Walker Shane C, Garbino Alejandro, Ray Kristi, Hardwick Renny, Fitzpatrick Daniel T, Sanders Robert W
School of Medicine, University of California, San Francisco, San Francisco, California U.S.
University of Texas Medical Branch, Galveston, Texas.
Undersea Hyperb Med. 2018 Jul-Aug;45(4):427-436.
Astronauts training for extravehicular activity (EVA) operations can spend many hours submerged underwater in a pressurized suit, called an extravehicular mobility unit (EMU), exposed to pressures exceeding 2 atmospheres absolute (ATA). To minimize the risk of decompression sickness (DCS) a 46% nitrox mixture is used. This limits the nitrogen partial pressure, decreasing the risk of DCS. The trade-off with using a 46% nitrox mixture is the increased potential for oxygen toxicity, which can lead to severe neurologic symptoms including seizures. Suited runs, which typically expose astronauts of 0.9-1.1 ATA for longer than six hours, routinely exceed the recommendation for central nervous system oxygen toxicity limits (CNSOTL) published by the National Oceanic and Atmospheric Administration (NOAA). Fortunately, in over 50,000 hours of suited training dives spanning 20 years of EVA training operations at NASA's Neutral Buoyancy Laboratory (NBL) there has never been an occurrence of oxygen toxicity. This lends support to anecdotal sentiment among certain members of the hyperbaric community that the NOAA CNSOTL recommendations might be overly conservative, at least for the oxygen pressure and time regime in which NBL operates. The NOAA CNSOTL recommendations are the result of expert consensus with a focus on safety and do not necessarily reflect rigorous experimental evidence. The data from the NBL suited dive operations provide a foundation of evidence that can help inform the expert discussion on dive-related neurologic oxygen toxicity performance and overnight recovery in young, healthy males.
接受舱外活动（EVA）操作训练的宇航员可能要在水下穿着一种名为舱外机动装置（EMU）的加压航天服浸泡数小时，所承受的绝对压力超过2个大气压（ATA）。为了将减压病（DCS）的风险降至最低，会使用46%的氮氧混合气。这限制了氮分压，降低了患减压病的风险。使用46%氮氧混合气的代价是增加了氧中毒的可能性，氧中毒可能导致包括癫痫发作在内的严重神经症状。穿着航天服进行的训练，通常会使宇航员在0.9 - 1.1 ATA的环境中暴露超过6小时，这通常超过了美国国家海洋和大气管理局（NOAA）发布的中枢神经系统氧中毒极限（CNSOTL）建议值。幸运的是，在美国国家航空航天局（NASA）中性浮力实验室（NBL）进行的长达20年的EVA训练操作中，超过50000小时的穿着航天服训练潜水从未发生过氧中毒事件。这支持了高压氧治疗领域某些成员的一种观点，即NOAA的CNSOTL建议可能过于保守，至少对于NBL的氧压和时间范围来说是这样。NOAA的CNSOTL建议是专家共识的结果，重点是安全，不一定反映严格的实验证据。NBL穿着航天服潜水操作的数据提供了证据基础，有助于为关于年轻健康男性潜水相关神经氧中毒表现和夜间恢复的专家讨论提供参考。
