Spectral analysis of heart rate variability in evaluation of sympathetic function in elderly subjects.

Plasma concentration of noradrenaline is often used as a measure of sympathetic nervous activity. Recently, the method of spectral analysis of heart rate variability has been introduced to detect autonomic dysfunction. To examine whether spectral analysis of heart rate variability is useful in evaluating sympathetic function, changes in the heart rate variability in the low-frequency spectral band were compared with the change of plasma noradrenaline in response to head-up tilt in elderly hypertensives (n = 13) and diabetics (n = 13). In hypertensive subjects, there was an increase in relative low-frequency power (p = 0.015) and an increase in plasma noradrenaline level (p = 0.040) in response to head-up tilt. Diabetics did not show corresponding changes. There was no change in absolute low-frequency power in either group. It is concluded that spectral analysis of heart rate variability can be useful in evaluating sympathetic function in elderly subjects.