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Another variable
coming to the forefront as an indicator of autonomic nervous system
(ANS) function is heart rate variability. The ANS regulation of
the heart rate is known in significant detail and high performance
computer analysis of the electrocardiogram (ECG) allows quantification
of the modulations in heart rate that are a product of ANS regulation.
Heart rate (or beat-to-beat interval), even in the absence of
external perturbations or challenges is not constant but rather
oscillates (or varies) around a mean value. Rhythmic fluctuations
in the sinus rate over time constitute heart rate variability.
A typical
HR time series and power spectrum shows that most of the ECG power
is concentrated in two frequency bands, a low (0.03 - 0.15 Hz)
and a high (usually 0.15 - 0.5 Hz) frequency band. Their relationship
to one another is considered to reflect a relative balance of
SNS versus parasympathetic (PSNS) activity as depicted in the
figures below:
| Figure
3.3.4: Typical Heart Rate Time Series and Corresponding
Heart Rate Power Spectrum for Supine, Healthy Adult
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Source:
Akselrod S. Component of heart rate variability. In:
Malik M, Camm AJ eds. Heart Rate Variability. Armonk,
NY. Futura Publishing Company, Inc. 1995: 147-163.
Reprinted by permission of Blackwell Science, Inc
and Solange Akselrod.
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| Figure
3.3.5: Heart Rate Time Series and Power Spectrum for
Same Adult Upon Standing
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Source:
Akselrod S. Component of heart rate variability. In:
Malik M, Camm AJ eds. Heart Rate Variability. Armonk,
NY. Futura Publishing Company, Inc. 1995: 147-163.
Reprinted by permission of Blackwell Science, Inc
and Solange Akselrod.
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