ObjectiveTo explore the association between obstructive sleep apnea syndrome (OSAS) and heart rate variability (HRV) or circadian rhythm of blood pressure in hypertensives.MethodsA total of 102 inpatients and outpatients with hypertension were selected in our study, and they were divided into hypertension with OSAS group (55 cases) and primary hypertension group (47 cases). This study enrolled 50 concurrent healthy subjects(all with organic diseases excluded, and without comorbidities of hypertension or OSAS) as a control group. We compared and analyzed the HRV time-domain indexes of SDANN and rMSSD, and HRV frequency-domain indexes of LF and HF, as well as apnea hypopnea index (AHI), nocturnal mean oxygen saturation level, daytime and nocturnal blood pressure levels, and changes of circadian blood pressure rhythm.ResultsThe nocturnal minimum saturation of arterial oxygen (SaO₂) and nocturnal mean SaO₂ of patients in the hypertension with OSAS group were both lower than those of patients in the primary hypertension group, while AHI was higher (all P< 0.05). There were no statistically significant differences in the above sleep respiratory parameters between the primary hypertension group and the control group (all P> 0.05). There were no statistically significant differences in the daytime and nocturnal blood pressure levels, and the incidence of non-dipper pattern between the primary hypertension group and the control group (all P> 0.05). Comparisons of the aforementioned parameters between the hypertension with OSAS group and the control group all demonstrated statistically significant differences (all P< 0.01). The hypertension with OSAS group exhibited a significantly higher prevalence of non-dipper circadian blood pressure rhythm compared to the other two groups (all P< 0.05). Compared to the other two groups, the values of SDANN and LF of patients in the hypertension with OSAS group were higher, while the values of rMSSD and HF were lower (all P< 0.05). There were no statistically significant differences in the LF, HF, SDANN and rMSSD values between the primary hypertension group and the control group (all P> 0.05).ConclusionPatients with OSAS demonstrate increased nocturnal blood pressure level, enhanced sympathetic nerve tension and decreased vagus nerve tension, as well as increased risk of cardiovascular and cerebrovascular diseases.