Peripheral airways (PA)

The peripheral airways, commonly referred to as the small airways, are defined as those with an internal diameter of less than 2 mm, encompassing the terminal and respiratory bronchioles [1]. In a healthy lung, these airways contribute minimally to total airway resistance, leading them to be described as the "silent zone," where significant disease progression can occur without detection by standard spirometry [2]. They play a critical biological role in transitioning conducted air into the respiratory zones for gas exchange and maintaining immune homeostasis through mucociliary and cellular defenses [1][3]. In obstructive diseases such as asthma and COPD, the peripheral airways are primary sites of inflammation, mucus plugging, and structural remodeling [2]. While the peripheral airways are an anatomical region rather than a single molecular receptor, they serve as a vital therapeutic target for extra-fine aerosol formulations designed to reach the deep lung. These medications typically interact with beta-2 adrenergic receptors or glucocorticoid receptors located on the local smooth muscle and epithelial cells to alleviate obstruction and inflammation [3][4]. Sources: [1] StatPearls, "Anatomy, Thorax, Lung Airways," NIH.gov. [2] Burgel PR, et al., "The role of small airways in obstructive airway diseases," European Respiratory Review, 2011. [3] Usmani OS, "Small-airway disease in asthma: overlooking the role of the periphery?" Expert Review of Respiratory Medicine, 2010. [4] Postma DS, et al., "The small airways as a target for inhaled corticosteroids," European Respiratory Journal, 2014.

Other names

Small airwaysBronchiolesTerminal bronchiolesRespiratory bronchiolesSilent zone of the lung

Drugs targeting this region typically involve the activation of beta-2 adrenergic receptors to relax smooth muscle or the activation of glucocorticoid receptors to suppress inflammatory gene expression within the small airway epithelium and interstitium.