End-tidal CO2 levels in rest, during and after respiratory challenges: a comparison between patients with medically unexplained physical symptoms, panic disorder patients and healthy controls

Abstract

Background. Although a dysregulated autonomic stress physiology is hypothesized to play a crucial role in the etiology and perpetuation of Medically Unexplained Physical Symptoms (MUPS), the respiratory system tends to be overlooked in current available literature. Objectives. The aim of our study was 1) to examine end-tidal CO2 concentration (PetCO2) in patients experiencing MUPS in daily life, diagnosed with overstrain, burnout, and functional somatic syndromes (FSS), compared to patients with panic disorder (PD) and healthy controls (HC) and 2) to explore the triangular relationship between psychological variables (maladaptive perfectionism, experiential avoidance, and exposure to traumatic experiences), the stress response system, and MUPS. Methods. Three groups of MUPS patients (overstrain [n=35], burnout [n=44] and fibromyalgia/chronic fatigue syndrome (CFS) [n=36]), PD patients (n=36) and HC (n=30) filled out trait questionnaires and went through a baseline measurement of PetCO2 and two respiratory challenges with recovery whilst PetCO2 was continuously monitored by a capnograph. Results. Our data showed respiratory abnormalities in MUPS and PD patients compared to HC, suggesting a transdiagnostic mechanism for both stress and anxiety related disorders. This dysfunction was found to be partially mediated by maladaptive perfectionism, experiential avoidance, and exposure to traumatic experiences. Furthermore, we found preliminary evidence for a chronicity and severity-based MUPS-continuum underlying 1) overstrain, 2) burnout, and 3) fibromyalgia/CFS in ascending order, characterized by an increasing depletion of the stress-response system. Conclusion. Our results are indicative for dysfunctional activity of the autonomic nervous system, including the respiratory system, to be an underlying working mechanism of MUPS.