An efficient pulsed-solenoid powered cardiac assist system

Spring decoupled solenoid technology has received more than ten years of intensive development as the basis for a permanently implanted left ventricular assist system (LVAS). In the latest energy converter design, a balanced, symmetric, C-core solenoid drives a pair of preloaded beam springs which directly couple to a dual pusher-plate blood pump. This configuration produces a reaction-free closure at nearly constant pump pressure through the ejection stroke. Solenoid geometries are chosen to promote a progressive saturation behavior, resulting in an enlarged peak field region for high currents and large gaps. This effect permits a small, lightweight solenoid to develop the high starting force required to overcome the preloaded initial spring force. Using this approach, 55% overall efficiency has been realized for a 280-gm solenoid at 1.64 joules mechanical output. The complete LVAS provides beat-to-beat synchronism and ventricular decompression, and has supported the systemic circulation for as long as 161 days in calf experiments at Stanford.