The Importance of Small Airway Dysfunction in Asthma: The GEMA-FORUM III Task Force

The small airways have an internal diameter of 2 mm or less. Their role in asthma and other obstructive lung diseases is important, as inflammation or smooth muscle contraction induced by inhalation of allergic and nonallergic irritants reduces their diameter, thus increasing resistance in the airways. Peripheral airway obstruction, also known as small airway dysfunction (SAD), can occur in patients with asthma irrespective of severity, and prevalence increases with severity. SAD also considerably worsens the clinical expression and control of asthma, is associated with more frequent exacerbations and more severe bronchial hyperresponsiveness and requires higher doses of inhaled corticosteroids (ICS). The main predictors of SAD are exercise-induced asthma, overweight, asthma-related night awakenings, smoking, and older age. Although conventional spirometry measurements lack sensitivity for evaluation of SAD, their combination with physiological tests, oscillometry, body plethysmography, chest computed tomography (CT), multiple breath nitrogen washout, and nitric oxide would facilitate assessment of the complexity of this dysfunction and the response to drug therapy.