Aberrant respiratory sensitivity to CO 2 as a trait of familial panic disorder

Abstract

Background: According to three earlier studies, well individuals with a family history of panic disorder experience more anxiety following a single breath of 35% CO 2 than do those without such a family history. This study sought to determine whether a heightened sensitivity to CO 2 manifests specifically in respiratory changes. Methods: Subjects were 18–35 years old and had no history of panic attacks and no current DSM-IV diagnosis other than simple or social phobia. Those at high risk for panic disorder (HR-P) ( n = 46) had a first-degree relative with treated panic disorder. Low-risk control subjects (LR-C) ( n = 39) had no first-degree relative with panic disorder. Respiratory measurements were taken continuously while subjects breathed room air through an attached mask for 3 min and, subsequently, while they breathed a 5% CO 2/air mixture for an additional 3 min. Results: HR-P subjects did not differ from control subjects by group means of the principal measure of respiratory response, changes in minute volume (MV) during CO 2 inhalation. However, these values assumed clearly different distributions in the two groups. Fifteen (32.6%) of the HR-P subjects showed a paradoxical decrease in MV while breathing CO 2 and six (13%) displayed a particularly rapid increase in MV. Only one (2.6%) of the control subjects had a negative MV slope and none had a high value [χ 2(1) = 12.3, p < .001, p = .021, Fisher exact test, respectively]. Though the subjects with high MV increases also described greater increases in anxiety after breathing CO 2, a regression analysis indicated that the MV increase was the more important in discriminating high-risk from control subjects. Conclusions: These results suggest that respiratory sensitivity to CO 2 inhalation is operative in the familial transmission of panic disorder.