246 * A MONITORING AND PHYSIOLOGICAL CONTROL SYSTEM FOR DETERMINING AORTIC VALVE CLOSING

Abstract

Objectives: Accurate monitoring and assessment of the residual cardiac function of a patient supported by a ventricular assist device (VAD) is critical for better patient management and potential weaning. Information regarding the VAD speed at which the aortic valve remains closed can assist clinicians to maintain appropriate unloading, reduce the risk of aortic insufficiency and potentially reduce the risk of aortic leaflet fusion. Methods: A pressure sensor implanted in the inlet cannula determines the left ventricular (LV) pressure. The area of the LV pressure and motor power is calculated for each heart beat. A feedback signal is monitored at high speed and low speed to determine the change in the system. Small amplitude (<300 rpm) and low frequency (<0.1 Hz) square wave changes to the VAD speed are made. Results: Ten ovine trials have been completed with the DP3 pump (LV to aortic cannulation). The feedback variable (pressure power area) proved to have a peak at the speed of aortic valve closure The gradient (Δ pressure power area) could be measured by using the square wave speed modulation. In both the baseline and beta blocked heart the zero-crossing of gradient occurred at the aortic closure speed. Conclusions: Feedback gives a definite peak around aortic valve closure point and uses pump speed modulation for more accuracy; there is no sensitivity to sensor drift or haematocrit changes, and it provides noninvasive, continuous measurement.