The small airways are characterized by an internal diameter < 2mm and absence of cartilage. Approximately 10-25% of total airways resistance in healthy lungs is due to the small airways, with their contribution to total airways resistance increasing substantially in chronic obstructive pulmonary disease (COPD). As the small airways are located in the lung periphery, they are not easily evaluable, which can potentially interfere with the diagnosis (especially at early stages), monitoring, detection of responses to clinical interventions, and prognostic evaluation in COPD.

Here, we will discuss the currently available methods in clinical practice to evaluate small airways disease in COPD, focusing on...