[Hydrodynamic in vitro comparison of a new artificial heart valve with the Björk-Shiley valve (standard)]

Measurements performed to compare a newly developed tilting disc valve with the Björk-Shiley valve included velocity profiles downstream of the heart valves, valve-induced flow turbulence and pressure drop across the opened valves. The velocity profiles measured with pulsed Doppler ultrasound are similar, although they do not permit a quantitative comparison of the valves. The interpretation of the 90 degrees-component of Doppler signals as a measure of the turbulence permits a quantitative comparison without the need for extensive measurements. However, only large vortices are recorded, so that our turbulent shear stresses are lower than these reported in the literature. The pressure drop across the opened valve is a measure of the energy loss, and important parameters for the valve can be derived from it. The pressure drop is dependent on the test conditions, and is therefore not a characteristic constant of the valve. The transformation of the power law Q = C delta P beta into a relation between Re- and Eu-number gives a nondimensional similarity number that is characteristic for tilting disc valves. Its verification requires more investigations, involving variation of valve size and the viscosity of the test fluid.