Role of basal autonomic functions in patients with increased morning blood pressure surge.

Background: Morning blood pressure (BP) surge (MS) is associated with cardiovascular events. The autonomic nervous system plays an active role in the regulation of BP and its function can be evaluated by heart rate variability (HRV) analysis. This study aimed to evaluate autonomic nervous system functions in patients with increased MS.

Methods: Patients who underwent ambulatory BP monitoring (ABPM) and 24-h rhythm Holter in our hospital during the same period between 2017 and 2022 were evaluated. HRV parameters were obtained from 24-h rhythm Holter recordings. MS values of the patients were calculated from ABPM records and patients were divided into four groups according to the MS quartiles. HRV parameters and other parameters were compared between the groups.

Results: A total of 129 patients were included in the study. The mean age of the patients was 57.2 ± 18.2 years, and 63 (48.8%) were male. HF, the square root of the mean squared differences of successive normal-to-normal intervals (rMSSD), and the proportion of adjacent RR intervals differing by >50 ms in the 24-h recording (pNN50) were statistically significant between the groups ( P  = 0.039, P  = 0.013, P  = 0.011, respectively). In univariate regression analysis, low-frequency/high-frequency ratio was positively associated with MS and HF, SDNNi, rMSSD, and pNN50 were negatively associated ( β  = 0.207, P  = 0.019; β  = -0.272, P  = 0.002; β  = -0.201, P  = 0.022; β  = -0.265, P  = 0.002; β  = -0.278, P  = 0.001, respectively). Multiple linear regression analysis showed an independent association between HF, low-frequency/high-frequency ratio, rMSSD, pNN50, and MS ( β  = -0.247, P  = 0.005; β=0.206, P  = 0.017; β  = -0.209, P  = 0.005; β  = -0.227, P  = 0.008, respectively).

Conclusion: We found an independent association between HRV parameters associated with vagal tone and MS. The findings of our study suggest that the increased sympathetic activity detected in patients with high MS in previous studies may be due to a decrease in basal vagal tone.