The Statistical Analysis of Systolic Blood Pressure and Pulse Intervals Mutual Adjustment Rate

The joint analysis of the systolic blood pressure and heart rate is essential for a better understanding of the reflection of the regulatory mechanisms in the cardiovascular system dynamics. Here we consider two methods to analyze the mutual adjustment rate of these two processes. The first one is based on the coherence function analysis, while the second one implies the analysis of time intervals between zero-level crossings. We applied these methods to observational data records obtained under different phases of the head-up tilt table test performed in three groups of patients with various autonomic status. Our results indicate that even under stationary conditions typical for the supine test phase approximations of the data by Gaussian distribution fails thus requiring the use of nonparametric statistics. We found that the average values of the coherence function in patients with diabetes mellitus and with non-diabetic moderate autonomic dysfunction are significantly lower than in the control group consisting of healthy volunteers (p <; 0.001). Moreover, these coefficients significantly increased during the transition from the supine to the orthostatic phase of the tilt test (p <; 0.001). An additional quantity based on the analysis of the cross-correlation function of the two sequences characterizing zero-level crossings by SBP and PI, respectively, and calculating the corresponding correlation time, also significantly differed between the considered patient groups in the supine phase (p <; 0.005). Therefore we think that the suggested quantities might appear useful as prognostic markers of the patient's autonomic regulation status.