Abstract： Objective:To investigate the association between oxygen desaturation rate and blood pressure (BP) among severe obstructive sleep apnea syndrome (OSAS) and the possible mechanism.Methods:Patients with snoring were enrolled from the Department of Sleep Medicine Center, the Affiliated Huaian No.1 People′s Hospital of Nanjing Medical University form March 2018 to January 2019 and underwent polysomnography (PSG). Noninvasive BP and Heart rate variability were full-night monitored continuously and synchronized with PSG. Based on the PSG results and exclusion criteria, a total of 86 severe OSAS patients were enrolled in this study and divided into two groups according to the ambulatory BP measurements: hypertensive group ( n=44) and normotensive group ( n=42). Oxygen desaturation rate was expressed as the change in the percentage of pulse oxyhemoglobin saturation (SpO 2) per second during desaturation events after the obstructive apnea events occurred. The PSG parameters were compared between the two group and the multiple regression analyses were used to explore the association between oxygen desaturation rate and BP and its possible mechanism. Results:The apnea-hyperpnoea index (AHI) and respiratory event-related arousals (RERAs) were significantly higher in hypertensive group than those in normotensive group [(69.8±18.2) vs. (56.5±13.9) event/h; (40.5±17.4) vs. (30.2±14.6) event/h, both P<0.01]. In addition, hypoxia exposure conditions in the hypertensive group were more severe than those in the normotensive group, especially oxygen desaturation rate [(0.45±0.14)%/s vs. (0.33±0.10)%/s, P<0.001]. After adjusting for age, sex, neck circumference, waist circumference, smoking, drinking, the regression analyses showed that only the oxygen desaturation rate was significantly associated with both awake and asleep BP in OSAS patients ( β=0.473, 0.478, both P<0.01) and the correlation analyses suggested that the oxygen desaturation rate was related to the both awake and asleep sympathetic-parasympathetic imbalance ( r=0.367, 0.337, both P<0.01). Conclusion:Oxygen desaturation rate is closely related to BP levels in patients with severe OSAS, and the underlying mechanism is associated with the increased sympathetic activity.