Bronchodilator Response in COPD and Asthma: Correlation Between Spirometry, IOS Indices, and Dyspnea Relief

A bronchodilator reversibility test is widely used in the diagnosis and management of obstructive lung diseases. Bronchodilators relieve symptoms in asthma and COPD. Traditionally, their effectiveness has been assessed using spirometric indices, particularly FEV₁. However, changes in FEV₁ often do not correlate well with patients' subjective experience of dyspnoea relief or with changes in small airway function. Impulse oscillometry (IOS) provides an effort-independent assessment of respiratory mechanics during tidal breathing and is more sensitive to small airway dysfunction than spirometry. Despite this, the clinical utility of IOS in routine COPD and asthma assessment remains underexplored, and its relationship to both spirometric response and symptom relief is not fully established, and the Minimal Clinically Important Difference (MCID) for IOS parameters has not been firmly established. Determining the MCID is essential for interpreting individual patient responses in a clinically meaningful way and for guiding treatment decisions in both research and practice. Hypothesis & Aims In patients with either asthma or COPD baseline values and bronchodilator responses are compared. More specifically, this study aims to: 1. assess baseline correlations: Evaluate the correlation between ΔX5-baseline (EFL expiratory flow limitation=small airway collapse during expiration), RV/TLC-baseline, X5-average at baseline, FEV1-baseline, VAS-dyspnea at baseline, and ACQ-6-baseline. 2. compare bronchodilator responses across methods: Examine the correlation between bronchodilator-induced changes in FEV₁ and IOS parameters (including both average and delta values) and explore their relationship with short-term changes in dyspnea. 3. establish clinical relevance: Determine the MCID for key IOS variables using both anchor-based and distribution-based approaches, anchored to perceived changes in lung symptoms.