Detecting Well-Harmonized Homeostasis in Heart Rate Fluctuations

Analyzing heart rate variability from electrocardiographic recordings has been an important method for assessing cardiovascular autonomic regulation. Researchers have conducted extensive analyses on normal as well as pathological hearts, however, it is still unclear whether increasing or decreasing the complexity of heart rate variability is a characteristic of healthy systems. In this study, we find the existence of well-harmonized homeostasis in heart rate fluctuations, in particular, the evidence is verified among different individuals including healthy subjects (n=25) and ICU patients (n=25). The methodology we used is composed of two parts, in which one is the consideration of reduction of cardiorespiratory fluctuations inherited in the original R-R intervals and the other is based upon the concept of nonlinear dynamics to construct the low- dimensional trajectory in the angle plot. In addition, we report that the cross-correlation measure between the theoretical angle map and the numerically derived angle trajectory can well separate recovery (0.73plusmn0.13) from deterioration (0.25plusmn0.08) of ICU patients. Our results suggest that the prognostic homeostasis index could be valuable for clinical applications.