To address the utility of the forced oscillation technique (FOT) in assessing bronchodilator responsiveness compared with FEV1 and PEF.
In 126 patients with clinical history of asthma, the following measures were obtained three times each, before and after two doses of pirbuterol 0.2mg inhalation. FOT measures: *the respiratory resistance at 5 Hz (R5) and at 20 Hz (R20), *R5-R20, *the total respiratory resistance (Rrs) *the total respiratory conductance (Grs). Spirometric measures: *FEV1 *peak expiratory flow (PEF) with spirometry. These measures were transformed into dimentionless subject-specific effect-size “d-scores” by dividing them by the estimated pooled within-subject standard deviation.
Descriptive statistics for mean raw scores, delta scores and d-scores are presented in Table 1Table 1
Descriptive statistics for FOT measurement and FEV1 before and after pirbuterolMeasureVariableMeanSDMin.Max.p value (vs FEV1)FEV1 (L)Baseline Post-drugΔd1.90 2.10 0.20 1.830.64 0.68 0.25 2.270.50 0.55 -0.73 -6.724.18 4.01 0.96 8.90N/AGrs (L·s-1 kPa-1)Baseline Post-drugΔd1.79 2.18 0.39 2.640.53 0.65 0.43 2.900.93 1.15 -0.74 -4.943.82 4.17 1.68 11.27p=0.0063R5 (kPa·L-1·s)Baseline Post-drugΔd0.78 0.62 -0.16 2.520.25 0.20 0.16 2.440.31 0.27 -0.62 -5.311.60 1.31 0.35 9.55p=0.0095Rrs (kPa·L-1·s)Baseline Post-drugΔd0.60 0.50 -0.10 2.560.16 0.14 0.11 2.660.26 0.24 -0.37 -6.131.08 0.87 0.25 9.08p=0.0102. The mean effect size among these measures were different between measures[omnibus test of difference, p<0.0001]. Post-hoc test analysis indicated that Grs,Rrs,R5 are most sensitive for changing in response to pirputrol inhalation, and that PEF & R5-R20 are least sensitive. [Tukey p<0.0001 in all cases]. The pattern of unadjusted p-values (p < 0.05) suggests three homogeneous sets of measures for sensitivity to change after pirputerol. In descending order of sensitivity they are: Grs, Rrs and R5; FEV1 and R20; and R5-R20 and PEF.
Several forced oscillation measures, namely Grs, Rrs and R5, are very sensitive for detecting bronchodilator response in patients with asthma.
Measurement of forced oscillation may be useful to detect bronchodilator response in asthmatic patients.
M. Yaegashi, None.