Purpose

It is believed that non-physiological leakage flow through hinge gaps during diastole contributes to thrombus formation in Bileaflet Mechanical Heart Valves (BMHVs). Because of the small scale and difficulty of experimental access, fluid dynamics inside the hinge cavity has not yet been characterised in detail. The objective is to investigate small-scale structure inside the hinge experimentally, and gain insight into its role in stimulating cellular responses.

Methods

An optically accessible scaled-up model of a BMHV hinge was designed and built, preserving dynamic similarity to a clinical BMHV. Particle Image Velocimetry (PIV) was used to visualize and quantify the flow fields inside the hinge at physiological Reynolds number and dimensionless pressure drop. The flow was measured at in-plane and out-of-plane spatial resolution of 32 and 86 μm, respectively, and temporal resolution of \(297\,\mu\hbox{s}.\)

Results

Likely flow separation on the ventricular surface of the cavity has been observed for the first time, and is a source of unsteadiness and perhaps turbulence. The shear stress found in all planes exceeds the threshold of platelet activation, ranging up to 168 Pa.

Conclusions

The scale-up approach provided new insight into the nature of the hinge flow and enhanced understanding of its complexity. This study revealed flow features that may induce blood element damage.

中文翻译：

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大型双叶机械心脏瓣膜铰链模型铰链内泄漏流的高分辨率测量。

目的

据信，在舒张期通过铰链间隙的非生理性泄漏流有助于双叶机械心脏瓣膜 (BMHV) 中的血栓形成。由于实验规模小和困难，铰链腔内的流体动力学尚未得到详细表征。目的是通过实验研究铰链内部的小型结构，并深入了解其在刺激细胞反应中的作用。

方法

设计并构建了 BMHV 铰链的光学可访问放大模型，保留了与临床 BMHV 的动态相似性。粒子图像测速仪 (PIV) 用于在生理雷诺数和无量纲压降下可视化和量化铰链内的流场。分别以 32 和 86 μ m的面内和面外空间分辨率 以及\(297\,\mu\hbox{s}.\)的时间分辨率测量流量。

结果

腔的心室表面可能存在流动分离，这是第一次观察到，并且是不稳定和可能是湍流的来源。在所有平面上发现的剪切应力都超过了血小板激活的阈值，范围高达 168 Pa。

结论

放大方法提供了对铰链流动性质的新见解，并增强了对其复杂性的理解。该研究揭示了可能引起血液元素损伤的流动特征。