Maternal and personal cigarette smoking synergize to increase airflow limitation in adults

Susceptibility of the lungs to cigarette smoke is poorly understood. It is not known whether maternal smoking increases chronic obstructive pulmonary disease (COPD) risk. In 1998 we reported an inverse association between maternal smoking (prerecorded) and FEV1 in adults. Because FEV1 and FVC are strongly correlated, it is unclear whether the association in question reflects a link with lung volume, airflow limitation, or both. We extended our original analysis to investigate whether maternal and personal smoking synergize to increase airflow limitation. We estimated residual FEV1 to express FEV1 variation that was not associated with FVC. Maternal smoking was inversely associated with FVC and FEV1 irrespective of personal smoking. It was inversely associated with FEV1/FVC, forced midexpiratory flow rates (FEF25-75 [mean forced expiratory flow during the middle half of the FVC], FEF25-75/FVC), and residual FEV1 in current smokers but not in never or former smokers (heterogeneity p = 0.016, 0.024, 0.021, and 0.016, respectively). We tested the clinical relevance of findings in ever smokers without asthma: 10 cigarettes/day maternal smoking increased prevalent COPD by 1.7 (95% confidence interval: 1.2-2.5) after adjustment for covariates. Maternal smoking impairs lung volume irrespective of personal smoking and appears to synergize with personal smoking to increase airflow limitation and COPD.