Strangman Gary E, Zhang Quan, Marshall-Goebel Karina, Mulder Edwin, Stevens Brian, Clark Jonathan B, Bershad Eric M
Neural Systems Group, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts;
Center for Space Medicine, Baylor College of Medicine, Houston, Texas.
J Appl Physiol (1985). 2017 Jul 1;123(1):62-70. doi: 10.1152/japplphysiol.00947.2016. Epub 2017 Mar 30.
Astronauts aboard the International Space Station (ISS) have exhibited hyperopic shifts, posterior eye globe flattening, dilated optic nerve sheaths, and even optic disk swelling from spaceflight. Elevated intracranial pressure (ICP) consequent to cephalad fluid shifts is commonly hypothesized as contributing to these ocular changes. Head-down tilt (HDT) is frequently utilized as an Earth-based analog to study similar fluid shifts. Sealed environments like the ISS also exhibit elevated CO, a potent arteriolar vasodilator that could further affect cerebral blood volume (CBV) and cerebral blood flow, intracranial compliance, and ICP. A collaborative pilot study between the National Space Biomedical Research Institute and the German Aerospace Center tested the hypotheses that ) HDT and elevated CO physiologically interact and ) cerebrovascular pulsatility is related to HDT and/or elevated CO In a double-blind crossover study ( = 6), we measured CBV pulsatility via near-infrared spectroscopy, alongside noninvasive ICP and intraocular pressure (IOP) during 28-h -12° HDT at both nominal (0.04%) and elevated (0.5%) ambient CO In our cohort, CBV pulsatility increased significantly over time at cardiac frequencies (0.031 ± 0.009 μM/h increase in total hemoglobin concentration pulsatility amplitude) and Mayer wave frequencies (0.019 ± 0.005 μM/h increase). The HDT-CO interaction on pulsatility was not robust but rather driven by one individual. Significant differences between atmospheres were not detected in ICP or IOP. Further work is needed to determine whether individual differences in pulsatility responses to CO relate to visual changes in space. Cerebral blood volume (CBV) pulsatility-as measured by near-infrared spectroscopy-increases over time during -12° head-down tilt at both cardiac and Mayer wave frequencies. CBV pulsatility appeared to increase more under elevated (0.5%) CO at Mayer wave frequencies in some individuals. If similar dynamic pulsatility increases occur in astronauts, there is the potential to initiate vascular and possibly other remodeling processes that lead to symptoms associated with sustained increases in intracranial pressure.
国际空间站（ISS）上的宇航员出现了远视偏移、眼球后部扁平化、视神经鞘扩张，甚至因太空飞行导致视盘肿胀。因头向脑脊液移位导致的颅内压（ICP）升高通常被认为是这些眼部变化的原因。头低位倾斜（HDT）经常被用作地面模拟实验来研究类似的脑脊液移位。像国际空间站这样的密封环境也会出现二氧化碳升高，二氧化碳是一种强效的小动脉血管扩张剂，可能会进一步影响脑血容量（CBV）、脑血流量、颅内顺应性和颅内压。美国国家太空生物医学研究所和德国航空航天中心合作开展的一项试点研究，检验了以下假设：1）HDT和二氧化碳升高存在生理相互作用；2）脑血管搏动性与HDT和/或二氧化碳升高有关。在一项双盲交叉研究（n = 6）中，我们通过近红外光谱测量CBV搏动性，并在28小时的-12°HDT期间，分别在正常（0.04%）和升高（0.5%）的环境二氧化碳水平下测量无创颅内压和眼压（IOP）。在我们的队列中，CBV搏动性在心脏频率（总血红蛋白浓度搏动幅度每小时增加0.031±0.009μM）和迈尔波频率（每小时增加0.019±0.005μM）下随时间显著增加。HDT与二氧化碳对搏动性的相互作用并不显著，而是由一个个体驱动的。在颅内压或眼压方面未检测到不同环境之间的显著差异。需要进一步开展研究，以确定搏动性对二氧化碳反应的个体差异是否与太空中的视觉变化有关。通过近红外光谱测量的脑血容量（CBV）搏动性在-12°头低位倾斜期间，在心脏和迈尔波频率下均随时间增加。在某些个体中，在迈尔波频率下，升高（0.5%）的二氧化碳水平似乎使CBV搏动性增加得更多。如果宇航员也出现类似的动态搏动性增加，就有可能引发血管以及可能的其他重塑过程，从而导致与颅内压持续升高相关的症状。
