Forms of Cardio-Respiratory Coupling and their Modulation in Health and Disease

The cardiac and respiratory systems play a key role in maintaining healthy physiologic function. Pathological deviations from normal cardiac and respiratory dynamics have been linked to increased risk of disability and mortality, and often heart diseases affect respiratory health and vice versa due to their mutual coupling. Quantifying cardio-respiratory coupling is a challenging problem, as little is known about the specific nature of this interaction and how it changes with different physiologic states (such as sleep/wake transitions, sleep stages, rest/exercise), advanced age and pathologic conditions. The problem is further complicated because cardio-respiratory coupling is often masked by the noisy/fluctuating output signals of the cardiac and respiratory systems, which show complex behavior and exhibit temporal organization characterized by scale-invariant (fractal), multifractal, and nonlinear features over a broad range of time scales. Although the origins of such rich complexity in cardiac and respiratory fluctuations remain not fully understood, there is growing evidence that they are related to particular mechanisms of regulation involving networks of multiple neuronal (sympathetic/parasympathetic) inputs and nonlinear feedback interactions.
In recent years, research in the fields of nonlinear dynamics, information theory and statistical physics have led to the development of advanced numeric approaches that can detect and quantify cardio-respiratory interaction beyond the traditionally-studied respiratory sinus arrhythmia (RSA). In particular, new forms of coupling such as cardio-respiratory phase synchronization, cardio-respiratory time delay stability and cardio-respiratory coordination have been discovered and shown to represent different and often complementary aspects of cardio-respiratory interaction. These findings indicate that cardio-respiratory interaction is carried not only by one form of coupling but instead is mediated through multiple forms acting over a range of time scales. Moreover, recent studies have found that different forms of coupling may simultaneously coexist, and that at any given moment the cardiac and respiratory system can interact through different coupling forms with intermittent “on” and “off” periods.

This Research Topic aims on broadening our understanding on the various forms of cardio-respiratory coupling, coordinate interdisciplinary efforts on developing analytic and computational methodology, and systematize different visions, approaches and models. We welcome multidisciplinary contributions that review the current state of the art on cardio-respiratory coupling analysis, clinical applications as well as opinion and review articles pointing towards open challenges, and original and translational research articles.

Particular emphasis will be given to work on:
• inference of cardio-respiratory coupling
• estimating the directionality in coupling under different physiologic states and pathologic conditions
• causality in different forms of cardio-respiratory coupling
• control mechanisms, temporal modulation and adaption of cardio-respiratory interactions
• identification and quantification of linear and nonlinear components of cardio-respiratory coupling
• co-existing forms of cardio-respiratory coupling
• models of cardio-respiratory interaction under different physiological states and clinical conditions
• to derive sensitive measures characterizing the degree of cardio-respiratory interaction
• clinical measures, diagnostic and prognostic markers derived from cardio-respiratory coupling