A COMPLETELY MAGNETICALLY LEVITATED AXIALI-FLOW BLOOD PUMP TECHNICAL ASPECTS

Abstract

An axial-flow pump as an assist device with magnetic bearings was developed with the following characteristics: Power consumption at 8,600 rpm and S L/min flow at 100 mmHg pressure is 8.5 W. Flow may be increased up to 7 L/min against 150 mmHg. Weight is 200 g and diameter 30 mm. For the levitation of the impeller the pump is equipped with radially passive and axially active magnetic bearings. Magnetic and additional pressure forces act on the rotor in an axial direction. A sensor and a controlling unit are required to keep the rotor in optimal position with minimal energy input. Therefore, the magnetic bearings are used to measure the pressure difference across the pump. This difference, together with the rotor speed and the known flow characteristics of the pump, can be used to calculate the actual pump flow. Pressure head and flow rate measurement can be used to modulate the speed of the rotor synchronously to the heart cylcle, thus minimizing suction and improving pulsatility ot pressure and waveforms. The magnetic bearings give the pump the advantages of both detecting and influencing important flow parameters and generating favorable conditions for low thrombogenicity and virtually unlimited durability. Testing of hydraulic performance and in vitro and in vivo testing for hemolysis confirmed excellent properties in this respect. In in vivo experiments a NIH of 6 mg/100L and MIH of 1 were achieved. In animal experiments in calves no increase of plasma-free hemoglobin was seen. Clinical trials will be started in spring 2002.