Background: Some hospitalized patients develop severe pulmonary complications with unknown post COVID-19 outcomes.

Objective: To investigate the effect of CT pulmonary abnormality, lung function, and the possibility of small airway dysfunction after COVID-19.

Methods: A prospective analysis was performed on 154 patients with COVID-19. These patients were assessed 3, 6, and 9 months after hospital discharge. HRCT abnormalities were calculated by semiquantitative total CT score (0?25) by adding five lobes scores (0?5) according to the range of lesion involvement. Lung function test (LFT) was measured, including forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), forced expiratory volume in the first second to expiratory vital capacity (FEV1/FVC), maximum mid-expiratory flow rate (MEF 25-75), peak expiratory flow rate (PEF), and total lung capacity (TLC), residual value (RV), carbon monoxide dispersion (DLCO).

Results: There were no differences in LFT parameters between analyzed periods and between both examined groups. The CT abnormalities were the highest after 3 months in both groups and significant correlations with DLCO and MEF 25-50 were observed in severe/critical patients. In the latter observational period, the significant correlations occurred only between TLC, DLCO, MEF- 25-75 in moderate group and FVC and FEV1 in severe/critical group.

Conclusions: The significant association between functional lungs and CT radiographic abnormalities observed at 6 and 9 months, especially in the moderate group, may be related potentially due to the small airway disease and lung parenchyma. This was likely due to the different treatment approaches based on the disease severity.