Ambulatory Blood Pressure and Autonomic Imbalance: Associations Between 24-Hour Blood Pressure Monitoring and Holter-Derived Heart Rate Variability.

Objective: To assess the association between ambulatory blood pressure indices and cardiac autonomic modulation assessed by heart rate variability derived from 24-hour holter electrocardiography. Design and method: This cross-sectional analysis included 132 adult participants who underwent 24-hour ambulatory blood pressure monitoring and simultaneous 24-hour holter electrocardiography. Systolic blood pressure, diastolic blood pressure and mean arterial pressure were obtained for 24-hour, daytime and night-time periods. Heart rate variability indices included the low-frequency to high-frequency ratio and coefficients of variation of very low- and high-frequency components. Body mass index was calculated from measured weight and height. Associations between ambulatory blood pressure indices and heart rate variability parameters were assessed using Pearson correlation analysis. Multivariable linear regression was performed to evaluate the independent association between heart rate variability indices and night-time diastolic blood pressure after adjustment for age, sex and body mass index. Results: The low-frequency to high-frequency ratio correlated positively with diastolic blood pressure during daytime (r=0.348, p=7.49×10-5), the 24-hour period (r=0.348, p=7.58×10-5) and night-time (r=0.260, p=0.00353). Similar associations were observed for mean arterial pressure during daytime (r=0.298, p=0.000783), the 24-hour period (r=0.286, p=0.00135) and night-time (r=0.199, p=0.0269). In multivariable analysis, a higher low-frequency to high-frequency ratio remained independently associated with higher night-time diastolic blood pressure (β=4.41 mmHg per 1-unit increase; 95% confidence interval 0.45- 8.38; p=0.029).Conclusions: 1. Higher ambulatory diastolic and mean arterial blood pressure, particularly during the night, are associated with autonomic imbalance reflected by an increased low-frequency to high-frequency ratio. 2.. These findings support the relevance of integrated ambulatory blood pressure and autonomic assessment for characterising hypertension-related pathophysiology.