Published in Physiol. Meas. 22, 551–564 (2001). Modelling couplings among the oscillators of the cardiovascular system Aneta Stefanovska‡‖, Dmitrii Luchinsky† and Peter V E McClintock† ‡ Group of Nonlinear Dynamics and Synergetics, Faculty of Electrical Engineering, University of Ljubljana, Trˇ zaˇ ska 25, 1000 Ljubljana, Slovenia. (aneta@osc.fe.uni-lj.si) † Department of Physics, University of Lancaster, Lancaster LA1 4YB, UK. (d.luchinsky@lancaster.ac.uk, p.v.e.mcclintock@lancaster.ac.uk) Abstract. A mathematical model of the cardiovascular system is simulated numerically. The basic unit in the model is an oscillator that possesses a structural stability and robustness motivated by physiological understanding and by the analysis of measured time series. Oscillators with linear couplings are found to reproduce the main characteristic features of the experimentally obtained spectra. To explain the variability of cardiac and respiratory frequencies, however, it is essential to take into account the rest of the system, i.e. to consider the effect of noise. It is found that the addition of noise also results in epochs of synchronization, as observed experimentally. Preliminary analysis suggests that there is a mixture of linear and parametric couplings, but that the linear coupling seems to dominate. PACS numbers: 87.10.+e, 5.45.Xt, 5.40.Ca, 87.19.Hh ‖ To whom correspondence should be addressed.