The purpose of this study is to assess the prevalence of COPD among individuals aged 35 - 59 years based results of spirometry before and after bronchodilator, presence of structural changes in lungs (emphysema, inflammatory changes and thickening of the walls of the large and small airways)detected by computer tomography as well as the symptoms of COPD. The study has three study groups: smokers of conventional cigarettes; those who had quit smoking 1 - 5 years ago, and those who haven't smoked cigarettes.