Effects of 7.5% CO2 challenge in generalized anxiety disorder.

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 ...