Entropy and multiscale time irreversibility in the analysis of complex systems in human physiology

Abstract

Biological organisms act far from equilibrium and they behave as complex systems controlled by non linear dynamics. The Deterministic Chaos Theory developed mathematical methods which have demonstrated to be useful studying complexity in biological signals. The most recent of them are Entropy and Multiscale Time Irreversibility. Entropy quantifies regularity in a system, so a more regular series will be more predictable and less complex and its entropy will be lower. Low entropy reflects a less adaptable system and this may be observed in aging and illness. The auto-organizing capacity in a live organism is related to the uni-directionality of energy flow throw its systems and to the irreversibility of their processes. Time irreversibility consists in the loss of soundness in the statistic properties of a signal when one reverses its reading along the time. Two asymmetric trajectories are shown and the asymmetry index is higher in the healthy systems than in pathologic or aged one. The aim of this manuscript is to review the applications of these concepts to human physiology.