Safe cooling limits from exercise-induced hyperthermia |
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Authors: | CI Proulx MB Ducharme GP Kenny |
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Institution: | (1) Laboratory of Human Bioenergetics and Environmental Physiology, University of Ottawa, Montpetit Hall, Room 367, 125 University Ave., K1N 6N5 Ottawa, Canada;(2) Ottawa Health Research Institute, Ottawa, ON, K1Y 4E9, Canada;(3) Defence R&D Canada – Toronto, Toronto, ON, M3M 3B9, Canada |
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Abstract: | We evaluated the cooling rate of hyperthermic subjects, as measured by three estimates of deep core temperatures (esophageal,
rectal and aural canal temperatures), during immersion in a range of water temperatures. The objective of the study was to
compare the three indices of core temperature and define safe cooling limits when using rectal temperature to avoid the development
of hypothermia. On 4 separate days, seven subjects (four males, three females) exercised for 45.4±4.1 min at 65%
at an ambient temperature of 39°C, RH: 36.5%, until rectal temperature (T
re) increased to 40.0°C (39.5°C for two subjects). Following exercise, the subjects were immersed in a circulated water bath
controlled at 2, 8, 14 and 20°C until T
re returned to 37.5°C. When T
re reached normothermia during the cooling period (37.5±0.05°C), both esophageal (T
es) (35.6±1.3°C) and aural canal (T
ac) (35.9±0.9°C) temperatures were approaching or reaching hypothermia, particularly during immersion in 2°C water (T
es=34.5±1.2°C). On the basis of the heat loss data, the heat gained during the exercise was fully eliminated after 5.4±1.5,
7.9±2.9, 10.4±3.8 and 13.1±2.8 min of immersion in 2, 8, 14 and 20°C water, respectively, with the coldest water showing a
significantly faster cooling rate. During the immersion in 2°C water, a decrease of only 1.5°C in T
re resulted in the elimination of 100% of the heat gained during exercise without causing hypothermia. This study would therefore
support cooling the core temperature of hyperthermic subjects to a rectal temperature between 37.8°C (during immersion in
water >10°C) and 38.6°C (during immersion in water <10°C) to eliminate the heat gained during exercise without causing hypothermia. |
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Keywords: | Whole-body cooling Indices of core temperature Heat stress Heat illness Cold-water bath |
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