RESPIRATORY HEAT LOSS WITH HIGH DENSITY GAS MIXTURES.

Abstract : Heat loss from the respiratory tract of resting and working subjects was measured while they were breathing air, 20% O2 - 80% HE, and 20% O2 - 80% SF6 through an instrumented SCUBA mouthpiece at 1 atmosphere. Similar data were taken in a hyperbaric wet chamber with air and 20% O2 - 80% HE at 4 ata, and 4% O2 and 96% HE at 8 ata. Heat loss was directly proportional to respiratory minute volume and to the product of density and specific heat of each gas mixture. With higher density mixtures, respiratory heat loss was as high as 25% of the total heat production, either resting or working. Individual values for the respiratory loss ranged from 0.1 to 2.5 kcal/min. Respiratory heat loss was reduced by the presence of the mouthpiece, since the portion of the airway through which both inspired and expired gas travels heats inspired air, and cools expired air and condenses out some of its water vapor. Methods are given for calculating respiratory heat loss and the densities of different gas mixtures. (Author)