After COVID-19, a number of patients report long-lasting dyspnea and chronic fatigue that are not sufficiently explained by peripheral organ dysfunction. Those symptoms can be severely impairing and frequently lead to increased health care consultation. To investigate their cause, we implemented a standard rebreathing paradigm developed at the KU Leuven (Belgium). Here, we describe an improved, simplified experimental setup, its validation and comparison with data obtained previously in healthy participants.
The set-up comprises a capnograph, pneumotachograph and rebreathing bag behind a visual barrier connected to a two-way-valve for single-blinded switching of the source of breathing between room air and rebreathing bag. We compared the course of minute ventilation and end-tidal CO2 concentration of healthy participants from our study (N=25) with data from healthy participants published by Bogaerts et al. (2010) and Van den Houte et al. (2018).
The observed changes in minute ventilation correlated with those reported by Bogaerts (r=0.834; p=0.001) and Van den Houte (r=0.857; p<0.001). The same was true for the course of end-tidal CO2 reported by Bogaerts (r=0.962; p<0.001) and Van den Houte (r=0.966; p=0.001).
In conclusion, our findings validate the improved setup for the rebreathing paradigm. This is essential for its diagnostic use, which is already providing first hints on specific alterations and relationships between breathing and perception in patients with long-lasting symptoms after COVID-19.