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 (PC 20 value) and by the slope and intercept of the FVC values recorded at each step of the challenge against the corresponding FEV 1 values. Results The slope and intercept FVC versus FEV 1 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 PC 20 values decreased significantly during the pollen season. However, the mean (95% CI) slope FVC versus FEV 1 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 FEV 1 and FVC is not equivalent and may be complementary.