Panic disorder subtypes: Differential responses to CO2 challenge

Objective: The purpose of this study was to investigate the possibility of a differential sensitivity to CO2 in patients diagnosed with panic disorder subtypes that were defined by the presence of prominent respiratory sympto ms. Method: The authors used a 35% CO2 and 65% O-2 mixture as a challenge a gent. Fifty-one unmedicated subjects with DSM-III-R panic disorder, who wer e divided into respiratory (N=28) and nonrespiratory (N=23) subtypes by the ir symptom profiles, underwent a CO2 challenge procedure. Patients in the t wo groups were compared with regard to physiological and psychological meas ures, pulmonary function tests, panic rates, and smoking habits. Results: T he patients in the respiratory group were significantly more sensitive to C O2 than were the patients in the nonrespiratory group. The respiratory grou p also had higher scores on the Panic and Agoraphobia Scale and had a longe r duration of illness; both of these factors can be indicators of illness s everity. In addition, the respiratory group's higher cigarette consumption (mean=12.46 package-years, SD=2.49) may have been a contributory factor not only for illness severity but also for the pathogenesis of panic disorder. Conclusions: The CO2 challenge procedure appears to be a good dissection t ool in the understanding of different subtypes of panic disorder. Moreover, there may be a more specific association with prominent respiratory sympto m subtype and CO2 hypersensitivity.