Objective: The linear relationship between blood pressure (BP) and heart rate (or period) over 24 h has been suggested to be a marker for neural regulation of the circadian variations in BP and heart rate. We investigated the predictive power of indices defined by the ratio between BP and heart period variability that is a known expression for such a relationship.
Methods: We analysed BP and heart rate data obtained by standard 24-h BP monitoring in 1246 hypertensive patients, 76 of whom died from all causes during 5-year follow-up. SBP, DBP and heart period (T) variabilities were estimated by standard deviations. Studied indices were the SBP-T variability ratio (dS/dT) and the DBP-T variability ratio (dD/dT). Standardized hazard ratios and odds ratios were determined using Cox regression and logistic regression, respectively.
Results: Significant covariates adjusted hazard ratios for dS/dT and dD/dT that gradually increased across the following cohorts: entire sample, high-median age and high-median age and heart period: mean [95% confidence interval (95% CI)] 1.23 (1.03-1.47), 1.26 (1.05-1.52) and 1.55 (1.19-2.02), and 1.36 (1.07-1.72), 1.40 (1.09-1.80) and 1.57 (1.15-2.14), respectively. The corresponding odd ratios were similar in all cohorts: about 1.5 (1.2-2.0) and 1.3 (1.1-1.5). The adjusted indices size was greater in nonsurvivors (P =0.000001 and P = 0.003, respectively).
Conclusion: The 24-h BP to heart period variability ratios are powerful independent predictors of all-cause mortality, especially for elderly hypertensive patients with slow heart rate. The results support their interpretation as integrative indices of cardiovascular function and markers for cardiovascular dysregulation during low DBP states, with potential use in clinical practice.