The prevalence of bronchodilator responsiveness of the small airway (using mid-maximal expiratory flow) in COPD - a retrospective study

BACKGROUND: Bronchodilator responsiveness (BDR) using FEV(1) is often utilised to separate COPD patients from asthmatics, although it can be present in some COPD patients. With the advent of treatments with distal airway deposition, BDR in the small airways (SA) may be of value in the management of COPD. We aimed to identify the prevalence of BDR in the SA, utilizing maximal mid-expiratory flow (MMEF) as a measure of SA. We further evaluated the prevalence of BDR in MMEF with and without BDR in FEV(1) and its association with baseline demographics, including conventional airflow obstruction severity and smoking history. METHODS: Lung function data of ever-smoking COPD patients were retrospectively analysed. BDR was evaluated 20 min after administering 2.5 mg of salbutamol via jet nebulizer. Increase in percent change of ≥ 12% and absolute change of ≥ 200 ml was used to define a BDR in FEV(1), whereas an increase percent change of MMEF ≥ 30% was used to define a BDR in MMEF. Patients were classified as one of three groups according to BDR levels: group 1 (BDR in MMEF and FEV(1)), group 2 (BDR in MMEF alone) and group 3 (no BDR in either measure). RESULT: BDR in MMEF was present in 59.2% of the patients. Of note, BDR in MMEF was present in all patients with BDR in FEV(1) (group 1) but also in 37.9% of the patients without BDR in FEV(1) (group 2). Patients in group 1 were younger than in groups 2 and 3. BMI was higher in group 1 than in group 3. Baseline FEV(1)% predicted and FVC % predicted were also higher in groups 1 and 2 than in group 3. CONCLUSION: BDR in the SA (evaluated by MMEF) is common in COPD, and it is also feature seen in all patients with BDR in FEV(1). Even in the absence of BDR in FEV(1), BDR in MMEF is detected in some patients with COPD, potentially identifying a subgroup of patients who may benefit from different treatment strategies. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12890-022-02235-0.