Rostrup Egill, Larsson Henrik B W, Born Alfred P, Knudsen Gitte M, Paulson Olaf B
Danish Research Centre for Magnetic Resonance, Copenhagen University Hospital Hvidovre, Denmark.
Neuroimage. 2005 Dec;28(4):947-55. doi: 10.1016/j.neuroimage.2005.06.032. Epub 2005 Aug 10.
Acute normobaric hypoxia as well as longstanding hypobaric hypoxia induce pronounced physiological changes and may eventually lead to impairment of cerebral function. The aim of the present study is to investigate the effect of hypoxia on the cerebral activation response as well as to explore possible structural changes as measured by diffusion weighted imaging. Eleven healthy sea-level residents were studied after 5 weeks of adaptation to high altitude conditions at Chacaltaya, Bolivia (5260 m). The subjects were studied immediately after return to sea-level in hypoxic and normoxic conditions, and the examinations repeated 6 months later after re-adaptation to sea-level conditions. The BOLD response, measured at 1.5 T, was severely reduced during acute hypoxia both in the altitude and sea-level adapted states (50% reduction during an average S(a)O(2) of 75%). On average, the BOLD response magnitude was 23% lower in altitude than sea-level adaptation in the normoxic condition, but in the hypoxic condition, no significant differences were found. A small but statistically significant decrease in the apparent diffusion coefficient (ADC) was seen in some brain regions during acute hypoxia, whereas ADC was slightly elevated in high altitude as compared to sea-level adaptation. It is concluded that hypoxia significantly diminishes the BOLD response, and the mechanisms underlying this finding are discussed. Furthermore, altitude adaptation may influence both the magnitude of the activation-related response, as well as micro-structural features.
急性常压缺氧以及长期低压缺氧会引发显著的生理变化，并最终可能导致脑功能受损。本研究的目的是调查缺氧对脑激活反应的影响，并通过扩散加权成像探索可能的结构变化。11名健康的海平面居民在适应玻利维亚查卡尔塔亚（海拔5260米）的高海拔条件5周后接受了研究。受试者在返回海平面后立即在缺氧和常氧条件下接受研究，并在重新适应海平面条件6个月后重复检查。在1.5T磁场下测量的血氧水平依赖（BOLD）反应在急性缺氧期间，无论是在海拔适应状态还是海平面适应状态下均显著降低（平均动脉血氧饱和度为75%时降低50%）。在常氧条件下，平均而言，海拔适应状态下的BOLD反应幅度比海平面适应状态低23%，但在缺氧条件下，未发现显著差异。在急性缺氧期间，一些脑区的表观扩散系数（ADC）出现了轻微但具有统计学意义的下降，而与海平面适应相比，高海拔地区的ADC略有升高。研究得出结论，缺氧会显著降低BOLD反应，并对这一发现的潜在机制进行了讨论。此外，海拔适应可能会影响激活相关反应的幅度以及微观结构特征。
