Pulmonary function 3-6 months after acute COVID-19: A systematic review and multicentre cohort study.

Aims: To describe pulmonary function 3-6 months following acute COVID-19, to evaluate potential predictors of decreased pulmonary function and to review literature for the effect of COVID-19 on pulmonary function. Materials and methods: A systematic review and cohort study were conducted. Within the P4O2 COVID-19 cohort, 95 patients aged 40-65 years were recruited from outpatient post-COVID-19 clinics in five Dutch hospitals between May 2021-September 2022. At 3-6 months post COVID-19, medical records data and biological samples were collected and questionnaires were administered. In addition, pulmonary function tests (PFTs), including spirometry and transfer factor, were performed. To identify factors associated with PFTs, linear regression analyses were conducted, adjusted for covariates. Results: In PFTs (n = 90), mean ± SD % of predicted was 89.7 ± 18.2 for forced vital capacity (FVC) and 79.8 ± 20.0 for transfer factor for carbon monoxide (DLCO). FVC was <LLN in 24.4%, and DLCO was <LLN in 40.2% of patients. Univariable analyses showed that higher age, severe acute infection, pulmonary embolism during acute infection, and male sex were associated with lower DLCO. Multivariable analysis showed that age (adjusted difference [95%CI] = -0.07 [-0.13,-0.02] per one year increase) and severe acute infection (-0.80 [-1.54,-0.05]) were independently associated with a decreased DLCO. In literature we found days on oxygen supplementation, female sex, longer length of hospital stay, obesity and higher age to be associated with lower DLCO after COVID-19. Conclusion: A low DLCO 3-6 months following acute COVID-19 was observed more often than a low FVC, both in the P4O2 COVID-19 study and the literature review.