Airways dilate with each inspiration. This normal rhythmic dilation, and even more so, the
dilation that occurs with deep inspirations (DI) such as sighing, are thought to play an
important role in maintaining airway patency. For example, in the absence of deep
inspirations, healthy individuals develop airway obstruction to inhaled stimuli such as
methacholine or histamine, whereas, when the inhalation challenge is performed with
conventional spirometry (which involves multiple deep inspiration maneuvers), no …