Inclusion Criteria:  ● Subjects who complete a standard polysomnography study.  Exclusion Criteria:  Patients who have heart failure (as determined by clinical symptoms or signs with elevated brain natriuretic peptide and echocardiography showing structural or functional abnormalities) Coronary artery disease (stress electrocardiography, myocardial scintigraphy, or coronary angiography proven coronary artery lesion) Hypertrophic cardiomyopathy Known infiltrative disease e.g. amyloidosis Chronic kidney disease severe than stage III Ischemic or hemorrhagic stroke Central sleep apnea, Hypoventilation syndrome (TCO2 or artery PaCO2 exceed 50 mmHg) Unstable hemodynamic state Eastern Cooperative Oncology Group Performance Status higher than grade 2 Pregnant women will be excluded. Polysomnography exam showing sleep time less than 2 hours Patients who receive surgery or oral appliance during the study period