Comparing Changes in FEV₁ and Impulse Oscillometry Parameters Following Methacholine Challenge Testing: Physiological...

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology

Background:

• Spirometry-based methacholine challenge testing (MCT) using FEV1 (forced expiratory volume in 1 second) PD20 is standard for assessing airway hyperresponsiveness.
• Impulse oscillometry (IOS), performed during tidal breathing, may reveal airway mechanics missed by spirometry.

Purpose of the Study:

• Compare FEV1- and IOS-based methacholine responsiveness in a large adult cohort.
• Examine associations between IOS/spirometry responses and clinical markers/symptoms.
• Investigate predictors of IOS response.

Main Methods:

• Analyzed 794 adults undergoing concurrent spirometry and IOS methacholine challenge testing.
• Defined IOS positivity as a ≥40% increase in resistance at 5 Hz (ΔR5 ≥ 40%).
• Evaluated agreement between FEV1-PD20 and IOS positivity, and correlated continuous responses.

Main Results:

• IOS positivity (70.6%) was higher than FEV1-PD20 positivity (37.5%), with limited agreement (κ = 0.09).
• ΔFEV1 and ΔR5 showed weak correlation (r = -0.287).
• Referral diagnosis and age predicted ΔR5; baseline FEV1% modified the ΔFEV1-ΔR5 relationship.

Conclusions:

• IOS identifies a larger, distinct group of methacholine-responsive individuals than FEV1-PD20.
• IOS detects mechanical changes even with minimal spirometric impairment.
• IOS provides complementary physiological and symptom data when used with spirometry, but requires standardized definitions and validation.