Cardio-respiratory phase locking in newborn and one month infants as a function of sleep state

Respiratory and cardiac rhythms of newborn infants have been extensively investigated, in order to highlight pathological conditions. Nonetheless, given their tight dependency, methods observing their interactions could provide further insight. This study investigates the phase synchronization of heart rate (HR) and respiration in a group of healthy newborn and one month infants. Synchronous epochs of different n:m orders are identified (n cardiac : m respiratory cycles). Synchrograms provide their graphical representation while λ is an index of circular variance. Differences between epochs of quiet and active sleep and between newborn and one month infants are observed. Results show that the percentage of time spent in synchronization and the average length of periods of synchronization significantly increase during quiet sleep, both for the newborn and the one month infants. In Sudden Infant Death Syndrome (SIDS) the occurrence of infant distress generated by uncoupled cardio-respiratory response has been hypothesized. This confirms the relevance of the proposed analysis and results.