Physical activity and respiratory behavior in daily life of patients with panic disorder and healthy controls

Panic disorder (PD) has been linked in laboratory investigations to respiratory alterations, particularly persistent respiratory variability. However, studies of PD respiratory pattern outside the laboratory are rare, have not controlled for the confounding influence of varying levels of physical activity, and have not addressed whether abnormalities in respiratory pattern vary depending on the intensity of physical activity. Cognitive and biological theories of PD, in fact, predict that respiratory alterations may be particularly pronounced when patients are physically active. This study assessed physical activity and respiratory pattern of 26 PD patients and 26 healthy controls (HC) during two waking periods of daily life (9:00-21:00) one week apart. Respiratory data were stratified for predefined levels of physical activity (inactivity, minimal movement, slow/moderate/fast walking, and running) and analyzed using linear mixed models. Groups did not generally differ in respiratory measures, although PD patients did show elevated variability of absolute levels of tidal volume during minimal movement and slow walking (root mean squared successive differences). Other ways of analyzing tidal volume variability based on relative levels, percentage of sighing, or pooled activity levels did not substantiate this finding. Amount of time spent at different activity levels did not differ between groups, which is at variance with studies linking anticipatory anxiety with motoric agitation, and PD with self-reported avoidance of exercise. In conclusion, results provided little evidence for respiratory abnormalities or central respiratory dysregulation in PD at varying levels of activity, although instability of tidal volume regulation during low activity remains a possibility. Our research approach indicates the usefulness of stratification of real life data on the basis of levels of activity, as well as how ambulatory assessment strategies, complementarily to laboratory studies, may improve understanding of biological and psychological factors contributing to development and maintenance of PD and other anxiety disorders.