Chaos in blood pressure control

Abstract

A number of control mechanisms are comprised within blood pressure regulation, ranging from events on the cellular level up to circulating hormones. Despite their vast number, blood pressure fluctuations occur preferably within a certain range (under physiological conditions). A specific class of dynamic systems has been extensively studied over the past several years: nonlinear coupled systems, which often reveal a characteristic form of motion termed "chaos". The system is restricted to a certain range in phase space, but the motion is never periodic. The attractor the system moves on has a non-integer dimension. What all chaotic systems have in common is their sensitive dependence on initial conditions. The question arises as to whether blood pressure regulation can be explained by such models. Many efforts have been made to characterise heart rate variability and EEG dynamics by parameters of chaos theory (e.g., fractal dimensions and Lyapunov exponents). These method were successfully applied to dynamics observed in single organs, but very few studies have dealt with blood pressure dynamics. This mini-review first gives an overview on the history of blood pressure dynamics and the methods suitable to characterise the dynamics by means of tools derived from the field of nonlinear dynamics. Then applications to systemic blood pressure are discussed. After a short survey on heart rate variability, which is indirectly reflected in blood pressure variability, some dynamic aspects of resistance vessels are given. Intriguingly, systemic blood pressure reveals a change in fractal dimensions and Lyapunov exponents, when the major short-term control mechanism--the arterial baroreflex--is disrupted. Indeed it seems that cardiovascular time series can be described by tools from nonlinear dynamics [66]. These methods allow a novel description of some important aspects of biological systems. Both the linear and the nonlinear tools complement each other and can be useful in characterising the stability and complexity of blood pressure control.

Increased peripheral vascular disease risk progressively constrains perfusion adaptability in the skeletal muscle microcirculation

“…As has been demonstrated previously for the experimental conditions of the present study, all of the conditions of elevated PVD risk were associated with an impaired endothelial function, as evidenced by a reduced upper bound of the acetylcholine concentration-response relationship (9,17,19,24,33,34,39,49,58), although the degree of impairment was similar in magnitude regardless of the severity of the PVD risk score. However, the contribution of oxidant stress to each condition of PVD risk was more variable, with some of the states of more severe PVD risk showing a robust role for oxidant stress in compromising endothelial function while others demonstrated a more modest or minimal contribution.…”

Arterial baroreflex function and cardiovascular variability: interactions and implications

“…Cardiovascular variability comprises a very complex interaction between hemodynamic, humoral, and electrophysiological variables, integrated by a sophisticated system of controllers within the autonomic and central nervous systems (33,121,122).…”

“…29,63,66,85,112,121,122). In addition to the periodic oscillatory behavior observed in arterial blood pressure, R-R interval, and peripheral sympathetic activity (66,85,112), a less specific variability occurs with nonperiodic behavior, which can be described by methods based on nonlinear system theory ("chaos theory and fractal analysis") (29,63,121,122). Although the physiological basis for this nonharmonic beat-to-beat behavior, which extends over a wide time scale range (seconds to hours), is still unsettled, evidence is increasing that this fractallike variability may encode clinically relevant information (10,29,40,64).…”

Prediction of hypertensive crisis based on average, variability and approximate entropy of 24-h ambulatory blood pressure monitoring

“…[8][9][10][11] Animal studies detected chaotic components in the time series of BP. [12][13][14][15] One property inherent in chaotic systems is the possibility of a sudden dissipation. Theoretically, hypertensive crises could be understood as a chaotic dissipation of BP regulation.…”