Spontaneous and forced non-linear oscillations in heart period: role of the sino–atrial node

The aim of this study is to investigate whether and to which extent the non-linearity of the sino–atrial node contributes to the complex interactions between autonomic control and heart period. A non-linear model of the autonomic control on the sino–atrial node has been analyzed under particular experimental conditions: the autonomic nervous system was forced to act at established frequencies, by a controlled breathing procedure and a non-invasive periodic modulation of carotid baroreceptors. We quantify the non-linear coupling between the stimuli and both the experimental and the simulated heart period fluctuations by using the recurrence plot quantification analysis. Our results show that the non-linear interaction between external stimuli and heart period fluctuations is due to a certain extent to the non-linear features of the sino–atrial node.