Since studies about clinical status after COVID-19 are scarce, we conducted a cross sectional study with assessment of residual symptoms, lung function and chest CT. Materials and Methods: During an outpatient follow-up visit, chest CT, pulmonary function and COVID-19 related symptoms were assessed approximately 10 weeks after diagnosis. Demographics, baseline (time of diagnosis) CT score and blood results were collected from patient files. Association between lung function and clinical characteristics (baseline), blood markers (baseline), chest CT (baseline and follow-up) and symptom score (followup) was analysed. Mann-Whitney U tests and Chi squared tests were used for statistical comparison between subgroups with and without restriction. Results and discussion: Two hundred-twenty subjects were evaluated at a median follow-up of 74±12 (SD) days. Median symptom and median CT score at follow-up were 1(IQR=0-2) and 2(IQR=0-6) respectively. Forty-six percent of patients had normal lung function, while TLC and TLCO below the lower limit of normal were observed in 38% and 22% of subjects respectively. This restrictive pulmonary impairment was associated with length of hospital stay (8 vs 6 days; p=0.003), admission to the intensive care unit (27% vs 13%;p=0.009), and invasive mechanical ventilation (10% vs 0.7%;p=0.001), but not with symptom score or CT score at baseline and follow-up. Conclusions: Fifty-four percent of COVID-19 survivors had abnormal lung function 10 weeks after diagnosis. Restriction was the most prevalent pulmonary function, with the more critically ill patients being more prone to this condition. Yet, restriction could not be linked with abnormal imaging results or residual symptoms.

We showed combined imaging experiments and CFD simulations to systematically study aerosol deposition patterns in human airways down to generation 5, where particle deposition could be spatially linked to the airway geometry. As particles are negotiating an increasing number of airways in subsequent branching generations, CFD predicts marked deviations of aerosol distribution with respect to ventilation distribution, even in the normal human lung.

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Introduction Most post COVID-19 follow-up studies are limited to a follow-up of 3 months. Whether a favorable evolution in lung function and/or radiological abnormalities is to be expected beyond 3 months is uncertain. Materials and methods We conducted a real-life follow-up study assessing the evolution in lung function, chest CT and ventilation distribution between 10 weeks and 6 months after diagnosis of COVID-19 pneumonia. Results and discussion: Seventy-nine patients were assessed at 6 months of whom 63 had chest CT at both follow-up visits and 46 had multiple breath washout testing to obtain lung clearance index (LCI). The study group was divided into a restrictive (n=39) and a non-restrictive subgroup (n=40) based on TLC z-score. Restriction was associated with a history of intubation, neuromuscular blockade use and critical illness polyneuropathy. Restriction significantly improved over time, but was not resolved by 6 months (median TLC z-score of -2.2 [IQR: -2.7; -1.5] at 6 months versus -2.7 [IQR: -3.1; -2.1] at 10 weeks). LCI did not evolve between both follow-up visits. Symptoms and chest CT score improved irrespective of restriction. Conclusion We observed a disconnect between the improvement of COVID-19 related symptoms, chest CT lesions, and corresponding lung function. While CT imaging is almost normalized at 6 months, a further reduction of pulmonary restriction may be hoped for beyond 6 months in those patients showing restriction at their first follow-up visit.

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