Xu J, et al. - The properties and associated influential factors of blood pressure (BP) fluctuation in severe obstructive sleep apnea syndrome (OSAS) with and without hypertension were determined. Nocturnal and awake BP levels were shown to be related more to the nocturnal hypoxic duration and BP fluctuation than with apnea-hypopnea index (AHI) in severe OSAS. Furthermore, it was noted that both hypoxia and arousal, especially hypoxia, could induce nocturnal BP fluctuation.