Changes in cardiovascular autonomic regulation among elderly subjects: follow-up of sixteen years.

BACKGROUND. Previous cross-sectional studies have suggested that cardiac autonomic regulation, measured as heart rate (HR) variability, is altered upon ageing, and that altered HR variability may predict mortality. However, there are no longitudinal follow-up reports of the changes of HR dynamics in elderly subjects. AIM & METHOD. This study was designed to examine the longitudinal changes in the spectral, fractal, and complexity measures of HR variability in a random sample of 41 elderly subjects (mean age 69 +/- 4 years), who underwent repeated 24-hour Holter recordings at the baseline and after 16 years' follow-up. Several cardiovascular risk factors were determined at the baseline. RESULTS. A time-domain index, standard deviation of N-N intervals (SDNN) (142 +/- 34 msec versus 133 +/- 50 msec, not significant (NS)), and the high frequency spectral component of HR variability (219 +/- 222 msec(2) versus 268 +/- 287 msec(2), NS) did not change during the follow-up. The low frequency power (LF) of HR variability decreased from 678 +/- 654 msec(2) to 436 +/- 651 msec(2) (P < 0.01). Among the fractal HR variability indexes, the power-law slope (beta) (-1.31 +/- 0.20 versus -1.47 +/- 0.21, P < 0.001) and the short-term fractal exponent alpha(1) (1.16 +/- 0.19 versus 1.06 +/- 0.18, P < 0.01) decreased significantly. Approximate entropy remained unchanged. CONCLUSIONS. The magnitude of total HR variability and the respiratory vagal modulation of HR do not change over time in the elderly. However, the spectral and fractal characteristics of HR behavior still undergo alterations upon ageing.