Coupled oscillators approach to identification of directionality in cardiorespiratory interaction

A previously proposed method aimed to identify the directionality of interaction in weakly coupled oscillator systems is presented, tested on simulated data and applied to the problem of experimental detection of directionality of cardiorespiratory interaction in healthy newborns. The results reveal that the direction of coupling between the cardiovascular system and respiratory system varies with age within the first six months of life. We find a tendency to change from nearly symmetric bi-directional interaction to nearly unidirectional one (from respiration to the heart rate). Stronger cardiorespiratory interaction appears to be mainly related to the driving effect of respiration on the heart rate. Moreover, the dependency of the directionality index on the respiratory frequency indicates the possible existence of distinct regimes of interaction.