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METHODS

The Human Subjects Research Protection Program of the University of California San Diego approved this study, and the procedures followed conformed with this institution’s guidelines. Healthy, nonsmoking subjects were recruited by advertisement, informed of the risks of the study, and signed informed consent. A clinical history was obtained, with particular reference to smoking and the cardiopulmonary system, and subjects underwent routine spirometry. Subjects were excluded if they had smoked more than 200 cigarettes (10 packs) in their lifetime; however, virtually all the subjects had never smoked. In all, 56 subjects (19 women and 37 men) participated in the study.