High-dose carbon dioxide challenge test in anxiety disorder patients

Many investigators have shown that panic disorder patients and possibly social phobics are hypersensitive to the anxiogenic effects of inhaled carbon dioxide (CO 2). In this study we administered double-breath inhalation of 35% CO 2 and 65% oxygen (O 2) to panic disorder patients, social phobics, and normal controls. At baseline, panic disorder patients were characterized by higher pulse, anxiety score, and evidence of hyperventilation. Panic patients and social phobics panicked more often to 35% CO 2 than to room air; normal controls did not have a higher rate of panic to CO 2 than to room air. However, we did not find significant group differences in anxiety level, physiological measures, or biochemical measures in response to CO 2 breathing compared with room air breathing. These results confirm earlier reports of baseline hyperventilation in panic disorder patients. However, 35% CO 2 may be too high a dose to differentiate respiratory responses of patients compared with normals.