Post-ischemia reperfusion kinetics are markedly dissociated when comparing the macro- versus microvasculature. We used Doppler ultrasound and near-infrared diffuse correlation spectroscopy (NIR-DCS), an emerging technique for continuously and non-invasively quantifying relative changes in skeletal muscle microvascular perfusion (i.e., Blood Flow Index; or BFI), to measure macro- and microvascular reactive hyperemia (RH) in the non-dominant arm of 16 healthy young adults. First, we manipulated the duration of limb ischemia (3 vs 6 min) with the limb at heart level (neutral, -N). Then, we reduced/increased forearm perfusion pressure (PP) by positioning the arm above (3min-A, 60°) or below (3min-B, 30°) the heart. The major novel findings were two-fold: Changes in the ischemic stimulus similarly affected peak macrovascular (i.e., conduit, mL·min^-1) and microvascular (i.e., peak NIR-DCS derived BFI) reperfusion during reactive hyperemia (6min-N>3min-N, p<0.05, both) but did not affect the rate at which microvascular reperfusion occurs (i.e. BFI slope). Second, changing forearm PP predictably affected both peak macro- and microvascular reperfusion during RH (3min-B>N>A, p<0.05, all), as well as the rate at which microvascular reperfusion occurred (BFI Slope; 3min-B>N>A, p<0.05). Together, the data suggest that kinetic differences between macro- and microvascular reperfusion are largely determined by differences in fluid mechanical energy (i.e., pressure, gravitational, and kinetic energies) between the two compartments that work in tandem to restore pressure across the arterial tree following a period of tissue ischemia.

中文翻译：

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反应性充血的大血管和微血管测量之间的动力学差异。

比较宏观与微血管系统时，缺血后再灌注动力学显着分离。我们使用多普勒超声和近红外漫反射相关光谱 (NIR-DCS)，这是一种新兴技术，用于连续和非侵入性地量化骨骼肌微血管灌注（即血流指数；或 BFI）的相对变化，以测量宏观和16 名健康年轻人的非优势臂的微血管反应性充血 (RH)。首先，我们在肢体处于心脏水平（中性，-N）时操纵肢体缺血的持续时间（3 对 6 分钟）。然后，我们通过将手臂置于心脏上方（3min-A，60°）或下方（3min-B，30°）来降低/增加前臂灌注压 (PP)。主要的新发现有两个方面：缺血刺激的变化同样影响大血管峰值（即导管，mL·min^-1 ) 和微血管（即峰值 NIR-DCS 衍生的 BFI）再灌注（6min-N>3min-N，p<0.05，两者）但不影响微血管再灌注发生的速率（即 BFI 斜率） . 其次，改变前臂 PP 可预测地影响 RH 期间的峰值大血管和微血管再灌注（3min-B>N>A，p<0.05，全部），以及发生微血管再灌注的速率（BFI 斜率；3min-B> N>A，p<0.05)。总之，数据表明大血管和微血管再灌注之间的动力学差异很大程度上取决于两个隔室之间的流体机械能（即压力、重力和动能）的差异，这两个隔室协同工作以恢复动脉树的压力一段时间的组织缺血。