An Implantable Ventricular Assist System Employing a Radially Controlled Maglev Centrifugal Blood Pump with Capability to Measure Blood Flow Rate without Additional Sensors

In order to solve the problems of lack of heart donors for transplant, implantable ventricular assist systems (VAS) have been developed to assist the failing heart ventricle. One of the components of a VAS is a blood pump that connects the left ventricle to the aorta. Therefore, the pump flow rate is influenced by the cardio-vascular system. To control the flow rate through the blood pump, real-time measurement of flow rate is required. However, the use of conventional flow sensors is not desirable due to issues of compactness and durability. In a magnetically levitated (maglev) rotary blood pump, the radial thrust acting on the maglev impeller depends on the pump flow rate. In this study, we present a centrifugal blood pump (CBP), incorporating a radial-controlled magnetic bearing (MB) and a brushless DC motor to be used in an implantable VAS. We also present a method for estimating average pump flow rate during ventricular assistance, based on the radial thrust estimated by a disturbance force observer of the MB. The magnetic bearing of the CBP is composed of two pairs of electromagnets located in the stator and a sandwich of two iron rings and a permanent magnet (PM) ring embedded in the impeller. To design the observer, parameters of the dynamic model of a maglev 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 rate and radial thrust was first identified experimentally under continous flow conditions. Then, using this relationship and the measured radial thrust, the pump average flow rate was estimated under pulsatile flow conditions. The maglev CBP is 69.0 mm in diameter, 28.5 mm in height, 50.0 mm in impeller’s diameter and the pump priming volume is 20 ml. The pump mass is 370 g, while the impeller mass is 98 g. Under rotational speed of 1700 rpm, the operating point (5 L/min, 100 mmHg) can be achieved. Using the proposed estimation method, the pump average flow rate estimation error was less than 11% (0.4L/min).