1. The Clinic for Obstructive Pulmonary Diseases and Acute Pneumopathies, Institute for Pulmonary Diseases of Vojvodina, Sremska Kamenica, Serbia
2. Faculty of Medicine, University of Novi Sad, Novi Sad, Serbia
3. Clinical Centre of Vojvodina, Clinic for Otorhinolaryngology and Head and Neck Surgery, Novi Sad, Serbia