An isoflow-volume technique for assessing airway dynamics in children and adults

Background: We propose a new approach to the measurement of small airway fu nction as an alternative to recordings of maximal expiratory flow-volume (M EFV) curves. Objectives: A newly developed technique to record isoflow-volu me (IFV) curves to be tested against maximal respiratory flow curves. Metho ds: An isoflow whistle (IFW; Iflopen(R)) measures the length of a constant expiration after full inspiration. The note of the whistle enables a subjec t to generate an even expiration, and the isoflow maintenance times at 1 l. s(-1) (FMT1) and 21.s(-1) (IFMT2) are recorded. The accuracy and reproducib ility of the IFV technique were evaluated in 17 healthy adults (age 17-55 y ears) and in 14 asthmatic children (age 6-14 years), Comparisons with stand ard lung function parameters, such as forced expiratory volume in 1 s (FEV1 ), maximal expiratory flow at 50% (MEF50) and 25% (MEF25) vital capacity an d peak expiratory flow (PEF), obtained with a Wright(R) Peakflow Meter were undertaken in 102 healthy (aged 8-14 years) and 101 asthmatic children (ag ed 6-17 years). A bronchial challenge test was performed in 13 asthmatic ch ildren. Results: The expired volume measured by the IFW showed an acceptabl e 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 correlation s between FEV1 and IFMT1 or IFMT2 (r = 0.92 and 0.94, respectively) were fo und to be greater than that between FEV1 and PEF (r = 0.68). During bronchi al challenge tests in 13 asthmatic children, the FEV1 decreased to 69% of b aseline and IFMT1 to 58% of baseline. Conclusions: The IFV technique accura tely measured airway obstruction and closely followed changes in standard p arameters of the MEFV curve. Copyright (C) 2001 S. Karger AG, Basel.