Cognitive factors in carbon dioxide therapy.

The effects of CO2 inhalation on subjective state, heart rate and blood pressure were studied in two differently instructed groups, with use of air for placebo. Participants who were told that inhalation would produce a state of pleasant relaxation reported a statistically significant, confirming change when administered CO2, whereas air was found not to alter the subjective state appreciably. Those who had expected unpleasant feelings of tension did show a non-significant change in this respect after CO2 inhalation and no such reaction at all to the placebo. Heart rate and diastolic blood pressure dropped significantly after CO2 intake. Surprisingly, participants were subject to a significant decrease in heart rate upon inhalation of air when relaxation was expected. Finally, a number of theoretical inferences are made and the role of cognitive processes in the clinical use of CO2 therapy is underscored.