Comparison of bronchodilator responsiveness between forced oscillation technique and spirometry

Aims: Forced oscillation technique (FOT) may provide a different aspect of lung mechanics compared to spirometry. We aimed to clarify discrepancies in bronchodilator responsiveness (BDR) results between FOT and spirometry in a clinical audit. Methods: Data were available for analysis in 54 subsequent FOT and spirometry BDR measurements in sequentially recruited 3-17 years old asthmatic children. Results BDR tests were in agreement in 87% (47/54): two cases (3.7%) were negative in spirometry but positive in FOT, and 5 (9.3%) positive in spirometry but negative in FOT (Figure 1). There was no statistical difference in age, sex, ethnicity, height, weight or BMI between cases with test agreement and disagreement. Use of bronchodilator (tiotropium+/-SABA/LABA) before the BDR testing was present in 71% (5/7) of the outliers vs. 17% (8/47) in those with test agreement (p=0.002). Conclusion: We found a good agreement of BDR between the two techniques. In case of test-to-test discrepancy, bronchodilator use before BDR testing may be a confounding factor in children with asthma. Figure 1 Scatterplot of baseline to post-bronchodilator spirometry FEV1 (%-baseline) against FOT Rrs8 (%-pred).