Aging in autonomic control by multifractal studies of cardiac interbeat intervals in the VLF band

Abstract

The heart rate responds dynamically to various intrinsic and environmental stimuli. The autonomic nervous system is said to play a major role in this response. Multifractal analysis offers a novel method to assess the response of cardiac interbeat intervals. Twenty-four hour ECG recordings of RR interbeat intervals (of 48 elderly volunteers (age 65-94), 40 middle-aged persons (age 45-53) and 36 young adults (age 18-26)) were investigated to study the effect of aging on autonomic regulation during normal activity in healthy adults. Heart RR-interval variability in the very low frequency (VLF) band (32-420 RR intervals) was evaluated by multifractal tools. The nocturnal and diurnal signals of 6 h duration were studied separately. For each signal, the analysis was performed twice: for a given signal and for the integrated signal. A multifractal spectrum was quantified by the h(max) value at which a multifractal spectrum attained its maximum, width of a spectrum, Hurst exponent, extreme events h(left) and distance between the maxima of a signal and its integrated counterpart. The following seven characteristics are suggested as quantifying the age-related decrease in the autonomic function ('int' refers to the integrated signal): (a) h(sleep)(max) - h(max)(wake) > 0.05 for a signal; (b) h(int)(max) > 1.15 for wake; (c) h(int)(max) - h(max) > 0.85 for sleep; (d) Hurst(wake) - Hurst(sleep) < 0.01; (e) width(wake) > 0.07; (f) width(int) < 0.30 for sleep; (g) h(int)(left) > 0.75. Eighty-one percent of elderly people had at least four of these properties, and ninety-two percent of young people had three or less. This shows that the multifractal approach offers a concise and reliable index of healthy aging for each individual. Additionally, the applied method yielded insights into dynamical changes in the autonomic regulation due to the circadian cycle and aging. Our observations support the hypothesis that imbalance in the autonomic control due to healthy aging could be related to changes emerging from the vagal function (Struzik et al 2006 IEEE Trans. Biomed. Eng. 53 89-94).

Multifractality in heartbeat dynamics in patients undergoing beating-heart myocardial revascularization

“…However, employing multifractal technique in healthy individuals, inconsistent findings regarding the changes in circadian rhythm were reported. While Ivanov et al and Makowiec et al have shown that nighttime possesses stronger multifractal organization and stronger anti-correlation as compared to daytime, Ramchurn suggested, that nighttime is less anti-correlated but that it has the same complexity as daytime [7,18,22]. Over recent years several authors have reported on diminished circadian pattern in different cardiac pathologies [1,4,19].…”

“…For certain values of q, the exponents τ(q) have familiar meanings. In particular, τ(q¼2) is related to the global Hurts exponent (H), a measure of long-range correlations, through the well known relation: H ¼½ (τ(q ¼2) þ1) [7,18]. Fluctuations in the heartbeat dynamics are strongly anticorrelated (i.e.…”

“…Although the exact physiological mechanisms underlying this phenomenon are far from being clearly identified, it is believed, that the transition between the sleep and wake phases is a period of potentially increased neuroautonomic instability because it requires a transition from a more to a less dynamic regulation of the heart [16][17][18]. Using established nonlinear HRV methods, loss of circadian rhythm in chaotic behavior of RR time series was observed in patients with (un)stable coronary artery disease, heart failure or following myocardial infarction and in survivors of cardiac arrest [1,4,17,[19][20][21].…”

“…Using multifractal HRV analysis, the majority of authors have implied, that in healthy individuals a higher degree of complexity and stronger anti-correlation with vagal predominance exist during the night (nighttime period), whereas a lesser degree of complexity and a weaker anti-correlation behavior with sympathetic domination occurs during the day (daytime period) [6,16,17,20]. Whether invasive medical or surgical procedures can affect the circadian patterns as assessed my multifractal approach and thus subjecting patients to additional risk by enhancing neurohumoral instability with additionally pronounced transitions between more and less anti-correlated states, remains unveiled [18,21,22].…”

Factors predicting incremental administration of antihypertensive boluses during deep brain stimulator placement for Parkinson’s disease

“…Aging results in a shift of autonomic balance toward sympathetic predominance in higher age groups, limiting the reactiveness of the cardiovascular system to adjust to different demands [13]. Aging is also associated with poor autonomic balance mechanisms [14].…”