FORMATION AND TRAVEL OF VORTICES IN MODEL VENTRICLES - APPLICATION TOTHE DESIGN OF SKELETAL-MUSCLE VENTRICLES

Vortex-ring production was studied in axisymmetric elastomeric ventric les designed to simulate flow in a cardiovascular assist device. A flo w visualization technique was used to investigate the effects of reduc ing the inlet diameter and predilating the ventricle on vortex travel in two ventricles of different shape and size. In most cases, vortex r ings formed during the filling phase. They were bounded by the incomin g jet of fluid and the ventricular wall. The velocity of their centres during the filling period was proportional to the inflow velocity. Du ring filling, vortex velocity was substantially independent of the sha pe and diameter of the two ventricles studied. It was dependent mainly on orifice diameter: a narrower inlet led to greater inflow velocitie s and proportionately greater vortex velocities. At the end of the fil ling phase, each vortex increased in size to occupy the full radial ex tent of the ventricle. This process was associated with a decrease in the axial velocity and strength of the vortex. At low flow rates, thes e losses resulted in the arrest of the vortex at end filling. Vortex m otion in ventricles is particularly important in the design of a cardi ovascular device such as the skeletal muscle ventricle (SMV), where sm all ejection fractions may leave blood at the apex of the ventricle re latively undisturbed. It is suggested that inlet diameter could be sel ected to favour the formation and travel of vortices, with a resultant reduction in apical residence time and hence a reduced risk of thromb us formation.