Interrupter technique and pressure oscillation analysis during bronchoconstriction in children.

The use of interrupter resistance (R(int)) is a feasible method of measuring bronchodilator responsiveness and bronchial hyperresponsiveness in preschool children. It has been suggested that analysis of recorded oscillations of the mouth pressure may provide additional indices of changes in airway mechanics. The aim of our study was to determine whether amplitude or damping properties of oscillations were more sensitive than R(int) in describing changes during bronchoconstriction. Data from 44 children (24 boys) who completed tripling dose methacholine (Mch) challenge were analysed. The median (range) age of children was 4.9 (3.1-6.1 years). In addition to baseline and maximal R(int) after Mch [mean (SD) were 0.92 (0.19) and 1.44 (0.35) kPa l(-1) s, respectively], obtained from a commercial device we analysed the following parameters: difference between the first maximum and minimum (A(MxMn)), maximum instantaneous amplitude (A(inst)), amplitudes of fitted mathematical model and the dominant frequency, sum of frequency component amplitudes, two damping factors and frequency. All amplitude parameters changed significantly after Mch. For comparison of the decrease in amplitudes and increase in R(int) we additionally used reciprocals of amplitudes. Using the sensitivity index (SI) i.e. the change after intervention divided by the baseline SD, 1/A(inst) and 1/A(MxMn) were the most sensitive indices to describe the change (with median SI of 6.29 and 6.28, respectively). R(int) had a median SI of 5.13. Frequency and damping factors were less sensitive, with median SI values <1. These findings suggest that oscillation amplitude analysis implemented in the software of commercial devices could have further applications in assessing respiratory mechanics.