Seasonal and Allergenic Predictors of Bronchial Responsiveness to Distilled Water

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Abstract
To evaluate a possible seasonal change in bronchial responsiveness and the relation of such change to atopy, we administered 2,537 bronchial challenge tests in winter and spring to a dynamic population cohort of children 7 to 10 yr of age. The bronchial challenge test consisted of 10 min of tidal inhalation of an aerosol of ultrasonically nebulized distilled water; the resulting percentage decrease in FEV1 (dFEV1%) was recorded. Atopy was determined on the basis of skin-test positivity (any wheal with a diameter greater than that obtained with a positive control) to seven allergens (cat dander, dog dander, house-dust mite, birch, raygrass, orchard grass, and Alternaria). Greater bronchial responsiveness in winter was independently and significantly predicted by a physician's diagnosis of asthma (difference in dFEV1%, 5.6; 95% confidence intervals [95% CI], 2.8 to 8.5; p = 0.0001) and by shortness of breath (difference in dFEV1%, 4.2; 95% CI, 2.1 to 6.3; p = 0.0001). These factors were also predictive of greater responsiveness in the spring, as was atopy (difference in dFEV1%, 3.2; 95% CI, 1.8 to 4.6; p = 0.0001). Analysis of specific allergens further revealed that reactivity to perennial allergens (house-dust mite, cat dander) was predictive of bronchial responsiveness in both winter and spring. However, the change in responsiveness between seasons was most significantly predicted by allergy to seasonal grass pollen, i.e., ragweed or orchard grass (change in dFEN1%, 2.6; 95% CI, 0.6 to 4.5; p = 0.01). In summary, our study demonstrates increased bronchial responsiveness in spring among children allergic to grass pollen. This increased springtime responsiveness is paralleled by increased ambient aeroallergen exposure, which might be one of the mechanisms accounting for greater springtime mortality among asthmatic children.