Does well-harmonized homeostasis exist in heart rate fluctuations? Time series analysis and model simulations.

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, ICU patients, and one child with brainstem dysfunction. 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. The cross-correlation measure between the theoretical angle map and the numerically derived angle trajectory is used to separate recovery (0.73+/-0.13) from deterioration (0.25+/-0.08) of ICU patients. In addition, a simple physiologic (deterministic) model of the interaction between the cardiovascular system and baroreceptor control of arterial pressure is used to explain why homeostasis can exist in heart rate fluctuations. Our study provides a potential link between the clinical data and circulatory system.