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Abstract
• Particle deposition and tracheobronchial clearance were measured in six pairs of male monozygotic twins, four of which were discordant for cigarette smoking. The fraction of an inhaled aerosol that deposited on the ciliated airways showed variations within twin pairs comparable with variations in repeated tests on a single subject, and significantly smaller (P<.001) than among tests on different subjects. Variations that did occur were consistent with differences in forced expiratory volume (FEV1.0) values. The proximal shift of aerosol deposition and reduced FEV1.0 values in smokers indicated that they had some degree of bronch α-constriction.
Mucociliary clearance characteristics are qualitatively and quantitatively similar for nonsmoking and smoking concordant monozygotic twins, ie, comparable with repeated tests on a single individual, reflecting their constitutional similarity. With one exception, clearance curves for twin pairs discordant with respect to smoking were also qualitatively indistinguishable. Nonsmokers, however, had greater upper bronchial clearance rates than their smoking twins.