Robust Assistance Control of Left Ventricular Assist Devices

Rotary blood pumps (RBPs) are increasingly used as left ventricular assist devices (LVADs) to treat patients with advanced heart failure. In clinical practice, RBPs are fixed speed controlled which causes an insufficient adaption of the pump flow to the varying blood flow demand of the patient. This can lead to undesired or even dangerous operating conditions and impedes patients leading a normal life with an LVAD. This paper presents a robust nonpulsatile control strategy that amplifies the remaining native physiological control loops that affect the total cardiac output (CO). The setting option of this control strategy is called Assistance, which is defined as the time-averaged ratio of pump flow and total CO. By keeping the Assistance at a constant level, the cardiac workload is shared between the native heart and the LVAD, even when the blood flow demand is changing. The control strategy was implemented on a real-time computer operating a transvalvular LVAD. The Assistance is determined using estimations of the pump flow and the aortic flow rate. The latter is estimated with an extended Kalman filter based on pressure measurements provided by optical pressure sensors mounted on the pump inlet and outlet. Proof-of-concept was established in hybrid mock circulatory loop trials, in which stable Assistances ranging from 20 % to 77.5 % were achieved. In case the native CO control loops are still intact, the Assistance control strategy adequately maintains the systemic circulation and offers an intuitive setting option for the treating physician.