Purpose

A number of studies has well described central cardiovascular changes caused by changing gravity levels as they occur e.g. during parabolic flight. limited data exists describing the effect of microgravity on the cerebrovascular system and brain perfusion.

Methods

In this study middle cerebral artery velocity (MCAv) of 16 participants was continuously monitored on a second-by-second basis during 15 consecutive parabolas (1G, 1,8G, 0G, 1,8G) using doppler ultrasound. Simultaneously central cardiovascular parameters (heart rate, mean arterial blood pressure, cardiac output) were assessed.

Results

Results revealed an immediate reaction of central cardiovascular parameters to changed gravity levels. In contrast, changes in MCAv only initially were in accordance with a normal cerebral autoregulation. Whereas all of the measured central cardiovascular parameters seemed to have reached a steady state after approximately 8 s of microgravity, MCAv, after an initial decrease with the onset of microgravity, increased again during the second half of the microgravity phase.

Conclusion

It is concluded that this increase in MCAv during the second half of the microgravity period reflects a decrease of cerebrovascular resistance caused by a pressure driven increased venous outflow and/or a contraction of precapillary sphincters in order to avoid hyperperfusion of the brain.

中文翻译：

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在微重力作用下短暂的脑血流反应。

目的

许多研究已经很好地描述了由于重力水平发生变化（例如在抛物线飞行过程中）而引起的中央心血管变化。有限的数据描述了微重力对脑血管系统和脑灌注的影响。

方法

在这项研究中，使用多普勒超声在15个连续抛物线（1G，1,8G，0G，1,8G）中以每秒为单位连续监测16名参与者的大脑中动脉速度（MCAv）。同时评估中心心血管参数（心率，平均动脉血压，心输出量）。

结果

结果显示，中心心血管参数对重力水平的改变会立即产生反应。相反，MCAv的变化仅在最初是与正常的大脑自身调节一致的。尽管在大约8 s的微重力作用下，所有测得的中心心血管参数似乎都达到了稳定状态，但随着微重力作用的开始下降，MCAv在微重力作用阶段的后半段又增加了。

结论

结论是，微重力作用后半段MCAv的增加反映了由压力驱动的静脉流出增加和/或毛细血管前括约肌收缩引起的脑血管阻力降低，从而避免了大脑的过度灌注。