An Isoflow-Volume Technique for Assessing Airway Dynamics in Children and Adults

Abstract

Background: We propose a new approach to the measurement of small airway function as an alternative to recordings of maximal expiratory flow-volume (MEFV) curves. Objectives: A newly developed technique to record isoflow-volume (IFV) curves to be tested against maximal respiratory flow curves. Methods: An isoflow whistle (IFW; Iflopen^®) measures the length of a constant expiration after full inspiration. The note of the whistle enables a subject to generate an even expiration, and the isoflow maintenance times at 1 l·s^–1 (IFMT₁) and 2 l·s^–1 (IFMT₂) are recorded. The accuracy and reproducibility of the IFV technique were evaluated in 17 healthy adults (age 17–55 years) and in 14 asthmatic children (age 6–14 years). Comparisons with standard lung function parameters, such as forced expiratory volume in 1 s (FEV₁), maximal expiratory flow at 50% (MEF₅₀) and 25% (MEF₂₅) vital capacity and peak expiratory flow (PEF), obtained with a Wright^® Peakflow Meter were undertaken in 102 healthy (aged 8–14 years) and 101 asthmatic children (aged 6–17 years). A bronchial challenge test was performed in 13 asthmatic children. Results: The expired volume measured by the IFW showed an acceptable agreement with that of a pneumotachograph (mean error of 4.32% for IFMT₁ and 5.93% for IFMT₂). In healthy and in asthmatic children, the correlations between FEV₁ and IFMT₁ or IFMT₂ (r = 0.92 and 0.94, respectively) were found to be greater than that between FEV₁ and PEF (r = 0.68). During bronchial challenge tests in 13 asthmatic children, the FEV₁ decreased to 69% of baseline and IFMT₁ to 58% of baseline. Conclusions: The IFV technique accurately measured airway obstruction and closely followed changes in standard parameters of the MEFV curve.