Magnetic levitation design for the PediaFlow ventricular assist device

Over the past few decades, we have seen a tremendous progress in the development of implantable ventricular assist devices (VAD). However, these devices are mainly developed for adult patients. For the patients under age 5 who have chronic heart failures, physicians must resort to extracorporeal circulatory support devices which often result in infection, thromboembolism, or excessive blood transfusions. In this paper, we describe a design process for a pediatric ventricular assist device (PVAD). The central part of the device is a magnetically levitated rotating pump which creates a pressure rise (~100 mmHg) at a required flow rate (~0.5 L/min) suitable for infants and small children. We have considered several different pump topologies, of which an axial mixed-flow pump configuration was chosen for further development. The pump impeller is supported by two radial permanent-magnet passive bearings. The rotor-dynamics analysis of the pump shows that the critical speeds of the pump are affected by the radial and yaw stiffnesses of the PM bearings. Hence, analytical expressions for the stiffnesses are derived and verified through FEA. In contrast to the radial suspension, the axial motion of the impeller is actively controlled using a voice-coil actuator. A toroidally-wound motor drives the pump with high efficiency and little additional negative radial stiffness. The design process relies heavily on optimization at the component-level and system-level. The preliminary results of the design optimization are presented in this paper