FIELD OF THE INVENTION

The present disclosure relates to a blood pump system that includes a pump, conduits, a control unit, and a source of power, whereby the system may be used for a variety of clinical indications. In addition, the present disclosure relates to various inflow and outflow conduits, conduit tips, and support structures for use with the blood pump system. Specifically, the devices disclosed herein may be useful for persistently increasing the overall diameter and lumen diameter of veins and arteries in patients needing a vascular access site for hemodialysis, a bypass graft, or other type of surgery or procedure where a larger vein or artery diameter is desired. The devices, methods, and systems disclosed herein may also be useful for increasing lower extremity venous return and reducing lower extremity venous pressure in patients with lower extremity venous hypertension, including those patients with skin discoloration and ulceration. The disclosed devices, methods, and systems may be further useful for providing increased local blood flow to organs and tissues in need thereof, such as the lower extremities of patients with peripheral arterial disease (PAD).

BACKGROUND INFORMATION

There are over 650,000 chronic kidney disease (CKD) patients in the US, with over 100,000 new CKD patients each year. There is a four percent annual increase projected for the prevalent population, due to factors as high blood pressure, diabetes, and an aging population.

Hemodialysis is the treatment of choice for >90% of CKD patients in the US. Without hemodialysis or some other form of renal replacement therapy, most patients with CKD would die. A typical CKD patient undergoing hemodialysis treatment must have their vascular system connected to a hemodialysis machine two to three times per week. For hemodialysis, there are three common vascular access site options. The preferred access site option is an arteriovenous fistula (AVF), which is a direct, surgically created connection between an artery and a vein, preferably in the wrist, or alternatively, in the forearm or upper arm. Another access site option is an arteriovenous graft (AVG), which is a surgically created connection between an artery and vein using an interposed synthetic conduit, preferably in the forearm, or alternatively, in the upper arm, chest, groin, or leg. The final major access site option is a catheter inserted into a large vein in the neck, chest, leg, or other anatomic location.

Patients with an AVF have less morbidity, less mortality, and a lower cost of care compared with patients with an AVG or a catheter; therefore, AVF is the preferred form of vascular access for hemodialysis. Patients with an AVG or catheter have substantially higher rates of infection and death than patients having an AVF, with catheter patients having the worst outcomes. In addition, patients having an AVG or catheter have a higher average cost of care, with catheter patients having the highest costs. If a patient is eligible for an AVF, the wrist or forearm is generally preferred over an AVF in the upper arm due to higher rates of hand ischemia and the generally shorter and deeper vein segments of the upper arm. One generally accepted principle that is followed when creating AVF and AVG vascular access sites is to start as far distal as possible and to preserve the more proximal veins for vascular access site creation later. This means starting at the wrist for AVF patients and in the forearm for AVG patients. However, the smaller diameter of more distal veins often reduces the success of vascular access surgery in these locations.

Unfortunately, about 85 percent of patients are ineligible for an AVF in the wrist, mostly due to vein and artery diameters that are too small. Furthermore, about 50-60 percent of all AVFs created are not useable without additional surgical and interventional procedures due to an occurrence commonly referred to as “maturation failure,” which is correlated with small vein and artery diameter. The availability of veins and arteries with larger diameters is correlated with higher AVF eligibility, lower rates of maturation failure, faster AVF maturation, and prolonged primary and secondary patency rates.

Currently, there are few options for permanently or persistently increasing the diameter of a vein or artery. All current methods use mechanical methods of dilation, such as balloon angioplasty, that can lead to vein or artery injury. Since a patient needs to have peripheral veins and arteries of a certain size for a physician to create an AVF, it is desirable to have a method and system for persistently and permanently increasing the size or diameter of peripheral veins or arteries.

Approximately 7 million people in the US suffer from chronic venous insufficiency and hypertension, which can progress to venous ulceration. Lower extremity ulcer is the most common form of chronic wound, with an estimated prevalence of 1% of the US population. About 2.5 million people in the US have a lower extremity ulceration and about 600,000 people seek treatment for a venous ulceration of the lower extremity each year in the US. The incidence of venous ulceration is expected to rise as the population ages.

In a survey of patients with venous ulcers, 81% of patients reported an adverse effect on mobility, 56% reported spending up to 8 hours per week on ulcer care, 68% reported a negative emotional impact, including fear, social isolation, anger, depression, and negative self-image. In the survey, 80% of patients are not working outside the home; and of the 20% employed, leg ulceration correlated with time lost from work, job loss, and adverse effects on finances.

Lower extremity venous hypertension and ulceration is costly to treat and places a substantial burden on health care providers and systems. In a study of 78 venous ulcer patients at the Cleveland Clinic, median ulcer size was 2.8 cm2(mean=9.4 cm2) and 5% had bilateral ulcers. The median time to ulcer healing was 77 days (mean=108 days) and the mean cost of treatment was $2,400 per month. The mean total cost of treatment to heal an ulcer was $9,685 per patient. For patients requiring more than a year to heal, the average total cost per patient was $18,534.

In most cases, venous hypertension and ulceration results from valvular incompetence secondary to deep vein thrombosis or an unknown cause. In a substantial minority of cases, venous hypertension and ulceration results from femoral or pelvic venous obstruction secondary to deep vein thrombosis, vein injury, or extrinsic vein compression. Chronic tissue exposure to localized venous hypertension leads to dilation of capillaries with increased permeability and leakage of plasma and erythrocytes, trapping and activation of leukocytes in the microcirculation, and the release of free radicals and other toxic products, such as tumor necrosis factors and collagenase, which can promote cell death and tissue damage. Leakage of fibrinogen into surrounding tissues binds or “traps” growth factors and cytokines, and renders them unavailable for maintenance and repair of tissue integrity.

Lower extremity venous hypertension presents clinically as leg redness and discoloration, swelling, pain, edema, pruritus, scaling, discharge, and lipodermatosclerosis. Ulcers generally develop on the medial aspect of the leg, possess irregular borders, and can be associated with severe pain. Venous ulcers are often complicated by superimposed bacterial infection. The arterial circulation is usually adequate. Current treatments for lower extremity venous hypertension and ulcer are often inadequate. Patients are mostly offered palliative treatments, with the goal of healing ulcers and preventing recurrence, including aggressive wound care, compression therapy to decrease lower extremity venous pressure and increase venous return, lower extremity vein stripping or ablation, and skin grafting. However, current treatments often fail to heal ulcers and recurrence rates for healed ulcers are high.

Currently, small “heart pumps” exist; however, such pumps are costly and not designed and dimensioned for use in an extremity or for the uses described herein. As such, there is an unmet clinical need for systems, components, methods, and pump devices that can increase the diameter of peripheral veins and arteries at a reasonable cost, amongst other clinical indications. Additionally, there is a need for a systems, components, methods, and pump devices that can increase lower extremity venous return, reduce lower extremity venous hypertension, and heal venous ulcers. Several medical procedures and medical devices rely on pump and conduit systems to move various fluids, such as blood, into and out of a patient. Various studies have shown that the configuration of the inflow conduit and inflow conduit tip directly affects the flow characteristics of the fluid entering the inflow conduit of a blood pump system. Various studies have shown that the configuration of the outflow conduit and outflow conduit tip directly affects the flow characteristics of the fluid leaving the outflow conduit of a blood pump system. When conduits are used to pump blood out of and back into a patient, there is the risk of thrombogenesis caused by regions of low and high wall shear stress (WSS) in the flow, along with the associated risk of thromboembolic events. For example, it is well understood that regions of low WSS may cause platelet aggregation, while regions of high WSS may cause platelet activation. Regions of very high WSS may also present the risk of hemolysis. For example, a region of WSS greater than 150 Pa is likely to lead to hemolysis.

SUMMARY OF THE DISCLOSURE

The present application relates to blood pump systems, including blood pump systems with wide operating ranges, low cost-of-goods-sold (COGS), and intermediate duty times. These blood pump systems are designed for use in a variety of clinical situations and for a variety of clinical indications, as described herein.

The blood pump systems described herein can be used for increasing the diameter of veins and arteries, preferably peripheral veins and arteries. The system will function to move blood in such a way as to cause an increase in vein or artery diameters. This can be accomplished by discharging (“pushing”) blood into a vein or artery or by removing (“pulling”) blood from a vein or artery. By either method, the system increases the flow of blood in a vessel, which ultimately leads to a persistent increase in vessel diameter. As such, the system (and more particularly the pump) uses mechanical means to activate biological response pathways resulting in the enlargement of veins or arteries and modifications in the structure of the dilated artery and veins walls, a process sometimes described as “vascular remodeling.” The system has a blood pump, conduits to carry or convey blood to and from the blood pump, a control system to monitor the blood pump and modify the operation of the blood pump, and a power source. As such, the system comprises a group of members that can be, for example, fluidly connected to an artery at one end and fluidly connected to a vein at the other, whereby, when activated, blood is pumped at a rate such that wall shear stress (WSS) on the endothelium of the vein, artery, or both is elevated for a period of time sufficient to cause a persistent enlargement in the vein or artery. Any of a variety of pumps and pump systems may be used so long as the flow of blood through the pump system can be controlled to produce the desired increase in blood vessel diameter.

The blood pump systems described herein can be used to increase lower extremity venous return, reduce lower extremity venous hypertension, and heal venous ulcers. The system will function to move blood from a vein in the affected lower extremity, such as a femoral, saphenous vein, or iliac vein, to a location in the venous circulation such that the return of venous blood from the lower extremity to the heart is improved. Locations for return to the venous circulation include the jugular vein, the axillary vein, the subclavian vein, the brachiocephalic vein, the superior vena cava, and the right atrium. The system has a blood pump, one or more conduits to carry or convey blood to and from the blood pump, a control system to monitor the blood pump and modify the operation of the blood pump, and a power source. As such, the system comprises a group of members that can be, for example, fluidly connected at one end to a peripheral vein and fluidly connected to a peripheral, central vein, or right atrium at the other end, whereby, when activated, blood is pumped at a rate such that venous blood pressure is lowered in the treated lower extremity for a period of time sufficient to cause partial or complete healing of a venous ulcer to occur. Any of a variety of pumps and pump systems may be used so long as the flow of blood through the pump system can be controlled to produce the desired effect.

Various types of blood pumps may be employed, including positive displacement and rotary pumps, with rotary type pumps being preferred. In one embodiment, a rotary blood pump system includes a pump having a housing defining an inlet to receive blood and an outlet to discharge blood. The pump housing is designed and dimensioned to house a rotating impeller suspended on bearings. The pump housing can have a first bearing proximal to the inlet portion of the housing and a second bearing proximal to the outlet portion of the housing. Blood enters and exits the rotating impeller, whereby the impeller increases the exit velocity of the blood. This increased velocity is recovered or translated as increased pressure as the blood decelerates within the pump diffuser, which terminates in the pump outlet.

In other embodiments, various types of rotary blood pumps may be used. For example, an axial flow pump, a mixed flow pump, or preferably, a centrifugal blood pump may be used. In addition, a variety of pump impeller bearings may be used, including, but not limited to magnetic bearings, hydrodynamic bearings, and, preferably pivot (contact) types. Similarly, various types of pump diffusers may be used, including but not limited to a collector diffuser, or preferably a volute diffuser.

In one embodiment, a centrifugal blood pump with pivot bearings includes a pump housing defining a pump inlet having an inflow diffuser to receive blood and direct blood onto an impeller, the pump housing having a top bezel and top pivot bearing extending from a top of the housing into the inlet, and a bottom bezel and bottom pivot bearing extending from a bottom of the housing into the interior space of the housing. The pump also includes the impeller suspended within the housing, the impeller further having a bearing lumen to receive an impeller pivot. The impeller pivot has a first end to engage the top pivot bearing, proximal to the inlet portion and a second end to engage the bottom pivot bearing, proximal to the outlet portion. In one embodiment, at least one end of the impeller pivot is convex and the end of at least one pivot bearing is concave. In another embodiment, the end of at least one end of the impeller pivot is concave and at least one end of each pivot bearing is convex. In another embodiment, both ends of the impeller pivot are concave and both pivot bearings are convex. In another embodiment, both ends of the impeller pivot are convex and both pivot bearings are concave. The impeller can include a variety of fin or blade constructions designed to contact and accelerate blood into the volute. For example, the impeller defines a plurality of blades on the top surface of the impeller and extending radially from a center of the impeller to an outer edge of the impeller. The blades accelerate blood from the impeller's central inlet to its peripheral outlet. In another option, the impeller does not include blades or fins, but does include means to move or propel blood. The impeller optionally includes at least one washout lumen, cut-away, or bore extending generally parallel to a central axis of the impeller from a bottom surface through the impeller to a top surface. In some embodiments, the lumen is designed to prevent stagnation of blood under the impeller and around the bottom pivot bearing.

The blood pump includes a motor, preferably electric, designed to actuate the impeller. In one embodiment, the blood pump includes a drive motor having at least one magnet mechanically attached to the impeller and at least one armature mechanically attached to the housing. The armature induces an electromotive force on the at least one magnet attached to the impeller. The pump motor can be an axial-gap brushless direct current (DC) torque motor with sensorless back electromotive force (back-EMF) commutation. The motor may employ a sintered alloy of neodymium iron boron (NdFeB) for the magnets in the impeller and a 3-phase planar “racetrack” coil configuration in the stator. The motor may have a pancake aspect ratio with a very small axial length in comparison to its diameter.

In one embodiment, the blood pump system includes a centrifugal blood pump with an operating range between about 50 milliliters per minute (mL/min) and about 1500 mL/min. The system also includes a pump housing defining a pump inlet to receive blood and direct blood onto an impeller. The pump housing has a top pivot bearing extending from a top of the housing into the inlet, and a bottom pivot bearing extending from a bottom of the housing into the interior space of the housing. The pump also includes an impeller suspended within the housing wherein a first gap between the impeller and a top portion of the housing is in a first range between about 0.05 mm and about 0.2 mm.

The impeller includes an impeller pivot having a first end to engage the top pivot and a second end to engage the bottom pivot and a plurality of blades on the top surface of the impeller and extending radially away from a center of the impeller, the blades to force blood received at the inlet through the pump housing and to the outlet. The impeller also includes at least one lumen extending parallel to a central axis of the impeller from the bottom surface through the impeller to a top surface.

The pump further includes at least one magnet mechanically engaged to the impeller and an electric motor to magnetically engage the at least one magnet, wherein the electric motor rotates the at least one magnet and the impeller. In other embodiments, the pump also includes a ferromagnetic backplate to magnetically engage the at least one magnet.

The blood pump system has one or more conduits including a first (inflow) conduit having two ends, a first end that is fluidly connected to a location in the vascular system and receives blood from that location, and a second end that is fluidly connected to the pump. The inflow conduit delivers blood to the pump. The blood pump system has a second (outflow) conduit having two ends, a first end that is fluidly connected to the pump and receives blood from the pump, and a second end that is fluidly connected to a location in the vascular system and delivers blood to that location.

In some embodiments, the conduits of the blood pump system have an individual length of between 2 cm and 110 cm and a combined length between 4 cm and 220 cm, and may be trimmed to a desired length by a physician, including during implantation of the pump system. The conduits each have an inner diameter between 2 mm and 10 mm, and preferably between 3 mm and 5 mm. The conduits may be formed at least in part from polyurethane (e.g. Pellethane® or Carbothane®), polyvinyl chloride, polyethylene, silicone elastomer, polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (ePTFE), polyethylene terephthalate (PET, e.g. Dacron), and combinations thereof. The conduits may further include an elastic reservoir.

All or portions of the conduits may be reinforced with a braided or spiral coiled shape memory material, such as nitinol, or other self-expanding or radially expansive material, such as stainless steel. For pump systems designed for the treatment of lower extremity venous hypertension and venous ulcers, the conduit that conveys blood from a lower extremity vein to the pump portion of the pump system may further comprise a distal segment of ePTFE or Dacron such this segment can be fluidly connected to the lower extremity vein by a surgical anastomosis. This ePTFE or Dacron segment may further comprise an external reinforcement, such as additional ePTFE or Dacron material, or with a self-expanding or radially expansile material such as nitinol or stainless steel. This external reinforcement may take the form of a spiral or a braid, or may comprise a more completely circumferential and uniform support structure, or may be configured in another manner that resists collapse, compression, or coaptation when the pressure within the conduits is low or negative. The conduits may have chamfered ends that fluidly connect to the vascular system. The ends can be chamfered at an angle between 10 degrees and 80 degrees. One or more of the conduits may have one or more holes or fenestrations in the walls of the distal ends, when configured for placement within the lumen of a blood vessel or other intravascular location. The conduits may be secured to the pump using radially-compressive connectors.

In another embodiment, a blood pump system comprising a centrifugal blood pump further comprising a pump housing defining a pump inlet to receive blood and direct blood onto an impeller. The pump housing has a top pivot bearing extending from a top of the housing into the inlet, and a bottom pivot bearing extending from a bottom of the housing into the interior space of the housing. The pump also includes an impeller suspended within the housing wherein a first gap between the impeller and a top portion of the housing is in a first range between about 0.05 mm and about 0.2 mm.

The impeller includes an impeller pivot having a first end to engage the top pivot and a second end to engage the bottom pivot and a plurality of blades on the top surface of the impeller and extending radially away from a center of the impeller, the blades to force blood received at the inlet through the pump housing and to the outlet. The impeller also includes at least one lumen extending parallel to a central axis of the impeller from the bottom surface through the impeller to a top surface.

The pump further includes at least one magnet mechanically engaged to the impeller and an electric motor to magnetically engage the at least one magnet, wherein the electric motor rotates at least one magnet and the impeller. The blood pump also includes having at least one conduit having an end in communication with the pump inlet or pump outlet and a distal end for insertion into a blood vessel. The distal end includes a tapered, non-chamfered distal tip defining a generally circular end opening coaxial with a central longitudinal axis of the distal end. The distal end also includes a first plurality of side holes symmetrically arranged about a circumference of the distal tip, where the first plurality of side holes are proximal to the circular end opening and oriented at an angle relative to the central longitudinal axis. The distal tip also includes a second plurality of side holes arranged about a circumference of the distal tip.

In some embodiments, the conduits of the blood pump systems also include one or more side ports in communication with the conduits. The blood pump systems also include one or more attachable conduit cuffs to engage the at least one conduit.

In one embodiment, a blood pump system includes a blood pump and a control system to monitor the blood pump system and modify the operation of the blood pump to maintain an increased mean WSS within an artery or vein fluidly connected to the blood pump. The control system is further configured to maintain mean WSS within a vein in the range of 0.76 to 23 Pascals (Pa), or preferably in the range of 2.5 to 10 Pa. In another embodiment, the control system monitors and maintains an increased mean blood velocity within an artery or vein fluidly connected to the blood pump. In this embodiment, the control system is configured to maintain mean blood velocity within an artery or vein in the range of 10 cm/s and 120 cm/s, or preferably in the range of 25 cm/s and 100 cm/s. In either embodiment, the blood pump system is configured to maintain increased mean wall shear stress or increased mean blood velocity for at least 1 day, 7 days, 10 days, 14 days, 28 days, 42 days, 56 days, 84 days, or 112 days. As used herein, term velocity may refer to speed of the blood regardless of directional component or vector.

The blood pump system has a control system to achieve and maintain the desired flow rate, which can optionally include a control device for receiving information and controlling the operation of the pump of the blood pumping system. At a minimum, the control system can be manually actuated to adjust speed of the motor. Alternately, an automatic (i.e. “smart”) control system can be used. Optionally, the control system includes sensors that can be in the pump, the conduits, or in the vascular system of the patient. In one embodiment, the control device can measure the rotational speed of the motor based on the zero-crossings of the back-EMF waveform. These zero crossings indicate magnetic pole reversals of the impeller. With this configuration, the speed of the motor is controlled by pulse width modulation (PWM) of the input voltage, and torque is controlled by PWM of the input current. The control device may also monitor other state variables of the pump motor, such as current and voltage, from which both the flow rate through the blood pumping system and the WSS in the peripheral blood vessel can be estimated and controlled.

The control device preferably includes a “processor,” which comprises a sensing stage, processing stage, and power stage to drive and control the pump motor. The processor energizes the motor windings and controls the motor speed by analyzing the back-EMF in the motor windings, as well as information from optional sensors. The processor can execute control algorithms encoded on a computer-readable medium. The blood pump system includes a cable for electrically connecting the control device to the pump and optional sensors. The blood pump system also includes a power source that, in some embodiments, may be integrated into the control device. In some embodiments, the power source for the blood pump system may be mobile (e.g. a rechargeable battery or fuel cell) or stationary (e.g. a power base unit connected to AC mains).

The control system may acquire information from various sources. The motor drive electronics within the control device can measure at least one of the motor speed, input power, or current required to operate the pump. In other embodiments, the control system includes sensors in the blood pump or conduits that measure at least one of a blood velocity, a blood flow rate, a resistance to blood flow in a peripheral blood vessel, a blood pressure, a pulsatility index, and combinations thereof. In other embodiments, the control system includes sensors in the vascular system of the patient that measure at least one of a blood velocity, a blood flow rate, a blood pressure, a pulsatility index, a vessel diameter, and combinations thereof.

In some embodiments, the control system may estimate and maintain a desired and elevated level of WSS in a target vessel or a donating artery or vein, using the information from the control device and/or sensors, such as a motor speed, motor input power, pump flow rate, pump pressure head, pressure near the junction of the outflow conduit, and the target vessel, pressure drop across a blood vessel, and combinations thereof. For this application, “target vessel”, “target blood vessel”, “target vein”, or “target artery” refers to a specific segment of an artery or a vein that is intended for treatment to achieve a persistently increased overall diameter and lumen diameter when a pump-conduit assembly is implanted, configured, and operated in such a manner as to result in the persistent increase in the overall diameter and lumen diameter.

Various control system methods may be used to automatically control the operation of the blood pump system. In one embodiment, a method of determining and controlling a WSS in a blood vessel includes the steps of measuring a blood viscosity, measuring a blood flow rate in a blood pump system or the blood vessel, and measuring a radius of the blood vessel. The steps also include determining the WSS in the blood vessel from the measured blood viscosity, the measured flow rate, and the radius of the blood vessel, comparing the determined WSS to a predetermined reference value, and adjusting a blood pump speed when the determined WSS does not approximate the predetermined reference value. The steps are repeated until the determined WSS approximates the predetermined reference value.

In another embodiment, a method of computing and controlling a WSS in a blood vessel includes the steps of estimating a blood viscosity, measuring a blood flow rate in a blood pump system or the blood vessel, and measuring a radius of the blood vessel. The steps also include determining the WSS from the estimated blood viscosity, the measured blood flow rate, and the radius of the blood vessel, comparing the determined WSS with a predetermined reference value, and adjusting a blood pump speed when the determined WSS does not approximate the predetermined reference value. The steps are repeated until the determined WSS approximates the predetermined reference value.

In one embodiment, a method of estimating and controlling a WSS in a blood vessel includes the steps of estimating a blood viscosity, measuring at least one motor state variable of a blood pump system selected from a voltage, a current, or a pump speed, and estimating a blood flow rate in the blood pump system. The steps also include measuring a pressure in the blood vessel, determining a vascular resistance of the blood vessel from the estimated blood flow rate and the measured pressure in the blood vessel, estimating a radius of the blood vessel. The steps further include determining the WSS from the estimated blood viscosity, the estimated blood flow rate, and the radius of the blood vessel, comparing the determined WSS with a predetermined reference value, and adjusting the pump speed when the determined WSS does not approximate the predetermined reference value. The steps are repeated until the determined WSS approximates the predetermined reference value.

In another embodiment, a method of estimating and controlling a WSS in a blood vessel using a blood pump system includes the steps of estimating a blood viscosity, measuring at least one motor state variable of the blood pump system selected from a voltage, a current, or a pump speed, and estimating a blood flow rate and a pressure head in the blood pump system. The steps also include calculating a vascular resistance of the blood vessel from the estimated blood flow rate and the estimated pressure head, estimating a radius of the blood vessel, and determining the WSS from the estimated blood viscosity, the estimated blood flow rate, and the estimated radius of the blood vessel. The steps further include comparing the determined WSS with a predetermined reference value and adjusting the pump speed when the determined WSS does not approximate the predetermined reference value. The steps are repeated the determined WSS approximates the predetermined reference value.

In one embodiment, a method of estimating and controlling a WSS in a blood vessel using a blood pump system includes the steps of estimating at least one member selected from a group consisting of a blood viscosity, a blood flow rate, a pressure head in the blood pump system, and a radius of the blood vessel, measuring at least one motor state variable of the blood pump system selected from a group consisting of a voltage, a current, and a pump speed, and determining the WSS in the blood vessel. The steps also include comparing the determined WSS with a predetermined reference value and adjusting the pump speed when the determined WSS does not approximate the predetermined reference value. The steps are repeated until the determined WSS approximates the predetermined reference value.

In yet another embodiment, a sensorless method to avoid a collapse or coaptation of a blood vessel or atrial chamber fluidly connected to a blood pump system upon detecting an imminence of the collapse at an inlet of the blood pump system includes the steps of measuring a blood pump motor current and continually determining a spectral analysis representation of the blood pump motor current in a form of a Fourier series. The steps also include providing a detection indication when an amplitude of the second harmonic term of the Fourier series exceeds a reference value and decrementing a pump speed when the amplitude of the second harmonic term of the Fourier series exceeds the reference value. The steps are repeated until the amplitude of the second harmonic term falls below the reference value.

In another embodiment, a blood pump system includes a blood pump and a control system to monitor the blood pump system and modify the operation of the blood pump to maintain a reduction in venous blood pressure in the treated lower extremity. The blood pump is also configured to maintain the lumen area of the inflow conduit and the fluidly connected peripheral vein segment during changes in body position, such as a change from standing to lying down. In one embodiment, the control system monitors blood pressure in the lower extremity vein fluidly connected to the inflow conduit of the blood pump system and adjusts the pump speed to maintain vein pressure in a desired range that is low enough to result in adequate venous return through the blood pump system while simultaneously avoiding vein wall collapse, coaptation, or prolapse. In this embodiment, the control system is configured to maintain a pressure in the lower extremity vein segment adjacent to the inflow conduit in the range of 5 mmHg and 100 mmHg, or preferably in the range of 10 mmHg and 50 mmHg or the range of 10 mmHg and 25 mmHg. In either embodiment, the blood pump system is configured to generally maintain this lower extremity vein segment pressure range for at least 7 days, 28 days, 56 days, 112 days, 224 days, or 356 days.

The blood pump system has a control system to generally achieve and maintain the desired lower extremity vein segment pressure range, which can optionally include a control device for receiving information and controlling the operation of the pump of the blood pumping system. At a minimum, the control system can be manually actuated to adjust speed of the motor. Alternately, an automatic (i.e. “smart”) control system can be used. Optionally, the control system includes sensors that can be in the pump, the conduits, or the vascular system of the patient. The sensors, including but not limited to position sensors, may be in or on the patient at various other locations. The control device can measure the rotational speed of the motor based on the zero-crossings of the back-EMF waveform. These zero crossings indicate magnetic pole reversals of the impeller. The speed of the motor is controlled by PWM of the input voltage, and torque is controlled by PWM of the input current. The control device also monitors other state variables of the pump motor, such as current and voltage, from which both the flow rate through the blood pumping system can be estimated and controlled. The control device preferably includes a memory, a processor for controlling the pump motor speed, analyzing the information coming from the motor drive electronics and optional sensors, and executing instructions encoded on a computer-readable medium. The blood pump system includes a cable for electrically connecting the control device to the pump and optional sensors. The blood pump system also includes a power source that, in some embodiments, may be integrated into the control device. In some embodiments, the power source for the blood pump system may be mobile (e.g. a rechargeable battery or fuel cell) or stationary (e.g. a power base unit connected to AC mains).

The control system may acquire information from various sources. The motor drive electronics within the control device can measure at least one of the motor speed, input power, or current required to operate the pump. In other embodiments, the control system includes sensors in the blood pump or conduits that measure at least one of a blood velocity, a blood flow rate, a blood pressure, a body position, and combinations thereof. In other embodiments, the control system includes sensors in the vascular system of the patient that measure at least one of a blood velocity, a blood flow rate, a blood pressure, and combinations thereof.

Various control system methods may be used to automatically control the operation of the blood pump system. In one embodiment, a method of reducing lower extremity vein segment pressure includes the steps of estimating body position and adjusting the speed of the pump based on body position. In another embodiment, a method of reducing lower extremity vein segment pressure includes the steps of estimating body position, measuring a blood pressure in the inflow conduit or the segment of vein fluidly connected to the inflow conduit, and adjusting the speed of the pump based on body position and blood pressure in the inflow conduit or the segment of vein fluidly connected to the inflow conduit. In another embodiment, a method of reducing lower extremity vein segment pressure includes the steps of measuring at least one motor state variable of the blood pump system selected from a group consisting of a voltage, a current, and a pump speed, and setting the speed of the blood pump system to provide at least a certain minimum flow of blood through the blood pump system. In another embodiment, a method of reducing lower extremity vein segment pressure includes the steps of measuring a blood flow through the pump system, and setting the speed of the blood pump system to provide at least a certain minimum flow of blood through the blood pump system.

In yet another embodiment, a sensorless method to avoid a collapse or coaptation of a lower extremity vein segment fluidly connected to a blood pump system upon detecting an imminence of the collapse of the vein or an inflow conduit at or near an inlet of the blood pump system includes the steps of measuring a blood pump motor current and continually determining a spectral analysis representation of the blood pump motor current in a form of a Fourier series. The steps also include providing a detection indication when an amplitude of the second harmonic term of the Fourier series exceeds a reference value and decrementing a pump speed when the amplitude of the second harmonic term of the Fourier series exceeds the reference value. The steps are repeated until the amplitude of the second harmonic term falls below the reference value.

In some other embodiments, the systems and methods disclosed herein may be encoded on computer-readable media that may be executed by a processing device. Any reference values or predetermined standards used by the systems and methods may be stored in a database or other suitable storage medium.

The disclosure also relates to various conduit tips. In one embodiment, the inflow conduit tip includes a tubular body having a proximal end and a distal end wherein the tubular body defines a lumen between the proximal end and the distal end. The proximal end defines an annular barb about an exterior surface of the inflow conduit tip and the distal end defines an annular flange about a circumference of the tubular body and a distal opening. The distal opening further includes a distal end surface having at least one peak portion and at least one valley portion.

In some embodiments, the inflow conduit tip consists essentially of a metal or a metal alloy. The inflow conduit tip may further comprise an antithrombotic coating, including a coating comprising heparin. Additionally, the distal opening may be defined by a distal end surface that is fully arcuate from an external surface of the inflow conduit tip to an internal surface of the conduit tip. In another aspect, the distal opening comprises two peak regions and two valley regions. Alternatively, the distal end surface may have a generally undulating configuration. In one aspect, the distal end surface has a profile generally defined by a sine function.

In other aspects, the proximal end defines another annular barb. The other annular barb is disposed distally of the annular barb. Moreover, the other annular barb extends from a longitudinal axis of the inflow conduit tip at an angle greater than that of the annular barb.

The present disclosure also relates to an intravascular outflow conduit tip. In one embodiment, the conduit tip includes a tubular body having a proximal end and a distal end wherein the tubular body defines a lumen between the proximal end and the distal end.

In another embodiment, the outflow conduit tip is configured for insertion into a peripheral vein, wherein the outflow conduit tip includes a generally tubular structure having an extravascular inflow branch in fluid communication with an intravascular branch. The inflow branch intersects the intravascular branch at an oblique angle and generates a jet-like blood flow where the velocity of blood exiting a distal end of the inflow branch into the intravascular branch is higher than that of the blood entering a proximal end of the inflow branch. In one aspect, the extravascular inflow branch includes a barb fitting at the proximal end. In this embodiment of the outflow conduit tip, a stenosis within the tip is intentionally formed to create a jet flow that increases the WSS within the outflow blood vessel immediately downstream, causes vascular remodeling, and paradoxically promotes vessel dilation. This method mimics the mechanism of post-stenotic dilation (PSD) frequently observed in atherosclerotic arteries (Ojha, 1990). In Ojha's published in vitro studies using a pulsatile flow model, a stenosis with a 65% area reduction caused mean WSS to increase from a value of 1 Pa upstream of the stenosis to a value of 2.3 Pa between 3 and 5 vessel diameters downstream of the stenosis.

The present disclosure also relates to an intravascular inflow conduit assembly that includes a cage structure having one or more elongated ribs extending distally from a region proximal (toward the pump side) to the conduit assembly tip and surrounding the conduit assembly tip. In one embodiment, the cage structure extends distally from a ring or ring-like structure at a proximal end of the cage to a distal end of the cage. In another embodiment, the cage structure extends distally from a ring or ring-like structure at a proximal end of the cage to a ring or ring-like structure at the distal end of the cage. In one aspect, the cage also includes a distal ring engaged to a distal end of the one or more elongated ribs. The elongated ribs, including a distal ring in some embodiments, can be translated along a longitudinal axis of the cage structure to expand or contract the cage structure.

