Peripheral airway function in antigen-induced bronchoconstriction

The density dependence of the maximum expiratory flow-volume curve, functional residual capacity (FRC) and specific airway conductance (SGaw) were studied in 16 asymptomatic subjects with ragweed hypersensitivity and a history of bronchial asthma, before and during bronchial provocation with ragweed extract (dose-response curve), and following inhalation of isoetharine. In ten of these subjects (seven 'reactors' and three 'non-reactors'), the baseline volume of isoflow (VisoV) was found to be greater than 20% of forced vital capacity. During antigen challenge. VisoV increased in all subjects; ten of these showed a greater than 35% decrease in SGaw (mean 45%) while the remaining six showed a decrease in SGaw of less than 20% (mean 9%), suggesting central and peripheral airway constriction in the former 'reactors' and primarily peripheral airway constriction in the latter 'non-reactors'. The beta-adrenergic agonist isoetharine increased SGaw and decreased VisoV, suggesting dilation of both central and peripheral airways. We conclude that in asymptomatic subjects with asthma and ragweed hypersensitivity a) peripheral airway dysfunction is frequently present, b) during antigen challenge VisoV may be a more sensitive indicator of airway response than SGaw, and c) the beta-adrenergic agonist isoetharine exhibits its bronchodilator effect in both central and peripheral airways following antigen challenge.