Sensorless measurement of the pulsatile flow through an implantable maglev centrifugal blood pump during ventricular assistance

We developed a centrifugal blood pump (CBP), incorporating a radial-controlled magnetic bearing (MB) and a brushless DC motor to assist the failing heart ventricle. To control the flow through the CBP, real-time measurement of pulsatile flow is required. However, the use of conventional flow sensors is not desirable due to issues of compactness and durability. The radial thrust acting on a magnetically levitated impeller depends on the pump flow. In this study, we present a method for estimating pulsatile flow during ventricular assistance, based on the radial thrust estimated by a disturbance force observer of the MB. To design this observer, parameters of the dynamic model of a magnetically levitated impeller were identified under different flow conditions, assuming the density and viscosity of water to be constant. The disturbance force observers were designed based on linear models that were obtained for a given rotational speed. The relationship between pump flow and radial thrust was first identified experimentally under non-pulsatile flow conditions. Then, using this relationship and the measured radial thrust, the pump flow was estimated under pulsatile flow conditions and a high correlation was achieved between the measured and the estimated flows.