Antipanic effect of fluoxetine measured by CO2 challenge test

Background: Respiratory symptoms are important in panic disorder for frequency and intensity. Patients with this disorder are often chronic hyperventilators, and inhalation of carbon dioxide is a strong panicogenic stimulus. We tested the hypothesis of whether respiratory parameters may be used as indicators of the course of panic disorder during its treatment with fluoxetine. Methods: Nine patients with panic disorders, previously shown to panic in response to intravenously administered lactate, and 10 control subjects underwent the Read rebreathing test by a 5-min inhalation of a 7% CO₂/93% O₂ mixture before and after 1 month of fluoxetine treatment. Results: At baseline, patients differed from controls for higher percent value of expiratory reserve volume/vital capacity ratio and ventilatory response. Eight of the 9 patients had panic in response to the CO₂ challenge. After fiuoxetine, respiratory parameters decreased significatively, and only 3 patients remained hypercarbic challenge responders. Conclusions: The carbon dioxide challenge may represent a useful tool to evaluate the individual respiratory set, which may be a marker of the vulnerability to panic attack. Assessment of respiratory parameters may represent a biological marker to measure the efficacy of antipanic treatment.