Baroreflex contribution to linear and nonlinear blood pressure and heart rate coupling in daily life: an assessment by cross-mutual information

A new procedure has been developed to (1) investigate the coupling between arterial blood pressure and heart rate variability in daily life and (2) identify the baroreflex contribution to such a coupling. The algorithm is based on the estimation of cross-mutual information (CMI) between systolic blood pressure (SBP) and RR-interval (RRI) beat-to-beat values. CMI has been selected because of its capability to quantify both linear and nonlinear components of the coupling between variables. This procedure has been used to analyze data recorded in spontaneously behaving cats before and seven days after surgical opening of the baroreflex loop as obtained by a sino-aortic denervation. Use of CMI indicates that over a time scale on the order of minutes the arterial baroreflex is the major determinant of the SBI-RRI link, accounting for about 2/3 of the total (linear and nonlinear) coupling measured between these variables.