Circadian variations in heart rate spectrums

This investigation was undertaken to develop and test methods for tracking the state of the autonomic nervous system. Different regions of the heart rate spectrum are known to reflect changes in tone of the two branches of the autonomic nervous system. Because these changes have been shown to affect prognosis of patients with coronary heart disease, a commercial Holter analysis system was adapted to track them. The mid-frequency range was shown to be too corrupted by vagal activity to be useful as a measure of sympathetic tone. Significant circadian variations in high-frequency RR variations were observed but changes preceding periods of ST segment depression were not