Portable blood pumping system

TECHNICAL FIELD

The present invention relates to a portable blood pumping system for use in cardiopulmonary bypass, extracorporeal membrane oxygenation, and other surgical procedures.

BACKGROUND OF THE INVENTION

Cardiopulmonary bypass (CPB), the shunting of blood around the heart and lungs, is a well-established surgical technique that enables repairs of cardiac structures, such as the heart and its blood vessels, that would otherwise not be possible. Extracorporeal membrane oxygenation (ECMO), increasing the oxygen content and decreasing the carbon dioxide content of the blood, is also a well-established technique. In trauma care, CPB and EMCO can be used to maintain patients with a variety of critical injuries until they receive definitive care. CPB and EMCO can also be used to help support patients until damaged organ(s) heal.

Both CPB and EMCO are typically performed in sophisticated medical facilities that have operating rooms equipped to perform these procedures. CPB and EMCO procedures could, however, have profound impact with regard to on-site emergency trauma treatment, such as in military battlefield scenarios and in civilian accident or disaster scenarios. In on-site emergency trauma care, extracorporeal blood cooling can be used to induce a hypothermic state of “suspended animation” to maintain the patient while being transported to a medical facility for treatment. CPB and EMCO procedures also could impact patient care in rural settings where access to sufficient medical facilities are not available. Accordingly, there exists a need to promote more widespread use of CPB and EMCO through the development of equipment that may be used outside the confines of a medical facility.

SUMMARY OF THE INVENTION

The present invention relates to a pump that includes a pump housing having a fluid inlet and a fluid outlet. An impeller is disposed within the pump housing and is rotatable about an axis to move fluid from the inlet to the outlet. A flexible drive spring connects the impeller to a rotating drive mechanism. The spring transmits torque to the impeller from the drive mechanism and preloads the impeller against a surface of the pump housing.

The present invention also relates to a pump including a pump housing having a fluid inlet and a fluid outlet. An impeller is disposed within the pump housing and is rotatable about an axis to move fluid from the fluid inlet to the fluid outlet. A face seal includes a fixed face on the pump housing and a rotatable face on the impeller. A resilient member preloads the rotatable face against the fixed face and transmits torque to the impeller.

The present invention also relates to a pump including a prime mover and a pump housing having a fluid inlet and a fluid outlet. An impeller is disposed within the pump housing and is rotatable about an axis to move fluid from the fluid inlet to the fluid outlet. A face seal includes a fixed face on the pump housing and a rotatable face on the impeller. A spring preloads the rotatable face against the fixed face and transmits torque to the impeller from the prime mover. A sleeve encircles the spring along a substantial portion of the length of the spring and helps prevent buckling of the spring. The pump also includes means for reinforcing at least one end portion of the spring.

The present invention further relates to a blood pumping system including an extracorporeal blood pump. The blood pump includes a motor, a pump housing having an inlet and an outlet, and an impeller disposed within the pump housing and rotatable about an axis to move fluid from the inlet to the outlet. A portable control unit is operative to supply power to the pump and receive signals from the pump. The control unit includes a battery power supply. The blood pump has a priming volume of no more than 12 milliliters and has a pump head hydraulic efficiency of at least 40 percent.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a blood pumping system according to the present invention;

FIG. 2 is a functional block diagram illustrating a control unit of the system of FIG. 1;

FIG. 3 is an exploded perspective view, partially in section, of a pump of the system of FIG. 1;

FIG. 4 is a sectional view of the pump of FIG. 3;

FIG. 5 is a sectional view of a pump head portion of the pump of FIGS. 3 and 4;

FIG. 6 is an exploded perspective view of the pump head portion of FIG. 5;

FIG. 7 is an exploded view, partially in section, of an impeller assembly of the pump; and

FIG. 8 is a sectional view of the impeller assembly of FIG. 7 illustrating an assembled condition of the impeller assembly.

DESCRIPTION OF EMBODIMENTS

The present invention relates to a portable blood pumping system for use in applications such as cardiopulmonary bypass, extracorporeal membrane oxygenation, hypothermic blood cooling, and other surgical procedures. As described herein, the entire pumping system is economically disposable, yet durable enough that non-blood contacting components may be employed repeatedly. This provides economic benefits and allows for stockpiling, which can make the system readily available for multiple or widespread uses. Also, as described herein, the blood pumping system is lightweight and compact, making it practical for rapid deployment to, and transportation with, a patient.

FIG. 1 illustrates an example configuration of a blood pumping system 10 of the present invention. The system 10 includes a control unit 20 and a pump 100. The control unit 20 is operatively connected to the pump 100 by cables 30 and 32. The cable 30 is used to provide power to the pump 100, provide power to one or more speed sensors of the pump, and to receive speed signals from the speed sensors. The cable 32 is used to provide power to one or more pressure sensors of the pump 100 and to receive pressure signals from the pressure sensors. In an alternative embodiment, the functions performed by the cables 30 and 32 could be combined and implemented with a single cable.

The control unit 20 is operative to supply pump motor control voltage, such as pulse width modulated (PWM) motor control voltages, to the pump 100 via the cable 30. The control unit 20 is also operative to receive feedback or other I/O from the pump via the cables 30 and 32.

Portions of the control unit 20 are shown schematically in FIG. 2. Referring to FIG. 2, the control unit 20 includes a battery power supply 40 and an AC power/charging circuit 42, and a power switching circuit 46. The AC power/charging circuit 42 is connectable with an external AC power source (not shown), such as a conventional AC power outlet or vehicle power port, via a power cord 44. The battery power supply 40 and AC circuit each are operative to power the control unit 20 and also to power the pump 100 and associated sensors on the pump via the power switching circuit 46. The control unit 20 may be configured such that the switching circuit 46 provides power from the AC circuit 42 when available and provides power from the battery power supply 40 when AC power is not available. The system 10 may thus run for limited intervals on the battery power supply 40 or may run indefinitely on the AC circuit 42.

The battery power supply 40 may comprise a rechargeable battery power supply or a non-rechargeable, primary cell battery power supply. A rechargeable battery power supply 40 may be advantageous in settings, such as medical facilities, where the system 10 could be stored with the charging circuit 42 energized to maintain the batteries charged and ready for use. In settings where the system 10 is stored for long periods without recharging the batteries, such as a military setting, a primary cell battery power supply 40 may be advantageous. This is because, a primary cell battery power supply 40 does not require charging and may retain a full or substantially full charge for 1-5 years or longer.

The control unit 20 also includes a controller 50 and memory 52. The memory 52 may include random access memory (RAM) 54, non-volatile random access memory (NVRAM) 56, such as an electronically erasable programmable read only memory (EEPROM), or any other memory or data storage medium. The controller 50 may include one or more electronic devices suited to perform the control functions of the control unit 20 described herein. For example, the controller 50 may include one or more microcontrollers, microprocessors, state machines, discrete components, one or more application specific integrated circuits (“ASIC”), field programmable gate arrays (FPGAs), or a combination of these devices.

The control unit 20 also includes one or more user input devices 60 and a user display 62. The user input devices 60 may, for example, include a keypad 64 (see FIG. 1) and a knob 66. In this example, the keypad 64 may be used to navigate menu options and the knob 66 may be used to set or select parameters. Any other suitable user input device may be incorporated into the user interface 60. The user display 62 is operative to provide visual indication of system information, such as pump performance data, configuration settings, control settings, system status, and alarms. The user display 62 may be any suitable display device, such as an LCD display.

The control unit 20 also includes power and I/O ports 70 connectable with the cables 30 and 32. These connections may be made in any suitable manner. For example, the ports 70 and cables 30 and 32 may be fit with mating portions of electrical connectors that provides for a quick, reliable, and error-free connection, both mechanical end electrical.

A pulse-width modulation (PWM) circuit 72 and a feedback interface circuit 74 are operatively connected to one or more of the ports 70. The PWM circuit 72 is operative to provide pulse-width modulated motor control voltages to the pump 100 via the ports 70 and cable 30. The feedback interface circuit 74 is operative to receive feedback signals from the pump 100 via the cables 30 and 32 and the ports 70.

The control unit 20 also includes a communication port 34 that allows for communication and data transfer between the control unit and a device suitably configured for desired functions, such as data acquisition and display. The communication port 34 may also be used to transfer data stored in memory 52 during patient transport so that events that occur during transport can be viewed by a physician. The control unit 20 may implement any suitable media or method for transferring data via the communication port 34, such as USB, Bluetooth, Firewire, or other suitable technology.

The controller 50 is operative to control the pump 100 by executing instructions defined by firmware or other computer code stored in the memory 52. The instructions defined in the firmware draw from information stored in memory 52, user inputs received via the input devices 60, and feedback from the instrumentation of the pump 100. For example, the firmware may implement closed-loop control algorithms, such as proportional-integral-derivative (PID) control algorithms to control pump motor speed via the PWM circuit 72 with a pump motor speed feedback signal being used to close the loop. In this example, the pump motor speed setpoint may be determined as a function of a desired flow value input by the user. Predetermined pump parameters stored in memory 52, such as in a look-up table, correlate the desired pump flow with measured values for pump head differential pressure and pump speed. This speed can be used as the setpoint in the PID control loop. Other feedback signals, such as pressures, pump speed, and motor current, may also be used to help control the pump motor.

The firmware may also implement other functions, such as a power up function, a hardware watchdog function, and a system brownout function. During the power up function, processor functions and variables are initialized, processor interrupts are activated, on-board timer(s) are activated, and battery voltage is checked.

The hardware watchdog function monitors correct software execution and is operative to generate a hardware reset if the execution fails. To accomplish this, the watchdog function implements a timer that will generate a hardware reset if it is not cleared in program execution at given intervals. As an example, the hardware reset may be generated approximately every 18 ms. To ensure correct operation of the firmware, watchdog function also implements a watchdog timer interrupt that is issued at given intervals that are shorter than the interval of the watchdog timer. In the current example, the watchdog timer interrupt may be issued every 10 ms. The watchdog timer interrupt thus prevents the watchdog timer from expiring and causing a reset while the control unit 20 is operating normally. If the controller 50 encounters an exception or a malfunction, the watchdog timer interrupt is not issued, leaving the watchdog timer free to expire and trigger a hardware reset. The hardware reset will restart the control unit 20 to help avoid any erroneous measurements.

The system brownout function monitors the voltage of the battery power supply 40. Upon detecting a low voltage condition of the battery power supply 40, the brownout system function is operative to cease operation of the controller 50 in order to help avoid any erratic operation of the system 10. In a brownout situation, in order to conserve the battery power supply 40, the brownout function may also inhibit certain non-essential functions that draw power from the battery power supply. For example, certain non-essential display items and audible alarms or indicators may be inhibited in a brownout situation. To provide for an emergency scenario where the batteries fail and an alternative power source is not available, the aft end of the pump 100 could be fit with a mechanism, such as a one-way clutched socket, to allow for handle insertion for manual operation of the pump.

Referring to FIGS. 3 and 4, the pump 100 includes a base assembly 110 that supports a prime mover in the form of a pump motor 150, a drive magnet assembly 180, and a pump housing or pump head 200. The base assembly 110 includes a base housing 112 that has a generally cup-shaped configuration with a cylindrical side wall 114 and an end wall 116 that define a chamber 118 of the base assembly. The base assembly 110 also includes one or more baffles 130 that provide cooling air flow through the base housing 112 and also provide splash protection for the base assembly and the components housed therein.

The base housing assembly 110 also includes a locking collar 120 that is fixed to a terminal end of the side wall 114 opposite the end wall 116 by means 108, such as screws. The locking collar 120 includes a sleeve portion 122 that fits over an outer surface of the side wall 114 of the base housing 112. The locking collar 120 also includes a locking flange 124 that extends radially inward from the sleeve portion 122. The locking flange 124 together with an annular shoulder 126 in the terminal end of the side wall 114 define a locking grooves 128 spaced about the periphery of the side wall 114.

The motor 150 may be any suitable electric motor, such as a multi-phase motor in which each phase is excited via pulse-width modulated voltage provided by the control unit 20. The motor 150 is connected to the base housing 112 by means (not shown) such as screws. A motor housing 152 encloses the motor 150. A terminal end portion 162 of the motor housing 152 is received in an annular groove 164 in the end wall 116 of the base housing 112 and is bonded to the base housing by suitable means, such as an adhesive, epoxy, or welding. The motor housing 152 provides splash protection for the motor 150 and includes passages 154 for providing cooling air to the motor 150. The motor housing 152 also includes helical ribs 158 that promote circulation of the cooling air.

The drive magnet assembly 180 includes a drive magnet cup 182 that supports a drive magnet 184. The drive magnet cup 182 has a cylindrical side wall 186 and an end wall 188. The drive magnet 184 has a ring shaped configuration with a cylindrical outer surface 190 and a cylindrical central opening 192. The drive magnet 184 is seated in and secured to an annular recess 194 of the drive magnet cup 182 by suitable means, such as an adhesive. The drive magnet assembly 180 is positioned in the chamber 118 of the base housing 112. The drive magnet cup 182 may include vanes or blades 134 that protrude from a lower surface of the end wall 188. During operation of the pump 100, the blades 134 may create cooling air flow between the base housing 112 and the motor housing 152 through passages 132 in the base housing 112.

The motor 150 includes a shaft 160 that is rotatable about the axis 156. The motor shaft 160 extends into a central opening 196 in the end wall 188 of the drive magnet cup 182. The drive magnet assembly 180 is secured to the motor shaft 160 via suitable means, such as an adhesive, a setscrew, a key on the shaft, or an interference fit of the two parts. The drive magnet assembly 180 is thus supported in the base housing assembly 110 for rotation with the motor shaft 160 about the axis 156.

The pump head 200 includes a volute housing 210 and a housing base 230 that together support an impeller assembly 250. The volute housing 210 and housing base 230 define a pumping chamber 240 that houses an impeller 252 of the impeller assembly 250. The pump head 200 is best shown in FIGS. 5 and 6. Referring to FIGS. 5 and 6, the volute housing 210 includes a plate portion 212 that helps define the pumping chamber 240. A pump inlet 214 and a pump outlet 216, extend from the plate portion 212 and are in fluid communication with the pumping chamber 240. The inlet 214 is centered on and extends parallel to the axis 156 into the pumping chamber 240. The outlet 216 is spaced radially from the axis 156 and extends transverse and generally tangentially from the pumping chamber 240. The inlet 214 and outlet 216 include means, such as barbs 218, for preventing failure of connections with conduits (not shown), such as hoses or plastic tubing.

The pump 100 supports components or electronics for controlling operation of the pump 100. For example, the pump head 200, more particularly the volute housing 210, supports an inlet pressure transducer 220 for allowing measurement of fluid pressure in the pump inlet 214 and an outlet pressure transducer 222 for allowing measurement of fluid pressure in the pump outlet 216. The inlet pressure transducer 220 and outlet pressure transducer 222 may be used to determine a pump head differential pressure or other performance parameters. For example, the pump head differential pressure could be used to determine flow based on pump speed and known pump characteristics. The pressure transducers 220 and 222 may also be used to make other determinations, such as a detrimental suction condition. For example, a detrimental suction condition may be one caused by the collapse of the inlet vasculature, to which the control unit 20 may provide an appropriate response.

The pump 100 may also include a speed sensor for providing motor speed feedback to the control unit 20. For example, referring to FIG. 3, the pump 100 may include a speed sensor 370 associated with the base housing assembly 110 to sense the rotational speed of the drive magnet assembly 180. For example, the speed sensor 370 may comprise a stationary optical transducer, mounted to or embedded in the baffle 130 or in the side wall 114 of the base housing 112. The optical transducer speed sensor 370 may be operative to detect a moving target 372 mounted for rotation on an outer surface of, or integral to the geometry of, the side wall 186 of the drive magnet cup 182.

The pump 100 may further include other sensors (not shown) for providing signals to the control unit 20. For example, the pump 100 may include a motor current sensor, a motor temperature sensor, a pump inlet temperature sensor, a pump outlet temperature sensor, or a combination of these sensors. Sensors, such as pump temperature sensors, may be integrated into the volute housing 210 in a manner similar or identical to the pressure transducers 220 and 222. In fact, inlet and outlet temperature sensors may be combined with the inlet and outlet pressure transducers 220 and 222, respectively and integrated into the volute housing 210. Sensors, such as motor current or temperature sensors, may be integrated into the motor 150.

Referring to FIGS. 3 and 4, the pump head 200 may further support an electrical port 224. In the illustrated embodiment, the electrical port 224 is mounted to or integral with the volute housing 210 and includes terminals (not shown) connected with the pressure transducers 220 and 222. The electrical port 224 facilitates a connection with the cable 30, which provides power to the pressure transducers 220 and 222 and pressure signals to the control unit. For example, the port 224 and cable 30 may be fit with mating portions of an electrical connector that provides for a quick, reliable, and error-free connection, both mechanical and electrical.

The components or electronics for controlling operation of the pump 100, such as the pressure transducers 220 and 222, and the electrical port 224, may be connected to the structure of the pump or integrated with the structure of the pump 100. For example, in the illustrated embodiment, the inlet pressure transducer 220 is integrated into the structure of the inlet 214 on the volute housing 210 and the outlet pressure transducer 222 is integrated into the structure of the outlet 216 on the volute housing.

As best shown in FIGS. 5 and 6, the housing base 230 includes a plate portion 232 and an impeller drive housing portion 234. The impeller drive housing portion 234 has a cylindrical outer surface 236 (FIG. 5) and a support chamber 238. The support chamber 238 is defined by a series of axially aligned cylindrical bores in the impeller drive housing portion 234. The plate portion 232 includes locking tabs 242 spaced about an outside diameter of the plate portion and an annular groove 244. As shown in FIG. 5, the volute housing 210 may include an annular protrusion 226 that mates with the annular groove 244 on the plate portion 232 to help align the parts and to help facilitate forming a seal between the parts. Such a seal may be formed, for example, with a silicon sealant applied to the groove, or an O-ring 244.

Referring now to the impeller assembly 250, as best shown in FIGS. 7 and 8, the impeller 252 includes a plurality of vanes 254 that extend radially from the axis 156. The impeller 252 also includes a drive tube portion 260. The drive tube portion 260 includes an axially extending cylindrical side wall 262 that defines a cylindrical chamber 264. The side wall 262 includes radially opposed pin receiving openings 266 positioned adjacent or near an upper end of the chamber 264.

The impeller assembly 250 also includes a drive spring 270. By use of the “spring” herein, it is meant to encompass any suitable resilient member capable of transmitting rotational torque to the impeller 252 and biasing or loading the impeller. For example, the drive spring 270 may comprise a resilient elastomeric member. In the illustrated embodiment, the drive spring 270 is a helical coil spring constructed of a suitable material, such as a steel wire material. The drive spring 270 has a coil portion 272, a first end turn 274 and a second end turn 276. The coil portion 272 has an axially extending helical configuration. The end turns 274 and 276 each have a generally circular or semi-circular configuration and project from opposite ends of the coil portion 272.

The impeller assembly 250 also includes a spring retainer sleeve 280. The retainer sleeve 280 has a generally hollow cylindrical configuration with a cylindrical side wall 282. The retainer sleeve 280 has a length about equal to the inside diameter of the side wall 262 of the drive tube portion 260. Opposite ends 284 of the retainer sleeve 280 are rounded so as to have a radius about equal to the radius of the inside radius of the cylindrical side wall 262 of the drive tube portion 260.

The impeller assembly 250 also includes a spring retainer adjustment screw 290 that has a threaded outer surface 292. A spring receiving slot 294 extends axially into an end of the retainer screw 290. A pin receiving opening 296 extends through the retainer screw 290, transverse to a longitudinal axis of the screw, and intersects the spring receiving slot 294. The retainer screw 290 may also include portions 298 opposite the spring receiving slot 294 for cooperating with a tool (not shown), such as a screwdriver.

In the assembled condition of the impeller assembly 250 (FIG. 8), the retainer sleeve 280 is positioned extending through the inner diameter of the first end turn 274 of the drive spring 270. The first end turn 274 and the retainer sleeve 280 are then inserted into the chamber 264 of the drive tube portion 260. The length of the retainer sleeve 280, coupled with the radius of the ends 284, causes the retainer sleeve to mate with the inside diameter of the side wall 262 of the drive tube portion 260. The drive spring 270 and retainer sleeve 280 are maneuvered such that the retainer sleeve aligns with the pin receiving openings 266 in the drive tube portion. Thereafter, a retainer pin 300 is inserted through the openings 266, through the retainer sleeve 280, and through the first end turn 274 to retain the drive spring 270 in the drive tube 260 and to help preventing disengagement of the spring and the impeller 252. The retainer pin 300 may be secured to the drive tube 260 by suitable means, such as a press-fit with the drive tube.

The retainer sleeve 280 helps prevent undesired movement or deformation, such as twisting or bending, of the first end turn 274 of the drive spring 270 relative to the drive tube portion 260 while transmitting torque to the impeller 252. The retainer sleeve 280 is sized to occupy a substantial portion of the volume of the drive tube portion 260 adjacent the first end turn 274. The retainer sleeve 280 leaves little space into which the first end turn 274 can move, thereby preventing the undesired movement or deformation of the first end turn relative to the drive tube portion 260. It will be appreciated that alternative measures could be implemented to help prevent this undesired movement or deformation of the first end turn 274. For example, the first end turn 274 could be bonded to the adjacent coil of the spring 270 by means, such as welding. As another example, the pin 300 could be enlarged to match the diameter of the first end turn 274 of the spring 270. As a further example, a filler, such as an epoxy, could be used to fill the space in the drive tube portion 260 surrounding the first end turn 274.

Also, in the assembled condition of the impeller assembly 250, the second end turn 276 of the drive spring 270 is positioned in the spring receiving slot 294 of the retainer screw 290. Thereafter, a retainer pin 302 is inserted through the opening 296 and through the second end turn 276 to secure the drive spring 270 to the retainer screw 290. The retainer pin 302 may be secured to the retainer screw 290 by suitable means, such as a press-fit with the screw. The receiving slot 294 of the retainer screw 290 helps prevent undesired movement or deformation, such as twisting or bending, of the second end turn 276 of the drive spring 270 relative to the screw while transmitting torque.

The pump head 200 facilitates assemblage of the impeller assembly 250 in the impeller drive housing portion 234 of the housing base 230. Referring to FIGS. 5 and 6, a ring-shaped driven magnet 310 is mounted on an outer surface of a spring receiving tube 312 such that when the pump head 200 is mated with the base housing 230, the driven magnet will align axially with the drive magnet 184. The spring receiving tube 312 has a threaded inner surface 314.

A bearing 330 and washer 332 are installed over a first end 316 of the spring receiving tube 312 adjacent the driven magnet 310. A bearing 334 and washer 336 are installed over a second end 318 of the spring receiving tube 312 adjacent the driven magnet 310. The first end 316 of the spring receiving tube 312, with the bearing 330 and washer 332 installed, are inserted into the impeller drive housing portion 234. The impeller assembly 250 is inserted through a central opening 320 in the housing base 230. The opening 320 extends from an upper surface 322 of the plate portion 232 into the support chamber 238. As the impeller assembly 250 is inserted in the opening 320, the retainer screw 290 eventually reaches the spring receiving tube 312.

The retainer screw 290 is threaded into the first end 316 of the spring receiving tube 312, which causes the screw and the drive spring 270 to be drawn into the receiving tube. As this occurs, the bearing 330 becomes seated in an annular shoulder 340 of the housing portion 234. Once the retainer screw 290 reaches a predetermined axial position in the spring receiving tube 312, further rotation of the screw causes the drive spring 270 to stretch and bias the impeller 252 against an upper surface 322 of the plate portion 232. Those skilled in the art will appreciate that the retainer screw 290 could be omitted and the second end turn 276 of the drive spring 270 could be connected to the spring receiving tube 312 by alternative means, such as a sleeve and pin arrangement similar to that used to connect the first end turn 274 to the impeller 252.

Once the retainer screw 290 is threaded to the desired axial position in the spring receiving tube 312, a flat washer 350 and a spring washer 352 are installed over the second end 318 of the spring receiving tube 312 and an impeller housing end cap 354 is installed. The end cap 354 helps maintain the axial alignment of the bearing 334 in the impeller drive housing portion 234. This helps maintain the axial alignment of the impeller assembly 250, bearings 330, 334, spring receiving tube 312, and driven magnet 310, in the impeller drive housing portion 234. The spring washer 352 helps maintain an axial load on these components in the impeller drive housing portion 234.

To secure the pump head 200 to the base housing assembly 110, the pump head is positioned such that the locking tabs 242 of the housing base 230 align with corresponding cutout portions 350 in the locking flange 124 of the locking collar 120. The pump head 200 is moved along the axis 156 until that the locking tabs 242 engage the annular shoulder 126 in the side wall 114 of the base housing 112. The pump head 200 is then rotated about the axis 156 so that the locking tabs 242 enter the locking grooves 128, thus connecting the pump head to the base housing assembly 110. Releasable locking means 356 such as a spring biased plunger, may be used to prevent unintentional counter-rotation of the pump head 200 that may disconnect the pump head from the base housing assembly 110. To disconnect the pump head 200 from the base housing assembly 110, the plunger 356 is depressed to release the pump head for unlocking rotation relative to the base housing assembly.

The connection between the pump head 200 and the base housing assembly 110 may facilitate easy installation and removal of the pump head from the base housing assembly. This is beneficial because it facilitates disposal of the pump head 200 while the base housing assembly 110, especially the motor 150, is reusable. The pump head 200 could, however, be connected to the base housing assembly 110 by alternative means, such as simple fastener connections, such as screws. This may be beneficial in the case where the entire pump 100 is disposable. For example, for an entirely disposable pump configuration, instead of magnetically coupling the motor 150 to the pump head 200, the motor shaft 160 could be directly coupled to the drive spring 270. This would eliminate the need for easy installation and removal of the pump head 200 from the base housing assembly 110, as well as eliminating the need for the magnetic coupling, and thereby permit the use of more conventional fasteners, such as screws.

The pump 100 may also be configured such that the connection between the pump head 200 and the base housing assembly 110 may also facilitate a power or sensor connection. Referring to FIGS. 3 and 4, the pump 100 may include contacts 400 for providing one or more electrical connections between the pump head 200 and the remainder of the pump, i.e., the base housing assembly 110 and the motor 150. The contacts points 400 may, for example, include one or more first contacts 402 mounted or otherwise connected to the plate portion 232 of the housing base 230 and one or more second contacts 404 mounted or otherwise connected to the annular shoulder 126 in the side wall 114 of the base housing 112.

The first contacts 402 are connected with means 406, such as lead wires electrically connected with one or more electrical components on the pump head 200, such as the pressure transducers 220 and 222. The second contacts 404 are connected with means 408, such as lead wires, electrically connected with an electrical component on the base housing assembly 110, the motor 150, or both, such as the cable 30 or a connector (not shown) that connects with the cable. Referring to FIG. 4, in the assembled condition of the pump 100, the first and second contacts 402 and 404 engage each other and provide an electrical connection between the lead wires 406 and 408. The contacts 400 may thus provide signal communication between the electrical components on the pump head 200 (e.g., the pressure transducers 220 and 222) the cable 30 and, thus, may facilitate communication between the pump 100 and the control unit 20 via the single cable 30.

Also, in the assembled condition of the pump 100, the impeller assembly 150 is supported in the impeller drive housing portion 234, which is positioned in drive magnet assembly 180. In this condition, the drive magnet 184 and the driven magnet 310 are positioned coaxially and in axial and radial alignment with each other, with the drive magnet extending radially around the driven magnet. The magnetic polarities of the drive magnet 184 and the driven magnet 310 are arranged such that the magnets tend to maintain predetermined radial positions relative to each other. Rotation of the drive magnet assembly 180 thus induces rotation of the driven magnet 310 and, thus, the impeller assembly 250, via the drive spring.

In the assembled condition, there is a seal between the impeller 252 and the housing base 230. More particularly, referring to FIG. 5, there is a face seal 364 between a moving seal face or surface 360 of the impeller 252 and a fixed seal face or surface 362 of the housing base 230. To form the face seal 364, the seal faces 360 and 362 are machined or otherwise formed to a high degree of flatness. The mating seal faces 360 and 362 prevent fluid migration from the outer diameter of the seal between the impeller 252 and the housing base 230 into the chamber 238 of the impeller drive housing portion 234 where the drive spring 270 and other components are located. Additionally, a surface modification treatment may be performed on the seal faces 360 and 362 to help improve their durability and reduce friction. For example, a biocompatible surface treatment, such as a diamond-like carbon (DLC) coating, may be applied to the seal faces 360 and 362 to help improve their durability and reduce friction.

In the assembled condition, the drive spring 270 provides the only direct coupling between the impeller and the remainder of the pump 100. The drive spring 270 biases the impeller 252 axially against the housing base 230 and, therefore, helps maintain the axial position of the impeller in the pumping chamber 240. The mating contours of the impeller 252 and the housing base 230, in conjunction with the bias provided by the drive spring 270, also help maintain the radial position of the impeller in the pumping chamber 240. The axial load of the drive spring 270 thus helps overcome the low fluid pressure at the pump inlet 214 and the radial hydraulic forces so that the surfaces 360 and 362 remain in contact, thus maintaining the integrity of the face seal 364.

The drive spring 270 imparts an axial load on the face seal 364. This may be referred to as “preloading” the seal 364. The design of the impeller and seal location are such that the required axial load may be relatively light, so as to provide an effective seal without creating undue friction. The retainer screw 290 allows for adjusting or fine-tuning the axial load imparted on the impeller 252 and, thus, the face seal 364 by the drive spring 270. The face seal 364 may thus have a high degree of reliability that can be maintained while friction is minimized.

This high degree of reliability allows the face seal 364 to be the sole seal for preventing fluid leakage from the pumping chamber 240 into the chamber 238 of the impeller drive housing portion 234. In the configuration illustrated in FIGS. 1-8, the only other seal formed in the pump head 200 is the seal formed where the annular groove 244 of the housing base 230 interfaces with the annular protrusion 226 of the volute housing 210 to seal the pumping chamber 240. The pump head 200 thus includes only two seals, or part seams, exposed to fluid flow. Incorporation of this minimal number of seals exposed to fluid flow may help prevent the formation of thrombosis.

Because of the light axial force required of the drive spring 270, the drive spring may have a relatively low spring constant that will allow greater tolerance during assembly for setting the spring tension. A soft drive spring 270 could, however, experience failures, such as lateral buckling or torsional buckling when a torque is applied during operation of the pump 100. To help prevent this, according to the present invention, the drive tube portion 260 of the impeller 252 and the spring receiving tube 312 encircle the drive spring 270 with a relatively close fit. The spring receiving tube 312 encircles the drive spring 270 along a substantial portion of the length of the drive spring. The drive tube portion 260 and the spring receiving tube 312, having a close fit with the drive spring 270, help prevent buckling. Also, to help prevent this buckling, the drive spring 270 is arranged such that direction of motor 150 and impeller 252 rotation is counter to with the winding direction of the spring. Thus, torque applied to the drive spring 270 by the motor 150 would tend to wind further or tighten the coil of the spring. It will thus be appreciated that the configuration of the present invention allows for use of a relatively soft drive spring 270 to maintain an effective and efficient face seal 364 while avoiding failure under pump operating torques.

The drive spring 270 also functions to help minimize the effects of misalignment between the impeller 252 and the driven magnet 310/spring receiving tube 312. This is because the drive spring 270 is the only means provided for coupling the impeller 252 to the driven magnet. While imparting the axial load on the impeller 252, the portion of the drive spring 270 at the interface between the drive tube portion 260 of the impeller and the spring receiving tube 312 will permit a radial displacement or offset between the same. Advantageously, this may permit the impeller 252 to remain in the desired position on the housing base 230 with the face seal 364 remaining in tact, even when there is some misalignment between the impeller and the driven magnet 310/spring receiving tube 312.

The drive spring 270 further helps to line-up the lower seal surface 360 of the impeller with the seal surface 362 of the housing base 230 through the tension imparted on the impeller 252. This helps prevent the impeller 252 from “orbiting” or “drifting” radially while the face seal 364 remains in-tact. As an alternative, instead of relying on the drive spring 270 to provide this radial alignment, a bearing (not shown) may be provided to support the drive tube portion 260 of the impeller 252 on the housing base 230. For example, a split, externally barrel-shaped, spring loaded journal bearing may be fit to and self-align with the drive tube portion 260. Such a split bearing would provide a radial load that prevents the impeller 252 from orbiting or drifting radially at the face seal 364.

As best shown in FIG. 5, the mating contours of the impeller 252 and the housing base 230 are configured such that the axial position of the face seal 364 relative to the impeller vanes 254 is on the reaction plane of the radial hydraulic forces of the impeller (the face seal 364 has an axial position that falls within the height of terminal edges 380 of the impeller vanes 254). This helps reduce tipping moments that may tend to cause tipping or wobble in the impeller 252 which may, in turn, cause the face seal 364 to leak. This is because, in this configuration, what would otherwise be a tipping moment would be felt as a radial load through the plane of the seal 364. Such radial loads are borne by a radial bearing 390 formed at the interface of an outer surface 392 of the drive tube portion 260 and an inner surface 394 of the passage 320 in the base housing 230. A surface modification treatment may be performed on these surfaces 392 and 394 to help improve their durability and reduce friction. For example, a diamond-like carbon coating may be applied to the surfaces 392 and 394 to help improve their durability and reduce friction.

The stationary and rotating seal faces, i.e., the lower seal surface 360 of the impeller 252 and the seal surface 362 of the housing base 230, are constructed from a heat conductive material, such as metal. For example, the lower seal surface 360 of the impeller 252 and the seal surface 362 of the housing base 230 may be constructed of a material that has a thermal conductivity exceeding 35 BTU-in/hr-ft²-° F. Such materials may include titanium and titanium alloys, stainless steel and stainless steel alloys, certain plastics, and certain composite materials, such as carbon fiber materials. This helps the parts to conduct or carry heat away from the face seal 364, which improves thrombosis resistance, as well as seal performance. The primary fluid flow also runs over the face seal 364, which also helps cool the seal and helps prevent the formation of thrombosis.

To operate the system 10, the pump head 100 is implemented in a pump circuit, which may include a variety of devices. For example, a typical pump circuit may include a cannula that draws blood from the body, perhaps into a reservoir, the pump 100, an oxygenator, a heat exchanger, an arterial filter, and a cannula back to the patient. The pump circuit may also includes any tubing that connects these components. The cables 30 and 32 are connected to the pump head 100 and the control unit 20 to provide power and I/O signals. The control unit 20 displays operating parameters to the user and accepts user input via the input devices 60 and 64. The control unit 20 controls operation of the pump 100 in accordance with these user inputs and with feedback received from the pump. Other medical equipment may be connected in the blood flow path of the pump 100. For example with the use of an oxygenator, a device, such as a Starling resistor, may be implemented downstream of the oxygenator to help prevent gas bubbles from entering the bloodstream.

When the pump 100 is operated, the impeller 252 imparts its energy to the blood, which, after overcoming the resistances of the circuit, is seen as flow. The volute design of the pumping chamber 240 helps optimize the ability of the pump to utilize the energy in the fluid to overcome the system pressure losses. System pressures are monitored via the inlet and outlet pressure transducers 220 and 222. Motor or pump speed is monitored via the speed sensor 370. Knowing the pressure developed in the pump 100, the motor or pump speed, the power delivered to the motor 150, and pump characteristics programmed or otherwise stored in the control unit 20, an estimate can be made of the resulting flow. The system 10 may thus achieve a desired flow rate input into the control unit 20 by a user.

Because the system 10 is capable of rapid deployment and transportation with a patient, the system is designed to be small and disposable. Among the factors that allow the pump 100 to be small and disposable is the implementation of a high speed, high efficiency, 12-volt motor design. Efficiency is a higher priority than would be usual in a conventional cardiopulmonary bypass pump because of the desire to power the pump with a low cost disposable motor and a low cost disposable battery pack.

To achieve an efficient design, a highly electromechanically efficient motor 150 was selected. The small size of the pump 100 also lends well to an efficient design. The diameter of the impeller 252 is small in comparison with conventional blood pumps, which results in low operating torques that require less energy to produce. The small size of the impeller 252, particularly the small surface areas of the contacting parts of the impeller 252 and the housing base 230, and their respective DLC coatings, helps reduce the amount of friction generated during operation of the pump 100. The impeller 252 and the volute housing 210 are also designed to be hydraulically efficient. Testing has shown that, under normal operating conditions, the pump head 200 can consistently operate with a hydraulic efficiency of at least 40% by implementing the features of the pump 100 described herein.

Because the human body has a limited volume of blood, an area of concern when performing CPB or ECMO is the volume or “prime volume” of the pump circuit. The volume of the pump head 200, particularly the volume of the pumping chamber 240, may account for a significant portion of the prime volume of the pump circuit. Because of this, according to the present invention, the size of the pump 100 and, therefore, the pumping chamber 240, is minimized while maintaining desired flow and pressure characteristics. The pumping chamber of the present invention has a prime volume of less than 12 milliliters (mL).

In one particular configuration of the pump 100 in accordance with the present invention, the pumping chamber 240 had a prime volume of less than 7 mL. Because of this small size and resulting light weight of the pump 100, it is not required to be anchored or rest on the floor/ground. Rather, the small size and light weight of the pump 100 allows it to be able to hang freely in the pumping circuit. This feature allows for shorter tubing lengths, which further reduce the system prime volume. Further, because the face seal 364 is maintained by the bias of the spring 270 and the hydraulic forces in the pumping chamber 240, the pump 100 may be operated at any orientation or attitude without adversely affecting its performance. This promotes the transportability of the pump 100 with a patient.

Typically, there is about 100 mm Hg resistance in a human blood vessel system. Losses in the pumping circuit account for an additional resistance of about 250 mmHg. A typical blood flow rate in a healthy, resting individual is three liters per minute (3 LPM). This being the case, the pump 100 is designed to provide 5 LPM at a 350 mmHg resistance. Because the pump 100 has a given size, achieving these values is a matter of determining an appropriate speed at which to operate the motor 150. By way of example, testing a prototype configuration of the pump 100 was designed to provide 5 LPM at a 350 mmHg resistance. Using a blood analogue test fluid with a viscosity of ˜3.5 cP, the pump 100 produced a flow of 5 LPM against 350 mmHg at a constant speed of about 8000 RPM. Holding this speed constant, the pump 100 can produce more flow against less resistance, and less flow against more resistance, with flow dropping to zero at what is referred to as a shut-off pressure for a given speed. Adjusting this speed can allow for maintaining the desired flow against varying resistances.

From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.

Portable blood pumping system

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