In addition to deconditioning, persistent low-grade inflammation following acute SARS-CoV-2 infection may contribute to systemic problems, which supports the need for further assessment of cardiopulmonary conditioning. In fact, the impairment of the respiratory system in the acute phase of COVID-19 has the potential to significantly impact functional capacity in patients with post-COVID-19 syndrome (PCS), with dynamic hyperinflation (DH) and reduced ventilatory reserve (RV).

To investigate the dynamic ventilatory responses and their influence on the functional capacity to exercise in these patients.

Between March and October 2022, a cross-sectional study was carried out with 16 patients with PCS aged ≥18 years attended at the Piquet Carneiro Polyclinica, at the State University of Rio de Janeiro. Patients with a history of COVID-19 pneumonia with persistence of respiratory symptoms after 3 months of the acute phase were included. Patients without a previous diagnosis of COVID-19 confirmed by RT-PCR (reverse-transcription polymerase chain reaction) and those who failed to perform the protocol tests were excluded. Patients underwent impulse oscillometry (IOS), spirometry, 6-minute walk test (6MWT) with Spiropalm®-6MWT, and cardiopulmonary exercise test (CPET). A ≥100 ml decrease in inspiratory capacity (IC) during exercise was defined as HD. Ventilatory reserve (VR) indicates how close minute ventilation (VE) approaches maximum voluntary ventilation (MVV) during a given activity and was calculated as the difference between MVV and VEpeak ([MVV-VEpeak]/MVV); VR <30% was considered to be ventilatory limitation on exertion.

Median age and time since diagnosis of COVID-19 were 57 (50–59) years and 98 (93–106) days, respectively. Regarding spirometry, 12.5% and 50% of the participants had an abnormal spirometry and an altered IOS, respectively, and the difference in resistance between 4 Hz and 20 Hz (R4-R20) was detected in 31.2% of the participants. cases. Regarding cardiopulmonary performance during exercise, the median distance in the 6MWT was 83 (78–97) % of predicted, with HD and VR <30% observed in 62.5% and 12.5% of participants, respectively. In CPET, the median peak oxygen consumption (VO2peak) was 19 (14–37) ml/kg/min. There was a significant correlation of the distance covered in the 6MWT with both R4-R20 (rs = -0.499, P = 0.039) and VO2peak (rs = 0.628, P = 0.009).

Our findings suggest that HD and, to a lesser extent, low VR are contributors to poor exercise performance that is associated with peripheral airway disease.

Based on these results, we obtained precise ventilatory and metabolic measurements, which we can consider as an important factor for more assertive exercise prescription during the rehabilitation of these patients. Moreover, these results are promising if we consider that they were obtained with simple, cheap, and portable ventilatory and metabolic measurement systems, easily applicable in real-world environments.