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 after 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.