1. Department of Physiological Sciences II, Medical School, University of Barcelona, L'Hospitalet, Barcelona, Spain.
2. Internal Medicine Unit, Hospital of Valle d'Hebrón, Barcelona, Spain
3. Intensive Care Unit, Hospital University of Bellvitge, Idibell, L'Hospitalet, Barcelona, Spain.
4. Chronic Fatigue Syndrome Unit, Delfos Clinical Centre, Barcelona, Spain.
5. University of Vic, Barcelona, Spain.