Comparison of impulse oscillometry indices and FEV1 during methacholine challenge and bronchodilation tests

<bold>Background:</bold> Spirometry is the most used technique in methacholine challenge test (MCT) and bronchodilation test (BDT), however impulse oscillometry (IOS) could also be used as an alternative method. <bold>Objective:</bold> To demonstrate that IOS can be a reliable alternative to spirometry in MCT and BDT. <bold>Methods:</bold> Study included 20 subjects with suspected asthma (12 males, 8 females, mean age 41.5 ± 15.1). All participants underwent MCT using dosimeter (ProvoX, Ganshorn, Germany). FEV₁ (Spiroscout, Ganshorn, Germany) and IOS (Tremoflo C-100, Thorasys, Canada) parameters – airway resistance at 5 Hz (R₅), 20 Hz (R₂₀), 5–20 Hz (R_5-20), reactance at 5 Hz (X₅), reactance area at 5 Hz (AX₅) were recorded at the beginning of the test and after each methacholine dose. In subjects for whom MCT was positive, bronchodilation using salbutamol was performed and FEV₁ and IOS indices were re-recorded. <bold>Results:</bold> At baseline and after the last methacholine dose a significant correlation was observed between FEV₁ and all IOS indices <italic>(p < 0.05)</italic>, except R_5-20 at baseline. Δ_MCTFEV₁ (difference between baseline and after the last methacholine dose) significantly correlated with Δ_MCTR₅, Δ_MCTX₅ and Δ_MCTAX₅ in all subjects <italic>(p < 0.05)</italic>. Six subjects (30%) had a positive MCT for whom Δ_BDTFEV₁ (difference between the value before and after BDT) significantly correlated with Δ_BDTX₅ and Δ_BDTR_5-20 <italic>(p < 0.05)</italic>. <bold>Conclusion:</bold> IOS may be a valuable alternative to spirometry in MCT and BDT. Our findings show that the most suitable IOS indices for MCT assessment are R₅, X₅ and AX₅, and for BDT – X₅ and R_5-20.