Forced expiratory flow between 25% and 75% of vital capacity and FEV1/forced vital capacity ratio in relation to clinical and physiological parameters in asthmatic children with normal FEV1 values

Background: The assumption that the assessment of forced expiratory flow between 25% and 75% of vital capacity (FEF25-75) does not provide additional information in asthmatic children with normal FEV1 percent predicted has not been adequately tested. Objective: We sought to determine whether the measurement of FEF25-75 percent predicted offers advantages over FEV1 percent predicted and FEV1/forced vital capacity (FVC) percent predicted for the evaluation of childhood asthma. Methods: This is a secondary analysis of data from the Pediatric Asthma Controller Trial and the Characterizing the Response to a Leukotriene Receptor Antagonist and Inhaled Corticosteroid trials. Pearson correlation coefficients, Pearson partial correlation coefficients, canonical correlations, and receiver operating characteristic (ROC) curves were constructed. Results: Among 437 children with normal FEV1 percent predicted, FEF25-75 percent predicted, and FEV1/FVC percent predicted were (1) positively correlated with log(2) methacholine PC20, (2) positively correlated with morning and evening peak expiratory flow percent predicted, and (3) negatively correlated with log(10) fraction of exhaled nitric oxide and bronchodilator responsiveness. Pearson partial correlations and canonical correlations indicated that FEF25-75 percent predicted was better correlated with bronchodilator responsiveness and log(2) methacholine PC20 than were FEV1 percent predicted or FEV1/FVC percent predicted. In the ROC curve analysis, FEF25-75 at 65% of predicted value had a 90% sensitivity and a 67% specificity for detecting a 20% increase in FEV1 after albuterol inhalation. Conclusion: FEF25-75 percent predicted was well correlated with bronchodilator responsiveness in asthmatic children with normal FEV1. FEF25-75 percent predicted should be evaluated in clinical studies of asthma in children and might be of use in predicting the presence of clinically relevant reversible airflow obstruction. (J Allergy Clin Immunol 2010;126:527-34.)