Session S22.5

Nonlinear Heart Rate Variability in a Healthy Population: Influence of Age

S Vandeput*, B Verheyden, AE Aubert, S Van Huffel

Katholieke Universiteit Leuven
Leuven, Belgium

Heart Rate Variability (HRV) measurements are used as markers of autonomic modulation of heart rate. Standard time and frequency domain methods of HRV are well described, but in recent years, new dynamic methods of HRV quantification have been used to uncover apparent nonlinear fluctuations in heart rate. These nonlinear variations would enable the cardiovascular system to respond more quickly to changing conditions. Here the numerical noise titration technique is used which provides a highly sensitive test for deterministic chaos and a relative measure for tracking chaos of a noise-contaminated signal in short data segments.
Holter recordings of 276 healthy subjects (135 men and 141 women) between 18 and 71 years of age and with a detailed medical history were monitored. White linearly correlated noise of increasing standard deviation (s) is added to the RR interval time series until its nonlinearity becomes undetected by the Volterra-Wiener nonlinear identification method at a limiting value of s = Noise Limit (NL). NL > 0 indicates chaos and the value of NL gives an estimate of its relative intensity. Conversely, if NL = 0, then it may be inferred that the series either is not chaotic or the chaotic component is already neutralized by the background noise in the data. After some preprocessing steps and resampling the RR interval time series to the mean heart rate (Hz), numerical noise titration was applied using a 300-second window and sliding the window every 30 seconds. The mean Noise Limit was calculated for 24 h and separately during day and night, as well as all standard HRV parameters and some other nonlinear HRV measures.
In men, nearly all standard HRV parameters decreased with age while in woman, SD and SDANN showed no correlation at all with age. Most nonlinear indexes declined with age, especially during daytime hours and in the female population, which can be related to the concept of decreasing autonomic modulation with advancing age. At higher ages, the relation between heart rate and heart rate variability weakens.

(Abstract Control Number: 168)