Factors related to methacholine airway responsiveness in children

Studies of airway responsiveness (AR) have typically used similar dose schedules of methacholine for adults and children despite large ranges in subject size. Reported declines in AR with increasing age in children could be due to maturational changes or to proportionately smaller doses of methacholine in taller (older) children. Other investigators have related both height and various measures of lung function to AR. We examined data related to AR in 471 children, aged 6 to 8 yr, from a birth cohort. Each child underwent spirometry followed by sequential challenge with five doses of methacholine, ranging from 0.025 to 25 mg/ml, given with a dosimeter. Continuous slope and end FEV₁-change indexes of responsiveness were computed. Using stepwise regression modeling, we found no significant association between AR and either height or age after entering a variable reflecting asthma or wheezing. In contrast, we found that baseline measures of FVC, FEV₁/FVC, and FEF_25-75(%) were significantly related to AR after controlling for other variables (p = 0.001). However, when all three of the latter measures were added to models, FEF_25-75(%) was most closely related to AR. We conclude that after control for other variables, FEF_{25- 75}(%) and FVC, but not height, are significantly related to methacholine responsiveness in children.