Ten males with COPD ( FEV ( 1 ) = 47 + / - 17 % pred [ mean + / - SD ] ) performed randomized constant-load cycling at 60 % of maximal work rate breathing air , hyperoxia ( 40 % O ( 2 ) , 60 % N ( 2 ) ) , normoxic helium ( 21 % O ( 2 ) , 79 % He ) , or helium-hyperoxia ( 40 % O ( 2 ) , 60 % He ) .
