35% carbon dioxide and breath-holding challenge tests in panic disorder: A comparison with spontaneous panic attacks

Respiration and its control mechanisms may represent an important system involved in abnormal anxiety. Our aim was to compare the demographic and clinical features of patients with panic disorder (PD) with agoraphobia (DSM-IV) who had a panic attack after both the 35% carbon dioxide (CO2) test and the breath-holding test (CPA group), and compare them with PD patients who did not have a panic attack after both tests (NPA group). We examined 76 patients with PD who were administered a 35% CO2 test and a breath-holding test within a 1-week interval. Anxiety scales were applied before and after each test. A 2 panic attack was induced in 50 (65.8%) patients during the CO2 test (chi(2) = 28.44, df = 1, P <.001) and in 40 (52.6%) patients during the breath-holding test (chi(2) = 15.35, df = 1, P=.036). All patients who had a panic attack during the breath-holding test also bad a panic attack during the CO2 test (n = 40; CPA group). Twenty-six (34.2%) patients with PD did not have a panic attack after both respiratory tests (NPA group). The CPA group had more (chi(2) = 21.67, df = 1, P=.011) respiratory PD subtype. In the CPA group, the disorder started earlier (Mann-Whitney, P <.001), had a higher familial prevalence of PD (chi(2) = 18.34, df = 1, P=.028), and had more previous depressive episodes (chi(2) = 23.59, df = 1, P <.001). Our data suggest that there is an association between respiratory PD subtype and the response to respiratory challenge tests: CO2 and breath-holding. The CPA may be confirmed as a subgroup of respiratory PD subtype.