Gas density and the work of breathing

Abstract

Man, living at 300 meters under the sea, will breathe gas mixture of oxygen and helium which are extremely dense, due to their pressures. These high densities will cause gas flow through the tracheo-bronchial tree to be turbulent, and the work of breathing will become a function of gas density. To stimulate this dense gas, an 80% sulfur hexafluoride-20% oxygen mixture was breathed by human subjects at one atmosphere. The work of breathing was determined by measuring the oxygen consumption during quiet breathing and during hyperventilation produced by 7% carbon dioxide. Under resting conditions, breathing room air, the oxygen consumption was 273 ml STPD/min for a minute volume of 5.5 liters BTPS/min. While breathing 7% carbon dioxide in air, the oxygen consumption was 353 ml STPD/min for a minute volume of 36 liters BTps/min, and while breathing 7% carbon dioxide in sulfur hexafluoride-oxygen, the oxygen consumption for a similar minute volume was 537 ml STPD/min. It is concluded that the oxygen cost of breathing high density gas mixtures in this experiment was not a factor which limits the capacity to do useful work.