Effects of Asthma on Pulmonary Function in Children: A Longitudinal Population-based Study

Abstract

Data from a longitudinal study of childhood factors influencing the development of chronic obstructive lung disease were used to assess the effects of asthma on lung function development in male and female children. A population-based cohort of 602 white children, initially aged 5 to 9 yr, was observed prospectively for 13 yr. Spirometry was performed and a standardized respiratory and illness questionnaire was administered by trained interviewers on a yearly basis. Forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), and forced expiratory flow between 25 and 75% of vital capacity (FEF_25–75) were used as measures of lung function. The total number of children reporting asthma over the course of the study was 67. Male asthmatic subjects (n = 42) had larger average percentage of predicted FVC than nonasthmatic males (n = 277). Female asthmatic subjects (n = 23) had a lower average percentage of predicted FEV₁ than nonasthmatic females (n = 260). In a multivariate analysis of the individual lung function measures, adjusting for previous level of pulmonary function, age, height, change in height, and personal and maternal smoking, males reporting active asthma had a significantly larger FVC than males with no history of asthma. In contrast, females with active asthma had a significantly smaller FEV₁ than females with no history of asthma. Both males and females with active asthma had decreased FEF_25–75. From our analysis, we would predict that a female who develops asthma at age 7 would experience a 5% reduction in FEV₁ by age 10 and a 7% deficit by age 15. In our sample, asthmatic females had a greater risk of hospitalization for asthma than male asthmatic subjects (4 of 23, 6%, versus 1 of 42, 2%; p = 0.049). These results demonstrate apparent sex differences in the relationship between asthma and lung function development, with males more likely to have asthma but females experiencing a greater deficit in pulmonary function.