Effects of 7.5% CO 2 challenge in generalized anxiety disorder

Abstract

We have previously developed a putative model of generalized anxiety disorder in healthy volunteers using a 20-minute 7.5% carbon dioxide (CO₂) inhalation challenge. The aim of this study was to validate the 7.5% CO₂ paradigm by assessing its effects in patients with generalized anxiety disorder in a test–retest design. Twelve medication-free generalized anxiety disorder patients attended our lab for two study days. On each study day placebo (compressed air) and 7.5% CO₂ mixture were randomly administered over 20 min, at least 30 min apart, in a single blind, randomized, placebo-controlled cross-over design. Subjective ratings, cardiovascular measures and cortisol levels were collected throughout. CO₂ challenge significantly increased ratings for anxiety and other subjective symptoms associated with generalized anxiety disorder, compared with air. It also significantly increased systolic blood pressure on day 2, indicating increased autonomic arousal. There was no change between the two test days in mean anxiety rating scores, and there also appeared to be a correlation for individual scores on a number of the subjective measures. In conclusion, 20 min of 7.5% CO₂ gas inhalation increases anxiety responses in patients with generalized anxiety disorder, and this is reliable over time.