1 Pulmonary Diseases/Home Mechanical Ventilation, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands m.l.duiverman@umcg.nl.
2 Groningen Research Institute of Asthma and COPD (GRIAC), University of Groningen, Groningen, The Netherlands.
3 Respiratory Medicine Unit, Policlinico "G. Rodolico-San Marco" University Hospital, Catania, Italy.
4 Department of Clinical and Experimental Medicine, University of Catania, Catania, Italy.