1 Department of Tobacco Control and Prevention of Respiratory Disease, China-Japan Friendship Hospital, Beijing, China; Center for Respiratory Diseases, China-Japan Friendship Hospital, Beijing, China; National Clinical Research Center for Respiratory Diseases, China-Japan Friendship Hospital, Beijing, China; National Center for Respiratory Medicine, China-Japan Friendship Hospital, Beijing, China; World Health Organization Collaborating Centre for Tobacco Cessation and Respiratory Diseases Prevention, Beijing, China; Institute of Respiratory Medicine, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100029, China. Electronic address: danxiao@263.net.
2 Center for Respiratory Diseases, China-Japan Friendship Hospital, Beijing, China; National Clinical Research Center for Respiratory Diseases, China-Japan Friendship Hospital, Beijing, China; National Center for Respiratory Medicine, China-Japan Friendship Hospital, Beijing, China; World Health Organization Collaborating Centre for Tobacco Cessation and Respiratory Diseases Prevention, Beijing, China; Institute of Respiratory Medicine, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100029, China.