1. Biocruces Bizkaia Health Research Institute; Barakaldo Spain
2. Respiratory Physiotherapy Unit, Rehabilitation Service, Pneumology; Biocruces Health Research Institute, Cruces University Hospital; Barakaldo Spain
3. Department of Preventive Medicine and Public Health; University of the Basque Country; Leioa Spain
4. University of the Basque Country; San Sebastián Spain