Fractal correlation of heart rate variability in obese children

Comprehensive linear and nonlinear heart rate variability normative data in children

BACKGROUND

The autonomic nervous system (ANS) is critical in regulating involuntary bodily functions, including heart rate. Heart rate variability (HRV) reflects the complex interplay between the ANS and humoral factors, making it a valuable noninvasive tool for assessing autonomic function. While HRV has been extensively studied in adults, normative data for HRV in children, primarily based on long-term rhythm recordings, are limited.

OBJECTIVE

This study aimed to establish comprehensive normative data for HRV in children.

METHODS

In this retrospective study, we examined 24-h Holter monitors of children aged 1 day to 18 years, divided into six age groups, at Nemours Children's Health in Orlando, Florida, spanning the years 2013-2023. HRV analysis encompassed time-domain, frequency-domain, and nonlinear indices.

RESULTS

Holter data for a total of 247 patients in six age groups were included. An age-related uptrend was observed in all time- and frequency-domain variables except the normalized unit of low-frequency power. Entropy analysis revealed contradictory results among different entropy techniques. Sample and approximate entropy analyses were consistent and showed less complexity and more predictability of HRV with decreasing heart rate, while Shannon entropy analysis showed the opposite. Fractal detrended fluctuation analysis exhibited significant decreases across the age groups, suggestive of diminishing self-similarity of HRV patterns.

CONCLUSION

Control of heart rate and HRV is a highly complex process and requires further study for a better understanding. It seems that no single parameter can fully elucidate the entire process. A combination of time-domain, frequency-domain, and nonlinear indices may be necessary to explain HRV behavior in the growing body.

Evaluation of cardiac autonomic function and low-grade inflammation in children with obesity living in the Northeast Brazilian region

OBJECTIVE

Evaluate autonomic function and low-grade inflammation and characterize the correlation between these variables in schoolchildren with obesity living in the Brazilian northeast region.

METHODS

84 children with obesity and 41 with normal weight were included in this cross-sectional study. Anthropometry, body composition, blood pressure (BP), inflammatory biomarkers, and heart rate variability (HRV) indexes were analyzed in children aged 7 to 11 years.

RESULTS

children with obesity had increased systolic (p = 0.0017) and diastolic (p = 0.0131) BP and heart rate (p = 0.0022). The children with obesity displayed significantly lower SDNN, RMSSD, NN50, HF (ms), HF (nu), SD1, SD2, and higher LF (ms), LF (nu), LF/HF, SD1/SD2, DFA-α1, and DFA-α2, compared to normal weight. A lower and higher capacity for producing IL-10 (p = 0.039) and IL-2 (p = 0.009), respectively, were found in children with obesity compared to children with normal weight. Although IL-2, IL-4 and IL17A did not correlate with HRV parameters, IL-6 was positively correlated with SDNN, LF (ms) and SD2, TNF-α was positively correlated with LF/HF and SD1/SD2 ratio, and IFN-γ was positively correlated with SDNN, RMMSSD, NN50, LF (ms), HF (ms), SD1, and SD2.

CONCLUSIONS

The findings suggest that children with obesity have impaired autonomic function and systemic low-grade inflammation compared to children within the normal weight range, the inflammatory biomarkers were correlated with HRV parameters in schoolchildren living in the northeastern region of Brazil.

Pre- and peri-operative clinical information, physiological observations and outcome measures following flexible ureterorenoscopy (FURS), for the treatment of kidney stones. A single-centre observational clinical pilot-study in 51 patients

BACKGROUND

Kidney stone disease contributes to a significant proportion of routine urological practice and remains a common cause of worldwide morbidity. The main aim of this clinical-pilot study was to investigate the effect of flexible ureterorenoscopy (FURS) on pre- and peri-operative clinical information, physiological observations and outcome measures.

METHODS

Included were 51 patients (31 males, 20 females), who underwent elective FURS, for the treatment of kidney stones. Pre-operative and peri-operative clinical information, and post-operative physiological observations and outcome measures were collected using a standard case report form. Pre-operative clinical information included age, gender, BMI, previous history of stone formation and hypertension. Pre-operative stone information included the size (mm), Hounsfield units (HU), laterality and intra-renal anatomical location. Peri-operative surgical details included surgical time in minutes; Laser use; Duration and energy of laser; and post-operative stenting. The physiological outcomes measured included systolic and diastolic blood pressure (mmHg), Likert pain score, temperature, heart rate (bpm) and respiration rate (bpm). Following initial descriptive analysis, a series of Pearson's correlation coefficient tests were performed to investigate the relationship between surgical factors other variable factors.

RESULTS

A series of significant, positive correlations were observed between; age and surgical time (p = 0.014, r = 0.373); stone size and Hounsfield unit (p = 0.029, r = 0.406); surgical time and duration of laser (p < 0.001, r = 0.702); surgical time and BMI (p = 0.035, r = 0.322); baseline heart rate and Hounsfield unit (p = 0.026, r = - 0.414); base line heart rate and BMI (p = 0.030, r = 0.307).; heart rate at 120-min post FURS and age (p = 0.038, r = - 0.308); baseline pain score and BMI (p = 0.010, r = 0.361); baseline respiration rate and BMI (p = 0.037, r = 0.296); respiration rate at 240-min post FURS and BMI (p = 0.038, r = 0.329); respiration rate at 120 min post FURS and age (p = 0.022, r = - 0.330). Four patients developed post-operative complications (3-UTIs with urinary retention, 1-urosepsis).

CONCLUSIONS

We report that following FURS there is an association between various physiological, clinical and surgical parameters. Although these correlations are weak, they warrant further investigation as these may be linked with untoward complications, such as infection that can occur following FURS. This data, however, will need to be validated and reproduced in larger multi-centre studies.

On the Validity of Detrended Fluctuation Analysis at Short Scales

Detrended Fluctuation Analysis (DFA) has become a standard method to quantify the correlations and scaling properties of real-world complex time series. For a given scale ℓ of observation, DFA provides the function F(ℓ), which quantifies the fluctuations of the time series around the local trend, which is substracted (detrended). If the time series exhibits scaling properties, then F(ℓ)∼ℓα asymptotically, and the scaling exponent α is typically estimated as the slope of a linear fitting in the logF(ℓ) vs. log(ℓ) plot. In this way, α measures the strength of the correlations and characterizes the underlying dynamical system. However, in many cases, and especially in a physiological time series, the scaling behavior is different at short and long scales, resulting in logF(ℓ) vs. log(ℓ) plots with two different slopes, α1 at short scales and α2 at large scales of observation. These two exponents are usually associated with the existence of different mechanisms that work at distinct time scales acting on the underlying dynamical system. Here, however, and since the power-law behavior of F(ℓ) is asymptotic, we question the use of α1 to characterize the correlations at short scales. To this end, we show first that, even for artificial time series with perfect scaling, i.e., with a single exponent α valid for all scales, DFA provides an α1 value that systematically overestimates the true exponent α. In addition, second, when artificial time series with two different scaling exponents at short and large scales are considered, the α1 value provided by DFA not only can severely underestimate or overestimate the true short-scale exponent, but also depends on the value of the large scale exponent. This behavior should prevent the use of α1 to describe the scaling properties at short scales: if DFA is used in two time series with the same scaling behavior at short scales but very different scaling properties at large scales, very different values of α1 will be obtained, although the short scale properties are identical. These artifacts may lead to wrong interpretations when analyzing real-world time series: on the one hand, for time series with truly perfect scaling, the spurious value of α1 could lead to wrongly thinking that there exists some specific mechanism acting only at short time scales in the dynamical system. On the other hand, for time series with true different scaling at short and large scales, the incorrect α1 value would not characterize properly the short scale behavior of the dynamical system.

Impact of exercise in high-humidity on heart rate variability and salivary oxidative stress in obese and lightweight asthmatic children

BACKGROUND

Asthma and obesity are becoming increasingly common among children. Such conditions are known to negatively affect both cardiac autonomic function and oxidative stress. We therefore investigated the heart rate variability (HRV) and oxidative (malondialdehyde, MDA) response to exercise within a high humidity environment (~65%) in obese and lightweight asthmatic children.

METHODS

Forty-two children participated in this study and were categorized into four groups: obese asthmatic (OA, N.=10), obese non-asthmatic (ONA, N.=15), lightweight asthmatic (LA, N.=10), and lightweight non-asthmatic (LNA, N.=7). Time-domain and nonlinear indices of HRV were assessed at rest, during, and immediately after exercise. Further, saliva samples were collected immediately before and after exercise and analyzed for the determination of MDA.

RESULTS

HRV significantly decreased during and after exercise compared to baseline (P<0.05) with short-term fractal scaling exponent (α1) for the LNA group significantly smaller than the OA group after exercise (P<0.05). In contrast, the long-term fractal scaling exponent (α2) was greater after exercise compared to baseline and during exercise for all groups (P<0.05). MDA significantly decreased after exercise compared to baseline (P<0.05). We also found significant correlations after exercise between salivary levels of MDA with HRV components (i.e., RMSSD, SD1, and α2) in asthmatic groups (all P<0.05).

CONCLUSIONS

Our findings showed that exercise in high humidity environment does not significantly differentiate the autonomic response among children with various conditions (i.e., obese, asthmatic and healthy). However, a significant relationship was found between HRV and MDA in asthmatic children after exercise, highlighting the inter-relationship between oxidative stress markers and autonomic function in asthmatic children.

Fractal correlations and linear analyses of heart rate variability in healthy young people with different levels of physical activity

Changes in cardiac autonomic regulation, expressed by increased sympathetic activity and decreased heart rate variability, have an important relationship with the onset of lethal cardiac phenomena. Therefore, we aimed to evaluate the cardiac autonomic behaviour in young people according to their level of physical activity. Through the International Physical Activity Questionnaire, 55 healthy young non-smokers with no history of previous diseases and whose parents did not suffer from metabolic syndrome were assessed and divided into groups: sedentary (n=12), insufficiently active (n=16), active (n=14), and very active (n=13). We collected respiratory rate, systolic and diastolic blood pressure at rest, and body mass index. Subjects remained supine at rest, and without mental stress for 15 minutes in a controlled environment. Using a cardiofrequency meter (Polar® RS800CX), data were analysed in the time domain, frequency domain, and detrended fluctuation analysis. For the sedentary group, the mean RR and rMSSD were significantly lower, and the insufficiently active group showed higher means, but significantly only for rMSSD. The insufficiently active group showed in the detrended fluctuation analysis that α2 was significantly lower compared with the sedentary, active, and very active groups. We conclude that young, healthy, sedentary individuals present an increased heart rate and that insufficiently active individuals present a decreased fractal correlation and increased parasympathetic activity.

Correlation properties of heart rate variability during endurance exercise: A systematic review

Background

Non‐linear measures of heart rate variability (HRV) may provide new opportunities to monitor cardiac autonomic regulation during exercise. In healthy individuals, the HRV signal is mainly composed of quasi‐periodic oscillations, but it also possesses random fluctuations and so‐called fractal structures. One widely applied approach to investigate fractal correlation properties of heart rate (HR) time series is the detrended fluctuation analysis (DFA). DFA is a non‐linear method to quantify the fractal scale and the degree of correlation of a time series. Regarding the HRV analysis, it should be noted that the short‐term scaling exponent alpha1 of DFA has been used not only to assess cardiovascular risk but also to assess prognosis and predict mortality in clinical settings. It has also been proven to be useful for application in exercise settings including higher exercise intensities, non‐stationary data segments, and relatively short recording times.

Method

Therefore, the purpose of this systematic review was to analyze studies that investigated the effects of acute dynamic endurance exercise on DFA‐alpha1 as a proxy of correlation properties in the HR time series.

Results

The initial search identified 442 articles (351 in PubMed, 91 in Scopus), of which 11 met all inclusion criteria.

Conclusions

The included studies show that DFA‐alpha1 of HRV is suitable for distinguishing between different organismic demands during endurance exercise and may prove helpful to monitor responses to different exercise intensities, movement frequencies, and exercise durations. Additionally, non‐linear DFA of HRV is a suitable analytical approach, providing a differentiated and qualitative view of exercise physiology.

Effects of a Short-Term Cycling Interval Session and Active Recovery on Non-Linear Dynamics of Cardiac Autonomic Activity in Endurance Trained Cyclists

Measurement of the non-linear dynamics of physiologic variability in a heart rate time series (HRV) provides new opportunities to monitor cardiac autonomic activity during exercise and recovery periods. Using the Detrended Fluctuation Analysis (DFA) technique to assess correlation properties, the present study examines the influence of exercise intensity and recovery on total variability and complexity in the non-linear dynamics of HRV. Sixteen well-trained cyclists performed interval sessions with active recovery periods. During exercise, heart rate (HR) and beat-to-beat (RR)-intervals were recorded continuously. HRV time domain measurements and fractal correlation properties were analyzed using the short-term scaling exponent alpha1 of DFA. Lactate (La) levels and the rate of perceived exertion (RPE) were also recorded at regular time intervals. HR, La, and RPE showed increased values during the interval blocks (p < 0.05). In contrast, meanRR and DFA-alpha1 showed decreased values during the interval blocks (p < 0.05). Also, DFA-alpha1 increased to the level in the warm-up periods during active recovery (p < 0.05) and remained unchanged until the end of active recovery (p = 1.000). The present data verify a decrease in the overall variability, as well as a reduction in the complexity of the RR-interval-fluctuations, owing to increased organismic demands. The acute increase in DFA-alpha1 following intensity-based training stimuli in active recovery may be interpreted as a systematic reorganization of the organism with increased correlation properties in cardiac autonomic activity in endurance trained cyclists.

Development and validation of warning system of ventricular tachyarrhythmia in patients with heart failure with heart rate variability data

Implantable-cardioverter defibrillators (ICD) detect and terminate life-threatening ventricular tachyarrhythmia with electric shocks after they occur. This puts patients at risk if they are driving or in a situation where they can fall. ICD's shocks are also very painful and affect a patient's quality of life. It would be ideal if ICDs can accurately predict the occurrence of ventricular tachyarrhythmia and then issue a warning or provide preventive therapy. Our study explores the use of ICD data to automatically predict ventricular arrhythmia using heart rate variability (HRV). A 5 minute and a 10 second warning system are both developed and compared. The participants for this study consist of 788 patients who were enrolled in the ICD arm of the Sudden Cardiac Death-Heart Failure Trial (SCD-HeFT). Two groups of patient rhythms, regular heart rhythms and pre-ventricular-tachyarrhythmic rhythms, are analyzed and different HRV features are extracted. Machine learning algorithms, including random forests (RF) and support vector machines (SVM), are trained on these features to classify the two groups of rhythms in a subset of the data comprising the training set. These algorithms are then used to classify rhythms in a separate test set. This performance is quantified by the area under the curve (AUC) of the ROC curve. Both RF and SVM methods achieve a mean AUC of 0.81 for 5-minute prediction and mean AUC of 0.87-0.88 for 10-second prediction; an AUC over 0.8 typically warrants further clinical investigation. Our work shows that moderate classification accuracy can be achieved to predict ventricular tachyarrhythmia with machine learning algorithms using HRV features from ICD data. These results provide a realistic view of the practical challenges facing implementation of machine learning algorithms to predict ventricular tachyarrhythmia using HRV data, motivating continued research on improved algorithms and additional features with higher predictive power.

Effects of 9 Months of Martial Arts Training on Cardiac Autonomic Modulation in Healthy Children and Adolescents

PURPOSE

The aim of the study was to evaluate the cardiac autonomic modulation after 9 months of martial arts practice in healthy children and adolescents.

METHOD

The study included 59 children and adolescents who were divided into 3 groups: judo, Muay Thai, and control. Heart rate variability was measured by a heart rate monitor, model Polar RS800CX. The intervention occurred twice a week on nonconsecutive days, lasting 60 minutes each session. A 1-way analysis of variance was used to compare participants at baseline. The comparisons between groups at baseline and after the intervention were carried out by a 2-way analysis of variance for repeated measures.

RESULTS

After 9 months of intervention, significant increases were observed for root mean square successive differences, with higher values post compared with baseline (19.5%; P = .04). For SD1, an interaction effect was observed, with increased posttraining values compared with baseline (24.1%; P = .04) for the judo group. Qualitative analysis of the Poincaré plot showed greater dispersion of RR intervals, mainly beat to beat, after the judo intervention compared with the baseline. The Muay Thai and control groups presented no improvement.

CONCLUSION

After 9 months of intervention, there were increases in cardiac autonomic modulation of children and adolescents participating in judo training. The practice of martial arts, such as judo, can be encouraged from an early age to improve cardiovascular system functioning, possibly providing protection against cardiovascular problems.

Application of Heart Rate Variability in Diagnosis and Prognosis of Individuals with Diabetes Mellitus: Systematic Review

BACKGROUND

The use of heart rate variability as a tool capable of discriminating individuals with diabetes mellitus is still little explored, as its use has been limited to comparing those with and without the disease. Thus, the purpose of this study was to verify the use of heart rate variability as a tool for diagnostic and prognostic evaluation in person with diabetes and to identify whether there are cutoff points generated from the use of this tool in these individuals.

METHODS

A search was conducted in the electronic databases MEDLINE, Cochrane Library, Web of Science, EMBASE, and LILACS starting from the oldest records until January 2015, by means of descriptors related to the target condition, evaluated tool, and evaluation method. All the studies were evaluated for methodological quality using the QUADAS-2 instrument.

RESULTS

Eight studies were selected. In general, the studies showed that the heart rate variability is useful to discriminate cardiac autonomic neuropathy in person with diabetes, and the sample entropy, SD1/SD2 indices, SDANN, HF, and slope of TFC have better discriminatory power to detect autonomic dysfunction, with sensitivity and specificity values ranging from 72% to 100% and 71% to 97%, respectively.

CONCLUSION

Although there are methodological differences in indices used, in general, this tool demonstrated good sensitivity and specificity and can be used as an additional and/or complementary tool to the conventional autonomic tests, in order to obtain safer and more effective diagnostic, collaborating for better risk stratification conditions of these patients.

Differentiation of Overweight from Normal Weight Young Adults by Postprandial Heart Rate Variability and Systolic Blood Pressure

INTRODUCTION

Obesity and cardiovascular disease are inextricably linked and the health community's response to the current epidemic of adolescent obesity may be improved by the ability to target adolescents at highest risk for developing cardiovascular disease in the future. Overweight manifests early as autonomic dysregulation and current methods do not permit differentiation of overweight adolescents or young adults at highest risk for developing cardiovascular disease.

AIM

This study was designed to test the hypothesis that scaling exponents motivated by nonlinear fractal analyses of Heart Rate Variability (HRV) differentiate overweight, otherwise healthy adolescent/young adult subjects at risk for developing prehypertension, the primary forerunner of cardiovascular disease.

MATERIALS AND METHODS

The subjects were 18-20year old males with Body Mass Index (BMI) 20.1-42.5kg/m(2). Electrocardiographic inter-beat (RR) intervals were measured during 3h periods of bed rest after overnight fasting and ingestion of 900Cal high-carbohydrate and high-fat test beverages on separate days. Detrended Fluctuation Analysis (DFA), k-means cluster and ANOVA analyses of scaling coefficients α, α(1), and α(2), showed dependencies on hourly measurements of systolic blood pressure and on premeasured BMI.

RESULTS

It was observed that α value increased during the caloric challenge, appears to represent metabolically-induced changes in HRV across the participants. An ancillary analysis was performed to determine the dependency on BMI without BMI as a parameter. Cluster analysis of the high-carbohydrate test beverage treatment and the high-fat treatment produced grouping with very little overlap. ANOVA on both clusters demonstrated significance at p<0.001. We were able to demonstrate increased sympathetic modulation of our study group during ingestion and metabolism of isocaloric high-carbohydrate and high-fat test beverages.

CONCLUSION

These findings demonstrate significantly different clustering of α, α1, and α2 and Systolic Blood Pressure (SBP) with respect to normal, overweight and obese BMI.

Impact of obesity on autonomic modulation, heart rate and blood pressure in obese young people

INTRODUCTION

Obesity can be understood as a comorbidity of increasing systemic impact, including a deficit in the autonomic nervous system.

OBJECTIVE

To analyze cardiac autonomic behavior and hemodynamic parameters in obese young people.

METHODS

92 individuals (20.58±1.48 years) were evaluated, divided into two groups: obese and eutrophic. Heart rate (HR) was captured for 30 min in the supine position whilst breathing spontaneously. Blood pressure (BP) values were obtained prior to performance of the protocol. For the autonomic analysis, 1000 beats were used for the calculation of heart rate variability indices in the time (Mean RR, SDNN and RMSSD) and frequency (LF, HF and LF/HF) domains, in addition to the Poincaré plot (SD1, SD2, SD1/SD2 and qualitative visual analysis).

RESULTS

The obese group presented higher baseline BP and HR values compared to the eutrophic. Regarding autonomic modulation a significant decrease was observed in the RMSSD; SD1, HFms and HFnu indices in the obese group, indicating a decrease in vagal activity and reduced SDNN and SD2 rates, with statistical significance for the former, suggesting a reduction in overall variability. The high value of the LFnu index and decrease in Mean RR in the obese group pointed to relative sympathetic predominance in these individuals. The visual analysis of the Poincaré plot showed less dispersion of the points in the obese group.

CONCLUSION

The obese group presented higher BP and HR values at rest and autonomic impairment, characterized by a reduction in parasympathetic activity and relative predominance of sympathetic activity.

SCD-HeFT: Use of R-R interval statistics for long-term risk stratification for arrhythmic sudden cardiac death

BACKGROUND

In the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT), a significant fraction of the patients with congestive heart failure ultimately did not die suddenly of arrhythmic causes. Patients with CHF will benefit from better tools to identify if implantable cardioverter-defibrillator (ICD) therapy is needed.

OBJECTIVES

We aimed to identify predictor variables from baseline SCD-HeFT patients' R-R intervals that correlate to arrhythmic sudden cardiac death (SCD) and mortality and to design an ICD therapy screening test.

METHODS

Ten predictor variables were extracted from prerandomization Holter data from 475 patients enrolled in the ICD arm of the SCD-HeFT by using novel and traditional heart rate variability methods. All variables were correlated to SCD using the Mann-Whitney-Wilcoxon test and receiver operating characteristic analysis. ICD therapy screening tests were designed by minimizing the cost of false classifications. Survival analysis, including log-rank test and Cox models, was also performed.

RESULTS

A short-term fractal exponent, α1, and a long-term fractal exponent, α2, from detrended fluctuation analysis, the ratio of low- to high-frequency power, the number of premature ventricular contractions per hour, and the heart rate turbulence slope are all statistically significant for predicting the occurrences of SCD (P < .001) and survival (log-rank, P < .01). The most powerful multivariate predictor tool using the Cox proportional hazards regression model was α2 with a hazard ratio of 0.0465 (95% confidence interval 0.00528-0.409; P < .01).

CONCLUSION

Predictor variables extracted from R-R intervals correlate to the occurrences of SCD and distinguish survival functions among patients with ICDs in SCD-HeFT. We believe that SCD prediction models should incorporate Holter-based R-R interval analysis to refine ICD patient selection, especially to exclude patients who are unlikely to benefit from ICD therapy.

Salivary alpha amylase diurnal pattern and stress response are associated with body mass index in low-income preschool-aged children

Physiological stress responses are proposed as a pathway through which stress can "get under the skin" and lead to health problems, specifically obesity. We tested associations of salivary alpha amylase (sAA) diurnal patterns and stress responses with body mass index (BMI) in young, low-income children (51% male; 54% non-Hispanic white). Diurnal saliva samples were collected three times per day across three days for 269 children (M age 50.8 months, SD 6.3). Individual sAA intercept and slope values were calculated using random effect models to represent morning sAA levels and rate of sAA change across the day. A subset of children (n=195; M age 56.6 months, SD 6.9) participated in a lab-based behavioral stress protocol. Area under the curve increase (AUCI) across four timepoints was calculated to represent increase in sAA output during stress elicitation. Children were weighed and height measured and BMI z-score was calculated. Linear regression was used to evaluate associations of sAA intercept, sAA slope, and sAA AUCI with BMI z-score, controlling for child age, sex, and race/ethnicity; maternal weight status; and family income-to-needs ratio. Diurnal and stress-response sAA patterns were related to child adiposity: for each 1-standard deviation unit (SDU) decrease in morning sAA level, the child's BMI z-score increased by 0.11 (SE 0.05) SDU's (p<.04); for each 1-SDU increase in sAA slope across the day, the child's BMI z-score increased by 0.12 (SE 0.05) SDU's (p<.03); and for each 1-SDU decrease in sAA AUCI during the stress elicitation, the child's BMI z-score increased by 0.14 (SE 0.06) SDU's (p<.03). Blunted stress responses and atypical diurnal patterns of sAA have been found following exposure to chronic life stressors such as poverty. Findings suggest that associations of stress, sAA, and elevated body mass index may develop very early in the lifespan.

Computation of nonlinear parameters of heart rhythm using short time ECG segments

We propose the method to compute the nonlinear parameters of heart rhythm (correlation dimension D₂ and correlation entropy K₂) using 5-minute ECG recordings preferred for screening of population. Conversion of RR intervals' time series into continuous function x(t) allows getting the new time series with different sampling rate dt. It has been shown that for all dt (250, 200, 125, and 100 ms) the cross-plots of D₂ and K₂ against embedding dimension m for phase-space reconstruction start to level off at m = 9. The sample size N at different sampling rates varied from 1200 at dt = 250 ms to 3000 at dt = 100 ms. Along with, the D₂ and K₂ means were not statistically different; that is, the sampling rate did not influence the results. We tested the feasibility of the method in two models: nonlinear heart rhythm dynamics in different states of autonomous nervous system and age-related characteristics of nonlinear parameters. According to the acquired data, the heart rhythm is more complex in childhood and adolescence with more influential parasympathetic influence against the background of elevated activity of sympathetic autonomous nervous system.

The influence of age and weight status on cardiac autonomic control in healthy children: a review

Heart rate variability (HRV) analyses can provide a non-invasive evaluation of cardiac autonomic activity. How autonomic control normally develops in childhood and how this is affected by obesity remain incompletely understood. In this review we examine the evidence that childhood age and weight status influence autonomic control of the heart as assessed using HRV. Electronic databases (Pubmed, EMBASE and Cochrane Library) were searched for studies examining HRV in healthy children from birth to 18 years who adhered to the Task Force (1996) guidelines. Twenty-four studies met our inclusion criteria. Seven examined childhood age and HRV. A reduction in 24-hour LF:HF was reported from birth to infancy (1 year), while overall HRV (SDNN) showed a marked and progressive increase. From infancy to early-to-late childhood (from 12 months to 15 years) LF:HF ratio was reported to decline further albeit at a slower rate, while RMSSD and SDNN increased. Twenty studies examined the effects of weight status and body composition on HRV. In a majority of studies, obese children exhibited reductions in RMSSD (n = 8/13), pNN50% (n = 7/9) and HF power (n = 14/18), no difference was reported for LF (n = 10/18), while LF:HF ratio was elevated (n = 10/15). HRV changes during childhood are consistent with a marked and progressive increase in cardiac parasympathetic activity relative to sympathetic activity. Obesity disrupts the normal maturation of cardiac autonomic control.

Latino children's body mass index at 2-3.5 years predicts sympathetic nervous system activity at 5 years

BACKGROUND

To understand whether the relationship between young children's autonomic nervous system (ANS) responses predicted their BMI, or vice versa, the association between standardized BMI (zBMI) at 2, 3.5, and 5 years of age and ANS reactivity at 3.5-5 years of age, and whether zBMI predicts later ANS reactivity or whether early ANS reactivity predicts later zBMI, was studied.

METHODS

Low-income, primarily Latino children (n=112) were part of a larger cohort study of mothers recruited during early pregnancy. Study measures included maternal prenatal weight, children's health behaviors (i.e., time watching television, fast food consumption, and time playing outdoors), children's height and weight at 2, 3.5, and 5 years, and children's ANS reactivity at 3.5 and 5 years. ANS measures of sympathetic nervous system (i.e., pre-ejection period) and parasympathetic nervous system (i.e., respiratory sinus arrhythmia) activity were monitored during rest and four challenges. Reactivity was calculated as the difference between mean challenge response and rest. Structural equation models analyzed the relationship between children's zBMI at 2, 3.5, and 5 years and ANS reactivity at 3.5 and 5 years, adjusting for mother's BMI, children's behaviors, and changes in height.

RESULTS

There was no association between zBMI and ANS cross-sectionally. Children with high zBMI at 2 or 3.5 years or large zBMI increases from 2 to 3.5 years of age had decreased sympathetic activity at 5 years. Neither sympathetic nor parasympathetic reactivity at 3.5 years predicted later zBMI.

CONCLUSIONS

Increased zBMI early in childhood may dampen young children's SNS responses later in life.

A Review of Theoretical Perspectives in Cognitive Science on the Presence of 1/f Scaling in Coordinated Physiological and Cognitive Processes

Time series of human performances present fluctuations around a mean value. These fluctuations are typically considered as insignificant, and attributable to random noise. Over recent decades, it became clear that temporal fluctuations possess interesting properties, however, one of which the property of fractal 1/f scaling. 1/f scaling indicates that a measured process extends over a wide range of timescales, suggesting an assembly over multiple scales simultaneously. This paper reviews neurological, physiological, and cognitive studies that corroborate the claim that 1/f scaling is most clearly present in healthy, well-coordinated activities. Prominent hypotheses about the origins of 1/f scaling are confronted with these reviewed studies. It is concluded that 1/f scaling in living systems appears to reflect their genuine complex nature, rather than constituting a coincidental side-effect. The consequences of fractal dynamics extending from the small spatial and temporal scales (e.g., neurons) to the larger scales of human behavior and cognition, are vast, and impact the way in which relevant research questions may be approached. Rather than focusing on specialized isolable subsystems, using additive linear methodologies, nonlinear dynamics, more elegantly so, imply a complex systems methodology, thereby exploiting, rather than rejecting, mathematical concepts that enable describing large sets of natural phenomena.

Effect of pursed-lip breathing in patients with COPD: Linear and nonlinear analysis of cardiac autonomic modulation

OBJECTIVE

The aim of the present study was to evaluate the effect of pursed-lip breathing (PLB) on cardiac autonomic modulation in individuals with chronic obstructive pulmonary disease (COPD) while at rest.

METHODS

Thirty-two individuals were allocated to one of two groups: COPD (n = 17; 67.29 ± 6.87 years of age) and control (n = 15; 63.2 ± 7.96 years of age). The groups were submitted to a two-stage experimental protocol. The first stage consisted of the characterization of the sample and spirometry. The second stage comprised the analysis of cardiac autonomic modulation through the recording of R-R intervals. This analysis was performed using both nonlinear and linear heart rate variability (HRV). In the statistical analysis, the level of significance was set to 5% (p ≤ 0.05).

RESULTS

PLB promoted significant increases in the SD1, SD2, RMSSD and LF (ms(2)) indices as well as an increase in α1 and a reduction in α2 in the COPD group. A greater dispersion of points on the Poincaré plots was also observed. The magnitude of the changes produced by PLB differed between groups.

CONCLUSION

PLB led to a loss of fractal correlation properties of heart rate in the direction of linearity in patients with COPD as well as an increase in vagal activity and impact on the spectral analysis. The difference in the magnitude of the changes produced by PLB between groups may be related to the presence of the disease and alterations in the respiration rate.

Overweight and reduced heart rate variability in British children: an exploratory study

OBJECTIVE

To investigate the associations between heart rate variability (HRV) and weight status in children.

METHOD

Following ethics approval, 182 children (87 males, 95 females) aged between 6 and 11 years old (Mean (SD) age 9.1 (1.4) years) were assessed for height and body mass from which body mass index (BMI, kg/m(2)) was calculated. Data were collected in Central England, March-June 2011. Resting HRV was assessed in the supine position. Time domain (RMSSD and pNN50) and frequency domain (HF and LF power (ms(2)), LF/HF ratio) measures of HRV were calculated. Pearson correlations were used to assess the associations between BMI and HRV parameters. Differences in HRV parameters according to gender or weight status were analysed using t-tests.

RESULTS

BMI was significantly and inversely related to RMSSD (r=-0.23, p=0.001) and pNN50 (r=0.20, p=0.008) but not frequency domain measures of HRV (p>0.05). Overweight/obese children demonstrated lower HF power compared to normal weight children (p=0.02). RMSSD and pNN50 were significantly lower in overweight/obese children compared to normal weight children (p<0.05). Age was associated with changes in Mean R-R and RMSSD (p<0.05).

CONCLUSION

This exploratory study suggests that HRV is reduced in overweight/obese children.

Heart rate variability and pre-competitive anxiety in BMX discipline

Altered neural mechanisms implying autonomic functioning have been described related to anxiety. Pre-competitive stress may be considered as an anxiety-state associated with disorders (i.e. somatic and cognitive alterations, and self-confidence worsening) that severely impair sport performance, conditioning short-lasting strength-related disciplines like BMX. From the psychological perspective, coaches use questionnaires like CSAI-2R to identify these alterations. However, with the emergence of psycho-physiological and non-linear approaches, recent studies suggest that HRV analysis provides a non-invasive tool to assess them. Hence, our purpose was to analyze how BMX competition affects subjective perception of anxiety, and if this emotional alteration is reflected in HR dynamics, analyzed both linear and nonlinearly, exploring the evolution of this relationship in a 2-day competition. Eleven male athletes from the BMX Spanish National Team were assessed from baseline HRV the morning of a training session (rT) and on two successive days of competition (rC1 and rC2), repeating HRV recording with CSAI-2R 20 min prior to training (aT) and competition (pre-competitive: aC1 and aC2). Repeated measures MANOVA showed significant vagal slow-down responses in aC1 and aC2 comparing not only with aT, but also comparing with rT, rC1 and rC2, coinciding with significant greater scores for the somatic and cognitive anxiety (SA and CA) in aC1 and aC2 versus aT. Pearson analysis showed a large and positive correlation between α1 and SA in C1, and close to it between SampEn and CA in aC2; both were confirmed by Bland-Altman chart analysis. Our results confirm that HRV analysis provide a complementary tool to assess competitive pressure.

Fractal immunology and immune patterning: potential tools for immune protection and optimization

Fractals are self-similar geometric patterns that are inherently embedded throughout nature. Their discovery and application have produced significant benefits across a wide variety of biomedical applications. Recently, complex physiological systems (e.g., neurological, respiratory, cardiovascular) have been shown to exhibit fractal dimensions that are capable of distinguishing among physiologic function versus dysfunction and, in turn, health versus disease. Additionally, fractal data suggest that the immune system operates under similar patterned relationships, and this is in keeping with the recent findings that immune-based diseases are organized according to specific patterns. This review considers the potential benefits of using fractal analysis along with considerations of nonlinearity, scaling, and chaos as calibration tools to obtain holistic information on immune-environment interactions. The potential uses of both synthetic and artificial immune systems for improved protection of the biological immune system are also discussed. The addition of holistic measures of immune status to currently collected biomarkers of immunotoxicity has the potential to increase the effectiveness of health risk assessment. The objective of extending fractal physiology analyses to the immune system would be to promote immune optimization as a public health benefit, which would include improved: (1) immunotoxicity testing and effective health risk reduction and (2) measures of effective immune management for children, adults, and aged individuals.

Fractal correlation property of heart rate variability in chronic obstructive pulmonary disease

BACKGROUND

It was reported that autonomic nervous system function is altered in subjects with chronic obstructive pulmonary disease (COPD). We evaluated short- and long-term fractal exponents of heart rate variability (HRV) in COPD subjects.

PATIENTS AND METHODS

We analyzed data from 30 volunteers, who were divided into two groups according to spirometric values: COPD (n = 15) and control (n = 15). For analysis of HRV indices, HRV was recorded beat by beat with the volunteers in the supine position for 30 minutes. We analyzed the linear indices in the time (SDNN [standard deviation of normal to normal] and RMSSD [root-mean square of differences]) and frequency domains (low frequency [LF], high frequency [HF], and LF/HF), and the short- and long-term fractal exponents were obtained by detrended fluctuation analysis. We considered P < 0.05 to be a significant difference.

RESULTS

COPD patients presented reduced levels of all linear exponents and decreased short-term fractal exponent (alpha-1: 0.899 ± 0.18 versus 1.025 ± 0.09, P = 0.026). There was no significant difference between COPD and control groups in alpha-2 and alpha-1/alpha-2 ratio.

CONCLUSION

COPD subjects present reduced short-term fractal correlation properties of HRV, which indicates that this index can be used for risk stratification, assessment of systemic disease manifestations, and therapeutic procedures to monitor those patients.