Airway remodeling in COVID-19 lungs

Besides parenchymal changes that have been described extensively in COVID-19, bronchiectasis is also reported but detailed characterization of airway changes is lacking. Hence, we aimed to quantify the number of visible airways and their diameters in end-stage COVID-19 lungs. Explanted right lungs, obtained after lung transplantation (n=2) or autopsy (n=1) (65.3±26.7 days after symptom onset), were inflated to total lung capacity, frozen and scanned with whole lung microCT (155 µm). Airways were segmented using Mimics Innovation Suite (Materialise, Belgium) and airway count and diameter were assessed using Neuronstudio. Three discarded donor lungs were used as controls. Number of visible airways increased in COVID-19 lungs compared to controls (fig.1a) potentially caused by airway remodeling and bronchiectasis (fig.1b, red arrows) due to fibrotic rearrangement (fig. 1b). Small airway count (diameter 0-2 mm) in generation (G) 1-11 was lower in COVID-19 patients compared to controls, with a shift of small airways from lower generations (G1-11) to higher generations (G12-27) in COVID-19 patients. Simultaneously, airways with a diameter > 2 mm were increased in all generations in COVID-19 (present until G21 compared to G13 in controls). This study shows that COVID-19 causes a remodeling of the (small) airways, leading to an increase of visible airways and diameter of large and small airways, similar to that seen in idiopathic pulmonary fibrosis due to traction bronchiectasis.