Cardiovascular autonomic function in healthy adolescents

Acute effect of aerobic exercise on inhibitory control and task-related heart rate variability in preadolescent children

OBJECTIVES

To investigate whether a single session of aerobic exercise improves inhibitory control in preadolescent children and whether this effect is mediated by changes in parasympathetic activity.

DESIGN

In this experimental study, an intervention and control group were pair-matched by age, sex and moderate-to-vigorous physical activity.

METHOD

114 participants either completed a 20 min moderately-intense exercise bout on a cycling ergometer or watched a 20 min video. Prior to and after these conditions, a computer-based Stroop task was administered. During the cognitive task, heart rate variability (HRV) was measured using electrocardiography.

RESULTS

Path-analyses did not support an association between group and posttest accuracy on the Stroop task, while controlling for pretest scores. However, the intervention group had lower time-domain based HRV at posttest. The examination of mediation models revealed a moderation by sex, as the relation of lower time-domain based HRV with higher accuracy on both congruent and incongruent trials of the Stroop task was observed in girls only.

CONCLUSION

A single aerobic exercise session does not necessarily improve inhibitory control in preadolescent children. However, the manipulation of the autonomic state towards a parasympathetic withdrawal has the potential to alter inhibitory control in girls in particular.

Hyperglycemia: A determinant of cardiac autonomic dysfunction in youth with obesity across the spectrum of glycemic regulation

OBJECTIVES

To characterize the determinants of heart rate variability (HRV) in youth with obesity across the glycemia spectrum.

METHODS

A total of 94 adolescents, 15 ± 2.1 years (21 with normal weight, 23 with overweight-normal glucose tolerance, 26 with prediabetes and 24 with type 2 diabetes [T2D]) underwent an assessment of body composition (dual-energy x-ray absorptiometry), 2-h oral glucose tolerance test with the calculation of indices of glycemia and insulin sensitivity (IS), inflammatory markers (high-sensitivity C-reactive protein [hs-CRP] and tumour necrosis factor-α [TNF-α]), and HRV by peripheral arterial tonometry.

RESULTS

The HRV frequency-domain index (low-frequency to high-frequency ratio [LF/HF]), an estimate of the ratio between sympathetic and parasympathetic activity, increased across the glycemic spectrum, and was highest in T2D compared with the other three groups (p = 0.004). LF/HF correlated with %body fat (r = 0.22, p = 0.04); fasting (r = 0.39, p < 0.001), 2-h (r = 0.31, p = 0.004), and area under the curve glucose (r = 0.32, p = 0.003); hs-CRP (r = 0.33, p = 0.002) and TNF-α (r = 0.38, p = 0.006). In a linear regression model, fasting glucose (β = 0.39, p = 0.003) and hs-CRP (β = 0.21, p = 0.09) contributed to the variance in Ln LF/HF independent of IS, %body fat, age, sex, race-ethnicity and Tanner stage (R2  = 0.23, p = 0.013).

CONCLUSIONS

Youth with impaired glucose regulation have evidence of cardiac autonomic dysfunction with decreased HRV, and sympathetic overdrive (increased LF/HF). This dysfunction is mainly related to glycemia and systemic inflammation.

Adolescent girls' cardiovascular responses to peer rejection: exploring the impact of early life stress

Detrimental effects of early life stress on cardiovascular health are evident in adolescence. Cardiovascular reactivity and recovery in response to interpersonal stress may be a mechanism. This study aimed to evaluate if adolescent girls with higher early life stress demonstrated greater cardiovascular reactivity and slower recovery to peer rejection. A sample of 92 adolescent girls (age: M = 13.24) self-reported early life stressors. Systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were continuously measured before, during, and after a laboratory peer rejection paradigm. Counter to hypotheses, adolescent girls with higher early life stress had lower, not higher, HR during the recovery period. Early life stress was not associated with SBP or DBP recovery. Additionally, early life stress was not associated with SBP, DBP, or HR reactivity. Future research is needed to assess if blunted cardiovascular reactivity to interpersonal rejection during adolescence is a mechanism linking early life stress and later cardiovascular disease risk in women.

The impact of social disadvantage on autonomic physiology of latinx adolescents: The role of environmental risks

The experience of poverty embodies complex, multidimensional stressors that may adversely affect physiological and psychological domains of functioning. Compounded by racial/ethnic discrimination, the financial aspect of family poverty typically coincides with additional social and physical environmental risks such as pollution exposure, housing burden, elevated neighborhood unemployment, and lower neighborhood education levels. In this study, we investigated the associations of multidimensional social disadvantage throughout adolescence with autonomic nervous system (ANS) functioning at 17 years. Two hundred and twenty nine low-income Mexican-American adolescents (48.6% female) and their parents were assessed annually between the ages of 10 and 16. Participants' census tracts were matched with corresponding annual administrative data of neighborhood housing burden, education, unemployment, drinking water quality, and fine particulate matter. We combined measures of adolescents' electrodermal response and respiratory sinuses arrhythmia at rest and during a social exclusion challenge (Cyberball) to use as ANS indices of sympathetic and parasympathetic activity, respectively. Controlling for family income-to-needs, youth exposed to greater cumulative water and air pollution from ages 10-16 displayed altered patterns of autonomic functioning at rest and during the social challenge. Conversely, youth living in areas with higher housing burden displayed healthy patterns of autonomic functioning. Altogether, results suggest that toxin exposure in youths' physical environments disrupts the ANS, representing a plausible mechanism by which pollutants and social disadvantage influence later physical and mental health.

Sleep quality and heart rate variability in adolescents with type 1 or type 2 diabetes

INTRODUCTION

Decreased sleep quality and lower heart rate variability (HRV) have both independently been associated with diabetes and may contribute to risks for cardiovascular disease. Although poor sleep quality has been associated with lower HRV in adults with type 2 diabetes (T2D), studies of sleep quality in adolescents with (T2D) or studies examining the possible association of poor sleep quality with lower HRV in adolescents with T2D or T1D are not available.

AIM

Thus, we conducted a secondary analysis of data from an existing study to determine if there were associations between sleep quality and HRV in adolescents with T1D or T2D.

METHODS

Adolescents with T1D (n = 101) or T2D (n = 37) completed 24-h HRV Holter monitoring and analysis and a self-reported global measure of sleep quality.

RESULTS

Poor sleep quality was significantly associated with lower HRV, a known predictor for CV risk. Those with T2D had lower measures of HRV.

CONCLUSIONS

The evaluation of sleep quality and early signs of cardiovascular autonomic changes should be considered in routine assessments of adolescents with diabetes. Future research is warranted to examine more robust measures of sleep and HRV in adolescents with diabetes.

Decrements in Adolescent Cardiac Complexity During Mother-Adolescent Conflicts

The present study aimed to provide further evidence on the usefulness of non-linear cardiac measures when examining the output of the cardiac system. Scale-invariant self-similarity and entropy, in addition to heart rate variability (HRV) given by time- and frequency-domain measures were calculated in a sample of N = 55 healthy adolescents (M_age = 14.122, SD_age = 0.698) during 10-min positive (non-stressful) and negative (stressful) interactions with their mothers. We also explored sex influence in adolescents' cardiac output using both HRV measures and non-linear cardiac measures. Repeated measures MANOVA revealed a marginal within-group effect for HRV measures, F(3,51) = 2.438, p = 0.075, η²_p = 0.125), and a significant within-group effect for non-linear cardiac measures, F(6, 48) = 3.296, p = 0.009, η²_p = 0.292, showing a significant decrement in adolescents' cardiac complexity during the negative interaction. No significant effect for sex was found in either non-linear cardiac measures or HRV measures, but results suggest lower cardiac scaling in females than in males. These findings suggest a real-time scale predominance in heart rate output when adolescents face an aversive situation and support the importance of non-linear cardiac measures to gain insight into the cardiac system and its regulatory mechanisms. Further research is needed to examine sex-differences in cardiac complexity during aversive situations.

Autonomic Dysregulation in Adolescent Concussion Is Sex- and Posture-Dependent

OBJECTIVE

To study autonomic responses to postural changes in concussed adolescents. The influence of sex was also studied.

DESIGN

Longitudinal cohort observational study.

PARTICIPANTS

Concussed adolescents (CONC; n = 65; 26 male adolescents; age 15 ± 1 years, range = 12-18 years) and a control (CTRL) group of nonconcussed adolescents of similar age and sport (CTRL; n = 54; 29 male adolescents; age 14 ± 1 years, range = 12-18 years).

INTERVENTIONS

Concussed participants were monitored through 6 weekly visits throughout usual physician care. Control participants underwent 2 visits separated by at least 1 week to account for intrapersonal variation in testing measures.

MAIN OUTCOME MEASURES

Heart rate variability as the root mean square of successive differences in R-R intervals (RMSSD), heart rate (HR), and blood pressure [mean arterial pressure (MAP) and diastolic blood pressure (DBP)] were measured in supine, sitting, and standing postures.

RESULTS

A mixed analysis of variance revealed a group × sex × posture interaction (P = 0.04) where seated values of RMSSD were less in concussed female participants versus control female participants (42 ± 4 vs 61 ± 7 ms; P = 0.01; Mann-Whitney rank test). Compared with CTRL, CONC exhibited increased pretesting seated DBP (69 ± 1 vs 74 ± 1 mm Hg; P < 0.01), MAP (83 ± 1 vs 86 ± 1 mm Hg; P = 0.02), and baseline seated HR (72 ± 1 vs 77 ± 2 bpm; P = 0.03). Values of DBP (P = 0.03) and MAP (P < 0.01) improved at clinical discharge, whereas the RMSSD in female participants did not (P > 0.5). Data are mean ± SEM.

CONCLUSIONS

A modest reduction in female cardiac autonomic regulation was observed during seated postures. Alterations in seated concussed DBP and MAP, but not RMSSD, resolved at clinical discharge (median = 37 days). The results indicate that, in adolescents, concussion may impair cardiovagal function in a sex- and posture-dependent manner. The findings also suggest that BP metrics, but not RMSSD, are associated with clinical concussion recovery.

Race and sex differences in cardiovascular autonomic regulation

Racial and ethnic differences in cardiovascular morbidity and mortality persist despite advances in risk factor identification and implementation of evidence-based treatment strategies. African American men and women are disproportionately affected by cardiovascular risk factors, particularly hypertension. In this context, previous studies have identified sex and racial differences in autonomic cardiovascular regulation which may contribute to the development of hypertension and its high morbidity burden among African Americans. In this review, we provide a comprehensive evaluation of the potential pathophysiological mechanisms of blood pressure control and their differences based on sex and race. These mechanisms include obesity-induced sympathetic activation, sympatho-vascular transduction, baroreflex sensitivity and adrenoreceptor vascular sensitivity, which have been the subjects of prior investigation in this field. Understanding the racial differences in the pathophysiology of hypertension and its co-morbid conditions would allow us to implement better treatment strategies tailored to African Americans, with the ultimate goal of reducing cardiovascular mortality in this population.

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.

Heart rate variability following youth concussion: how do autonomic regulation and concussion symptoms differ over time postinjury?

OBJECTIVES

Following youth concussion, objective physiological indicators are needed to corroborate changes in subjective clinical measures. The objectives of the current study were to: (1) explore the effect of concussion on heart rate variability (HRV) across days postinjury in youth athletes aged 13-18 years old, compared with healthy age-matched and sex-matched controls and (2) examine the relationship between postconcussion symptom domains (physical, cognitive, fatigue and emotional) and HRV.

METHODS

Prospective, longitudinal, case-control study (N=44). This study comprised 29 concussed athletes between the ages of 13 and 18 years old (21 females, 8 males) and 15 age-matched and sex-matched controls). All participants completed baseline testing, which included demographic information (age, sex, concussion history), self-reported concussion symptoms (Post-Concussion Symptom Inventory [PCSI]) and a 24-hour heart rate recording via the Polar RS800CX system. The PCSI and HRV were collected weekly while the participant was symptomatic and then 1, 3 and 6 months following symptom resolution. HRV variables included time and frequency domain measures. Data visualisations and mixed effects modelling were used to derive parsimonious models.

RESULTS

HRV increased across days postinjury. Concussion symptom domains (physical, cognitive, fatigue and emotional) all had a significant main effect on HRV; concussed participants who reported more symptoms had higher HRV compared with those who reported fewer symptoms. Visualisations of HRV depict the recovery trajectory as non-linear across time. No significant differences on HRV measures were found between concussed and control participants.

CONCLUSION

These preliminary findings provide the foundation to understand the varied trajectory and relationship between objective physiological measures and subjective symptom reporting.

Altered Heart Rate Regulation in Adolescent Girls and the Vulnerability for Internalizing Disorders

Background: The association between decreased heart rate variability (HRV) and increased internalizing symptoms is well documented. Adolescence is a critical period for the development of mental health problems, in particular internalizing symptoms. Previous research has illustrated sex differences in adolescent HRV, such that females have reduced short-term resting state HRV compared to males. Studies on long-term ecological recordings of HRV in adolescents are scarce. The aims of the present study were, (a) to test if adolescent females show decreased long-term HRV and cardiac complexity (CC) compared to males, and (b) to explore whether sex and HRV and CC measures, as well as their interaction, would predict internalizing symptoms. Materials and Methods: HRV was recorded in n = 166 adolescents (86 girls), on a normal school day. HRV and CC measures were calculated on the interbeat interval time series. Results: Females showed lower HRV and CC in most of the assessed indices. Internalizing symptoms were mainly predicted by HRV whereas sex only predicted symptoms of social anxiety. The interaction between sex and HRV did not predict internalizing symptoms. Conclusions: Results suggest that reduced HRV should be considered as a potential contributor to exacerbating internalizing symptoms in adolescence. Girls with reduced HRV and CC might be prone to the development of internalizing disorders. HRV is a promising tool for the early identification of vulnerability.

Diminished heart rate complexity in adolescent girls: a sign of vulnerability to anxiety disorders?

BACKGROUND AND OBJECTIVES

Diminished heart rate variability has been found to be associated with high anxiety symptomatology. Since adolescence is the period of onset for many anxiety disorders, this study aimed to determine sex- and anxiety-related differences in heart rate variability and complexity in adolescents.

METHODS

We created four groups according to sex and anxiety symptomatology: high-anxiety girls (n = 24) and boys (n = 25), and low-anxiety girls (n = 22) and boys (n = 24) and recorded their cardiac function while they performed regular school activities. A series of two-way (sex and anxiety) MANOVAs were performed on time domain variability, frequency domain variability, and non-linear complexity.

RESULTS

We obtained no multivariate interaction effects between sex and anxiety, but highly anxious participants had lower heart rate variability than the low-anxiety group. Regarding sex, girls showed lower heart rate variability and complexity than boys.

CONCLUSIONS

The results suggest that adolescent girls have a less flexible cardiac system that could be a marker of the girls' vulnerability to developing anxiety disorders.

Sex- and Age-Dependent Differences in Autonomic Nervous System Functioning in Adolescents

PURPOSE

We assessed sex- and age-dependent differences in a cross-sectional analysis of cardiac autonomic nervous system (ANS) regulation during sleep in adolescents.

METHODS

Nocturnal heart rate (HR) and heart rate variability (HRV) metrics, reflecting ANS functioning, were analyzed across the night and within undisturbed rapid eye movement (REM) and non-REM sleep in 149 healthy adolescents (12-22 years; 67 female) from the National Consortium on Alcohol and Neurodevelopment in Adolescence.

RESULTS

Nocturnal HR was slower in older, more pubertally advanced boys than in younger boys. In girls, HR did not vary according to age or maturity, although overall HRV and vagal modulation declined with age. Although younger boys and girls had similar HR, the male-female HR difference increased by ~2.4 bpm every year (p < .01, higher in older girls). Boys and girls showed expected increases in total HRV across the night but this within-night "recovery" was blunted in girls compared with boys (p < .05). Also, the non-REM and REM difference in HR was greater in girls (p < .01). Models exploring a role of covariates (sleep, mood, reproductive hormones, activity) in influencing HR and HRV showed few significant effects, apart from sedentary activity (higher in older girls), which partially mediated the sex × age interaction in HR.

CONCLUSIONS

Sex-related differences in cardiac ANS function emerge during adolescence. The extent to which sex-age divergences in ANS function are adaptive or reflect underlying sex-specific vulnerability for the development of psychopathology and other health conditions in adolescence needs to be determined.

Heart Rate Variability in Healthy Non-Concussed Youth Athletes: Exploring the Effect of Age, Sex, and Concussion-Like Symptoms

BACKGROUND

Heart rate variability (HRV) is a non-invasive neurophysiological measure of autonomic nervous system regulation emerging in concussion research. To date, most concussion studies have focused on the university-aged athlete with no research examining healthy active youths. Corroborating changes in HRV alongside traditional subjective self-report measures (concussion symptoms) in the non-concussed state provides a foundation for interpreting change following concussion. The objectives were to (1) explore the influence of age and sex on HRV and (2) examine the relationship between HRV and baseline/pre-injury concussion symptom domains (physical, cognitive, emotional, and fatigue) in healthy youth athletes.

METHOD

Healthy, youth athletes 13-18 years of age [N = 294, female = 166 (56.5%), male = 128 (43.5%)] participated in this cross-sectional study. Age, sex, and concussion-like symptoms were collected as part of a baseline/pre-injury assessment. The Post-Concussion Symptom Inventory-SR13 (PCSI-SR13) was used to collect domain scores for physical, cognitive, emotional, and fatigue symptoms. HRV was collected for 24 h. HRV measures included time (SDNN, RMSSD, and pNN50) and frequency (HF, HFnu, LF, LFnu, and total power) domain HRV measures. Variables were logarithmically transformed to increase robustness of linear regression models.

RESULTS

Older youth participants displayed significantly higher HRV compared to younger participants (p < 0.05). Females displayed significantly lower HRV compared to males (p < 0.05). A significant interaction effect between concussion-like symptoms and HRV indicated differential patterns as a function of sex (p < 0.05). Youth athletes who reported more cognitive symptoms had lower HRV (p < 0.05).

CONCLUSION

HRV was found to have a significant relationship with a traditional clinical measure (subjective self-report of concussion-like symptoms) utilized in concussion assessment and management. Baseline/pre-concussion trends in HRV were significantly associated with age and sex, highlighting the value in understanding key demographic factors within the context of concussion-like symptoms.

A Meta-Analysis on Sex Differences in Resting-State Vagal Activity in Children and Adolescents

Lower vagal activity is associated with psychopathology independent of age. Research suggests that alterations of vagal activity precede the development of psychopathology. The present review aimed to quantify sex differences in vagal activity in children and adolescents. Studies reporting on sex differences on measures of vagally-mediated heart rate variability derived from short-term recordings under resting conditions in boys and girls were included. Drawing on data from more than 5,000 children and adolescents, we provide evidence that healthy young girls display lower vagal activity and greater mean heart rate compared to boys, a finding that may have implications for risk associated with the development of internalizing psychopathology and somatic ill-health.

Acute Cognitively Engaging Exergame-Based Physical Activity Enhances Executive Functions in Adolescents

The study aimed to elucidate the influence of cognitive engagement comprised in an acute bout of exergame-based physical activity on executive functions (inhibition, cognitive flexibility) in adolescents. Therefore, the level of cognitive engagement and the intensity of physical activity were systematically varied across three experimental conditions. Sixty-five healthy male adolescents (13-16 years) were randomly assigned to one of three conditions: (a) physical activity with high levels of cognitive engagement during active video gaming, (b) physical activity with low levels of cognitive engagement during active video gaming, (c) sedentary with low levels of cognitive engagement during passive video watching. Manipulation checks, including subjective and objective operationalizations of cognitive engagement, were applied. Executive functions were assessed before and after each condition using the D-KEFS design fluency test. Results showed that cognitive engagement, operationalized by subjects' ratings and heart rate variability, differed between conditions. The physical activity condition with a high level of cognitive engagement resulted in significantly better performance in cognitive flexibility compared to conditions with low levels of cognitive engagement. Regarding benefits for executive functions in male adolescents, the results indicate that acute physical activity with high cognitive engagement could be more efficient than physical activity of the same intensity with low cognitive engagement. Even though further evidence is needed, these results extend previous research and suggest a methodological approach for measuring cognitive engagement.

Getting to the Heart of Emotion Regulation in Youth: The Role of Interoceptive Sensitivity, Heart Rate Variability, and Parental Psychopathology

Emotion regulation and associated autonomic activation develop throughout childhood and adolescence under the influence of the family environment. Specifically, physiological indicators of autonomic nervous system activity such as interoceptive sensitivity and vagally mediated heart rate variability (HRV) can inform on emotion regulation. Although the effect of parental emotion socialization on emotion regulation appears to be influenced by autonomic processes, research on physiological regulation and the influence of parental factors remains scarce. This study investigated the relationship between self-reported habitual emotion regulation strategies and HRV at rest as well as interoceptive sensitivity in forty-six youngsters (27 female; age: M = 13.00, SD = 2.13). Secondly, the association between these autonomic correlates and parental psychopathology was also studied. Whereas better interoceptive sensitivity was related to reduced maladaptive emotion regulation, specifically rumination, high HRV was related to more use of external emotion regulation strategies (i.e., support seeking). In addition, increased HRV and decreased interoceptive sensitivity were associated with maternal internalizing and there was evidence for a possible mediation effect of HRV in the relationship between maternal internalizing and child external emotion regulation. This study elucidates the link between cognitive emotion regulation strategies and underlying physiological regulation in adolescents but also indicates a putative influence of maternal internalizing symptoms on emotion regulation in their offspring.

Antroduodenal Manometry Is Abnormal in Children Presenting With Orthostatic Intolerance and Gastrointestinal Symptoms

OBJECTIVES

Gastrointestinal (GI) symptoms of nausea, vomiting, and abdominal pain are common in patients with orthostatic intolerance (OI), including neurally mediated hypotension (NMH) and postural orthostatic tachycardia syndrome (POTS). Autonomic dysregulation is considered the underlying pathophysiology behind the cardiovascular symptoms of POTS. Because the autonomic nervous system also regulates GI motility, we hypothesized that patients with POTS and GI symptoms will have evidence of autonomic dysmotility of the upper GI tract.

METHODS

Thirty-five subjects with OI and GI symptoms were studied. All the subjects had a 24-hour antroduodenal manometry (ADM) study, in conjunction with pharmacologic challenge and autonomic and tilt table testing (TTT).

RESULTS

The mean subject age was 16.2 ± 2.8 years (range 10-23.8 years), and male to female ratio was 10:25. TTT was abnormal in all the 35 subjects, whereas Valsalva testing was abnormal (+40 mmHG) in 21 of 34 (62%) subjects, and corrected QT interval was ≥0.44 seconds in 19 of 35 (54%) subjects. During TTT, GI symptoms were reproduced in 31 of 35 (89%) studies. ADM was found to be abnormal at baseline, before the TTT in 5 of 35 (14%) subjects, whereas it became abnormal in 23 of 34 (68%) subjects during TTT. In addition, the expected response to the pharmacologic challenge was limited. Overall, ADM was abnormal in 26 of 35 (74%) patients either at baseline or during TTT in these subjects with OI.

CONCLUSIONS

ADM is frequently abnormal in children with OI and GI symptoms. Upper GI motility studies should be a part of the comprehensive evaluation in this population.

Test-Retest Reliability of Pediatric Heart Rate Variability: A Meta-Analysis

Heart rate variability (HRV), an established index of autonomic cardiovascular modulation, is associated with health outcomes (e.g., obesity, diabetes) and mortality risk. Time- and frequency-domain HRV measures are commonly reported in longitudinal adult and pediatric studies of health. While test-retest reliability has been established among adults, less is known about the psychometric properties of HRV among infants, children, and adolescents. The objective was to conduct a meta-analysis of the test-retest reliability of time- and frequency-domain HRV measures from infancy to adolescence. Electronic searches (PubMed, PsycINFO; January 1970-December 2014) identified studies with nonclinical samples aged ≤ 18 years; ≥ 2 baseline HRV recordings separated by ≥ 1 day; and sufficient data for effect size computation. Forty-nine studies (N = 5,170) met inclusion criteria. Methodological variables coded included factors relevant to study protocol, sample characteristics, electrocardiogram (ECG) signal acquisition and preprocessing, and HRV analytical decisions. Fisher's Z was derived as the common effect size. Analyses were age-stratified (infant/toddler < 5 years, n = 3,329; child/adolescent 5-18 years, n = 1,841) due to marked methodological differences across the pediatric literature. Meta-analytic results revealed HRV demonstrated moderate reliability; child/adolescent studies (Z = 0.62, r = 0.55) had significantly higher reliability than infant/toddler studies (Z = 0.42, r = 0.40). Relative to other reported measures, HF exhibited the highest reliability among infant/toddler studies (Z = 0.42, r = 0.40), while rMSSD exhibited the highest reliability among child/adolescent studies (Z = 1.00, r = 0.76). Moderator analyses indicated greater reliability with shorter test-retest interval length, reported exclusion criteria based on medical illness/condition, lower proportion of males, prerecording acclimatization period, and longer recording duration; differences were noted across age groups. HRV is reliable among pediatric samples. Reliability is sensitive to pertinent methodological decisions that require careful consideration by the researcher. Limited methodological reporting precluded several a priori moderator analyses. Suggestions for future research, including standards specified by Task Force Guidelines, are discussed.

Postnatal Cardiac Autonomic Nervous Control in Pediatric Congenital Heart Disease

Congenital heart disease is the most common congenital defect. During childhood, survival is generally good but, in adulthood, late complications are not uncommon. Abnormal autonomic control in children with congenital heart disease may contribute considerably to the pathophysiology of these long term sequelae. This narrative review of 34 studies aims to summarize current knowledge on function of the autonomic nervous system in children with a congenital heart defect. Large scale studies that measure both branches of the nervous system for prolonged periods of time in well-defined patient cohorts in various phases of childhood and adolescence are currently lacking. Pending such studies, there is not yet a good grasp on the extent and direction of sympathetic and parasympathetic autonomic function in pediatric congenital heart disease. Longitudinal studies in homogenous patient groups linking autonomic nervous system function and clinical outcome are warranted.

Sex differences in healthy human heart rate variability: A meta-analysis

The present meta-analysis aimed to quantify current evidence on sex differences in the autonomic control of the heart, indexed by measures of heart rate variability (HRV) in healthy human subjects. An extensive search of the literature yielded 2020 titles and abstracts, of which 172 provided sufficient reporting of sex difference in HRV. Data from 63,612 participants (31,970 females) were available for analysis. Meta-analysis yielded a total of 1154 effect size estimates (k) across 50 different measures of HRV in a cumulated total of 296,247 participants. Females showed a significantly lower mean RR interval and standard deviation of RR intervals (SDNN). The power spectral density of HRV in females is characterized by significantly less total power that contains significantly greater high- (HF) and less low-frequency (LF) power. This is further reflected by a lower LF/HF ratio. Meta-regression revealed significant effects of age, respiration control and the length of recording available for analysis. Although women showed greater mean heart rate, they showed greater vagal activity indexed by HF power of HRV. Underlying mechanisms of these findings are discussed.

Intravenous Hydration for Management of Medication-Resistant Orthostatic Intolerance in the Adolescent and Young Adult

Orthostatic intolerance (OI) is common in teenagers (T) and young adults (A). Despite treatment with oral fluids, medication, and exercise, a significant number have symptoms from multiple organ systems and suffer low quality of life (QOL). Previous studies showed that acute intravenous (IV) hydration (IH) could help restore orthostatic tolerance; however, no data are available about the intermediate-term effects of IH. We therefore studied the efficacy of IH to improve QOL and manage medication-refractory OI patients. Our study population consisted of 39 patients (mean age = 16.1 ± 3.3) years; thirty-two were female. Average number of medications failed = 3.1. Average QOL score on self-reported OI questionnaire was 4.2 (normal QOL = 10). IV hydration consisted of normal saline (1-2 l/day, 3-7 days/week). 1) Orthostatic testing revealed Postural Orthostatic Tachycardia (24), Neurally Mediated Hypotension (14) or OI (1). 2) Average orthostatic change in heart rate was 48 ± 18 bpm. 3) IH was performed via intermittent IV access (10), PICC line (22), and Port (7). 4) Duration of IH varied from 1 week to 3.8 years (mean = 29 ± 47 weeks). 5) Overall, 79 % (n = 31) demonstrated clinically improved self-reported QOL. 6) Six patients who discontinued IH requested to restart treatment. (7) Complications consisted of upper extremity deep vein thrombosis (n = 3) and infection (n = 4). IH is an effective therapy to improve QOL in T&A with medication-resistant OI. Most patients continued to report improved QOL once IH was discontinued. IH should be considered a therapeutic option in medication-resistant OI patients with low QOL.

Interaction Between Heart Rate Variability and Heart Rate in Pediatric Population

Background: Heart rate variability (HRV) is primarily heart rate (HR) dependent, and therefore, different HR may exert different impact on HRV. The objectives of the study were to evaluate the effect of HR on HRV in children and to determine whether HRV indices normalized to HR are sex- and age-related.

Methods: Short-term ECG recordings were performed in 346 healthy children. Standard time and frequency domain HRV parameters and HR were analyzed in four age subgroups (6–7, 8–9, 10–11, and 12–13 years old). To investigate the HR impact on HRV, standard HRV parameters were normalized to prevailing HR.

Results: Standard HRV measures did not differ between age subgroups, however, HR significantly decreased with subjects age and turned out to be the strongest determinant of HRV. The normalization of HRV to prevailing HR allowed to show that sex-related differences in standard HRV resulted from differences in HR between boys and girls. The normalized HRV significantly decreased with age—before the normalization this effect was masked by age-related HR alterations.

Conclusions: HR significantly impacts HRV in pediatric population and turns out to be the strongest determinant of all standard HRV indices. The differences in standard HRV between boys and girls result from differences in their HR. The normalized HRV is decreasing with age in healthy children and it is accompanied by the reduction of HR—as a net result, the standard HRV is constant in children at different ages. This may reflect the maturation of the autonomic nervous system.

Effects of exercise on cardiac autonomic modulation in children: literature update

AbstractIntroduction It is known that physical exercise is beneficial and precipitates adjustments to the autonomic nervous system. However, the effect of exercise on cardiac autonomic modulation in children, despite its importance, is poorly investigated.Objective To bring together current information about the effects of exercise on heart rate variability in healthy and obese children.Methods The literature update was performed through a search for articles in the following databases; PubMed, PEDro, SciELO and Lilacs, using the descriptors “exercise” and “child” in conjunction with the descriptors “autonomic nervous system”, “sympathetic nervous system”, “parasympathetic nervous system” and also with no descriptor, but the key word of this study, “heart rate variability”, from January 2005 to December 2012.Results After removal of items that did not fit the subject of the study, a total of 9 articles were selected, 5 with healthy and 4 with obese children.Conclusion The findings suggest that exercise can act in the normalization of existing alterations in the autonomic nervous system of obese children, as well as serve as a preventative factor in healthy children, enabling healthy development of the autonomic nervous system until the child reaches adulthood.

Sympathetic Activity Assessed during Exercise Recovery in Young Obese Females

OBJECTIVE

To evaluate differences in sympathetic activity, as assessed by an exercise recovery index (ERI; heart rate/oxygen consumption [VO2] plateau), between black and white obese female adolescents. An additional aim was to determine the association of ERI with insulin resistance (homeostasis model assessment of insulin resistance [HOMA-IR]), cardiovascular fitness per fat-free mass (VO2 per fat-free mass), systolic blood pressure (SBP), and percent body fat (%FAT) in both black and white obese adolescents.

STUDY DESIGN

Sixty-one females volunteered to participate in this study. HOMA-IR, SBP, and %FAT were assessed during resting conditions in black (n = 49, 13.7 ± 1.6 years, 38.1 ± 6.1 kg/m(2)) and white (n = 12, 13.3 ± 2.2 years, 34.3 ± 4.9 kg/m(2)) obese adolescents. An ERI was calculated during a 5-minute passive recovery period immediately following a graded treadmill exercise test to exhaustion.

RESULTS

The ERI was significantly greater in black compared with white obese adolescent females (29.8 ± 6.4 vs 24.1 ± 3.1 bpm·mLO2(-1)·min(-1), P = .004). Using multiple linear regression modeling, there was a significant independent association between ERI and VO2 per fat-free mass (r = -0.310, P = .027) and %FAT (r = 0.326, P = .020) in black obese adolescents after controlling for HOMA-IR and SBP.

CONCLUSIONS

These results suggest that black obese adolescent females have greater sympathetic activity, as assessed by an ERI, than white obese adolescent females. These findings support the need for weight management efforts aimed at both reducing %FAT and improving fitness in obese adolescents, specifically black females.

TRIAL REGISTRATION

Registered with Clinicaltrials.gov: NCT00562293.

Heart rate variability, adiposity, and physical activity in prepubescent children

PURPOSE

This study aimed at examining the associations between weight status, body fat mass, and heart rate variability in prepubescent children, adjusting for physical activity levels.

METHODS

A cross-sectional investigation in which a total of 50 Caucasian pre-pubertal children (21 normal weight; 8 overweight; 21 obese), aged 6-10 years (8.33 ± 1.14), including both boys (n = 24) and girls (n = 26), were recruited from local schools. Total body fat and trunk fat were evaluated through dual-energy X-ray absorptiometry. Free-living physical activity levels were evaluated by accelerometer. Short-term heart rate variability acquisition was performed; time- and frequency-domain parameters were analysed. Logarithmic transformations of the low-frequency (LnLFnu), high-frequency (LnHFnu) normalized units and low-frequency/high-frequency (LnLFnu/HFnu) ratio were computed.

RESULTS

Adjusting for age, Tanner stage, and moderate to vigorous physical activity levels, obese children compared to normal weight children showed a significant decreased LnHfnu (3.8 ± 0.2 vs 4.1 ± 0.2 %) and both higher LnLFnu (4.0 ± 0.4 vs 3.7 ± 0.3 %) and LnLFnu/LnHFnu ratio (1.1 ± 0.1 vs 0.9 ± 0.1). LnHFnu showed significant negative correlation with waist circumference (r = -0.598; P = 0.000), total body fat (r = -0.409; P = 0.011) and trunk fat (r = -0.472; P = 0.003). Both LnLFnu and LnLFnu/LnHFnu ratio showed positive correlations with waist circumference (r = 0.455; r = 0.513) and trunk fat (r = 0.370; r = 0.415).

CONCLUSIONS

A higher amount of body fat mass, particularly central fat, was shown to be related to decreased parasympathetic modulation in time-domain heart rate variability. This finding highlights the potential cardiovascular risk that excessive fat mass may represent even at very young age.

Ethnic differences in resting heart rate variability: a systematic review and meta-analysis

BACKGROUND

Ethnic disparities in cardiovascular morbidity and mortality are widely documented in the literature. Recently, research has shown that decreased parasympathetic cardiac modulation is associated with the established and emerging risk factors for cardiovascular disease (CVD) and stroke. In consideration of the disproportionate CVD risk and disease profile of African Americans (AAs), it is plausible that decreased cardiac parasympathetic functioning may partially explain these disparities. In the present systematic review and meta-analysis, we assess the available evidence for a reliable ethnic difference in tonic vagally mediated heart rate variability (HRV), an indicator of parasympathetic cardiac modulation.

METHODS

A systematic literature search was conducted yielding studies comparing tonic HRV in AAs and European Americans. Adjusted standardized effect sizes (Hedges g) were calculated using a mixed-effects model, with restricted maximum likelihood estimation for 17 studies containing appropriate measures of vagally mediated HRV.

RESULTS

Meta-analysis results suggest that AAs have greater HRV than do European Americans (Hedges g = 0.93, 95% confidence interval = 0.25-1.62), even after consideration of several covariates including health status, medication use, and subgroup stratification by sex and age.

CONCLUSIONS

These findings suggest that decreased vagally mediated HRV is not likely to account for the persistent health disparities experienced by AAs with respect to CVD risk and burden. These disparities underscore the need for continued research addressing socioethnic cardiovascular differences and the biobehavioral mechanisms involved.

Short-term heart rate variability in a population-based sample of 10-year-old children

Heart rate variability (HRV) is a non-invasive quantitative marker of cardiac autonomic function derived from continuous electrocardiogram (ECG) recordings. Normative HRV values and development factors have not been established in pediatric populations. The objective was to derive referent time- and frequency-domain HRV values for a population-based sample of children. Children aged 9-11 years (N = 1,036) participated in the Québec Longitudinal Study of Child Development cohort cardiovascular health screening. Registered nurses measured anthropometrics (height, weight) and children wore an ambulatory Holter monitor to continuously record an ECG signal. HRV variables included time (SDNN, pNN50, RMSSD, SDANN) and frequency (HF, LF, LF/HF ratio) domain variables. Normative HRV values, stratified by age, sex, and heart rate, are presented. Greater heart rate (β avg  = -0.60, R avg (2)  = 0.39), pubertal maturation (β avg = -0.11, R avg (2)  = 0.01), later ECG recording times (β avg = -0.19, R avg (2)  = 0.07), and higher diastolic blood pressure (β avg = -0.11, R avg (2)  = 0.01) were significantly associated with reduced HRV in 10-year-old children. The normative HRV values permit clinicians to monitor, describe, and establish pediatric nosologies in primary care and research settings, which may improve treatment of diseases associated with HRV in children. By better understanding existing values, the practical applicability of HRV among clinicians will be enhanced. Lastly, developmental (e.g., puberty) and procedural (e.g., recording time) factors were identified that will improve recording procedures and interpretation of results.

The circadian pattern of cardiac autonomic modulation and obesity in adolescents

PURPOSE

To assess the impact of obesity and population attributes on the circadian pattern of cardiac autonomic modulation (CAM) in a population-based sample of adolescents.

METHODS

We used data from 421 adolescents who completed the follow-up exam in the Penn State Children Cohort study. CAM was assessed by heart rate variability (HRV) analysis of beat-to-beat, normal R-R intervals from a 24-hour ECG, on a 30-minute basis. The HRV indices included frequency-domain (HF, LF, and LF/HF ratio) and time-domain (SDNN, RMSSD, and HR) variables. Nonlinear mixed-effect models were used to calculate a cosine periodic curve, each having three parameters quantifying its circadian period: M (mean levels of the HRV variables), Â (amplitude of the oscillation), and θ (the time of the highest oscillation).

RESULTS

The mean (SD) age was 16.9 (2.2) years, with 54 % male and 77 % white. The mean BMI percentile was 66, with 16 % obese (BMI percentile ≥ 95). Overall, HF (a marker of parasympathetic modulation) gradually increased from the late afternoon, reached peak amplitude around 3 a.m., and then decreased throughout the daytime until late afternoon. In contrast, obesity had adverse effects on all circadian parameters. The age, sex and race showed varying differences on the CAM circadian parameters. The adjusted means (95 %Cls) of M, Â, and θ for HF were 5.99 (5.79-6.19), 0.77 (0.66-0.89), 3:15 (2:15-4:15) a.m., and 6.21 (6.13-6.29), 0.66 (0.61-0.70), 2:45 (2:30-3:15) a.m. for obese and non-obese subjects, respectively.

CONCLUSION

The circadian pattern of CAM can be quantified by the three cosine parameters. Obesity is associated with lower HRV even in young individuals like children/adolescents.

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.

Childhood obesity and autonomic dysfunction: risk for cardiac morbidity and mortality

OPINION STATEMENT

The epidemic of childhood obesity is becoming a major predictor for risk of cardiovascular diseases (CVD) and mortality during adulthood. Alterations in the morphology of the heart due to obesity could be a predictor for the dysfunction of cardiac autonomic modulation (CAM). A number of epidemiologic studies have evaluated the effect of obesity and CAM in children, finding that obesity impaired the balance of CAM toward a sympathetic overflow and reduced parasympathetic modulation, a significant predictor of CVD morbidity and mortality in adults. Lifestyle modifications, for example long-term exercise programs, have been shown to improve CAM in the obese. This review discusses the recent evidence on childhood and adolescent obesity and its impact on CAM, as well as how early lifestyle changes could help improve CAM, which may in turn reduce the burden of CVD in adults.

Developmental differences in the effects of alcohol and stress on heart rate variability

Adolescent rats differ in their responses to stress and ethanol from their adult counterparts, although not much is known about the contribution of the autonomic nervous system (ANS) to these differences. This study assessed the impact of stress, ethanol, and their combination on parameters of heart rate variability (HRV) in adolescent and adult male Sprague-Dawley rats. Animals were habituated to the testing box and neck sensors (MouseOX, STARR Life Sciences Corp.) used for recording heart rate (HR). After 8-10min of baseline recording, animals were restrained for 90min or returned home, followed by intraperitoneal injection of 0, 0.5, 1.0, or 1.5g/kg ethanol. The 8-10min test recording occurred 30min post-injection. Ethanol-related decreases in LF (an index of sympathetic activity) were evident under non-stressed conditions in adolescents but only after stress in adults, perhaps in part due to apparent ethanol-induced sympathetic deactivation in adolescents. Parasympathetic tone, indexed by HF, was unaffected by both ethanol and stress in adolescents, while again both the 1.0 and 1.5g/kg ethanol doses decreased HF in adults following stress. Ethanol also decreased low frequency/high frequency tone (LF/HF), an index of sympathovagal balance, only in adolescents, with no decrease evident in adults. Further, stressed adults, and not adolescents, had significantly lower CORT and PROG values than their non-stressed counterparts. Taken together, these results demonstrate notable age differences in the ANS response to ethanol under stressful vs. non-stressful circumstances, reflected by ethanol-mediated autonomic effects that were more pronounced following stressor exposure in adults but under non-stressed conditions in adolescents.

Heart rate variability reflects the natural history of physiological development in healthy children and is not associated with quality of life

Background

Quality of life (QoL), being the sum expression of diverse influencing factors, is not easy to determine. A clinically relevant option would be to identify and measure quality of life on the basis of physiological parameters which correlate plausibly and statistically with psychometrically measured QoL. Analysis of heart rate variability (HRV) offers readily measurable physiological parameters which could be of use here. A correlation of HRV with both course of disease and QoL has been reported in patients with chronic illness. Various psychometric instruments have been developed for use in paediatric oncology. The aim of this study was to obtain data on HRV and QoL and their correlations, initially in healthy children.

Methods

Holter ECG and quality of life were examined in 160 children and adolescents (72 male) aged between 8 and 18 years. QoL was determined with the established questionnaire PEDQoL. Standard parameters of HRV from the frequency domain were calculated and correlated with QoL domains using Spearman (nonparametric) correlation analysis.

Results

Minor but significant associations were revealed only with regard to the PEDQoL domain “autonomy” on the one hand and heart rate and HRV (e.g. MRR, MRRn, MRRd, HRV_ULF, SDNN) parameters which evidently reflect distinct physiological functions on the other.

Conclusions

In healthy children and adolescents we have a first indication that there is a correlation between parameters of HRV and QoL. However, to a greater extent, HRV reflects associated physiological processes of the autonomic nervous system. A higher correlation is more likely to be found in chronically ill children.

The assessment of cardiac autonomic functions in adolescents with a family history of premature atherosclerosis

OBJECTIVES

Subclinical atherosclerosis has been recently detected in adolescents with a family history of premature atherosclerosis. However, no studies in the literature have assessed the cardiac autonomic functions of these adolescents. The aim of this study was to evaluate the cardiac autonomic functions of adolescents with a family history of premature atherosclerosis compared with those of age- and gender-matched adolescents without a family history of atherosclerosis.

METHOD

We evaluated the cardiac autonomic functions of 36 adolescents with a family history of premature atherosclerosis (Group 1) and compared them with those of 31 age- and gender-matched adolescents whose parents did not have premature atherosclerosis (Group 2). Twenty-four-hour time domain (standard deviation of all normal sinus RR intervals [SDNN], standard deviation of the mean of normal RR intervals in each 5-minute segment [SDANN], root-mean-square differences in successive RR intervals) and frequency domain (very low frequency, low frequency, high frequency, low frequency/high frequency) parameters of heart rate variability were used for the evaluation of cardiac autonomic functions.

RESULTS

There were no differences in the time and frequency domain parameters of heart rate variability between the two groups. Heart rate was negatively correlated with SDNN (r=-0.278, p=0.035), while age was significantly correlated with root-mean-square differences in successive RR intervals, high frequency, low frequency and low frequency/high frequency (r=-0.264, -0.370, 0.265 and 0.374, respectively; p<0.05 for all).

CONCLUSION

We found that the cardiac autonomic functions of adolescents with a family history of premature atherosclerosis were not different compared with those of adolescents without a positive family history of premature atherosclerosis. It appears that subclinical atherosclerosis does not reach a critical value such that it can alter cardiac autonomic functions in adolescence.

Measurement fidelity of heart rate variability signal processing: the devil is in the details

Heart rate variability (HRV) is a particularly valuable quantitative marker of the flexibility and balance of the autonomic nervous system. Significant advances in software programs to automatically derive HRV have led to its extensive use in psychophysiological research. However, there is a lack of systematic comparisons across software programs used to derive HRV indices. Further, researchers report meager details on important signal processing decisions making synthesis across studies challenging. The aim of the present study was to evaluate the measurement fidelity of time- and frequency-domain HRV indices derived from three predominant signal processing software programs commonly used in clinical and research settings. Triplicate ECG recordings were derived from 20 participants using identical data acquisition hardware. Among the time-domain indices, there was strong to excellent correspondence (ICC(avg)=0.93) for SDNN, SDANN, SDNNi, rMSSD, and pNN50. The frequency-domain indices yielded excellent correspondence (ICC(avg)=0.91) for LF, HF, and LF/HF ratio, except for VLF which exhibited poor correspondence (ICC(avg)=0.19). Stringent user-decisions and technical specifications for nuanced HRV processing details are essential to ensure measurement fidelity across signal processing software programs.

Prediabetes and blood pressure effects on heart rate variability, QT-interval duration, and left ventricular hypertrophy in overweight-obese adolescents

This ancillary, descriptive correlational study examined the effect of glucose regulation, blood pressure (BP), and their combined effects on cardiac autonomic function in 128 overweight-obese 11-18-year-olds. Measures included body mass index, resting BP, fasting glucose, glucose tolerance, and cardiac autonomic function (heart rate variability, QT, and Cornell voltage). After adjusting for age and gender, multivariate analysis of covariance revealed no differences in cardiac autonomic measures based on glucose regulation (p = .319), BP (p = .286), or the interaction between glucose regulation and BP (p = .132). The additive effect of prediabetes and elevated BP did not impact cardiac autonomic function in overweight-obese youth.

Heart rate variability is related to self-reported physical activity in a healthy adolescent population

This study investigated whether there is a relationship between heart rate variability (HRV) versus lifestyle and risk factors for cardiovascular disease in a population of healthy adolescents. HRV is as an index of tonic autonomic activity and in adults HRV is related to lifestyle and risk factors for cardiovascular disease, but it is not known if this is the case in adolescents. HRV was registered for 4 min in sitting position in 99 healthy adolescents (age range 15 years 11 months–17 years 7 months) and repeated after 6 months. On both occasions there were significant correlations (P < 0.05) between physical activity and HRV, with respective r values: high frequency (HF) 0.26, 0.30; low frequency power (LF) 0.35, 0.29 and the standard deviation of inter-beat intervals (SDNN) 0.28, 0.37. There was no significant interaction between first and second measurements. In contrast, there were no correlations to sleeping patterns, eating habits and smoking. Risk factors for cardiovascular disease [body mass index (BMI = weight (kg)/length in m²), systolic blood pressure and p-glucose] did not show any repeatable significant correlations to HRV. Multiple regression models showed that physical activity was a predictor for HF, LF and SDNN in both measurements. In conclusion HF, LF and SDNN were reproducible after 6 months and were related to physical activity on both occasions.

Evaluation of the autonomic nervous system using the FAN device -- range of normal and examples of abnormal

Different components of the autonomic nervous system may be affected by different disorders to varying degrees. The aim of this study is to report first experiences with a new device (FAN®, Schwarzer, Germany) which measures heart rate variability (HRV), sympathetic skin responses (SSR) and the pulse wave transit time (PTT). We examined 190 healthy volunteers (102 men, 88 women) and in 89 subjects (46 men, 43 women) PTT during VM was investigated. In a subset of 24 subjects PTT was compared to conventional blood pressure recording. Thereafter, normal data were compared to patients with polyneuropathy (PNP) and Parkinson syndromes. All parameters of HRV decreased with age. 6 parameters for HRV at rest, during deep respiration and the valsalva ratio were reclassified into three age categories: under 40 (n=96), 40 – 60 (n=71) and 60 or older (n=23). Applying the lower limits of normal (5%-tile) subjects did not have more than 2 of these 6 parameters in the pathological range PTT reduction during phase IV of the valsalva manoeuvre was greater than 7.7 ms (5%-tile) but not age dependent. Patients with PNP had reduced HRV and SSR, Parkinson patients had more frequently impaired blood pressure regulation according to PTT assessment. Our investigation shows that the FAN® might be useful for clinicians to detect autonomic disorders.

Wavelet transform: A better approach for the evaluation of instantaneous changes in heart rate variability

The aim of our study was to validate the Vaidyanathan wavelet tool for HRV analysis during orthostatic testing. Two groups of normotensive male subjects were studied: 13 adolescents and 27 young adults. Both groups consisted of subjects with negative, (N-), and with positive family history for hypertension, (N+). These subjects underwent 5-minute active standing upright, preceded and followed by 5-minute periods in supine position. Continuous electrocardiogram (ECG) was recorded and HRV indices were calculated using wavelet (WT) and fast Fourier transform (FFT) simultaneously. WT and FFT data showed high level of correlation (>0.9). Due to its inherent properties, WT proved to be more informative than FFT in the analysis of the non-stationary ECG signal during orthostatic testing. WT revealed HRV dynamics more accurately since it allowed HRV evaluation for shorter intervals (60 s) than FFT (256 s). During the initial and recovery period lower parasympathetic activity (P < 0.0001; P < 0.02) and higher ratio of autonomic balance (sympathetic vs. parasympathetic) (P < 0.0001; P < 0.02) were evidenced in (N+) as compared to (N-). The upright posture was accompanied by a prompt decrease in HRV and by an elevation of the index of autonomic balance. These alterations were more pronounced in N(+). In conclusion, we believe that wavelet analysis is an appropriate approach for the estimation of HRV dynamics in non-stationary conditions. Furthermore, we demonstrate certain essential alterations in the autonomic modulation of the cardiovascular system in young normotensives with positive family history for essential hypertension.

Differences in heart rate variability between Asian and Caucasian children living in the same Canadian community

Heart rate variability (HRV) is an umbrella term for a variety of measures that assess autonomic influence on the heart. Reduced beat-to-beat variability is found in individuals with a variety of cardiac abnormalities. A reduced HRV positively correlates with obesity, poor aerobic fitness, and increasing age. Racial (black-white) differences are apparent in adults and adolescents. We aimed to evaluate (i) Asian-Caucasian differences in HRV and (ii) differences in HRV between girls and boys. Sixty-two children (30 male (15 Caucasian, 15 Asian) and 32 female (15 Caucasian, 17 Asians)) with a mean age of 10.3 +/- 0.6 y underwent 5 min resting HRV recording, fitness testing (Leger's 20 m shuttle), and self-assessed maturity. Outcome HRV measures were a ratio of low to high frequency power (LF:HF), standard deviation of R-R intervals (SDRR) and root mean square of successive R-R intervals (RMSSD). Data were compared between groups using analysis of covariance (ANCOVA). There were no race or sex differences for time domain variables, mean R-R, body mass index, or blood pressure. Compared with Caucasian children, Asian children displayed a higher adjusted (fitness, R-R interval) LF:HF ratio (72.9 +/- 59.4 vs. 120.6 +/- 85.3, p < 0.05). Girls demonstrated a higher adjusted LF:HF power than boys (117.2 +/- 85.1 vs. 76.6 +/- 62.4, p = < 0.05). In conclusion, Asian and Caucasian children display different frequency domain components of heart rate variability.

Heart rate variability during recovery from a Wingate test in adolescent males

PURPOSE

To evaluate the effect of maturity status on the autonomic nervous system at rest and recovery after short-term, high-intensity exercise in adolescents.

METHODS

A biological maturity age was estimated in 27 males by calculating the years from peak height velocity (PHV) using a multiple regression equation. Subjects were divided into two groups: pre-PHV (years from PHV < 0.49), N = 14, mean age = 12.29 +/- 0.91 yr; post-PHV (years from PHV > 0.5, N = 13, mean age = 15.12 +/-0.76 yr). HR variability was used to evaluate autonomic function. ECG tracings were collected during 5 min at rest and recovery after a Wingate test and were analyzed in the frequency domain (low-frequency (LF), high-frequency (HF), LF/HF, total power (TP)). Data are presented as natural logarithms (LN).

RESULTS

Changes in HR from HR(peak) during exercise to HR measured at minute 4 after exercise ([DELTA]HR4) were significantly greater in the pre-PHV group (84.31 +/-17.58 bpm) compared with the post-PHV group (69.42 +/-17.63 bpm). There were no significant differences in resting HR variability between pre- and post-PHV groups (P > 0.05). Significant group x time interactions were found for LF(LN) (ms(2)) and TP(LN) (ms(2)) measured during recovery (P < 0.05). Post hoc tests showed that the pre-PHV group had significantly higher postexercise LF(LN) (5.02 +/- 0.97 vs 4.19 +/- 0.79) and TP(LN) (6.36 +/- 1.02 vs 5.62 +/- 0.65) compared with the post-PHV group. When postexercise LF(LN) (ms(2)) was normalized for TP(LN) (ms(2)), there were no significant differences between groups (P > 0.05).

CONCLUSION

The pre-PHV group had higher total HR variability than the post-PHV group after a Wingate test, suggesting that maturity status significantly affects total HR variability during recovery after high-intensity exercise.

Age and ethnicity differences in short-term heart-rate variability

OBJECTIVE

Hypertension is more frequent and more severe in older individuals and in African Americans. Differences in autonomic nervous system activity might contribute to these differences. Autonomic effects on the heart can be studied noninvasively through analysis of heart rate variability (HRV). We examined the effects of age and ethnicity on HRV.

METHODS

We studied 135 subjects (57 African Americans and 78 Caucasian Americans), aged 23 to 54 years. Using their surface electrocardiogram (ECG) data, we calculated the HRV indices with spectral analyses. High frequency (HF) power was used to index parasympathetic activity, whereas the ratio of low to high frequency power (LF/HF) was used to index sympathovagal balance.

RESULTS

Three HRV indices (HF, LF power, and LF/HF) were significantly related to age in Caucasian Americans but not in African Americans. The effect of age, ethnicity, and the age-by-ethnicity interaction on HF and LF power was significant, even after controlling for gender, body mass index, and blood pressure.

CONCLUSIONS

Young African Americans manifested a pattern of HRV response similarly to older Caucasian Americans. These results suggest that young African American individuals might show signs of premature aging in their autonomic nervous system.

Central serotoninergic response to orthostatic challenge in patients with neurocardiogenic syncope

AIMS

To determine whether central serotoninergic system activity is impaired by orthostatic challenge in patients with neurocardiogenic syncope (NCS).

METHODS AND RESULTS

Thirty-five [mean age: 24 (SD): 6 years] patients with a clinical history of NCS and positive head-up tilt test and 35 age-matched healthy volunteers (CON = 25+/-5 years) with negative response were studied. Overnight dexamethasone suppression test (DST) (1.5 mg given at 11 p.m.) was performed to assess the sensitivity of the hypothalamic-pituitary-adrenal axis by measuring next day cortisol (microg/dL) at 8 a.m. and 4 p.m. Cardiac autonomic function, cortisol, and prolactin (ng/dL) were also determined at baseline supine (BAS) and after 5, 10, and 15 min of orthostatic stress (OS) at 60 degrees . No significant differences were observed in cortisol plasma levels after the DST: CON = 0.6+/-0.6 microg/dL vs. NCS = 0.6+/-0.5; P = 0.7. Cardiac autonomic function, cortisol, and prolactin responses were similar in both study groups (CON vs. NCS; P > 0.05) during BAS: cortisol = 8.6+/-4 vs.8.7+/-4 microg/dL and prolactin = 16.8+/-9 vs. 16.8+/-9 ng/dL; OS-5: cortisol = 8.7+/-5 vs. 8.5+/-4 microg/dL and prolactin = 16.9+/-9 vs. 15.8+/-9 ng/dL; OS-10: cortisol = 8.5+/-5 vs. 8.1+/-3 microg/dL; prolactin = 16.2+/-9 vs. 15.8+/-9 ng/dL, and OS-15: cortisol = 9.0+/-5 vs. 8.4+/-4 microg/dL; prolactin = 17.1+/-9 vs. 15.5+/-9 ng/dL.

CONCLUSION

Central serotoninergic response during orthostatic challenge was not impaired in patients with recurrent NCS. These findings suggest that the activation of the hypothalamic-pituitary-adrenal axis is not altered in patients with recurrent NCS.