Mean flow velocity patterns within a ventricular assist device.

A laser Doppler anemometry system was used to measure fluid velocities at 127 locations within a plexiglas model of the 70 cm3 Penn State electric ventricular assist device (VAD) fitted with Bjork-Shiley convexo-concave tilting disk valves. The velocity measurements were made using a seeded blood analog fluid that matched the kinematic viscosity of blood and the refractive index of plexiglas. At each location, 250 instantaneous velocity realizations were collected at eight instances during the pump cycle. The data were filtered and averaged to calculate mean (ensemble averaged) velocities. The results indicate that the largest mean velocities are created during systole in the VADs outlet tract, and during diastole in the major orifice of the mitral valve. A single vortex centered roughly about the axis of the cylindrical portion of the pump is created during early diastole. This vortex, which persists into early systole, provides good washing of the VAD walls. However, it does appear to impede the flow entering the VAD through the minor orifice of the mitral valve. High velocities also occur during diastole along the minor orifice wall of the outlet tract and are directed into the chamber. These retrograde velocities suggest the presence of a regurgitant jet near the wall of the prosthetic valve.