Temporal age-related changes in spectral, fractal and complexity characteristics of heart rate variability

Cross-sectional studies have suggested that heart rate (HR) variability, an alysed using traditional time and frequency domain methods, is related to a geing, but no longitudinal studies have estimated the age dependence of HR fluctuation. This study evaluated temporal age-related changes in 12-h meas ures of HR variability among 109 patients with coronary artery disease (CAD ), who underwent repeat Holter recordings at 32-month intervals. Time and f requency domain measures, along with fractal and complexity measures of HR variability, were determined at the baseline and after 32 months. Changes i n HR dynamics were compared with various laboratory variables, exercise dat a and angiographic progression of CAD. Traditional time and frequency domai n measures of HR variability did not change significantly during the follow -up, but the power-law scaling slope decreased from -1.29 +/- 0.20 to -1.36 +/- 0.23 (P<0.01) and the short-term fractal exponent (al) of HR dynamics from 1.29 +/- 0.14-1.22 +/- 0.18 (P<0.001). The approximate entropy value a lso decreased from 1.00 +/- 0.19 to 0.95 +/- 0.18 (P<0.05). The changes in HR behaviour were not related to demographic data, laboratory values or ang iographic progression of CAD. Only a weak correlation was observed between the change in the power-law slope and the baseline glucose value (P<0.05). This longitudinal study shows that the fractal characteristics of HR dynami cs and the complexity properties of R-R intervals undergo rapid changes alo ng with ageing, and that fractal and complexity analysis techniques are mor e sensitive than traditional analysis methods in documenting temporal age-r elated changes in HR behaviour.