1. Department of Respiratory Medicine, Onze-Lieve Vrouw Ziekenhuis, 9300 Aalst, Belgium
2. Faculty of Medicine and Life Sciences, Ghent University, 9000 Ghent, Belgium
3. Clinical Trial Center and Center of Biostatistics, Onze-Lieve Vrouw Ziekenhuis, 9300 Aalst, Belgium
4. Department of Respiratory Medicine, Antwerp University Hospital, 2650 Edegem, Belgium