stems from after-load reduction of the left ventricle during systole and providing increased diastolic pressure for perfusing the coronary and other arteries during diastole. Typical patients needing this type of treatment suffer from cardiogenic shock or need perioperative circulatory support. The nature of IABP design restricts IABP to acute use only, since the bulky balloon drive mechanism remains outside the patient's body, necessitating patient confinement to a hospital bed.
U.S. Pat. No. 4,051,840 discloses a “dynamic aortic patch” which is surgically and permanently attached to the patient's descending aorta and is pneumatically activated by an external air pump. That pump lowers the LV after-load, facilitating left ventricular contraction and increasing stroke volume.
Pouch-type auxiliary ventricles attached to the patient's aorta have also been described. These devices use mechanical or pneumatic devices for pumping the blood contained in the pouch. See U.S. Pat. Nos. 3,553,736 and 4,034,742. Some of these devices have a single access port to the aorta that serves as both the inlet and the outlet for blood flow. Single port designs have the disadvantage of recirculation and relative flow stagnation, increasing the risk of clot formation and thromboembolism. Pouch-type auxiliary ventricles having both inlet and outlet ports to the aorta and are typically connected in parallel with the aorta. See, for example, U.S. Pat. Nos. 4,195,623 and 4,245,622.
U.S. Pat. Nos. 5,676,162, 5,676,651, and 5,722,930, disclose a single-stroke, moving valve pump designed for ascending aortic placement. That device uses a commercially available artificial heart valve with attached magnets and requires excision of a portion of the aorta. A series of separate electric coils step the valve/magnet combination forward in a sliding action within a cylinder. The device is quite large for the limited space available between the heart and the take-off vessels from the aorta to the upper body and brain. The device is designed to have one stroke in synchronization with each LV systole. The blood volume required for closing commercially available heart valves is typically 2-5 ml and therefore multiple smaller oscillations per heart contraction in such devices would suffer from volumetric inefficiency. Another problem with such devices is the tight crevice between the cylinder wall and the moving valve. This tight space results in high blood shear and the corresponding risk of stroke or blood clotting complications if anti-coagulant therapy is necessary. The same problem exists with a moving valve pump disclosed in U.S. Pat. No. 4,210,409, which included two valves (one stationary and one moving).
U.S. Pat. No. 5,147,281 discloses an oscillatory valve blood pump that is external to the body and fits in an enclosure the size of a briefcase. The pump uses a stationary coil to attract a magnetic tube encasing a one-way valve. A forward stroke of the one-way valve propels blood until the tube assembly stops and is repelled backward by return leaf springs that are charged during the forward stroke. A second stationary valve is sometimes in the circuit. A stretchable silicone rubber tube connects the tube or pipe-valve assembly with the pump inlet and outlet.
Nitta, S. et al., “The Newly Designed Univalved Artificial Heart,” ASAIO Transactions Vo. 37, No. 3, M240-M241 (1991) describes a “univalved artificial heart” powered electro-magnetically wherein the valve oscillates within a frequency range of 1 to 30 Hz. The valve is contained in a tube, with attached magnetic material. Stationary electric coils actuate the tube-magnet-valve combination. The valve is described as a jellyfish valve. A problem with jellyfish valves is the compound curvature or wrinkling of the membrane that occurs when the valve opens and closes. One can liken the action of the jellyfish valve to that of an umbrella that oscillates between a circular flat membrane and a wrinkled umbrella shape as it closes and opens. Wrinkling of the membrane is virtually impossible to prevent in a jellyfish valve and introduces stresses and strains that significantly limit the life of the valve.
U.S. Pat. No. 5,266,012 also uses a jellyfish valve in a vibrating pipe blood pump intended for use outside the body. Because the vibrating tube pump portion is separable from the drive mechanism. the blood-contacting portion of the pump is disposable.
U.S. Pat. No. 7,588,530, describes a moving valve pump having a curved blood flow path as well as a moving valve pump having a linear blood flow path. U.S. Pat. No. 7,588,530 discloses various drive mechanisms to oscillate the moving valve in synchronization with the R wave of the patient's electrocardiogram. In the case of a pump having a linear blood flow path, a linear motor is disclosed to drive the moving valve thereof. U.S. Pat. No. 7,588,530 further discloses moving valves including a plurality of openings or ports wherein each port includes a resilient flap of material to open the port upon rearward movement of the moving valve and close the port upon forward movement of the moving valve.
U.S. Pat. No. 5,545,216 disclose a typical mechanical heart valve used as a substitute for a malfunctioning natural human aortic heart valve, which includes a valve ring with two hard leaflets that swing nearly 90 degrees to open and close the valve. The leaflets used in mechanical heart valves are typically hard ceramic materials that block backward flow when closed. The opening and closing of the leaflets is caused by the direction of blood passing through the valve. To prevent the leaflets from escaping the confines of the valve ring, the leaflets have bilateral “ears” that are positioned within valve ring cavities. Thus, the leaflets cannot escape the valve ring but are allowed to freely pivot by ability of the ears to rotate within the valve ring cavities.
Patients with mechanical heart valves have a risk of cerebrovascular strokes that are caused by blood clots coming from the mechanical valve. This stroke risk is on the order of 1 to 3 percent per patient per year. To minimize this clotting risk, patients with mechanical valves are prescribed the anti-coagulation drug Coumadin, that is known to retard the ability of the blood to clot. There are several suspected causes for the blood clotting risk. Flow turbulence within the valve ring cavities causes shear strain on blood. Shear strain is known to activate blood platelets, and activated platelets are known to start the blood clotting process. Leakage of blood through tight crevices of coapted surfaces of the closed or closing leaflets on to the leaflet landing surfaces can also be a source of blood shear strain. Another possible cause of clotting/stroke risk is the non-biologic nature of the valve materials.
Numerous pharmacologic, biologic, and mechanical interventions have been devised to address heart disease/failure. Nonetheless, heart failure remains a major public health problem with an estimated five million victims in the United States alone.
In one aspect, an implantable pump system for assisting blood flow includes a conduit adapted to be placed in fluid connection with a blood vessel and at least one movable valve in fluid connection with the conduit. The valve includes at least one closure member in operative connection with an opening therein. The pump system further includes and an activating system adapted to actively move the closure member toward at least one of a closed position or an open position and a drive system to move the valve. The closure member may, for example, be biased toward an open position. The conduit may be flexible over at least a portion thereof.
The activating system may, for example, be adapted to maintain the at least one closure member at or near the closed position during at least a portion of forward motion of the valve. The activating system may, for example, be adapted to move the closure member toward a closed position so that the opening of the valve is closed or nearly closed upon the initiation of forward motion of the valve relative to a direction of flow of blood through the blood vessel from the heart.
In a number of embodiments, the activating system includes at least one abutment member. An abutment member may, for example, be positioned within a blood flow path of the pump system to contact at least one of the plurality of closure members to move the at least one of the plurality of rigid closure member toward a closed position.
The valve may, for example, include a plurality of closure members in operative connection with the control system. At least one of the closure members may, for example, be biased to an open position.
In a number of embodiments, the activating system is positioned outside of a blood flow path of the pump system. In a number of embodiments, the activating system includes at least one abutment member positioned outside the conduit.
The valve may include a support structure including the opening. The conduit, which may be a flexible conduit, may be attached to the support structure. In a number of embodiments, the conduit is flexible and is attached to the support structure. The closure member is positioned within the opening and is rotatable about an axis to a closed position and to a range of open positions. The axis may, for example, be defined by a rotatable shaft connected to the closure member. In a number of embodiments, the rotatable shaft passes through the valve support structure. The pump system may further include a seal between the rotatable shaft and the valve support structure that prevents blood leakage through a space between the rotating shaft and valve support structure.
In a number of embodiments, the valve includes a first closure member positioned within the opening and at least a second closure member positioned within the opening. The first closure member may be rotatable about a first axis to a closed position and to a range of open positions, and the second closure member may be rotatable about a second axis to a closed position and to a range of open positions. The first closure member may, for example, have a generally semicircular cross-section, and the second closure member may, for example, have a generally semicircular cross-section.
The first axis may be defined by a first rotatable shaft connected to the first closure member, and the second axis may be defined by a second rotatable shaft connected to the second closure member. In a number of embodiments, the first shaft passes through at least a portion of the support structure. The pump system may further include a first seal in contact with the first shaft and the support structure. The second shaft may also pass through at least a portion of the support structure. The pump system may further include a second seal in contact with the second shaft and the support structure.
In a number of embodiments, the first seal includes a first inner connecting member fixed in position relative to the first shaft, a first outer connecting member in fixed position relative to the support member and a first flexible sealing member extending between the first inner connecting member and the first outer connecting member. At least a portion of the first flexible sealing member moves with rotation of the first shaft. The second seal may, for example, include an second inner connecting member fixed in position relative to the second shaft, a second outer connecting member fixed in position relative to the support member and a second flexible sealing member extending between the second inner connecting member and the second outer connecting member. At least a portion of the second flexible sealing member moves with rotation of the first shaft.
In a number of embodiments, the first inner connecting member includes a resilient annular member, the first outer connecting member includes a resilient annular member and the first flexible sealing member includes an elastomeric material. Likewise, in a number of embodiments, the second inner connecting member includes a resilient annular member, the second outer connecting member includes a resilient annular member and the second flexible sealing member includes an elastomeric material.
In a number of embodiments, the activating system includes a first gear in operative connection with the first shaft external to conduit blood flow path of the pumps system, a second gear in operative connection with the second shaft external to the blood flow path and an extending rack positioned between the first gear and the second gear. The pump system can further include an abutment member positioned outside the blood flow path. Cooperation of the abutment member with the extending rack causes the extending rack to move in a first direction to cause the first gear and the first shaft to rotate the first rigid closure member toward the closed position and to cause the second gear and the second shaft to rotate the second rigid closure member toward the closed position.
The first gear and the second gear may, for example, be biased by a biasing system to rotate the first rigid closure member toward an open position and to rotate the second rigid closure member toward an open position. The biasing system can be in operative connection with the extending rack.
The activating system may be adapted to maintain the first closure member and the second closure member at or near the closed position during at least a portion of forward motion of the valve.
In a number of embodiments, the pump system further includes a system in operative connection with the biasing system to maintain the first closure member and the second closure member at or near the closed position during initial forward motion of the valve. The biasing system may, for example, include a collapsible enclosure within a fluid. The collapsible enclosure may be operatively connected to the extending rack. The collapsible enclosure may, for example, be forced against a contact element when the extending rack is moved in the first direction upon contact with the abutment member to collapse the collapsible enclosure. The collapsible enclosure may include a one-way valve via which fluid is expelled from the enclosure when the enclosure is collapsed. The collapsible enclosure may further include a fluid inlet system including at least one inlet port to allow fluid to enter the collapsible enclosure in a controlled manner upon expansion of the collapsible enclosure. Expansion of the collapsible enclosure causes the rack to move in a direction opposite the first direction.
The position of the at least one abutment member may, for example, be changeable to prevent maintaining of closure of the valve. In a number of embodiments, a shape memory alloy is used to change position of the at least one abutment member via a change in current applied to the shape memory alloy.
In a number of embodiments, the closure member is rigid over at least a portion thereof. In a number of such embodiments, the first closure member includes a first rigid base fixed to the first shaft and a first blood contacting layer encompassing the first base. The first rigid base can, for example, include a rigid material connected to the first shaft. The first blood contacting layer can include a blood compatible flexible material.
In a number of embodiments, the drive system includes a rotary motor, a speed reducing system in operative connection with the rotary motor and a convertor operatively connected to the speed reducing system. The converter is operatively connected to the valve to drive the valve in a reciprocating manner. In a number of embodiments, the speed reducer includes a spur gear driving a ring gear, wherein the converter is operatively connected to the speed reducer. The ring gear may, for example, be in operative connection with the converter. In a number of embodiments, the converter includes an eccentric member extending from the ring gear. In a number of embodiments, the converter further includes a rotating element connected to the eccentric member that engages a cam member operatively connected to the valve to drive the valve in a reciprocating, linear manner.
The conduit may, for example, be a flexible conduit positioned within a sealed housing. A volume between the flexible conduit and housing may, for example, be filled with an aqueous fluid having dissolved solutes to provide an osmolarity approximately equal to the osmolarity of blood. The fluid may, for example, be an aqueous salt solution. The drive system may, for example, be in fluid connection with the volume, and the fluid may be present within the drive system. In a number of embodiments, the fluid is adapted to dissipate heat from the drive system. The fluid may, for example, include at least one hydrophilic lubricant.
In another aspect, an implantable pump system for assisting blood flow includes a conduit adapted to be placed in fluid connection with a blood vessel and at least one movable valve in fluid connection with the conduit. The movable valve includes a support structure including an opening. At least one closure member is positioned within the opening. The closure member is rotatable about an axis to a closed position and to a range of open positions. The closure member is rigid over at least a portion thereof. The pump system further includes a drive system to move the valve. In a number of embodiments, the closure member is biased to move toward an open position.
In a number of embodiments, a first closure member is positioned within the opening and a second closure member is positioned within the opening. The first closure member is rotatable about a first axis to a closed position and to a range of open positions, and the second closure member is rotatable about a second axis to a closed position and to a range of open positions. The first closure member is rigid over at least a portion thereof, and the second closure member is rigid over at least a portion thereof. The first closure member can, for example, have a generally semicircular cross-section, and the second closure member can, for example, have a generally semicircular cross-section.
The first axis may, for example, be defined by a first rotatable shaft connected to the first closure member. The second axis may, for example, be defined by a second rotatable shaft connected to the second closure member. The first shaft can pass through at least a portion of the support structure. A first seal may, for example, be in contact with the first shaft and the support structure. The second shaft may also pass through at least a portion of the support structure. A second seal may, for example, be in contact with the second shaft and the support structure.
In a number of embodiments, the first seal includes a first inner connecting member fixed in position relative to the first shaft, a first outer connecting member in fixed position relative to the support member and a first flexible sealing member extending between the first inner connecting member and the first outer connecting member. At least a portion of the first flexible sealing member moves with rotation of the first shaft. The second seal may similarly include a second inner connecting member fixed in position relative to the second shaft, a second outer connecting member in fixed position relative to the support member and a second flexible sealing member extending between the second inner member and the second outer member. At least a portion of the second flexible sealing member moves with rotation of the first shaft.
The first inner connecting member may, for example, include a resilient annular member. The first outer connecting member may, for example, include a resilient annular member. The first flexible sealing member can, for example, include an elastomeric material. The second inner connecting member may, for example, include a resilient annular member. The second outer connecting member may, for example, include a resilient annular member. The second flexible sealing member may, for example, include an elastomeric material.
In a number of embodiments, the pump system further includes an activating system in operative connection with the closure member to actively move the member. The first closure member may, for example, be biased to move toward an open position, and the second closure member may, for example, be biased to move toward an open position.
The activating system may, for example, be in operative connection with the first closure member and the second closure member to actively move the first rigid member to the closed position and to actively move the second rigid member toward the closed position before initiation of forward motion of the valve relative to a direction of flow of blood through the blood vessel from the heart.
In a number of embodiments, the pump system includes at least one bearing in operative connection with the first rotatable shaft outside of the first seal and at least one bearing in operative connection with the second rotatable shaft outside of the second seal. The bearing in operative connection with the first rotatable may, for example, be a rolling element bearing. and the bearing in operative connection with the second rotatable may, for example, be a rolling element bearing.
In another aspect, a seal to form a seal between a first element and a second element, wherein at least one of the first element and the second element is moveable relative to the other of the first element and the second element, includes a first connecting member, a second connecting member and a flexible sealing member extending between the first connecting member and the second connecting member. The first connecting member is adapted to be fixedly attached to the first element, and the second connecting member is adapted to be fixedly attached to the second element. The flexible sealing member provides for relative movement between the first member and the second member while maintaining a seal therebetween. In a number of embodiments, the first inner connecting member includes a resilient annular member, the first outer connecting member includes a resilient annular member, and the first flexible sealing member includes an elastomeric material. In a number of embodiments, the second inner connecting member includes a resilient annular member, the second outer connecting member includes a resilient annular member, and the second flexible sealing member includes an elastomeric material.
In a further aspect, a method of operating a pump system for assisting blood flow, wherein the pump system includes a conduit adapted to be placed in fluid connection with a blood vessel and at least one movable valve in fluid connection with the conduit, and wherein the movable valve includes an opening and at least a first closure member in operative connection with the opening therein, includes actively moving the first closure member toward at least one of a closed position or an open position.
In a number of embodiments, the method includes actively moving the first closure member toward a closed position so that the opening of the valve is closed or nearly closed upon the initiation of forward motion of the valve relative to a direction of flow of blood through the blood vessel from the heart. The method may also include actively maintaining the first closure member closed or nearly closed for at least a period of time upon initiation of forward motion of the valve. The method may further include biasing the first closure member to move toward an open position.
In a number of embodiments, the valve includes second closure member positioned within the opening, and the method further includes actively maintaining the second closure member closed or nearly closed for at least a period of time upon initiation of forward motion of the valve. The method may further include biasing the second closure member to move toward and open position.
In still a further aspect, an implantable pump system for assisting blood flow includes a conduit adapted to be placed in fluid connection with a blood vessel. at least one movable valve in fluid connection with the conduit, the valve including at least one closure member in operative connection with an opening therein, a biasing system adapted to actively bias the closure member to move toward an open position; and a drive system to move the valve.
In a number of embodiments, the projected average life of pump systems hereof is intended to be that of current heart transplants, namely approximately 10 years.
The technology described herein, along with the attributes and attendant advantages thereof, will best be appreciated and understood in view of the following detailed description taken in conjunction with the accompanying drawings.
As used herein and in the appended claims, the singular forms “a,” “an”, and “the” include plural references unless the content clearly dictates otherwise. Thus, for example, reference to “a valve assembly” includes a plurality of such valve assemblies and equivalents thereof known to those skilled in the art, and so forth, and reference to “the valve assembly” is a reference to one or more such valve assemblies and equivalents thereof known to those skilled in the art, and so forth.
In a number of embodiments hereof devices, systems and methods are disclosed for assisting blood flow using a moving (for example, oscillating) valve assembly or a plurality of such valve assemblies to propel blood. Pump systems hereof can be fully implanted or temporarily connected to the circulation using percutaneous blood conduits. Pump systems hereof can, for example, be fully or completely implanted for a period of months to years to alleviate or correct heart failure and related symptoms.
Inline moving valve pumps located in the space normally occupied by, for example, the ascending human aorta have been proposed in which a linear motor actuates valve movement. As used herein, the terms “in line or “inline” when used in connection with the position of a pump system hereof within the body refers to a moving valve pump in which the flow path of blood through the pump is in series with a blood vessel (for example, the aorta or the ascending aorta) and the path of the moving valve passes through at least a portion of the volume occupied by the blood vessel (for example, the aorta or the ascending aorta) prior to implantation of the moving valve pump. Because of the critical organs surrounding the ascending human aorta, there is very limited space for a valve drive mechanism. A compact linear motor was previously believed to be required for use in the limited space around the aorta. Moreover, the ascending aorta is typically three inches or less in length (approximately two inches in length for an average adult), which is a very short distance for the provision of a flow conduit assembly of an inline moving valve pump system (for example, including one or more flexible conduits, sealing end rings, and blood tight aortic connections at each end of the pump system). The present inventors have discovered that suitably sized linear motors have inadequate output power for driving a moving valve pump at motor temperatures reasonably suitable for implantation in the human body, and, for example, to be in series with and/or in line with a blood vessel such as aorta (for example, the ascending aorta).
Rotary motors have the advantage of higher power compared to an equally sized linear motor. However, implantable rotary motors for an inline moving valve pump would have to be placed in the vicinity of the aorta, consuming organ space. In a number of embodiments hereof, pump systems having a drive system including a rotary motor and a converter (to convert the rotary motion of the rotary motor to the desired reciprocating motion of the moving valve) exhibit sufficient driving power for the moving valve with acceptable heat emission. A rotary-to-linear drive or converter can be used for reciprocating, linear valve motion, or a rotary-to-curvilinear drive or convertor can be used for reciprocating, curvilinear valve motion. A speed reduction system or speed reducer can, for example, be provided between the rotary motor and the converter. Such a speed reduction system can, for example, be used to decrease the size (volume) of the rotary motor required. Representative embodiments of the pump systems hereof exhibit a form factor that does not significantly interfere with the function of the critical organs surrounding, for example, the aorta.
Review of the physics describing motor power illustrates the power output advantages of a rotary motor compared to a linear motor, and particularly, a rotary motor including a speed reducer. Output power is the product of torque and rotational speed for a rotary motor, while power is the product of force and velocity in the case of a linear motor. Electromagnetically induced force, expressed in Newtons, is the product of magnetic field strength expressed in Tesla, the length of an electric conductor in meters, and the current flowing in the conductor expressed in amperes, provided the current is flowing perpendicular to the magnetic flux lines. If one assumes an equal volume of copper for carrying current and a rare earth magnet material such as neodymium, for establishing magnetic field strength, equally sized linear and rotary motors will be capable of creating roughly the same amount of electromagnetic force. However, the generated power will be the product of this force and the corresponding velocities. A linear motor, directly linked with a valve might, for example, move the valve 0.015 meters (1.5 centimeters) in 50 milliseconds for a velocity of approximately 0.3 meters per second. A rotary motor linked to the valve through, for example, a 5× speed reducer, and a rotary-to-linear converter (for example, including a cam element), and having a rotor diameter of 0.02 meters (2 centimeters), will have rotor surface motion per valve stroke of (pi radians×0.01 meters/radian×5)/0.05 or 3.14 meters per second. In this representative example, the rotary motor thus provides more than ten times the velocity of the linear motor. Therefore, for an equivalent mass and size of linear and rotary motors, the rotary motor can be expected to produce roughly ten times the output power compared with the same input power. The substantial difference in power generation efficiency allows use of a suitably small rotary motor, especially when coupled with a speed reducer to perform the required work of a moving valve pump located in the limited space of the ascending aorta, with acceptable heat generation. A linear motor suitable to perform the same amount of work would have to be too large and/or would emit too much heat.
The total volume displaced by the pump system can, for example, be less than 400 cc, less than 200 cc or even less than 180 cc. The volume of flow conduit assembly 200 and the extending housing section of the drive system may, for example, be less than 300 cc, less than 200 cc or even less than 120 cc. The volume displaced by the extending housing section of the drive system may, for example, be less than 150 cc, less than 100 cc or even less than 50 cc. A distance D1 (see
In one embodiment, the total volume of pump system 100 is approximately 170 cc, the volume of flow conduit assembly housing section 210, a curved connector 205 attached thereto and a suture connector 208 attached thereto is approximately 136 cc; the volume of flow conduit assembly housing section 210 is approximately 79.08 cc; the volume of drive system housing section 122 (encompassing rotary motor 120 and speed reducer 160) is approximately 34 cc; distance D1 is approximately 7.75 cm; and distance D3 is approximately 4.52 cm. In that embodiment, the volume of aorta 20 displaced by pump system 100 is approximately 75 cc (calculated using an average aorta radius of 1.75 cm). The net increase in volume which impinges on non-aortic structures is approximately 95 cc (170 cc-75 cc).
As described above, in the embodiment illustrated, for example, in
In the illustrated embodiment, speed reducer or speed reduction system 160 is in operative connection with rotor shaft 128. In
In the illustrated embodiment, speed reducer 160 includes a spur gear or a pinion gear 162 attached to rotor shaft 128. Spur gear 162 engages and rotates a ring gear 164. Ring gear is suspended or positioned by a bearing such as a rolling element bearing 170 including roller elements 171 as described below in connection with rolling element bearings 130 of rotary motor 120. The combination of spur gear 162 and ring gear 164, provide a number of advantages over, for example, a planetary speed reducer because of the need for bushings or bearings for each planet gear of the planetary speed reducer and the additional need for a power takeoff from the centers of each of the planets thereof. Using spur gear 162 to drive ring gear 164 is much simpler, and requires only two gears for achieving a suitable speed reduction. In the illustrated embodiment, speed reducer 160 is operatively connected to a rotary-to-linear converter 180 (see, for example,
As described above, speed reducer 160 can be eliminated in the case of certain rotary motors. In such an embodiment, the rotary motor would be connected directly to the converter to convert rotary motion to the reciprocating motion of the valve assembly. However, a rotary motor providing sufficient torque at lower speeds would be required. Such a rotary motor would have a substantially increased volume and weight as compared to a rotary motor suitable for use in connection with a speed reducer.
The magnitude of the lifetime requirements for a moving valve pump which is intended to be an alternative to a heart transplant is substantial. Although, heart transplants are very effective solutions for severe heart failure, heart transplants are limited by availability of suitable donor hearts (approximately 2,400 per year in the US). The need for a heart transplant equivalent replacement pump is therefore great. However, the desired lifetime for a pump system equivalent to a heart transplant is on the order of ten years of very reliable operation. If a moving valve pump system such as pump system 100 averages three cycles/forward strokes per heartbeat, and the average heart rate of a pump recipient patient is 80 beats per minute, 1.26 billion reliable valve cycles are required from the pump system 100 (10 years×365 days/year×24 hours/day×60 minutes/hour×80 heartbeats/minute×3 cycles/heartbeat). This is a high number of cycles for reliable operation of mechanical linkages from rotary motor 120 to valve assembly 300.
Transferring energy from rotary motor 120 to valve assembly 300 with such a long lifetime requirement presents a problem of wear of bearings used in pump system 100. As used herein, a “bearing” refers to a device that allows constrained relative motion between two or more components (most commonly, rotational or linear movement). Bushings, which are independent plain bearings inserted into a housing to provide a bearing surface for rotary or linear applications, can be overly susceptible to wear. In general, sliding or friction bearings are subject to wear and would be expected to decrease pump system lifetime. Rolling element bearings carry a load by placing rolling elements between two race components. The relative motion of the components causes the rolling elements to roll with little resistance. Rolling element bearing can provides improved wear resistance as compared to bushings. A ball bearing is a type of rolling element bearing in which balls maintain separation between the moving parts of the bearing. Because of cost and availability reasons, ball-shaped rolling elements are typically used in motors to link mechanical assemblies. However, ball-shaped rolling elements provide a single point of contact with the moving component(s) of the bearing. Rolling element bearings, which provide a generally linear contact with moving parts (for example, cylindrical rolling elements), exhibit higher load carrying capability and can provide improved wear resistance compared to some ball bearings. A problem with a number of currently available rolling element bearings, given the relatively long lifetime requirements for pump system 100, is the use of cages to maintain proper placement of the rolling elements. Because rubbing between the cage and the rolling elements is unavoidable and generates wear and debris, rolling element bearings which do not include cages (sometimes referred to herein as cageless rolling element bearings) are used in several embodiments hereof Cageless rolling element bearings can, for example, be provided by using matched or meshing gear teeth on the rolling elements and the cooperating races to properly locate the rolling elements within the rolling element bearing assemblies. Since the respective gear teeth of the rolling elements and races mesh, rubbing is virtually eliminated and bearing life is increased. Additionally, roller element bearings with extending bearing surfaces can be used instead of balls for the rolling elements in at least some of the mechanical linkages of pump systems hereof. As described above, rollers provide greater load bearing capacity compared to balls, which provide only point contact for load bearing. Rolling elements or rollers with extended contact bearing surfaces for use herein can, for example, include angled, tapered, canted or arced extending bearing surfaces to better accommodate bending moments and stresses on the rolling element bearings.
Certain caged rolling element bearings, including ball bearings, may also be suitable for use in at least some of the mechanical linkages of the pump systems hereof. For example, “hybrid” rolling element bearings are available wherein the inner and outer races are formed from a bearing hard steel, while the rolling balls are formed from a ceramic material such as silicon nitride. Hard ceramic balls, formed from silicon nitride are lighter than steel and have a higher modulus of elasticity, which makes them stiffer than steel. Moreover, ceramic balls are smoother than steel balls and do not microscopically weld to the steel races because of the dissimilarities of the materials. Hybrid rolling element bearings including ceramic rolling balls or rollers and durable cages are, for example, available from The Barden Corporation of Danbury, Conn. Durable or long-life cages can, for example, be formed from a thermoplastic material.
Whether the bearings used in the pump systems hereof are caged or cageless, and whether such bearings include balls or rollers with extending bearing surfaces, such bearing can, for example, include shielding. Shielding (for example, a metallic cover or shield) covers the rolling elements and races of shielded bearings. Typically, shielding is used to keep debris from entering the bearing or to retain a lubricant such as grease within the bearing. In the case of bearings used in the pump systems hereof, however, shieling can be used to prevent debris caused by wear of one or more components of the bearing from escaping the bearing. Typically, shielding on both sides of a bearing is desirable.
As described above, rotor shaft 128 is supported by rolling element bearings 130. In the illustrated embodiment of, for example, in
Rotary shaft 128 has two relatively larger gear wheels 128a keyed or otherwise fixed thereto. The geared teeth of roller elements 131 cooperate with the teeth of gear wheels 128a.
As illustrated, for example, in
As illustrated, for example, in
Flow conduit assembly 200 can, for example, include sealing end rings 242 and 244 to which the ends of flow conduit 240 are attached. Rearward (relative to the flow of blood through flow conduit 240 from heart 10) end ring 244 can, for example, have attached thereto a curved connective portion 205 for connection to ascending aorta 22 which corresponds generally to the form of ascending aorta 22 as it is connected to heart 10 and assists in positioning the blood flow path of conduit assembly 200 in line with ascending aorta 22. A connector such as suturable connectors 208 (illustrated in
A space or volume 212 surrounding flow conduit 240 and bounded and sealed by housing 210 can, for example, be filled with a fluid (that is, a liquid, sometimes referred to herein as the peri-bellows fluid). The fluid can, for example, operate, in part, to equalize pressure within housing 210 and outside of flow conduit 240 with the pressure within flow conduit 240. The fluid in space 212 can, for example, be a blood compatible, aqueous salt solution (including, for example, sodium chloride). In a number of embodiments, the salt solution has an osmotic pressure, an osmolarity or an osmolality approximately equal to that of blood (for example, an osmolarity within 5% or even within 2% of the osmolarity of blood).
As described above, in the case that, for example, a semipermeable material (such as an elastomeric polymer) is used for fluid conduit 240, the fluid/liquid may, for example, exhibit a similar osmolarity/osmotic pressure to that of blood to, for example, prevent fluid from moving into or out of peri-bellows space 212. Such fluid movement could, for example, damage flexible fluid conduit or bellows 240 either by the fluid conduit 240 rubbing against case or housing 210 upon fluid volume shrinkage or crinkling of fluid conduit 240 upon fluid volume expansion. Fluid movement into or out of the housing of pump system 100 (and thus a change of the volume of fluid within the housing) can occur because of the semi-permeable nature of polyurethane and/or other materials (in which a fluid can be transported through the material) which may be used in flexible fluid conduit 240 where there is a significant osmotic pressure difference across flexible conduit 240. Human blood contains 292 plus or minus ˜12 milliosmols of osmotic pressure. A sodium chloride aqueous solution of approximately 0.852% by weight approximately matches blood osmotic pressure and can be used to limit or prevent fluid movement into or out of the space 212. Further, aqueous salt solutions such a sodium chloride aqueous fluid solution in space 212 also provides the advantage of being biocompatible if released into the blood stream.
In the case that fluid conduit 240 is impermeable to the aqueous fluid/liquid surrounding flow conduit 240, it may not be necessary to match the osmolarity of the aqueous fluid to that of blood. In the case that a semipermeable polymeric material such as BIONATE is used for fluid conduit 240, the outer surface thereof can, for example, be surrounded with or coated by a layer of a flexible, impermeable polymer or other impermeable material to reduce or eliminate permeability.
In a number of embodiments, the fluid within space 212 also surrounds the components of rotary-to-linear converter 180 and the components of speed reducer 140 and also fills the space of volume between stator rotor 124 and rotor 126. The fluid can also fill a space 123 between the rotary motor components (for example, bearings 130 and stator 124) and housing 123. Rotary motor 120 can, for example, be spaced from housing 122 and fixed or stabilized in position relative thereto by spacer or standoffs 122′ (see
A lubricant, which can, for example, be a biocompatible, aqueous or hydrophilic lubricant can, for example, be included in the bathing fluid. An example of such a fluid is the glycosaminoglycan hyaluronic acid, which occurs naturally in the body.
As valve assembly 300 moves forward (that is, in the direction of blood flow from left ventricle 14 of heart 10), one or more openings or ports thereof are closed and valve assembly 300 drives blood forward toward the upper portion of ascending aorta 22. The motion of valve assembly 300 is then reversed and it's port(s) are opened, allowing the momentum of the blood to continue forward blood flow.
In the illustrated embodiment, valve assembly 300 includes a single port 320 having a generally circular shape (see, for example,
The distance traveled in any one direction by valve assembly 300 can, for example, be in the range of approximately 1 to 2 centimeters. The cross sectional area of the blood contacting surface of valve assembly 300 can, for example, be approximately 10 square centimeters. As one example, the valve stroke of such a valve assembly can be 1.5 centimeters, resulting in a displaced volume of 15 milliliters. It has been found by experimentation that at cycle rates between, for example, 10 and 16 cycles per second, an aqueous fluid will flow continuously forward because of a momentum effect even though roughly half the time valve assembly 300 is moving backwards. For example, three cycles of 1.5 centimeter valve movement of the above-described valve assembly displaces roughly 3 times 15 or 45 milliliters of blood, and the actual flow in the forward direction could be the same or even greater than this amount. This output provide sufficient extra flow to compensate for the low cardiac output found in typical heart failure. In a number of embodiments, valve thickness and end ring thicknesses are kept below approximately 70 mils (1.78 mm) and approximately 100 mils (2.54 mm), respectively, to facilitate stroke lengths and flow assist volumes as described above.
In the illustrated embodiment, a valve assembly carriage or bearing assembly 400 (see, for example,
Annular connector 410 can, for example, be operatively connected to a plurality of generally linear rolling element bearings 405 (three in the illustrated embodiment). See, for example,
Roller elements or rollers 460 are operatively connected between races 430 of inner race members 420 and the races of outer race members 450. Roller elements 460 include a central gear or toothed section 462 and bearing surfaces 464 on each side thereof. Bearing surfaces 464 are angled, tapered or canted in the illustrated embodiment to include a dual taper corresponding to and mating with dual tapered bearing surfaces 434 of races 430 and the dual tapered bearing surfaces (not shown) of the races of outer race members 450.
As annular connector 410 is driven in a linear reciprocating manner to drive valve assembly 300, roller elements 460 roll along races 430 of inner race members 420 and along the races of outer race members 450. The relative positions of roller bearing elements 460 on a race are fixed by the cooperation or intermeshing of central gear section 462 and the gear sections of the bordering races. As described above for rolling element bearing 130, cages are not required between roller elements 460.
In the embodiment illustrated, for example, in
The geared roller elements of the rolling element bearings described above each include an intermediate or central gear section from which tapered bearing surfaces extend. However, roller elements including two geared sections having an intermediate roller bearing surface extending therebetween can be used. The intermediate roller bearing surface can, for example, have a generally circular cross section that changes in diameter over the length thereof to provide an angled, tapered or canted bearing surface. As also described above, other types of bearings, and particularly rolling element bearings, including ball bearings with races can be suitable for at least some mechanical linkages of the pump systems hereof.
Pump lifetime reliability considerations described above are complicated when the fluid surrounding flow conduit or bellows 240 also bathes the mechanical motor to valve assembly linkage. Once again, this fluid should be compatible with blood so that if any leakage of this fluid should occur into the blood stream, such peri-bellows fluid would not result in significant or any injury to the patient. As described above, oily or hydrophobic lubricant fluid, normally used with mechanical linkages having multiple bearings would be injurious if released. A truly blood compatible fluid can, for example, include dissolved sodium chloride and possibly other salts in similar concentrations as found in the blood. However, such salt solutions are quite corrosive when placed in contact with virtually all bearing hard steels, including so-called bearing hard 440 series stainless steels. In a number of embodiments hereof, bearing-hard, nitrided martensitic stainless steel (for example, CRONIDUR R 30 ™, available from Energietechnik Essen GmgH of Essen, Germany) that is corrosion resistant is used in the bearings or rolling element bearings of pump system 100. See German Patent No. DE3901470, the disclosure of which is incorporated herein by reference. Bearings including races and/or rolling elements formed from CRONIDUR are, for example, available from The Barden Corporation. Further, bearings having races and/or rolling elements made from a hard ceramic material can be used to provide corrosion resistance and suitable lifetime requirements.
In addition to the risk of bearing corrosion, there is also a risk of corrosion of copper wire conductors of rotary motor stator 124. Corrosion of such wires when exposed to the corrosive salt water environment of the fluid within housing sections 122 and 210 poses a failure mode for pump system 100. To lessen or eliminate this risk, stator 124 can, for example, be sealed in a hermetically welded titanium case using feedthroughs and sealed crimp joints to connect the copper wires of stator 124 with corrosive resistant conductors such as, for example, platinum wire in the feedthroughs and DFT® silver filled stainless tubing conductors in the leads exiting the motor stator hermetically sealed case. DFT® wire is a metal-to-metal composite available from Fort Wayne Metals of Fort Wayne, Ind.
Using, for example, a three dimensional depiction of the human anatomy surrounding ascending aorta 22, as found, for example, in the commercially available Visual Human software produced by the University of Washington Medical School, one can analyze the dimensions of the various organs in this peri-aortic space. In the case of pump system 100, the volume of drive system 110 (including, rotary motor 120, speed reducer 160 and rotary-to-linear convertor 180) can fit within the volume of lung space without significantly impinging on the other critical structures. As described above, the components of drive system 110 can, for example, be generally cylindrical in shape and extend into the right lung space in a right anterior oblique direction from the aorta at approximately a right angle from flow conduit assembly 200, which can also be generally cylindrical in shape. As described above, the displacement volume of drive system 110 may be made as small as, for example, less than 150 cc, less than 100 cc, or even less than 50 cc. As also described above, distance D1 from axis A1 to the distal end of housing section 122 of drive system 110 may, for example, be less than 12 cm, less than 10 cm or even less than 8 cm. The amount of sacrificed lung volume arising from pump system 100 should not significantly affect lung function, given, for example, an average right lung volume of 3200 cc.
Compared with currently available implantable heart assist pump systems, system 100 affords substantial functional improvements and minimally impacts upon surrounding organs and their function (and, particularly, minimally impacts lung function).
As discussed above, left ventricle 14 is typically weak in heart failure, and the forward strokes of moving valve assembly 300 add an assist or boost to blood coming from the left ventricle 14. Closure members 330 of valve assembly 300 are constructed so that closure members 330 move toward a closed position to close or to substantially close opening or port 320 when the forward velocity of valve assembly 300 is greater than the ambient blood flow velocity. In a number of embodiments, opening 320 is substantially sealingly closed during at least some portion of the forward stroke of valve assembly 300. “Leaking” blood flowing through one or more small openings between closure members 330 and valve support structure 310 during the forward stroke of valve assembly 300 may, for example, activate blood platelets, which can lead to blood clotting and, for example, strokes. When valve assembly 300 is returning or travelling rearward, port 320 opens because the forward blood velocity during left ventricle contraction is always greater than backward moving valve assembly 300 velocity.
Bench testing with high speed photography of valve assembly movement has revealed that a valve assembly such as valve assembly 300 typically requires approximately one third of its forward stroke to cause closure members 330 to move to a closed position to close port 320. Delayed valve closing during a forward valve stroke was found to be responsible for a significant loss in flow boosting efficiency of valve assembly 300. Testing of pump efficiency when closure members were moved/forced to a closed position at or around the beginning of the forward stroke (for example, near the end of the rearward valve stroke and just prior to the forward stroke) of a valve assembly such as valve assembly 300 demonstrated substantial improvement in pumping efficiency.
In this regard, testing demonstrated that actively moving the closure members of a valve assembly toward a closed position to close the valve opening at the beginning of the forward stroke can increase pumping efficiency by approximately 50 percent. Actively moving closure members of a moving valve pump system toward a closed state is thus desirable for the purpose of increasing pump efficiency. As used herein, the term “actively” refers to using one or more devices, mechanisms, systems and/or methods for moving closure members toward an open or closed position or state independent of the force asserted upon the closure members by blood flow. Actively moving the closure members of a valve assembly in a moving valve pump system can, for example, be effected using a mechanism or system that activates closure member movement based on the position of the valve assembly.
A valve closure member activating device or system can, for example, be a component of valve assembly 300 or be a component separate from, but in operative connection with, valve assembly 300. In a number of embodiments, such an activating system can, for example, include a component positioned within the blood flow pathway of flow conduit 240. Referring to
In
In the case of activating system 500, support member 530 and abutment members 510 are located in the blood stream to contact closure members 330 and force closure members 330 toward the closed position as the valve assembly 300 is moved to its rearwardmost position. In certain situations, the presence of such components in the blood stream can increase the risk of clotting. Such a risk can be substantially reduced or eliminated by positioning a valve closure system outside of or separate from the blood flow path.
In several embodiments of closure member activating systems hereof, the activating system is outside of or sealed from the blood flow path through the pump system (that is, outside or sealed from the flow path of flow conduit 240 in the case of pump system 10). In a number of such embodiments, at least one component of the valve closure members (or a component attached thereto) which moves (for example, rotates or pivots) with the valve closure members extends through at least a portion of the valve support structure so that the movement thereof (and, thereby, the movement of the valve closure members from and/or toward the closed to open positions) can be controlled by the activating system which resides outside of the flow path of blood through the pump system.
A seal can, for example, be provided around a component in operative connection with the closure members which extends through the valve support structure to prevent blood from exiting the pump system flow path. In the case of a pump system to be implanted for an extended period of time as discussed above, such a seal should be designed to survive more than a billion valve assembly stroke cycles over the life of the pump system. Typically, seals on moving components (for example, rotating shafts, rods or axels) include tight fitting bushings which compress against the moving component to create the seal. In the case of a blood contacting seal for a moving component and, particularly, for a component that will be moved through a very high number of cycles, bushings or compression seals present a number of problems. For example, there is a small crevice at the interface between the seal and the moving component (for example, at an axel-bushing joint) at which (at the microscopic blood cell level) some degree of undesirable blood cell shear and/or crushing can occur. Further, compression seals such as bushing are subject to wear over time. To compensate for problems associated with wear, elastic compression of the seal against the moving component is typically employed. However, such compression changes with wear, and a certain amount of force/torque exerted by the seal must be overcome to move the moving component. With wear over time, the resisting force/torque exerted by the compression seal can change, which complicates the design of a reliable valve closure system.
In several embodiments, seals hereof include a first connecting member attachable to a moving component so that it moves with the moving component, but not relative thereto, and a flexible sealing member attached to the first connecting member. The flexible sealing member is fixed to, for example, the valve support. Such a seal can, for example, include a first connecting member attached to a moving component so that it moves with the moving component, but not relative thereto, a second connecting member attached to a another component (which can be movable or stationary) and a flexible sealing member extending between the first connecting member and the second connecting member. The flexible sealing members can, for example, be formed as a layer, film, sheet or membrane through which the fluid to be sealed has limited or no mobility.
In a number of embodiments, closure members similar to closure members 330 are used in pump systems hereof wherein the axels, shafts or rods fixed to the closure members are extended to pass through at least a portion of the valve support structure and to extend outside of the flow conduit.
Each of first connecting member 344a and second connecting member 346a can, for example, include a biasing or spring-loaded annular member (for example, a metallic ring). Inner, first connecting member 344a biases to seal the inner arm or section 347a of the U-shaped annulus of flexible sealing member 348 against shaft 332a (see radially inward directed arrows in
Each of first connecting member 344a and second connecting member 346a can, for example, be formed as a split ring. An assembler can, for example, compress the ring of second connecting member 346a with dedicated pliers and insert the ring into the sealing annulus of flexible sealing member 348a. The assembler can then release the ring to expand the ring and force outer wall 349a of flexible sealing member 348a radially outwardly against the wall of valve support structure 310a to achieve a fluid seal therewith. Similarly, dedicated pliers can, for example, be used to expand the ring of inner, first connecting member 344a to a more open position and, when in proper position around shaft 332a and around inner member 347a of flexible sealing member 348a, release the ring to contract, thereby compressing inner wall 347a of flexible sealing member 348a against shaft 332a to achieve a fluid seal therewith.
Other components of valve assembly 300a can, for example, present difficulties with or interfere with the installation of seals 340a (for example, in forming a sealing connection with valve support structure 310a). To facilitate installation of seals 340a, seals 340a can first be installed to form a sealed connection with an outer sleeve or sheath 370 and with shaft 332a as illustrated in
To assist in providing proper alignment and relatively free movement thereof, each shaft 332a can cooperate with (for example, pass through) one or more bearings. In the embodiment of
External to (or radially outward from, with reference to axis A1) rolling element bearings 350a, at least one end of shafts 332a includes an extending section 332a′ (which can be a part of shaft 332a or connected thereto). Rotational activation of extending sections 332a′ results in rotation of closure members 330a operatively connected thereto in an opening or closing direction via an activating system such as activating system 500 illustrated, for example, in
In the illustrated embodiment, valve support structure 310a is formed in two sections 312a and 314a (see
In the embodiment illustrated in
An abutment member (not shown in
Rack 520 need, for example, travel only a short distance between the positioning gears 510 to activate closing or opening of both closure members 330a. In one embodiment, positioning gears 510 rotate closure members approximately 90 degrees from a fully open position illustrated in
As described above in connection with valve assembly 300, pressure from the flow of blood through valve opening 320a (particularly during rearward movement of or the backstroke of valve assembly 300a) tends to force closure members 330a to an open position. However, a mechanism or system can be provided to, for example, cooperate with activating system 500 to bias closure members 330a to an open position or state (that is, to actively cause movement of closure members 330a toward an open position or state, which is a default or normal state). Activating system 500 can, for example, include or have in operative connection therewith a biasing mechanism or system 540a that applies force to rack 510 to cause rack 510 to move (in the direction of arrow R in
Shafts 332a can, for example, be formed from a blood compatible polymeric material or a metal such as titanium. Support structure 310a can also be formed from a blood compatible polymeric material or a metal such as titanium. As illustrated in
Forming a sealed coaptation with the valve support structure and preventing of bouncing upon closing can also be facilitated with closure members which are rigid around the outer periphery thereof by providing a flexible element on a landing of the valve support structure which is contact by the closure members upon closing.
A situation that may arise during actively moving closure members 330a toward a closed position as valve assembly 300a reaches its rearwardmost position is that the natural flow rate of blood coming from the heart may be greater than the early forward velocity of valve assembly 300a during its forward stroke. In that case, closure members 330a may be opened by biasing mechanism 540a and/or the flowing blood prior to valve assembly 300a reaching a velocity that is greater than the ambient blood flow produced by the heart (at which velocity force exerted upon closure members 330a by the blood forces closure members 330a to a closed state), thereby reducing the pumping efficiency of valve assembly 300a.
A method for limiting or preventing reopening of valve assembly closure members during the early forward stroke of the valve assembly is to include a temporary latching or delaying system that will hold or otherwise maintain the closure members in the closed state for a period of time even if the natural flow from the heart exceeds the velocity of the valve assembly. Such a latching or delaying mechanism can, for example, operate only temporary (for example, until valve velocity exceeds blood flow velocity) to prevent the closure members from being locked in a close position. If the forward stroke of the valve assembly takes, for example, between 30 to 50 milliseconds, the latching or delaying mechanism can, for example, hold or maintain the doors in a close state for approximately 25% of the forward stroke time or roughly 7 to 12 milliseconds. Such a temporary delaying or latching time period may, for example, be accomplished using a biasing system (which biases closure members 332a to an open state) with a timed release mechanism or dampening mechanism that takes, for example, 7 to 12 milliseconds to release the rack and allow the biasing action thereof to compete with the closing force of the valve assembly moving forward at a velocity greater than the natural velocity of the blood stream behind the valve assembly.
Rather than spring biasing mechanism or system 540 of activating system 500, activating system 600 includes biasing system 640, which includes one or more resilient, expandable/compressible enclosures 642 which is/are fluid filled and surrounded by (or immersed in) fluid (for example, filled with and surrounded by the fluid present within housing 210 of fluid conduit assembly 200 and within housing 122 of pump system 10). Filling of enclosure(s) 642 during expansion is controlled in a manner to effect latching or delaying of movement of closure members 330b toward and open state. In the illustrated embodiment, the material of enclosure 642 is folded or corrugated in, for example, the manner of a bellows. Enclosure 642 can, for example, be formed of a resilient metal. Resilient, enclosure or biasing bellows 642 is compressed by forward (with reference to blood flow as discussed in connection with
When the valve assembly 300 is moved near its rearwardmost position, abutment member 660 engages the free end of rack 610 (opposite the end in operative connection with enclosure 642). Rack 610 is moved forward upon such contact, and enclosure 642 is compressed against a contact member 670. Contact member 670 is connected to activating system 500. Compression of enclosure 642 rapidly forces fluid out of enclosure 642 via one-way valve 644. As describe above, the forward motion of rack 610 rotates positioning gears 610 so that shafts 332b and attached closure members 330b rotate, for example, 90 degrees to a closed position. Inlet hole(s) or passage(s) 646 are dimensioned such that a predetermined range of time (for example, approximately 7 to 12 milliseconds) is required before resilient enclosure 642 begins to refill with fluid flowing through inlet holes 646. As valve assembly 300b accelerates forward, pushing blood, a positive pressure differential develops across closure members 330b that keeps them closed for the remainder of the forward stroke. At the end of the forward stroke, compressed resilient enclosure 642 fills with fluid and expands, forcing rack 610 rearward and opening closure members 330b. When valve assembly 330b moves forward to pump blood, closure members 330b are thus biased or maintained toward a closed or nearly closed position until the velocity of the moving valve assembly 300b exceeds the velocity of the blood exiting the heart. Because collapsed enclosure 642 is filled with a fluid at a controlled refill rate, closure members 330b are held near or at the fully closed position for a controlled time, (for example, 5 to 20 milliseconds or 7 to 12 milliseconds). As described above, when the velocity of moving valve assembly 300b exceeds the velocity of blood coming from the heart, the valve is biased or forced closed by the force of the blood. When valve assembly 300b nears the end of its forward or pumping stroke, it begins to slow down and then reverses. The force of blood upon closure members 330b during this slowing down and reversal drops. Enclosure 642 can then expand and move closure members 330b toward an open position. The force exerted upon closure members 330b upon expansion of enclosure 642 is assisted by the forward flow of blood against the rearward moving closure members 330b.
As a safety or failsafe feature, abutment member or mechanical stop 660, which is fixed to mechanical ground of the pump system 10 (or another moving valve pump system hereof) can be moved “out of the way” by, for example, changing an applied current (that is, either increasing current or decreasing current applied). For example, abutment member 660 can include or be connected to a component such as a shape memory alloy component (for example, a Nitinol component, which is a metal alloy of nickel and titanium), whereby the position of abutment member 660 can be changed by electrically activating/deactivating the shape memory alloy (or other) component of abutment member 660 (which can be the entirety of abutment member 660). In one embodiment, current must be applied to a shape memory alloy component to position abutment member 660 to contact rack 610. If current is removed from the shape memory alloy component, abutment member 660 is moved to a position wherein it cannot contact rack 610 (see, for example, dashed lines in
The foregoing description and accompanying drawings set forth a number of representative embodiments the present time. Various modifications, additions and alternative designs will, of course, become apparent to those skilled in the art in light of the foregoing teachings without departing from the scope hereof, which is indicated by the following claims rather than by the foregoing description. All changes and variations that fall within the meaning and range of equivalency of the claims are to be embraced within their scope.
This application claims benefit of U.S. Patent Application Ser. No. 61/444,414, filed Feb. 18, 2011, and U.S. Patent Application Ser. No. 61/444,510, filed Feb. 18, 2011, the disclosures of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61444510 | Feb 2011 | US | |
| 61444414 | Feb 2011 | US |
