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 (FEF_25-75) 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 FEF_25-75 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, FEF_25-75 percent predicted, and FEV₁/FVC percent predicted were (1) positively correlated with log₂ methacholine PC₂₀, (2) positively correlated with morning and evening peak expiratory flow percent predicted, and (3) negatively correlated with log₁₀ fraction of exhaled nitric oxide and bronchodilator responsiveness. Pearson partial correlations and canonical correlations indicated that FEF_25-75 percent predicted was better correlated with bronchodilator responsiveness and log₂ methacholine PC₂₀ than were FEV₁ percent predicted or FEV₁/FVC percent predicted. In the ROC curve analysis, FEF_25-75 at 65% of predicted value had a 90% sensitivity and a 67% specificity for detecting a 20% increase in FEV₁ after albuterol inhalation. Conclusion: FEF_25-75 percent predicted was well correlated with bronchodilator responsiveness in asthmatic children with normal FEV₁. FEF_25-75 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. [Copyright &y& Elsevier]