The utility of the forced oscillation technique in assessing bronchodilator responsiveness in patients with asthma

Objective: To address the utility of the forced oscillation technique (FOT) in assessing bronchodilator responsiveness compared with forced expiratory volume in 1 s (FEV₁). Methods: This is a retrospective analysis of consecutive 126 patients with a clinical history of asthma without any other lung diseases at a pulmonary function testing laboratory. The following measurements were obtained three times each, before and after two doses of pirbuterol 0.2 mg inhalation: the respiratory resistance at 5 Hz (Rrs5), the mean respiratory resistance between 5 and 20 Hz (Rrs5-20), and the mean respiratory conductance (Grs5-20) by FOT and the FEV₁ by spirometer. These measurements were transformed into dimensionless subject-specific effect-size "d-scores" by dividing them by the estimated pooled within-subject standard deviation. Results: Descriptive statistics for each value were the following [mean baseline value (±sd), Δ value (pre- minus post value), and d-score (P value compared to FEV₁)]: Grs5-20 (L s^-1 kPa^-1) [1.79±0.53, Δ=+0.39, d=2.64 (P<0.001)], Rrs5-20 (kPa L^-1 s) [0.60±0.16L, Δ=-0.10, d=2.56 (P=0.001)], Rrs5 (kPa L^-1 s) [0.78±0.25, Δ=-0.16, d=2.52 (P<0.001)], and FEV₁ (L) [1.90±0.64, Δ=-0.20, d=1.83]. The higher d-score of Grs5-20, Rrs5-20 and Rrs5 compared to FEV₁ indicates that these are better indicators for bronchodilator response than FEV₁. The percentages of subjects exhibiting change in the expected direction after bronchodilator were not significantly different between each value: Rrs5 (85.7%), Rrs5-20 (83.3%), Grs5-20 (83.3%), and FEV₁ (83.3%) [P>0.05]. Conclusions: Several forced oscillation measures, namely Grs5-20, Rrs5-20 and Rrs5, are more accurate and sensitive for detecting bronchodilator response than FEV₁ in patients with asthma.