Heart Rate Variability

Can be used as a prognastic marker of cardiovascular diseases and its application in estimation of cardiac autonomic nervous system activity (Stauss, 2003)
1. ANS imbalance associating with increased SNS and decreased PNS has been strongly correlated with arhythmogensis and sudden cardiac death (Sztajzel, 2004).
2. in a normal heart with an integer ANS, there will be a continuous physiological variation of the sinus cycle reflecting a good symptho-vagal balance (Sztajzel, 2004)
In healthy individuals the SAN inititiates each heart beat due to an unstable membrane potential of myocites located within that region, causing action potentials to be generated at a fairly constant frequency (Stauss, 2003)
1. This contstant frequency is generated by the autorhythmicity of the SAN and is modulated my many factors causing variability in the HR signal at differing frequencies (Stauss, 2003)
  1. According to the task force of european society of cardiology etc classifed these frequencies to be divided in to the following bands:
    1. ULF (>5hour cycle length);
      1. Associated with circadian rhythm
    2. LF (>6s cycle length)
      1. Sensititive to sympathetic nervous system (and perhaps parasympathetic activity)
    3. HF (2.5-6s cycle length)
      1. syncronised with the respiratory system, and primarily inervated by parasympathetic innervation
    4. VLF (> 25s cylcle length)
      1. asociated with temp regulation
LF power
1. Used to help depict SNS which is responsible for speading up the HR, interestingly can only be depicted by LF due to PNS being much faster than sympathetic mediated effects of the HR (Straus, (2003), 27, 30 47a
2. Sympathetic activity
  1. a negative pressure on lower extremity has been known to increase sympathetic activity (Stauss, 2003)
HF Power
1. Parasympathic NS is the only thing that factors HF power, but is also known to effect LF power (Stauss, 2003)
2. Most researched componant within HRV due to its high correlation with vagal modulation (Stauss, 2003)
non-invasive way to detect the sympatetic and vagal componants of the ANS on SAN level (Szatjzel, 2004)
Autonomic Nervous system
1. Sympathetic nervous activity enhanceds automoaticacy, wheras Parasympathetic inhibits it
  1. Parasympathic NS is responsible for the hyperpolarisation and reduce the rate of depolarisation, whereas the sympathetic NS causes chronotrophic effects by increasing the rate fo SAN depolarisation (Szatjzel, 2004)
Measurement
1. HRV analysis consists of a series od measurements of successive R-R interval variations of sinus origin, providing information about autonomic tone (Szatjzel, 2004) 18
2. Different factors may influence HRV
  1. Age
  2. Gender
  3. Respiration
  4. circardian rhythm
  5. Body position
3. usually used in 24 hour holter recordings but can also be used in shorter recordings between 0.5-5 minutes
  1. Short term recordings are caracterised by the VLF, LF anf HF componants
4. The LF/HF ratio reflects the global sympatho-vagal balance and can be used within this balance.
  1. In a normal adult resting values tend to be around 1-2
5. Normalisation
  1. LF or HF (nu)= LF or HF/ (total power[ms2]- VLF [ms2])
Effect of Exercise
1. It is well known that endurance athletes have profound Brachycardia
  1. When comparing HRV indices trained vs general population they have found that trained athletes have a significantly longer R-R interval
  2. When using absolute values data has shown mixed results on if trained atheltes have a higher HF dominance (Achten & Jeukendrup, 2004) [15, 48, 53] [49, 50, 54]
  3. When using normalised data 4/6 studies found a greater vagal dominance, in trained athletes (Achten & Jeukend, r, up, 2004) [28,53,56,58]
2. Predictor of overtraining?
  1. Could be used to predict overtraining or overreaching (Achten & Jeukendrup, 2004) [13, 99]

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Heart Rate Variability

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	Created by nick1swin almost 12 years ago