njit-etd2003-081 - New Jersey Institute of Technology

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average heart rate was measured under normal resting conditions. Then the average heart
rate was measured under the administration of drugs. The drugs used were atropine,
which blocks the effects of the parasympathetic nervous system, and propranolol, which
masks the effects of the sympathetic nervous system. A qualitative assessment can then
be made of the autonomic nervous system by comparing the reference heart rate to the
heart rate while under the administration of the drugs. This method looks at the average
over time of heart rate. However, when the ECG is looked at on a beat-to-beat basis,
rather than over a period of time, fluctuations in the heart rate are observed [8]. Recent
research indicates that fluctuations in heart rate are a healthy sign. In fact, one
hypothesis is that the larger variations in the heart rate correlate to a healthier autonomic
nervous system.
By contrast a number of physiologic and disease states produce alterations in
autonomic function, which reduce the variability in heart rate [8].
2.5.3 Baroreflex Response
A decrease in blood pressure sensed by the baroreceptors produces an increase in
sympathetic activity and a decrease in parasympathetic activity, resulting in an increase
in heart rate and therefore an increase in blood pressure. An increase in blood pressure
sensed by the baroreceptors produces an increase in parasympathetic activity and a
decrease in sympathetic activity, resulting in a decrease in heart rate and therefore a
decrease in blood pressure. The oscillations that result from this negative feedback loop
have been shown to occur in the low frequency range (0.05-0.15Hz) [16].