Seasonal variation of airway function in allergic rhinitis.

We set out to examine seasonal variation in airway bronchoconstriction in patients with seasonal allergic rhinitis. Airway conductance and response to methacholine challenge were measured during pollen season, as well as in winter when pollen exposure was not present. Airway conductance and spirometry were performed on 17 subjects during allergy season and in winter. In eight of these subjects the measurements were repeated in the successive allergy season. Methacholine bronchoprovocation was performed on 17 of the subjects in winter and in eight subjects in allergy season. We found airway constriction in both allergy seasons as evidenced by specific airway conductance (SGaw) of 0.188 +/- 0.06 and 0.203 +/- 0.03. In contrast, SGaw during winter was 0.27 +/- 0.11. When winter and summer seasons were compared, both summer SGaw values were significantly lower than winter SGaw, p less than 0.01 and p less than 0.05, respectively. Mean airway sensitivity to methacholine during allergy season was 16.1 breath units and not different than out of season 11.7 breath units; p = NS. The reactivity to methacholine (slope of the dose-response curve) and spirometry (FVC, FEV1, FEV1/FVC) in and out of allergy season were likewise not different. The data indicate that patients with allergic rhinitis have unique physiologic behavior separating them from patients with asthma or normal subjects. They develop seasonal bronchoconstriction unassociated with clinical bronchospasm, but this seasonal bronchoconstriction does not potentiate their sensitivity to methacholine. However, they have increased airway sensitivity to methacholine, and this feature distinguishes them from normal subjects.