Effect of Albuterol on Compliance and Distensibility of the Trachea and Lungs

Tracheomalacia (TM), the most common abnormality of the pediatric trachea, results in dynamic expiratory airway collapse due to weakened cartilage and reduced smooth muscle tone. Although bronchodilators such as albuterol are widely used in children with wheezing, their impact on TM remains unclear, because prior studies have not simultaneously evaluated tracheal and lung mechanics in vivo. This study aimed to separately quantify the effects of albuterol on both tracheal distensibility and compliance, as well as lung compliance, using a controlled porcine model. Ten spontaneously breathing swine underwent high-resolution computed tomography (CT) imaging at multiple controlled tracheal lumen pressures (P _LUM ) ranging from +10 to -10 cmH _₂ O, both before and after administration of 5 mg nebulized albuterol. Tracheal and pleural pressures were simultaneously recorded. Three-dimensional airways and lungs were segmented from CT images to calculate cross-sectional areas and volumes. Tracheal distensibility and compliance, as well as lung compliance, were determined by the slope of area or volume versus transmural pressure. Albuterol significantly increased tracheal distensibility (4.30 ± 1.0 to 4.78 ± 1.3 mm ^² /mmHg, p=0.010) and tracheal compliance (327 ± 102 to 367 ± 117 mm ^³ /mmHg, p=0.018). Lung compliance also increased significantly in 9 evaluable swine ((2.9 ± 1)×10 ^⁴ to (3.8 ± 1.1)×10 ^⁴ mm ^³ /mmHg, p=0.010). Albuterol increases both tracheal and lung compliance, supporting clinical concerns that bronchodilators may exacerbate airway collapse in TM. These findings demonstrate the complex and competing mechanical effects of bronchodilators in TM and stress the importance of accounting for both tracheal and lung responses in managing dynamic airway collapse.