In-vitro hydrodynamic evaluation of aortic valve protheses
Lim Cheng Chye, Lawrence
Picologlou, Basil F.
Master of Science
A mock circulatory loop was designed for the hydrodynamic evaluation of aortic valve prostheses. It had features of low priming volume (1 to 1.2 liters) and its fluid was protected from direct contact with air. The prostheses were mounted in the anatomic subcoronary position of a plexiglas model of the human aorta. Four commercial valve prostheses were tested in the loop in one case with the sinuses of Valsalva intact and in another case in the absence of the sinus cavities. They were the Lillehei-Kaster pivoting disc, Bjork-Shiley tilting disc Smeloff-Cutter caged ball and the Starr-Edwards caged ball valves. Tests were conducted at heart rates of 6 and 9 beats/minute and the aortic flow rates of 4 and 6 liters/minute. A valve performance index was formulated, based on the energy dissipation that occurs in flow through a valve. This dissipation coefficient, as it was called, was shown to be a fair, consistent means of rating valve performance. The results showed that the pivoting/tilting disc valves were superior in performance to the caged ball valves in terms of the mean pressure gradients across the valve, percentage backflows and energy dissipations recorded. The valves also functioned more efficiently in the straight tube section than in the section with sinuses. Plausible explanations were offered, based on the flow dynamics of the valves and their relation to the immediate geometry. The results of this work were compared with those of other investigators. Although no direct comparisons were possible because of differences in flow conditions, valve sizes and flow chamber dimensions, approximate comparisons showed fair consistency.