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Heart Rate
Variability (HRV),
Heartbeats, and
Autonomic Nervous
System (ANS)
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Do you have     
- are you monitoring   
- are you taking
prescription drugs?
- are you aware of drug
side effects on ANS?
- self-improvement tips
Read more......
Feeling dizzy      
or even fainted?
- are you low in blood
pressure or heart rate?
- are you taking
prescription drugs?
- You may experience
Baroreflex failure
Read more......
Irregular heartbeats?
- often noticing abnormal
heartbeats (missing,
uneven, or super-fast)?
- Yo might have cardiac
- Most sudden death
events are preceded by
irregular heartbeats
Read more......
Mitral Valve Prolapse?
- Mitral valve is the
bicuspid valve between left
atrium and ventricle
- If mitral valve is not
closed properly (called
mitral valve prolapse
MVP), the blood may
backflow during pumping
- there is a strong
connection between panic
attackes and MVP
- How to detect it?
Read more......
Am I having   
- autonomic nervous
system works to fine tune
body conditions depending
on physiological needs
- ANS consists of two
branches: sympathetic and
- do you have balanced
- what are the symptoms of
Read more......
What is Heart Rate Variability (HRV)?
Glimpse of Facts on HRV

  • Heart Rate Variability (HRV), the most frequently used method for ANS test
  • Our heart pumps 72 cycles per minute on average
  • Within the seemly constant heart rhythm there exists fine, dynamic fluctuations
  • The cyclic fluctuations are caused by ANS modulation of heart rate
  • ANS divides into sympathetic nervous system and parasympathetic nervous system; The former
    promotes a higher heart rate while the latter a slower rate
  • The heart rate of healthy people is 72 beats / min.  Average beat-to-beat interval is 0.833 sec
    or 833 ms, while its standard deviation is about 40ms. This value is defined as heart rate
    variability or HRV
  • HRV represents total activity index of ANS; The higher the HRV, the better the ANS control
  • HRV is highly dependent on age. At age of 20, HRV is about 50-60 ms; As people get old, HRV
    decreases to 20-25 ms.  HRV in female is slightly higher than male, but the difference
    disappears post-menopause.  See Figure 1 for normal values of HRV as function of sex and
  • HRV approaches zero for people (1) being close to death, due to multiple organ failure (2)
    wearing a pacemaker, due to a fixed, programmed heart rate, and  (3) with a transplanted
    heart, due to lack of ANS modulation
More facts about HRV
A good heart: fast and slow beats alternating!

  • Before 1960’s, it was thought that the heartbeat frequency was constant
  • Lee et al. and other groups discovered heart rate variability
  • Definition of HRV: standard deviation of peak-to-peak intervals
  • The source of HRV comes from ANS modulation on heart rate
  • Sympathetic signals cause heart to beat faster (narrower gaps) while
    parasympathetic signals opposite (see Figure 2 below)

Reference (1) Hon EH, Lee ST. Electronic evaluations of the fetal heart rate patterns
preceding fetal death: further observations. Am J Obstet Gynecol. 1965;87:814-826
(2) Sayers BM. Analysis of heart rate variability. Ergonomics. 1973;16:17-32
Figure 2: Illustration of Heart Rate Variability
Note: Faster heart rates (with narrower gaps, indicated by a "Narrow" arrow) are stimulated by
sympathetic nerve signals,  while slower heart rates (with wider gaps, indicated by a "Wide"
arrow) are stimulated by parasympathetic nerve signals.
  • HRV has become the golden standard for ANS testing
  • The biggest contributor of such development was the 1996 publication of "Heart
    Rate Variability - Standards of Measurement, Physiological Interpretation, and
    Clinical Use" by Task Force of the European Society of Cardiology and  the North
    American Society of Pacing Electrophysiology in the journal Circulation
    (Circulation. 1996;93:1043-1065.; © 1996 American Heart Association, Inc.)
HRV - the Golden Standard of Autonomic
Nervous System Testing
Power Spectrum Analysis of HRV
- to obtain LF, HF, and LF/HF
1. Obtain peak-to-peak intervals
2. Conduct Fast Fourier Transfer (FFT) analysis
3. Plot power spectrum density distribution
Power Spectrum Analysis of HRV
- to obtain LF, HF, and LF/HF
  • Using pharmaceutical agents (sympathetic and parasympathetic blockage) to
    identify FFT peaks
1996 HRV International Task Force Standard

  • HRV:Total ANS activity index (ms); equal to standard deviation of adjacent peak-
    to-peak intervals (also called SDNN)
  • LF(AU):Low frequency (0.04 ~0.15 Hz) (ms2); sympathetic (and some
    parasympathetic) activity index
  • HF(AU):High frequency (frequency range 0.15~0.4 Hz) (ms2); parasympathetic
    activity index
  • LF(NU):LF%, [LF/(TP-VLF)]*100; contribution of sympathetic activity
  • HF(NU):HF%, [HF/(TP-VLF)]*100; contribution of parasympathetic activity
  • LF/HF: Ratio of LF to HF; sympathetic-parasympathetic balance index
  • VLF(AU):Very low frequency (0.0001~0.04 Hz) (ms2); physiological meaning not
    defined by the standard
  • Irregular heartbeats (including cardiac arrhythmias) must be excluded from HRV

Be aware: Some older and current HRV analyzers do not conform to the 1996
international standard
Figure 1: HRV-Sex-Age Correlations (Normal
  • The above statistical correlation is established by taking HRV data
    published in literature for healthy volunteers and conducting regression
    analysis (30 peer-reviewed journal papers covering world-wide regions and
    demographics including our own published data; report on file with Sun
  • 1996 International HRV Standard does provide certain HRV normal ranges.  
    However, the range is too broad to be useful as a guide for health status