Fixed airflow obstruction (FAO)
Fixed airflow obstruction was defined as the ratio of the forced expiratory volume in the first second to the forced vital capacity (FEV1/FVC) being persistently below the lower limit of normal range (LLN), according to reference equations, even after the use of a postbronchodilator (BD) (3). For adolescents with FEV1/FVC ratios lower than the LLN persistently on the two consecutive visits, oral corticosteroids (OC) were prescribed for seven consecutive days (the OC dose ranged from 1 to 2 milligrams (mg) per kg of body weight, up to a maximum dose of 40 mg/day) (1). After seven days of OC treatment, the adolescents returned to the hospital and underwent a new spirometry test. The presence of FAO was noted if the FEV1/FVC ratio remained lower than the LLN (3).