Decreased R-R variance in panic disorder patients.

To investigate autonomic function in panic disorder patients (n = 30), we compared postural changes in heart rate and the R-R interval variance in patients and normal controls (n = 20). There was no significant difference in the immediate changes in heart rate upon standing between the groups. R-R variance was significantly decreased during resting supine condition in patients as indicated by the corrected standard deviation of the R-R intervals. The standing R-R variance was significantly lower than that of normal controls as indicated by the corrected standard deviations, the corrected mean consecutive difference and the corrected standard deviation of the mean consecutive difference of the R-R intervals, suggesting an increase in vagal withdrawal in patients, especially upon standing. If this finding is specific to panic disorder patients, it may be a useful peripheral marker for this condition.