Clinical Research Directory

Inclusion Criteria: * Age ≥20 years * Chronic respiratory symptoms (cough, sputum, chest tightness, dyspnea, or wheezing) for ≥8 weeks * Preserved spirometry: FEV1/FVC ≥0.7, FVC ≥80% predicted, and negative bronchodilator reversibility (increase in FEV1 or FVC \<12% and \<200 mL after salbutamol) * IOS-defined small airway dysfunction and small airway reversibility (SAR): AX \>0.44 kPa/L with post-bronchodilator reduction in AX ≥35% after salbutamol inhalation Exclusion Criteria: * Age \<20 years * Impaired spirometry (FEV1/FVC \<0.7, FVC ≤80% predicted, or positive bronchodilator reversibility) * Absence of SAD or lack of significant SAR * Respiratory symptoms absent or \<8 weeks * Acute respiratory condition within 4 weeks before enrollment (upper/lower respiratory tract infection, acute exacerbation, pneumonia requiring antibiotics, ED visit or hospitalization) * Current diagnosis of COPD, chronic respiratory infection, or structural lung disease (active/prior tuberculosis, bronchiectasis, interstitial/restrictive lung disease, arteriovenous malformation, or prior pulmonary surgery) * Use of any bronchodilator (oral/inhaled), theophylline, steroid (inhaled/oral/IV), or beta-blocker within 4 weeks before enrollment * Known hypersensitivity to beclomethasone dipropionate/formoterol fumarate or salbutamol * Contraindication to pulmonary function testing or venous blood sampling (severe/unstable cardiovascular disease, recent major thoracic/abdominal surgery, unresolved pneumothorax, uncontrolled bronchospasm or hemoptysis, need for FiO2 \>50%, impaired consciousness or dementia) * Other physician-assessed unsuitability for pulmonary function testing or blood sampling * Incomplete informed consent * Known HIV/AIDS infection * Pregnant or breastfeeding women