Department of Biomedical Engineering, Toyo University, Saitama, Japan.
Neurovascular Research Laboratory, Faculty of Life Sciences and Education, University of South Wales, Pontypridd, UK.
Physiol Rep. 2022 May;10(10):e15248. doi: 10.14814/phy2.15248.
Head-up tilt (HUT)-induced gravitational stress causes collapse of the internal jugular vein (IJV) by decreasing central blood volume and through mass-effect from the surrounding tissues. Besides HUT, lower body negative pressure (LBNP) is used to stimulate orthostatic stress as an experimental model. Compared to HUT, LBNP has less of a gravitational effect because of the supine position; therefore, we hypothesized that LBNP causes less of a decrease in the cross-sectional area of the IJV compared to HUT. We tested the hypothesis by measuring the cross-sectional area of the IJV using B-mode ultrasonography while inducing orthostatic stress at levels of -40 mmHg LBNP and 60° HUT. The cross-sectional area of IJV decreased from the resting baseline during both LBNP and HUT trials, but the LBNP-induced decrease in the cross-sectional area of IJV was smaller than that of HUT (right, -45% ± 49% vs. -78% ± 27%, p = 0.008; left, -49% ± 27% vs. -78% ± 20%, p = 0.004). Since changes in venous outflow may affect cerebral arterial circulation, the findings of the present study suggest that orthostatic stress induced by different techniques modulates cerebral blood flow regulation through its effect on venous outflow.
头高位倾斜（HUT）引起的重力应激通过减少中心血容量并通过周围组织的质量效应导致颈内静脉（IJV）塌陷。除 HUT 外，下体负压（LBNP）用于刺激直立应激作为实验模型。与 HUT 相比，由于仰卧位，LBNP 的重力效应较小；因此，我们假设与 HUT 相比，LBNP 引起 IJV 横截面积的减少较小。我们通过使用 B 型超声测量 IJV 的横截面积来测试该假设，同时在 -40mmHg LBNP 和 60°HUT 水平下诱导直立应激。在 LBNP 和 HUT 试验期间，IJV 的横截面积均从静息基线下降，但 LBNP 引起的 IJV 横截面积下降小于 HUT（右侧，-45%±49%比-78%±27%，p=0.008；左侧，-49%±27%比-78%±20%，p=0.004）。由于静脉流出量的变化可能会影响脑动脉循环，因此本研究的结果表明，不同技术引起的直立应激通过对静脉流出量的影响来调节脑血流调节。
