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njit-etd2003-081 - New Jersey Institute of Technology

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31<br />

Figure 2.7 Effect <strong>of</strong> autonomic stimulation on the slope <strong>of</strong> the pacemaker potential.<br />

(From A.J. Vander, J.H. Sherman, and D.S. Luciano, Human Physiology, 1994.)<br />

2.5.2 Heart Rate Variability as a Measure <strong>of</strong> Autonomic Function<br />

Changes in heart rate usually involve the reciprocal action <strong>of</strong> the two divisions <strong>of</strong> the<br />

autonomic nervous system. An increased heart rate is the result <strong>of</strong> reduced<br />

parasympathetic tone and a concomitant increase in sympathetic activity. A decrease in<br />

heart rate is usually the result <strong>of</strong> increased parasympathetic tone and a simultaneous<br />

decrease in sympathetic tone. Therefore, changes in heart rate reflect the action <strong>of</strong> the<br />

sympathetic and parasympathetic nervous systems on the heart. However, under certain<br />

conditions, it is possible for heart rate to change by activity <strong>of</strong> only one division <strong>of</strong> the<br />

autonomic nervous system, independent <strong>of</strong> the other division, rather than reciprocal<br />

changes in both [8].<br />

Initially, the effect <strong>of</strong> the autonomic nervous system on the heart was estimated<br />

by utilizing the traditional technique <strong>of</strong> average heart rate [8]. As a reference, the

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