Physiological and psychological effects associated with high carbon dioxide levels in healthy men

Background: Perception of CO₂ in ambient air may be of fundamental importance to the health, safety, and job performance of persons occupationally exposed to increased levels of CO₂. Few studies have examined the perceptual responses to inhaled CO₂ at levels between 6-10%. Hypothesis:We hypothesized that healthy, highly-active men would be able to determine the difference between 6% and 8% CO₂ concentrations. Methods: Thirty-two male students (21 ± 1 yr) served as subjects. Experimental trials (counterbalanced design) included breathing air (control, 21% O₂, 79% N₂), 6% CO₂ (21% O₂, 73% N₂), and 8% CO₂, (21%, O₂, 71% N₂) conditions. The Body Sensations Questionnaire (BSQ) was completed twice during each trial. Results: End tidal CO₂ (FETCO₂) and BSQ values increased (p < 0.05) as a function of the percentage of inhaled CO₂. Respiratory rates during the 8% trial were greater (p < 0.05) than control and 6% CO₂ trial measures. BSQ scores were significantly correlated with FETCO₂ and respiratory rate measures during the 6% and 8% CO₂ conditions. Conclusions: We conclude that these subjects recognized their exposure to both the 6% and 8% CO₂ concentrations, and their responses were more profound during the 8% CO₂ condition.