Jun Brian H, Saikrishnan Neelakantan, Yoganathan Ajit P
G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA.
Ann Biomed Eng. 2014 Mar;42(3):526-40. doi: 10.1007/s10439-013-0919-y. Epub 2013 Oct 2.
A number of clinical, in vitro and computational studies have shown the potential for thromboembolic complications in bileaflet mechanical heart valves (BMHV), primarily due to the complex and unsteady flows in the valve hinges. These studies have focused on quantitative and qualitative parameters such as velocity magnitude, turbulent shear stresses, vortex formation, and platelet activation to identify potential for blood damage. However, experimental characterization of the whole flow fields within the valve hinges has not yet been conducted. This information can be utilized to investigate instantaneous damage to blood elements and also to validate numerical studies focusing on the hinge's complex fluid dynamics. The objective of this study was therefore to develop a high-resolution imaging system to characterize the flow fields and global velocity maps in a BMHV hinge. In this study, the steady leakage hinge flow fields representing the diastolic phase during the cardiac cycle in a 23 mm St. Jude Medical regent BMHV in the aortic position were characterized using a two-dimensional micro particle image velocimetry system. Diastolic flow was simulated by imposing a static pressure head on the aortic side. Under these conditions, a reverse flow jet from the aortic to the ventricular side was observed with velocities in the range of 1.47-3.24 m/s, whereas low flow regions were observed on the ventricular side of the hinge with viscous shear stress magnitude up to 60 N/m². High velocities and viscous shearing may be associated with platelet activation and hemolysis, while low flow zones can cause thrombosis due to increased residence time in the hinge. Overall, this study provides a high spatial resolution experimental technique to map the fluid velocity in the BMHV hinge, which can be extended to investigate micron-scale flow domains in various prosthetic devices under different hemodynamic conditions.
多项临床、体外和计算研究表明，双叶机械心脏瓣膜（BMHV）存在血栓栓塞并发症的可能性，主要原因是瓣膜铰链处的血流复杂且不稳定。这些研究集中在诸如速度大小、湍流剪切应力、涡旋形成和血小板活化等定量和定性参数上，以确定血液损伤的可能性。然而，尚未对瓣膜铰链内的整个流场进行实验表征。这些信息可用于研究血液成分的瞬时损伤，也可用于验证专注于铰链复杂流体动力学的数值研究。因此，本研究的目的是开发一种高分辨率成像系统，以表征BMHV铰链内的流场和整体速度图。在本研究中，使用二维微粒图像测速系统对位于主动脉位置的23毫米圣犹达医疗Regent BMHV在心动周期舒张期的稳定泄漏铰链流场进行了表征。通过在主动脉侧施加静压头来模拟舒张期血流。在这些条件下，观察到从主动脉侧到心室侧的反向流动射流，速度范围为1.47 - 3.24米/秒，而在铰链心室侧观察到低血流区域，粘性剪切应力大小高达60牛/平方米。高速度和粘性剪切可能与血小板活化和溶血有关，而低血流区域由于在铰链内的停留时间增加可能导致血栓形成。总体而言，本研究提供了一种高空间分辨率的实验技术，用于绘制BMHV铰链内的流体速度，该技术可扩展到研究不同血流动力学条件下各种假体装置中的微米级流动区域。
