Cardiovascular dynamics - Analysis and
modelling of its oscillations and their synchronization
Prof. Dr. Aneta Stefanovska
Dr. Maja Bračič-Lotrič
The cardiovascular system serves to keep the blood in continuous motion
and does so with the help of the lungs and the heart, which generate pressure
difference, and the vessels which actively regulate the resistance or
conductance throughout the network. It has long been known that the heart of a
healthy human subject in repose does not beat regularly. The rhythmic variation
in the heart rate occurring at the frequency of respiration, known as
respiratory sinus arrhythmia, has been studied intensively over many years.
Recently it has been established that comparable phenomena also occur on longer
timescales: the blood distributions system is characterised by five
characteristic frequencies ranging from 0.01-1.0 Hz. The same frequencies
can be detected in diverse measurements (ECG, respiration, blood pressure and
blood flow-rate) on widely separated sites.
The
modulation of cardiac frequency bears the signatures of other cardiovascular
functions and their demands for adaptation. In the resting but waking state in
humans, this causes synchronization between the cardiac and respiratory systems
to occur only episodically.
Recent studies have illuminated the way in which the pattern of phase
synchronization changes during anesthesia. They have shown that, with diminished
nerve control, the two systems pass reversibly through a sequence of
phase-synchronized states as the anesthesia level changes, indicating
that they can undergo phase transition like phenomena.
The frequency and amplitude variations and phase synchronization are
reminiscent of phenomena observed in coupled oscillators, raising the
possibility that it may be useful to model the cardiovascular system as a system
of coupled autonomous oscillators; it is likely that random noise also plays a
role. Each oscillator is coupled to each of the others, thus mutually
influencing all their frequencies and amplitudes. Preliminary numerical results
were obtained that reproduce well the state of the system in coma, for which the
couplings are very weak. However, the physiological characteristics of the
coupling functions need to be identified in order to achieve a more realistic
description of the healthy cardiovascular system.