RESUMEN
The long-term effects of coronavirus disease 2019 (COVID- 19) pneumonia on the lungs and pulmonary circulation require further characterization. We assessed progression of pathophysiological pulmonary changes during 1 year of follow-up of patients who had been hospitalized because of COVID-19. After discharge, recruited patients had up to four MRI examinations at a median of 6 (n=9), 12 (n=9), 25 (n=7) and 52 (n=3) weeks. Lung MRI examinations included: ultra-short echo time (UTE), dynamic contrastenhanced (DCE) lung perfusion, 129Xe diffusion weighted (DW-MRI), 129Xe ventilation and 129Xe 3D dissolved phase imaging. Nine patients (age 56 +/-9 years;six male) were recruited. Ventilation defect percentage and whole lung coefficient of variation of lung ventilation decreased significantly at 25 weeks (visit 3) compared with visit 1 at 6 weeks (p=0.010 and p=0.048). The UTE imaging indicated no evidence of lung scarring, and DW-MRI indicated normal lung microstructure across all visits. Dissolved phase xenon imaging showed that RBC:TP increased significantly at visits 2 and 3 compared with visit 1 (p=0.048). Median RBC:TP was abnormally low at all visits compared with reference age- and sex-matched data. An individual's RBC:TP was associated significantly and positively with an increase in their pulmonary blood volume (p=0.026). For patients with 52-week data available, one showed a continued improvement in RBC:TP;however, two of the patients maintained a low RBC:TP. In patients recovering from COVID-19, xenon gas transfer improves alongside pulmonary blood volume. Further work is needed to establish the proportion of post-COVID-19 patients who have longer-term impairment in xenon transfer and to correlate changes in lung MRI parameters with symptoms, lung function tests and other imaging modalities. Persistent impairment of xenon transfer might represent a physiological mechanism underlying ongoing symptoms in some patients and might indicate damage to the pulmonary microcirculation.