California Medical Innovations Institute, San Diego, Calif.
Vascular Surgery, Department of Surgery, University of Michigan, Ann Arbor, Mich.
J Vasc Surg Venous Lymphat Disord. 2018 Jul;6(4):517-522.e1. doi: 10.1016/j.jvsv.2018.02.005.
It has been shown that venous valves have pairing arrangements with specific relative orientation and spacing that contribute to helical flows. The studies to date have not quantified the hemodynamic impact of helical flow formation. A computational model allows various valve orientations and spacings to be studied to better understand the hemodynamic effect of valve pairing.
Simulations were performed for paired valves at physiologically relevant spacing and orientations to study the flow features and hemodynamics associated with valve pairing configurations. The wall shear stress (WSS), residence time, and pressure drop were evaluated for the various valve pairing cases.
It was found that the WSS on the lumen flow side (front) of the leaflet is several times higher than on the valve pocket side (back). With orthogonal paired valves, the WSS at the critical back side is increased. Helical flow was clearly observed only with orthogonal valve pairing. The residence time was reduced to less than half (0.47 vs 1.16 seconds) in the orthogonal valve case compared with the parallel valve cases. The farther spaced valves (6 cm) had the highest residence time.
This simulation study shows that helical flow in the veins of lower extremities is strongly dependent on the relative orientation and spacing of the valves. For optimal orientation (∼90 degrees) and spacing (∼4 cm), strong helical flow is seen, which enhances WSS and reduces the flow resistance and residence time. These findings demonstrate a structure-function relation that optimizes flow patterns in normal physiology, which can be compromised in venous valve disease. The results of this study provide valuable insights that improve the current understanding of blood flow patterns around venous valves and the design of future multiple paired prosthetic valves.
已有研究表明静脉瓣具有特定相对取向和间距的配对排列，这有助于形成螺旋流。迄今为止，尚未对螺旋流形成的血液动力学影响进行量化。计算模型允许研究各种瓣膜取向和间距，以更好地了解瓣膜配对的血液动力学效应。
为生理相关间距和取向的配对瓣膜进行模拟，以研究与瓣膜配对构型相关的流场特征和血液动力学。评估了各种瓣膜配对情况下的壁面切应力（WSS）、停留时间和压降。
发现瓣叶腔流侧（前）的 WSS 比瓣窦侧（后）高几倍。正交配对瓣膜时，关键后瓣窦侧的 WSS 增加。仅在正交瓣膜配对时才明显观察到螺旋流。与平行瓣膜情况相比，正交瓣膜情况下的停留时间减少到一半以下（0.47 秒比 1.16 秒）。间隔较远的瓣膜（6 厘米）的停留时间最长。
这项模拟研究表明，下肢静脉中的螺旋流强烈依赖于瓣膜的相对取向和间距。对于最佳取向（约 90 度）和间距（约 4 厘米），可以看到强烈的螺旋流，从而增加 WSS 并降低流动阻力和停留时间。这些发现表明了一种结构-功能关系，优化了正常生理中的血流模式，而静脉瓣膜疾病会损害这种关系。本研究的结果提供了有价值的见解，有助于提高对静脉瓣膜周围血流模式的现有理解，并为未来的多个配对人工瓣膜设计提供参考。
