A MAGNETICALLY SEALED, HYDRODYNAMICALLY SUSPENDED MECHANICALLY NON-CONTACT AXIAL FLOW BLOOD PUMP

Abstract

Magnetic bearings and hydrodynamic bearings have been used in rotary blood pumps for contact-free rotation of the impeller. However, magnetic bearings use complex control systems and require extra power. Hydrodynamic bearings use blood as a working fluid and squeeze flow can cause severe hemolysis. To overcome these problems, an axial flow blood pump consisting of a magnetic fluid seal and a hydrodynamic bearing, which enabled contact-free rotation of the impeller without the above problems, was developed. The axial flow pump consists of a brushless DC motor and an impeller. The motor rotor is directly connected to the impeller by a motor shaft. A hydrodynamic 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. Axial and radial displacements of the shaft were only a few micrometers for motor speed up to 8500 rpm. The shaft did not make contact with the bearing housing. The magnetic fluid seal worked perfectly for 60 days against 150 mmHg at 4.8 L/min and 30+ days against 68 mmHg at 4.7 L/min. A left ventricular bypass experiment was performed using a mechanical mock loop. With increase in motor speed, bypass flow increased. The hydrodynamic bearing worked normally under variable load conditions. The axial flow pump was implanted in a goat between the left ventricle and the aorta. Circulation was maintained with the pump at a bypass rate of 80%. The axial flow blood pump provides contact-free rotation of the impeller without the use of complex control systems and without causing hemolysis.