Pulmonary and functional hallmarks after SARS-CoV-2 infection across three WHO severity level-groups: an observational study.

Background: The manifestations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection range from flu-like symptoms to severe lung disease. The consequences of this inflammatory process impact overall function, which can be detected through both short- to long-term assessments. This study aimed to assess the pulmonary functional and structural characteristics of post-SARS-CoV-2 infection in patients with mild/moderate, severe, and critical clinical presentations.

Methods: An observational, analytical, and cross-sectional study was conducted between 2020 and 2022, including participants with a confirmed diagnosis of coronavirus disease (COVID)-19, with mild/moderate (G1), severe (G2), and critical (G3) clinical presentations, all evaluated at least 3 months after acute infection. Spirometry, impulse oscillometry, fractional exhaled nitric oxide (FeNO), chest computed tomography, the 6-min walk test (6MWT), hand grip strength, maximum inspiratory pressure, and maximum expiratory pressure were assessed.

Results: We enrolled 210 participants aged 18-70 years, 32.6% of whom were male, with older age observed in G3. The participants were grouped as follows: G1 (42.3%), G2 (25.7%), and G3 (31.9%). Percentage of predicted X5 differed between G1 and G2, being higher in G1. The percentage of predicted forced vital capacity (FVC) according to the Global Lung Function Initiative and its z-score were higher in G1. The FVC by Pereira was lower in G3 compared to G1. The percentage of predicted forced expiratory volume in 1 s (FEV) by Pereira was also lower in G3. The Tiffeneau (FEV/FVC) index was different among groups, increasing with disease severity. The percentage of predicted forced expiratory flow rate at 25-75% (FEF) of the FVC and FeNO were both higher in G2 than G1. Chest computed tomography revealed the presence of interstitial abnormalities, associated with disease severity. The respiratory muscle strength evaluation showed an association between higher maximum expiratory pressure values in G3 compared to G1, but no association with maximum inspiratory pressure was observed. The 6MWT distance covered decreased with increasing severity, with a lower percentage of predicted values in G3 compared to G1. The right-hand grip strength was also lower in G3 compared to G1.

Conclusion: Alterations in pulmonary and functional markers were observed in post-COVID-19 evaluations, increasing with disease severity, as seen in G2 and G3. These findings highlight the complexity of post-COVID-19 functional assessments, given the long-term pulmonary sequelae and the consequent impairment of functional capacity.