The utility of forced expiratory flow between 25% and 75% of vital capacity in predicting childhood asthma morbidity and severity

Objectives. The forced expiratory volume in 1 second (FEV ₁) felt to be an objective measure of airway obstruction is often normal in asthmatic children. The forced expiratory flow between 25% and 75% of vital capacity (FEF _25-75) reflects small airway patency and has been found to be reduced in children with asthma. The aim of this study was to determine whether FEF _25-75 is associated with increased childhood asthma severity and morbidity in the setting of a normal FEV ₁, and to determine whether bronchodilator responsiveness (BDR) as defined by FEF _25-75 identifies more childhood asthmatics than does BDR defined by FEV ₁. Methods. The Boston Children's Hospital Pulmonary Function Test database was queried and the most recent spirometry result was retrieved for 744 children diagnosed with asthma between 10 and 18 years of age between October 2000 and October 2010. Electronic medical records in the 1 year prior and the 1 year following the date of spirometry were examined for asthma severity (mild, moderate, or severe) and morbidity outcomes for the three age, race, and gender-matched subgroups: Group A (n = 35) had a normal FEV1, FEV ₁forced vital capacity (FVC), and FEF _25-75; Group B (n = 36) had solely a diminished FEV ₁/FVC; and Group C (n = 37) had a normal FEV ₁, low FEV ₁/FVC, and low FEF _25-75. Morbidity outcomes analyzed included the presence of hospitalization, emergency department visit, intensive care unit admission, asthma exacerbation, and systemic steroid use. Results. Subjects with a low FEF _25-75 (Group C) had nearly 3 times the odds ratio (OR) (OR = 2.8, p < .01) of systemic corticosteroid use and 6 times the OR of asthma exacerbations (OR = 6.3, p > .01) compared with those who had normal spirometry (Group A). Using FEF _25-75 to define BDR identified 53 more subjects with asthma than did using a definition based on FEV ₁ Conclusions. A low FEF _25-75 in the setting of a normal FEV ₁ is associated with increased asthma severity, systemic steroid use, and asthma exacerbations in children. In addition, using the percent change in FEF _25-75 from baseline may be helpful in identifying BDR in asthmatic children with a normal FEV ₁.