Small airways disease in asthma.

A mounting body of physiologic and pathologic evidence indicates that asthma involves the central and the more distal airways. In patients with asthma, the peripheral lung accounts for a significant portion of airway resistance and, similar to the large airways, the small airways have been shown to be hyperresponsive to nonspecific stimuli, such as methacholine. Cellular inflammation, consisting of an infiltrate rich with lymphocytes and eosinophils, is present in the small airways of patients with asthma and may be more intense than that observed in the large airways. Clinical assessment of the peripheral airways continues to be a challenge, and new techniques, such as quantitative analysis of chest CT images, have proven to be useful research tools. The recognition of small airways involvement in asthma has clinical relevance, as new formulations of inhaled corticosteroids with smaller particle aerosols may be more effective in addressing this component of asthma.