Content on this page requires a newer version of Adobe Flash Player. In practice airway responsiveness to bronchoconstrictors (most often histamine or methacholine) and bronchodilators (e.g. ß2-sympathomimetic or anticholinergic drugs) is usually assessed from changes in airways resistance or changes in forced expiratory volume in one second (FEV1). The multiple steps between delivery of the agonist to the mucosal surface and the resulting airway narrowing are not individually assessed, rather the end response as measured by a change in pulmonary function is assessed. For bronchial challenges