Study objective: Childhood exposure to environmental tobacco smoke (ETS) adversely affects dynamic spirometric indexes as a result of combined early life (including in utero) and current exposure to parental smoking. The aim of our study was to investigate the effect of ETS on lung function and to identify the most sensitive functional parameter for evaluating lung damage.

Design: Cross-sectional survey.

Setting: Health survey on secondary school children.

Subjects: Eighty adolescents boys (mean age +/- SD, 16 +/- 1 years) classified in three groups: 21 smokers, 30 nonsmokers, and 29 passive smokers.

Measurements: Standardized questionnaire on the smoking habits of the subjects and their parents; assay of urinary cotinine level and measurement of the cotinine/creatine ratio (CCR); and lung function tests, including measurements of lung volumes, spirometric dynamic parameters, and the single-breath diffusing capacity of the lung for carbon monoxide (DLCO).

Results: Passive smokers presented a higher residual volume than nonsmokers, and a lower maximal expiratory flow at 25% of FVC (MEF(25)) and DLCO. Passive smokers whose mothers had smoked during pregnancy had significantly lower MEF(25) percentage, DLCO, carbon monoxide transfer coefficient, and diffusion capacity of the alveolar-capillary membrane (DM) values than did passive smokers whose mothers had given up smoking during pregnancy. Nevertheless, the MEF(25) and DM values of subjects with mothers who had given up smoking during pregnancy were lower than those observed in nonsmokers (p < 0.05), suggesting a negative effect of passive smoking independent of the mother's smoking habit during pregnancy. A statistically significant, negative correlation was found between CCR and DLCO in smokers (r = - 0.63, p < 0.01) and in passive smokers (r = - 0.91, p < 0.001), but not in nonsmokers (r = 0.26, p = not significant), suggesting a dose-effect relationship.

Conclusions: Current exposure to ETS in healthy male adolescents is associated with lung function impairment independently of the effects of maternal smoking during pregnancy. More information may be obtained from determining static lung volumes and DLCO.