The Utility of Forced Expiratory Flow between 25% and 75% of Vital Capacity in Predicting Childhood Asthma Morbidity and Severity

Abstract

Objectives. The forced expiratory volume in 1 second (FEV₁) 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 FEV₁, and to determine whether bronchodilator responsiveness (BDR) as defined by FEF_25–75 identifies more childhood asthmatics than does BDR defined by FEV₁. 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, FEV₁/forced vital capacity (FVC), and FEF_25–75; Group B (n = 36) had solely a diminished FEV₁/FVC; and Group C (n = 37) had a normal FEV₁, low FEV₁/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 FEV₁. Conclusions. A low FEF_25–75 in the setting of a normal FEV₁ 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 FEV₁.

• bronchodilator responsiveness
• childhood asthma
• FEF_25–75
• spirometry

Acknowledgments

The author Wanda Phipatanakul has received funding from NIH/NIAID R-01grant AI-073964, R01AI073964-02S1, and NIH/NHLBI grant 1U10HL098102.

Declaration of Interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.