A physiological control strategy for continuous-flow left ventricular assist devices: The power ratio controller

摘要

The shortage of donor hearts is pushing the development of left ventricular assist devices (LVAD) as permanent solution for advanced cardiovascular diseases (CVD). In actual implants, the rotary speed of the LVAD is set to a constant speed leading to a non-physiological behaviour of the system. The missing adaption of the cardiac output (CO) produces serious problems like ventricular suction or pulmonary edema. In this paper, a novel physiological controller is designed. The Power Ratio (PR) controller regulates the rotary speed in order to obtain a fixed ratio (ρ) between the hydraulic and the ventricular power. This factor can be useful in future applications of ventricular recovery. The control strategy aims at imitating the Frank-Starling mechanism. A circulatory system model is used to study the controller response to changes in preload, afterload, contractility, heart rate and to a sudden preload drop. The restoration of the Frank-Starling mechanism is assessed. PR controller results are compared to constant speed mode and show a superior behavior. Over-sensitivity is detected in preload and contractility experiments. Therefore, a detailed analysis of the theoretical foundations is done. A flow limiter is designed to avoid problems related to that issue.