The investigators hypothesized that heated humidified high-flow nasal cannula oxygen(HFNC) along with high quality of sleep, in comparison with noninvasive positive pressure ventilation (NIV), could reduce the release of inflammatory marker C-reactive protein(CRP), which as independent predictor of atrial fibrillation（AF）, further lower the incidence of new-onset AF following coronary artery bypass grafting(CABG).