Forced oscillation technique: an alternative outcome measure for methacholine provocation test

Rationale: The standard methacholine provocation test repeatedly measures forced expiratory volume in 1 second (FEV 1 ) as index of bronchoconstriction to assess airway (hyper)responsiveness. Since this is labor intensive for the patient, the forced oscillation technique (FOT) could be an alternative. The FOT uses optimized pseudo-random noise to detect changes in respiratory resistance during normal breathing. Objective: We hypothesized that the FOT is an accurate alternative to FEV 1 during methacholine provocation test. Methods: This cross-sectional study included 78 new out-patient referrals for asthma diagnostics. The FOT and FEV 1 were measured in this order after each inhaled dose of methacholine. Provocation concentrations (PC) at given changes in resistance (R) and FEV 1 were used as outcome. Analysis was done by correlation and ROC analysis. Results: The PC values of resistance at 5 hertz (R 5 ) showed moderate and significant correlation with PC 20 FEV 1 (R 5 PC 30 : r=0.44, p= 5 PC 40 : r=0.41, p=0.0004; R 5 PC 50 : r=0.43, p=0.0001; R 5 PC 100 : r=0.40, p=0.0009). Comparisons of accuracies at different threshold values of R 5 with PC 20 FEV 1 showed 47% accuracy for PC 30 R 5 with negative predictive value (NPV) of 71% and positive predictive value (PPV) of 41%; PC 100 R 5 showed 86% accuracy, NPV of 87% and PPV of 85%. The mean (log)PC values were: PC 20 FEV 1 = 0.85 mg/ml; PC 30 R 5 = 0.27 mg/ml; PC 30 R 5-19 = 0.02 mg/ml. Conclusion: The FOT is an accurate alternative for FEV 1 in measuring bronchial responsiveness during methacholine provocation test. Using the FOT, lower concentrations of methacholine were needed for a positive test. Therefore, the FOT can help facilitate the diagnostic assessment of asthma.