Astronauts undergoing long-duration spaceflight are exposed to numerous health risks, including Spaceflight-Associated Neuro-Ocular Syndrome (SANS), a spectrum of ophthalmic changes that can result in permanent loss of visual acuity. The etiology of SANS is not well understood but is thought to involve changes in cerebrovascular flow dynamics in response to microgravity. There is a paucity of knowledge in this area; in particular, cerebrospinal fluid (CSF) flow dynamics have not been well characterized under microgravity conditions. Our study was designed to determine the effect of simulated microgravity (head-down tilt [HDT]) on cerebrovascular flow dynamics. We hypothesized that microgravity conditions simulated by acute HDT would result in increases in CSF pulsatile flow. In a prospective cohort study, we measured flow in major cerebral arteries, veins, and CSF spaces in fifteen healthy volunteers using phase contrast magnetic resonance (PCMR) before and during 15° HDT. We found a decrease in all CSF flow variables [systolic peak flow (p = 0.009), and peak-to-peak pulse amplitude (p = 0.001)]. Cerebral arterial average flow (p = 0.04), systolic peak flow (p = 0.04), and peak-to-peak pulse amplitude (p = 0.02) all also significantly decreased. We additionally found a decrease in average cerebral arterial flow (p = 0.040). Finally, a significant increase in cerebral venous cross-sectional area under HDT (p = 0.005) was also observed. These results collectively demonstrate that acute application of −15° HDT caused a reduction in CSF flow variables (systolic peak flow and peak-to-peak pulse amplitude) which, when coupled with a decrease in average cerebral arterial flow, systolic peak flow, and peak-to-peak pulse amplitude, is consistent with a decrease in cardiac-related pulsatile CSF flow. These results suggest that decreases in cerebral arterial inflow were the principal drivers of decreases in CSF pulsatile flow.

中文翻译：

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在模拟微重力条件下通过磁共振成像量化动脉、静脉和脑脊液流动动力学：一项前瞻性队列研究

进行长时间太空飞行的宇航员面临着许多健康风险，包括太空飞行相关的神经眼部综合症 (SANS)，这是一种可导致永久性视力丧失的眼科变化。SANS 的病因尚不清楚，但被认为与微重力引起的脑血管血流动力学变化有关。这方面的知识匮乏；特别是，脑脊液 (CSF) 流动动力学在微重力条件下尚未得到很好的表征。我们的研究旨在确定模拟微重力（低头倾斜 [HDT]）对脑血管血流动力学的影响。我们假设急性 HDT 模拟的微重力条件会导致 CSF 脉动流增加。在一项前瞻性队列研究中，我们在 15° HDT 之前和期间使用相差磁共振 (PCMR) 测量了 15 名健康志愿者的主要脑动脉、静脉和 CSF 空间的流量。我们发现所有 CSF 流量变量 [收缩期峰值流量 (p = 0.009) 和峰峰值脉冲幅度 (p = 0.001)] 都有所减少。脑动脉平均流量 (p = 0.04)、收缩期峰值流量 (p = 0.04) 和峰峰值脉冲幅度 (p = 0.02) 也都显着降低。我们还发现平均脑动脉流量减少（p = 0.040）。最后，还观察到 HDT 下脑静脉横截面积显着增加 (p = 0.005)。这些结果共同表明，-15° HDT 的急性应用导致 CSF 流量变量（收缩峰流量和峰峰值脉冲幅度）的减少，其中，当与平均脑动脉流量、收缩期峰值流量和峰峰值脉冲幅度的减少相结合时，与心脏相关的脉动脑脊液流量的减少是一致的。这些结果表明脑动脉流入的减少是脑脊液脉动流减少的主要驱动因素。