Sex-specific effects of asthma on pulmonary function in children

To evaluate the effects on lung function of asthma, time since diagnosis of asthma, and age at diagnosis of asthma, we examined school children in a c ohort of 2,277 fourth- and seventh-graders at least twice during a 4-yr fol low-up period. Sex-specific models for each lung function were fitted throu gh mixed-effects models that used regression splines and captured age-depen dent trends in the effect of asthma on lung function. In males, a history o f asthma was associated with large and statistically significant deficits i n maximum midexpiratory flow (MMEF) (-4.89%) and forced expiratory flow at 75% of expired FVC (FEF75) (-6.62%), whereas in females these deficits were smaller (-1.93% and -2.45%, respectively) and were not statistically signi ficant. However, larger deficits were seen in both males and females with l onger time since diagnosis. In males with more than 6 yr since diagnosis, t here were significant deficits in FEV1 (-3.91%), MMEF (-7.39%), FEF75 (-8.1 2%), and peak expiratory flow rate (PEFR) (-4.65%) as compared with childre n with less than 3 yr since diagnosis. There were fewer females with more t han 6 yr since diagnosis, but deficits were similar to those of males for F EV1 (-2.52%), MMEF (-9.26%), and FEF75 (-14.28%). Large deficits in flow ra tes in both large and small airways were observed in males and females for whom asthma was reported to have been diagnosed before age 3 yr. There was little evidence that lung growth in children with asthma "catches up" at ol der ages. Therefore, because a constant percent deficit in lung function im plies an increasingly large absolute deficit in older children with larger lungs, these results are consistent with prior evidence that lung function deficits in children with asthma persist into adulthood. We also suggest th at in children, commonly observed differences between sexes in the impact o f asthma on lung function may reflect differences in the duration and age o f onset of asthma in males and females.