The investigators are looking at the effect of humidified nasal high-flow with oxygen (HNHF-O2) on air exchange during exacerbations of COPD. HNHF-O2 therapy may have beneficial effects in patients with severe breathing impairment that results in low oxygen in the blood. Some studies show that patients with low blood oxygen levels who use HFNC oxygen have lower rates of needing mechanical ventilation.