Herbertson L H, Deutsch S, Manning K B
Bioengineering Department, The Pennsylvania State University, University Park, PA 16802, USA.
J Biomech Eng. 2011 Sep;133(9):094507. doi: 10.1115/1.4005167.
Blood damage and thrombosis are major complications that are commonly seen in patients with implanted mechanical heart valves. For this in vitro study, we isolated the closing phase of a bileaflet mechanical heart valve to study near valve fluid velocities and stresses. By manipulating the valve housing, we gained optical access to a previously inaccessible region of the flow. Laser Doppler velocimetry and particle image velocimetry were used to characterize the flow regime and help to identify the key design characteristics responsible for high shear and rotational flow. Impact of the closing mechanical leaflet with its rigid housing produced the highest fluid stresses observed during the cardiac cycle. Mean velocities as high as 2.4 m/s were observed at the initial valve impact. The velocities measured at the leaflet tip resulted in sustained shear rates in the range of 1500-3500 s(-1), with peak values on the order of 11,000-23,000 s(-1). Using velocity maps, we identified regurgitation zones near the valve tip and through the central orifice of the valve. Entrained flow from the transvalvular jets and flow shed off the leaflet tip during closure combined to generate a dominant vortex posterior to both leaflets after each valve closing cycle. The strength of the peripheral vortex peaked within 2 ms of the initial impact of the leaflet with the housing and rapidly dissipated thereafter, whereas the vortex near the central orifice continued to grow during the rebound phase of the valve. Rebound of the leaflets played a secondary role in sustaining closure-induced vortices.
血液损伤和血栓形成是植入机械心脏瓣膜患者常见的主要并发症。在这项体外研究中，我们分离出双叶机械心脏瓣膜的关闭阶段，以研究瓣膜附近的流体速度和应力。通过操纵瓣膜外壳，我们获得了对先前无法进入的流动区域的光学观察通道。使用激光多普勒测速仪和粒子图像测速仪来表征流动状态，并有助于确定导致高剪切力和旋转流动的关键设计特征。关闭的机械瓣叶与其刚性外壳的碰撞产生了心动周期中观察到的最高流体应力。在瓣膜最初碰撞时观察到平均速度高达2.4 m/s。在瓣叶尖端测量的速度导致持续剪切率在1500 - 3500 s(-1)范围内，峰值约为11000 - 23000 s(-1)。通过速度图，我们确定了瓣膜尖端附近以及通过瓣膜中心孔的反流区域。在每个瓣膜关闭周期后，来自跨瓣射流的夹带流和瓣叶尖端在关闭过程中脱落的流相结合，在两个瓣叶后方产生一个主导涡旋。周边涡旋的强度在瓣叶与外壳最初碰撞的2毫秒内达到峰值，此后迅速消散，而中心孔附近的涡旋在瓣膜的回弹阶段继续增长。瓣叶的回弹在维持关闭诱导的涡旋中起次要作用。
