Mild hyperventilation with preserved exercise capacity in patients with self-reported long-term dyspnea after COVID-19—a prospective cohort study in a primary healthcare setting

Background Post COVID-19 condition remains a complex and challenging issue, with diverse manifestations, despite accumulating research and clinical experience. Dyspnea is one of the most common symptoms reported in post COVID-19 condition. Cardiopulmonary exercise testing (CPET) offers a cohesive assessment of dyspnea and exercise limitations. The Nijmegen questionnaire is a form for assessment of dysfunctional breathing.Aim The aim was to explore relationships between self-reported post COVID-19 respiratory symptoms, assessed by Nijmegen questionnaire, and the results of a 6-minute walk test (6MWT) and CPET, in patients with mild primary infection of COVID-19, managed within primary healthcare.Methods A total of 15 participants with long-term dyspnea after a mild COVID-19 infection were prospectively included at primary healthcare facilities between July 2021 and April 2022. At inclusion, all subjects performed a 6MWT and answered the Nijmegen questionnaire. All subjects underwent CPET within 4 months of study inclusion. We estimated correlations between Nijmegen score (both total score and a subset of the questionnaire focusing on respiratory symptoms), and the 6MWT and CPET derived variables, respectively.Results Nijmegen scores (both total and particularly a respiratory subset) were inversely correlated to 6MWT walking distance, but not to spirometric parameters. Subjects with more self-reported symptoms had higher end-tidal O2 and lower end-tidal CO2, indicating mild hyperventilation. Nijmegen scores also correlated with CPET variables reflecting breathing pattern.Conclusions Nijmegen score was associated with CPET variables and walking distance at 6MWT. Post COVID-19 condition could be associated with mild hyperventilation, also in subjects without overt dysfunctional breathing pattern.