School of Kinesiology, Western University, London, ON, Canada.
Department of Kinesiology, McMaster University, Hamilton, ON, Canada.
Appl Physiol Nutr Metab. 2024 Sep 1;49(9):1210-1216. doi: 10.1139/apnm-2023-0447. Epub 2024 May 22.
The aim of this study was to determine the effect of posture changes on vascular compliance in intracranial (brain) versus extracranial vascular beds (forearm). Eighteen young adults (nine females) performed a supine-to-seated-to-standing protocol involving 5 min of rest in each position. Continuous blood pressure, middle cerebral artery (MCA) blood velocity, and brachial artery blood velocity were recorded at each posture. Three to five consecutive steady-state cardiac cycles at each posture were analyzed by a four-element lumped parameter modified Windkessel model to calculate vascular compliance. Mean arterial pressure (MAP) increased from supine to seated (76(9) vs. 81(12) mmHg; = 0.006) and from supine to standing (76(9) vs. 82(13) mmHg; = 0.034). Mean blood flow was greater in the MCA relative to the forearm (forearm: 40(5) mL·min, MCA: 224(17) mL·min; main effect < 0.001). Conversely, vascular resistance (forearm: 3.25(0.50) mmHg·mL·min, brain: 0.36(0.04) mmHg·mL·min; main effect < 0.001) and compliance (forearm: 0.010(0.001) mL·min·mmHg, brain: 0.005(0.001) mL·min·mmHg; main effect = 0.001) were greater in the forearm compared to the brain. Significant main effects of posture were observed with decreasing values in upright positions for mean blood flow ( = 0.001) in both vascular beds, but not for resistance ( = 0.163) or compliance ( = 0.385). There were no significant interaction effects between vascular bed and posture for mean flow ( = 0.057), resistance ( = 0.258), or compliance ( = 0.329). This study provides evidence that under steady-state conditions, posture does not affect cerebrovascular compliance.
本研究旨在确定体位变化对颅内（脑）与颅外血管床（前臂）血管顺应性的影响。18 名年轻成年人（9 名女性）进行了仰卧位-坐位-站立位的方案，每个体位各有 5 分钟的休息时间。在每个体位下记录连续血压、大脑中动脉（MCA）血流速度和肱动脉血流速度。通过四元素集总参数修正的 Windkessel 模型分析每个体位的 3 到 5 个连续稳定的心动周期，以计算血管顺应性。平均动脉压（MAP）从仰卧位到坐位（76(9) vs. 81(12)mmHg; = 0.006）和仰卧位到站立位（76(9) vs. 82(13)mmHg; = 0.034）均增加。MCA 的平均血流大于前臂（前臂：40(5)mL·min，MCA：224(17)mL·min；主效应 < 0.001）。相反，血管阻力（前臂：3.25(0.50)mmHg·mL·min，大脑：0.36(0.04)mmHg·mL·min；主效应 < 0.001）和顺应性（前臂：0.010(0.001)mL·min·mmHg，大脑：0.005(0.001)mL·min·mmHg；主效应 = 0.001）在前臂比大脑中更大。在两种血管床中，直立位时平均血流（ = 0.001）的体位主效应显著降低，但阻力（ = 0.163）或顺应性（ = 0.385）没有显著降低。在平均血流（ = 0.057）、阻力（ = 0.258）或顺应性（ = 0.329）方面，血管床与体位之间没有显著的交互效应。本研究提供的证据表明，在稳态条件下，体位不会影响脑血管顺应性。
