Effects of carbon dioxide-oxygen inhalations on subjective anxiety and some neurovegetative parameters.

The immediate effects of double inhalations of a 35% CO2-65% O2 mixture were studied on 12 subjects, all of them undergraduate students. For placebo control double inhalations of compressed air were administered to the same experimental subjects. In comparison, CO2/O2 inhalations were found to provoke significantly stronger autonomic reactions, viz, drops in heart rate and diastolic blood pressure. Reduction in subjective feeling of anxiety was observed with both CO2/O2 and air intake. On this parameter of subjective feeling the order in which the treatments were received interacted with the gas variable, i.e. CO2/O2 and air. The occurrence of a carry-over effect was indicated: Subjects having taken the placebo before CO2/O2 showed lower SUD scores than did those treated reversely.