Compliance of continuous positive airway pressure （CPAP） derived from auto-titration is similar to that derived from manual titration, although pressure derived from the former was usually 2-5 cmH2O higher than the latter. Therefore the Investigators hypothesize that accurate titration maybe not necessary for successful treatment of obstructive sleep apnea (OSA) as long as CPAP pressure was not lower than the minimal effective pressure.

Study Design: A randomized, cross-over and double-blind study. Objective: To compare the pressure of 10 cmH2O and minimal effective pressure derived from manual titration on the effect of CPAP treatment in OSA. Methods: Patients with suspected OSA (age, body mass index and symptom) to be referred to a sleep centre were recruited. Patients with OSA confirmed by overnight full polysomnography (PSG) were invited to do standard overnight manual titration under PSG based on the Academy of Sleep Medicine (AASM) manual guidelines. Patients whose manual titration pressure lower than 10cmH2O and willing to participate in the study were invited to repeat two more nights (3th PSG and 4th PSG) under CPAP pressure at both 10cmH2O and the pressure derived from manual titration in random order. The sleep apnea-hypopnea index (AHI), obstructive sleep apnea index (OHI), arousal index (ArI), oxygen desaturation index (ODI), sleep structure, and treatment preference were to be observed.

Inclusion Criteria:

1. reported snore, apnea and daytime sleepiness;
2. a diagnosis of obstructive sleep apnea with polysomnography according to ASSM guideline(apnoea-hypopnea-index(AHI)≥5 events/h) and need to be treated with continuous positive airway pressure;
3. willing to participate after informed consent.

Exclusion Criteria:

1. Evidence of severe coronary or cerebral, cardiovascular disease and significant memory, perceptual or behavioural disorder;
2. Severe respiratory disease defined as severe chronic obstructive pulmonary disease(ie. FEV1/FVC<70% and FEV1<50%predicted) or resting awake SaO2<90%
3. Have known contraindications with CPAP, like current pneumothorax and hemoptysis, et al.
4. Central sleep apnea>10 events/h；
5. Frequent nasal congestion；
6. Optimal treatment CPAP pressure(by manual titration) equal or higher than 10cmH2O.