Relationship between age and heart rate variability in supine and standing postures: a study of spectral analysis of heart rate

Heart rate variability in children and adolescents with major depressive disorder: A systematic review and meta-analysis

Although reduced heart rate variability (HRV) has been observed in adults with major depressive disorder (MDD), the correlation between HRV and MDD in children and adolescents remains uncertain and requires to be systematically reviewed. Our meta-analysis included ten articles comprising 410 MDD patients and 409 healthy controls. Adolescents with MDD showed significant reductions in most HRV measures, such as HF-HRV, RMSSD, and PNN50, and depressive symptom severity was statistically associated with RMSSD, HF-HRV, and LF/HF ratio. A large heterogeneity across studies was detected. Sensitivity analysis revealed that removal of a specific study would significantly decline the heterogeneity for measures of HF-HRV, LF-HRV, and SDNN, and meta-regression analysis found that sample size and year of publication substantially moderated the differences between depressed samples and controls in RMSSD. Compared with adults, depression-induced autonomic dysfunction was more detectable in children and adolescents with substantial effects. Moreover, excluded studies which reported both HRV and MDD or depression symptoms were summarized based on objectives. Findings indicate that it is promising for HRV to be an appropriate and objective candidate biomarker for clinically depressed children and adolescents.

Effect of Age on Heart Rate Variability in Patients with Mitral Valve Prolapse: An Observational Study

Age is an important determinant of heart rate variability (HRV) in healthy individuals. The incidence of arrhythmia is high in patients with mitral valve prolapse (MVP). However, the correlation of HRV in patients with MVP in different age groups is not well established. We presumed that increasing age would be prospectively associated with declining HRV measurement in MVP. Sixty patients with MVP and 120 control individuals were included and underwent 24 h HRV analysis. No significant difference was found in all parameters calculated in the time domain or in the frequency domain between the two groups. However, as patients' age increased, a significant time domain (SDNN, RMSSD, NN50, and pNN50) decline was found in the MVP group, but not in the control group. This suggests that patients with MVP may have autonomic nervous system involvement that increases the risk of arrhythmia and heart disease with increasing age.

Autonomic tone in children and adults: Pupillary, electrodermal and cardiac activity at rest

Considering the suspected involvement of the autonomic nervous system (ANS) in several neurodevelopmental disorders, a description of its tonus in typical populations and of its maturation between childhood and adulthood is necessary. We aimed to arrive at a better understanding of the maturation of the sympathetic (SNS) and parasympathetic (PNS) tonus by comparing children and adults at rest, via recordings of multiple ANS indices. We recorded simultaneously pupil diameter, electrodermal activity (EDA) and cardiac activity (RR interval and HRV: heart rate variability) in 29 children (6-12 years old) and 30 adults (20-42 years old) during a 5-min rest period. Children exhibited lower RR intervals, higher LF peak frequencies, and lower LF/HF (low frequency/high frequency) ratios compared to adults. Children also produced more spontaneous EDA peaks, reflected in a larger EDA AUC (area under the curve), in comparison with adults. Finally, children displayed a larger median pupil diameter and a higher pupillary hippus frequency than adults. Our results converged towards higher SNS and PNS tones in children compared to adults. Childhood would thus be characterized by a high autonomic tone, possibly reflecting a physiological state compatible with developmental acquisitions.

Patient Position Affects Venodilation for Peripheral Intravenous Cannulation

BACKGROUND

Larger veins are associated with a higher rate of success of peripheral intravenous cannulation. Although patient position affects venodilation during central venous cannulation, the association between patient position and vein size for peripheral intravenous cannulation remains unclear.

PURPOSE

We examined the effect of seated versus supine positioning on vein size during peripheral intravenous cannulation before and after tourniquet application.

METHODS

In the present study, we recruited 81 participants (20-64 years) and included 80 in the analysis. We measured outcomes before and after tourniquet application in the seated and supine positions. The primary outcome was the cross-sectional area of the target forearm vein (ultrasonography by a blinded assessor). Subgroup analysis was used to test the effects of positioning combined with difficult peripheral intravenous cannulation (DPIVC) defined as poor visibility and/or palpability of the target vein.

RESULTS

Results of paired t tests demonstrated that the venous cross-sectional area significantly increased in the supine position with tourniquet application compared with the seated position with tourniquet application. Subgroup analysis with two-way repeated measures analysis of variance revealed that the venous cross-sectional area was significantly larger in the supine position than in the seated position despite DPIVC.

CONCLUSION

Vein size during tourniquet application was greater in the supine than in the seated position even in cases of DPIVC. We thus recommend the supine position over the seated position for peripheral intravenous cannulation.

The acute physiological stress response to an emergency alarm and mobilization during the day and at night

The purpose of this study was to investigate the acute physiological stress response to an emergency alarm and mobilization during the day and at night. Sixteen healthy males aged 25 ± 4 years (mean ± SD) spent four consecutive days and nights in a sleep laboratory. This research used a within-participants design with repeated measures for time, alarm condition (alarm or control), and trial (day or night). When an alarm sounded, participants were required to mobilize immediately. Saliva samples for cortisol analysis were collected 0 min, 15 min, 30 min, 45 min, 60 min, 90 min, and 120 min after mobilization, and at corresponding times in control conditions. Heart rate was measured continuously throughout the study. Heart rate was higher in the day (F(20,442) = 9.140, P < 0.001) and night (F(23,459) = 8.356, P < 0.001) alarm conditions compared to the respective control conditions. There was no difference in saliva cortisol between day alarm and day control conditions. Cortisol was higher (F(6,183) = 2.450, P < 0.001) following the night alarm and mobilization compared to the night control condition. The magnitude of difference in cortisol between night control and night alarm conditions was greater (F(6,174) = 4.071, P < 0.001) than the magnitude of difference between the day control and day alarm conditions. The augmented heart rate response to the day and night alarms supports previous observations in field settings. Variations in the cortisol responses between conditions across the day and night may relate to differences in participants' ability to interpret the alarm when sleeping versus when awake.

Relation between Respiratory Sinus Arrythymia and Startle Response during Predictable and Unpredictable Threat

Research suggests that lower respiratory sinus arrhythmia (RSA) is associated with greater aversive responding. One physiological indicator of aversive responding is startle potentiation. While a few studies have demonstrated an inverse association between RSA and startle potentiation, no study to date has distinguished whether this relation is similar for predictable versus unpredictable aversive stimuli. This is an important distinction, given that degree of predictability has been shown to be an important determinant of aversive responding. The present study examined whether resting RSA was associated with startle eye blink responding during predictable and unpredictable threat of electric shock. Resting RSA was collected during a 6-minute seated baseline phase at the beginning of the experimental session. Participants then completed a computerized startle task in which predictable and unpredictable shocks were administered. Results indicated that lower resting RSA was associated with greater startle potentiation during unpredictable threat, but not during predictable threat. These findings are consistent with a growing body of literature suggesting that individual differences in RSA are associated with aversive responding, and extend previous work by suggesting that RSA may be more robustly associated with a heightened sensitivity to unpredictable threat. This pattern of results may have implications for the understanding of pathological anxiety given that individuals with anxiety disorders typically exhibit low RSA and heightened responding during unpredictable threat.

The association between baroreflex sensitivity and blood pressure in children

Low baroreflex sensitivity (BRS) and heart rate variability (HRV) are associated with the pathogenesis of adult hypertension. However, limited information exists about the negative consequences of elevated childhood blood pressure (BP) and autonomic regulation. Additionally, there are developmental changes in autonomic regulation throughout puberty, yet studies have not appropriately accounted for this. The objective of this study was to investigate BRS and HRV in children with 2 different BP profiles, while controlling for the effects of maturation, age, sex, and body composition. A sample of 11- to 14-year-old participants were divided into 2 BP groups: high BP (HBP; ≥95th percentile; n = 21) and normal BP (NBP; <90th percentile; n = 85). Automated BP was measured at 2 time points. In lab-based testing, 5 min of beat-to-beat BP (Finapres) and R-R interval (RRI) were recorded (standard electrocardiogram) after 15 min of supine rest. Spectral indices were computed using fast Fourier transform, and transfer function analysis was used to compute BRS. High frequency (HF) and low frequency (LF) power spectral areas were set to 0.15-0.4 Hz and 0.04-0.15 Hz, respectively, and BRS was determined for the LF area. After adjustment for age, sex, maturation, and body composition, BRS (p = 0.04), LF (p = 0.008), and HF (p = 0.01) RRI variability, and RRI total power (p = 0.005) were lower in the HBP than in the NBP participants. As well, the LF/HF systolic BP variability ratio was higher in the HBP than in the NBP group (p = 0.03). Despite their young age, these children with high, yet not clinically hypertensive BP, display reduced autonomic regulation.

Age-grouped differences in adverse drug events from psychotropic medication

OBJECTIVE

This review aims to detail specific psychotropic medication treatment differences in adverse drug events (ADEs) between children, adolescents, and adults.

METHOD

A thorough data-based search of ADEs was made, augmented by findings from approved and updated U.S. Food and Drug Administration (FDA) drug labels, controlled clinical trial reports, and from FDA information on ADEs at scheduled public hearings.

RESULTS

Children were found to generally exhibit more ADEs to psychotropic medication than adolescents and adults. These ADEs primarily include altered growth velocity, rash, vomiting, dystonia, tics, affect lability, activation, metabolic blood test abnormalities, sedation, sialorrhea, and electrocardiogram irregularities.

CONCLUSION

Children have more biological vulnerabilities than older individuals, which could account for their greater rate of ADEs to psychotropic medication treatment.

Cardiovagal modulation upon postural change is altered in Huntington's disease

BACKGROUND

Cardiac autonomic nervous system (ANS) dysfunction in Huntington's disease (HD) might affect both the sympathetic and parasympathetic branch of the ANS.

RESULTS AND CONCLUSIONS

The pattern of linear heart rate variability we found in mid stage HD patients points towards a predominately reduced cardiovagal modulation compared with healthy subjects, which might influence HD patients' susceptibility for cardiovascular complications such as syncopes and cardiac arrhythmias.

Fractal scale-invariant and nonlinear properties of cardiac dynamics remain stable with advanced age: a new mechanistic picture of cardiac control in healthy elderly

Heart beat fluctuations exhibit temporal structure with robust long-range correlations, fractal and nonlinear features, which have been found to break down with pathologic conditions, reflecting changes in the mechanism of neuroautonomic control. It has been hypothesized that these features change and even break down also with advanced age, suggesting fundamental alterations in cardiac control with aging. Here we test this hypothesis. We analyze heart beat interval recordings from the following two independent databases: 1) 19 healthy young (average age 25.7 yr) and 16 healthy elderly subjects (average age 73.8 yr) during 2 h under resting conditions from the Fantasia database; and 2) 29 healthy elderly subjects (average age 75.9 yr) during approximately 8 h of sleep from the sleep heart health study (SHHS) database, and the same subjects recorded 5 yr later. We quantify: 1) the average heart rate (<R-R>); 2) the SD sigma(R-R) and sigma(DeltaR-R) of the heart beat intervals R-R and their increments DeltaR-R; 3) the long-range correlations in R-R as measured by the scaling exponent alpha(R-R) using the Detrended Fluctuation Analysis; 4) fractal linear and nonlinear properties as represented by the scaling exponents alpha(sgn) and alpha(mag) for the time series of the sign and magnitude of DeltaR-R; and 5) the nonlinear fractal dimension D(k) of R-R using the fractal dimension analysis. We find: 1) No significant difference in (P > 0.05); 2) a significant difference in sigma(R-R) and sigma(DeltaR-R) for the Fantasia groups (P < 10(-4)) but no significant change with age between the elderly SHHS groups (P > 0.5); and 3) no significant change in the fractal measures alpha(R-R) (P > 0.15), alpha(sgn) (P > 0.2), alpha(mag) (P > 0.3), and D(k) with age. Our findings do not support the hypothesis that fractal linear and nonlinear characteristics of heart beat dynamics break down with advanced age in healthy subjects. Although our results indeed show a reduced SD of heart beat fluctuations with advanced age, the inherent temporal fractal and nonlinear organization of these fluctuations remains stable. This indicates that the coupled cascade of nonlinear feedback loops, which are believed to underlie cardiac neuroautonomic regulation, remains intact with advanced age.

Regulation of cognitive resources during sustained attention and working memory in 10-year-olds and adults

We examined differences between 10-year-olds and young adults in resource recruitment and regulation during tasks of sustained attention and spatial working memory. We administered participants spatial 0- and 1-back tasks and used pupillary dilation as a measure of resource recruitment. Repeated administration of 0-back led to smaller pupillary dilations and greater response time (RT) variability, revealing a vigilance decrement. Effects of repeated administration of 0-back and differences between 0- and 1-back in d' and RTs were similar between ages. Results further suggested that the children may not have been as effective as adults in extracting frequency information. Thus, on simple tasks of sustained attention and working memory, children recruit resources in a manner similar to adults. Finally, d' was correlated with RT variability on both tasks at both ages, highlighting the role of attentional fluctuations on both tasks.

Temperament and vagal tone in boys with fragile X syndrome

Physiological hyperarousal, an elevated state of physiological arousal and poor modulation, has been postulated to be a significant source of behavior problems in children with fragile X syndrome (FXS). Temperament has been associated with behavior problems and may also reflect biological reactivity. Young boys with FXS display poorly modulated and low levels of vagal tone (Roberts, Dev Psychobiol 2001;39:107-123) and high activity, poor attention, low adaptability, poor persistence, and low intensity when compared with a reference sample of typically developing (Hatton, Dev Med Child Neurol 1991;41:625-632). In this study, we integrated physiological indices of vagal tone with temperament ratings and compared a sample of 29 young boys with FXS to 31 typically developing boys matched on chronological age and ethnicity. Boys with FXS were more active, less adaptable, and less persistent than the comparison group. Boys with FXS also showed lower baseline levels and less suppression of vagal tone in response to changing task demands. A relationship between baseline vagal tone and persistence was shown across both groups. However, group differences in temperament dimensions did not appear to be mediated or moderated by vagal tone.

[Analysis of heart rhythm variability by linear and non-linear dynamics methods]

INTRODUCTION

Spectral analysis of heart rhythm variability is a noninvasive method to study cardiovascular autonomic control. Nonlinear methods of analysis of heart rhythm variability may provide an additional information on properties of RR interval dynamics, which cannot be revealed by linear methods. The aim of this study was to investigate and to compare some parameters of deterministic chaos, tractal and spectral properties of heart rhythm variability in healthy subjects.

METHODS

Sixty healthy subjects, who participated in this study, were divided in four different age groups: children (< 15 years old), young (15-24 years), adults (25-39 years) and middle-aged (40-61 years). We analyzed the heart period variability extracted from a 5-minute electrocardiograms recordings in supine rest. Short-term fractal scaling exponent, sample entropy, minimum embedding dimension and the largest Lyapunov exponent along with the spectral measures (low-frequency and high-frequency power) were determined.

RESULTS

Heart frequency, short-term fractal scaling exponent, and the largest Lyapunov exponent did not differ between the tested groups (p > 0.05). Middle-aged subjects had the lower low-frequency power as compared to the children (p < 0.001) and the young (p < 0.05), and the lower high-frequency power as compared to the other three groups (p < 0.001). Middle-aged also had a significantly lower power of high frequency and sample entropy as compared to the other three groups (p < 0.001). Children had lower values of minimum embedding dimension compared to the middle aged (p < 0.001). Significant negative correlation between the age of the tested subjects, and the low-and, high-frequency power and sample entropy was found.

CONCLUSION

The obtained results suggested that healthy aging was associated with significant alteration in heart rhythm dynamics reflected on a higher regularity and lower variability of heart rhythm time-series. Significant decrease in a high-frequency power with aging suggested that reduction in parasympathetic activity was the basic cause of these changes.

Nonlinear and chaos characteristics of heart period time series: Healthy aging and postural change

In this study we investigated nonlinear and linear characteristics of heart period variability with aging in supine and standing posture. Sixty healthy subjects (8-61 years) divided in three age groups participated in the study. Heart period variability was assessed by measurement of short-term scaling exponent, sample entropy, largest Lyapunov exponent and spectral low-frequency and high-frequency power. In standing, there was significant increase in short-term scaling exponent and largest Lyapunov exponent in all subjects, and significant decrease in sample entropy in children (<15 years) and young adults (15-39 years). Increasing age is associated with reduction in sample entropy in supine posture. Mutual effect of aging and postural change was reflected on heart rate and sample entropy. Correlation between low-frequency-to-high-frequency power ratio and short-term scaling exponent was found in supine posture. In standing both low-frequency and high-frequency powers are correlated with short-term scaling exponent and sample entropy. These results show that posture, standing compared to supine, has significant effect on nonlinear properties of heart period variability in healthy subjects while the influence of healthy aging is less pronounced. The findings indicate that intrinsic properties of heart period dynamics, reflected on nonlinear measures, are altered only by robust changes of autonomic modulation of heart rate.

Effect of posture on heart rate variability spectral measures in children and young adults with heart disease

BACKGROUND

Reduction of heart rate variability as a consequence of heart disease and postural change has been well documented. However, the data on the effect of postural change in pediatric patients are incomplete and the effect is not fully understood. The aim of the study was to investigate effect of postural change on heart rate variability in relation to the extent of severity of heart disease.

METHODS

The dependence of heart rate variability on posture in 41 children and young adults (8-20 years) with heart disease has been investigated and compared with control. Short-term electrocardiograms (ECGs) were assessed in supine rest and active standing, and spectral measures of heart rate variability were determined.

RESULTS

Two types of response to the change of supine to standing posture were determined in both healthy and diseased subjects. In majority of subjects, the increased heart rate induced by standing was accompanied by a decrease in high-frequency power. However, in about 30% of all subjects, increased heart rate during standing was accompanied by an increased high-frequency power. Independently of posture and disease, high-frequency and low-frequency power were positively correlated. In subjects characterized by a reduction of heart rate variability in standing, the high-frequency power in both postures is reduced in diseased subjects compared to control.

CONCLUSIONS

These results demonstrate that in this age range, the response to posture is not unique because of the difference in high-frequency power, which implies a variety of vagal modulations of heart rate.

Spectral analysis of heart period variability in anorexia nervosa

The aim of this study was to investigate the response of autonomic cardiac control to postural change using spectral analysis, in patients with anorexia nervosa. Spectral components of total variability as well as of low and high frequencies were analyzed for 17 anorexic patients with mean body mass index (14.9 ? 1.9) kg/m2 and for 9 healthy age-matched women with body mass index (20.3 ? 1.7) kg/m2, in supine and standing postures. During standing posture, increased heart rate in all subjects was accompanied by the decrease in total variability and high frequency spectral powers. In supine posture, anorexic patients demonstrated the reduced low frequency spectral power. Compared to control women, during standing posture anorexic patients showed higher heart rate, reduced total variability and high frequency spectral powers. Statistically significant correlation was noticed between body mass index and spectral power of low frequency in both supine and standing posture. Alterations in autonomic cardiac control induced by anorexia nervosa could be estimated by spectral analysis of heart period variability.

Respiratory Sinus Arrhythmia During Stress Predicts Resting Respiratory Sinus Arrhythmia 3 Years Later in a Pediatric Sample

The author examined whether respiratory sinus arrhythmia (RSA) responses to stress predicted resting RSA approximately 3 years later in children and adolescents. A total of 149 children and adolescents (49% girls and women, 44% African Americans) participated in 2 laboratory protocols approximately 3 years apart. RSA reactivity during tasks was consistent within participants across tasks during each session. Resting RSA at Visit 1 explained 17% of the variance in resting RSA at Visit 2 when body mass index, duration between visits, race, gender, and age were controlled for. Visit 1 RSA reactivity explained an additional 5% of the variance in resting RSA at Visit 2. The positive relationship between Visit 1 reactivity and Visit 2 resting levels suggests that larger decreases in RSA during stress predicted lower resting RSA. Conversely, increases in RSA during stress were associated with higher resting RSA an average of 3 years later.

Effect of age on diurnal changes of 24-hour QT interval variability

QT interval on the surface electrocardiogram (ECG) reflects the time for repolarization of myocardium and prolongation of QTc is strongly associated with sudden cardiac death. Studies using novel techniques on beat-to-beat QT interval variability (QTV) have shown that it is influenced by the autonomic nervous system and is a predictor of sudden cardiac death. In this study, we examined the awake and sleep changes in QTV in 39 normal adults (mean age, 35 years) and 10 children (mean age, 11 years) using 24-hour ECG records. We obtained eight 5-minute segments of ECG sampled at 1000 Hz from the 24-hour records. Our results show that there is a diurnal variation of QTvm, detrended QT interval variance corrected for mean QT, and QTvi, an index of QTvm divided by heart rate variability corrected for mean heart rate. There was a significant increase in mean QT during sleep, whereas there was a significant decrease in QTvm and QTvi. QTvi significantly increased during the early morning hours. There were significant but modest correlations between the average 24-hour and awake QTvi and age (p < 0.01). There were also decreased low-frequency and high-frequency powers of QT during sleep. Coherence between heart rate and QT interval fluctuations in the range of 0-0.5 Hz, and especially in the high-frequency range (0.15-0.5 Hz), was significantly lower in adults than in children (p < 0.0002). These findings demonstrate diurnal fluctuations in ventricular repolarization lability. We speculate that these effects may relate to changes in cardiac autonomic function and may contribute to the well-known diurnal variation in the incidence of ventricular arrhythmias.

Effect of fluoxetine, pemoline and placebo on heart period and QT variability in normal humans

OBJECTIVE

To measure the effects of fluoxetine and pemoline on heart period and QT variability.

METHODS

Healthy volunteers were randomly assigned treatment with 20 mg daily of fluoxetine (n=7), 56.25 mg of pemoline (n=7) or placebo (n=9). Twenty-four-hour Holter ECGs were obtained before and after approximately 8 weeks of double-blind treatment.

RESULTS

There were no significant changes in the fluoxetine group. Pemoline was associated with a significant decrease in the high frequency (HF) power (0.15-0.5 Hz, P=.02) and fractal dimension of RR time series (P=.03). QTvi, a measure of QT interval variability, increased in the pemoline group (P=.05).

CONCLUSION

Pemoline, but not fluoxetine, decreases heart period variability (HPV) in the HF power, suggesting a vagolytic effect on cardiac autonomic function. Pemoline is also associated with an increase in QT interval variability, a measure that is sensitive to adrenergic agonists.

Side effects of desipramine and age

INTRODUCTION

The treatment response of children and adolescents to tricyclic antidepressants differs from that of adults. Few data exist on the impact of age on side effects. This study compares desipramine-associated side effects in children, adolescents, and adults.

METHODS

Data from three trials of desipramine were combined to produce a sample of 148 subjects, aged 7 to 66 years. Pulse and blood pressure were measured at baseline and while participants were receiving desipramine. Side effects were rated by a clinician. For data analysis, subjects were divided into two groups, younger patients (18 and younger) and older patients (19 and older). Group means of side effect ratings and vital signs were compared. Results were also analyzed covarying for plasma levels of desipramine.

RESULTS

There were significant differences between younger and older patients in pulse and blood pressure at baseline, on desipramine, and in changes in vital signs between baseline and medicated states. Younger patients had significantly lower mean ratings for constipation and dry mouth.

DISCUSSION

Treatment with desipramine results in differing degrees of subjective side effects and changes in vital signs across the life cycle. Physicians should not assume that side effects experienced by children and adolescents are identical to those experienced by adults.

Autonomic nervous system activity and the state and development of obesity in Japanese school children

OBJECTIVE

The autonomic nervous system (ANS) plays an important role in regulating energy expenditure and body fat content; however, the extent to which the ANS contributes to pediatric obesity remains inconclusive. The aim of this study was to evaluate whether sympathetic and/or the parasympathetic nerve activities were altered in an obese pediatric population. We further examined a physiological association between the duration of obesity and the sympatho-vagal activities to scrutinize the nature of ANS alteration as a possible etiologic factor of childhood obesity.

RESEARCH METHODS AND PROCEDURES

Forty-two obese and 42 non-obese healthy sedentary school children were carefully selected from 1080 participants initially recruited to this study. The two groups were matched in age, gender, and height. The clinical records of physical characteristics and development of the obese children were retrospectively reviewed to investigate the onset and progression of obesity. The ANS activities were assessed during a resting condition by means of heart rate variability power spectral analysis, which enables us to identify separate frequency components, i.e., total power (TP), low-frequency (LF) power, and high-frequency (HF) power. The spectral powers were then logarithmically transformed for statistical testing.

RESULTS

The obese children demonstrated a significantly lower TP (6.77 +/- 0.12 vs. 7.11 +/- 0.04 ln ms(2), p < 0.05), LF power (6.16 +/- 0.12 vs. 6.42 +/- 0.05 ln ms(2), p < 0.05), and HF power (5.84 +/- 0.15 vs. 6.34 +/- 0.07 ln ms(2), p < 0.01) compared with the non-obese children. A partial correlation analysis revealed that the LF and HF powers among 42 obese children were negatively associated with the duration of obesity independent of age (LF: partial r = -0.55, p < 0.001; HF: partial r = -0.40, p < 0.01). The obese children were further subdivided into two groups based on the length of their obesity. All three spectral powers were significantly reduced in the obese group with obesity of >3 years (n = 18) compared to the group with obesity of <3 years.

DISCUSSION

Our data indicate that obese children possess reduced sympathetic as well as parasympathetic nerve activities. Such autonomic depression, which is associated with the duration of obesity, could be a physiological factor promoting the state and development of obesity. These findings further imply that preventing and treating obesity beginning in the childhood years could be an urgent and crucial pediatric public health issue.

Abnormal postexercise cardiovascular recovery and its determinants in patients after right ventricular outflow tract reconstruction

BACKGROUND

Abnormal responses of heart rate (HR) and oxygen uptake (VO2) during exercise characterize patients after right ventricular outflow tract reconstruction (RVOTR) for congenital heart defects. However, little is known about the postexercise dynamics.

METHODS AND RESULTS

We evaluated postexercise cardiovascular dynamics in 52 patients after closure of an atrioventricular septal defect (group A), 79 patients after RVOTR (group B), and 44 control subjects. HR variability, arterial baroreflex sensitivity (BRS), plasma norepinephrine, and hemodynamics were measured. Although there was no difference between group A and control subjects, declines in HR and VO2 after light and peak exercise and in systolic blood pressure (SBP) after peak exercise were delayed in group B. Age, low-frequency component of HR variability, and plasma norepinephrine were independent determinants of early HR decline. Peak SBP and VO2 had a great impact on the corresponding recoveries. When the peak values were excluded, body weight, BRS, and right ventricular ejection fraction were independent determinants of early SBP decline. BRS and the pulmonary artery resistance were independent determinants of VO2 decline throughout recovery, and age and right systolic ventricular pressure also determined the early VO2 decline. BRS and low-frequency component of HR variability were determined independently by the number of surgical procedures.

CONCLUSIONS

In RVOTR patients, in addition to metabolic and autonomic maturation, surgery-related abnormal cardiac autonomic nervous activity and impaired hemodynamics have a great impact on delayed postexercise cardiovascular recovery.

Effect of standing on short term heart rate variability across age

This study examined the response of heart rate variability measures to standing in three age groups of male subjects: Children (6-11 years), young adults (20-30 years) and elderly (60-70 years). Supine and standing heart rate variability indices were measured in all the subjects using power spectral analysis. The effect of posture on heart rate variability was assessed using the change in heart rate variability measures over resting values during the first 2 min following active standing. There was an attenuated response in normalized low frequency (LF) and high frequency (HF) power to standing in the elderly as compared with young adults and children. Heart rate variability responses to standing were highest in the young adults, followed by the children and the elderly, although the differences between the young adults and children were not significant. More studies are needed to characterize HRV responses to posture in children.

Decreased chaos of heart rate time series in children of patients with panic disorder

This study examined the differences of heart rate variability measures between children of parents with panic disorder and children of healthy controls using linear as well as nonlinear techniques. Supine and standing heart rate variability indices were measured in all children using power spectral analysis and a measure of chaos, the largest Lyapunov exponent (LLE) of heart rate time series. No significant differences emerged between the children of panic disorder parents and children of normal controls on any of the spectral heart rate variability measures. However, children of patients with panic disorder had significantly lower LLE of heart rate time series in supine posture, suggesting a relative decrease of cardiac vagal function in this group of children. This suggests a possible heritable effect of certain measures of heart rate variability, as previous studies showed decreased heart rate variability in patients with panic disorder using spectral as well as nonlinear techniques. Recent evidence also suggests that some of these nonlinear measures are superior or of additional value to the traditional time and frequency domain measures of heart rate variability to predict serious ventricular arrhythmias and sudden death.

Heart rate variability in healthy children and adolescents is partially related to age and gender

We evaluated 24-h time-domain heart rate variability (HRV) in 103 (46 females) healthy children and adolescents. Subjects were divided into four male and four female groups (ages 1-5, 6-10, 11-15, 16-20 years) and 24-h ambulatory Holter monitoring was performed. HRV was assessed by SDNN, SDNN index (SDNN-i), SDANN, rMSSD, pNN50. Males showed SDNN and SDANN values significantly higher than females while for SDNN-i, rMSSD, pNN50 there were no significant differences between sexes. With increasing age, there is a progressive and significant decrease of HR and increase of SDANN. On the other hand, SDNN, SDNNi, pNN50 and rMSSD increased significantly only between the first two age-groups. rMSSD and pNN50 were significantly related to body mass index. Thus, SDNN and SDANN, overall HRV measures, increased with age and were gender-related. HRV indices of parasympathetic function (rMSSD, pNN50) and SDNN-i increased up to 10 years of age and were gender-unrelated. These data demonstrate that in healthy children and adolescents there is a progressive modification of HRV that may reflect a progressive evolution of the autonomic nervous system, with different pattern measure-dependent. This paper enables us to compare, in future works, HRV in pediatric subjects in different groups according to the different HRV measures under examination.

Cardiovascular indices of physiological arousal in boys with fragile X syndrome

In this study, the relationship between physiological arousal, as indexed by heart rate variability, was examined in boys with fragile X syndrome (FXS) and typically developing boys matched on chronological age. In addition, the relationship of heart activity to clinical and molecular factors in the group of boys with FXS was examined. Results suggest that boys with FXS have higher levels of heart activity during the passive phases, as reflected in shorter heart periods. This high level of heart activity appears to be due to increased sympathetic activity and reduced parasympathetic activity. Boys with FXS did not display the expected patterns of heart activity in response to phases of increasing challenge, and sympathetic and parasympathetic systems did not appear coordinated in these boys with FXS. Clinical factors may be related to neural regulation of heart activity while molecular factors do not appear to be.

Standardized tests of heart rate variability: normal ranges obtained from 309 healthy humans, and effects of age, gender, and heart rate

The authors undertook this study to determine the effects of age, gender, and heart rate (HR) on the results of cardiac autonomic function tests for measuring heart rate variability (HRV) in a large sample of healthy subjects (n = 309). Conventional tests (deep breathing, maximum/minimum 30:15 ratio), and a standardized 5-minute resting study, including spectral analysis of HR, were used. The main findings included (1) the indices of all tests, except for the ratio of the low- (LF) to high-frequency (HF) spectral power (LF/HF ratio) and HR itself, are inversely related to age in both sexes; (2) the 5-minute spectral bands (except for the LF/HF ratio), the variation coefficient, expiratory-inspiratory ratio during deep breathing, and the maximum/minimum 30:15 ratio are independent of HR; (3) women up to the age of 55 years have a higher resting HR compared with men; (4) young and middle-aged women show a significantly lower LF power and LF/HF ratio compared with age-matched men, whereas no significant gender differences are observed in the absolute HF power. The authors computed age- and gender-dependent normal values for each of the HRV indices studied here and discuss the clinical consequences arising from gender differences in HRV.

Spectral analysis of left ventricular area variability as a tool to improve the understanding of cardiac autonomic control

Spectral analysis of the fluctuations in heart rate (HR) or blood pressure (BP) has been extensively used as a tool for the noninvasive assessment of autonomic control of the heart. The recently developed echocardiographic acoustic quantification allows noninvasive continuous measurement of the left ventricular cross-sectional area (LVA) signal. In this study, we investigated whether the LVA signal, and more specifically its fluctuations, can be reliably subjected to spectral analysis, and whether the results of such analysis may improve the understanding of the cardiovascular control mechanisms. Our results show that the general pattern of power spectra of LVA fluctuations, as well as their reproducibility, is similar to the power spectra of HR and BP fluctuations. Analysis of LVA signals obtained in normal subjects at rest as well as under vagal blockade and under held respiration, and in patients with known autonomic dysfunction, showed significant differences between groups and states. The effects of age, related to the reduction in parasympathetic activity, were not evident in the spectral content of the LVA and BP signals. The high frequency LVA fluctuations are mainly of mechanical origin, since they were eliminated by breath-holding. We observed an increase in the high frequency LVA fluctuations under vagal blockade, indicating that under normal (control) conditions, these high frequency fluctuations are attenuated by parasympathetic activity. The enhancement in high frequency fluctuations in LVA observed in diabetic patients can thus be attributed to reduced parasympathetic activity. The analysis of LVA variability may be used as a tool for basic research and, possibly, as a quantitative clinical measure for specific disease states.

Heart rate recovery after exercise and cardiac autonomic nervous activity in children

To investigate the difference in heart rate (HR) recovery after exercise between children and young adults, we administered a constant load of light exercise intensity and progressive treadmill exercise tests to nine children (aged 9 to 12 y, group A) and eight young adults (six male and two female, aged 17 to 21 y, group B) who had a history of Kawasaki disease without significant coronary arterial lesions. HR after both exercise protocols was analyzed. The low-frequency (LF) and high-frequency (HF) components of HR variability were measured, and LF/HF was calculated (log LF, log HF, log L/H). Arterial baroreflex sensitivity was assessed by the phenylephrine method. There were no differences between groups A and B in resting HR, peak HR, peak oxygen uptake, and decreases in systolic blood pressure during the recovery period. HR 1 and 2 min after peak exercise and 1 min after constant-load exercise was significantly lower in group A than in group B (p < 0.05), and the changes in HR from peak values after both exercise tests were also greater in group A than in group B (p < 0.05-0.01). Although no difference in arterial baroreflex sensitivity was observed, log HF was significantly higher in group A than in group B (p < 0.01), and log L/H was significantly lower in group A than in group B (p < 0.05). The value of log HF correlated inversely with the decrease in HR immediately after both exercise protocols (p < 0.05-0.01). Although log L/H correlated with the decrease in HR after peak exercise (p < 0.05-0.0005), the early decline in HR after constant-load exercise did not correlate with log L/H. Arterial baroreflex sensitivity did not correlate with the decrease in HR at any recovery time. These data suggest that the early phase of HR recovery after light to severe exercise is influenced by the cardiac parasympathetic nervous activity at rest and that the greater central cholinergic modulation of HR in children than in young adults may be responsible in part for children's faster HR recovery after exercise.

Effects of sleep stage and age on short-term heart rate variability during sleep in healthy infants and children

STUDY DESIGN

Power spectrum analysis of heart rate variability (HRV) is a noninvasive technique that provides a quantitative assessment of cardiovascular neural control. Using this technique, we studied the autonomic nervous system changes induced by sleep in 14 healthy subjects: 7 infants (mean age, 9.40 +/- 2.32 months) and 7 children (mean age, 8.93 +/- 0.65 years) during a standard all-night polysomnographic recording. Our primary aim was to assess the effect of sleep stage and age on short-term HRV during sleep in healthy infants and children. Power spectral density was estimated by autoregressive modeling over 250 consecutive R-R intervals. In this study, we mainly considered two spectral components: the high-frequency (HF) component (0.15 to 0.40 Hz), which reflects parasympathetic cardiovascular modulation; and the low-frequency (LF) component (0.04 to 0.15 Hz), generally considered due to both parasympathetic and sympathetic modulation.

RESULTS

Heart rate was higher (p < 0.01 in all sleep stages) and total power lower (p < 0. 02) in infants than in children. HF power was higher in children than in infants (p < 0.05). In infants and children, the ratio between LF and HF powers changed with the various sleep stages (p < 0.02 in infants; p < 0.01 in children): it decreased during deep sleep and increased during rapid eye movement sleep. However, it was invariably lower in children than in infants.

CONCLUSION

These findings show that the sleep stage and age both significantly influence short-term HRV during sleep in healthy infants and children. Hence, to provide unbiased results, HRV studies investigating the effects of age on autonomic nervous system activity should segment sleep into the five stages. In addition, despite a relatively small study sample, our data confirm greater parasympathetic control during sleep in children than in infants.

Short-term rhythms of the cardiorespiratory system and their significance in neonatology

Latent disturbances in the control of respiration and heart rate (HR) may be important factors in the pathogenesis of life-threatening events during infancy. A method of determining the control of the autonomic nervous system functions involves the analysis of time-dependent ultradian changes of its parameters. The breathing signal and HR variability contain rhythmic components that are generated within the cardiorespiratory network of the brain stem, through reflexes, and by feedback mechanisms. The analysis of these components may provide insights into the functioning of the cardiorespiratory control system. The prominence and precision of the rhythms are correlated with states of vigilance and underlie distinct development during the first months of life. The results of studies on infants at risk (for example, for sudden infant death), with the help of statistical and spectral analysis of time series to obtain new indices, have proved to be inconsistent in their prognostic value of thus studied parameters. Recently, the importance of qualitative and quantitative assessment of the dynamic and complex behavior of time series, based on nonlinear characteristics of the control system, has been emphasized. To what extent, however, the analysis of the dynamic behavior can be utilized for clinical purposes, such as judging the prognosis of deficiencies in control, requires further study regarding physiological baselines and the possible changes resulting from pathological states.

Heart rate variability; an index for monitoring and analyzing human autonomic activities

Heart rate variability (HRV), a non-invasive index of autonomic controls of the heart, has extensively been employed in various fields of study. The application range of this index persists to expand over the research horizon, and the need continues to demand technical complements for hitherto known deficiencies. Concurrent technical advances in recent years have yielded methodological techniques capable of performing quantitative analysis of HRV. However, as various approaches designed for HRV analysis exist, quantitative comparisons of the investigations have become difficult. Current physiological interpretations of the components of HRV are also inconsistent. Moreover, the issue of respiratory control has been much disputed when determining the HRV. In an attempt to clarify the current controversial state in HRV measurement, the present paper, based on the physiological background of HRV, pursued various procedures of HRV measurement and furnished global explanations for special features characterizing the various analytical approaches adopted thereof.

Impairment of autonomic function induced by posture change in postmenopausal women

This study was designed to determine if there is a difference in autonomic regulation induced by posture change between postmenopausal and young women. To evaluate autonomic nervous system function, spectral analysis of heart rate variability (HRV) was done in postmenopausal women (n = 13, 46-59 years of age), age-matched men (n = 8, 45-55 years of age), and young women (n = 10, 20-37 years of age) for 3-min periods of controlled frequency breathing (15 breaths/min) in supine followed by sitting positions. In the supine position, the R-R interval variation in older persons decreased significantly compared with that during the follicular phase in young women. Furthermore, the high-frequency (HF) components of HRV, which reflect only parasympathetic activity, were lower in older subjects than in young women. Following a change of position from supine to sitting, the HF component did not change significantly in the postmenopausal women or the men, but the low/high frequency (LF/HF) component ratio, which reflects the balance of autonomic nerve activities, increased significantly in the men. These results suggest that cardiac parasympathetic tone may be reduced in older persons in comparison with young women. Furthermore, arterial baroreflex control of parasympathetic nerve activity caused by posture changes is impaired in the postmenopausal women and aged-matched men. The baroreflex control of the sympathetic component is maintained in the men but not in the postmenopausal women. These differences might result in part from changes in the level of female hormones.

Decreased heart-period variability in patients with panic disorder: a study of Holter ECG records

This study investigated cardiac autonomic function in patients with panic disorder and normal controls using Holter ECG records. A decrease in ultra-low frequency power (< 0.0033 Hz) is known to be associated with an increased risk for cardiovascular mortality in humans. Twenty-four-hour ECG was recorded in 29 patients with panic disorder and 23 normal controls using Holter records. Data for 20 h and also 20000 s of awake and 20000 s of sleep periods were analyzed using spectral analysis to quantify absolute and relative heart-period variability in ultra low (ULF: < 0.0033 Hz), very low (VLF: 0.0033-0.04 Hz), low (LF: 0.04-0.15 Hz) and high (HF: 0.15-0.5 Hz) frequency bands. The patients with panic disorder had significantly lower total and absolute ULF power, which was more pronounced during sleep. The patients also had significantly lower relative ULF power and significantly higher relative LF power during sleep. There was a significant increase of relative LF power from awake to sleep period only in the patient group. The decrease in total and ULF power may increase the risk of mortality and sudden arrhythmic death in patients with panic disorder if they experience a cardiac event. The higher relative LF power during sleep also suggests a possible higher sympathetic drive in the patients during sleep.

Tricyclic antidepressants and cardiac autonomic control in children and adolescents

OBJECTIVE

To elucidate the effects of tricyclic antidepressants on sympathetic and vagal modulation of heart rate variability.

METHOD

Seventy-five children and adolescents (mean age 10.5 years, SD 2.0) from therapeutic and regular schools underwent challenges of paced breathing and orthostatic postural change, while heart rate was continuously recorded. Teachers completed dimensional ratings of behavior to quantity anxiety and conduct disorder. Spectral analysis of heart rate variability was utilized to decompose the postural (sympathetic) and respiratory (vagal) contributions to beat-to-beat variations in heart rate.

RESULTS

Under conditions in which cardiac vagal effects were expected to predominate, subjects medicated with tricyclic antidepressants (n = 13) showed significantly reduced vagal modulation of heart rate variability (F[5,69] = 5.23, p < .003), higher heart rates (F[5,69] = 5.54, p < .002), and higher relative sympathovagal balance (F[5,69] = 5.51, p < .002) than nonmedicated (n = 42) and medicated comparison groups (n = 20), even after controlling for the effects of age and psychopathology.

CONCLUSIONS

The relative loss of cardiac vagal control in young subjects medicated with tricyclic antidepressants, considered in the context of factors known to be associated with the development of tachyarrhythmias, presents as yet another risk, especially when coupled with factors such as maturational effects and psychopathology.

Age effects on interrelationships between lung volume and heart rate during standing

To determine the effects of aging and posture on the relationship between respiration and heart rate (HR), we collected 5 min of lung volume and R-R interval data from 7 young (27 +/- 3 yr, mean +/- SD) and 10 old (69 +/- 6 yr) healthy humans during spontaneous breathing while they were supine (SU) and standing (ST). Lung volume and HR power spectra and transfer functions between lung volume and HR were estimated. Age and position effects and age-position interactions were determined by analysis of variance for repeated measures. Older subjects had a lower and more variable respiration rate (P < 0.03, P < 0.04), but both age groups exhibited decreased rate of respiration and increased tidal volume with ST (P < 0.05, P < 0.005). ST decreased lung volume-to-HR transfer function magnitude in both groups (P < 0.07). The more marked age-related differences were in phase angle. Both SU and ST phase angles were greater in older subjects (P < 0.003). ST decreased phase angle in young but increased phase angle in older subjects (P < 0.001). In conclusion, respiration, and respiration-HR interrelationships are altered by aging, with increased time delays between lung volume and HR and altered relationships with ST.

Effect of age on long-term heart rate variability

OBJECTIVE

Previous studies on short-term time series of heart rage suggest an inverse relationship between age and spectral powers of heart rate variability in various frequency bands. In this study, we examined the relationship between age (6-61 years) and long-term heart rate variability.

METHODS

We obtained 24-h Holter ECG in 33 healthy human subjects (11 children and 22 adults). The heart rate data were analyzed by using spectral analysis and fractal dimensions of the time series.

RESULTS

We found a significant negative correlation between age and very low frequency (VLF, 0.0033-0.04 Hz), low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-0.5 Hz) powers and fractal dimensions during awake as well as sleep periods, and a positive correlation between age and LF/HF ratios. Age and ultra-low frequency (ULF, < 0.0033 Hz) were modestly and negatively correlated only during the awake period.

CONCLUSIONS

Sleep ULF power is not significantly affected by age, whereas VLF, LF and HF powers and fractal dimensions of heart rate significantly decrease with age during awake as well as sleep periods.

Plasma neuropeptide Y and catecholamines in pediatric patients undergoing cardiac operations

OBJECTIVE

Our objective was to assess the sympathoadrenal response in pediatric patients undergoing repair of congenital cardiac defects.

METHODS

Plasma catecholamine (norepinephrine and epinephrine) and neuropeptide Y concentrations were quantified before and after cardiopulmonary bypass to assess the response to cardiopulmonary bypass. To determine the response to aortic occlusion, levels of plasma catecholamines and neuropeptide Y were measured at the time of and immediately after release of the aortic crossclamp.

RESULTS

During cardiopulmonary bypass, no significant change in levels of plasma norepinephrine (n = 43), epinephrine (n = 37), or neuropeptide Y (n = 46) was observed. Aortic occlusion induced a significant increase in plasma neuropeptide Y, but not in catecholamines. There was a greater increase in plasma neuropeptide Y in children older than age 1 year than in those younger than 1 year.

CONCLUSIONS

Plasma neuropeptide Y may be a useful marker of sympathetic nervous system activity. Children younger than age 1 year showed a lesser sympathetic response compared with the response in older children.

Presyncopal sympathetic withdrawal is the same in patients with vasodepressor syncope and controls who faint on head-up tilting

Head-up tilt provokes vasodepressor syncope in patients with this disorder but may also cause fainting in unaffected subjects. The aims of this study were to examine autonomic function and sequential changes in heart rate variability and plasma catecholamines during graded head-up tilt in patients with vasodepressor syncope compared with healthy subjects. Studies were performed in 10 patients and 15 control subjects. Eight negative controls completed the study; presyncope or syncope developed in seven positive controls and all 10 patients. The negative control group showed a progressive increase in mid-frequency from the supine position to end tilt. Patients and positive controls showed significant and similar falls in mid-frequency in the presyncope period. The rise in plasma norepinephrine was blunted in patients and positive controls, whereas plasma epinephrine increased more in these groups compared with the negative control group. In conclusion, the patterns of heart rate variability and catecholamine changes could not be distinguished in patients and positive control subjects.

Heart rate variability and the outcome of head-up tilt in syncopal children

Neurocardiogenic syncope may be caused by enhanced sympathetic activity evoking a vasodepressor-cardioinhibitory reflex. Heart rate variability (HRV) methods can be used to assess the modulation of sympathetic and parasympathetic activity. To determine whether HRV measurements are related to the outcome of head-up tilt testing (HUT), we studied 29 syncopal patients aged 7-19 y. After 30 min supine, patients were tilted to 80 degrees for 30 min or until syncope occurred. Sequential beats free from ectopy were analyzed. Time domain indices included SD (SDNN), root mean square successive differences (RMSSD), percent exceeding 50 ms (pNN50). An autoregressive model was used to calculate power spectra. Low frequency power (LFP, 0.05-0.15 Hz), high frequency power (HFP, 0.15-0.40 Hz), and total power (TP, 0.01-0.40 Hz) were compared before and after tilt. Data were obtained supine before tilt (baseline), within 5 min after HUT (early), 5-10 min after HUT (mid), and 15 min after HUT or presyncope (late). Seventeen patients fainted (HUT+), and 12 patients did not (HUT-). Variability indices were different for HUT- and HUT+ at baseline: SDNN was 123 +/- 17 versus 78 +/- 6, RMSSD was 127 +/- 23 versus 64 +/- 6 ms, pNN50 was 51 +/- 6 versus 31 +/- 4, respectively. Spectral data demonstrated decreased HFP and TP in HUT+ (834 +/- 133 and 2855 +/- 420 ms2) versus HUT- (3433 +/- 840 and 7062 +/- 1500). With tilt, SDNN, RMSSD, and pNN50 decreased proportionately in HUT- and HUT+. However, sympathovagal balance, measured by the ratio LFP/HFP and by normalized LFP, was markedly increased in HUT+ (2.2 +/- 0.7 and 0.43 +/- 0.03) compared with HUT- (0.8 +/- 0.2 and 0.31 +/- 0.02) at baseline and differences increased with tilt. With syncope, sympathetic activity decreased, and parasympathetic activity increased. Decreased RR variability with decreased parasympathetic activity and increased indices of sympathovagal balance before HUT predict a positive tilt test in children referred for evaluation of neurocardiogenic syncope.

Postural effect on respiratory sinus arrhythmia with various respiratory frequencies

Heart rate variations during steady state respiration with various frequencies were studied on seven healthy male students at two different body positions. Respiration was controlled at four different frequencies (0.083, 0.100, 0.200, 0.250Hz), and the tidal volume was simultaneously controlled at 1500ml (0.083, 0.100Hz) or 1000ml (0.200, 0.250Hz). A tilting bed was used for changing body position, and the measurements were conducted at horizontal and vertical position. RSA (respiratory sinus arrhythmia) amplitude at 0.250Hz was significantly decreased at vertical position compared with horizontal position. At 0.200Hz the significant decrease could not be obtained although some tendency of decrease appeared. Contrary to these high frequencies, the amplitudes at low frequencies (0.083, 0.100Hz) were significantly increased (p < 0.01) during vertical position. This postural effect on the low frequency RSA could be regarded as a similar result on MWSA (Mayer wave relate sinus arrhythmia) which reflects sympathetic nervous activity. Furthermore, the ratio between the amplitude at 0.100Hz and that at 0.250Hz was significantly correlated with mean heart rate (n = 56, r = 0.73). From these results it was assumed that the RSA amplitude at low frequency associate a with not only parasympathetic nerves but also sympathetic nerves whereas the amplitude at high frequency was solely mediated by parasympathetic nerves.

Sodium lactate increases sympathovagal ratios in normal control subjects: spectral analysis of heart rate, blood pressure, and respiration

We used spectral analysis of heart rate (HR), blood pressure (BP), and respiration to examine the effects of lactate on cholinergic and adrenergic influences on HR and BP variability, a technique found to be very useful in cardiovascular research. We specifically used high frequency (0.2-0.5 Hz) and midfrequency (0.07-0.15 Hz) powers to study cholinergic and adrenergic activity in nine normal control subjects before and after lactate and placebo infusions. Our results demonstrate a marked decrease in cholinergic activity and a significant increase in sympathovagal ratios of HR modulation after lactate infusions. This altered sympathovagal balance may contribute to the panicogenic effects of lactate in panic disorder patients.