Gerlach Darius A, Marshall-Goebel Karina, Hasan Khader M, Kramer Larry A, Alperin Noam, Rittweger Joern
Division of Space Physiology, Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany.
Neural Systems Group, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA USA.
NPJ Microgravity. 2017 Jun 21;3:18. doi: 10.1038/s41526-017-0023-y. eCollection 2017.
More than half of astronauts present with significant neuro-ophthalmic findings during 6-month missions onboard the International Space Station. Although the underlying cause of this Microgravity Ocular Syndrome is currently unknown, alterations in cerebrospinal fluid dynamics within the optic nerve sheath may play a role. In the presented study, diffusion tensor imaging was used to assess changes in diffusivity of the optic nerve and its surrounding sheath during head-down tilt, a ground-based model of microgravity. Nine healthy male subjects (mean age ± SD: 25 ± 2.4 years; mean body mass index ± SD: 24.1 ± 2.4 kg/m) underwent 5 head-down tilt conditions: -6°,-12°, -18°,-12° and 1% CO, and -12° and lower body negative pressure. Mean diffusivity, fractional anisotropy, axial diffusivity, radial diffusivity were quantified in the left and right optic nerves and surrounding sheaths at supine baseline and after 4.5 h head-down tilt for each condition. In the optic nerve sheath, mean diffusivity was increased with all head-down tilt conditions by (Best Linear Unbiased Predictors) 0.147 (SE: 0.04) × 10 mm/s ( < 0.001), axial diffusivity by 0.188 (SE: 0.064) × 10 mm/s ( < 0.001), and radial diffusivity by 0.126 (SE: 0.04) × 10 mm/s ( = 0.0019). Within the optic nerve itself, fractional anisotropy was increased by 0.133 (SE: 0.047) ( = 0.0051) and axial diffusivity increased by 0.135 (SE: 0.08) × 10 mm/s ( = 0.014) during head-down tilt, whilst mean diffusivity and radial diffusivity were unaffected ( > 0.3). These findings could be due to increased perioptic cerebral spinal fluid hydrodynamics during head-down tilt, as well as increased cerebral spinal fluid volume and movement within the optic nerve sheath.
超过半数的宇航员在国际空间站执行6个月任务期间出现显著的神经眼科检查结果。尽管这种微重力眼综合征的潜在病因目前尚不清楚，但视神经鞘内脑脊液动力学的改变可能起了作用。在本研究中，利用扩散张量成像来评估头低位倾斜（一种地面微重力模型）期间视神经及其周围鞘的扩散率变化。9名健康男性受试者（平均年龄±标准差：25±2.4岁；平均体重指数±标准差：24.1±2.4kg/m²）接受了5种头低位倾斜条件：-6°、-12°、-18°、-12°和1%二氧化碳，以及-12°和下体负压。在仰卧位基线以及每种条件下头低位倾斜4.5小时后，对左右视神经及其周围鞘的平均扩散率、分数各向异性、轴向扩散率、径向扩散率进行量化。在视神经鞘中，所有头低位倾斜条件下平均扩散率均增加（最佳线性无偏预测值）0.147（标准误：0.04）×10⁻³mm²/s（P<0.001），轴向扩散率增加0.188（标准误：0.064）×10⁻³mm²/s（P<0.001），径向扩散率增加0.126（标准误：0.04）×10⁻³mm²/s（P=0.0019）。在视神经本身，头低位倾斜期间分数各向异性增加0.133（标准误：0.047）（P=0.0051），轴向扩散率增加0.135（标准误：0.08）×10⁻³mm²/s（P=0.01），而平均扩散率和径向扩散率未受影响（P>0.3）。这些发现可能是由于头低位倾斜期间视神经周围脑脊液流体动力学增加，以及视神经鞘内脑脊液体积和流动增加所致。
