WET-COLD EXPOSURE AND HYPOTHERMIA - THERMAL AND METABOLIC RESPONSES TO PROLONGED EXERCISE IN RAIN

Simulated conditions of hiking in rain, wind, and cold, without protec tive rainwear, were used to investigate wet-cold hypothermia in 18 mal e subjects. Thermal, metabolic, and motor responses were monitored dur ing an attempted 5-h walk (5.1 km/h) at 5 degrees C, with continuous e xposure to rain (7.4 cm/h) and wind (8.0 km/h) over the final 4 h. Til e majority of subjects (11) could not complete the protocol because of intolerance of wet-cold conditions during the last 2 h. Therefore, da ta from 5 subjects who completed the protocol in rain and control cond itions were used to describe the general pattern of response. During t he Ist h of walking, core temperature rose 1 degrees C to 38.1 degrees C. The subsequent 2 h of rain caused substantial cold stress, indicat ed by a 40% increase in heat production due to shivering and significa nt loss of strength and manual dexterity. However core temperature onl y decreased to 37.1 degrees C, merely eliminating the initial exercise hyperthermia. Over the last 2 h of rain, core temperature remained re latively stable at 36.8 degrees C, decreasing slightly to 36.4 degrees C by 5 h. Two other subjects developed significant hypothermia (35 de grees C). One demonstrated fatigue of shivering after 2.5 h of rain, c onfirming the exhaustion hypothesis of wet-cold hypothermia. The other cooled rapidly when he failed to maintain the walking pace. We conclu de that if a person can tolerate the intense discomfort of prolonged w et-cold exposure, he or she has the potential to resist: significant c ore hypothermia for at least 4 h of walking under the conditions of th is experiment. Exceptions to this generalization occur, making exposur e of <4 h a hypothermia risk for some individuals. Exposures >4 h woul d involve increasing probability of rapid decline into hypothermia, as sociated with exhaustion of shivering and exercise heat production.