Obstructive sleep apnea-hypopnea syndrome (OSAHS) is highly prevalent but is underdiagnosed in hypertensive patients. There are few studies on the internal association of OSAHS with two predictors of cardiovascular events, namely heart rate variability (HRV) and blood pressure variability (BPV), in hypertensive patients.

To explore the influence of OSAHS on HRV and BPV in hypertension patients, and to develop and validate a nomogram for predicting the risk of OSAHS in these patients using HRV and BRV related indicators.

Two hundred and twenty-eight hypertensive patients〔including 114 without OSAHS (simple hypertension subgroup) and 114 with OSAHS (hypertension with OSAHS subgroup) assessed by the diagnostic criteria of OSAHS〕were selected as internal validation group from the Second Xiangya Hospital of Central South University from January 2018 to December 2020, and other 34 hypertensive patients with or without OSAHS who hospitalized in the same hospital during January to February 2021 were selected as an independent external verification group. General information (age, gender, BMI, etc.〕, average blood pressure level〔nighttime systolic blood pressure (nSBP), etc.〕, BPV related indices〔nighttime systolic blood pressure standard deviation (nSSD), nighttime diastolic blood pressure standard deviation (nDSD), 24-hour diastolic blood pressure standard deviations (24 hDSD), etc〕, blood pressure circadian rhythm, HRV related parameters〔standard deviation of the mean RR intervals (SDANN), low frequency (LF), etc.〕, polysomnography parameters〔oxygen desaturation index (ODI), apnea hypopnea index (AHI), minimum oxygen saturation (MinSpO₂), etc.〕. Multiple linear regression analysis were used to explore the influencing factors of HRV and BPV. Restricted cubic splines were used to test the correlation of the average blood pressure level, BPV and HRV related indicators with the risk of OSAHS. Multivariate Logistic regression model was used to analyze the influencing factors of OSAHS, and the screened factors were used to construct a nomogram for predicting OSAHS risk. The Bootstrap method was used to validate the performance of the internal and external groups in the nomogram model. And its predictive value for OSAHS risk in the two groups was assessed using the receiver operating characteristic (ROC) curve with the area under the curve (AUC) and other indicators calculated.

Multiple linear regression analysis showed that BMI, ODI and MinSpO₂ were independently associated with nSSD, nDSD or HRV related indices in hypertensive patients with OSAHS (P<0.05). Restricted cubic splines revealed that BPV related indices had a nonlinear relationship with OSAHS, and so did HRV related indices (P<0.05). Multivariate Logistic regression analysis showed that nSBP, nSSD, 24 hDSD, SDANN, LF, age and BMI were associated with OSAHS in hypertensive patients (P<0.05). The Bootstrap method showed that, the absolute error of the nomogram constructed using age, BMI, nSBP, nSSD, 24 hDSD, SDANN and LF was 0.013 in internal verification group, and was 0.021 in external verification group, indicating that the model had good calibration. The values of the AUC of the nomogram in predicting the risk of OSAHS in hypertension in internal and external validation groups were 0.861〔95%CI (0.818, 0.919), P<0.001〕 and 0.744〔95%CI (0.691, 0.839), P<0.001〕, respectively.

OSAHS can increase the nSSD and nDSD and decrease HRV in hypertensive patients. Both HRV and BPV are closely related to the severity of OSAHS. Nocturnal hypoxia may be more likely to cause changes in blood pressure and heart rate. Our nomogram could be used to facilitate individualized prediction of OSAHS risk in hypertensive patients. HRV and BPV parameters might be powerful tools to screen for OSAHS.