Assessment of bronchial reactivity by forced oscillation admittance avoidsthe upper airway artefact

The forced oscillation technique (FOT) allows easy assessment of bronchial reactivity, The use of a standard FOT generator (SG) results in changes in respiratory system resistance (Delta Rrs,SG) which are affected by an artef act caused by the extrathoracic upper airway (EUA), The aim was to improve the FOT assessment of bronchial reactivity with the SG by computing the cha nge in FOT admittance (Delta Ars,SG), which is theoretically unaffected by this artefact. Delta Rrs,SG and Delta Ars,SG after bronchial challenge in 17 children were compared with the values measured with a head generator (HG) FOT setup (De lta Rrs,HG and Delta Ars,HG, respectively), which were taken as a reference , since HG provides data virtually freed from the EUA artefact, At 10 Hz, the SG significantly underestimated the resistance change: Delta Rrs,SG=1.77+/-0.62 versus Delta Rrs,HG=6.09+/-1.23 hPa.L-1.s. Delta Rrs,SG and Delta Rrs,HG did not show a significant correlation. By contrast, the a mplitude of the change in admittance measured by SG was close to the one ob tained with the reference HG: \Delta Ars,SG\=29.5+/-4.6 versus \Delta Ars,H G\=32.7+/-3.9 mL.hPa(-1).s(-1). \Delta Ars,SG\ and \Delta Ars,HG\ showed a significant correlation (r=0.65, p>0.01), Similar results were found up to 20 Hz, The extrathoracic upper airway artefact was minimized when computing the ch ange in admittance with the standard generator. This forced oscillation tec hnique index may improve the sensitivity in assessing bronchial reactivity with the standard generator setup, which is the most common and easiest to use method for routine lung function testing.