Chaos: introduction to the spotlight issue

Abstract

A few times each century a scientific revolution challenges prevailing beliefs. New paradigms are formed and connections between previously disparate fields suddenly appear. The development of nonlinear science may be one such revolution. It seems set to bring about a fundamental shift in the way that we view living systems. The present Spotlight Issue on Chaos contains a series of reviews and original contributions applying concepts from the theory of nonlinear science to a broad range of topics within the field of cardiovascular research. One of the major deficiencies in science and medicine has been the absence of an adequate theoretical framework for understanding and describing complex biological phenomena. The wide range of new experimental methods and techniques that has emerged in recent years has led to a major increase in the amount of information regarding the cellular and molecular aspects of living systems. This has led to a realization of the enormous complexity of biological systems. Much less progress has been made towards integrating this knowledge into a coherent picture of the operating principles of biological systems. Our understanding of regulation, behavior, morphogenesis, and evolution remains inadequate and unsatisfactory. Part of the problem has been the lack of a paradigm able to encompass the huge variety of phenomena observed in living systems. Nonlinear science, which includes the theory of nonlinear dynamical systems (“chaos theory”), could provide such a paradigm, and thereby complement reductionist approaches. Like all major scientific developments, the advent of nonlinear science has had a profound impact in many different fields. It is an example of an interdisciplinary endeavor where new developments arise within different scientific fields. This is a challenge for researchers wanting to apply nonlinear methods in their work. The present issue of Cardiovascular Research should be helpful in this respect. It contains a series of reviews and original contributions that illustrates the interdisciplinary scope of nonlinear techniques and their applicability to a range of problems within the cardiovascular field. Many of the papers deal with heart rate and blood pressure variability, a promising area for the implementation of nonlinear approaches, where the goals are to understand the sources and the physiological mechanisms responsible for the fluctuations over time, and to assess the clinical usefulness of nonlinear measures in identifying cardiac patients at high risk for sudden cardiac death. Another group of papers concerns the application of nonlinear methods to the microcirculation, an area where nonlinear dynamical phenomena such as vasomotion have been observed for decades. Vasomotion is a ubiquitous phenomenon observed in all vascular bods, but it is probably fair to say that without the insight now provided by nonlinear dynamical systems theory we would still regard it as an esoteric subject of little physiological significance. As illustrated by the papers in this issue, vasomotion may be central to the physiological function of the microcirculation. A field as large as nonlinear science, even as applied just to cardiovascular issues, is impossible to cover adequately, for there have been so many important contributions during the last decade. It is our hope, however, that the present issue may provide a sample of the work that goes on in this exciting new area of research.