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.