THE EFFECT OF VARYING DEGREES OF STENOSIS ON THE CHARACTERISTICS OF TURBULENT PULSATILE FLOW-THROUGH HEART-VALVES

Many problems and complications associated with heart valves are relat ed to the dynamic behavior of the valve and the resultant unsteady flo w patterns. An accurate depiction of the spatial and temporal velocity and rms distributions imparts better understanding of flow related va lve complications, and may be used as a guideline in valve design. Whi le the generalized correlation between increased turbulence level and the severity of the stenosis is well established, few studies addresse d the issue of the intermittent nature of turbulence and its timing in the cardiac cycle, and almost none assessed the effect of a progressi ve stenosis on the flow characteristics through heart valves. In this experimental work we simulated the type of flow which is present in no rmal and stenosed valves and conducted a comprehensive investigation o f valve hemodynamics, valvular turbulence and morphology under varying degrees of stenosis. The characteristics of valves and stenoses were simulated closely, to achieve the flow conditions that initiate turbul ent flow conditions. Laser Doppler anemometry (LDA) measurements were carried out in a pulse duplicator system distal to trileaflet polyuret hane prosthetic heart valves, installed at mitral and aortic positions . The effect of the degree of the stenosis was comparatively studied t hrough the structure of the turbulent jets emerging from normal and st enotic heart valves. Maximum turbulence level was achieved during the decelerating phase and correlated to the severity of the stenosis, fol lowed by relaminarization of the flow during the acceleration phase. T he intermittent nature of the turbulence emphasized the importance of realizing the timing of the turbulence production and its spatial loca tion for optimizing current valve designs. The plug flow through the n ormal aortic valve prosthesis was replaced by jet like behavior for a 65% stenosis, with the jet becoming narrower and stronger for a 90% st enosis. The morphology of the velocity and turbulence waveforms was fo und to be governed by the stenosis geometry and the valve position (ao rtic, mitral).