1 Faculty of Medicine and Life Sciences, Hasselt University, Hasselt, Belgium, Department of Respiratory Medicine, Ziekenhuis Oost-Limburg, Genk, Belgium Faculty of Medicine and Life Sciences, Hasselt University, Hasselt, Belgium, Department of Respiratory Medicine, Algemeen Ziekenhuis Vesalius, Tongeren, Belgium Faculty of Medicine and Life Sciences, Hasselt University, Hasselt, Belgium, Department of Respiratory Medicine, Ziekenhuis Oost-Limburg, Genk, Belgium.