Small airway disease in COPD patients: A Q&A approach for everyday clinical practice.

Small airways are recognized as the main site of disease progression and airflow limitation in patients with chronic obstructive pulmonary disease (COPD). Whereas conventional lung function testing, e.g. spirometry, is non-specific to small airway disease (SAD), the advent and wider availability of techniques sensitive to SAD, such as oscillometry, has improved our understanding of the clinical importance of small airway dysfunction. Despite this progress, a gap between the recent advances in knowledge of SAD to its implementation in daily clinical practice remains. We aimed to answer key questions that would allow practitioners (e.g. family doctors, internists, pulmonologists) to introduce oscillometry in their clinical practice. COPD pathogenesis is characterized by small airway disease, with an increasing prevalence with more advanced disease. Evaluation of small airway dysfunction with sensitive techniques (e.g. oscillometry, nitrogen washout) contributes to early disease detection and plays a significant role in almost every aspect of disease assessment, including confirmation of diagnosis, functional severity grading and monitoring of lung function decline. Moreover, small airway dysfunction shows equivalent or even better correlation with patient reported outcomes, including symptoms, quality of life and exacerbations, compared to conventional lung function testing. The above suggests a role of small airway assessment as a "treatable trait" in COPD to target and monitor therapeutic interventions. Accumulating evidence and recent advances have delineated the role of small airway assessment in COPD and warrant its implementation in the management plan of COPD patients in daily clinical practice.