Early detection of airway obstruction by impulse oscillometry system in methacholine challenge testing in preschool children

Background: Small airway hyperresponsiveness is a critical aspect in preschool children with asthmatic symptoms in terms of asthma control. The aim of this study was to elucidate the relationship of changes in reactance (Xrs) and resistance (Rrs) of iOS and FEV1 with those in clinical parameters and to determine which IOS parameter is correlated with bronchial hyperresponsiveness before positive clinical endpoints. Methods: We performed the methacholine challenge test in ninety-four preschool children (4.2 +/- 1.1 years) with suspected asthma. The end of test (EOT) was defined as one or more of the following: audible wheezing (PCw(+)), a fall in the oxygen saturation (< 92%, PCs+) or development of respiratory symptoms (PCr+). Results: Mean changes in FEV1, Xrs(5), and Rrs(5) in the EOT group were 39.2 +/- 14.3% (95% CI 35.1-43.2%), 176.8 +/- 78.0 (95% CI 154.9-198.8) and 53.6 +/- 30.2 (45.1-62.0), respectively. The changes of Xrs(5) in three EOT+ groups exceeded 80% and were lowest in PCr+(median, 95.9, IQR; 73.4 to 132.4), followed by PCw(+) and PCs+. However, Rrs(5) did not show greater than 40% changes in PCr+. Xrs(5) showed a higher correlation with changes in saturation (r = -0.578) than Rrs(5) (r=-0.426). A49% decrease in Xrs(5) was the optimal point for predicting a 80% change of Xrs(5) at the following step. Conclusion: When examining the 5 step methacholine challenge test in preschoolers, the use of clinical parameters alone as an endpoint is of little value. The reactance value of 5 Hz is a useful predictive marker for bronchial hyperresponsiveness.