Background: Bronchodilator response (BDR) is associated with poor asthma control and increased airway inflammation, indicating its potential role in asthma assessment. Although spirometry is still the gold standard for measuring BDR, oscillometry (FOT) might be a more sensitive technique for detecting BDR. This is due to its ability of measuring both central and peripheral airway obstruction unlike spirometry predominantly measuring the central airways.

Aim: To compare spirometry and FOT in demonstrating BDR.

Methods: Retrospective study using data from patients with asthma GINA 4-5. Measurements were performed on the same day before and after bronchodilator administration and the % change was determined. BDR was determined by recent thresholds (Oostveen/Johansson). FEV1 and FVC were used as spirometric parameters and R5, X5 and AX as oscillometric parameters.

Results: 119 patients (37 male; mean age 50.70±1.37, mean ACQ 2.69±0.10) were included. BDR was identified more frequently with FOT than spirometry (37 vs 29 patients). 17 patients met BDR criteria with both FOT and spirometry. BDR was best detected with AX and FEV1 (both 29 patients) and least detected with FVC (10 patients). % change in AX was best correlated with % change in FEV1 (r=-0.439, p<0.001) and FVC (r=-0.357, p<0.001). 

Conclusions: FOT is more sensitive in detecting BDR than spirometry of which reactance parameter AX was the most sensitive. AX was also best correlated with spirometric BDR. However, not all patients with spirometric BDR had oscillometric BDR and vice versa, likely due to addressing of different airway compartments. This supports the use of a combination of spirometry and FOT in the diagnosis of BDR in asthma.