Reference Ranges for Shape Indices of the Flow-Volume Loop of Healthy Children

Background: The concavity of the descending limb of the maximum expiratory flow-volume loop (MEFVL) is the earliest change associated with airflow obstruction in small airways (ATS/ERS Task Force). The shape of the MEFVL changes with age but there are no reference values for shape indices for preschool and school children. Objectives: To define pediatric reference values for spirometric data and 3 shape indices of MEFVL: 2 geometric indices: the beta angle i.e., the angle between the first 1/2 part and the 2nd part of the MEFVL and the forced expiratory flow after 50% of the forced vital capacity (FVC) has been exhaled/peak expiratory flow (FEF50/PEF) ratio; and a ratio that describes relative growth between airway and lung parenchyma, the forced expiratory flow between 25 and 75% of FVC/FVC ratio (FEF25-75/FVC ratio). Methods: Data were obtained from 446 Caucasian children (2.5 to 15-year-old). The lambda, mu, sigma method was applied. Results: References for spirometric parameters and 3 shape indices. The geometric indices decreased with age from 3 years of age (mean b angle was 2158 and FEF50/PEF ratio was 0.82) until 8 years of age (mean b angle was 1918 and FEF50/PEF ratio was 0.60) and then remained constant. The FEF25-75/FVC ratio also decreased with age. Sex was a significant determinant for FEF25-75/FVC ratio predicted values. Conclusions: This study provides standard reference equations for indices ofmid-expiratory flows in children and we suggest using the FEF50/PEF index. (C) 2014 Wiley Periodicals, Inc.