NITROGEN-OXYGEN MIXTURE PHYSIOLOGY. PHASE 4. CARBON DIOXIDE SENSITIVITY AS A POTENTIAL MEANS OF PERSONNEL SELECTION. PHASE 6: CARBON DIOXIDEREGULATION UNDER DIVING CONDITIONS

Abstract

Resting subjects were exposed to mixtures containing elevated CO2 concentrations until the end expiratory CO2 reached 45, 50, 55, and 60 mm Hg. The RMV was recorded at each pCO2 level. The end-expiratory pCO2 of the subjects swimming at the surface and at depths of 26 ft and 99 ft was measured while breathing air, oxygen, 55 percent nitrogen - 45 percent oxygen and 55 percent helium - 45 percent oxygen. In some experiments, the respiratory resistance and dead space was varied. All individuals demonstrated a tendency to retain CO2 when swimming at moderate depth, especially when breathing N2-O2 mixtures. Increased breathing resistance and dead space favored CO2 retention. When breathing HeO2 mixtures, CO2 retention is absent or small. The degree to which individuals retain CO2 varies and there is a relationship between their tendency and their ventilatory response to CO2. Nitrogen-Oxygen mixtures should be abandoned in favor of helium-oxygen mixtures for mixed gas scuba diving.