1. Department of Pulmonary MedicineHelsinki University Central Hospital, Heart and Lung Center and the University of Helsinki, Helsinki, Finland
2. Department of Internal MedicineRespiratory Diseases, Institute of Clinical Medicine, University of Oulu, Oulu, Finland
3. Medical Research Center Oulu, Respiratory Research Unit, Oulu University Hospital, Oulu, Finland
4. Unit of Medicine and Clinical ResearchPulmonary Division, University of Eastern Finland, Kuopio, Finland
5. Division of Respiratory MedicineCenter for Medicine and Clinical Research, Kuopio University Hospital, Kuopio, Finland