ANXIOGENIC EFFECTS OF CO2 AND HYPERVENTILATION IN PATIENTS WITH PANICDISORDER

Objective: Previous studies have indicated that patients with panic di sorder are more likely than normal subjects to have acute panic attack s during inhalation of CO2, but methodological objections have been ra ised. In this study the authors attempted to address three of these me thodological problems by ensuring that raters who assessed whether pan ic attacks occurred were blind to subjects' diagnoses, by randomizing the order of administration of 5% CO2 and hyperventilation, and by cha llenging a greater number of subjects with 7% CO2. Method: Patients wi th panic disorder and normal subjects underwent 20-minute inhalations of 5% CO2 and 7% CO2 and 15 minutes of room-air hyperventilation. Rati ngs of panic/no panic during each condition were made separately by an assessor blind to diagnosis and by the subject. Scores on four panic rating scales were also recorded before and after each intervention. R esults: Room-air hyperventilation caused panic attacks in a small numb er of patients; the difference in panic rate between patients and comp arison subjects was statistically significant by the subjects' but not by the raters' assessment. Panic rates during 5% CO2 and 7% CO2 were significantly greater among the patients by both assessments; the pani c rate was greatest during 7% CO2. Order of administration did not sig nificantly affect panic rates for hyperventilation and 5% CO2. Conclus ions: Panic patients were clearly more sensitive to the anxiogenic eff ects of CO2 than comparison subjects, and CO2 was a more potent anxiog enic stimulus than room-air hyperventilation. Seven percent CO2 discri minated best between patients and comparison subjects and should be th e focus of further research.