Heart rate variability: from bench to bedside

Abstract

Power spectrum analysis of cardiovascular signal variability, and in particular of the RR period (heart rate variability, HRV), is a widely used methodology for investigating autonomic neural regulation in health and disease that can quantify the sympathovagal balance modulating the sinus node pacemaker. In some cases, it can also quantify the neural regulation of other organs or apparatuses. However, use of the correct methodology is crucial to extract the information embedded in the frequency domain. In numerous abnormal conditions, such as essential arterial hypertension, acute myocardial infarction and heart failure, the sympathovagal balance may be altered in basal conditions. However, a reduced responsiveness to an excitatory stimulus is the most common feature that characterizes numerous pathophysiological states. The attenuation of an oscillatory pattern can also reflect an altered target function, thus providing important prognostic markers. The general features of this approach correspond well to the needs of an internist attempting to envisage the involvement of the whole organism in a disease process.

Introduction

There is a strange paradox in the current interpretation of the role of neural mechanisms. In physiological conditions, when the organism is working perfectly, neural and autonomic regulation is considered of paramount importance. On the other hand, disease states are usually analyzed at the level of organ disease (a concept largely influenced by Morgagni during the 18th century), cellular disease (pioneered by Virchow a century later), or molecular disease (first introduced by Pauling in 1949, when he described hemoglobin S). Surprisingly, abnormal neural control has been disregarded as a mechanism participating in a disease process, suggesting that science considers disease states to be denervated entities. This conceptual discontinuity is hard to accept, given the continuum that often links physiology and pathophysiology. A possible explanation for the disregard of neural mechanisms is that science often ignores what cannot be measured. This article will show that many diseases are indeed highly innervated entities and that visceral neural regulation is important to clinical medicine.