We hypothesize that HFNC may increases exercise time in COPD patients recovering from acute exacerbation compare to VM. A randomized, cross-over clinical trial in which either HFNC or VM may be used as an adjunct in 10-MST in random order, respectively, will be performed to compare the endurance time. The physiological effect of HFNC and VM during exercise will also be measured to explore the mechanism.
