Bifurcation in a simple model of the cardiovascular system

A simple nonlinear beat-to-beat model of the human cardiovascular system ha s been studied. The model, introduced by DeBoer et al. was a simplified lin earized version. We present a modified model which allows to investigate th e nonlinear dynamics of the cardiovascular system. We found that an increas e in the or-sympathetic gain, via a Hopf bifurcation, leads to sustained os cillations both in heart rate and blood pressure variables at about 0.1 Hz (Mayer waves). Similar oscillations were observed when increasing the beta- sympathetic gain or decreasing the vagal gain. Further changes of the gains , even beyond reasonable physiological values, did not reveal another bifur cation. The dynamics observed were thus either fixed point or limit cycle. Introducing respiration into the model showed entrainment between the respi ration frequency and the Mayer waves.