To Cool, But Not Too Cool: That Is the Question-Immersion Cooling for Hyperthermia

TAYLOR, NIGEL A. S.1; CALDWELL, JOANNE N.1; VAN DEN HEUVEL, ANNE M. J.1; PATTERSON, MARK J.2

Medicine & Science in Sports & Exercise: November 2008 - Volume 40 - Issue 11 - pp 1962-1969
doi: 10.1249/MSS.0b013e31817eee9d
BASIC SCIENCES: Original Investigations

Introduction: Patient coolingtime 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.

Methods: Eight males participated in three trials and were heated to an esophageal temperature of 39.5°C by exercising in the heat (36°C, 50% relative humidity) while wearing a water-perfusion garment (40°C). Subjects were cooled using each of the following methods: air (20-22°C), cold-water immersion (14°C), and temperate-water immersion (26°C).

Results: The time to reach an esophageal temperature of 37.5°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.

Conclusion: 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.

1Human Performance Laboratories, School of Health Sciences, University of Wollongong, Wollongong, AUSTRALIA; and 2Defence Science and Technology Organisation, Melbourne, AUSTRALIA

Address for correspondence: Nigel A. S. Taylor, Ph.D., School of Health Sciences, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia; E-mail: nigel_taylor@uow.edu.au.

Submitted for publication January 2008.

Accepted for publication May 2008.

©2008The American College of Sports Medicine