The effects of age and sex on the body cooling rates.
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When the head was cooled for 30 minutes, sublingual temperature fell by as much as 4.45°C below oesophageal which remained steady. Insulation of the head prevented this local cooling. There was an increased flow of cold parotid saliva when the head was exposed to cold and this appeared to be the major factor which depressed sublingual temperature. The estimation of deep body temperature from sublingual readings is meaningful only if precautions are taken to prevent local cooling of the head. Local cooling has been shown to depress temperature measured from the external auditory canal. A portable device (The Zero Gradient Aural Thermometer) was developed and used to measure external auditory canal temperature keeping the outer ear, monitored by a second thermistor, at the same level as the canal by servo-controlled heating. Measured in this way, aural temperature was always within 0.35°C of oesophageal under a variety of thermal stress. Rates of fall of deep body temperature in 28 children swimming in cold water correlated highly with overall subcutaneous fat thickness and a higher' correlation was obtained when allowance was made for differences in surface area/mass ratios. Young swimmers who were thin and with high surface area/mass ratios were shown to be at considerable risk from death due to hypothermia when swimming in water as warm as 20.30 C. Differences in fat distribution had a small effect on cooling rates. Cooling in air at 10°C, women generally had greater falls in deep body temperature than men even allowing for differences in surface area/mass ratio and subcutaneous fat thickness. This was mainly due to a smaller metabolic response to cold in the women.
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