In-vitro evaluation of physiological controller response of rotary blood pumps to changes in patient state.

Abstract

Rotary blood pumps (RBPs) have a low sensitivity to preload changes when run at constant speed, which can lead to harmful ventricular suction events. Therefore a control mechanism is needed to adjust RBP speed in response to patient demand, but an appropriate response time for physiological control strategies to these changes in patient demand has not been determined. This paper aims to evaluate the response of a simulated healthy heart with those of different RBP control techniques during exercise simulations and a Valsalva manoeuver. A mock circulation loop was used to simulate the response of a healthy heart to these changes in patient state. The generated data was compared with a simulated RBP (VentrAssist) supported left heart failure condition. A range of control techniques including constant speed, proportional integral (PI) (active control) and a compliant inflow cannula (passive control) were used to achieve restored haemodynamics and evaluate controller response time. Controllers that responded faster (active control) or slower (active control and constant speed mode) than the native heart's response led to ventricular suction. Active control systems can respond both faster or slower than the heart depending on the controller gains. A control system that responded similar to the native heart was able to prevent ventricular suction. This study concluded that a physiological control system should mimic the response of the native heart to changes in patient state in order to prevent ventricular suction.