Heart Rate Variability: A Tool to Explore Autonomic Nervous System Activity in Health and Disease

Abstract

It is accepted that several biological (genetic, physiological), psychological (personality, mood), social (family, work), and ecological (living environment) factors interact to allow the preservation of quality of life and health. The autonomic nervous system (ANS) is structural and rhythmically interfaced between forebrain, internal, and external environments, to regulate energy, matter, and information exchanges, thus expressing the biopsychosocial nature of the individual. During last year strong evidence has been produced that demonstrates the influence of the ANS into beat-to-beat fluctuations of cardiac heart period. Stephen Hales was the first in describing the association between respiratory cycle and heart rate. However, it was not until the second half of the twentieth century that subtle relations between ANS activity and heart rate variability (HRV) were systematically explored in several physiological conditions, including physical activity, sleep, and stress. In addition, autonomic imbalance may configure a final common pathway to increased morbidity and mortality from a host of physical, such as metabolic disorders and cardiovascular disease, and psychological conditions, like anxiety or depression. This chapter will focus on the physiological mechanisms underlying HRV, the methods for assessing it and the information that has provided about ANS activity in certain physiological and pathological situations.