Spatial Synchronization in the Human Cardiovascular System

Abstract

Concepts developed for the synchronization analysis of noisy coupled nonlinear oscillators are used to study the spatial synchronization of oscillations in the blood distribution system. We reveal that the cardiac and respiratory oscillations observed at different sites of the system are strongly phase and frequency synchronized, while the spatial synchronization of oscillations that originate locally is weaker. The results obtained support the hypothesis that the entire cardiovascular system is characterised by the same dynamics. The human cardiovascular system distributes matter and energy to the cells and removes byproducts of their metabolism. The cells extract matter and energy from the blood which is pumped by the heart into the network of vessels. The lungs, where the blood becomes oxygenated, are also part of the cardiovascular network. The heart of a relaxed, healthy subject, pumps an amount equivalent to the total amount of blood in the body in approximately one minute. 1) Thus, in cardiovascular dynamics we consider the dynamics of blood distribution through the cardiovascular network on a time scale of around one minute. It can be characterised by the dynamics of the blood flow and the blood pressure in the system, and the activity of the lungs and heart pump. The function of the heart is manifested as electric potentials spread across the heart muscle, and as a mechanical pump that rhythmically expels the blood into the arterial network approximately once per second. However, the period of the heart cycle is not constant but, rather, varies in time. The frequency of respiration also varies, between 0.15 and 0.3 Hz. Consequently, the flow and the pressure change in an oscillatory fashion with time, and do so on several different time scales. The vessel walls are not stiff: their radii continually alter, thus giving rise to a variable resistance to flow. Three peripheral mechanisms are known to contribute to the resistance or compliance of the vessels: the intrinsic myogenic mechanism, based on continuous contraction and relaxation of smooth muscle cells; the neurogenic control provided by the autonomous nerve innervation of vessels; and endothelium mediated contraction and relaxation of the vessels. 2) - 4) Each of these processes manifests in an oscillatory manner, and their characteristic frequencies are around 0.1, 0.04 and 0.01 Hz, respectively. Arterial blood flow is characterised by high pressure and low resistance, and the heart frequency dominates in both the flow and pressure. Flow in veins is