Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Dallas, Dallas, Texas.
University of Texas Southwestern Medical Center, Dallas, Texas.
J Appl Physiol (1985). 2020 Nov 1;129(5):1220-1231. doi: 10.1152/japplphysiol.00250.2020. Epub 2020 Sep 17.
Astronauts have presented with a constellation of visual changes referred to as spaceflight-associated neuro-ocular syndrome (SANS). However, neither have early markers of microgravity-induced optic remodeling been fully identified nor have countermeasures been developed. To identify early markers of SANS, we studied 10 subjects with optical coherence tomography and ultrasonography when upright and supine and again after 24 h of 6° head-down tilt (HDT) bed rest. Upon acute transition from the upright to the supine position, choroid area (2.24 ± 0.53 to 2.28 ± 0.52 mm, = 0.001) and volume (9.51 ± 2.08 to 9.73 ± 2.08 mm, = 0.002) increased. After 24 h of HDT bed rest, subfoveal choroidal thickness (372 ± 93 to 381 ± 95 µm, = 0.02), choroid area (2.25 ± 0.52 to 2.33 ± 0.54 mm, = 0.08), and volume (9.64 ± 2.03 to 9.82 ± 2.08 mm, = 0.08) increased relative to the supine position. Subsequently, seven subjects spent 3 days in -6°HDT bed rest to assess whether low-level lower body negative pressure (LBNP) could prevent the observed choroidal engorgement during bed rest. Maintaining the -6° HDT position for 3 days caused choroid area (Δ0.11 mm, = 0.05) and volume (Δ0.45 mm, = 0.003) to increase. When participants also spent 8 h daily under -20 mmHg LBNP, choroid volume still increased, but substantially (40%) less than in the control trial (Δ0.27 mm, = 0.05). Moreover, the increase in choroid area was diminished (Δ0.03 mm, = 0.13), indicating that low-level LBNP attenuates the choroid expansion associated with 3 days of -6° HDT bed rest. These data suggest that low-level LBNP may be an effective countermeasure for SANS. Choroid measurements appear to be sensitive to changes in gravitational gradients, as well as periods of head-down tilt (HDT) bed rest, suggesting that they are potential indicators of early ocular remodeling and could serve to evaluate the efficacy of countermeasures for SANS. Eight hours of lower body negative pressure (LBNP) daily attenuates the choroid expansion associated with 3 days of strict -6° HDT bed rest, indicating that LBNP may be an effective countermeasure for SANS.
宇航员表现出一系列被称为航天相关神经眼综合征（SANS）的视觉变化。然而，尚未完全确定与微重力诱导的视神经重塑相关的早期标志物，也没有开发出相应的对策。为了确定 SANS 的早期标志物，我们使用光学相干断层扫描和超声检查研究了 10 名受试者，他们在直立和仰卧位时进行了检查，然后在 6°头低位卧床休息 24 小时后再次进行了检查。在从直立位置突然变为仰卧位置时，脉络膜区域（2.24±0.53 至 2.28±0.52mm， = 0.001）和体积（9.51±2.08 至 9.73±2.08mm， = 0.002）增加。经过 24 小时的头低位卧床休息后，下穹窿脉络膜厚度（372±93 至 381±95µm， = 0.02）、脉络膜区域（2.25±0.52 至 2.33±0.54mm， = 0.08）和体积（9.64±2.03 至 9.82±2.08mm， = 0.08）与仰卧位相比增加。随后，7 名受试者在 -6°头低位卧床休息 3 天，以评估低水平下肢负压（LBNP）是否可以防止卧床休息期间观察到的脉络膜充血。维持 -6°头低位卧床休息 3 天导致脉络膜区域（Δ0.11mm， = 0.05）和体积（Δ0.45mm， = 0.003）增加。当参与者每天还在 -20mmHg 的 LBNP 下接受 8 小时治疗时，脉络膜体积仍然增加，但幅度明显（40%）小于对照试验（Δ0.27mm， = 0.05）。此外，脉络膜区域的增加幅度减小（Δ0.03mm， = 0.13），表明低水平 LBNP 减轻了与 3 天 -6°头低位卧床休息相关的脉络膜扩张。这些数据表明，低水平 LBNP 可能是 SANS 的有效对策。脉络膜测量结果似乎对重力梯度的变化以及头低位卧床休息（HDT）期很敏感，表明它们是早期眼重塑的潜在指标，并可用于评估 SANS 对策的效果。每天 8 小时的下肢负压（LBNP）可减轻与严格 -6°头低位卧床休息 3 天相关的脉络膜扩张，表明 LBNP 可能是 SANS 的有效对策。
