Signal processing in Network Physiology: quantifying network dynamics of organ interactions

A fundamental problem in new field of Network Physiology is how organ systems in the human body dynamically interact to coordinate and synchronize their functions, and integrate as a network to generate distinct states and behaviours at the organism level. Physiological systems exhibit complex dynamics, operate at different time scales, and are regulated by multi-component mechanisms, which poses challenges to studying physiologic coupling and network interactions. We present a method based on the concept of time delay stability to probe transient physiologic network interactions in a group of healthy subjects during sleep. We investigate the multi-layer network structure and dynamics of interactions among (i) physiologically relevant brain rhythms within and across cortical locations, (ii) brain rhythms and key peripheral organ systems, and (iii) organ systems with each other. We demonstrate that each physiologic state (sleep stage) is characterized by a specific network structure and link strength distribution, and that the entire physiological network undergoes hierarchical reorganization across layers with transition from one stage to another. Our findings are consistent across subjects, and indicate a robust association of network structure and dynamics with physiologic state and function. The presented approach provides a new framework to explore physiologic states through networks of organ interactions.