Sex differences in the regulation of autonomic and cerebrovascular responses to orthostatic stress remain unclear. The objectives of this study were to concurrently investigate autonomic control and cerebrovascular resistance indices, including critical closing pressure (CrCP) and resistance area product (RAP), during upright tilt in men and women. In 13 women and 14 men (18-29 years), ECG, non-invasive blood pressure, middle cerebral artery blood velocity, and end-tidal CO2 (ETCO2) were continuously measured during supine rest and 70° tilt. Heart rate variability (HRV), cardiovagal baroreflex sensitivity (cBRS), and transfer function parameters of dynamic cerebral autoregulation were calculated. Compared to supine, upright tilt increased the low frequency-to-high frequency ratio of HRV in men only (P = 0.044), and decreased cBRS more in women (P = 0.001). Cerebrovascular resistance index (CVRi) increased during tilt only in men (sex-by-time interaction: P = 0.004). RAP was lower in women throughout tilt (main effect of sex: P = 0.022). CrCP decreased during tilt in both sexes (main effect of time: P < 0.001). Normalizing to ETCO2 did not alter the effect of tilt on cerebrovascular resistance. Men displayed a greater increase of sympathetic indices and CVRi during tilt while women had greater parasympathetic withdrawal. We hypothesize that increased sympathetic activity in men may drive sex differences in the cerebrovascular response to upright posture.

中文翻译：

---

直立倾斜的自主神经和脑血管反应的性别差异

自主神经和脑血管对直立性应激反应的调节的性别差异仍不清楚。本研究的目的是同时调查男性和女性在直立倾斜期间的自主神经控制和脑血管阻力指数，包括临界闭合压 (CrCP) 和阻力面积乘积 (RAP)。在 13 名女性和 14 名男性（18-29 岁）中，在仰卧休息和 70°倾斜期间连续测量心电图、无创血压、大脑中动脉血流速度和呼气末 CO2 (ETCO2)。计算心率变异性 (HRV)、心迷走神经压力反射敏感性 (cBRS) 和动态大脑自动调节的传递函数参数。与仰卧相比，直立倾斜仅增加男性 HRV 的低频与高频比（P = 0.044），女性 cBRS 降低更多（P = 0.001）。仅男性在倾斜期间脑血管阻力指数 (CVRi) 增加（性别与时间的相互作用：P = 0.004）。在整个倾斜过程中，女性的 RAP 较低（性别的主要影响：P = 0.022）。两性在倾斜期间 CrCP 均下降（时间的主要影响：P < 0.001）。对 ETCO2 的正常化并没有改变倾斜对脑血管阻力的影响。男性在倾斜期间表现出更多的交感神经指数和 CVRi 增加，而女性则有更多的副交感神经退缩。我们假设男性交感神经活动增加可能会导致脑血管对直立姿势的反应存在性别差异。两性在倾斜期间 CrCP 均下降（时间的主要影响：P < 0.001）。对 ETCO2 的正常化并没有改变倾斜对脑血管阻力的影响。男性在倾斜期间表现出更多的交感神经指数和 CVRi 增加，而女性则有更多的副交感神经退缩。我们假设男性交感神经活动增加可能会导致脑血管对直立姿势的反应存在性别差异。两性在倾斜期间 CrCP 均下降（时间的主要影响：P < 0.001）。对 ETCO2 的正常化并没有改变倾斜对脑血管阻力的影响。男性在倾斜期间表现出更多的交感神经指数和 CVRi 增加，而女性则有更多的副交感神经退缩。我们假设男性交感神经活动增加可能会导致脑血管对直立姿势的反应存在性别差异。