So far, continuous positive airway pressure (CPAP) is the standard treatment for patients with severe OSA. CPAP could improve daytime wakefulness, blood pressure and quality of life (QOL). Several studies tried to identify factors predicting the CPAP effect and most concluded CPAP was not effective for patients with high apnea-hypopnea index but not sleepy. All of them determine the CPAP effect in terms of daytime function, lowering of blood pressure and QOL. None of these studies evaluate the CPAP effects in terms of improvement of sympathetic hyperactivity, inflammatory mediators and metabolic abnormalities. Therefore, we assumed patients whose daytime functions didn't improve after CPAP treatment still possibly got benefit from altering factors contributing to cardiovascular consequences.