Sympathetic Nerve Adjustment to Artificial Circulation

Abstract

To analyze the dynamical behavior of the autonomic nervous system while being driven by an artificial heart, sympathetic nerve discharges were analyzed by the use of nonlinear mathematics, including chaos and fractal theory. For the comparison of the natural and artificial circulation, a biventricular bypass type, total artificial circulation model was adopted under ventricular fibrillation in short-term animal experiments on four healthy mongrel dogs. After the implantation of a biventricular assist pneumatic pump, bipolar stainless steel bipolar electrodes were attached to the left renal sympathetic nerve via a retroperitoneal approach, to record the sympathetic nerve discharges. After amplifying the nerve activity with a preamplifier, the sympathetic discharges were further amplified with a main amplifier and integrated with a resistance-capacitance (R-C) integrator (time constant 0.1s). After control natural-circulation data were recorded without biventricular assistance, ventricular fibrillation was induced electrically, and the biventricular bypass pneumatic pump was started, constituting the total artificial circulation model. Driving parameters for the bypass pumps were manually controlled to maintain the hemodynamic parameters within the normal range. Time-series data of the hemodynamics and sympathetic nerve discharges were recorded in the data recorder and calculated in a personal computer system (PC9801RA) through an analog-digital (A-D) converter. Even during artificial heart circulation, the reconstructed attractor of the sympathetic discharges in the phase space appeared to be a strange attractor, which is a feature of deterministic chaos. However, the Kolomosov-Sinai (KS) entropy of the reconstructed attractor decreased during artificial circulation, suggesting changes in the nonlinear dynamics in the autonomic nervous system. Various values of the KS entropy were observed according to the various drive rates of the artificial heart. Our results suggest that there is chaotic itineracy in the autonomic nervous system according to variations in the natural and artificial circulation, and artificial heart drive rate. These results suggest sympathetic nerve adjustments of the circulatory regulatory system in response to the artificial heart. It becomes possible to analyze the information-processing mechanism of the central nervous system by such an open loop experiment using an artificial organ. This mechanism is a focus of attention in the scientific community. We expect that this paper will contribute to understanding this field.