INFLUENCE OF VISCOSITY AND PRESSURE ON PROSTHETIC VALVE REGURGITATION

Blood viscosity varies during the course of artificial heart implants and is affected by pathological conditions. To gauge the potential eff ect of changing viscosity on valve performance, leakage rates were mea sured across a closed Medtronic-Hall valve with water, water/glycerol and fresh whole bovine blood for aortic and pulmonary pressure ranges. As might be expected from the low Reynolds numbers (< 140), losses ac ross the valve were found to be primarily viscous. For the two Newtoni an fluids, leakage was slightly less than linearly proportional to pre ssure. This is comparable with empirical data for orifice flow, which predicts three fifths power dependence on pressure. For blood, however , the greater than linear dependence on pressure found suggests that t he pseudoplasticity (shear-thinning behavior) of blood is important. T hese data provide evidence that the viscous and non-Newtonian properti es of blood must be taken into account in modelling prosthetic valve p erformance and may affect the test methods and flow regulation strateg ies for prosthetic blood pumps.