The panic disorder respiratory ratio: a dimensional approach to the respiratory subtype.

OBJECTIVE The respiratory ratio is a dimensional construct of the respiratory subtype of panic disorder (PD). The respiratory subtype has been correlated with an increased sensitivity to CO₂ inhalation, positive family history of PD and low comorbidity with depression. The objective of our study was to determine whether the respiratory ratio is correlated with CO₂-induced panic attacks and other clinical and demographic features. METHODS We examined 91 patients with PD and submitted them to a double-breath 35% CO₂ challenge test. The respiratory ratio was calculated based on the Diagnostic Symptom Questionnaire (DSQ) scores recorded in a diary in the days preceding the CO₂ challenge. The scores of the respiratory symptoms were summed and divided by the total DSQ score. RESULTS The respiratory ratio was correlated with CO₂ sensitivity, and there was a non-statistically significant trend towards a correlation with a family history of PD. CONCLUSIONS The positive correlation between the respiratory ratio and the anxiety elicited by the CO₂ inhalation indicates that the intensity of respiratory symptoms may be proportional to the sensitivity to carbon dioxide.