The PediaFlow Pediatric Ventricular Assist Device

This paper describes a design process for a new pediatric ventricular assist device (VAD), the PediaFlow. The VAD is a magnetically levitated turbodynamic pump design for chronic support of infants and small children. The design entailed the consideration of multiple pump topologies, from which an axial mixed-flow configuration was chosen for further optimization via computation fluid dynamics. The magnetic design includes permanent-magnet (PM) passive bearings for radial support of the rotor, an actively controlled thrust actuator for axial support, and a brushless DC motor for rotation. These components are closely coupled both geometrically and magnetically, and were therefore optimized in parallel, using electromagnetic, rotordynamic and fluid models. Multiple design objectives were considered including efficiency, size, and margin between critical speed to operating speed. The former depends upon the radial and yaw stiffnesses of the PM bearings. Analytical expressions for the stiffnesses were derived and verified through FEA. A toroidally-wound motor was designed for high efficiency and minimal additional negative radial stiffness. The design process relies heavily on optimization at the component-level and system-level. The results of this preliminary design optimization yielded a pump design with an overall stability margin of 15 percent, based on a pressure rise of 100 mmHg at 0.5 lpm running at 16,000 RPM.