Changes in the “U-Shaped” Distribution of Airway Hyperresponsiveness and Characterization of Inflammatory Phenotypes in Different Age Groups

AHR is more prominent in adolescents and the elderly, showing a "U-shaped" age distribution. Adolescents exhibited Th2-type inflammation (mainly eosinophil-driven), while the elderly showed non-Th2-type inflammation (mainly neutrophil- and monocyte-driven). Pulmonary function peaks in young adulthood and declines more rapidly after middle age, with small airway obstruction worsening in the elderly. The elevated CaNO in the elderly group dissociated from decreased blood eosinophils, suggesting localized eosinophilic inflammation or impaired migration, potentially indicating an eosinophil non-dependent inflammatory phenotype.