Smoking and respiratory irregularity in panic disorder

BACKGROUND: The biological mechanisms underlying the link between smoking and panic attacks are unknown. Smoking might increase the risk of panic by impairing respiratory system function. METHODS: We evaluated the effect of smoking on respiratory irregularity in patients with panic disorder (PD) and healthy comparison subjects and the role of the respiratory disorders in this effect. We applied the Approximate Entropy index (ApEn), a nonlinear measure of irregularity, to study breath-by-breath baseline respiratory patterns in our sample. RESULTS: Both smoker and nonsmoker patients had more irregular respiratory patterns than healthy subjects. Smoker patients showed higher ApEn indices of baseline respiratory rate and tidal volume than nonsmoker patients (R = 5.4, df = 2,55, p < .01), whereas smoking in healthy subjects did not influence the regularity of respiratory patterns. Respiratory disorders did not account for the influence of smoking on respiratory irregularity. Smokers had more severe panic attacks than nonsmokers. CONCLUSIONS: Smoking may impair vulnerable respiratory function and act as disruptive factor on intrinsic baseline respiratory instability in patients with PD, possibly influencing the onset or maintenance of the disorder.