Cardiac Autonomic Regulation Research Articles

Utilizing heart rate variability to predict ICU patient outcome in traumatic brain injury

BackgroundPrediction of patient outcome in medical intensive care units (ICU) may help for development and investigation of early interventional strategies. Several ICU scoring systems have been developed and are used to predict clinical outcome of ICU patients. These scores are calculated from clinical physiological and biochemical characteristics of patients. Heart rate variability (HRV) is a correlate of cardiac autonomic regulation and has been evident as a marker of poor clinical prognosis. HRV can be measured from the electrocardiogram non-invasively and monitored in real time. HRV has been identified as a promising ‘electronic biomarker’ of disease severity. Traumatic brain injury (TBI) is a subset of critically ill patients admitted to ICU, with significant morbidity and mortality, and often difficult to predict outcomes. Changes of HRV for brain injured patients have been reported in several studies. This study aimed to utilize the continuous HRV collection from admission across the first 24 h in the ICU in severe TBI patients to develop a patient outcome prediction system.ResultsA feature extraction strategy was applied to measure the HRV fluctuation during time. A prediction model was developed based on HRV measures with a genetic algorithm for feature selection. The result (AUC: 0.77) was compared with earlier reported scoring systems (highest AUC: 0.76), encouraging further development and practical application.ConclusionsThe prediction models built with different feature sets indicated that HRV based parameters may help predict brain injury patient outcome better than the previously adopted illness severity scores.

Cardiac Autonomic Responses and Adaptation to Repeated Bouts of Eccentric Exercise

PURPOSE:The current study was performed to examine the effects of acute eccentric resistance exercise (ERE) on heart rate variability (HRV) and to determine whether cardiac autonomic regulation adapts to the repeated bout effect.METHODS: Isokinetic eccentric exercise consisted of five sets of six maximal contractions of the knee extensor with an angular velocity of 90°/second. College-aged men (n=11) underwent two sessions of ERE with a 3-week interval. Muscle damage indicators such as the range of motion (ROM) and muscle echo intensity (EI) were measured. The post-exercise cardiac autonomic response was assessed by spectral analysis of HRV. Low frequency (LF) and high frequency (HF) bands, the normalized unit (nu) for each band power, and the LF-to-HF (LF/HF) ratio were determined. All variables were recorded at 24, 48, 72, and 96 hours post-exercise as well as before and immediately after ERE.RESULTS:The EI and ROM of the rectus femoris changed significantly after the maximal ERE. There was a significant interaction effect between the time and bout for EI. Significant changes in LF and HF nu were observed at 72 (1st ERE) and 96 hours (2nd ERE) after each ERE. The LF/HF ratio was also significantly increased at 24 (1st ERE) and 72 hours (2nd ERE) after each ERE. However, no interaction effects on changes in the HRV indices were observed.CONCLUSIONS: The present study suggests that acute ERE leads to cardiac autonomic imbalance for a sustained period and that repeated bouts of ERE cannot alleviate cardiac autonomic responses to exercise.

Heart rate variability as an autonomic biomarker in ischemic stroke.

Stroke is one of the leading causes of mortality and disability worldwide. Autonomic dysfunction after ischemic stroke is frequently associated with cardiac complications and high mortality. The brain-heart axis is a good model for understanding autonomic interaction between the autonomic central network and the cardiovascular system. Heart rate variability (HRV) analysis is a non-invasive approach for understanding cardiac autonomic regulation. In stroke patients, HRV parameters are altered in the acute and chronic stages of the disease, having a prognostic value. In this literature review we summarize the main concepts about the autonomic nervous system and HRV as autonomic biomarkers in ischemic stroke.

Exercise Enhances the Effect of Bariatric Surgery in Markers of Cardiac Autonomic Function.

Bariatric surgery improves cardiovascular health, which might be partly ascribed to beneficial alterations in the autonomic nervous system. However, it is currently unknown whether benefits from surgery on cardiac autonomic regulation in post-bariatric patients can be further improved by adjuvant therapies, namely exercise. We investigated the effects of a 6-month exercise training program on cardiac autonomic responses in women undergoing bariatric surgery. Sixty-two women eligible for bariatric surgery were randomly allocated to either standard of care (control) or an exercise training intervention. At baseline (PRE) and 3 (POST3) and 9 (POST9) months after surgery, we assessed chronotropic response to exercise (CR%; i.e., percentage change in heart rate from rest to peak exercise) and heart rate recovery (HRR30s, HRR60s, and HRR120s; i.e., decay of heart rate at 30, 60, and 120 s post exercise) after a maximal exercise test. Between-group absolute changes revealed higher CR% (Δ = 8.56%, CI95% 0.22-19.90, P = 0.04), HRR30s (Δ = 12.98 beat/min, CI95% 4.29-21.67, P = 0.01), HRR60s (Δ = 22.95 beat/min, CI95% 11.72-34.18, P = 0.01), and HRR120s (Δ = 34.54 beat/min, CI95% 19.91-49.17, P < 0.01) in the exercised vs. non-exercised group. Our findings demonstrate that exercise training enhanced the benefits of bariatric surgery on cardiac autonomic regulation. These results highlight the relevance of exercise training as a treatment for post-bariatric patients, ensuring optimal cardiovascular outcomes.

Heart rate variation and human body burdens of environmental mixtures in the Cree First Nation communities of Eeyou Istchee, Canada

IntroductionHeart rate variability (HRV) is a measure of cardiac autonomic regulation that examines the variation in beat-to-beat fluctuations in heart rate. While many exposure-based studies have examined the effects of single or similar groups of contaminants on HRV parameters, none have examined the association between complex environmental mixtures, including organic and elemental contaminants, and HRV. MethodsUsing data collected from the Multi-Community Environment-and-Health Study in Eeyou Istchee (Quebec, Canada), we assessed HRV in two time domain measures: root mean square of successive differences (RMSSD) and standard deviation of the N-N (RR) intervals (SDNN); and in three frequency domains: high frequency (HF), low-frequency (LF), and very-low frequency (VLF) in 443 participants. We first examined mixture effects of nineteen organic and metal contaminants in blood using principal component analysis (PCA) and a multivariable general linear regression on HRV responses, adjusting for age, sex, body mass index, smoking status, and kidney disease covariates. We subsequently assessed HRV outcome response variables using Bayesian kernel machine regression (BKMR) to further examine individual contaminant contribution and overall mixture effects. ResultsIn the PCA, a significant positive association was observed between RMSSD and principal component (PC) axis 2, which was highly positively-loaded for nickel and moderately negatively-loaded for mercury. A negative association between SDNN and PC-1, which was highly positively-loaded for all PCBs (polychlorinated biphenyls) and organochlorines and moderately positively-loaded for mercury, was observed. Additionally, a significant and positive association was observed between PC-2 and SDNN and a significant and negative association between PC-3 (negatively loaded for cadmium) and LF. Associations with contaminants were not observed for HF or VLF. BKMR results suggest that trans-nonachlor and cis-nonachlor are primarily responsible for reductions in HRV; however, their contributions to HRV deficits was non-significant when examined as a complete mixture. ConclusionsWhile PCA results suggested that organochlorines, mercury, nickel, and cadmium may all play a role in altering various HRV, subsequent BKMR analysis illustrated the individual components driving these effects may be trans- and cis-nonachlor and nickel and likely not mercury or cadmium. However, other contaminants appear to temper this effect when the entire mixture of chemicals is assessed as a whole. This study expands our knowledge of the effects of environmental contaminant mixtures on HRV, which is especially important in exposed populations such as those in the Eeyou Istchee territory, whilst utilizing novel statistical methods such as PCA and BKMR to examine co-exposures concurrently.

Propofol suppresses the His-ventricular conduction in paediatric patients.

What is known and objectivePropofol is the most commonly used intravenous anaesthetic worldwide and is considered to be safe for all ages. However, there have been some reports that propofol induces severe atrioventricular (AV) blocks in humans and some studies demonstrated that propofol suppressed the cardiac conduction system in animals. A precise mechanism by which the block is induced has not been elucidated yet in humans. The objective of this study was to investigate the effects of propofol on the cardiac conduction system and the cardiac autonomic nervous balance in children.MethodsWe enrolled 23 paediatric patients (age: 6‐15 years; males: 16, females: 7) who were scheduled to undergo radiofrequency catheter ablation (RFCA) under general anaesthesia. Anaesthesia was induced with 2 mg/kg propofol and 0.5 µg/kg/min remifentanil, and tracheal intubation was performed with the aid of 1 mg/kg rocuronium. Anaesthesia was maintained with 5‐7 mg/kg/h propofol and 0.2 µg/kg/min remifentanil during the RFCA. After the completion of the RFCA, anaesthesia was further maintained with 5 mg/kg/h propofol and 0.2 µg/kg/min remifentanil for at least 10 min (LC: low propofol concentration state), followed by the injection of 2 mg/kg propofol and the infusion of 10 mg/kg/h propofol for 10 min (HC: high propofol concentration state). The sinus node recovery time (SNRT), sinoatrial conduction time (SACT), atrial‐His (AH) interval and the His‐ventricular (HV) interval were measured at the end of both the LC and HC. Cardiac autonomic regulation was simultaneously assessed based on heart rate variability.Results and discussionPropofol significantly suppressed intrinsic cardiac HV conduction, but did not affect the SNRT, SACT or the AH interval. As HV blocks, which occur below the His bundle, are often life‐threatening, the HV conduction delay may be a cause of severe AV blocks induced by propofol. Propofol directly suppressed parasympathetic nerve activity, and sympathetic nerve activity was also suppressed.What is new and conclusionThese results indicate that propofol suppresses the HV conduction and might help to elucidate the mechanism by which propofol causes lethal AV blocks.

Binary symbolic dynamics analysis to detect stress-associated changes of nonstationary heart rate variability

Psychological stress may have harmful physiological effects and result in deteriorating health. Acute psychological stress acts also on cardiac autonomic regulation and may lead to nonstationarities in the interbeat interval series. We address the requirement of stationary RR interval series to calculate frequency domain parameters of heart rate variability (HRV) and use binary symbolic dynamics derived from RR interval differences to overcome this obstacle. 24 healthy subjects (12 female, 20–35 years) completed the following procedure: waiting period, Trier Social Stress Test to induce acute psychological stress, recovery period. An electrocardiogram was recorded throughout the procedure and HRV parameters were calculated for nine 5-min periods. Nonstationarities in RR interval series were present in all periods. During acute stress the average RR interval and SDNN decreased compared to rest before and after the stress test. Neither low frequency oscillations (LF), high frequency oscillations (HF) nor LF/HF could unambiguously reflect changes during acute stress in comparison to rest. Pattern categories derived from binary symbolic dynamics clearly identified acute stress and accompanying alterations of cardiac autonomic regulation. Methods based on RR interval differences like binary symbolic dynamics should be preferred to overcome issues related to nonstationarities.

A Simple Home-Based Lifestyle Intervention Program to Improve Cardiac Autonomic Regulation in Patients with Increased Cardiometabolic Risk

Lifestyle modification programs (LMP) represent a new approach to cardiometabolic/oncologic risk reduction. Successful LMP in clinical practice must be feasible, cost effective, efficacious and consider home-based exercise. Likewise, multiple mechanisms implied in cardiometabolic risk reduction such as cardiac autonomic regulation (CAR) should be easily evidenced, in spite of the computational complexity involved. This goal could be facilitated by employing novel, friendlier, simpler techniques, such as the Autonomic Nervous System Index (ANSI), which can be treated as a proxy of CAR. In this observational study, we introduce a simple LMP (based on cognitive behavioral strategies and patient-tailored prescription of nutrition and home-based exercise, managed by a single physician) into the currently existing clinical practice of secondary cardiometabolic prevention. In 26 subjects, we assessed CAR (autoregressive spectral analysis of cardiovascular variabilities), body mass composition (bioelectrical impedance analysis) and stress perception (questionnaires). After LMP, ANSI and lipid profile were improved; % of fat mass, waist circumference and stress perception were reduced. We conclude that this preliminary, proof of concept study provides significant evidence in favor of the hypothesis that it is possible to introduce a convenient, cost effective LMP into the currently existing clinical practice of secondary cardiometabolic prevention. Findings suggest a successful comprehensive behavioral change, possibly facilitated by the simplified approach employed in this study, capable of improving cardiac autonomic regulation in addition to body mass composition and stress perception.

Age-Related Change in Heart Rate Variability at Resting in Thai Professional Athletes

Background: Although regular exercise is beneficially acknowledged in promoting general health status, the cardiovascular risk of sudden cardiac death in highly training athletes has been reported. Unfortunately, the primary key factor in inducing cardiac problems in athletic populations is still questioned. Objectives: In the present study, we aim to determine factors that could affect the relationship between physical activity level and cardiac autonomic function in the Thai population. Methods: Forty participants were recruited and classified into three groups based on their physical activity level and sport profession, including sedentary men, elite handball players, and professional futsal players. In all participants, we measured predicted maximal oxygen consumption, time- and frequency- domain heart rate variability (HRV) variables at rest. Results: Results demonstrated a positive correlation between time-domain HRV and estimated maximal oxygen consumption, but not with frequency-domain HRV, in which athletes aged lower than 25 years old (18 - 25 years old) had a significantly higher in the standard deviation of normal RR intervals (SDNN) and root mean square of the successive differences (RMSSD) than that in age-matched sedentary subjects. Interestingly, athletes aged above 25 years old (25 - 32 years old) had lower SDNN and RMSSD with higher low frequency/high-frequency ratio than those athletes aged under 25. Since all athletes aged above 25 years old were world-class national futsal players, stress due to the competitive level might be another factor influencing cardiac autonomic activity in athletes. Conclusions: In conclusion, the study suggested the importance of age and stress exposure on cardiac autonomic regulation in elite athletes. The observed correlation also reinforced HRV as a potential marker in detecting abnormal changes in cardiac health even in an athletic population.

Effects of High-Intensity Interval Exercise and Acute Partial Sleep Deprivation on Cardiac Autonomic Modulation

ABSTRACT Sleep deprivation in healthy adults has been associated with disrupted autonomic nervous system function, which in turn has been linked to cardiovascular health. High-intensity interval exercise (HIIE) may affect both sleep and cardiac autonomic modulation. Purpose: To investigate the impact of acute partial sleep deprivation on autonomic cardiac regulation before and after an acute bout of HIIE and the length of time for the autonomic system to return to resting levels. Methods: Fifteen healthy males with body mass index (BMI) of 25.8 ± 2.7 kg·m−2 and age 31 ± 5 y participated in a reference sleep (~9.5 hr) with no HIIE (RS), a reference sleep with HIIE (RSX), and an acute partial sleep deprivation (~3.5 hr) with HIIE (SDX). HIIE was performed in 3:2 intervals at 90% and 40% of VO2 reserve. Autonomic regulation through HRV selected time and frequency domain indices were recorded the night before, the morning of the next day, 1 hr-, 2 hr-, 4hr-, and 6-hr post-exercise. Results: HIIE performed in a 3:2 W:R ratio decreased the HRV (p < .05) at 1-hr post exercise and it took up to 4 hr to return to baseline levels. Parasympathetic related HRV indices increased the morning of the next day for SDX (p < .05). Acute partial sleep deprivation and HIIE did not modify the HRV responses compared to reference sleep and HIIE. Conclusion: HRV disturbance typically seen in responses to an acute episode of HIIE is not influenced by acute partial sleep deprivation.

The impact of high-intensity interval training exercise on breast cancer survivors: a pilot study to explore fitness, cardiac regulation and biomarkers of the stress systems

BackgroundCardiovascular disease (CVD) remains the largest cause of death in breast cancer survivors. The aim of this study was to explore the impact of exercise intensity on aerobic fitness and autonomic cardiac regulation (heart rate variability (HRV)) and salivary biomarkers of the stress systems (HPA-axis, cortisol; sympathetic nervous system, α-amylase) and mucosal immunity (secretory(s)-IgA), markers of increased risk of CVD in breast cancer survivors.MethodsParticipants were randomly assigned to; 1) high intensity interval training (HIIT); 2) moderate-intensity, continuous aerobic training (CMIT); or 3) a wait-list control (CON) for a 12-week (36 session) stationary cycling intervention. Cardiorespiratory fitness (VO2peak), resting HRV and salivary biomarkers were measured at baseline 2–4 d pre-intervention and 2–4 d post the last exercise session.ResultsSeventeen participants were included in this study (62 ± 8 years, HIIT; n = 6, CMIT; n = 5, CON; n = 6). A significant improvement (p ≤ 0.05) was observed for VO2peak in the HIIT group; 19.3% (B = 3.98, 95%CI = [1.89; 4.02]) and a non-significant increase in the CMIT group; 5.6% (B = 1.96, 95%CI = [− 0.11; 4.03]), compared with a 2.6% (B = − 0.64, 95%CI = [− 2.10; 0.82]) decrease in the CON group. Post intervention improvements in HRV markers of vagal activity (log (ln)LF/HF, LnRMSSD) and sympathetic nervous system (α-amylase waking response) occurred for individuals exhibiting outlying (> 95% CI) levels at baseline compared to general population.ConclusionHigh intensity interval training improved cardiovascular fitness in breast cancer survivors and improved cardiac regulation, and sympathetic nervous system (stress) responses in some individuals. High-intensity interval training was safe and effective for breast cancer survivors to participate in with promising results as a time efficient intensity to improve physical health and stress, reducing CVD risk.Trial registrationThis pilot study was retrospectively registered through the Australian New Zealand Clinical Trials Registry (ANZCTR): ACTRN12620000684921.

Role of the autonomic nervous system in atrial fibrillation pathogenesis

The aim of this review was to study the role of the autonomic nervous system in the pathogenesis of atrial fibrillation (AF), as well as to establish the relationship of autonomic regulation with other mechanisms underlying the AF At present, the molecular and cellular mechanisms underlying the AF have not been precisely established. There is interest in evidence showing that both sympathetic outflow and an increased vagal tone can initiate and support AF. As modern studies have shown, autonomic cardiac regulation can be an important factor in the pathogenesis of AF.

Cross system autonomic balance and regulation: Associations with depression and anxiety symptoms.

The autonomic nervous system (ANS) has demonstrated utility for identifying alterations in emotion processing associated with common psychopathology, including depression and anxiety. To date though the majority of this ANS research has several limitations. Most studies have examined parasympathetic and sympathetic branches separately, requiring activity in the other branch be inferred. This is problematic as each branch may function independently. Composite indices such as cardiac autonomic balance (CAB) and cardiac autonomic regulation (CAR) which examine the relative input between respiratory sinus arrhythmia (RSA) and pre-ejection period (PEP) should provide more comprehensive measures of autonomic functioning and thus stronger predictors of psychopathology. However, the sympathetic branch is driven by multiple neurotransmitter systems, thus PEP does not necessarily reflect overall SNS arousal. We propose two new metrics for assessing ANS functioning associated with psychopathology: parasympathetic effects on cardiac control (RSA) relative to sympathetic effects on the eccrine system (electrodermal activity, EDA), which we term cross-system autonomic balance (CSAB) and regulation (CSAR). Eighty-five women (18-37) completed a baseline physiological assessment with parasympathetic (RSA) and sympathetic indices (PEP, EDA), along with self-reported depressive and anxiety symptoms. Lower CSAB, indicating sympathetic dominance driven by cholinergic neurotransmission, was associated with higher depressive and anxiety symptoms. Lower CAB indicating sympathetic dominance driven by beta-adrenergic neurotransmission was associated specifically with depressive symptoms. CSAB was a more robust index than RSA. Results support the utility of assessing multiple composite ANS indices for identifying physiological substrates of alterations in emotion regulation associated with internalizing disorders.

Hormonal, autonomic cardiac and mood states changes during an Antarctic expedition: From ship travel to camping in Snow Island

We evaluated the influence of an Antarctic expedition, consisting of 26-day ship travel followed by 24-day camping in the Antarctic field during the summer season, on hormonal responses, autonomic cardiac control, and mood states in individuals that live in tropical regions. Data collection was carried out in 10 individuals on the 2nd, 16th, and 26th days aboard the ship (characterized by exposure to low-luminosity and temperature-controlled environments) and on the 4th, 11th, and 23rd days of camping in the Antarctic field (prolonged exposure to natural luminosity and cold environments). Morning samples of saliva (to determine testosterone and cortisol concentrations) and blood [to determine thyroid-stimulating hormone (TSH) and thyroxine (T4) concentrations] were obtained. Next, resting heart rate variability (HRV) was recorded, and the volunteers answered a mood questionnaire. Samples of saliva for measurement of melatonin concentration were obtained at night. At the end of ship travel, blood TSH and salivary melatonin increased by 15.6% and 72.3%, respectively, whereas salivary cortisol reduced by 37.1% compared to initial values and T4 reduced by 12.2% compared to 16th day. These hormonal changes occurred alongside increased depression score and biphasic changes in HRV parameters; for example, the RMSSD, a parasympathetic-related parameter, initially decreased by 47.8% and then returned towards baseline values by the end of the ship travel. In contrast, during the camp period, blood TSH and T4 reduced by 26.5% and 34.1%, respectively, and salivary cortisol increased by 72.1%, without concomitant changes in melatonin and HRV. Also, tension score transiently reduced and then increased towards the pre-camp score by the end of the field period. Testosterone remained unaltered throughout the expedition. In conclusion, ship travel and camping in Antarctica induced distinct neuroendocrine changes, cardiac autonomic regulation, and mood states. These specific changes most likely resulted from exposure to different natural luminosity, degrees of confinement, and ambient temperature in these environments.

Continuous wavelet transform based processing for estimating the power spectrum content of heart rate variability during hemodiafiltration

Power spectral analysis of heart rate variability (HRV) offers a possibility to non-invasively quantify autonomic cardiac regulation. The technique splits the spectrum of the HRV into high frequency (HF), low frequency (LF) and very-low frequency (VLF) bands, and relates their power content to parasympathetic outflow, sympathetic outflow, and hormonal factors as well as thermoregulation, respectively. In this work, we applied this technique on HRV data from 20 end-stage renal disease (ESRD) patients to estimate power distribution in these three bands as well as their changes respect to time during hemodiafiltration (HDF) therapy; as an indirect way to assess the modulatory activity over the cardiac system. HRV data was processed using the continuous wavelet transform (CWT), power was estimated using 5-min as well as 10-min epochs for comparison purposes, and the results were normalized to unity before linear regression analysis. For 5-min epochs, the LF power increased (p = 0.035), while there were no significant changes in the HF power (p = 0.2). In contrast, for 10-min epochs, both the LF (p = 0.002) and HF (p = 0.043) power decreased, while the VLF power increased (p<<0.05) and had larger values than the other two spectral powers. There were no statistically significant changes in the LF/HF ratio for any of the two epochs evaluated (5-min: p = 0.56, 10-min: p = 0.44). Results based on 5-min epochs are in agreement with previous studies, while those based on 10-min epochs suggest that modulatory mechanisms within the VLF band override the sympathovagal balance and play a key role in managing the cardiovascular response during hemodiafiltration.

EFFECTS OF CONTRAST WATER THERAPY ON THE RECOVERY OF HEART RATE VARIABILITY FOLLOWING ECCENTRIC EXERCISE

PURPOSE: The aim of this study was to compare the effects of hot/cold immersion therapy and passive recovery following maximal eccentric exercise of the bilateral knee extensors on heart rate variability. METHODS: 14 health college males (18-22 yrs) were recruited and randimly assigned into the contrast water therapy (CWT) or passive recovery (CON) group (n=7 per group). Each participant performed 10 sets of 10 maximal isokinetic (30°/s) eccentric contractions (MaxECC) of each knee extensors. Contrast water therapy (8°C × 1 min and 45°C × 4 minutes, 3 reps), or the passive recovery interventions (15-min consecutive rest) were taken at 30 minutes post-MaxECC. Heart rate variability (HRV) parameters were collected by the portable heart rate monitor at 5 mins before, and 0-5, 10-15 and 25-30 mins after interventions. RESULTS: During the first 5 mins after interventions, mean HR (95.4 ± 11.1 bpm) and the normalized units of high frequency power (23.6 ± 10.3 nu) of the CWT group showed significantly higher value than the CON group (81.5 ± 11.6 bpm, 18.5 ± 9.0 nu; P<0.05), the mean R-R intervals (636.8 ± 78.8 ms), the standard deviation of normal R-R intervals (26.1 ± 6.6 ms) and the square root of the mean squared differences between adjacent R-R intervals (17.2 ± 7.7 ms) for CWT showed significantly lower than that of CON (749.3 ± 105.4 ms, 46.1 ± 17.7 ms, 33.0 ± 12.8 ms; P < .05). However, 10-15 and 25-30 mins after interventions, all HRV parameters between the two groups showed no significant difference (P > .05). CONCLUSION: These findings supported the hypothesis and suggested that one session of 15 mins CWT after eccentric exercise could be increased parasympathetic-related activation in cardiac autonomic regulation, but the effect only lasting for 10 mins. Keywords: autonomic nervous system, parasympathetic activation, normalization of high-frequency power

A Nonadapted Cardiac Autonomic Regulation Following Repeated Bouts Of Eccentric Exercise

A Nonadapted Cardiac Autonomic Regulation Following Repeated Bouts Of Eccentric Exercise

Post-aerobic-exercise autonomic responses in hypertensives — a randomized controlled trial

Background. Heart rate variability (HRV) response to an exercise bout may provide useful insight into autonomic stress reactivity. Considering that cardiovascular responses to a stressor may be predictive of certain diseases, it becomes critical to understand if high blood pressure can influence the autonomic nervous system response to acute exercise. We, therefore, undertook a study to investigate the effect of a single bout of aerobic exercise on autonomic responses in hypertensives. Material and methods. Twenty hypertensives were randomly assigned to one of the two experimental groups [control (CG) or exercise (EG)]. The exercise session was conducted on a treadmill and consisted of 40 min of running/walking at 60–70% HRreserve. In the control session, the participants remained seated in a quiet room for 40 min. After the exercise/control sessions, the HRV was recorded continuously for 60 min. Results. The EG presented an increase with a large effect size for LF [1.0 (post-30) and 1.0 (post-60)] and LF/HF [0.8 (post-30) and 1.1 (post-60)]. Additionally, a reduction with a large effect was observed for HF [–1.0 (post-30) and –1.0 (post-60)]. Conclusion. There is a considerable reduction in post-aerobic-exercise parasympathetic activity and an increase in sympathetic activity. Therefore, a single bout of aerobic exercise is not able to quickly improve the cardiac autonomic regulation.

Association of Severity of Autism Spectrum Disorder with Cardiac Autonomic Indices in Children

Background &amp; Objectives: Autism Spectrum Disorder (ASD) being a complex neuro-developmentaldisorder is found to be associated with Autonomic Nervous System (ANS) dysfunction. The sympathovagalcontinual dynamic excitatory- inhibitory interactions leads to Heart Rate Variability (HRV) which isan index of cardiac autonomic regulation. Aim of the study was to evaluate cardiac autonomic regulation inchildren with ASD at rest using short-term HRV analysis and to correlate it with severity of autism.Methods: A total of 30 subjects were evaluated in the study comprising of 15 ASD children and 15 healthycontrols. A five minutes recording of resting ECG was carried out from which R-R intervals were procuredand HRV indices were analysed. Frequency domain analysis of HRV was carried out and the followingparameters were evaluated: Spectral powers in low frequency (LF) bands, High frequency (HF) bands, totalpower (TP), LF/HF ratio and average heart rate (HR) were evaluated. HRV indices between the groups werecompared using Student’s t test. Severity of autism was correlated with the evaluated HRV indices usingPearson correlation test.Results: Cardiac sympathetic activity as assessed by low frequency power spectrum (‘p’ value 0.034) andtotal power (‘p’ value 0.023) of the HRV spectrum was significantly higher in autistic children comparedto that of normal controls. However, the association between severity of ASDs and HRV indices were notstatistically significant.Conclusion: Study concludes that here was no significant association between HRV indices and severity ofautism.

Snacking on Whole Almonds for Six Weeks Increases Heart Rate Variability during Mental Stress in Healthy Adults: A Randomized Controlled Trial.

Cardiac autonomic regulation can be indirectly measured by heart rate variability (HRV). Low HRV, which can be induced by mental stress, is a predictor of risk of sudden cardiac death. Few studies have investigated cause-and-effect relationships between diet and HRV. Nut consumption is associated with CVD risk reduction, but the impact on HRV, particularly in response to stress, is unclear. Men and women (30–70 y) with above average risk of developing CVD were randomly assigned in a 6-week randomized, controlled, parallel arm trial to consume either whole almond or isocaloric control snacks (20% of daily estimated energy requirement). Control snacks contained the average nutrient profile of UK snacks. Five-minute periods of supine heart rate (HR) and HRV were measured at resting and during mental stress (Stroop color-word test) at baseline and six weeks. High frequency (HF) power, which reflects parasympathetic regulation of HR, was increased following almonds during the mental stress task relative to control (mean difference between groups 124 ms2; 95% CI 11, 237; p = 0.031, n = 105), but other indices were unaffected. Snacking on whole almonds instead of typical snacks may reduce risk of CVD partly by ameliorating the suppression of HRV during periods of mental stress.