Circulatory support system

• US 20040191116A1
• Filed: 04/05/2004
• Published: 09/30/2004
• Est. Priority Date: 10/04/1996
• Status: Active Grant

• Current Assignee: United States Surgical Corporation (Medtronic Plc)
• Original Assignee: United States Surgical Corporation (Medtronic Plc)
• Inventors: Geiste, Robert J., Jarvik, Robert, Stern, Steven J., Alesi, Daniel E., Cashin, Deborah M., Howansky, Mark, Klinger, John F., Day, Steven R., Kaczynski, Francis X., Hammerquist, Kenneth G., Payea, Keith
• Granted Patent: US 7,264,606 B2
• Time in Patent Office: Days
• US Class Current: 422/44
• CPC Class Codes: A61M 1/3626 Gas bubble detectors
• CPC Class Codes: A61M 1/3639 Blood pressure control, pressure transducers specially adapted therefor
• CPC Class Codes: A61M 1/3653 Interfaces between patient blood circulation and extra-corporal blood circuit
• CPC Class Codes: A61M 1/3656 Monitoring patency or flow at connection sites; Detecting disconnections
• CPC Class Codes: A61M 1/3659 Cannulae pertaining to extracorporeal circulation
• CPC Class Codes: A61M 1/3666 Cardiac or cardiopulmonary bypass, e.g. heart-lung machines
• CPC Class Codes: A61M 1/3667 with assisted venous return
• CPC Class Codes: A61M 39/281 Automatic tube cut-off devices, e.g. squeezing tube on detection of air
• CPC Class Codes: A61M 60/117 for assisting the heart, e.g. transcutaneous or external ventricular assist devices
• CPC Class Codes: A61M 60/237 the blood flow through the rotating member having mainly axial components, e.g. axial flow pumps
• CPC Class Codes: A61M 60/806 Vanes or blades

Abstract

A method for providing at least partial bypass of the heart to supplement the pumping function of the heart to thereby enable the surgeon to perform various surgical procedures thereon includes providing a circulatory assist system having a portable extracorporeal axial flow pump with a pump housing, a rotating pumping member disposed in the pump housing and inlet and outlet cannulated tubes respectively connected to inlet and outlet ports of the pump housing, accessing the patient'"'"'s left atrium of the heart with the inlet cannulated tube, accessing the aorta with the outlet cannulated tube, actuating the rotating pumping member to draw oxygenated blood from the left atrium of the heart through the lumen of the inlet cannulated tube and into the inlet port of the pump housing whereby the pumping member imparts mechanical energy to the oxygenated blood passing through the pump housing and directs the oxygenated blood through the outlet port and through the lumen of the outlet cannulated tube to be transferred by the aorta to the systemic arteries and permitting the right side of the heart to function whereby oxygen-depleted blood returning through the systemic veins to the right atrium is directed through the right ventricle to the patient'"'"'s lungs for oxygenation and subsequent pulmonary circulation.

Claims

1. A circulatory support device to supplement the pumping function of the heart to thereby enable the surgeon to perform various surgical procedures thereon, which comprises:

an extracorporeal portable axial flow pump including a pump housing dimensioned for positioning directly on or adjacent to the chest area of a patient, and having inlet and outlet ports in substantial axial alignment, a rotating member rotatably mounted in the pump housing to impart mechanical energy to blood entering the inlet port and to direct the blood through the outlet port;

an inlet tube connected to the inlet port of the pump housing and having an inlet open end portion dimensioned for insertion within the patient'"'"'s heart whereby blood is drawn from the heart through a lumen of the inlet tube and directed into the pump housing; and

an outlet tube connected to the outlet port of the pump housing and having an outlet end portion dimensioned for insertion within a major blood vessel associated with the heart whereby blood exiting the outlet port of the pump housing is conveyed through a lumen of the outlet tube into a major blood vessel for transfer by the arterial system of the patient.

2. A method for providing at least partial bypass of the heart to supplement the pumping function of the heart to thereby enable the surgeon to perform various surgical procedures thereon, the heart having a left atrium for receiving oxygenated blood from the lungs and a left ventricle for pumping the oxygenated blood through the aorta to the systemic arteries, and a right atrium for receiving oxygen-depleted blood from the systemic veins and for directing the oxygen-depleted blood through the pulmonary artery and into the lungs for oxygenation, the method comprising the steps of:

providing a circulatory assist system including a portable extracorporeal axial flow pump having a pump housing defining a longitudinal axis, the pump housing having an inlet port and an outlet port, a rotating pumping member disposed in the pump housing, an inlet tube having a first end connected to the inlet port and a second end for contact with the body, an outlet tube having a first end connected to the outlet port and a second end for contact with the body, each tube having an axial lumen between the first and second ends defining a blood flow path for conveyance of blood therealong;

accessing the left ventricle of the heart with the inlet tube such that the second end of the inlet tube is in fluid communication with the left ventricle;

accessing the aorta with the outlet tube such that the second end of the outlet tube is in fluid communication with the aorta;

actuating the rotating pumping member to draw oxygenated blood from the left ventricle of the heart through the second end of the inlet tube and through the axial lumen of the inlet tube and into the inlet port of the pump housing whereby the pumping member imparts mechanical energy to the oxygenated blood passing through the pump housing and directs the oxygenated blood through the outlet port and through the axial lumen of the outlet tube and the second end of the outlet tube to be transferred by the aorta to the systemic arteries; and

permitting the right side of the heart to function whereby oxygen-depleted blood returning through the systemic veins to the right atrium is directed through the right ventricle to the patient'"'"'s lungs for oxygenation and subsequent pulmonary circulation.

3. The method according to claim 2 further including the step of positioning the portable pump either on the patient'"'"'s body or directly adjacent the patient'"'"'s body.

4. The method according to claim 2 wherein the step of accessing the left ventricle includes inserting the second end of the inlet tube through the mitral valve.

5. The method according to claim 4 wherein the step of accessing the left ventricle includes inserting the second end of the inlet tube through the region adjacent the juncture of the pulmonary veins and advancing the inlet tube whereby the second end passes through the mitral valve the and into the left ventricle.

6. The method according to claim 2 wherein the step of accessing the left ventricle includes inserting the second end of the inlet tube within the aorta and advancing the inlet tube through the aortic valve such that the second end is disposed in the left ventricle.

7. The method according to claim 6 wherein the step of accessing the aorta includes inserting the second end of the outlet tube within the descending aorta.

8. The method according to claim 7 further including the step of occluding the aorta of the patient adjacent the heart to isolate the left ventricle.

9. The method according to claim 8 including the step of introducing a cardioplegia solution into the left ventricle.

10. A method for providing at least partial bypass of the heart by supporting the left side of the heart to thereby enable the surgeon to perform various surgical procedures thereon, the heart having a left atrium for receiving oxygenated blood from the lungs and a left ventricle for pumping the oxygenated blood through the aorta to the systemic arteries, and a right atrium for receiving oxygen-depleted blood from the systemic veins and a right ventricle for directing the oxygen-depleted blood through the pulmonary artery and into the lungs for oxygenation, the method comprising the steps of:

providing a circulatory assist system including a portable extracorporeal axial flow pump having a pump housing defining a longitudinal axis, the pump housing having an inlet port and an outlet port, a rotating pumping member disposed in the pump housing, an inlet tube having a first end connected to the inlet port and a second end for contact with the body, an outlet tube having a first end connected to the outlet port and a second end for contact with the body, each tube having an axial lumen between the first and second ends defining a blood flow path for conveyance of blood therealong;

accessing the patient'"'"'s left atrium of the heart with the inlet tube such that the second end of the inlet tube is in fluid communication with the left atrium;

accessing the aorta with the outlet tube such that the second end of the outlet tube is in fluid communication with the aorta;

actuating the rotating pumping member to draw oxygenated blood from the left atrium of the heart through the second end of the inlet tube and through the axial lumen of the inlet tube and into the inlet port of the pump housing whereby the pumping member imparts mechanical energy to the oxygenated blood passing through the pump housing and directs the oxygenated blood through the outlet port and through the axial lumen of the outlet tube and the second end of the outlet tube to be transferred by the aorta to the systemic arteries; and

permitting the right side of the heart to function whereby oxygen-depleted blood returning through the systemic veins to the right atrium is directed through the right ventricle to the patient'"'"'s lungs for oxygenation and subsequent pulmonary circulation.

11. The method according to claim 10 further including the step of positioning the extracorporeal portable pump either on the patient'"'"'s body or directly adjacent the patient'"'"'s body.

12. The method according to claim 11 wherein the step of accessing the left atrium of the heart includes inserting the second end of the inlet tube through a heart wall portion adjacent the left atrium such that the second end is disposed in the left atrium.

13. The method according to claim 10 wherein the step of accessing the left atrium of the heart includes inserting the second end of the inlet tube through the region adjacent the juncture of the pulmonary veins and advancing the inlet tube whereby the second end is disposed in the left atrium.

14. The method according to claim 10 wherein the step of accessing the aorta comprises inserting the second end of the outflow tube through the aorta wall.

15. A method for providing at least partial bypass of the heart by supporting the heart to thereby enable the surgeon to perform various surgical procedures thereon, the heart having a left atrium for receiving oxygenated blood from the lungs and a left ventricle for pumping the oxygenated blood through the aorta to the systemic arteries, and a right atrium for receiving oxygen-depleted blood from the systemic veins and a right ventricle for directing the oxygen-depleted blood through the pulmonary artery and into the lungs for oxygenation, the method comprising the steps of:

supporting the pumping function of the left side of the heart by;

providing a circulatory assist system including-.a portable extracorporeal axial flow pump having a pump housing defining a longitudinal axis, the pump housing having an inlet port and an outlet port, the outlet port being in substantial axial alignment with the inlet port, a rotating pumping member disposed in the pump housing, an inlet tube having a first end connected to the inlet port and a second end for contact with the body, an outlet tube having a first end connected to the outlet port and a second end for contact with the body, each tube having an axial lumen between the first and second ends defining a blood flow path for conveyance of blood therealong;

accessing the patient'"'"'s left atrium of the heart with the inlet tube such that the second end of the inlet tube is in fluid communication with the left atrium;

accessing the aorta with the outlet tube such that the second end of the outlet tube is in fluid communication with the aorta;

actuating the rotating pumping member to draw oxygenated blood from the left atrium of the heart through the second end of the inlet tube and through the axial lumen of the inlet tube and into the inlet port of the pump housing whereby the pumping member imparts mechanical energy to the oxygenated blood passing through the pump housing and directs the oxygenated blood through the outlet port and through the axial lumen of the outlet tube and the second end of the outlet tube to be transferred by the aorta to the systemic arteries; and

supporting the pumping function of the right side of the heart while permitting the patient'"'"'s lungs to function in oxygenating the blood.

16. The method according to claim 15 wherein the step of supplementing the pumping function of the right side of the heart includes:

providing a second circulatory assist system including a portable extracorporeal axial flow pump having a pump housing defining a longitudinal axis, the pump housing having an inlet port and an outlet port, the outlet port being in substantial axial alignment with the inlet port, a rotating pumping member disposed in the pump housing, an inlet tube having a first end connected to the inlet port and a second end for contact with the body, an outlet tube having a first end connected to the outlet port and a second end for contact with the body, each tube having an axial lumen between the first and second ends defining a blood flow path for conveyance of blood therealong;

accessing the patient'"'"'s right atrium or the right ventricle of the heart with the inlet tube such that the second end of the inlet tube is in fluid communication with the right atrium or the right ventricle;

accessing the aorta with the outlet tube such that the second end of the outlet tube is in fluid communication with the aorta;

actuating the rotating pumping member to draw oxygenated blood from the right atrium or the right ventricle of the heart through the second end of the inlet tube and through the axial lumen of the inlet tube and into the inlet port of the pump housing whereby the pumping member imparts mechanical energy to the oxygenated blood passing through the pump housing and directs the oxygenated blood through the outlet port and through the axial lumen of the outlet tube and the second end of the outlet tube to be transferred by the pulmonary artery to the lungs for oxygenation.

17. A circulatory support device, which comprises:

a pump housing including an inlet end portion defining an inlet port for permitting blood to enter the pump housing and an outlet end portion defining an outlet port for permitting blood to exit the pump housing, the inlet and outlet end portions each having central hub portions with straightener blades extending therefrom for facilitating passage of blood through the pump housing;

a rotatable member mounted for rotational movement to the central hub portions of the pump housing, the rotatable member including at least one impeller blade for imparting pump energy to blood passing through the pump housing, the rotatable member having a magnetically actuated rotor; and

a motor stator disposed in the pump housing, the motor stator and the rotatable member having an annular space therebetween defining a blood path for blood to flow through the pump housing, the motor stator having at least one stator blade extending from an inner surface thereof, the one stator blade and the one impeller blade of the rotatable member cooperatively configured to exert a substantially axial flow pumping energy to blood flowing along the blood path.

18. The device according to claim 17 wherein the one impeller blade extends axially and peripherally with respect to a longitudinal axis of the pump housing.

19. The device according to claim 18 wherein the one stator blade extends axially and peripherally with respect to the longitudinal axis.

20. The device according to claim 19 including a plurality of impeller blades and a plurality of stator blades.

21. The device according to claim 19 wherein the one stator blade is disposed between the one impeller blade and the outlet end portion of the pump housing.

22. The device according to claim 17 including an inflow tube connected to the inlet end portion of the pump housing and configured for accessing one of a major blood vessel and the heart of a patient.

23. The device according to claim 22 further including an outflow tube connected to the outlet end portion of the pump housing for accessing one of a major blood vessel and the heart of a patient.

24. A method for providing at least partial bypass of the heart to supplement the pumping function of the heart to thereby enable the surgeon to perform various surgical procedures thereon, the heart having a left atrium for receiving oxygenated blood from the lungs and a left ventricle for pumping the oxygenated blood through the aorta to the systemic arteries, and a right atrium for receiving oxygen-depleted blood from the systemic veins and a right ventricle for pumping the oxygen-depleted blood through the pulmonary artery and into the lungs for oxygenation, the method comprising the steps of:

supplementing the pumping function of the left side of the heart by;

providing a circulatory assist system including a portable extracorporeal axial flow pump having a pump housing defining a longitudinal axis, the pump housing having an inlet port and an outlet port, the outlet port being in substantial axial alignment with the inlet port, a rotating pumping member disposed in the pump housing, an inlet tube having a first end connected to the inlet port and a second end for contact with the body, an outlet tube having a first end connected to the outlet port and a second end for contact with the body, each tube having an axial lumen between the first and second ends defining a blood flow path for conveyance of blood therealong;

accessing the left ventricle of the heart with the inlet tube such that the second end of the inlet tube is in fluid communication with the left ventricle;

accessing the aorta with the outlet tube such that -the second end of the outlet tube is in fluid communication with the aorta;

actuating the rotating pumping member to draw oxygenated blood from the left ventricle of the heart through the second end of the inlet tube and through the axial lumen of the inlet tube and into the inlet port of the pump housing whereby the pumping member imparts mechanical energy to the oxygenated blood passing through the pump housing and directs the oxygenated blood through the outlet port and through the axial lumen of the outlet tube and the second end of the outlet tube to be transferred by the aorta to the systemic arteries; and

supplementing the pumping function of the right side of the heart while permitting the patient'"'"'s lungs to function in oxygenating the blood.

25. The method according to claim 24 wherein the step of supplementing the pumping function of the right side of the heart includes:

providing a second circulatory assist system including a portable extracorporeal axial flow pump having a pump housing defining a longitudinal axis, the pump housing having an inlet port and an outlet port, the outlet port being in substantial axial alignment with the inlet port, a rotating pumping member disposed in the pump housing, an inlet tube having a first end connected to the inlet port and a second end for contact with the body, an outlet tube having a first end connected to the outlet port and a second end for contact with the body, each tube having an axial lumen between the first and second ends defining a blood flow path for conveyance of blood therealong;

accessing the right atrium or the right ventricle of the heart with the inlet tube such that the second end of the inlet tube is in fluid communication with the right atrium or the right ventricle;

accessing the pulmonary artery with the outlet tube such that the second end of the outlet tube is in fluid communication with the pulmonary artery;

actuating the rotating pumping member to draw oxygen-depleted blood from the right atrium or the right ventricle of the heart through the second end of the inlet tube and through the axial lumen of the inlet tube and into the inlet port of the pump housing whereby the pumping member imparts mechanical energy to the oxygen-depleted blood passing through the pump housing and directs the oxygen-depleted blood through the outlet port and through the axial lumen of the outlet tube and the second end of the outlet tube to be transferred by the pulmonary artery to the lungs for oxygenation.

26. A circulatory support system to supplement or temporarily replace the pumping function of a patient'"'"'s heart to thereby enable a surgeon to perform surgical procedures thereon, comprising:

an extracorporeal portable blood flow pump having inlet and outlet ports, a rotating member rotatably mounted in the pump housing to impart mechanical energy to blood entering the inlet port and to direct the blood through the outlet port;

an inlet cannula connected to the inlet port of the pump housing and having an inlet open end portion dimensioned for insertion within the patient'"'"'s heart or blood vessel associated with the heart so that blood is drawn from the patient through a lumen of the inlet cannula and directed into the pump housing;

an outlet cannula connected to the outlet port of the pump housing and having an outlet end portion dimensioned for insertion within the patient so that blood exiting the outlet port of the pump housing is conveyed through a lumen of the outlet tube into the patient for transfer by the arterial system of the patient;

a control unit having a processor, operatively coupled to the flow pump, for controlling operation thereof;

an air bubble sensor mounted to one of the cannulas for detecting air bubbles in the respective cannula and providing a bubble detect signal indicative of the presence of an air bubble;

a clamping device mounted to one of the cannulas and operative to clamp down on the respective cannula when the bubble detect signal is generated to prevent air from entering the patient'"'"'s bloodstream;

wherein the control unit is operative, responsive to receiving the bubble detect signal, to generate an air bubble alarm and to cause rotation of the rotating member of the pump to cease.

27. The system of claim 26 wherein the air bubble sensor is mounted to the inlet cannula and the clamping device is mounted to the outlet cannula.

28. The system of claim 26, wherein the control unit includes a manual switch to permit the pump to be restarted following activation of the bubble alarm, the control unit being responsive to manual operation of the switch to extinguish the bubble alarm and restart rotation of the rotating member.

29. The system of claim 26, further including a flow sensor coupled to one of the inlet or outlet cannulas and providing a flow sense signal to the control unit indicative of blood flow rate within the respective cannula, the control unit operative to generate a low flow rate alarm when the flow rate is determined to be below a predetermined threshold.

30. The system of claim 29 wherein, subsequent to the generation of the low flow rate alarm, the control unit is operative to extinguish the low flow rate alarm when the flow rate is determined to have risen above a predefined threshold.

31. The system of claim 26, further including a pressure transducer for sensing pressure on the inlet side of the pump and providing a pressure sense signal indicative of the pressure sensed, the control unit being operable to command a reduction in motor speed to a non-zero signal when the pressure is determined to be below a predetermined threshold.

32. The system of claim 31 wherein said pressure transducer is disposed in proximity to the inlet open end portion of the inlet cannula, and the system further including a wire running within an outer sheathing of the inlet cannula from the control unit to the pressure transducer, the pressure sense signal being transmitted to the control unit on the wire.

33. The system of claim 31, wherein, following the reduction in motor speed, the control unit is operative to ramp up the motor speed to a speed corresponding to a manually set dial, following a determination based on the pressure sense signal that the pressure has risen to a value above a predefined threshold for at least a specified period of time.

34. The system of claim 26 wherein the control unit includes circuitry for sensing motor current and for generating an alarm when the motor current has risen above a predetermined threshold.

35. The system of claim 26 wherein the axial flow pump includes a pump housing dimensioned for positioning directly on or adjacent to the chest area of a patient.

36. The system of claim 26 wherein the control unit includes a backup motor controller circuit and a manual engage backup switch, the control unit entering a backup mode upon activation of the engage backup switch, the control unit operative in the backup mode to control motor speed based on manual motor speed control independent of alarm conditions.

55. The system of claim 26 wherein said blood flow pump comprises an axial blood flow pump.

37. A control unit for use in a circulatory support system to supplement or temporarily replace the pumping function of a patient'"'"'s heart, the support system including a blood flow pump, inlet and outlet cannulas coupled to the flow pump for insertion within the patient, an air bubble detector, and a cannula clamp, each coupled to one of the cannulas, the control unit comprising:

circuitry for supplying power to the flow pump to cause the pump to rotate;

circuitry responsive to a bubble sense signal provided by the bubble detector, for generating a bubble alarm and for causing rotation of the pump to cease if the bubble sense signal indicates the presence of an air bubble; and

circuitry responsive to the bubble sense signal indicating the presence of an air bubble for causing the cannula clamp to clamp down on the respective cannula to prevent air from entering the patient'"'"'s bloodstream.

38. The control unit of claim 37, further comprising a manual switch to permit the pump to be restarted following activation of the bubble alarm, the control unit being responsive to manual operation of the switch to extinguish the bubble alarm, restart the pump and cease actuation of the cannula clamp.

39. The control unit of claim 38, wherein the system further includes a pressure transducer coupled to the inlet cannula and a flow rate sensor coupled to one of the cannulas, the control unit operative to receive a pressure sense signal from the pressure transducer and to command a reduction in motor speed to a non-zero speed and generate a low pressure alarm when the pressure is determined to be below a predetermined pressure threshold, and to generate a low flow rate alarm when the flow rate is determined to be below a predetermined flow threshold based on a flow rate signal received from the flow sensor.

40. The control unit of claim 39, wherein, following the reduction in motor speed, the control unit is operative to ramp up the motor speed to a speed corresponding to a manually set dial, following a determination based on the pressure sense signal that the pressure has risen to a value above a predefined threshold for at least a specified period of time.

41. The control unit of claim 40, further including circuitry for sensing motor current and for generating an alarm when the motor current has risen above a predetermined threshold.

42. The control unit of claim 37, further including a backup motor controller circuit and a manual engage backup switch, the control unit entering a backup mode upon activation of the engage backup switch, the control unit operative in the backup mode to control motor speed based on manual motor speed control independent of alarm conditions.

43. The control unit of claim 37, having a housing of a generally long, solid rectangular shape to facilitate use within an operating room.

44. The control unit of claim 43 wherein the control unit housing is about four feet in height, about one foot in width and several inches in thickness.

45. The control unit of claim 37, further including:

a front portion with a front display that displays motor speed and flow rate and visible alarm indicators corresponding to particular alarm conditions; and

a rear portion with a rear display that displays motor speed and flow rate and generally the same visible alarm indicators as the front display.

46. The control unit of claim 37, further including circuitry for receiving a flow rate signal from a flow rate sensor coupled to one of the cannulas, means for generating, responsive to the flow rate signal, a low flow rate alarm if flow rate is determined to be below a predetermined threshold, and a flow blockage alarm if the flow rate has dropped by more than a predefined amount or percent.

56. The control unit of claim 37 wherein said blood flow pump comprises an axial flood flow pump.

47. A circulatory support system to supplement or temporarily replace the pumping function of a patient'"'"'s heart to thereby enable a surgeon to perform surgical procedures thereon, comprising:

an extracorporeal portable blood flow pump having inlet and outlet ports, a rotating member rotatably mounted in the pump housing to impart mechanical energy to blood entering the inlet port and to direct the blood through the outlet port;

an inlet cannula connected to the inlet port of the pump housing and having an inlet open end portion dimensioned for insertion within the patient'"'"'s heart or blood vessel associated with the heart so that blood is drawn from the patient through a lumen of the inlet cannula and directed into the pump housing;

an outlet cannula connected to the outlet port of the pump housing and having an outlet end portion dimensioned for insertion within the patient so that blood exiting the outlet port of the pump housing is conveyed through a lumen of the outlet tube into the patient for transfer by the arterial system of the patient;

a control unit having a processor, operatively coupled to the flow pump, for controlling operation thereof; and

a pressure transducer for sensing pressure on the inlet side of the pump and providing a pressure sense signal indicative of the pressure sensed to the control unit, the control unit being operable to command a reduction in motor speed to a lower speed when the pressure is determined to be below a predetermined threshold.

48. The system of claim 47 wherein said pressure transducer is disposed in proximity to the inlet open end portion of the inlet cannula, and the system further including a wire running within an outer sheathing of the inlet cannula from the control unit to the pressure transducer, the pressure sense signal being transmitted to the control unit on the wire.

49. The system of claim 47 wherein the reduction in motor speed to a lower speed is repeated such that the motor speed is ramped down, until the pressure is determined to have risen to a value above a predefined threshold, and the control unit being operative to ramp up the motor speed if the pressure has risen above the predefined threshold.

50. The system of claim 47, further including an air bubble sensor mounted to one of the cannulas for detecting air bubbles in the respective cannula and providing a bubble detect signal indicative of the presence of an air bubble;

wherein the control unit is operative, responsive to receiving a bubble detect signal, to generate an air bubble alarm and to cause rotation of the rotating member of the pump to cease.

57. The system of claim 47 wherein said blood flow pump comprises an axial blood flow pump.

51. A control unit for use in a circulatory support system to supplement or temporarily replace the pumping function of a patient'"'"'s heart, the support system including a blood flow pump, inlet and outlet cannulas coupled to the flow pump for insertion within the patient, and a pressure transducer coupled to the inlet cannula, the control unit comprising:

circuitry for supplying power to the flow pump to cause the pump to rotate at a first speed; and

circuitry responsive to a pressure sense signal from the pressure transducer, the control unit being operable to command a reduction in motor speed to a lower motor speed when the pressure is determined to be below a predetermined threshold.

52. The control unit of claim 51 wherein the reduction in motor speed to a lower speed is repeated such that the motor speed is ramped down, until the pressure is determined to have risen to a value above a predefined threshold, and the control unit being operative to ramp up the motor speed if the pressure has risen above the predefined threshold.

53. The control unit of claim 52, wherein the motor speed is maintained at a reduced motor speed once it is determined that the pressure has risen above the predefined threshold, and the motor speed being ramped up only after it is determined that the pressure has been above the predefined threshold for a specified period of time.

54. The control unit of claim 51, further including circuit means, responsive to a bubble detect signal from an air bubble detector indicative of the presence of an air bubble in one of the cannulas, for generating an air bubble alarm and causing rotation of the rotating member of the pump to cease.

58. The control unit of claim 51 wherein said blood flow pump comprises an axial flood flow pump.