AUTOMATIC CONTROL ALGORITHMS FOR THE ABIOCOR® IMPLANTABLE REPLACEMENT HEART SYSTEM

Abstract

The AbioCor® Implantable Replacement Heart System (AbioCor) is designed to physically and functionally replace the failing human heart. There are three primary control algorithms that allow the device to automatically respond to changing physiologic demands of the patient: motor speed control, balance control, and beat rate control. The motor speed control algorithm adjusts the speed of the hydraulic pump resulting in the desired hydraulic fluid motion which, when coupled across flexible membranes, translates into optimal blood ejection on every beat to achieve a constant stroke. The motor speed control algorithm is based on the shape of pressure waveform generated in the hydraulic pumping chambers of the thoracic unit (TU). Specifically, for each half beat, the algorithm optimizes the left and right stroke motor speeds in order to achieve an appropriate “end of stroke” spike. This design allows the TU to produce a fixed left stroke volume despite changes in vascular tonc. Both balance control and beat rate control are based on estimates of the atrial pressures derived from the hydraulic pumping chamber pressures during the TU filling phases. For balance control, the desired difference in the left and the right side blood flow (primarily to compensate for bronchial shunt flow) is achieved by maintaining physiologic atrial pressures based on estimates derived from diastolic hydranlic pressures. Extreme atrial pressures must be avoided for the safety of the patient. Because the hydraulic fluid flow out of each side of the AbioCor are closeiy coupled, the blood flows must be correctly balanced by changing the stroke volume of the right side of the device via diversion of hydraulic fluid to a “balance chamber.” For beat rate control, an estimate of right atrial pressure is used to control the beat rate (and therefore flow). As the right atrial pressure rises from about 3 to 18mmHg, the flow increases from about 4 to 8L/min. This keeps the inflow pressures in a safe range and may increase blood flow as activity increases. All algorithms have performed adequately clinically. The beat rate control has not been exercised over a broad range.