Downie Steven P, Raynor Sheila M, Firmin David N, Wood Nigel B, Thom Simon A, Hughes Alun D, Parker Kim H, Wolfe John H N, Xu X Yun
Department of Chemical Engineering, Imperial College London, South Kensington, London, UK.
Am J Physiol Heart Circ Physiol. 2008 May;294(5):H2112-20. doi: 10.1152/ajpheart.01302.2007. Epub 2008 Mar 7.
The purpose of this study was to estimate wall shear stress (WSS) in individual vessels of the venous circulation of the calf and quantify the effects of elastic compression based on change of vessel geometry and velocity waveform. The great saphenous vein and either a peroneal or posterior tibial vein have been imaged in four healthy subjects using magnetic resonance imaging, with and without the presence of a grade 1 medical stocking. Flow through image-based reconstructed geometries was numerically simulated for both a range of steady flow rates and ultrasound-derived transient velocity waveforms, scaled to give a standardized time averaged flow rate. For steady flow, the stocking produced an average percentage increase in mean WSS of approximately 100% in the great saphenous vein across a range of 0.125-1.25 ml/s. The percentage increase in the peroneal/posterior tibial veins varied from 490 to 650% across a range of 0.5-5 ml/s. In addition, application of the stocking eliminated periods of very low or zero flow from the transient waveforms. The average minimum value of WSS in all vessels without the stocking was <0.1 Pa. With the stocking, this was increased to 0.7 Pa in the great saphenous and 0.9 Pa in the peroneal/posterior tibial veins. The pathophysiological effects of these changes are discussed. In conclusion, the flight stocking was effective in raising venous WSS levels in prone subjects, and this effect was much more pronounced in the deep vessels. The stocking also tended to prevent cessation of flow during periods of increased downstream pressure produced by respiration.
本研究的目的是估计小腿静脉循环中各血管的壁面剪应力（WSS），并根据血管几何形状和速度波形的变化量化弹性压迫的效果。在四名健康受试者中，使用磁共振成像对大隐静脉以及腓静脉或胫后静脉进行了成像，分别在有和没有一级医用弹力袜的情况下。针对一系列稳定流速和超声导出的瞬态速度波形，对基于图像重建的几何形状中的血流进行了数值模拟，并进行了缩放以给出标准化的时间平均流速。对于稳定流，在0.125 - 1.25 ml/s的流速范围内，弹力袜使大隐静脉的平均WSS平均百分比增加约100%。在0.5 - 5 ml/s的流速范围内，腓静脉/胫后静脉的百分比增加从490%到650%不等。此外，使用弹力袜消除了瞬态波形中极低或零流量的时段。在没有弹力袜的情况下，所有血管中WSS的平均最小值<0.1 Pa。使用弹力袜后，大隐静脉中该值增加到0.7 Pa，腓静脉/胫后静脉中增加到0.9 Pa。讨论了这些变化的病理生理效应。总之，弹力袜在提高俯卧位受试者的静脉WSS水平方面是有效的，并且这种效果在深部血管中更为明显。弹力袜还倾向于防止在呼吸引起的下游压力增加期间血流停止。
