Small Airway Dysfunction in Chronic Obstructive Pulmonary Disease Pathology: Assessment and Clinical Implications

Chronic obstructive pulmonary disease (COPD) is a progressive lung disease characterized by airflow limitation and persistent respiratory symptoms. A key factor in the progression of COPD is small airway dysfunction (SAD), which originates in airways smaller than 2 mm in diameter. Chronic exposure to smoke and toxins leads to inflammatory remodeling and luminal obstruction, detectable through micro-computed tomography (CT) studies before spirometric airflow limitations become evident. SAD exacerbates COPD by increasing airway resistance and promoting dynamic airway collapse during exhalation. Clinically, SAD presents as gas trapping, hyperinflation, and exercise intolerance, which are associated with a rapid decline in lung function. Recent evidence indicates that SAD may be a modifiable and clinically significant trait in COPD, with management strategies including extrafine-particle inhalers, smoking cessation, pulmonary rehabilitation, and emerging biologic therapies. Various assessment methods, such as pulmonary function tests and CT imaging, are used to assess SAD. This review focuses on the role of SAD in the pathophysiology of COPD and the clinical implications of easily applicable measurements, including forced expiratory flow between 25% and 75% of forced vital capacity, impulse oscillometry, Pi10, and parametric response mapping, as well as potential treatment modalities for SAD in COPD.