Searching for the Origin of Chaos

Abstract

The clinical significance of chaotic dynamics in the cardiovascular system has attracted attention. The circulatory system is a kind of complex system having many feedback circuits, so it has been difficult to investigate the origin of chaos in the circulatory system. In this study, we investigated the origin of chaos by using the methodology of open-loop analysis with an artificial heart, which did not have any fluctuation in its own pumping rate and contraction power, in chronic animal experiments using healthy adult goats. In the circulatory time series data of the artificial heart, which did not have any fluctuation, low-dimensional deterministic chaos was discovered by nonlinear mathematical analysis, suggesting the importance of the blood vessel system in the chaotic dynamics of the cardiovascular system. To investigate the origin of chaos further, sympathetic nerve activity was directly measured in the animal experiments with artificial heart circulation. Chaotic dynamics was also recognized in the sympathetic nerve action potentials, even during artificial heart circulation, suggesting the importance of a central nervous system. In the next step, in order to generate chaotic dynamics in the circulation, an electrical simulation model of left heart circulation with a feedback loop with some delay was tested, and we found that we can make chaos in the circulation by a feedback loop. Thus, we constituted an artificial baroreflex system with an artificial heart system and found that we could introduce chaos in an animal model. Finally, we proposed clinical application of these methodologies for the diagnosis of an autonomic nervous system and found that it may be useful. These findings may be useful for analyzing the nonlinear dynamics in the circulation.