Steady and transient flow analysis of a magnetically levitated pediatric VAD: time varying boundary conditions.

A magnetically levitated impeller within a pediatric ventricular assist device operates under highly transient flow conditions. In this study, computational analyses were performed to investigate the hydraulic performance and fluid forces on the impeller under the steady and dynamic flow conditions, including: 1) time-varying boundary conditions (TVBC) considering a pulsed pump flow rate and pulsed left ventricular pressure; 2) transient rotational sliding interfaces (TRSI) to capture virtual blade rotation. Under steady flow conditions, the pressure generation for 0.5-6 l/min over 6000-10000 rpm was 20-140 mmHg; experimental validation agreed to within 6-27%. Under transient flow conditions, the outflow pressure of the pump increased with higher inlet pressure during the TVBC simulation. During TVBC, the pressure rise across the pump decreased as a function of higher flow rates and increased as a function of lower flow rates. The radial fluid forces varied directly with the flow rate by demonstrating larger forces at higher flow rates. For TRSI simulations, pressure fluctuations due the blade passage frequency were found to have 12 peaks per revolution, having magnitude ranges of 
0.7 and 1.0 mmHg for 8 000 and 10 000 rpm, respectively. At 8 000 rpm, the fluid forces ranged from 1.15-1.17 N (axial) and 0.02-0.11 N (radial). Transient simulations model implant scenarios more realistically and provide critical information about the fluid conditions in the pump.