Obstructive sleep apnea (OSA) is associated with behavioral, cognitive, metabolic and cardiovascular conditions. Continuous Positive Airway Pressure (CPAP) is the gold standard treatment for OSA. Despite being the most effective treatment for OSA, 46 to 83% of patients do not adhere to CPAP. New technologies for CPAP treatment have been developed in order to improve patient`s comfort, adherence and effectiveness in reducing apnea, hypopneas and flow limitation events. As an example, the FLEX- PLUS technology which increases inspiratory positive pressure and decreases expiratory positive pressure would soften the rhythm of breathing. Sensawake is another technology which evaluates breathing pattern changes during CPAP therapy. When the breathing pattern suggests that patient is awake, a prompt relief in pressure is activated, like ramp feature. However, it is not clear whether CPAP FLEX- PLUS or Sensawake are superior compared with fixed pressure CPAP, in terms of polysomnographic parameters, especially flow limitation or adherence to treatment. Objective: To compare the effect of fixed pressure CPAP, CPAP FLEX- PLUS and Sensawake on sleep and compliance parameters in patients with moderate to severe OSA. Methods: Fifty male patients with moderate to severe OSA will be included in a crossover design study. All patients will use each CPAP modality for 30 days in a randomized order, namely CPAP with Fixed Pressure, Flex- PLUS and Sensawake. A week of washout period will be applied between treatments. All patients will wear the same nasal mask brand. At the end of each treatment (every 4 weeks), patients will undergo polysomnography and fill out Epworth, FOSQ, Pittsburgh questionnaires and a visual analogue scale assessing CPAP side effects and patient´s comfort. Finally, adherence to CPAP modalities will be systematically checked.