Division of Hygiene, Department of Social Medicine, Nihon University School of Medicine, Tokyo, Japan.
Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas.
J Appl Physiol (1985). 2022 Apr 1;132(4):938-946. doi: 10.1152/japplphysiol.00283.2021. Epub 2022 Feb 24.
Steady-state cerebral blood flow (CBF) and dynamic cerebral autoregulation are reportedly maintained during -10° head-down tilt (HDT) despite slight increases in intracranial pressure (ICP). However, the higher ICP during -30° HDT may alter steady-state CBF and dynamic cerebral autoregulation. The present study hypothesized that steady-state CBF and dynamic cerebral autoregulation would be altered by higher ICP during -30° HDT than during 0° and -10° HDT. Seventeen healthy participants were positioned horizontal (0°) and in -10° HDT and -30° HDT for 10 min in random order on separate days. The arterial blood pressure waveform was obtained using a finger blood pressure device and the cerebral blood velocity waveform in the middle cerebral artery was obtained using transcranial Doppler sonography (TCD) for the last 6 min in each position. ICP was estimated using noninvasive ICP (nICP) based on TCD. Dynamic cerebral autoregulation was evaluated by spectral and transfer function analysis. Although nICP was significantly higher during -30° HDT (12.4 mmHg) than during -10° HDT (8.9 mmHg), no significant differences in steady-state mean cerebral blood velocity or transfer function gain in any frequency ranges were seen among all angles of HDT. Counter to our hypothesis, the present results suggest that steady-state CBF and dynamic cerebral autoregulation may be preserved during short-term -30° HDT despite the higher ICP compared with that during -10° HDT. This appears to be the first study to evaluate steady-state cerebral blood flow (CBF), dynamic cerebral autoregulation, and intracranial pressure (ICP) during -30° head-down tilt (HDT) compared with those during -10° HDT using noninvasive measurements. The results suggest that steady-state CBF and dynamic cerebral autoregulation are preserved despite the higher ICP during short-term -30° HDT compared with -10° HDT.
在 -10°头低位倾斜（HDT）期间，据报道，尽管颅内压（ICP）略有升高，但脑血流（CBF）的稳态和动态脑自动调节仍得以维持。然而，在 -30°HDT 时更高的 ICP 可能会改变稳态 CBF 和动态脑自动调节。本研究假设，与 0°和 -10°HDT 相比，在 -30°HDT 时更高的 ICP 会改变稳态 CBF 和动态脑自动调节。17 名健康参与者在不同日子分别以随机顺序在水平（0°）和 -10°HDT 和 -30°HDT 下各保持 10 分钟。在每个位置的最后 6 分钟内，使用手指血压装置获得动脉血压波形，并使用经颅多普勒超声（TCD）获得大脑中动脉的脑血流速度波形。使用基于 TCD 的无创 ICP（nICP）估计 ICP。通过频谱和传递函数分析评估动态脑自动调节。尽管 -30°HDT 时 nICP（12.4mmHg）明显高于 -10°HDT（8.9mmHg），但在所有 HDT 角度下，稳态平均脑血流速度或任何频率范围内的传递函数增益均无显著差异。与我们的假设相反，本研究结果表明，尽管与 -10°HDT 相比，短期 -30°HDT 时 ICP 较高，但稳态 CBF 和动态脑自动调节可能得以维持。这似乎是第一项使用无创测量评估与 -10°HDT 相比，在 -30°HDT 时稳态脑血流（CBF）、动态脑自动调节和颅内压（ICP）的研究。结果表明，与 -10°HDT 相比，在短期 -30°HDT 时，尽管 ICP 较高，但稳态 CBF 和动态脑自动调节仍得以维持。
