A mechanical heart valve, an essential prosthetic for managing valvular heart disease, consists of a metal frame housing two or three leaflets (depending on the design) that control blood flow within the heart. However, leaflet dysfunction can impede their movement, leading to valve defects. This study extensively investigates the hemodynamics of such a bileaflet mechanical heart valve with dysfunctions of various extents with the help of direct numerical simulations (DNS) under both steady inflow and pulsatile flow conditions. The results are presented and discussed in terms of spatial variations of velocity magnitude, Reynolds stresses, and surface and time-averaged clinically important parameters such as wall shear stress (WSS), pressure drop, and blood damage. Under steady inflow conditions, the flow field becomes unsteady and turbulent even at a modest Reynolds number of 750 when the valve has 50% defective conditions, in contrast to a steady and laminar flow for a fully functional heart valve with 0% defect condition. The values of WSS also increase by around 50%, and net pressure drops by more than 200% with these defective conditions, which further increase as the defective condition increases. On the other hand, the same trend is also seen under pulsatile flow conditions, with maximum values of wall shear stress and blood damage seen during the peak systolic stage of the cardiac cycle, increasing by more than 200% as the defect condition increases from 0% to 50% for the latter parameter. Furthermore, the present study also investigates the effect of blood rheological behaviors such as shear-thinning and yield stress on hemodynamics past this dysfunctional heart valve. It is seen that blood rheological behavior has a substantial influence on hemodynamics at low Reynolds numbers, diminishing as the Reynolds number increases. Under pulsatile flow conditions, blood exhibiting non-Newtonian characteristics such as shear-thinning shows higher values of wall shear stress and blood damage values compared to Newtonian ones. Therefore, the present study highlights the importance of accounting for blood rheology in clinical assessments. However, this study simulates the cases where both valve leaflets are fixed in position, thereby excluding fluid–structure interaction (FSI) from the present simulations. Such conditions are representative of common occurrences in dysfunctional heart valves. All in all, the in-depth analysis and information obtained from this study are expected to facilitate early detection of valve leaflet dysfunction, thereby contributing to improved clinical management of patients with valvular heart disease.

中文翻译：

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功能失调的双叶机械心脏瓣膜后的血流动力学


机械心脏瓣膜是治疗心脏瓣膜病的重要假体，由一个金属框架组成，金属框架上装有两个或三个小叶（取决于设计），用于控制心脏内的血流。然而，瓣叶功能障碍会阻碍他们的运动，导致瓣膜缺损。本研究在稳定流入和脉动流条件下，借助直接数值模拟 （DNS） 广泛研究了这种具有不同程度功能障碍的双叶机械心脏瓣膜的血流动力学。根据速度大小、雷诺应力以及表面和时间平均临床重要参数（如壁剪切应力 （WSS）、压降和血液损伤）的空间变化来呈现和讨论结果。在稳定流入条件下，当瓣膜有 50% 的缺陷情况时，即使在 750 的适度雷诺数场也会变得不稳定和湍流，而对于缺陷为 0% 的全功能心脏瓣膜，则流场会变得不稳定和湍流。WSS 的值也增加了约 50%，在这些有缺陷的情况下，净压力下降了 200% 以上，随着有缺陷情况的增加，净压力会进一步增加。另一方面，在脉动流动条件下也会出现相同的趋势，在心动周期的收缩高峰期可以看到壁剪切应力和血液损伤的最大值，随着后一个参数的缺陷条件从 0% 增加到 50%，增加了 200% 以上。此外，本研究还调查了血液流变学行为（如剪切变稀化和产量应力）对通过这个功能失调的心脏瓣膜的血流动力学的影响。 可以看出，血液流变行为对低雷诺数的血流动力学有很大影响，随着雷诺数的增加而减弱。在脉动流动条件下，与牛顿血相比，表现出非牛顿特性（如剪切稀化）的血液显示出更高的壁剪切应力值和血液损伤值。因此，本研究强调了在临床评估中考虑血液流变学的重要性。然而，本研究模拟了两个瓣叶都固定在原位的情况，从而从目前的仿真中排除了流固耦合 （FSI）。这种情况是功能失调心脏瓣膜的常见情况。总而言之，从本研究中获得的深入分析和信息有望促进瓣叶功能障碍的早期发现，从而有助于改善心脏瓣膜病患者的临床管理。