| Summary: | 博士 === 淡江大學 === 水資源及環境工程學系博士班 === 99 === Previous researchers indicated that the phenomenon of hemolysis and thrombosis would occur in the flow fields across the monoleaflet or bileaflet mechanical heart valves. The probable reasons of causing hemolysis and thrombosis included shear stresses in the flow fields might be large enough to damage red blood cells, and the closing velocity of the leaflet was excessively large to cause cavitation phenomenon. Cavitation bubbles exploded and produced high pressures which would damage red blood cells and platelets. However, the closure mechanism of the trileaflet valve was based on the vortices in the aortic sinus which benefited leaflets to close, and it was apparently different to that of monoleaflet or bileaflet mechanical heart valves which mainly depended on the reverse flow. Therefore, the closing velocity of the trileaflet valve was much slower and the probability of cavitation was also smaller.
A pulsatile mock circulatory loop system that dynamically simulated physiologic circulation was used in this study. A St. Jude Medical 27 mm bileaflet valve and a 27mm new type trileaflet valve were used as test valves positioned in the aortic position. Flow field measurements were made with a digital particle image velocimeter. By applying LES and SGS, turbulent viscous shear stresses were quantified and evaluated whether red blood cells would be damaged or not. Furthermore, because manufacturing a new trileaflet valve would cost a lot of time and money, commercial software Fluent was also applied to run numerical simulations of these two valves in this study. The results of numerical simulations would be valid with the experiments and were expected to be useful for the development of the trileaflet valve in the future.
The results of the experiments showed that although the maximum value of turbulent viscous shear stress was not large enough to cause damage to red blood cells, it still might inflict damage to platelets. Besides, the closing velocity of the trileaflet valve was obviously slower than the St. Jude Medical bileaflet valve, and this would effectively reduce occurrences of cavitation. The results of the numerical simulations showed that the flow fields were similar to that of the experiments even if it should be improved further. The results also indicated that numerical simulations could be applied to reduce the cost for development a new trileaflet valve in the future.
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