Cross-correlation of heartbeat and respiration rhythms

The cross-correlation function between respiration and heart beat interval series shows that during metronomized breathing11Metronomized breathing refers to the situation where a subject breathes following the rhythm of a metronome. the heart beat follows the respiration more closely than during spontaneous breathing. We reproduced the heart beat interval modulations during metronomized breathing using a biophysical model of the sinoatrial node excited by an input signal formed by the recorded respiration. In the case of spontaneous breathing, a good agreement with the experimental data was obtained only by using an input signal formed by the sum of the recorded respiration and a realization of correlated noise.