A monitor for the quantitation of respiratory entrainment in the newborn infant

In order to define interactions between external stimuli and physiological systems, the Frequency Tracking Locus (FTL) was devised which describes the cycle-by-cycle changes in phase angle and amplitude between two signals. The Path Length Index (PLI), describing the departure of the system from a fully entrained state, was derived from the FTL. The FTL was applied to the study of spontaneous respiration during mechanical inflation in newborn babies. Persistent states of 1:1 interaction and other integer ratio relationships were seen at different rates of mechanical ventilation. Stable states of entrainment corresponded to a PLI value of near unity, and the value of PLI increased rapidly as interactions became unstable. A bedside monitor incorporating the FTL has been successfully used as a clinical tool to aid mechanical ventilation of the newborn infant