Only subjects who were not receiving medical treatment for respiratory diseases and who had a clean family medical history and personal habits were selected. Among smoking habits, those who smoked cigars other than filtered cigarettes or tobacco pipes were excluded. Only subjects who have been smoking for 1 to 3 years were included. We ensured that the research subjects fully understood the research project and signed consent was obtained from each participant. Our study was approved by the Committee of Clinical Testing at Korea Nazarene University and was screened according to the ethical standards of the Helsinki Declaration. General characteristics of study participants are summarized in Table 1.