# Impact of COVID-19 on Respiratory Function: A Post-Recovery Comparative Assessment

## TL;DR

This study examines how respiratory function changes over time in people recovering from COVID-19, finding that some lung function improvements occur but certain issues persist.

## Contribution

The study identifies persistent respiratory impairments in post-COVID-19 patients and highlights the need for long-term monitoring and personalized care.

## Key findings

- Progressive improvement in FVC up to 9–18 months post-infection was observed, while FEV1 remained stable.
- Diffusion abnormalities (DLCO and KCO) persisted beyond 12 months, indicating lasting alveolar-capillary impairment.
- TLC, AV, and KCO were the most discriminative parameters for residual dysfunction in post-COVID-19 patients.

## Abstract

Background: Post-COVID-19 syndrome (PCS) is defined as the persistence or development of new symptoms 3 months after the initial infection with the SARS-CoV-2 virus, these clinical aspects being most often associated with functional respiratory changes, as well as imagistic modifications. This study aimed to evaluate longitudinal changes in pulmonary function among patients with PCS, in relation to the severity of the acute COVID-19 episode and the time elapsed since infection. Methods: A retrospective, observational study was conducted at the Clinical Hospital of Pulmonary Diseases Iași, Romania, between January 2021 and December 2022, including 97 adult patients with confirmed PCS. Demographic, clinical, and functional data were collected from medical records. Pulmonary function tests (PFTs) were performed according to ATS/ERS standards, assessing Forced Vital Capacity (FVC), Forced Expiratory Volume in the First Second (FEV1), FEV1/FVC ratio (Tiffeneau Index), Maximal Expiratory Flow at 50% and 25% of FVC (MEF50, MEF25), Diffusing Capacity of the Lung for Carbon Monoxide (adjusted for haemoglobin) (DLCO), Carbon Monoxide Transfer Coefficient (KCO), Alveolar Volume (AV), Total Lung Capacity (TLC) and Residual Volume (RV). Patients were grouped by time elapsed since infection (1–3, 4–7, 9–12, and up to 22 months). Statistical analyses included the Mann–Whitney U test, Spearman’s correlation, ROC curve analysis, and Principal Component Analysis (PCA). Results: A progressive improvement in FVC was observed up to 9–18 months post-infection (p < 0.05), while FEV1 remained stable, suggesting a predominantly restrictive ventilatory pattern. Patients with moderate acute COVID-19 presented significantly lower FVC%, FEV1%, DLCO%, and KCO% values compared with those with mild disease (p < 0.05). Diffusion abnormalities (DLCO and KCO) persisted beyond 12 months, indicating lasting alveolar-capillary impairment. ROC analysis identified TLC (AUC = 0.857), AV (AUC = 0.855), and KCO (AUC = 0.805) as the most discriminative parameters for residual dysfunction. PCA revealed three major functional domains—airflow limitation, diffusion capacity, and lung volume—explaining up to 70% of total variance. Conclusions: We are facing the emergence of a new phenomenon, namely a secondary post-COVID-19 pandemic of patients confronting with persistent post-COVID-19 symptoms who present with functional respiratory changes and who require careful monitoring in dynamics, personalized treatments and a multidisciplinary approach.