Padilla Jaume, Sheldon Ryan D, Sitar Diana M, Newcomer Sean C
Department of Biomedical Sciences, University of Missouri, Columbia, Missouri, USA.
Am J Physiol Heart Circ Physiol. 2009 Sep;297(3):H1103-8. doi: 10.1152/ajpheart.00167.2009. Epub 2009 Jul 24.
Unlike quadrupeds, humans exhibit a larger hydrostatic pressure in the lower limbs compared with the upper limbs during a major part of the day. It is plausible that repeated episodes of elevated pressure in the legs may negatively impact the endothelium, hence contributing to the greater predisposition of atherosclerosis in the legs. We tested the hypothesis that an acute exposure to increased hydrostatic pressure would induce conduit artery endothelial dysfunction. In protocol 1, to mimic the hemodynamic environment of the leg, we subjected the brachial artery to a hydrostatic pressure gradient ( approximately 15 mmHg) by vertically hanging the arm for 3 h. Brachial artery flow-mediated dilation (FMD) was assessed in both arms before and following the intervention. In protocol 2, we directly evaluated popliteal artery FMD before and after a 3-h upright sitting (pressure gradient approximately 48 mmHg) and control (supine position) intervention. Our arm-hanging model effectively resembled the hemodynamic milieu (high pressure and low shear rate) present in the lower limbs during the seated position. Endothelium-dependent vasodilation at the brachial artery was attenuated following arm hanging (P < 0.05); however, contrary to our hypothesis, upright sitting did not have an impact on popliteal artery endothelial function (P > 0.05). These data suggest an intriguing vascular-specific response to increased hydrostatic pressure and reduced shear rate. Further efforts are needed to determine if this apparent protection of the leg vasculature against an acute hydrostatic challenge is attributable to posture-induced chronic adaptations.
与四足动物不同，在一天的大部分时间里，人类下肢的流体静压高于上肢。腿部反复出现的压力升高可能会对内皮产生负面影响，从而导致腿部动脉粥样硬化的易感性增加，这似乎是合理的。我们测试了这样一个假设：急性暴露于增加的流体静压会导致传导动脉内皮功能障碍。在方案1中，为了模拟腿部的血流动力学环境，我们通过垂直悬挂手臂3小时，使肱动脉承受流体静压梯度（约15 mmHg）。在干预前后，对双臂的肱动脉血流介导的舒张功能（FMD）进行评估。在方案2中，我们直接评估了3小时直立坐姿（压力梯度约48 mmHg）和对照（仰卧位）干预前后的腘动脉FMD。我们的手臂悬挂模型有效地模拟了坐姿时下半身存在的血流动力学环境（高压和低剪切率）。手臂悬挂后，肱动脉的内皮依赖性血管舒张功能减弱（P < 0.05）；然而，与我们的假设相反，直立坐姿对腘动脉内皮功能没有影响（P > 0.05）。这些数据表明，血管对增加的流体静压和降低的剪切率存在一种有趣的特异性反应。需要进一步努力来确定腿部血管系统对急性流体静压挑战的这种明显保护是否归因于姿势引起的慢性适应。
