ORIGIN OF CHAOS IN THE CIRCULATION - OPEN-LOOP ANALYSIS WITH AN ARTIFICIAL-HEART

To develop the optimal automatic control algorithm for an in vivo arti ficial heart system, investigation of the basic characteristics of the cardiovascular system may be important. The clinical significance of chaotic dynamics in the cardiovascular system has attracted attention. The circulation is a so-called complex system with many feedback circ uits, making it very difficult to investigate the origin of chaos with in the system. In this study, we investigated the origin of chaos by o pen loop analysis with an artificial heart (which has no fluctuation i n pumping rate or contraction power) in chronic animal experiments wit h healthy adult goats. As a result, in the artificial heart circulator y time series data, low dimensional deterministic chaos was discovered by nonlinear mathematical analysis, suggesting the importance of bloo d vessels in the chaotic dynamics of the cardiovascular system. To inv estigate the origin of chaos further, sympathetic activity was directl y measured in animals with artificial hearts. Chaotic dynamics was als o recognized in sympathetic action potentials, even during artificial heart circulation. Coupling of the nonlinear information between blood vessels and sympathetic activity was suggested by analysis of mutual information. In chaotic dynamics, the central nervous system (CNS) pla yed an important role through sympathetic activity. These findings may be useful for the development of an automatic control algorithm for a n artificial heart.