Further Experiences with the Measurement of Heat Production from Insensible Loss of Weight

Abstract

The results of this study are based upon observations made upon twenty different individuals. Most of them were young normal adults. The remainder were patients whose regulation of heat was presumably normal. Nine of them were studied in detail in the respiration chamber; four others while they remained in bed, and the remainder while they were pursuing active lives. The chamber permitted us to measure the percentage of heat removed by vaporization during 24 hours. There are twenty-nine such periods (omitting R.L.G.) from nine subjects. The lowest per cent was 21, the highest 28. The average of the twenty-nine periods was 25%. In the two earlier series of experiments, the conditions permitted only a determination of the average per cent of heat removed by vaporization. Here the least was 23.8% and the greatest 25.2%. The average was 24.5%. The grand average for the whole series is 24.7%. Since biological variation is evident, we have adopted the nearest whole number which is 25%. This narrow range is ample support for the belief that man possesses a mechanism designed to rid him by vaporization of water of a fixed percentage of the heat produced within his body. Conditions that cause him to feel uncomfortably warm or cool will disturb this relationship. The discomfort is the signal to adjust himself to the environment. He strives to do this by lessening or increasing the barrier between himself and the environment, by changing the rate of his activity or by making the surroundings more suitable. This mechanism has been used as a basis for the calculation of the heat produced by normal human beings whose activity varied from continuous residence in bed to that of the busy laboratory worker. It is evident from the experiments in the chamber that the percentage of heat removed by vaporization of water during a single 24 hours was not sufficiently fixed to afford a reliable determination of the total heat. However, when the average of several periods was used, the maximal errors (omitting R.L.G.) attributable to variability in the per cent of heat lost by vaporization was only ±5%. The second potential error in this calculation is due to the assumption that the carbohydrate oxidized is the same as the dietary carbohydrate. This error may be reduced to a negligible quantity by 1) feeding a fixed diet; 2) establishing a fixed plane of activity; 3) discarding the first few days of the study; 4) using the average of several consecutive days following the period of adjustment. The calculation of heat production from the insensible loss of weight, the carbohydrate of the diet and the urinary nitrogen by the technique described above yielded values that differed less than 5% from those obtained by indirect calorimetry, when averages of several 24-hourly periods were used.