General anesthesia reduces the information exchange between heart and circulation

The study demonstrates the ability of an information-theoretic measure, such as the transfer entropy (TE), in detecting the depression of the cardiac baroreflex control and circulatory-cardio mechanical feedforward link during propofol-induced general anesthesia. TE was computed from spontaneous variability of heart period (HP) and systolic arterial pressure (SAP) in patients undergoing coronary artery bypass graft (CABG). TE from SAP to HP and from HP to SAP were evaluated by accounting for the confounding effect of respiration (R) affecting both HP and SAP (i.e. TE_SAP→HP|R and TE_HP→SAP|R respectively). Both TE_SAP→HP|R and TE_HP→SAP|R decreased during general anesthesia, thus suggesting that the strength of the causal relation diminished over both arms of the closed loop HP-SAP control. The squared coherence function between HP and SAP confirmed the decreased HP-SAP coupling during general anesthesia, even though it could not distinguish directionality.