Abstract
The “MagScrew” TAH Mark II system consists of Cleveland Clinic pusher plate blood pumps, a Foster-Miller magnetic screw actuator, an a controller currently implemented with a combination of custom hardware and a personal computer. The blood pump is a long proven design, with extremely blood-compatible, protein-coated surfaces and tissue valves, and a Hexsyn rubber diaphragm of extraordinary flex fatigue resistance. Functionally, the actuator is a reciprocating screw mechanism, with a reversing electric motor providing the drive. Uniquely, the “threads” are magnetic, rather than mechanical, helices, so that force is transmitted without mechanical contact, friction, or wear The control system, implemented for evaluation purposes using the Labview software package, can operate in automatic mode by processing displacement signals from the pusher plates or in a fixed-rate, manually set mode. Auto mode maintains 90% left pump filling. I automatic mode, during bench testing, the preload response simulated Starling Law behavior, resulted in a maximum flow of 9.5 liters/minute, with a left atrial pressure of 11.8 mm Hg, at a beat rate of 172 bpm. Greater right-pump afterload sensitivity and lower right-side volumetric displacement maintained balanced left- and right-pump outputs at maximum flow rate. In manual mode, the controller trigger points are set to provide a safe relationship between right and left atrial pressure. The highly effective performance is obtained by a combination of desig factors, including high, passive filling sensitivity of the pumps, the powe capability of the actuator, a left master control logic, a reduced right-sid displacement, proper triggering relationships between pump pusher-plate and actuator positions, and a scale factor limiting right-stroke power relative to left-stroke power.
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