1. Respiratory Function Laboratory, Department of Pulmonology, Cruces University Hospital, Barakaldo, Bizkaia, Spain.
2. Service Health Technology Assessment of the Basque Country, Department of Health, Basque Government, Vitoria, Spain.
3. Network Research Center of Respiratory Diseases, Barakaldo, Bizkaia, Spain.
4. University of the Basque Country, Barakaldo, Bizkaia, Spain.