Lung function assessment
Participants attended Perth Children’s Hospital for lung function assessment. Respiratory mechanics were assessed using the TremoFlo C-100 (Thorasys Inc. Montreal, Canada). Spectral oscillometry was performed across 5-37Hz and intrabreath oscillometry was performed using a single 10Hz frequency. Spirometry was performed using the using the Medisoft Hypair or BodyBox 5500 (Medisoft Corporation, Sorinnes, Belgium). All tests were carried out according to American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines.1,28,29
Spirometry outcomes were expressed as z-scores according to the Global Lung Function Initiative equations.30 Spectral oscillometry outcomes including respiratory resistance at 5Hz (Rrs5), resonant frequency (Fres), area under the reactance curve (AX) and respiratory system reactance at 5Hz (Xrs5) were expressed as z-scores according to the reference equations published by Calogero et al (6-12 year data,31) and Oostveen et al , (16-23 year data,32). Rrs5-20, and intra-breath oscillometry measures were expressed as raw values and absolute difference.33
Oscillometry and spirometry were performed before and after administration of 400µg salbutamol via a spacer. A bronchodilator response by spirometry was defined according to ATS/ERS guidelines as an increase of ≥200mls and 12% in FEV1 or FVC29 (the 200ml rule was omitted for children ≤12 years). A bronchodilator response by spectral oscillometry was defined according to ERS guidelines as a change of ≤−40% in Rrs5, ≥50% in Xrs5 or ≤−80% in AX across all age groups.1