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136 lines
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<TITLE>Heart rate variability</TITLE>
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<H1><A NAME="SECTION00030000000000000000"></A>
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<A NAME="s:hrv"></A>
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<BR>
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Heart rate variability
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</H1>
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Analysis of variations in the instantaneous heart rate time series
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using the beat-to-beat RR-intervals (the RR tachogram) is known as
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Heart Rate Variability (HRV) analysis [<A
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HREF="node8.html#malik95">7</A>,<A
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HREF="node8.html#eursoccard96">10</A>].
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HRV analysis has been shown to provide an assessment of cardiovascular
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disease [<A
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HREF="node8.html#crawford99">11</A>].
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The heart rate may be increased by slow acting sympathetic activity
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or decreased by fast acting parasympathetic (vagal) activity.
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The balance between the effects of the sympathetic and parasympathetic
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systems, the two opposite acting branches of the autonomic nervous system,
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is referred to as the sympathovagal balance and
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is believed to be reflected in the beat-to-beat changes of the
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cardiac cycle [<A
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HREF="node8.html#malik95">7</A>].
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The heart rate is given by the reciprocal of the RR-interval in units
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of beats per minute.
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Spectral analysis of the RR tachogram is typically used to
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estimate the effect of the sympathetic and parasympathetic modulation
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of the RR-intervals. The two main frequency bands of interest
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are referred to as the Low-Frequency (LF) band (0.04 to 0.15 Hz)
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and the High-Frequency (HF) band (0.15 to 0.4 Hz) [<A
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HREF="node8.html#eursoccard96">10</A>].
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Sympathetic tone is believed to influence the LF component whereas
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both sympathetic and parasympathetic activity have an effect on the HF
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component [<A
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HREF="node8.html#malik95">7</A>]. The ratio of the power contained in
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the LF and HF components has been used as a measure of the sympathovagal
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balance [<A
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HREF="node8.html#malik95">7</A>,<A
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HREF="node8.html#eursoccard96">10</A>].
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Respiratory Sinus Arrhythmia (RSA) [<A
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HREF="node8.html#hales1733">12</A>,<A
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HREF="node8.html#ludwig1847">13</A>]
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is the name given to the oscillation in the RR tachogram due to
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parasympathetic activity which is synchronous with the respiratory cycle.
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The RSA oscillation manifests itself as a
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peak in the HF band of the spectrum. For example, 15 breaths per minute
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corresponds to a 4 second oscillation with a peak in the power spectrum at
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0.25 Hz. A second peak is often found in the LF
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band of the spectrum at approximately 0.1 Hz. While the cause of this
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10 second rhythm is strongly debated, one possible explanation is that it
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may be due to baroreflex regulation which creates the so-called
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<I>Mayer waves</I> in the blood pressure signal [<A
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HREF="node8.html#deboer87">14</A>].
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2003-10-08
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