Baroreflex-based physiological control of a left ventricular assist device

The new generation left ventricular assist devices (LVADs) for treating end-stage heart failure are based upon turbodynamic (rotary) pumps. These devices have demonstrated several advantages over the previous pulsatile generation of LVADs, however they have also proven more difficult to control. Limited availability of observable hemodynamic variables and dynamically changing circulatory parameters impose particular difficulties for the LVAD controller to accommodate the blood flow demands of an active patient. The heart rate (HR) and systemic vascular resistance (SVR) are two important indicators of blood flow requirement of the body; but these variables have not been previously well exploited for LVAD control. In this dissertation, we will exploit these two variables and develop a control algorithm, based upon mathematical models of the cardiovascular system: both healthy and diseased, with built in autoregulatory control (baroreflex). The controller will respond to change in physiological state by adjusting the pump flow based on changes in HR and SVR as dictated by the baroreflex. Specific emphasis will be placed on hemodynamic changes during exercise in which the blood flow requirement increases dramatically to satisfy the increased oxygen consumption. As the first step in the development of the algorithm, we developed a model which will include the autoregulation of the cardiovascular system and the hydraulic power input from the pump. This model provided a more realistic simulation of the interaction between the LVAD and the cardiovascular system regulated by the baroreflex. Then the control algorithm was developed, implemented, and tested on the combined system of the LVAD and the cardiovascular system including the baroreflex. The performance of the proposed control algorithm is examined by comparing it to other control methods in response to varying levels of exercise and adding noises to the hemodynamic variables. The simulation results demonstrate that the controller is able to generate more blood flow through the pump than the constant speed and constant pump head method, and the heart rate related pump speed method. The simulations with noise show that the controller is fairly robust to the measurement and estimate noises.