Psychophysiological responses to CO2 inhalation

Abstract

Inhalation of CO2-enriched air has been used as a laboratory model for a number of anxiety disorders, such as general anxiety disorder and panic disorder. Because studies describing psychophysiological responses to this challenge are scarce, the present studies investigated skin conductance level, eyeblink startle, self-reported anxiety and fractional end-tidal carbon dioxide during inhalation of CO2-enriched air. In study 1, thirty-five healthy volunteers inhaled 7.5% CO2 for 2min. In study 2, twenty healthy volunteers inhaled 20% CO2 for 30s. Control groups (N=20 in each study) inhaled room air during the same time periods. Compared to room air breathing, both CO2-mixtures were associated with increases in skin conductance levels, self-reported anxiety and fractional end-tidal CO2. Eyeblink startles were inhibited during CO2 compared to room air breathing in both experiments. Our findings suggest that inhalation of CO2-enriched air is associated with a circa-strike defensive response pattern, corroborating its application as an interoceptive, panic-relevant stimulus in fear research.