Cardiopulmonary Exercise Testing in Patients With Long COVID: Evaluating Functional Capacity and Exercise Limitations.

Background: After COVID-19, some patients present with ongoing symptoms (eg, breathlessness, exercise limitations), even after mild acute infection. Research Question: What is the exercise capacity of patients diagnosed with long COVID and does it change from baseline to 1-year follow-up? Study Design and Methods: This retrospective case series included patients with persistent symptoms after a confirmed diagnosis of COVID-19. Exercise capacity was examined by cardiopulmonary exercise testing (CPET), and parameters related to performance, ventilation, circulation, and gas exchange were compared with predicted values. A subgroup of patients was retested 1 year after baseline, and self-reported physical fitness was assessed at follow-up. Results: In total, 169 patients completed baseline CPET and 41 patients completed 1-year follow-up. Mean maximum workload was 172 W (95% CI, 161-182), with 19% not achieving at least 84% predicted workload. Mean peak oxygen uptake was 24.4 mL/kg/min (95% CI, 23.1-25.7), and 36% had a value below % predicted. Oxygen uptake/workload slope below the normal threshold of 8.4 mL/min/W was observed in 54% of patients. The 1-year follow-up results showed no statistically significant changes in any of the CPET parameters, which correspond to lack of improvement in self-reported physical fitness. Interpretation: Patients with long COVID demonstrated lowered peak oxygen uptake, oxygen uptake/workload slope, and/or ventilatory equivalent for carbon dioxide, but different parameters were lowered in different patients, illustrating a heterogeneous study population. No improvements in any parameters were found at 1-year follow-up.