Diaphragm fatigue during exercise at high altitude: the role of hypoxia and workload. - Gudjonsdottir,M.; Appendini,L.; Baderna,P.; Purro,A.; Patessio,A.; Vilianis,G.; Pastorelli,M.; Sigurdsson,S.B.; Donner,C.F. (Eur Respir J, 2001)