CONTROLLER FOR AN AXIAL-FLOW BLOOD PUMP

A rotary blood pump inherently provides only one noninvasive ''observa ble'' parameter (motor current) and allows for only one ''controllable '' parameter (pump speed). To maintain the systemic circulation proper ly, the pump speed must be controlled to sustain appropriate outlet fl ows and perfusion pressure while preventing pulmonary damage caused by extremes in preload. Steady-state data were collected at repeated int ervals during chronic trials of the Nimbus AxiPump (Nimbus, Inc., Ranc ho Cordova, California, U.S.A.) in sheep (n = 7) and calves (n = 12). For each data set, the pump speed was increased at increments of 500 r pm until left ventricular and left atrial emptying was observed by lef t atrial pressure diminishing to zero. The effect of decreasing preloa d was evaluated perioperatively by inferior vena cava occlusion at a c onstant pump speed. Fourier analysis established a relationship betwee n changes in the pump preload and the power spectra of the pump curren t waveform. Based on these results, a control method was devised to av oid ventricular collapse and maintain the preload within a physiologic range. The objective of this controller is the minimization of the se cond and third harmonic of the periodic current waveform. This method is intended to provide a noninvasive regulation of the pump by elimina ting the need for extraneous transducers.