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

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.

Maximal degree of airway narrowing induced by methacholine and adenosine monophosphate: relationship with the decrease in forced vital capacity.

BACKGROUND: Changes in forced vital capacity (FVC) may represent an indirect method for the detection of plateau in response to inhaled bronchoconstrictor agents. OBJECTIVE: To determine the relationship between the level of plateau obtained with either methacholine or adenosine monophosphate (AMP) and the decrease in FVC induced by each bronchoconstrictor agent. METHODS: Airway responsiveness to high concentrations of methacholine and AMP was determined in patients with intermittent asthma (n = 41) or allergic rhinitis (n = 26). Furthermore, allergen-induced changes in the response to each bronchoconstrictor agent were investigated in 18 pollen-sensitive patients. Concentration-response curves were characterized by the slope of the FVC values recorded at each step of the challenge against the corresponding forced expiratory volume in 1 second (FEV1) values and, if possible, by the level of plateau. RESULTS: The slope FVC vs FEV1 was similar in patients with plateau and in those without plateau. In patients with pollen allergy, the mean (95% confidence interval) for the level of plateau detected with methacholine increased from 16.8% (11.8%-22.0%) before the pollen season to 21.7% (14.8%-28.6%, P = .008) during the pollen season, whereas pollen-induced changes in the slope FVC vs FEV1 were not significant. Similar results were obtained with AMP. CONCLUSIONS: In patients with allergic rhinitis or intermittent asthma, methacholine or AMP-induced changes in FVC are not significantly related to the presence or level of plateau. Furthermore, these 2 constituents of the concentration-response curve can be modified independently by a proinflammatory stimulus. These results suggest that the bronchoconstrictor-induced change in FVC cannot be used as a surrogate estimation of the level of plateau.