Quantitation of the turbulent stress distribution downstream of normal, diseased and artificial aortic valves in humans

Damage to blood corpuscles seems to be related to the magnitude andexposure time of the turbulent shear stresses (TSS). According to in vitrostudies the critical TSS level for lethal erythrocyte and thrombocytedamage is 150-400 N/m2, for exposure times within physiological ranges. Tostudy the distribution of TSS in the human ascending aorta, a hot-filmanemometer needle probe was used to register blood velocities at 41 evenlydistributed measuring points in the cross-sectional area 5-6 cm downstreamof the aortic annulus. Measurements were made in the ascending aorta afternormal aortic valves (prior to coronary bypass surgery), after stenoticaortic valves, and after implantation of either St. Jude Medical or StarrEdwards Silastic Ball valves. Three-dimensional visualization of velocityprofiles were performed and Reynolds normal stresses (RNS) were calculatedwithin 50-ms overlapping time windows in systole. By coordinating the meanRNS for each time window and for all 41 measuring points, 2-dimensionalcolor-coded mapping of the RNS distribution was made. Based on the velocityprofiles and the RNS distribution a relative blood damage index (RBDI) wascalculated to incorporate the magnitude and exposure time for RNS in theentire cross-sectional area into one parameter. Turbulent shear stresseswere estimated by using a previously determined correlation equationbetween RNS and TSS. After normal aortic valves, RNS was below 4N/m2.