Nonlinear coordination of cardiovascular autonomic control.

The phylogenetic development of the autonomic nervous system (ANS) has presumably involved processes of self-organization with evolutionary selective pressure to optimize specific functions of the organism and the coordination of these functions. Our knowledge of the functional organization of the ANS is incomplete. However, at many different levels of function, nonlinear dynamics have been shown to provide a relevant description of operation of the system. We introduce some of the fundamentals of nonlinear coordination, including approaches based on chaos theory, synergetics, and general nonlinear dynamics. The term "autonomic nervous system" is valid for the basal functional unit, which includes essential neurophysiological mechanisms of cardiovascular control that are approximately independent of voluntary influences. The conclusion is that the cardiovascular autonomic control system is more appropriately investigated by multivariate than by univariate data analysis. A physiological organism can be considered as a highly complex dissipative structure; numerous widespread internal and external conditions lead to the small behavioral band of being alive. Subsystems of this structure can be modeled as dissipative dynamical systems. Deterministic chaos is a mathematical phenomenon in which a deterministic process produces a unpredictable output. Deterministic chaos is somewhat regular in that it is deterministic and somewhat irregular in that it is unpredictable. One of the distinctive features of the ANS is that its fluctuations are also somewhat regular and somewhat irregular. This duality may indicate that it may be useful to characterize ANS fluctuations in terms of concepts from chaos theory.