Veteran and Military Healthcare

Heart Rate Variability

Heart rate variability (HRV) is commonly used as the most reliable metric for determining autonomic nervous system function. HRV can be measured by both instantaneous heart rate and beat-to-beat alterations (R–R intervals) in heart rate. Heart rate (HR) fluctuates around a mean value over time. This autonomic nervous system greatly influences this fluctuation, which regulates HR through the sympathetic and parasympathetic nervous systems1. Low HRV has been associated with excessive cardiac sympathetic modulation, inadequate parasympathetic modulation, or both2.

HRV is also known as the respiratory sinus arrhythmia. HRV can be measured by use of ECG signals, either short 5-minute recordings or long-term 24-hour ambulatory ECG recordings. The data is generally analyzed in 5-minute epochs to achieve sufficient data to compute either time domain or frequency domain indices. The time domain indices include SDNN (a measure of the standard deviation of the HRV changes) and RMSSD (a measure of parasympathetic function). Frequency domain data are obtained by using a Fast Fourier transform of the RR data to convert from milliseconds to Hz. Several frequency bands are then identified including low frequency (LF) and high frequency bands (HF). Also, the total power, that is the sum of all the bands is computed along with a ratio of the LF/HF bands3.

The total power is a reflection of total heart rate variability. A reduction of total power indicates reduced heart rate variability. Reduced total power, for example, is seen in diabetes mellitus and congestive heart failure. The LF/HF ratio is used by many investigators as a reflection of sympathetic dominance but the measurements is not precise and parasympathetic effects influence the LF/HF ratio.

The HF frequency band is controlled almost entirely by changes in efferent parasympathetic impulses conducted through the vagus nerve from the dorsal nucleus of the vagus in the medulla oblongata to muscarinic receptors in the sinus node in the right atrium of the heart4. The relationship between the HF frequency band and parasympathetic function has been established by large number of studies and the relationship is non-controversial in the field.

  1. Cohen, H., Matar, M., Kaplan, Z., & Kotler, M. (1999). Power spectral analysis of heart rate variability in psychiatry. Psychotherapy and Psychosomatics, 68, 59–66.
  2. Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. (1996). Heart rate variability. Standards of measurement, physiological interpretation, and clinical use. European Heart Journal, 17, 354–381.
  3. Akselrod S, Gordon D, Ubel FA et al. Power spectrum analysis of heart rate fluctuation: a quantitative probe of beat-to-beat cardiovascular control. Science. 1981;213:220-222.
  4. Behrens S, Franz MR. Circadian variation of arrhythmic events, electrophysiological properties, and the autonomic nervous system. Eur Heart J. 2001;22:2144-2146.