2.7. Cardiorespiratory coupling

The directionality and the magnitude of interactions between breathing and heart rate time series oscillations were quantified with the mutual information theory and phase models using a three‐step protocol (Zhu et al., 2013). First, we evaluated the mutual information of the phases. After, we obtained the interaction functions of the oscillators by fitting the coupled oscillator model to the data, related to phase of the cycle. As a last step, we compared the joint probability of the empirical phases with that obtained from the simulated model, in order to validate the empirical oscillator model. The data were showed as power spectral density and coupling directionality (breath to heart and heart to breath). Analysis was performed using custom Matlab routines.