Ellis J T, Healy T M, Fontaine A A, Weston M W, Jarret C A, Saxena R, Yoganathan A P
Cardiovascular Fluid Mechanics Laboratory, School of Mechanical Engineering, Georgia Institute of Technology, Atlanta 30332-0100, USA.
J Heart Valve Dis. 1996 Nov;5(6):600-6.
Fluid stresses occurring in retrograde flow fields during valve closure may play a significant role in thrombogenesis. The squeeze flow and regurgitant jets can cause damage to formed blood elements due to high levels of turbulent shear stress. The aim of this study was to characterize in detail the spatial structure and temporal behavior of the retrograde flow fields of the St. Jude Medical and Medtronic Parallel bileaflet mechanical heart valves.
Three-component, coincident laser Doppler anemometry (LDA) velocity measurements were obtained facilitating the determination of the full Reynolds stress tensor and the principal stresses in the valve flow fields. The experiments were performed in the Georgia Tech aortic flow chamber under physiologic pulsatile flow conditions. Data were collected over several hundred cardiac cycles for subsequent phase window averaging and generation of mean velocity and turbulence statistics over 20 ms intervals. A region approximately 8 mm x 10 mm was mapped 1.0 mm upstream of one hinge of each valve with an incremental resolution of 0.13-0.25 mm. Animation of the data allowed the visualization of the flow fields and a quantitative display of mean velocity and turbulent stress values.
In the St. Jude Medical squeeze flow, the peak turbulent shear stress was 800 dynes/cm2 and the peak reverse velocity was 0.60 m/s. In the Medtronic Parallel squeeze flow, the peak turbulent shear stress was 1,000 dynes/cm2 and the peak velocity 0.70 m/s. The leakage jet fields of the two valves were very different: in the case of the St. Jude Medical valve, turbulent shear stresses reached 1,800 dynes/cm2 and peak jet velocity was 0.80 m/s; in the case of the Medtronic Parallel valve, turbulent shear stresses reached 3,690 dynes/cm2 and the peak jet velocity was 1.9 m/s.
The retrograde flow fields of these two bileaflet mechanical heart valves appear to be design-dependent. The elevated turbulent shear stresses generated by both valve designs may indicate a propensity for blood element damage during the reverse flow phase of the cardiac cycle, but the extent of flow disturbance was twice as high with the Medtronic Parallel than with the St. Jude Medical valve. This research should yield a better understanding of the significance of retrograde flow to the functionality and potential thrombogenicity of bileaflet mechanical heart valves and aid in the development of new designs.
瓣膜关闭期间逆行流场中出现的流体应力可能在血栓形成过程中起重要作用。挤压流和反流射流由于高水平的湍流剪切应力，可能会对已形成的血液成分造成损害。本研究的目的是详细表征圣犹达医疗公司（St. Jude Medical）和美敦力并行双叶机械心脏瓣膜逆行流场的空间结构和时间行为。
通过同步进行三分量激光多普勒测速仪（LDA）速度测量，有助于确定瓣膜流场中的全雷诺应力张量和主应力。实验在佐治亚理工学院主动脉流动腔中，在生理脉动流条件下进行。在数百个心动周期内收集数据，随后进行相位窗口平均，并生成20毫秒间隔内的平均速度和湍流统计数据。在每个瓣膜一个铰链上游1.0毫米处，绘制一个约8毫米×10毫米的区域，增量分辨率为0.13 - 0.25毫米。数据动画展示使流场可视化，并定量显示平均速度和湍流应力值。
在圣犹达医疗公司瓣膜的挤压流中，峰值湍流剪切应力为800达因/平方厘米，峰值反向速度为0.60米/秒。在美敦力并行瓣膜的挤压流中，峰值湍流剪切应力为1000达因/平方厘米，峰值速度为0.70米/秒。两种瓣膜的泄漏射流场差异很大：在圣犹达医疗公司瓣膜的情况下，湍流剪切应力达到1800达因/平方厘米，峰值射流速度为0.80米/秒；在美敦力并行瓣膜的情况下，湍流剪切应力达到3690达因/平方厘米，峰值射流速度为1.9米/秒。
这两种双叶机械心脏瓣膜的逆行流场似乎取决于设计。两种瓣膜设计产生的升高的湍流剪切应力可能表明在心动周期的反流阶段有血液成分受损的倾向，但美敦力并行瓣膜的流动紊乱程度是圣犹达医疗公司瓣膜的两倍。这项研究将有助于更好地理解逆行流对双叶机械心脏瓣膜功能和潜在血栓形成性的重要性，并有助于新设计的开发。
