Autonomic information flow during awakeness, sleep, and multiple organ dysfunction syndrome assessed by mutual information function of heart rate fluctuations

The autonomic information flow (AIF) represents the complex communication within the autonomic nervous system (ANS). It can be assessed by the mutual information function (MIF) of heart rate fluctuations (HRF). AIF represented by HRF is based on several interacting physiological mechanisms operating at different time scales. Therefore one prominent time scale for HRF complexity analysis is not given a priori. MIF reflects the information flow at different time scales. This allows a more specific characterization of the complex communication leading to dynamic stability (homeostasis) of the cardiovascular-respiratory system. Three clinically relevant examples of autonomic communication, namely AIF of normals during awake state and deep sleep, and of patients with multiple organ dysfunction syndrome (MODS) were investigated. In these states MIF clearly represents and distinguishes the different communication in dependence on the time scale of information transfer. The results confirm our systems-theoretical concept that AIF, represented by MIF, characterizes the complex communication of the ANS at different time scales.