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Biomedical subjects

T H Mäkikallio

Publications and source records attributed to T H Mäkikallio.

At least 19 recordsLinked to original sources
PubMed2005

Natriuretic peptides and mortality after stroke.

BACKGROUND AND PURPOSE: Measurement of natriuretic peptides provides prognostic information in various patient populations. The prognostic value of natriuretic peptides among patients with acute stroke is not known, although elevated peptide levels have been observed. METHODS: A series of 51 patients (mean age, 68+/-11 years) with first-ever ischemic stroke underwent a comprehensive clinical examination and measurements of plasma atrial natriuretic peptides (N-ANP) and brain natriuretic peptides (N-BNP) in the acute phase of stroke. The patients were followed-up for 44+/-21 months. Risk factors for all-cause mortality were assessed. Control populations, matched for gender and age, consisted of 51 patients with acute myocardial infarction (AMI) and 25 healthy subjects. RESULTS: Plasma concentrations of N-ANP (mean+/-SD, 988+/-993 pmol/L) and N-BNP (751+/-1608 pmol/L) in the stroke patients were at the same level as those in the AMI patients (NS for both), but significantly higher than those of the healthy subjects (358+/-103 pmol/L, P<0.001 and 54+/-26 pmol/L, P<0.01, respectively). Elevated levels of N-ANP and N-BNP predicted mortality after stroke (risk ratio [RR] 4.3, P<0.01 and RR 3.9, P<0.01, respectively) and after AMI (P<0.05), and remained independent predictors of death after stroke even after adjustment for age, diabetes, coronary artery disease, and medication (RR 3.9, P<0.05 and RR 3.7, P<0.05, respectively). CONCLUSIONS: Plasma levels of natriuretic peptides are elevated in the acute phase of stroke and predict poststroke mortality.

Aged↗
PubMed2004

Heart rate dynamics predict poststroke mortality.

BACKGROUND: Impaired cardiovascular autonomic regulation assessed by heart rate (HR) variability provides prognostic information in patients with heart disease as well as among elderly. Reduced HR variability has been described in stroke patients, but the prognostic significance of HR variability measures after stroke has not been studied. METHODS: A series of 84 patients (mean age 59 +/- 12 years) with an acute first-ever ischemic stroke underwent a comprehensive clinical investigation, laboratory tests, and 24-hour EKG recordings and were followed up for 7 years (mean 83 +/- 54 months). Various conventional and newer qualitative measures of HR variability were analyzed from the baseline 24-hour EKG. Risk factors for all-cause mortality were assessed. RESULTS: During the follow-up, 33 (39%) patients died and 51 survived. Among all the variables analyzed, abnormal long-term HR variability measure power-law slope beta (beta < -1.5), reflecting an altered distribution of spectral characteristics over ultra and very low frequency bands, was the best univariate predictor of death (hazard ratio 4.5, 95% CI 2.2 to 9.5, p < 0.001). High age, poor Scandinavian Stroke Scale score, and abnormal short-term HR variability scaling measure (alpha) also predicted mortality in univariate analysis. In multivariate analysis, after adjustment for age, the only independent predictor of the risk of death was abnormal long-term power-law slope beta (hazard ratio 3.8, CI 1.8 to 8.2, p < 0.001). Conventional HR variability measures showed no prognostic power. CONCLUSION: Abnormal long-term HR dynamics predict poststroke mortality. This measure may have value in the risk stratification of stroke patients.

Aged↗
PubMed2001

Heart rate variability in ischemic heart disease.

Major untoward events, such as life-threatening arrhythmias and acute coronary events, have been suggested to be triggered by the activation of the autonomic nervous system in patients with coronary artery disease. Analysis of heart rate variability by conventional time and frequency domain methods, as well as by newer methods derived from nonlinear system theory, has offered a novel approach for studying the abnormalities in cardiovascular neural regulation in ischemic heart disease. Heart rate variability has been shown to be altered among patients with ischemic heart disease as compared to their age-matched controls without the evidence of ischemic heart disease. There are also obvious differences in various measures of heart rate variability between patients with uncomplicated coronary artery disease and those with coronary artery disease with complicated myocardial infarction. Impaired high-frequency oscillations of heart rate is the most prominent feature in patients with uncomplicated coronary artery disease, suggesting mainly an impairment in vagal autonomic regulation. Patients with prior myocardial infarction have a reduced overall heart rate variability, and a specific spectral pattern with a reduced low-frequency spectral component has been observed in patients with prior myocardial infarction and impaired left ventricular function. Recent studies have shown that the new nonlinear measures, particularly fractal analysis methods of heart rate dynamics, can detect subtle changes in heart rate behavior that are not easily detected by traditional analysis methods from ambulatory recordings. Patients with prior myocardial infarction have steeper power-law slope analyzed from the ultra and very low-frequency spectral bands, and they also have more random short-term heart rate dynamics analyzed by the detrended fluctuation method. A large body of data indicate that reduced overall heart rate variability is associated with an increased risk of mortality and nonfatal cardiac events in patient with ischemic heart disease. Of particular note, recent studies indicate that fractal analysis methods perform even better than the traditional analysis methods of heart rate variability as predictors of death and the onset of life-threatening arrhythmic events in post-infarction populations. These findings support the notion that heart rate variability analysis methods, such as fractal and complexity measures as well as conventional techniques, give valuable clinical information among patients with ischemic heart disease.

Autonomic Nervous System↗
PubMed2001

Fractal analysis and time- and frequency-domain measures of heart rate variability as predictors of mortality in patients with heart failure.

Time-domain measures of heart rate (HR) variability provide prognostic information among patients with congestive heart failure (CHF). The prognostic power of spectral and fractal analytic methods of HR variability has not been studied in the patients with chronic CHF. The aim of this study was to assess whether traditional and fractal analytic methods of HR variability predict mortality among a population of patients with CHF. The standard deviation of RR intervals, HR variability index, frequency-domain indexes, and the short-term fractal scaling exponent of RR intervals were studied from 24-hour Holter recordings in 499 patients with CHF and left ventricular ejection fraction < or =35%. During a mean follow-up of 665 +/- 374 days, 210 deaths (42%) occurred in this population. Conventional and fractal HR variability indexes predicted mortality by univariate analysis. For example, a short-term fractal scaling exponent <0.90 had a risk ratio (RR) of 1.9 (95% confidence interval [CI] 1.4 to 2.5) and the SD of all RR intervals <80 ms had an RR of 1.7 (95% CI 1.2 to 2.1). After adjusting for age, functional class, medication, and left ventricular ejection fraction in the multivariate proportional-hazards analysis, the reduced short-term fractal exponent remained the independent predictor of mortality, RR 1.4 (95% CI 1.0 to 1.9; p <0.05). All HR variability indexes were more significant univariate predictors of mortality in functional class II than in class III or IV. Among patients with moderate heart failure, HR variability measurements provide prognostic information, but all HR variability indexes fail to provide independent prognostic information in patients with the most severe functional impairment.

Aged↗
PubMed2001

Prediction of sudden cardiac death by fractal analysis of heart rate variability in elderly subjects.

OBJECTIVES: The aim of this study was to test the hypothesis that abnormal scaling characteristics of heart rate (HR) predict sudden cardiac death in a random population of elderly subjects. BACKGROUND: An abnormality in the short-term fractal scaling properties of HR has been observed to be related to a risk of life-threatening arrhythmias among patients with advanced heart diseases. The predictive power of altered short-term scaling properties of HR in general populations is unknown. METHODS: A random sample of 325 subjects, age 65 years or older, who had a comprehensive risk profiling from clinical evaluation, laboratory tests and 24-h Holter recordings were followed up for 10 years. Heart rate dynamics, including conventional and fractal scaling measures of HR variability, were analyzed. RESULTS: At 10 years of follow-up, 164 subjects had died. Seventy-one subjects had died of a cardiac cause, and 29 deaths were defined as sudden cardiac deaths. By univariate analysis, a reduced short-term fractal scaling exponent predicted the occurrence of cardiac death (relative risk [RR] 2.5, 95% confidence interval [CI], 1.9 to 3.2, p < 0.001) and provided even stronger prediction of sudden cardiac death (RR 4.1, 95% CI, 2.5 to 6.6, p < 0.001). After adjusting for other predictive variables in a multivariate analysis, reduced exponent value remained as an independent predictor of sudden cardiac death (RR 4.3, 95% CI, 2.0 to 9.2, p < 0.001). CONCLUSIONS: Altered short-term fractal scaling properties of HR indicate an increased risk for cardiac mortality, particularly sudden cardiac death, in the random population of elderly subjects.

Aged↗
PubMed2001

Changes in cardiac autonomic regulation after prolonged maximal exercise.

Harmful cardiac events occurs frequently after exercise. However, the cardiac autonomic regulation after vigorous exercise is not well known. This study was designed to assess heart rate (HR) variability before and after a 75 km cross-country skiing race. HR variability was assessed by using standard statistical measures along with spectral and quantitative Poincarè plot analysis of HR variability in 10 healthy male subjects (age 36 +/- 11 years). The average HR was at the same level 1 day after the race as before the race, but on the second day, HR was significantly lower (P<0.001) compared with the prerace and 1 day after values. The normalized high-frequency (HF) spectral component of HR variability (nuHF) was lower (P<0.01) on the first day after the maximal exercise compared with the pre-exercise values but returned to or even exceeded the prerace level on the second day (P<0.01). The changes in short-term R-R interval variability analysed from the Poincaré plot were similar to those observed in the HF spectral component. The normalized low-frequency (LF) spectral component of HR variability (nuLF) was higher (P<0.01) on the first day after the exercise compared with the prerace levels and it also returned to the pre-exercise level or even dropped below it on the second day after the race. The mean time it took the HF spectral component to return to the pre-exercise level was 4.2 +/- 4.2 h (ranging from 0 to 12 h). This recovery time correlated inversely with the maximal oxygen consumption (VO2max) measured during the bicycle exercise test before the skiing race (r=-0.712, P<0.016). The cardiac vagal outflow is blunted for several hours after prolonged vigorous exercise. The recovery time of reduced vagal outflow depends on individual cardiorespiratory fitness and there is an accentuated rebound of altered autonomic regulation on the second day after prolonged exercise.

Adult↗
PubMed2001

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

Cross-sectional studies have suggested that heart rate (HR) variability, analysed using traditional time and frequency domain methods, is related to ageing, but no longitudinal studies have estimated the age dependence of HR fluctuation. This study evaluated temporal age-related changes in 12-h measures of HR variability among 109 patients with coronary artery disease (CAD), who underwent repeat Holter recordings at 32-month intervals. Time and frequency domain measures, along with fractal and complexity measures of HR variability, were determined at the baseline and after 32 months. Changes in HR dynamics were compared with various laboratory variables, exercise data and angiographic progression of CAD. Traditional time and frequency domain 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 (alpha1) of HR dynamics from 1.29 +/- 0.14-1.22 +/- 0.18 (P<0.001). The approximate entropy value also 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 angiographic 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 dynamics and the complexity properties of R-R intervals undergo rapid changes along with ageing, and that fractal and complexity analysis techniques are more sensitive than traditional analysis methods in documenting temporal age-related changes in HR behaviour.

Aged↗
PubMed2001

Effects of pharmacological adrenergic and vagal modulation on fractal heart rate dynamics.

Breakdown of short-term fractal-like behaviour of HR indicates an increased risk for adverse cardiovascular events and mortality, but the pathophysiological background for altered fractal HR dynamics is not known. Our aim was to study the effects of pharmacological modulation of autonomic function on fractal correlation properties of heart rate (HR) variability in healthy subjects. Short-term fractal scaling exponent (alpha1) along with spectral components of HR variability were analysed during the following pharmacological interventions in healthy subjects: (i) noradrenaline (NE) infusion (n=22), (ii) NE infusion after phentolamine (PHE) (n=8), (iii) combined NE + adrenaline (EPI) infusion (n=12), (iv) vagal blockade with high dose of atropine (n=10), (v) and vagal activation by low dose of atropine (n=10). Then alpha1 decreased progressively during the incremental doses of NE (from 0.85 +/- 0.250 to 0.55 +/- 0.23, P<0.0001). NE also decreased the average HR (P<0.001) and increased the high frequency spectral power (P<0.001). Vagal blockade with atropine increased the alpha1 value (from 0.82 +/- 0.22 to 1.24 +/- 0.41, P<0.05). Combined NE + EPI infusion and vagal activation with a low dose atropine did not result in any changes in alpha1, and alpha-adrenergic blockade by PHE did not completely reverse the effects of NE on alpha1. Increased levels of circulating NE result in reduction of short-term correlation properties of HR dynamics. The results suggest that coactivation of cardiac vagal outflow at the time of high levels of a circulating sympathetic transmitter explains the breakdown of fractal-like behaviour of human HR dynamics.

Adrenergic Fibers↗
PubMed2001

Differences in heart rate dynamics before the spontaneous onset of long and short episodes of paroxysmal atrial fibrillation.

BACKGROUND: Altered heart rate (HR) dynamics precede the spontaneous onset of atrial fibrillation (AF), but the factors related to the perpetuation and duration of paroxysmal AF episodes are not well established. This study was designed to test the hypothesis that HR dynamics preceding the onset of (AF) may influence the duration of AF. METHODS: Traditional time and frequency domain HR variability indices, along with a short-term fractal scaling exponent (alpha(1)) and approximate entropy (ApEn), were analyzed in 20-minute intervals before 92 episodes of spontaneous paroxysmal AF in 22 patients without structural heart disease. AF episodes were divided into two groups according to the duration of the arrhythmia episodes. RESULTS: The high-frequency (HF) spectral component in normalized units (nu) of heart rate variability was higher and low-frequency (LF) component lower before long (> 200 s, n = 41) compared to short (< 200 s, n = 51) AF episodes (HF nu; 40.1 +/- 14.8 vs 31.5 +/- 16.4, P < 0.0001 and LF nu; 59.9 +/- 14.8 vs 68.5 +/- 16.4, P < 0.0001). Short-term scaling exponent values also were lower before long compared to short AF episodes (e.g., alpha(1); 1.12 +/- 0.21 vs 1.24 +/- 0.23, P < 0.0001). Women had a larger number of long AF episodes than men, but the duration of AF was not related to any other clinical or demographic features or antiarrhythmic medication. CONCLUSION: Increased HF oscillations and decreased short-term correlation properties of R-R intervals, reflecting altered sympathovagal balance before the onset of AF, predispose to perpetuation of spontaneous arrhythmia episodes in patients with vulnerability to paroxysmal AF and without structural heart disease.

Adult↗
PubMed2001

Effects of exercise and passive head-up tilt on fractal and complexity properties of heart rate dynamics.

tk;1Passive head-up tilt and exercise result in specific changes in the spectral characteristics of heart rate (HR) variability as a result of reduced vagal and enhanced sympathetic outflow. Recently analytic methods based on nonlinear system theory have been developed to characterize the nonlinear features in HR dynamics. This study was designed to assess the changes in the fractal and complexity measures of HR behavior during the passive head-up tilt and during exercise. Fractal exponent (alpha(1)) and approximate entropy (ApEn), measures of short-term correlation properties and overall complexity of HR, respectively, along with spectral components of HR variability were analyzed during a passive head-up tilt test (n = 10) and a low-intensity steady-state exercise (n = 20) in healthy subjects. We observed that alpha(1) increased during the tilt test (from 0.85 +/- 0.22 to 1.48 +/- 0.20; P < 0.001) and during the exercise (from 1.00 +/- 0.22 to 1.37 +/- 0. 14; P < 0.001). ApEn also increased during the exercise (from 1.04 +/- 0.11 to 1. 11 +/- 0.08; P < 0.05), but it did not change during the tilt test. The normalized high-frequency spectral component decreased and the low-frequency component increased similarly during both the exercise and the tilt test (P < 0.001 for all). Exercise and passive tilt result in an increase of short-term fractal correlation properties of HR dynamics, which is related to changes in the balance between the low- and high-frequency oscillations in controlled situations. Overall complexity of HR dynamics increases during exercise but not during passive tilt.

Adult↗
PubMed2001

Determinants and interindividual variation of R-R interval dynamics in healthy middle-aged subjects.

Determinants and intersubject variations of fractal and complexity measures of R-R interval variability were studied in a random population of 200 healthy middle-aged women (age 51 +/- 6 yr) and 189 men (age 50 +/- 6 yr) during controlled conditions in the supine and sitting positions. The short-term fractal exponent (alpha(1)) was lower in women than men in both the supine (1.18 +/- 0.20 vs. 1.12 +/- 0.17, P < 0.01) and sitting position (P < 0.001). Approximate entropy (ApEn), a measure of complexity, was higher in women in the sitting position (1.16 +/- 0.17 vs. 1.07 +/- 0.19, P < 0.001), but no gender-related differences were observed in ApEn in the supine position. Fractal and complexity measures were not related to any other demographic, laboratory, or lifestyle factors. Intersubject variations in a fractal measure, alpha(1) (e.g., 1.15 +/- 0.20 in the supine position, z value 1.24, not significant), and in a complexity measure, ApEn (e.g., 1.14 +/- 0.18 in the supine position, z value 1.44, not significant), were generally smaller and more normally distributed than the variations in the traditional measures of heart rate variability (e.g., standard deviation of R-R intervals 49 +/- 21 ms in the supine position, z value 2.53, P < 0.001). These results in a large random population sample show that healthy subjects express relatively little interindividual variation in the fractal and complexity measures of heart rate behavior and, unlike the traditional measures of heart rate variability, they are not related to lifestyle, metabolic, or demographic variables. However, subtle gender-related differences are also present in fractal and complexity measures of heart rate behavior.

Adult↗
PubMed2000

Correlation properties and complexity of perioperative RR-interval dynamics in coronary artery bypass surgery patients.

BACKGROUND: Dynamic measures of heart rate variability (HRV) may uncover abnormalities that are not easily detectable with traditional time and frequency domain measures. The purpose of this study was to characterize changes in RR-interval dynamics in the immediate postoperative phase of coronary artery bypass graft (CABG) surgery using traditional and selected newer dynamic measures of HRV. METHODS: Continuous 24-h electrocardiograph recordings were performed in 40 elective CABG surgery patients up to 72 h postoperatively. In one half of the patients, Holter recordings were initiated 12-40 h before the surgery. Time and frequency domain measures of HRV were assessed. The dynamic measures included a quantitative and visual analysis of Poincaré plots, measurement of short- and intermediate-term fractal-like scaling exponents (alpha1 and alpha2), the slope (beta) of the power-law regression line of RR-interval dynamics, and approximate entropy. RESULTS: The SD of RR intervals (P < 0.001) and the ultra-low-, very-low-, low-, and high-frequency power (P < 0.01, P < 0.001, P < 0.001, P < 0.01, respectively) measures in the first postoperative 24 h decreased from the preoperative values. Analysis of Poincaré plots revealed increased randomness in beat-to-beat heart rate behavior demonstrated by an increase in the ratio between short-term and long-term HRV (P < 0.001) after CABG. Average scaling exponent alpha1 of the 3 postoperative days decreased significantly after CABG (from 1.22 +/- 0.15 to 0.85 +/- 0.20, P < 0.001), indicating increased randomness of short-term heart rate dynamics (i.e., loss of fractal-like heart rate dynamics). Reduced scaling exponent alpha1 of the first postoperative 24 h was the best HRV measure in differentiating between the patients that had normal (</= 48 h, n = 33) or prolonged (> 48 h, n = 7) intensive care unit stay (0.85 +/- 0.17 vs. 0.68 +/- 0.18; P < 0.05). In stepwise multivariate logistic regression analysis including typical clinical predictors, alpha1 was the most significant independent predictor (P < 0.05) of long intensive care unit stay. None of the preoperative HRV measures were able to predict prolonged intensive care unit stays. CONCLUSIONS: In the selected group of patients studied, a decrease in overall HRV was associated with altered nonlinear heart rate dynamics after CABG surgery. Current results suggest that a more random short-term heart rate behavior may be associated with a complicated clinical course. Analysis of fractal-like dynamics of heart rate may provide new perspectives in detecting abnormal cardiovascular function after CABG.

Aged↗
PubMed1999

Altered complexity and correlation properties of R-R interval dynamics before the spontaneous onset of paroxysmal atrial fibrillation.

BACKGROUND: Trigger mechanisms for the onset of paroxysmal atrial fibrillation (AF) in patients without structural heart disease are not well established. New analysis methods of heart rate (HR) variability based on nonlinear system theory may reveal features and abnormalities in R-R interval behavior that are not detectable by traditional analysis methods. The purpose of this study was to reveal possible alterations in the dynamics of R-R intervals before the spontaneous onset of paroxysmal AF. METHODS AND RESULTS: Traditional time and frequency domain HR variability indices, along with the short-term scaling exponent alpha(1) and approximate entropy (ApEn), were analyzed in 20-minute intervals before 92 episodes of spontaneous, paroxysmal AF in 22 patients without structural heart disease. Traditional HR variability measures showed no significant changes before the onset of AF. A progressive decrease occurred both in ApEn (1.09+/-0.26 120 to 100 minutes before AF; 0.88+/-0.24 20 to 0 minutes before AF; P<0.001) and in alpha(1) (1.01+/-0.28 120 to 100 minutes before AF, 0.89+/-0.28 20 to 0 minutes before AF; P<0.05) before the AF episodes. Both ApEn (0. 89+/-0.27 versus 1.02+/-0.30; P<0.05) and alpha(1) (0.91+/-0.28 versus 1.27+/-0.21; P<0.001) were also lower before the onset of AF compared with values obtained from matched healthy control subjects. CONCLUSIONS: A decrease in the complexity of R-R intervals and altered fractal properties in short-term R-R interval dynamics precede the spontaneous onset of AF in patients with no structural heart disease. Further studies are needed to determine the physiological correlates of these new, nonlinear HR variability measures.

Adult↗
PubMed1999

Dynamic behavior and autonomic regulation of ectopic atrial pacemakers.

BACKGROUND: Heart rate (HR) variability reflects the neural regulation of normal pacemaker tissue, but the autonomic nervous regulation of abnormal atrial foci originating outside the sinus node has not been well characterized. We compared the HR variability of tachycardias originating from the ectopic foci and the sinus node. METHODS AND RESULTS: R-R-interval variability was analyzed from 24-hour Holter recordings in 12 patients with incessant ectopic atrial tachycardia (average HR 107+/-14 bpm), 12 subjects with sinus tachycardia (average HR 106+/-9 bpm), and 24 age- and sex-matched subjects with normal sinus rhythm (average HR 72+/-8 bpm). Time- and frequency-domain HR variability measures, along with approximate entropy, short- and long-term correlation properties of R-R intervals (exponents alpha(1) and alpha(2)), and power-law scaling (exponent beta), were analyzed. Time- and frequency-domain measures of HR variability did not differ between subjects with ectopic and sinus tachycardia. Fractal scaling exponents and approximate entropy were similar in sinus tachycardia and normal sinus rhythm, but the short-term scaling exponent alpha(1) was significantly lower in ectopic atrial tachycardia (0.71+/-0.16) than in sinus tachycardia (1.16+/-0.13; P<0.001) or normal sinus rhythm (1.19+/-0.11; P<0.001). Abrupt prolongations in R-R intervals due to exit blocks from the ectopic foci or instability in beat-to-beat R-R dynamics were the major reasons for altered short-term HR behavior during ectopic tachycardias. CONCLUSIONS: HR variability obtained by time- and frequency-domain methods does not differ between ectopic and sinus tachycardias, which suggests that abnormal atrial foci are under similar long-term autonomic regulation as normal pacemaker tissue. Short-term R-R-interval dynamics are altered toward more random behavior in ectopic tachycardia, which may result from a specific autonomic disturbance or an intrinsic abnormality of ectopic atrial pacemakers.

Adult↗
PubMed1999

Cardiac interbeat interval dynamics from childhood to senescence : comparison of conventional and new measures based on fractals and chaos theory.

BACKGROUND: New methods of R-R interval variability based on fractal scaling and nonlinear dynamics ("chaos theory") may give new insights into heart rate dynamics. The aims of this study were to (1) systematically characterize and quantify the effects of aging from early childhood to advanced age on 24-hour heart rate dynamics in healthy subjects; (2) compare age-related changes in conventional time- and frequency-domain measures with changes in newly derived measures based on fractal scaling and complexity (chaos) theory; and (3) further test the hypothesis that there is loss of complexity and altered fractal scaling of heart rate dynamics with advanced age. METHODS AND RESULTS: The relationship between age and cardiac interbeat (R-R) interval dynamics from childhood to senescence was studied in 114 healthy subjects (age range, 1 to 82 years) by measurement of the slope, beta, of the power-law regression line (log power-log frequency) of R-R interval variability (10(-4) to 10(-2) Hz), approximate entropy (ApEn), short-term (alpha(1)) and intermediate-term (alpha(2)) fractal scaling exponents obtained by detrended fluctuation analysis, and traditional time- and frequency-domain measures from 24-hour ECG recordings. Compared with young adults (<40 years old, n=29), children (<15 years old, n=27) showed similar complexity (ApEn) and fractal correlation properties (alpha(1), alpha(2), beta) of R-R interval dynamics despite lower spectral and time-domain measures. Progressive loss of complexity (decreased ApEn, r=-0.69, P<0.001) and alterations of long-term fractal-like heart rate behavior (increased alpha(2), r=0.63, decreased beta, r=-0.60, P<0.001 for both) were observed thereafter from middle age (40 to 60 years, n=29) to old age (>60 years, n=29). CONCLUSIONS: Cardiac interbeat interval dynamics change markedly from childhood to old age in healthy subjects. Children show complexity and fractal correlation properties of R-R interval time series comparable to those of young adults, despite lower overall heart rate variability. Healthy aging is associated with R-R interval dynamics showing higher regularity and altered fractal scaling consistent with a loss of complex variability.

Adolescent↗