Imaging Program, Lawson Health Research Institute, London, Ontario, Canada.
Department of Medical Biophysics, Western University, London, Ontario, Canada.
J Appl Physiol (1985). 2023 Oct 1;135(4):717-725. doi: 10.1152/japplphysiol.00743.2022. Epub 2023 Aug 10.
The aim of the current study was to establish the interplay between blood flow patterns within a large cerebral artery and a downstream microvascular segment under conditions of transiently reduced mean arterial pressure (MAP). We report data from nine young, healthy participants (5 women; 26 ± 4 yr) acquired during a 15-s bout of sudden-onset lower body negative pressure (LBNP; -80 mmHg). Simultaneous changes in microvascular cerebral blood flow (CBF) and middle cerebral artery blood velocity (MCAv) were captured using diffuse correlation spectroscopy (DCS) and transcranial Doppler ultrasound (TCD), respectively. Brachial blood pressure (finger photoplethysmography) and TCD waveforms were extracted at baseline and during the nadir blood pressure (BP) response to LBNP and analyzed using a modified Windkessel model to calculate indices of cerebrovascular resistance (Ri) and compliance (Ci). Compared with baseline, rapid-onset LBNP decreased MAP by 22 ± 16% and Ri by 14 ± 10% (both ≤ 0.03). Ci increased (322 ± 298%; < 0.01) but MCAv (-8 ± 16%; = 0.09) and CBF (-2 ± 3%; = 0.29) were preserved. The results provide evidence that changes in both vascular resistance and compliance preserve CBF, as indexed by no significant changes in MCAv or DCS microvascular flow, during transient hypotension. To characterize the relationship between cerebrovascular patterns within the large middle cerebral artery (MCA) and a downstream microvascular segment, we used a novel combination of transcranial Doppler ultrasound of the MCA and optical monitoring of a downstream microvascular segment, respectively, under conditions of transiently reduced mean arterial pressure (i.e., lower body negative pressure, -80 mmHg). A rapid increase in vessel compliance accompanied the maintenance of MCA blood velocity and downstream microvascular flow.
本研究旨在确定在平均动脉压（MAP）短暂降低的情况下，大脑中动脉内的血流模式与下游微血管段之间的相互作用。我们报告了 9 名年轻健康参与者（5 名女性；26 ± 4 岁）在 15 秒突发下肢负压（-80mmHg）期间的数据。分别使用漫射相关光谱（DCS）和经颅多普勒超声（TCD）同时捕获微血管脑血流（CBF）和大脑中动脉血流速度（MCAv）的变化。使用改良的 Windkessel 模型从基线和 LBNP 下血压（BP）响应的最低点提取肱动脉血压（手指光体积描记法）和 TCD 波形，并分析其以计算脑血管阻力（Ri）和顺应性（Ci）指数。与基线相比，快速发作的 LBNP 使 MAP 降低了 22 ± 16%，Ri 降低了 14 ± 10%（均 ≤ 0.03）。Ci 增加（322 ± 298%； < 0.01），但 MCAv（-8 ± 16%； = 0.09）和 CBF（-2 ± 3%； = 0.29）保持不变。结果提供了证据，表明在短暂性低血压期间，血管阻力和顺应性的变化均保持 CBF，这可通过 MCAv 或 DCS 微血管流量无明显变化来确定。为了描述大脑中动脉（MCA）内的脑血管模式与下游微血管段之间的关系，我们分别使用 MCA 的经颅多普勒超声和下游微血管段的光学监测的新组合，在平均动脉压（即下肢负压，-80mmHg）短暂降低的情况下。血管顺应性的快速增加伴随着 MCA 血流速度和下游微血管流量的维持。
