Sensitivity to 35% carbon dioxide in patients with generalized anxiety disorder

Background: Panic disorder and generalized anxiety disorder (GAD) are both characterized by severe anxiety, but there is evidence that indicates a qua litative difference between these 2 anxiety disorders. To investigate the s pecificity of the association between carbon dioxide (CO2) hypersensitivity and panic disorder and the possible relationships between panic disorder a nd GAD, the responses to inhalation of a gas mixture of 35% CO2 and 65% oxy gen (O-2) were assessed. Method: Fifteen patients with panic disorder, 13 patients with GAD, and 10 patients with comorbid GAD and panic disorder according to a consensus diag nosis using Diagnostic Interview Schedule Version III-R (DIS-R) and DSM-IV criteria, and 12 healthy controls inhaled 2 vital capacities: 1 of 35% CO2 and I of compressed air. A double-blind, randomized, crossover design was u sed. Results: GAD patients showed reactions to 35% CO2 that were similar to thos e of healthy controls and significantly weaker than that of panic disorder patients. Patients with comorbid panic disorder and GAD had anxiogenic reac tions similar to those of subjects with panic disorder. Conclusion: The results of the present study support the idea that panic di sorder and GAD are separate disorders that have at least some differences i n pathogenetic mechanisms and suggest that the 35% CO2 test might be a vali d tool for discriminating between these 2 disorders.