Castellani J W, Young A J, Kain J E, Sawka M N
Thermal and Mountain Medicine Division, US Army Research Institute of Environmental Medicine, Natick, Massachusetts 01760-5007, USA.
J Appl Physiol (1985). 1999 Jul;87(1):243-6. doi: 10.1152/jappl.1999.87.1.243.
This study examined how time of day affects thermoregulation during cold-water immersion (CWI). It was hypothesized that the shivering and vasoconstrictor responses to CWI would differ at 0700 vs. 1500 because of lower initial core temperatures (T(core)) at 0700. Nine men were immersed (20 degrees C, 2 h) at 0700 and 1500 on 2 days. No differences (P > 0.05) between times were observed for metabolic heat production (M, 150 W. m(-2)), heat flow (250 W. m(-2)), mean skin temperature (T(sk), 21 degrees C), and the mean body temperature-change in M (DeltaM) relationship. Rectal temperature (T(re)) was higher (P < 0.05) before (Delta = 0.4 degrees C) and throughout CWI during 1500. The change in T(re) was greater (P < 0. 05) at 1500 (-1.4 degrees C) vs. 0700 (-1.2 degrees C), likely because of the higher T(re)-T(sk) gradient (0.3 degrees C) at 1500. These data indicate that shivering and vasoconstriction are not affected by time of day. These observations raise the possibility that CWI may increase the risk of hypothermia in the early morning because of a lower initial T(core).
本研究探讨了一天中的不同时间对冷水浸泡（CWI）期间体温调节的影响。研究假设，由于07:00时初始核心温度（T(core)）较低，07:00与15:00时对CWI的寒战和血管收缩反应会有所不同。9名男性在两天的07:00和15:00接受浸泡（20摄氏度，2小时）。在代谢产热（M，150 W·m(-2)）、热流（250 W·m(-2)）、平均皮肤温度（T(sk)，21摄氏度）以及M的平均体温变化（DeltaM）关系方面，未观察到不同时间之间存在差异（P>0.05）。直肠温度（T(re)）在15:00时浸泡前（Delta = 0.4摄氏度）及整个CWI过程中均较高（P<0.05）。15:00时T(re)的变化（-1.4摄氏度）大于07:00时（-1.2摄氏度）（P<0.05），这可能是因为15:00时T(re)-T(sk)梯度较高（0.3摄氏度）。这些数据表明，寒战和血管收缩不受一天中时间的影响。这些观察结果增加了一种可能性，即由于初始T(core)较低，清晨进行CWI可能会增加体温过低的风险。
