Introduction
COVID-19 has infected over 70 million people since it appeared just over a year ago in December 2019, and this number continues to grow daily. The clinical course ranges from asymptomatic or mild (loss of smell and taste, anorexia, muscle and joint pain, fatigue) to severe, particularly in older patients, patients with comorbidities such as hypertension, diabetes mellitus, or chronic kidney disease, pregnant women, and immunocompromised patients 1.
Acute respiratory failure and macrophage activation syndrome are the most common severe clinical manifestations of COVID-19. Both are characterized by overproduction of proinflammatory cytokines which can lead to endothelial dysfunction in several vital organs, especially the lungs. Recent studies have shown that COVID-19 causes extensive alveolar epithelial destruction, capillary damage/bleeding, hyaline membrane formation, alveolar septal fibrous proliferation, and pulmonary consolidation. Pulmonary function tests have been the most concrete indicator of this lung damage 2,3.
Studies involving 2-year follow-up of pulmonary function values in patients with severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) demonstrated that the main pathology was reduced diffusion capacity (15.5–43.6%), followed by decreased total lung capacity (5.2–10.9%) 4,5. It was also reported that pulmonary function tests performed at discharge revealed no significant difference in forced expiratory volume in the first second (FEV1) or forced vital capacity (FVC) values between COVID-19 patients with mild, moderate, and severe pneumonia, whereas diffusion capacity decreased in correlation with disease severity. Pulmonary function testing is often not recommended for patients with active COVID-19 infection in order to prevent excessive transmission6. However, despite clinical improvement in this patient group, ongoing hypoxia and persistent radiological findings cause considerable difficulty in predicting the extent of improvement in pulmonary function.
The aim of this study was to determine the relationship between pulmonary function tests and laboratory parameters for the demonstration of pulmonary dysfunction, which is an important problem for COVID-19 patients.