Effects of allergen exposure on methacholine and AMP-induced air trapping in pollen-sensitive subjects.

Summary: Background: The effect of pro-inflammatory stimuli on bronchoconstrictor-induced air trapping has not been studied. Objective: To determine the effect of natural allergen exposure, a pro-inflammatory stimulus, on methacholine- and adenosine 5′-monophospate (AMP)-induced air trapping. Methods: Airway responsiveness to methacholine and AMP before and during the pollen season was obtained in 25 subjects with pollen allergy and in 10 healthy controls. The response was expressed by the sensitivity (PC₂₀ value) and by the slope and intercept of the FVC values recorded at each step of the challenge against the corresponding FEV₁ values. Results: The slope and intercept FVC versus FEV₁ values for both methacholine and AMP were significantly higher in subjects with pollen allergy than in healthy controls. In the group with pollen allergy, both methacholine and AMP PC₂₀ values decreased significantly during the pollen season. However, the mean (95% CI) slope FVC versus FEV₁ values for methacholine were 1.00 (0.84–1.16) before the pollen season and 0.99 (0.86–1.12, P = 0.90) during the pollen season. Similar results were obtained with AMP. Conclusions: Although the air trapping induced by both methacholine and AMP is significantly greater in subjects with pollen allergy than in healthy controls, natural allergen exposure is associated with a selective increase in airway sensitivity without concomitant changes in bronchoconstrictor-induced air trapping. These findings suggest that the information provided by the bronchoconstrictor-induced change in FEV₁ and FVC is not equivalent and may be complementary. [Copyright &y& Elsevier]