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Heat balance precedes stabilization of body temperatures during cold water immersion

Defence Research and Development Canada, Human Performance and Protection, Toronto, Ontario, Canada M3M 3B9

Submitted 26 December 2002 ; accepted in final form 5 March 2003

Certain previous studies suggest, as hypothesized herein, that heat balance (i.e., when heat loss is matched by heat production) is attained before stabilization of body temperatures during cold exposure. This phenomenon is explained through a theoretical analysis of heat distribution in the body applied to an experiment involving cold water immersion. Six healthy and fit men (mean ± SD of age = 37.5 ± 6.5 yr, height = 1.79 ± 0.07 m, mass = 81.8 ± 9.5 kg, body fat = 17.3 ± 4.2%, maximal O₂ uptake = 46.9 ± 5.5 l/min) were immersed in water ranging from 16.4 to 24.1°C for up to 10 h. Core temperature (T_co) underwent an insignificant transient rise during the first hour of immersion, then declined steadily for several hours, although no subject's T_co reached 35°C. Despite the continued decrease in T_co, shivering had reached a steady state of 2 x resting metabolism. Heat debt peaked at 932 ± 334 kJ after 2 h of immersion, indicating the attainment of heat balance, but unexpectedly proceeded to decline at 48 kJ/h, indicating a recovery of mean body temperature. These observations were rationalized by introducing a third compartment of the body, comprising fat, connective tissue, muscle, and bone, between the core (viscera and vessels) and skin. Temperature change in this "mid region" can account for the incongruity between the body's heat debt and the changes in only the core and skin temperatures. The mid region temperature decreased by 3.7 ± 1.1°C at maximal heat debt and increased slowly thereafter. The reversal in heat debt might help explain why shivering drive failed to respond to a continued decrease in T_co, as shivering drive might be modulated by changes in body heat content.

body cooling; shivering; heat debt; prediction; model

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