Heart Rate Variability: Measures and Models

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Heart Rate Variability Measures and Models

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Outline

• Introduction
• Methods
• Conventional Point Process
• Fractal Point Process
• Measure
• Standard Measures
• Novel Measures

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Introduction

• ECG
• a recording of the cardiac-induced skin
  potentials at the bodys surface
• HRV
• called heart rate variability, the variability
  of the RR-interval sequence

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Methods

• The heartbeat sequence as a point process.
• The sequence of heartbeats can be studied by
  replacing the complex waveform of an individual
  heartbeat recorded in the ECG.
• The sequence of heartbeats is represented by

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ECG Analysis
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Conventional Point Process

• Simplest
• homogeneous Poisson point process
• Related point process
• nonparalyzable fixed-dead-time modified Poisson
  point process
• gamma-? renewal process

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Homogeneous Poisson point process

• The interevent-interval probability density
  function
• where ? is the mean number of events per unit
  time.
• interevent-interval mean1/?
• interevent-interval variance1/?2

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Dead-time modified Poisson point process

• The interevent-interval probability density
  function
• Here td is the dead time and ? is the rate of
  the process before dead time is imposed.

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Fractal Point Process

• Fractal stochastic processes exhibit scaling in
  their statistics.
• Suppose changing the scale by any factor a
  effectively scales the statistic by some other
  factor g(a), related to the factor but
  independent of the original scale
• w(ax) g(a)w(x).

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Fractal Point Process

• The only nontrivial solution of this scaling
  equation, for real functions and arguments, that
  is independent of a and x is
• w(x) bg(x) with g(x) xc
• The particular case of fixed a admits a more
  general solution
• g(x a) xc cos2pln(x)/ ln(a)

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Standard Frequency-Domain Measures

• A rate-based power spectral density
• Units of sec-1
• An interval-based power spectral density
• Units of cycles/interval
• To convert the interval-based frequency to the
  time-based frequency using

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Estimate the spectral density

1. Divided data into K non-overlapping blocks of L
   samples
2. Hanning window
3. Discrete Fourier transform of each block

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Measures in HRV

• VLF. The power in the very-low-frequency range
  0.0030.04 cycles/interval.
• LF. The power in the low-frequency range
  0.040.15 cycles/interval.
• HF. The power in the high-frequency range
  0.150.4 cycles/interval.
• LF/HF. The ratio of the low-frequency-range power
  to that in the high-frequency range.

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Standard Time-Domain Measures

• pNN50. proportion of successive NN intervals
• SDANN. Standard Deviation of the Average NN
  interval
• SDNN. Standard Deviation of the NN interval

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Other Standard Measures

• The event-number histogram
• The Fano factor

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Novel Scale-Dependent Measures

• Allen Factor A(T)
• The Allan factor is the ratio of the event-number
  Allan variance to twice the mean

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Wavelet transform using Haar wavelet