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Published November 02, 2009
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Contents of Heart Rate Variability(HRV)

a. Definition of Heart Rate Variability (HRV)

Heart Rate Variability (HRV) refers to the beat-to-beat alterations in heart rate. Under resting conditions, the ECG of healthy individuals exhibits periodic variation in R-R intervals. Heart Rate Variability (HRV)  rhythmic phenomenon, known as respiratory sinus arrhythmia (RSA), fluctuates with the phase of respiration - cardio-acceleration during inspiration, and cardio-deceleration during expiration. RSA is predominantly mediated by respiratory gating of parasymphathetic efferent activity to the heart : vagal efferent traffic to the sinus node occurs primarily in phase with expiration and is absent or attenuated during inspiration. Atropine abolishes RSA.

b. How Heart Rate Variability (HRV) measured?

Heart Rate Variability (HRV)  was assessed manually from calculation of the mean R-R interval and its standard deviation measured on short-term (e.g., 5 minute) electrocardiograms. The smaller the standard deviation in R-R intervals, the lower is the Heart Rate Variability (HRV) . To date, over 26 different types of arithmetic manipulations of R-R intervals have been used in the literature to represent Heart Rate Variability (HRV) . Exa. include: the standard deviations of the normal mean R-R interval obtained from successive 5-minute periods over 24-hour Holter recordings (called the SDANN index); the number of instances per hour in which two consecutive R-R intervals differ by more than 50msec over 24-hours (called the pNN50 index); the root-mean square of the difference of successive R-R intervals (the rMSSD index); the difference between the shortest R-R interval during inspiration and the longest during expiration (called the MAX-MIN, or peak-valley quantification of Heart Rate Variability (HRV) ); and the base of the triangular area under the main peak of the R-R interval frequency distribution diagram obtained from 24-hour recording; and so on. So, experimental and simulation data appear to indicate that the various methods of expressing Heart Rate Variability (HRV)  are largely equivalent, and there is no evidence that any one method is superior to another, provided measurement windows are 5 minutes or longer.

In contrast to the so-called time domain measures of Heart Rate Variability (HRV)  cited recent developments in microprocessor technology has enabled the calculation of frequency measures based on mathematical manipulations performed on the same ECG-derived data. Frequency measures involve the spectral analysis of Heart Rate Variability (HRV) . R-R interval data are represented on a tachogram in which the y-axis plots the R-R intervals, and the x-axis the total number of beats. Spectral analysis of the tachogram transforms the signal from time to frequency on the x-axis, by representing the signal as a combination of sine and cosine waves, with different amplitudes and frequencies.

As a measure of vagal activity, spectral analysis of the high-frequency component probably offers no additional information over time-domain measures of RSA. On the other hand, the meaning and utility of the low frequency component deserves further investigation.

In sum, the analysis of Heart Rate Variability (HRV)  (whether by time-domain or spectral approaches) offers a non-invasive method of evaluating vagal input into cardiac rhythm. The measurement of Heart Rate Variability (HRV)  is becoming increasingly standardized. Although, the assessment of Heart Rate Variability (HRV)  requires electrophysiologic expertise, the equipment is not prohibitively expensive, requiring only ECG equipment, microprocessors, and relevant software for carrying out Fourier analyses.

 

c. Does Heart Rate Variability (HRV)  predict disease?

The major reason for the interest in measuring Heart Rate Variability (HRV)  stems from its ability to predict survival after heart attack. Over half a dozen prospective studies have shown that reduced Heart Rate Variability (HRV)  predicts sudden death in patients with MI, independent of other prognostic indicators such as ejection fraction. Reduced Heart Rate Variability (HRV)  appears to be a marker of fatal ventricular arrhythmia. Moreover, a small number of studies have begun to suggest that reduced Heart Rate Variability (HRV)  may predict risk of survival even among individuals free of CHD.

d.  Further Readings

Heart Rate Variability (HRV)  concepts

Heart Rate Variability (HRV) (HRV) systems

Heart Rate Variability (HRV) professional programs

Heart Rate Variability (HRV) basics

Heart Rate Variability (HRV) analysis

Heart Rate Variability (HRV) Response to Controlled Autonomic Stimulation

Methods of Heart Rate Variability (HRV) analysis

Heart Rate Variability (HRV) research products

Heart Rate Variability (HRV)  in clinical research

Heart Rate Variability (HRV) Analysis and Diabetes

Heart Rate Variability (HRV) and Cardiovascular Disease

Heart Rate Variability (HRV) and Myocardial Infarction

Heart Rate Variability (HRV) and Fatigue

Heart Rate Variability (HRV) and Age

Health Risk Diagnosis and Heart Rate Variability (HRV)

Health Assessment tools and Heart Rate Variability (HRV)

Heart Rate Variability (HRV) tools for patient assessment

Cancer Detection on Early Stage.

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