Evaluation of impulse oscillometry during bronchial challenge testing in children.

BACKGROUND: The impulse oscillation system (IOS) allows easy measurement of respiratory system impedance (Zrs). The aim of this retrospective study was to evaluate the accuracy of IOS parameters obtained during methacholine challenge by comparison with "the gold standard" forced expiratory volume in the first second (FEV1).

METHODS: Measurements of FEV1 and resistances at 5 and 20 Hz, reactance at 5 Hz, impedance at 5 Hz and resonant frequency were performed in 227 children with suspected asthma, before and during methacholine challenge. Data were analyzed in the overall population and in three subgroups according to the final diagnosis: asthma (n = 72), chronic cough and nonspecific respiratory symptoms (n = 122), allergic rhinitis (n = 33).

RESULTS: All IOS parameters changed significantly during the tests but only changes in X5 were significantly different between responders and nonresponders. Moreover, changes in IOS parameters were not correlated with changes in FEV1 apart from a weak correlation for X5. The receiver operating characteristic (ROC) curve for changes in X5 (to predict a 20% decrease in FEV1 showed a best decision level for a 50% decrease in X5 with a sensitivity of 36% and a specificity of 85%. Results were not different in the asthma group.

CONCLUSION: The accuracy of measurements by IOS during methacholine bronchial challenge in children was not suitable when compared with FEV1 . It could be assumed that spirometry and IOS, while both providing indirect indices of airway patency, are exploring different mechanisms, each with its own methodological potentials and limitations.