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.

Introduction and aims: see brief summary.

Method and Patients This is a real-life, cross-sectional analysis of a single-centered, observational study on 60 adult patients with clinical diagnosed asthma and 60 COPD patients, consecutively recruited between February 1, 2026, and June 30, 2027, and followed at least 6 months for diagnostic clarification.

Inclusion Criteria:

Both asthma and COPD patients:

1. Written informed consent.
2. FEV1/Forced Vital Capacity (FVC) <0.7 at baseline )
3. Visual Analog Scale (VAS) dyspnea score ≥10 (0-100, 100 max).

Asthma: Doctor diagnosed asthma 1. less than 10 packyears.

COPD: Doctor diagnosed COPD with FEV1/FVC <0.7 post-bronchodilation

1. Smokers or ex-smokers with ≥10 packyears

Exclusion Criteria:

• Patients aged less than 18 years old.
• Not able to perform spirometry or impulse oscillometry.
• Cognitive disorders and not able to answer Asthma Control Questionnaire (ACQ), VAS dyspnea score, and COPD Assessment Test (CAT) score.
• Short-acting beta-agonists 6 h, long-acting beta-agonists 2 days, short-acting anti-muscarinic agent 12 h, Long-acting anti-muscarinic agents 2 days.
• Comorbidities with significant influence on dyspnea eg. bronchiectasis, ILS, mb. Cordis, lung resection, anemia, and active malignant disease
• BMI ≥40 kg/m2.

It is a real-life study where most patients are followed up within 6 months. The diagnosis - asthma, COPD, or other condition - may change after follow-up (maximum 6 months after the index examination).

Minimal Clinical Important Difference

Anchor-Based Methods:

1. The receiver operating characteristic (ROC) curve-based method determines the minimum clinically important difference (MCID) by identifying the value that maximizes the Youden Index. This index is calculated as the maximum sum of sensitivity and specificity. Using data from patients who rate themselves "a little better" and patients who rate themselves "no change"
2. The social comparison approach provides the MCID as the mean of two differences: the difference of mean score between patients who rate themselves as "a little worse" and patients who rate themselves "no change".
3. Within-patients score change MCID is the mean delta score of patients who rate themselves "a little better".
4. The methods of 95% limits of upper agreement: MCID is the mean delta score -1.96 standard error of the delta score of the patients who answered "no change"

Distribution-Based Methods:

1. MCID defined as standard error of measurement (SEM) evaluated on the baseline values from patients who rated themselves "no change".
2. MCID defined as 0.5 SD of delta score from patients who answered "a little better"
3. MCID is defined as 1.96 × √2 × SEM, assessed on baseline values from patients who reported "no change", which represents the smallest change in a measurement that can be considered a "real" change, rather than just random measurement error.

Brochodilator test and order of test To avoid or minimize the effect of deep inhalation on IOS, IOS was performed at least 15 minutes after spirometry and body box.

Patients were administered 4 doses of 0.1 mg Ventoline (salbutamol) via pressurized metered-dose inhaler and spacer (Aero Champer). Post-IOS and post-spirometry were performed 15-20 minutes after the bronchodilator inhalation

Inclusion Criteria:

• Both asthma and COPD patients:

  1. Written informed consent.
  2. FEV1/Forced Vital Capacity (FVC) <0.7 at baseline (7)
  3. Visual Analog Scale (VAS) dyspnea score ≥10 (0-100, 100 max) (25,26).

• Asthma: Doctor diagnosed asthma

  1. less than 10 packyears.

• COPD: Doctor diagnosed COPD with FEV1/FVC <0.7 post-bronchodilation 1. Smokers or ex-smokers with ≥10 packyears

Exclusion Criteria:

• Patients aged less than 18 years old.
• Not able to perform spirometry or impulse oscillometry.
• Cognitive disorders and not able to answer Asthma Control Questionnaire (ACQ), VAS dyspnea score, and COPD Assessment Test (CAT) score (25-28).
• Short-acting beta-agonists 6 h, long-acting beta-agonists 2 days, short-acting anti-muscarinic agent 12 h, Long-acting anti-muscarinic agents 2 days.
• Comorbidities with significant influence on dyspnea eg. bronchiectasis, ILS, mb. Cordis, lung resection, anemia, and active malignant disease
• BMI ≥40 kg/m2.

referred to Allergy and Lung Clinic Elsinore, Denmark for evaluation of Asthma and COPD (obstructive lung disease)

I have not applied for permission to share data with others.