Pretorius Thea, Bristow Gerald K, Steinman Alan M, Giesbrecht Gordon G
Laboratory for Excercise and Environmental Medicine, Health, Leisure and Human Performance Research Institute, Univ. of Manitoba, Winnipeg, Canada R3T 2N2.
J Appl Physiol (1985). 2006 Aug;101(2):669-75. doi: 10.1152/japplphysiol.01241.2005. Epub 2006 Apr 13.
This study isolated the effect of whole head submersion in cold water, on surface heat loss and body core cooling, when the confounding effect of shivering heat production was pharmacologically eliminated. Eight healthy male subjects were studied in 17 degrees C water under four conditions: the body was either insulated or uninsulated, with the head either above the water or completely submersed in each body-insulation subcondition. Shivering was abolished with buspirone (30 mg) and meperidine (2.5 mg/kg), and subjects breathed compressed air throughout all trials. Over the first 30 min of immersion, exposure of the head increased core cooling both in the body-insulated conditions (head out: 0.47 +/- 0.2 degrees C, head in: 0.77 +/- 0.2 degrees C; P < 0.05) and the body-exposed conditions (head out: 0.84 +/- 0.2 degrees C and head in: 1.17 +/- 0.5 degrees C; P < 0.02). Submersion of the head (7% of the body surface area) in the body-exposed conditions increased total heat loss by only 10%. In both body-exposed and body-insulated conditions, head submersion increased core cooling rate much more (average of 42%) than it increased total heat loss. This may be explained by a redistribution of blood flow in response to stimulation of thermosensitive and/or trigeminal receptors in the scalp, neck and face, where a given amount of heat loss would have a greater cooling effect on a smaller perfused body mass. In 17 degrees C water, the head does not contribute relatively more than the rest of the body to surface heat loss; however, a cold-induced reduction of perfused body mass may allow this small increase in heat loss to cause a relatively larger cooling of the body core.
本研究在通过药理学方法消除寒战产热的混杂效应后，分离出了冷水全头浸没对体表热散失和体核降温的影响。在17摄氏度的水中，对8名健康男性受试者在四种条件下进行了研究：身体要么隔热，要么不隔热，在每种身体隔热的子条件下，头部要么露出水面，要么完全浸没在水中。使用丁螺环酮（30毫克）和哌替啶（2.5毫克/千克）消除寒战，并且在所有试验过程中受试者均呼吸压缩空气。在浸没的前30分钟内，无论是在身体隔热条件下（头部露出：0.47±0.2摄氏度，头部浸没：0.77±0.2摄氏度；P<0.05）还是在身体暴露条件下（头部露出：0.84±0.2摄氏度，头部浸没：1.17±0.5摄氏度；P<0.02），头部暴露都会增加体核降温。在身体暴露条件下，头部浸没（占体表面积的7%）仅使总热散失增加了10%。在身体暴露和身体隔热条件下，头部浸没导致的体核降温速率增加幅度（平均为42%）远大于总热散失的增加幅度。这可能是由于头皮、颈部和面部的热敏和/或三叉神经受体受到刺激后，血流重新分布所致，在这种情况下，一定量的热散失对较小的灌注体重会产生更大的降温效果。在17摄氏度的水中，头部对体表热散失的贡献并不比身体其他部位相对更大；然而，寒冷引起的灌注体重减少可能会使这种小幅度的热散失增加导致体核相对更大程度的降温。
