Delayed lung function testing after COVID-19 to detect persistent lung function abnormalities - The DELTA - COVID-19 lung function study

Background: Coronavirus disease 2019 (COVID-19) has made its presence felt as the worst pandemic witnessed till date in the 21st century. The mortality and morbidity associated with COVID-19 does not end with the acute pneumonia and respiratory failure and consequences extend well into the subsequent weeks to months in a minority. After recovery from severe disease, symptoms, lung function abnormalities and radiological changes are known to persist for varying length of time in a small proportion of patients. Various studies report different incidences of lung function abnormalities post-COVID-19. The present study describes the occurrence, severity, pattern and risk factors for persistent lung function abnormalities post-COVID-19 patients. Aim: The present study was aimed to find out the occurrence of persistent lung function abnormalities in patients hospitalised with COVID-19 at three months of discharge who had normal previous lung function prior to COVID-19. In those with persisting abnormal lung function, the severity, pattern and risk factors for persistent lung function abnormalities were also studied. Methods: The present study was a retrospective study in patients hospitalised with COVID-19 who had radiological evidence of pneumonia at admission. Patients with prior abnormal lung function were excluded from the study. Lung function was analysed with spirometry, 6-min walk test and diffusion capacity between day 85 and 95 of hospital discharge and the occurrence, severity and pattern of impairment was described. Lung function impairment was correlated with baseline characteristics and univariate regression analysis was done to identify risk factors for persisting functional impairment. Results: 39 patients were included in the study. Spirometry at follow up showed a restrictive ventilatory defect in 26 out of 39 patients (64%) and a normal study was noted in 12 patients. One patient had an obstructive ventilatory defect. Diffusion impairment was present in 27 patients and normal transfer factor was seen in 12 patients. The degree of diffusion impairment was mild in 16 patients and moderate in 11 patients. Univariate regression analysis revealed that age, history of systemic hypertension, severe hypoxia at presentation, and extent of lung involvement by CT chest were associated with lung function impairment. Conclusion: Almost two-thirds of patients hospitalised with COVID-19 pneumonia have persistent lung function abnormalities at three months post-discharge. Advanced age, severe disease and medical comorbidities increase the risk of persistent functional abnormalities.