High-sensitivity pulsation estimation and application of heartbeat synchronization control in magnetically-levitated ventricular assist device

In recent years, the number of heart failure patients has been increasing. However, there is a shortage of donors for treatment. As a result, ventricular assist devices (VAD) are being used as an alternative, and long-term use has become common. However, there are issues such as aortic valve dysfunction caused by VAD's continuous flow support. As a solution to this problem, heartbeat synchronization control, which adjusts the motor speed to match the pulsation of the diseased heart, is being explored. Conventional studies have used electrocardiograms and flow meters to estimate the pulsations necessary for heartbeat synchronization control. However, it is difficult for patients to wear these devices continuously. Therefore, our research group has developed a technology that estimates pulsations using only sensors from a magnetic levitation system of an impeller, eliminating the need for additional ECG sensors and applying it to heartbeat synchronization control. However, one of the issues of this method is that it was difficult to estimate weak pulsations and hence, it is required to improve the signal-to-noise (S/N) ratio. To improve the S/N ratio, we established a control system that allows for high-sensitivity pulsation estimation while maintaining levitation stability by lowering the stiffness of the support impeller for pulsations (0.7-2 Hz) and increasing the stiffness for unbalanced forces (10-50 Hz) using the loop shaping method based on H-infinity control theory. We successfully applied the designed control system to a magnetically-levitated VAD and the estimated flow's S/N ratio was doubled.