The prevalence of OSA is 3.5~4.6% in Chinese adults. OSA leads to repetitive hypoxemia, hypercapnia, and arousal from sleep and is an independent risk factor for hypertension, stroke, coronary artery disease and congestive heart failure. CPAP is the first-line treatment for OSA. But many patients do not adhere to therapy. The upper airway(UA) anatomical abnormality is a prominent risk factor in Asian OSA patients, which might be improved by surgical strategies. However, surgery shows variable clinical effectiveness. One important reason for patients responding poorly to single treatment procedure is that multiple abnormal physiological traits contribute to OSA. High loop gain is one of the key non-anatomical risk factors. It will be useful to individualize therapy in OSA by better understanding the reversibility of increased LG, the interaction of LG and UA anatomical change as well as the condition that trigger reduction of LG. The project will test the hypothesis of 1) Elevated LG is induced in some patients and is reversible by treatment of OSA; 2) Change of LG is related to the improvement of sleep apnea; 3) An elevated LG is related to residual sleep apnea after upper airway surgery, which might be eliminated by adjunct CPAP therapy after surgery. The results would improve the efficiency of non-CPAP treatment and provide a potential combined treatment option for those patients with both elevated loop gain and anatomy risk factors in the Asian population.