Comparison of forced oscillometry and forced expirations for measuring dose-related responses to inhaled methacholine in asthmatic children.

The forced oscillation technique (FOT) is a lung function method which is applicable from the age of 2.5 years onwards, because only passive co-operation is needed. We used the method as described by Làndsér et al. The aim of this study was to compare indices of bronchial responsiveness obtained by FOT (Rrs6, Rrs, dRrs/df, Xrs), with indices derived from maximal and partial expiratory flow-volume curves (MEFV25, PEFV25, FEV1). Bronchial responsiveness was assessed by methacholine inhalation. Threshold dose (TD), i.e. the dose which caused a 2 SD change from baseline lung function, and provocation dose (PD), i.e. the dose which caused a 20% fall in FEV1, a 40% fall in MEFV25 and PEFV25 and a 40% increase in Rrs and Rrs6, were determined. We found that the indices derived from forced oscillometry compared well to those from maximal and partial flow-volume curves. PD20 FEV1 and PD40 Rrs6 were highly correlated (r = 0.84). TD appeared to be as good as PD to measure bronchial responsiveness and is preferred to PD because of the lower dose needed and limited bronchoconstriction obtained.