Bronchodilator response assessed by the forced oscillation technique identifies poor asthma control with greater sensitivity than spirometry

Background: Persistent bronchodilator response (BDR) following diagnosis of asthma is an underrecognized treatable trait, associated with worse lung function and asthma control. The forced oscillation technique (FOT) measures respiratory system impedance, and BDR cutoffs have been proposed for healthy adults; however, the relevance in asthma is unknown. We compared BDR cutoffs, using FOT and spirometry, in asthma and the relationship with asthma control. Methods: Data from patients with asthma who withheld bronchodilator medication for at least 8 h before a tertiary airway clinic visit were reviewed. All subjects performed FOT and spirometry before and after salbutamol administration, and completed the Asthma Control Test. FOT parameters examined included respiratory system resistance (R5) and reactance (X5) at 5 Hz, and area under the reactance curve (AX). BDR was defined by standard recommendations for spirometry and based on the 95th percentile of BDR in healthy adults for FOT. Results: Fifty-two subjects (18 men; mean age, 53 ± 18 years) were included. BDR was identified more frequently by FOT than spirometry (54% vs 27% of subjects). BDR assessed by X5 and AX, but not R5, was associated with spirometric BDR (χ², P < .01) and correlated with asthma control (X5: r_s = –0.36, P < .01; AX: r_s = 0.34, P = .01). BDR measured by reactance parameters identified more subjects with poor asthma control than did spirometry (AX, 69% vs spirometry, 41%). Conclusions: BDR assessed by FOT can identify poor asthma control. Reactance parameters were more sensitive in identifying poor asthma control than spirometry, supporting the use of FOT to complement spirometry in the clinical management of asthma.