Johnston C E, White M D, Wu M, Bristow G K, Giesbrecht G G
Laboratory for Exercise and Environmental Medicine, Health Leisure and Human Performance Research Institute, University of Manitoba, Winnipeg, Canada.
J Appl Physiol (1985). 1996 Feb;80(2):422-9. doi: 10.1152/jappl.1996.80.2.422.
Hypoxia lowers the basic thermoregulatory responses of animals and humans. In cold-exposed animals, hypoxia increases core temperature (Tco) cooling rate and suppresses shivering thermogenesis. In humans, the experimental effects of hypoxia on thermoregulation are equivocal. Also, the effect of hypoxia has not been separated from that of hypocapnia consequent to hypoxic hyperventilation. To determine the isolated effects of hypoxia on warm and cold thermoregulatory responses and core cooling during mild cold stress, we examined the Tco thresholds for sweating, vasoconstriction, and shivering as well as the core cooling rates of eight subjects immersed in 28 degrees C water under eucapnic conditions. On 2 separate days, subjects exercised on an underwater cycle ergometer to elevate Tco above the sweating threshold. They then rested and cooled until they shivered vigorously. Subjects inspired humidified room air during the control trial. For the eucapnic hypoxia trial, they inspired 12% O2-balance N2 with CO2 added to maintain eucapnia. Eucapnic hypoxia lowered the Tco thresholds for vasoconstriction and shivering by 0.14 and 0.19 degrees C, respectively, and increased core cooling rate by 33% (1.83 vs. 1.38 degrees C/h). These results demonstrate that eucapnic hypoxia enhances the core cooling rate in humans during mild cold stress. This may be attributed in part to a delay in the onset of vasoconstriction and shivering as well as increased respiratory heat loss during hypoxic hyperventilation.
低氧会降低动物和人类的基本体温调节反应。在暴露于寒冷环境的动物中，低氧会增加核心体温（Tco）的冷却速率并抑制寒颤产热。在人类中，低氧对体温调节的实验效果并不明确。此外，低氧的影响尚未与低氧性过度通气导致的低碳酸血症的影响区分开来。为了确定低氧对轻度冷应激期间的温热和寒冷体温调节反应以及核心体温冷却的单独影响，我们在等碳酸条件下，检测了8名浸泡在28摄氏度水中的受试者出汗、血管收缩和寒颤的Tco阈值以及核心体温冷却速率。在两个不同的日子里，受试者在水下自行车测力计上运动，以使Tco升高到出汗阈值以上。然后他们休息并降温，直到剧烈寒颤。在对照试验中，受试者吸入加湿的室内空气。在等碳酸低氧试验中，他们吸入含12%氧气 - 平衡氮气并添加二氧化碳以维持等碳酸状态。等碳酸低氧使血管收缩和寒颤的Tco阈值分别降低了0.14摄氏度和0.19摄氏度，并使核心体温冷却速率提高了33%（1.83对1.38摄氏度/小时）。这些结果表明，在轻度冷应激期间，等碳酸低氧会提高人类的核心体温冷却速率。这可能部分归因于血管收缩和寒颤的起始延迟以及低氧性过度通气期间呼吸热损失增加。
