Development of an axial flow blood pump using a hydrodynamic pressure bearing

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An axial flow blood pump was developed using a hydrodynamic pressure bearing, a magnetic fluid seal and a brushless direct current motor. This enabled contact-free rotation of the impeller without material wear. The motor rotor is directly connected to the impeller by a motor shaft. A hydrodynamic pressure bearing is installed on the motor shaft. The motor and the hydrodynamic bearing are housed in a cylindrical casing and are waterproofed by a magnetic fluid seal. The magnetic fluid seal was developed for use in an axial-flow blood pump. Sealing pressures at motor speeds of up to 10,000 rpm were measured with the seal immersed in water. The sealing pressure was above 400 mm Hg. The seal, installed in the pump, remained perfect for 60 days at a flow of 4 L/min against a pressure of 150 mmHg. Results of measurement of cell growth activity indicated that the magnetic fluid has no negative cytological effects. The developed blood pump could eject a flow of 5 L/min at a pressure difference of 100 mmHg with an allowable hemolysis level (N.I.H.<0.02).The axial flow blood pump was implanted in goats between the left ventricle and the descending aorta. The goat survived for two days and a total left ventricular bypass was obtained with the pump.A control system of the axial flow blood pump was developed. A prediction method of the pump flow based on power consumption of the motor and motor speed was proposed. Pump flow was predicted with an error of less than 10%. Backflow through the pump and obstruction of the inflow cannula were automatically detected based on the wave distortion rate of the motor current. The distortion rate was computed using the Walsh functions.