RANE Center, Jackson, Miss.
RANE Center, Jackson, Miss.
J Vasc Surg Venous Lymphat Disord. 2021 Jul;9(4):1041-1050.e1. doi: 10.1016/j.jvsv.2020.11.024. Epub 2020 Dec 9.
Veins are thin-walled tubes. Their lumen is roughly circular with an aspect ratio close to 1:1 under physiologic pressures. When they collapse owing to decreased internal pressure or external compression, the aspect ratio changes. The vertical diameter is usually diminished more than the transverse, with a considerable decrease in the lumen area. The recent emergence of stent correction of many venous compression syndromes, particularly iliac vein stenosis, has brought attention to the importance of the aspect ratio, quite apart from an overall decrease in caliber. The iliac vein pressure is influenced not only by stenosis, but also intra-abdominal pressure, right atrial pressure, and collaterals. We investigated the impact of aspect ratio in an experimental model incorporating these factors.
Inflow was provided from a header tank at 25 mm Hg pressure into a Penrose tubing enclosed in a polyethylene cylinder pressurized (Starling pressure) to simulate intra-abdominal pressures of 5 and 10 mm Hg. The Penrose drained into an outflow tank with a pressure of 7 mm Hg, simulating right atrial pressure. Stenosis was simulated with a series of three-dimensional, printed plastic nozzles with caliber areas of 50, 100, and 200 mm and varying in aspect ratios of 1:1 to 1:4. The flow and pressure in this system was monitored with the use of overflow collaterals in some experiments.
Free flow from the header tank through the Penrose (zero Starling pressure) with a 200 mm circle nozzle into the outflow tank with zero pressure resulted in flow pressure of approximately 1.5 mm Hg. Using nozzles of a smaller caliber or an increased aspect ratio resulted in an increase of flow pressures of up to approximately 3.7 mm Hg. Flow into an outflow tank of 7 mm Hg simulating right atrial pressure further increased flow pressures by approximately 7 mm Hg. The addition of Starling pressures of 5 and 10 mm Hg simulating abdominal pressure increased flow pressure even further to the 10 to 17 mm Hg range. When the Starling pressure was dominant, the additional contribution of nozzle caliber stenosis or aspect ratio reduction to the overall flow pressure ranged from 2 to 6 mm Hg. Collateral overflow varied inversely with collateral resistance. Some experiments yielded an anomalous flow/pressure phenomena known to occur in collapsible tube flows.
A decrease in the caliber or the aspect ratio of iliac vein stenosis was among several other factors that generate peripheral venous hypertension in an experimental model. Increased intra-abdominal pressure is a major influence that amplifies the pressure effects of aspect ratio or caliber reduction.
静脉是薄壁管。在生理压力下，其管腔大致呈圆形，纵横比接近 1:1。当由于内部压力降低或外部压迫而塌陷时，纵横比会发生变化。垂直直径通常比横向直径减小得更多，管腔面积会有明显减少。由于许多静脉压迫综合征（特别是髂静脉狭窄）采用支架矫正，人们越来越关注纵横比的重要性，而不仅仅是口径的整体减小。髂静脉压力不仅受狭窄影响，还受腹内压、右心房压和侧支循环的影响。我们在一个实验模型中研究了这些因素对纵横比的影响。
通过 25mmHg 的压力从一个储液器向被聚乙烯管包裹的彭罗斯管（Penrose tubing）内注水，该聚乙烯管被加压（Starling 压力）以模拟 5mmHg 和 10mmHg 的腹内压。彭罗斯管中的液体排入一个压力为 7mmHg 的流出槽，模拟右心房压。用一系列具有 50、100 和 200mm2 口径面积且纵横比为 1:1 至 1:4 的三维打印塑料喷嘴模拟狭窄。在一些实验中，使用溢流侧支来监测系统中的流量和压力。
从储液器通过彭罗斯管（零 Starling 压力）以 200mm 圆形喷嘴自由流动到零压力的流出槽时，流量压力约为 1.5mmHg。使用较小口径或较大纵横比的喷嘴会导致流量压力增加到约 3.7mmHg。在模拟右心房压的 7mmHg 流出槽中进一步增加流量压力会增加约 7mmHg。增加模拟腹内压的 5mmHg 和 10mmHg Starling 压力会将流量压力进一步增加到 10mmHg 至 17mmHg 范围。当 Starling 压力占主导地位时，喷嘴口径狭窄或纵横比降低对总流量压力的额外贡献范围为 2mmHg 至 6mmHg。侧支溢流与侧支阻力成反比。一些实验产生了一种异常的流量/压力现象，这种现象已知会发生在可折叠管流中。
在实验模型中，髂静脉狭窄的口径减小或纵横比减小是引起外周静脉高压的几个因素之一。增加腹内压是放大纵横比或口径减小对压力影响的主要因素。
