Characteristics of sighing in panic disorder

Background: Sighs, breaths with larger tidal volumes than surrounding breaths, have been reported as being more frequent in patients with anxiety disorders. Methods: Sixteen patients with panic disorder, 15 with generalized anxiety disorder, and 19 normal control subjects were asked to sit quietly for 30 min. Respiratory volumes and timing were recorded with inductive plethysmography and expired pCO2, from nasal prongs. Results: Panic disorder patients sighed more and had tonically lower end-tidal pCO2s than control subjects, whereas generalized anxiety disorder patients were intermediate. Sighs defined as >2.0 times the subject mean discriminated groups best. Sigh frequency was more predictive of individual pCO2 levels than was minute volume. Ensemble averaging of respiratory variables for sequences of breaths surrounding sighs showed no evidence that sighs were triggered by increased pCO2 or reduced tidal volume in any group. Sigh breaths were larger in panic disorder patients than in control subjects. After sighs, pCO2 and tidal volume did not return to baseline levels as quickly in panic disorder patients as in control subjects. Conclusions: Hypocapnia in panic disorder patients is related to sigh frequency. In none of the groups was sighing a homeostatic response. Panic disorder patients show less peripheral chemoreflex gain than control subjects, which would maintain low pCO2 levels after sighing.