Background: Patients affected by COVID-19 are known to have persistent pulmonary function impairment, but the extent of this and its associated factors are still unclear.

Methods: We conducted an observational study of monitoring the pulmonary function in 140 post-COVID patients, assessed by spirometry and single-breath carbon monoxide uptake in the lung. Variables of interest were: forced vital capacity (FVC) and diffusing capacity of lungs for carbon monoxide (DLCO), expressed as mean ± standard deviation (% from predicted).

Results: Patients were categorized by the extension of lung lesions evaluated using computer tomography: 50 (37.1%) had severe damage, 22 (15.7%) had moderate damage, 36 (25.7%) had mild damage, and 30 (21.4%) had no damage. Mean values of FVC and DLCO were 92±18.7, respectively 72±20.9, but both analyzed parameters were more affected in severe forms of disease: 83±17.5 vs 92±13.5 vs 95.7±20 vs 102.1±16.6 for FVC (p=0.001), and 65±21.8 vs 76.7±20.2 vs 77.4±19 vs 79±17.7 for DLCO (p=0.009), with significant improvement seen at reevaluation. However, patients that developed fibrotic lesions after COVID had a significant impairment for DLCO (45±11 vs 71.5±19, p=0.004). Moreover, we found a difference between patients with known interstitial lung disease (ILD) and patients without ILD in terms of FVC (82±15.5 vs 94±18.8, P=0.007) and DLCO (57±16.6 vs 76±20.04, p<0.001).

Conclusions: The study highlights a significant impact on lung function in post-COVID patients for extention of pulmonary lesions, the coexistence of previous pulmonary lesions and the development of fibrotic lesions.