The role of offset control in anxious responding: An experimental test using repeated administrations of 20% carbon dioxide-enriched air

The present investigation attempted to clarify whether a lack of control affects self-reported anxiety and physiological reactivity during eight administrations of 20% carbon dioxide (CO2)-enriched air. Thirty individuals who reported high levels of suffocation fear were randomly assigned to a condition that either permitted or did not permit control over the offset of CO2 gas inhalation. In contrast to participants with control, participants without control reported significantly more self-reported anxiety and intense panic experiences. Although 20% CO2-enriched air reliably evoked physiological arousal for both groups, no significant between-group differences for peripheral indices of somatic reactivity were observed. We discuss the implications of these findings for understanding how control over aversive environmental stimuli mediates anxious responding in panic disorder.