Characteristics of Obstructive Sleep Apnea Syndrome Related Hypertension and the Effect of Continuous Positive Airway Pressure Treatment on Blood Pressure

Continuous positive airway pressure (CPAP) prevents the airway collapse, avoids the occurrence of intermittent hypoxemia and arousal, is the preferred treatment for OSAS and has been widely used in clinical. The investigator would compare the effect of CPAP treatment on awake and sleep BP level at the first night and 2 weeks therapy among three groups. Moreover, whether or not the sympathetic-parasympathetic nerve balance and the renin-angiotensin-aldosterone system are different in three groups would also be evaluated.