Airway responsiveness to methacholine and deep inhalations in subjects with rhinitis without asthma

Airway hyperresponsiveness in asthma is believed to be caused in part by the inability of deep inspirations to modulate airway narrowing.

We investigated whether deep inspirations taken before or after methacholine inhalation attenuate bronchoconstriction in subjects with rhinitis. The results were compared with a group of healthy subjects.

Ten subjects with rhinitis without asthma and 10 healthy subjects were studied on 3 different occasions at random. Bronchial challenges were performed with a single dose of methacholine known to decrease the FEV(1) by 17% to 40%. Challenges were performed with avoidance of deep inspirations, or with 5 deep inspirations preceding or following the inhalation of methacholine. Lung function measurements were specific airway conductance, forced expiratory flow at 30% to 40% of vital capacity on a maneuver started from end-tidal inspiration (partial flow), and residual volume (partial residual volume).

In healthy subjects, deep inspirations taken after methacholine caused less changes in specific airway conductance, partial flow, and partial residual volume (P < .005 for all) than deep inspirations taken before methacholine or avoidance. In subjects with rhinitis, methacholine produced similar functional changes independently of the presence or absence of any deep inspirations. Compared with normal subjects, the attenuating effects of deep inspirations after methacholine on partial flow and partial residual volume were blunted in the subjects with rhinitis (P = .02 and P = .05, respectively).

The ability to dilate methacholine-constricted airways by deep inspirations is impaired in subjects with rhinitis, possibly because of an abnormal behavior of airway smooth muscle.