One limitation of the current study is that the sample consisted of highly tobacco dependent and treatment-seeking adolescents, and therefore was not representative of all teenage smokers. We did not control for degree of craving or time since last cigarette. Also, unexamined determinants of puff volume, such as nicotine and tar yield from cigarettes, may have affected our findings. Because of suboptimal data on usual brand smoked, our analyses did not control for nicotine and tar delivery which have been shown to impact volume of smoke inhaled [28]. Interestingly, the absence of a relationship between rate of metabolism and total puff volume suggests that any potential causal inference might be more attributable to pattern of puffing. Mechanisms for such relationships have been suggested (e.g., nicotine receptor activation, airway sensorial effect [29]) but remain speculative. Finally, the implications of our puff-duration findings are unclear, because in at least one study, puff duration did not affect nicotine concentrations [8].
