A LONGITUDINAL EVALUATION OF BRONCHIAL RESPONSIVENESS TO METHACHOLINEIN CHILDREN - ROLE OF BASE-LINE LUNG-FUNCTION, GENDER, AND CHANGE IN ATOPIC STATUS

A longitudinal study was done to evaluate the determinants of bronchia l responsiveness (BR) to methacholine in children and adolescents. A c ohort of 892 7- to 11-yr-old schoolchildren was restudied after a 3.5- yr interval. The same protocol for methacholine challenge (up to 64.0 mg/ml) and skin prick testing was employed at both the baseline survey and follow-up. An overall decline in the level of BR was observed, th e geometric mean slope (percent decline in FEV(1) per mg/ml of methach oline) decreasing from 0.68 (95% CI = 0.61 to 0.75) to 0.51 (95% CI = 0.46 to 0.57) (p < 0.001). At both surveys, the strongest determinants of slope were baseline pulmonary function level (FEF(25-75)) and degr ee of atopic status. After adjusting for log FEF(25-75), no gender dif ference was found in the first survey, whereas girls had greater BR th an boys at follow-up. Longitudinal changes in skin prick test reactivi ty were associated with the BR level. Subjects in whom an initially po sitive skin prick test became negative (5.3%) had an increased slope a t baseline but a follow-up slope similar to that of never skin-reactor s. Conversely, those whose skin prick test converted from negative to positive (13.0%) had a slope similar to that of never-reactors at base line but became stronger responders to methacholine than never-reactor s at follow-up. Finally, responsiveness was highest in the presence of persistently positive skin prick testing (13.5%). In conclusion, BR d eclines from childhood to adolescence, paralleling the increase in lun g function during this period; the decline is less pronounced in femal es. Changes in atopic status are associated with modifications in the BR level.