Abstract
Heart rate variability (HRV), the beat-to-beat variation in either heart rate or the duration of the R–R interval – the heart period, has become a popular clinical and investigational tool. The temporal fluctuations in heart rate exhibit a marked synchrony with respiration (increasing during inspiration and decreasing during expiration – the so called respiratory sinus arrhythmia, RSA) and are widely believed to reflect changes in cardiac autonomic regulation. Although the exact contributions of the parasympathetic and the sympathetic divisions of the autonomic nervous system to this variability are controversial and remain the subject of active investigation and debate, a number of time and frequency domain techniques have been developed to provide insight into cardiac autonomic regulation in both health and disease. It is the purpose of this essay to provide an historical overview of the evolution in the concept of HRV. Briefly, pulse rate was first measured by ancient Greek physicians and scientists. However, it was not until the invention of the “Physician’s Pulse Watch” (a watch with a second hand that could be stopped) in 1707 that changes in pulse rate could be accurately assessed. The Rev. Stephen Hales (1733) was the first to note that pulse varied with respiration and in 1847 Carl Ludwig was the first to record RSA. With the measurement of the ECG (1895) and advent of digital signal processing techniques in the 1960s, investigation of HRV and its relationship to health and disease has exploded. This essay will conclude with a brief description of time domain, frequency domain, and non-linear dynamic analysis techniques (and their limitations) that are commonly used to measure HRV.
Highlights
Heart rate variability (HRV), beat-to-beat variation in either heart rate or the duration of the R–R interval – the heart period, has become an important risk assessment tool
A reduced HRV is associated with a poorer prognosis for a wide range of clinical conditions while, robust periodic changes in R–R interval are often a hallmark of health (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology, 1996; Bigger, 1997; De Jong and Randall, 2005; Thayler et al, 2010)
A major portion of these temporal changes in heart rate occur synchronous with respiration [heart rate increases (R–R interval shortens) during inspiration and decreases (R–R interval prolongs) during expiration] and, are referred to as the respiratory sinus arrhythmia (RSA)
Summary
Heart rate variability (HRV), beat-to-beat variation in either heart rate or the duration of the R–R interval – the heart period (for an example see Figure 1), has become an important risk assessment tool. He was born in Chalcedon but spent the majority of his adult life in Alexandria He was perhaps the first anatomist and published at least nine volumes of his findings, all of which have been lost (Bedford, 1951; Bay and Bay, 2010). His original text was extensively quoted in the works of other authors, by the GrecoRoman physician Galen (Bedford, 1951; Boylan, 2007) Among his most notable findings was the demonstration that the veins carried blood, that veins and arteries were distinctly different, and that the arteries pulsed rhythmically (Bedford, 1951; Bay and Bay, 2010). These fragmentary quotations suggest that Herophilos was the first person to measure heart rate
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