Publication date: Jun 10, 2025

Few studies have examined post-COVID-19 sequelae in children, particularly regarding cardiopulmonary capacity. Longitudinal data are especially scarce. This study aimed to retest pediatric patients previously assessed in a cross-sectional design. In this longitudinal study, children meeting post-COVID-19 criteria and an age- and sex-matched control group underwent cardiopulmonary exercise testing at baseline and after 6 months. Thirteen of 20 post-COVID-19 children (mean age: 13. 6 +/- 2. 6 years, 48% female) and 23 of 28 controls (mean age: 11. 9 +/- 3. 1 years, 62% female) completed follow-up testing. All participants completed a maximal treadmill test. No significant differences were found in peak oxygen uptake ( 39. 5 +/- 11. 0 ml/kg/min vs. 45. 5 +/- 8. 4 ml/kg/min; p = 0. 101). Over 6 months, cardiopulmonary performance improved significantly across all subjects. Subgroup analysis showed improvements in both groups, although changes were not statistically significant. Oxygen pulse also proved to be significantly higher and the half-time recovery of proved to be significantly longer after 6 months which was true for the overall group but not for the subgroups. This is the first longitudinal study to reassess cardiopulmonary capacity in children with post-COVID-19. The initially reduced normalized, and all children showed improved cardiopulmonary capacity after 6 months. The primary improvement was observed in the O pulse, a surrogate marker of stroke volume and, by extension, cardiac output. This finding suggests an enhancement in cardiovascular performance, reflecting improved central hemodynamic in all children 6 months after the pandemic. Deconditioning thus remains a plausible cause for the post-COVID-19 symptoms. ClinicalTrials. gov Identifier: NCT05445531. • Children with post-COVID-19 (PASC) may exhibit reduced cardiopulmonary function (V̇O2 peak). Fatigue and exercise intolerance are common but poorly understood and objectified. • Previous studies have provided valuable cross-sectional insights but have yet to include longitudinal follow-up data. • First longitudinal CPET-based study reassessing children with PASC after 6 months. • Cardiopulmonary performance, including V̇O2 peak and O2 pulse, improved significantly over time, probably due to reversible deconditioning rather than organ damage.

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