Lung volume and density assessment over time in hospitalized COVID-19 patients

COVID-19 can have a devastating effect on the lungs, causing acute respiratory distress syndrome (ARDS) which, when not resolved, may progress to pulmonary fibrosis potentially leading to death or transplantation (LTx). We aim to describe the progression of COVID-19 ARDS and fibrosis on lung volume and density over time in vivo and ex vivo using high-resolution computed tomography (HRCT) and µCT. Volume and density of in vivo HRCT scans of 3 COVID-19 patients (P) were assessed over time (P1: 4 scans; P2: 5 scans; P3: 3 scans). After LTx (n=2) or autopsy (n=1) (65.3±26.7 days), explanted right lungs were inflated to total lung capacity, frozen and scanned with whole lung µCT. Lung volumes and density were calculated using Mimics Innovation Suite (Materialise, Belgium). Three discarded donor lungs were used as controls. In vivo lung volume decreased 4 days after symptom onset compared to 1 control and 1 COVID-19 patient before infection, with a steep decline in the first 20 days followed by a more gradual decline. Ex vivo volume of COVID-19 lungs decreased by 60% compared to ex vivo controls (4.2±0.3 vs 1.7±0.5 L; p<0.0058) (fig 1a,b). Volume reduction might be caused by fibroproliferative obliteration of alveolar ducts and spaces as reflected by the increase in density over time (fig 1c). COVID-19 affects lung volume and density rapidly over time, indicating the potential to follow up these parameters to monitor severely ill patients.