1. Department of Pulmonary Diseases, Medical Faculty, Medical University - Sofia, UMHAT "St. Ivan Rilski, Bulgaria
2. Department of Professional Diseases, Medical Faculty, Medical University - Sofia, UMHAT "St. Ivan Rilski", Bulgaria
3. Department of Intensive Care, Medical Faculty, Medical University - Sofia, Clinic for Cardiology, UMHAT "Alexandrovska", Bulgaria
4. Department of Pathology, Medical Faculty, Medical University-Sofia, Bulgaria