Gender, environmental tobacco smoke, and pulmonary function in rural children and adolescents: the Humboldt study.

We examined the gender-related association between household exposure to environmental tobacco smoke (ETS) and pulmonary function among 862 children and adolescents aged 6 to 17 years living in the town of Humboldt, Saskatchewan, in 1993. Pulmonary function tests included forced vital capacity (FVC), forced expiratory volume in one second (FEV1), maximum mid-expiratory flow rate (FEF25-75), and flow rates at 75%, 50%, and 25% of vital capacity (Vmax75, Vmax50, and Vmax25). Each pulmonary function test variable was regressed on age, height, weight, and their quadratic and cubic polynomials, with the terms significant at the alpha level of 0.10 being retained. Residuals for the pulmonary function test variables, which are the differences between the observed and predicted values, were calculated. Estimations of ETS exposure were parental smoking status, number of household smokers, total daily cigarette consumption, and number of cigarettes smoked daily at home by household members. Maternal smoking status was significantly related to residual FEF25-75, Vmax75, Vmax50, and Vmax25. Number of household smokers and daily cigarette consumption by household members were significantly associated with FEV1, FEF25-75, Vmax75, Vmax50, and Vmax25, and the association between ETS exposure and pulmonary function was stronger in girls than in boys. Interaction of gender and number of cigarettes smoked daily at home was significantly related to FEF25-75, Vmax75, Vmax50, and Vmax25 among the non-smoking subjects. We concluded that ETS exposure had a larger effect on pulmonary function in girls than in boys.