IDENTIFICATION OF PEAK STRESSES IN CARDIAC PROSTHESES - A COMPARISON OF 2-DIMENSIONAL VERSUS 3-DIMENSIONAL PRINCIPAL STRESS-ANALYSES

This study assessed the accuracy of using a two-dimensional principal stress analysis compared to a three-dimensional analysis in estimating peak turbulent stresses in complex three-dimensional flows associated with cardiac prostheses. Three-component, coincident laser Doppler an emometer measurements were obtained in steady flow downstream of three prosthetic valves: a St. Jude bileaflet, Bjork-Shiley monostrut tilti ng disc, and Starr-Edwards ball and cage. Two-dimensional and three-di mensional principal stress analyses were performed to identify local p eak stresses. Valves with locally two-dimensional flows exhibited a 10 -15% underestimation of the largest measured normal stresses compared to the three-dimensional principal stresses. In nearly all flows, meas ured shear stresses underestimated peak principal shear stresses by 10 -100%. Differences between the two-dimensional and three-dimensional p rincipal stress analysis were less than 10% in locally two-dimensional flows. In three-dimensional flows, the two-dimensional principal stre sses typically underestimated three-dimensional values by nearly 20%. However, the agreement of the two-dimensional principal stress with th e three-dimensional principal stresses was dependent upon the two velo city-components used in the two-dimensional analysis, and was observed to vary across the valve flow field because of flow structure variati on. The use of a two-dimensional principal stress analysis with two-co mponent velocity data obtained from measurements misaligned with the p lane of maximum mean flow shear can underpredict maximum shear stresse s by as much as 100%.