Manning Keefe B, Herbertson Luke H, Fontaine Arnold A, Deutsch Steven
Department of Bioengineering, The Pennsylvania State University, 205 Hallowell Building, University Park, PA 16802, USA.
J Biomech Eng. 2008 Aug;130(4):041001. doi: 10.1115/1.2927356.
Hemolysis and thrombosis are among the most detrimental effects associated with mechanical heart valves. The strength and structure of the flows generated by the closure of mechanical heart valves can be correlated with the extent of blood damage. In this in vitro study, a tilting disk mechanical heart valve has been modified to measure the flow created within the valve housing during the closing phase. This is the first study to focus on the region just upstream of the mitral valve occluder during this part of the cardiac cycle, where cavitation is known to occur and blood damage is most severe. Closure of the tilting disk valve was studied in a "single shot" chamber driven by a pneumatic pump. Laser Doppler velocimetry was used to measure all three velocity components over a 30 ms period encompassing the initial valve impact and rebound. An acrylic window placed in the housing enabled us to make flow measurements as close as 200 microm away from the closed occluder. Velocity profiles reveal the development of an atrial vortex on the major orifice side of the valve shed off the tip of the leaflet. The vortex strength makes this region susceptible to cavitation. Mean and maximum axial velocities as high as 7 ms and 20 ms were recorded, respectively. At closure, peak wall shear rates of 80,000 s(-1) were calculated close to the valve tip. The region of the flow examined here has been identified as a likely location of hemolysis and thrombosis in tilting disk valves. The results of this first comprehensive study measuring the flow within the housing of a tilting disk valve may be helpful in minimizing the extent of blood damage through the combined efforts of experimental and computational fluid dynamics to improve mechanical heart valve designs.
溶血和血栓形成是与机械心脏瓣膜相关的最有害的影响之一。机械心脏瓣膜关闭所产生的血流强度和结构与血液损伤程度相关。在这项体外研究中，对一种倾斜盘式机械心脏瓣膜进行了改进，以测量瓣膜关闭阶段瓣膜腔内产生的血流。这是第一项聚焦于心动周期这一阶段二尖瓣封堵器上游区域的研究，已知该区域会发生空化且血液损伤最为严重。在由气动泵驱动的“单次”腔室内研究倾斜盘式瓣膜的关闭情况。使用激光多普勒测速仪测量在包括瓣膜初始撞击和反弹的3 ms时间段内的所有三个速度分量。放置在瓣膜腔内的丙烯酸窗口使我们能够在距离关闭的封堵器仅200微米处进行血流测量。速度剖面显示在瓣膜大孔侧叶尖脱落处形成了心房涡流。涡流强度使该区域易发生空化。分别记录到平均轴向速度和最大轴向速度高达7 m/s和20 m/s。在关闭时，靠近瓣膜尖端处计算出的峰值壁面剪切率为80,000 s⁻¹。此处研究的血流区域已被确定为倾斜盘式瓣膜中溶血和血栓形成的可能位置。这项首次全面测量倾斜盘式瓣膜腔内血流的研究结果，可能有助于通过实验和计算流体动力学的共同努力来最小化血液损伤程度，从而改进机械心脏瓣膜设计。
