Relationship between age and heart rate variability in supine and standing postures: a study of spectral analysis of heart rate.

We compared heart rate variability measures of 11 normal children (4-12 years) to 23 normal adults (21-43 years) to study the effect of age on heart rate variability measures. Children had a significantly higher supine and standing heart rate and lower supine and standing systolic and diastolic blood pressure. Children also had a significantly higher supine standard deviation of HR, supine low frequency (0.01-0.05 Hz) (p < 0.005), supine high frequency (0.2-0.5 Hz) (p < 0.001), and standing high frequency powers (p < 0.005) compared to adults. The ratio of mid frequency (0.07-0.15 Hz) to high frequency power (0.2-0.5 Hz) upon standing was significantly lower in children (p < 0.005). While there was a significant increase of the mid frequency power from supine to standing posture in the adult group (p < 0.02), there was no such significant increase in children. There were also significant negative correlations between age and supine low frequency, mid frequency, and high frequency powers, and standing high frequency power. These findings illustrate a decrease of cholinergic and an increase of adrenergic modulation of heart rate variability with age (4-43 years).