Pulmonary function and dyspnea/suffocation theory of panic

This article presents a brief discussion of pulmonary function and panic attacks in the context of respiratory psychophysiology. Ley's (Behaviour Research and Therapy, 27, 549-554, 1989) earlier dyspnea/suffocation theory of panic is contrasted with Klein's (Archives of General Psychiatry, 50, 306-316, 1993) later false suffocation alarm theory. The distinction between "dyspnea" (the sensation of difficulty in breathing) and "suffocation" (a condition that sometimes gives rise to dyspnea) is emphasized. The brief discussion is followed by a critical comparison of two recent studies on pulmonary function and panic. Asmundson and Stein (Journal of Anxiety Disorders, 8, 63-69, 1994) reported an association between forced expiratory flow rate (a measure of pulmonary function) in panic disorder patients and the severity of panic-related symptoms. They interpreted their findings as support for the dyspnea/suffocation theory of panic since severity of dyspnea is a consequence of pulmonary function. Spinhoven et al. (Behaviour Research and Therapy, 33, 457-460, 1995) failed to replicate the findings of Asmundson and Stein. The present paper provides a critical analysis of the study by Spinhoven et al. and concludes that the failed attempt to replicate may have been a consequence of a flawed methodology (the subjects of the two studies are not comparable on a crucial pulmonary test) and a statistical anomaly (disproportionately small differences between means that exceed predictions based on sampling error). A recommendation is made that future attempts to replicate should pay special care to avoid the possibility of experimenter-demand effects.