Post-viral syndromes: Lessons learned from cardiopulmonary testing in patients with long COVID

To investigate the exercise capacity in patients with long COVID, with follow-up one year after the baseline test.

Included patients were diagnosed with long COVID at the long COVID clinic, Department of Infectious Diseases, Aarhus University Hospital, Denmark after referral from their general practitioner. Patients underwent cardiopulmonary exercise testing (CPET) at the Department of Physiotherapy and Occupational Therapy. Test parameters such as workload, oxygen uptake (VO₂ peak), ventilation, VO₂/workload slope (VO₂/workload), oxygen pulse (VO₂/pulse), and the ratio of ventilation to carbon dioxide (VE/VCO₂) were compared to normal values. Patients who were tested early in the period were re-tested after one year. The study was conducted from April 2021 to May 2023.

A total of 169 patients completed the baseline CPET, and 41 patients completed the 1-year follow-up. The average maximum workload at baseline was 172 watts (95% CI: 161; 182), and 19% of the patients did not achieve normal workload. The average VO₂ peak was 24.4 (ml/kg/min) (95% CI: 23.1; 25.7), and 36% of the patients had an abnormal low value. The VO₂/workload slope averaged 8.1 ml/min/watt (95% CI: 7.8; 8.4), with 54% of patients below the normal range, indicating that oxygen uptake did not increase proportionally with the work performed. The results at the 1-year follow-up showed no statistically significant changes in any of the CPET parameters, which aligned with lack of improvement in self-reported physical fitness.

A large proportion of patients with long COVID had lower CPET values during exercise compared to normal values. There was no statistically significant improvement after one year, even though patients reported an increased physical activity level.

Research indicates that long COVID share many similarities with sequelae of other viral infections. This suggests that the insights gained from this study may be applicable to other patient populations. In many healthcare settings worldwide, physiotherapists will continue to encounter patients with complex symptoms from post-viral syndrome. Assessing exercise capacity and physical function is a core competency for physiotherapists. The use of CPET offers a distinctive opportunity to evaluate patients during activity, in contrast to most other diagnostic assessments, which typically occur at rest. CPET provides valuable information regarding the specific components of the cardiopulmonary system that may be limiting exercise capacity.