The fluid mechanics of a sac-type ventricular assist device

Flow visualisation and velocity measurement studies have been carried out on the liquid side of a sac-type VAD. The objectives have been to identify both good (e.g. short residence times) and bad (e.g. high turbulence levels) flow characteristics. The flow was visualised using polystyrene micro-spheres illuminated with white light on selected transverse planes across the pumping chamber and its inlet and outlet connections. These results then served as a guide for velocity measurements using laser-Doppler anemometry. Flow tests were run using water or a water/glycerol mixture. Operating conditions were determined from the appropriate fluid mechanics modelling laws to ensure dynamical similarity. Initially, steady flow behaviour was investigated including the effects of removal and insertion of the tilting-disc inlet and outlet valves. In subsequent full pumping tests, using a pneumatic driver, regions of high shear, separation, and high turbulence intensity have been identified.