[Heat debt and thermal insulation in women exposed to cold : contribution of direct calorimetry to the study of a mathematical model (author's transl)].

1. Measurements of total heat losses by direct calorimetry, metabolic heat production by indirect calorimetry, body temperatures by thermometry, and thickness of subcutaneous fat with skin-fold calipers were made in four groups of subjects (anorexic, controls, trend to obesity, and obesity) at ambient temperatures of 28 degrees C and 20 degrees C. 2. At 28 degrees C, the four groups of subjects reached thermal equilibrium after 30 min. 3. Both metabolic heat production and total heat losses were lower in the anorexic group than in the control group. 4. Body thermal insulation was not simply related to the thickness of subcutaneous fat (passive insulation), but was actively regulated in such a way that thermal balance was attained by all subjects at 28 degrees C. Body tissues underlying the subcutaneous fat contributed to the thermal insulation of the subjects at both 28 degrees C and 20 degrees C. 5. At 28 degrees C, total body thermal insulation was higher in anorexic subjects than in controls. 6. At 20 degrees C, heat debt was similar in three of the four groups : the anorexic subjects showed a higher debt. 7. A highly significant correlation between subcutaneous fat and weight/area ratio, was found. 8. The heat exchange coefficient of radiation and convection was found to be 6,47 Wm-2 degrees C-1. 9. By combining our measured values with those of various tissue physical characteristics, it was possible to produce a mathematical model. With this model one can calculate the penetration of the thermal gradient into the body, and estimate the mean temperature of each tissue participating in the thermal insulation for moderately cold ambient temperatures.