Sensitivity to 35% CO2 in healthy first-degree relatives of patients with panic disorder

Objective: The authors tested the hypothesis that hyperreactivity to CO₂ in healthy subjects represents an underlying familial vulnerability to panic disorder. Method: One vital-capacity inhalation of 35% CO₂ and 65% O₂ was administered to each of 84 patients with panic disorder, 23 healthy first- degree relatives of probands with panic disorder, and 44 healthy subjects with no family history of panic disorder. Results: The first-degree relatives of the probands with panic disorder reacted significantly more than the healthy subjects and significantly less than the probands. Conclusions: These findings suggest an association between family history of panic disorder and hyperreactivity to 35% CO₂ in healthy subjects.