Caldwell Joanne N, van den Heuvel Anne M J, Kerry Pete, Clark Mitchell J, Peoples Gregory E, Taylor Nigel A S
Centre for Human and Applied Physiology, School of Medicine, University of Wollongong, Wollongong, NSW, 2522, Australia.
Exp Physiol. 2018 Apr 1;103(4):512-522. doi: 10.1113/EP086760. Epub 2018 Feb 28.
What is the central question of this study? Does the cold-water immersion (14°C) of profoundly hyperthermic individuals induce reductions in cutaneous and limb blood flow of sufficient magnitude to impair heat loss relative to the size of the thermal gradient? What is the main finding and its importance? The temperate-water cooling (26°C) of profoundly hyperthermic individuals was found to be rapid and reproducible. A vascular mechanism accounted for that outcome, with temperature-dependent differences in cutaneous and limb blood flows observed during cooling. Decisions relating to cooling strategies must be based upon deep-body temperature measurements that have response dynamics consistent with the urgency for cooling.
Physiologically trivial time differences for cooling the intrathoracic viscera of hyperthermic individuals have been reported between cold- and temperate-water immersion treatments. One explanation for that observation is reduced convective heat delivery to the skin during cold immersion, and this study was designed to test both the validity of that observation, and its underlying hypothesis. Eight healthy men participated in four head-out water immersions: two when normothermic, and two after exercise-induced, moderate-to-profound hyperthermia. Two water temperatures were used within each thermal state: temperate (26°C) and cold (14°C). Tissue temperatures were measured at three deep-body sites (oesophagus, auditory canal and rectum) and eight skin surfaces, with cutaneous vascular responses simultaneously evaluated from both forearms (laser-Doppler flowmetry and venous-occlusion plethysmography). During the cold immersion of normothermic individuals, oesophageal temperature decreased relative to baseline (-0.31°C over 20 min; P < 0.05), whilst rectal temperature increased (0.20°C; P < 0.05). When rendered hyperthermic, oesophageal (-0.75°C) and rectal temperatures decreased (-0.05°C) during the transition period (<8.5 min, mostly in air at 22°C), with the former dropping to 37.5°C only 54 s faster when immersed in cold rather than in temperate water (P < 0.05). Minimal cutaneous vasoconstriction occurred during either normothermic immersion, whereas pronounced constriction was evident during both immersions when subjects were hyperthermic, with the colder water eliciting a greater vascular response (P < 0.05). It was concluded that the rapid intrathoracic cooling of asymptomatic, hyperthermic individuals in temperate water was a reproducible phenomenon, with slower than expected cooling in cold water brought about by stronger cutaneous vasoconstriction that reduced convective heat delivery to the periphery.
本研究的核心问题是什么？对于体温过高的个体，冷水浸泡（14°C）是否会导致皮肤和肢体血流量减少到足以相对于热梯度大小损害散热的程度？主要发现及其重要性是什么？发现体温过高的个体进行温水冷却（26°C）快速且可重复。一种血管机制解释了这一结果，冷却过程中观察到皮肤和肢体血流量存在温度依赖性差异。有关冷却策略的决策必须基于具有与冷却紧迫性一致的响应动态的深部体温测量。
据报道，在冷水和温水浸泡治疗之间，体温过高个体胸腔内脏冷却的生理无关时间差异。该观察结果的一种解释是冷水浸泡期间对流热传递到皮肤减少，本研究旨在检验该观察结果及其潜在假设的有效性。八名健康男性参与了四次头部露出水面的浸泡：两次在体温正常时，两次在运动诱导的中度至深度体温过高后。在每种热状态下使用两种水温：温水（26°C）和冷水（14°C）。在三个深部身体部位（食管、耳道和直肠）和八个皮肤表面测量组织温度，同时从前臂（激光多普勒血流仪和静脉阻塞体积描记法）评估皮肤血管反应。在体温正常个体的冷水浸泡期间，食管温度相对于基线下降（20分钟内下降0.31°C；P<0.05），而直肠温度升高（0.20°C；P<0.05）。当体温过高时，在过渡期（<8.5分钟，主要在22°C空气中）食管温度（-0.75°C）和直肠温度（-0.05°C）下降，浸入冷水时食管温度降至37.5°C仅比浸入温水时快54秒（P<0.05）。在体温正常浸泡期间皮肤血管收缩最小，而当受试者体温过高时，两种浸泡期间均明显收缩，冷水引起更大的血管反应（P<0.05）。得出结论，无症状体温过高个体在温水中快速胸腔冷却是一种可重复的现象，冷水中冷却比预期慢是由于更强的皮肤血管收缩减少了对流热传递到外周。
