1. Department of Respiratory Medicine, National Hospital, University of Oslo, Oslo, Norway; Aker University Hospital, N 0514 Oslo, Norway
2. Lung Biology, School of Health and Life Sciences, King's College, London, UK
3. Pharmacology Department, J Uriach y Compania SA, Barcelona, Spain
4. Department of Respiratory Medicine and Allergy, University Hospital, Umeå, Sweden
5. National Institute of Occupational Health, Oslo, Norway
6. Norwegian Institute of Public Health, Oslo, Norway
7. Section of Medical Statistics, University of Oslo, Norway
8. Department of Respiratory Medicine, National Hospital, University of Oslo, Oslo, Norway