SEASONAL AND ALLERGENIC PREDICTORS OF BRONCHIAL RESPONSIVENESS TO DISTILLED WATER

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 o f children 7 to 10 yr of age. The bronchial challenge test consisted o f 10 min of tidal inhalation of an aerosol of ultrasonically nebulized distilled water; the resulting percentage decrease in FEV(1) (dFEV(1) %) was recorded. Atopy was determined on the basis of skin-test positi vity (any wheal with a diameter greater than that obtained with a posi tive control) to seven allergens (cat dander, dog dander, house-dust m ite, birch, raygrass, orchard grass, and Altemaria). Greater bronchial responsiveness in winter was independently and significantly predicte d by a physician's diagnosis of asthma (difference in dFEV(1)%, 5.6; 9 5% confidence intervals 95% CI, 2.8 to 8.5; p = 0.0001) and by short ness of breath (difference in dFEV(1)%, 4.2; 95% CI, 2.1 to 6.3; p = 0 .0001). These factors were also predictive of greater responsiveness i n the spring, as was atopy (difference in dFEV(1)%, 3.2; 95% CI, 1.8 t o 4.6; p = 0.0001). Analysis of specific allergens further revealed th at reactivity to perennial allergens (house-dust mite, cat dander) was predictive of bronchial responsiveness in both winter and spring. How ever, the change in responsiveness between seasons was most significan tly predicted by allergy to seasonal grass pollen, i.e., ragweed or or chard grass (change in dFEV(1)%, 2.6; 95% CI, 0.6 to 4.5; p = 0.01). I n summary, our study demonstrates increased bronchial responsiveness i n spring among children allergic to grass pollen. This increased sprin gtime responsiveness is paralleled by increased ambient aeroallergen e xposure, which might be one of the mechanisms accounting for greater s pringtime mortality among asthmatic children.