End-Tidal CO₂ in Patients with Panic Disorder, Stress-Related or Functional Syndromes, Versus Healthy Controls

A dysregulated autonomic stress physiology is hypothesized to play an important role in the etiology and perpetuation of somatic symptoms that cannot be (fully) explained by an organic disease. The aim of this study was to focus on the role of the respiratory system. We examined end-tidal CO₂ concentration (PetCO₂) in healthy controls (n = 30), patients with panic disorder (n = 36), and patients with stress-related (overstrain; n = 35, burnout; n = 44) or functional syndromes [fibromyalgia (FM) and/or chronic fatigue syndrome (CFS); n = 36]. Participants went through a rest period and a respiratory challenge with recovery, whilst PetCO₂ was continuously monitored by a capnograph. Taken together, our results suggest: (1) an overactive respiratory system to be a possible transdiagnostic underlying factor of overstrain, burnout, and panic disorder, and (2) the presence of a less active respiratory fight-flight response in the more chronic and severe functional syndromes (FM/CFS).