( 1 ) Epworth sleepiness scale ( ESS ) score , apnea-hypopnea index ( AHI ) and arousal index were significantly lower ( 8.25 5.41 vs. 4.08 3.43 , 39.95 7.32 vs. 4.71 1.80 and 39.69 4.40 vs. 15.20 2.05 , P < 0.01 ) while not rapid eye movement ( NREM ) III and rapid eye movement stage of sleep time and lowest pulse oxygen saturation ( LSaO2 ) were significantly higher in NPPV group than in control group [ ( 4.53 2.10 ) % vs. ( 16.78 2.59 ) % , ( 8.37 1.380 ) % vs. ( 15.25 1.41 ) % , ( 77.15 6.72 ) % vs. ( 93.35 2.03 ) % , P < 0.01 ] after 3 months therapy .