1 Department of Pneumology, La Paz University Hospital, Madrid, Spain ; Instituto de Investigación Sanitaria del Hospital Universitario La Paz (IdiPAZ), Autónoma de Madrid University, Madrid, Spain.
2 Department of Pneumology, Río Hortega Hospital, Valladolid University, Valladolid, Spain.
3 Department of Pneumology, Santiago de Compostela Hospital, Santiago de Compostela Universidad, A Coruña, Spain.
4 Hermann Buhl Institute for Hypoxia and Sleep Medicine Research, Research Program of the Paracelsus Medical University and Clinic Ghersburg for Geriatric Rehabilitation, Bad Aibling, Germany.