Taylor Nigel A S, Caldwell Joanne N, Van den Heuvel Anne M J, Patterson Mark J
Human Performance Laboratories, School of Health Sciences, University of Wollongong, Wollongong, Australia.
Med Sci Sports Exerc. 2008 Nov;40(11):1962-9. doi: 10.1249/MSS.0b013e31817eee9d.
Patient cooling time can impact upon the prognosis of heat illness. Although ice-cold-water immersion will rapidly extract heat, access to ice or cold water may be limited in hot climates. Indeed, some have concerns regarding the sudden cold-water immersion of hyperthermic individuals, whereas others believe that cutaneous vasoconstriction may reduce convective heat transfer from the core. It was hypothesized that warmer immersion temperatures, which induce less powerful vasoconstriction, may still facilitate rapid cooling in hyperthermic individuals.
Eight males participated in three trials and were heated to an esophageal temperature of 39.5 degrees C by exercising in the heat (36 degrees C, 50% relative humidity) while wearing a water-perfusion garment (40 degrees C). Subjects were cooled using each of the following methods: air (20-22 degrees C), cold-water immersion (14 degrees C), and temperate-water immersion (26 degrees C).
The time to reach an esophageal temperature of 37.5 degrees C averaged 22.81 min (air), 2.16 min (cold), and 2.91 min (temperate). Whereas each of the between-trial comparisons was statistically significant (P < 0.05), cooling in temperate water took only marginally longer than that in cold water, and one cannot imagine that the 45-s cooling time difference would have any meaningful physiological or clinical implications.
It is assumed that this rapid heat loss was due to a less powerful peripheral vasoconstrictor response, with central heat being more rapidly transported to the skin surface for dissipation. Although the core-to-water thermal gradient was much smaller with temperate-water cooling, greater skin and deeper tissue blood flows would support a superior convective heat delivery. Thus, a sustained physiological mechanism (blood flow) appears to have countered a less powerful thermal gradient, resulting in clinically insignificant differences in heat extraction between the cold and temperate cooling trials.
患者降温时间会影响中暑的预后。尽管冷水浸泡能迅速散热，但在炎热气候下，获取冰块或冷水可能受限。确实，有些人担心高温个体突然进行冷水浸泡，而另一些人则认为皮肤血管收缩可能会减少核心部位的对流散热。据推测，诱导较弱血管收缩的稍高浸泡温度，仍可能促进高温个体快速降温。
八名男性参与了三项试验，通过在高温环境（36摄氏度，相对湿度50%）中穿着水灌注服（40摄氏度）运动，将食管温度加热至39.5摄氏度。使用以下每种方法对受试者进行降温：空气（20 - 22摄氏度）、冷水浸泡（14摄氏度）和温水浸泡（26摄氏度）。
食管温度降至37.5摄氏度的平均时间分别为22.81分钟（空气）、2.16分钟（冷水）和2.91分钟（温水）。尽管每次试验间比较均具有统计学意义（P < 0.05），但温水冷却所用时间仅比冷水冷却略长，很难想象这45秒的冷却时间差异会有任何有意义的生理或临床影响。
据推测，这种快速散热是由于外周血管收缩反应较弱，核心热量能更快地传输到皮肤表面进行散发。尽管温水冷却时核心与水之间的热梯度小得多，但更大的皮肤和更深层组织血流量会支持更好的对流热传递。因此，一种持续的生理机制（血流量）似乎抵消了较弱的热梯度，导致冷水和温水冷却试验在散热方面的差异在临床上无显著意义。
