Caffeine and 35% carbon dioxide challenge tests in panic disorder.

Our aim was to compare the demographic and clinical features of panic disorder (PD) patients with agoraphobia-DSM-IV-who had a panic attack after both an oral caffeine and the 35% carbon dioxide (CO2) challenge tests (responsive group) and compare them with PD patients who did not have a panic attack after both tests (non-responsive group). We examined 83 PD patients submitted to a 35% CO2 test and to an oral caffeine (480 mg) intake within 1 week interval. A panic attack was induced in 51 (61.4%) patients during the CO2 test (chi2=31.67, df=1, p<0.001) and in 38 (45.8%) patients during the caffeine test (chi2=18.28, df=1, p=0.023). All patients who had a panic attack during the caffeine test also had a panic attack during the CO2 test (n=38)-responsive group. The responsive had more (chi2=24.55, df=1, p=0.008) respiratory PD subtype, disorder started earlier (Mann-Whitney, p<0.001) had a higher familial prevalence of PD (chi2=20.34, df=1, p=0.019), less previous alcohol abuse (chi2=23.42, df=1, p<0.001), and had more previous depressive episodes (chi2=27.35, df=1, p<0.001). Our data suggest that there is an association between respiratory PD subtype and hyperreactivity to challenge tests: CO2 and oral caffeine.