Functional changes in the respiratory system after COVID-19-associated lung injury

Since the beginning of the pandemic, COVID-19 (COronaVIrus Disease-2019) has been viewed as a respiratory disease with characteristic symptoms including cough, shortness of breath, and difficulty breathing. However, some patients still have respiratory complaints and post-inflammatory changes in the lung tissue according to high-resolution computed tomography of the chest organs (CT scan) even after discharge from the hospital.The aim. To assess the functional changes in the respiratory system in patients who had COVID-19-associated lung injury using a comprehensive testing of the respiratory function (spirometry, body plethysmography and diffusion test) in the first 6 months after discharge from the hospital.Methods. The study included 434 patients (252 men and 182 women, aged 20 to 79 years), who were divided into 3 groups depending on the time interval between discharge from the hospital and the respiratory function test: Group 1 – 15 – 45 days; Group 2 – 46 – 93 days; Group 3 – 94 – 183 days. All patients underwent a comprehensive testing of respiratory function.Results. The average pulmonary ventilation indicators remained within the normal range both in the general group and in separate groups. A decrease in DLCO was found in most patients: in 53% of people in the general group, in 54, 54 and 51% of cases in Groups 1, 2 and 3, respectively. Restrictive ventilation disorders (reduction of TLC below the lower limit of normal (LLN)) were detected in 29 % of people in the general group, 33, 27 and 26% in Groups 1, 2 and 3, respectively. Obstructive ventilation disorders (decrease in FEV1/FVC below LLN) were detected in 2 % in the general group, and in 3, 1 and 1% in groups 1, 2 and 3, respectively. Statistically significant correlations were found between the maximum volume of lung tissue damage in the acute period of COVID-19, the age of the patients, and the respiratory function indicators.Conclusion. The pulmonary ventilation indicators normalized within 6 months after COVID-19, while a decrease in lung diffusion capacity persisted in most patients and required further active follow-up.