Influence of age on ambulatory electrocardiogram-derived heart rate variability.

OBJECTIVE: To evaluate the quantitative change in heart rate variability with age by using 24 h Holter ambulatory monitoring of electrocardiogram and to set the lower limit of heart rate variability depending on age. PARTICIPANTS: Eighty healthy subjects without any medication (male to female ratio 40:40, 45.6 +/- 14.1 years of age, range 16 to 68 years). METHODS: Holter monitoring was performed, and frequency and time domain heart rate variability was obtained. RESULTS: A significant inverse relationship was found between age and heart rate variability, especially in the frequency domain, and, in the time domain analysis, in the root mean square of the difference in the RR intervals of sinus rhythm (NN) between successive beats and in the portion of NN cycles greater than 50 ms apart. Except for the standard deviation of the mean of RR intervals taken every 5 mins and averaged over 24 h and the ratio of low frequency high frequency power spectra, all parameters decreased to a certain age and did not change thereafter, and the rate of decrease differed among the parameters of heart rate variability. Because age had a strong influence on heart rate variability, the lower limit of heart rate variability for a certain age was determined by using the polynomial curve fitting of the moving average minus 2 SD of 10 consecutive subjects. By using these equations, it could be determined whether heart rate variability was normal or abnormal depending on age.