Three Independent Forms of Cardio-Respiratory Coupling: Transitions across Sleep Stages.

We demonstrate that the cardiac and respiratory system exhibit three distinct forms of coupling that are independent from each other, respond differently to key physiologic parameters, and act on different time scales. We find that all three forms of coupling undergo pronounced phase transitions across sleep stages characterized by different stratification patterns, indicating markedly different response to changes in neuroautonomic control. Our analyses show that all three forms of cardio-respiratory interaction are not of constant strength but are of transient and intermittent nature with "on" and "off" periods, and that these forms of coupling, representing different aspects of physiologic regulation, can simultaneously coexist.