Carbon dioxide induced panic attack in panic disorder in Japan.

1. The authors investigated the psychological and biochemical factors associated with challenge by 5% CO2-95% O2 inhalation for 20 min. While fifteen healthy people were used as control, thirteen cases who were diagnosed by DSM-III-R as suffering from panic disorder were used as subjects. CO2 inhalation induced panic in 38% of the panic disorder patients, but did not cause panic in any of the control cases (0%). 2. Acute panic inventory (API), heart rate and breathing rate of the panic group increased significantly after CO2 inhalation compared with the values in the control and non-panic groups. 3. Heart rates and systolic blood pressure were significantly higher those in the panic disorder and non-panic groups than in the control group prior to CO2 inhalation. The cortisol values in the panic and non-panic groups also were significantly higher than those in the control group before and after CO2 inhalation. 4. These results suggest elevated activity of the sympathetic nervous system during panic. The significantly higher heart rate, systolic blood pressure and cortisol values of the panic disorder subjects relative to the control before CO2 inhalation may have been due to circumstantial factors. The present findings of convincing evidence for behavioral, physiological, and biochemical hypersensitivity to CO2 in patients with panic disorders are consistent with a model of interoceptive conditioning in these patients.