The outcome of pulmonary function tests and high-resolution computed tomography of chest in post-coronavirus disease 2019-confirmed cases after 3 months of recovery
Authors: Mostafa Yasser , Khalil Mahmoud M.M. , Hegazy Sherif N.A. , Daif Marwa S. 
Published: February 2023

Background
Coronavirus disease (COVID-19) is a recently prevalent infectious disease that is caused by a virus from the coronavirus family and causes acute respiratory syndrome. It is a pandemic catastrophe that has affected more than 60 million people around the world and has caused about 1.5 million deaths, as reported by the WHO. This disease affects the respiratory system and leads to different forms of symptoms and signs. Pneumonia is a common cause for hospitalization, with most patients treated in hospital wards and others requiring ICU. Although the number of complete recoveries from COVID-19 has increased, there is still concern about complications associated with the disease that appear after recovery. The studies that have looked at past types and other forms of coronavirus epidemics, such as SARS have shown that some cases had respiratory complications from the infection after being full recovered, as 36 and 30% of the entire study population had clinical and high-resolution computed tomography (HRCT) changes at 3 and 6 months after recovery, respectively. Mostly, the abnormalities seen in pulmonary function test (PFT) results are sequelae of diffusion capacity defect. In recovered cases of Middle East respiratory syndrome, 36% of patients showed HRCT sequelae at follow-up of 6 weeks, because of fibrosis. Data on COVID-19 indicate that prolonged disease and persistent symptoms show post-PFT affection and follow-up radiographic changes after recovery from COVID-19 as interstitial pulmonary changes and a degree of pulmonary vasculopathy. In recovered cases of COVID-19, capacity of diffusion is the commonest defect in lung function, followed by the restrictive pattern defects on spirometry; both are related to the degree of severity of pneumonic COVID-19. PFTs (involving spirometry as well as diffusion capacity) are considered as routine follow-up examinations for some of the recovered cases, especially severe cases. Rehabilitation programs of the respiratory system are an option strategy that might be considered. This study aims to show changes in pulmonary function and HRCT of chest in post-COVID-19-infected patients to detect long-term effects on the lungs after 3 months as obstructive or restrictive, or both, lung diseases.

Patients and methods
The study was conducted on 100 confirmed PCR-positive COVID-19 cases that were admitted to Ain Shams University Isolation Hospitals, and the follow-up was performed in the outpatient clinic. PCR samples (Combined nasopharyngeal and oropharyngeal swab) were taken after 3 months from discharge of patients above the age of 18 years who become negative with clinical improvement. PFT [spirometry and diffusion for carbon monoxide (DLCO)] and chest HRCT were done. All patients’ clinical data were recorded, and CT chest imaging data of these patients were correlated with the clinical data.

Results
A total of 100 patients were included in this study, where males represented 58% and female represented 42%. The mean±SD age of cases in this study was 45.05 ± 11.80 years and ranged from 20 to 79 years. CT chest severity score (SS) of abnormality in COVID-19-infectedd patients based on HRCT chest findings before and after 3 months from treatment showed a highly significant correlation (P=0.000). The results of PFT in the studied group after 3 months of discharge showed restrictive pattern in 14.9%, obstructive pattern in 17.8%, and both obstructive and restrictive patterns in 5.9% of the total number of cases. There was a significant correlation between DLCO abnormality findings and age of studied group (P=0.032), a significant correlation between abnormality findings on PFT and HRCT chest SS after discharge of the studied group (P<0.001). There was a significant correlation between abnormality findings of DLCO and HRCT chest SS after 3 months of the studied group (P=0.000) and before treatment (P=0.001), whereas there was no significant correlation between other findings of PFT and HRCT chest SS after 3 months and before. There was a significant correlation between HRCT chest SS of the studied group and their age after (P=0.003) and before treatment (P=0.000). This cohort study provided the long-term dynamic sequelae and variations of lung function after hospital discharge.

Conclusion
DLCO-predicted value detected at 3 months is the most important factor associated with severe respiratory COVID-19, which is identified as the cause of impairment of any ordinary basic activity of patients in the stage of postrecovery from COVID-19. The radiological chest findings must be analyzed in conjunction with other functional parameters to provide accurate assessment of the disease. These findings highlight the significance of a comprehensive follow-up after severe and critical COVID-19 infection, with appropriate management of pulmonary consequences. Patients after discharge and on follow-up in outpatient clinics in the post-COVID-19 stage should be strictly followed up with PFTs. Further studies with longer follow-up periods might be needed.