Non-linear coupling between cardiovascular system and autonomic control: does the sino-atrial node play a role?

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 rate variability (HRV). The authors analyzed a non-linear model of the autonomic control on the sino-atrial node under particular experimental conditions: they forced the autonomic nervous system to act at established frequencies, by a controlled breathing procedure and a non-invasive periodic modulation of carotid baroreceptors. The authors quantify the non-linear coupling between the stimuli and both the experimental and the simulated HRV series by using the recurrence plot quantification analysis. These results show that the nonlinear interaction between external stimuli and HRV is due to a certain extent to the non-linear features of the sino-atrial node.