Sympathetic control of short-term heart rate variability and its pharmacological modulation

Changes in Negative Emotions Across Five Weeks of HRV Biofeedback Intervention were Mediated by Changes in Resting Heart Rate Variability

Resting heart rate variability (HRV) is typically higher in those with better emotional well-being. In the current study, we examined whether changes in resting HRV mediated changes in negative emotions during a 7-week clinical trial of HRV biofeedback. Younger and older adults were randomly assigned to one of two daily biofeedback practices for 5 weeks: (1) engage in slow-paced breathing to increase the amplitude of oscillations in heart rate at their breathing frequency (Osc+); or (2) engage in self-selected strategies to decrease heart rate oscillations (Osc-). We assessed negative emotion using the State Anxiety Inventory (SAI) and Profile of Mood States (POMS). Resting HRV at pre-intervention was significantly higher among those with lower negative emotion scores. Those participants showing greater increases in resting HRV showed greater decreases in negative emotion. In a mediation model with all participants, resting HRV changes significantly mediated the relationship between training performance (i.e., heart rate oscillation during practice sessions) and changes in negative emotion. However, additional analyses revealed this mediation effect was significantly moderated by condition and was only significant in the Osc+ condition. Thus, resting HRV changes mediated how biofeedback to increase amplitude of heart rate oscillations reduced negative emotion.

Enhancing Comprehensive Assessments in Chronic Heart Failure Caused by Ischemic Heart Disease: The Diagnostic Utility of Holter ECG Parameters

Background and Objectives: Chronic heart failure (CHF) caused by ischemic heart disease (IHD) is the leading cause of death worldwide and presents significant health challenges. Effective management of IHD requires prevention, early detection, and treatment to improve patient outcomes. This study aims to expand the diagnostic utility of various 24 h Holter ECG parameters, such as T-wave alternans (TWA), late ventricular potentials (LVPs), and heart rate variability (HRV) in patients with CHF caused by IHD. Additionally, we seek to explore the association between these parameters and other comorbid conditions affecting the prognosis of CHF patients. Materials and Methods: We conducted a prospective case-control study with 150 patients divided into two subgroups: 100 patients with CHF caused by IHD, and 50 patients in the control group. Data included medical history, physical examination, laboratory tests, echocardiography, and 24 h Holter monitoring. Results: Our comparative analysis demonstrated that both TWA and LVPs were significantly higher in patients with CHF compared to the control group (p < 0.01), indicating increased myocardial electrical vulnerability in CHF patients. Both time and frequency-domain HRV parameters were significantly lower in the CHF group. However, the ratio of NN50 to the total count of NN intervals (PNN50) showed a borderline significance (p = 0.06). While the low-frequency (LF) domain was significantly lower in CHF patients, the high-frequency (HF) domain did not differ significantly between groups. Acceleration and deceleration capacities were also significantly altered in CHF patients. Categorizing CHF patients by left ventricular ejection fraction (LVEF) revealed that the mean of the 5-min normal-to-normal intervals over the complete recording (SDNN Index) was significantly higher in patients with LVEF ≥ 50% compared to those with CHF with reduced EF and CHF with mildly reduced EF (p < 0.001), whereas the other HRV parameters showed no significant differences among the groups. Conclusions: Holter ECG parameters can become a reliable tool in the assessment of patients with CHF. The integration of multiple Holter ECG parameters, such as TWA, LVPs, and HRV, can significantly enhance the diagnostic assessment of CHF caused by IHD. This comprehensive approach allows for a more nuanced understanding of the patient's condition and potential outcomes.

The Clinical Significance and Application of Heart Rate Variability in Dialysis Patients: A Narrative Review

Autonomic nervous system (ANS) dysfunction is prevalent in end-stage kidney disease (ESKD) patients, carrying significant risks for morbidity and mortality. Heart rate variability (HRV) is a simple and non-invasive method to evaluate ANS functions and predict prognoses in specific patient populations. Since there is a lack of a clear understanding of the clinical significance of HRV in predicting prognoses in ESKD patients, an updated review on this topic is urgently warranted. The clinical significance of HRV in dialysis patients includes its associations with metabolic syndrome, nutritional status, intradialytic hypotension, vascular access failure, major adverse cardiovascular events, and mortality. These findings underscore the essential role of the autonomic reserve, which might denote the elevation of ANS activity as a response to external stimulus. Patients with a higher level of sympathetic activity at the resting stage, but who are unable to adequately elevate their sympathetic activity under stress might be susceptible to a worse outcome in critical circumstances. Further applications of HRV include HRV biofeedback, risk classification, and real-time HRV monitoring. Overall, HRV is an optimal tool for predicting prognoses in dialysis patients. Further study is encouraged in order to gain a clearer understanding of the clinical significance and application of HRV, and thereby enhance the care of ESKD patients.

Heart Rate Variability as a Translational Dynamic Biomarker of Altered Autonomic Function in Health and Psychiatric Disease

The autonomic nervous system (ANS) is responsible for the precise regulation of tissue functions and organs and, thus, is crucial for optimal stress reactivity, adaptive responses and health in basic and challenged states (survival). The fine-tuning of central ANS activity relies on the internal central autonomic regulation system of the central autonomic network (CAN), while the peripheral activity relies mainly on the two main and interdependent peripheral ANS tracts, the sympathetic nervous system (SNS) and the parasympathetic nervous system (PNS). In disease, autonomic imbalance is associated with decreased dynamic adaptability and increased morbidity and mortality. Acute or prolonged autonomic dysregulation, as observed in stress-related disorders, affects CAN core centers, thereby altering downstream peripheral ANS function. One of the best established and most widely used non-invasive methods for the quantitative assessment of ANS activity is the computerized analysis of heart rate variability (HRV). HRV, which is determined by different methods from those used to determine the fluctuation of instantaneous heart rate (HR), has been used in many studies as a powerful index of autonomic (re)activity and an indicator of cardiac risk and ageing. Psychiatric patients regularly show altered autonomic function with increased HR, reduced HRV and blunted diurnal/circadian changes compared to the healthy state. The aim of this article is to provide basic knowledge on ANS function and (re)activity assessment and, thus, to support a much broader use of HRV as a valid, transdiagnostic and fully translational dynamic biomarker of stress system sensitivity and vulnerability to stress-related disorders in neuroscience research and clinical psychiatric practice. In particular, we review the functional levels of central and peripheral ANS control, the main neurobiophysiologic theoretical models (e.g., polyvagal theory, neurovisceral integration model), the precise autonomic influence on cardiac function and the definition and main aspects of HRV and its different measures (i.e., time, frequency and nonlinear domains). We also provide recommendations for the proper use of electrocardiogram recordings for HRV assessment in clinical and research settings and highlight pathophysiological, clinical and research implications for a better functional understanding of the neural and molecular mechanisms underlying healthy and malfunctioning brain-heart interactions in individual stress reactivity and psychiatric disorders.

Combined effect of transcutaneous auricular vagus nerve stimulation and 0.1 Hz slow-paced breathing on working memory

Background

Previous research has found that transcutaneous auricular vagus nerve stimulation (taVNS) can improve working memory (WM) performance. It has also been shown that 0.1 Hz slow-paced breathing (SPB, i.e., breathing at a rate of approximately 6 breaths/min) can significantly influence physical state and cognitive function via changes in autonomic afferent activity. In the present study, we investigated the synergistic effects of taVNS and SPB on WM performance.

Methods

A total of 96 healthy people participated in this within-subjects experiment involving four conditions, namely taVNS, SPB, combined taVNS with SPB (taVNS + SPB), and sham. Each participant underwent each intervention for 30 min and WM was compared pre- and post-intervention using the spatial and digit n-back tasks in a random order four times. Permutation-based analysis of variance was used to assess the interaction between time and intervention.

Results

For the spatial 3-back task, a significant interaction between time and intervention was found for the accuracy rate of matching trials (mACC, p = 0.03). Post hoc analysis suggested that both taVNS and taVNS + SPB improved WM performance, however, no significant difference was found in the SPB or sham groups.

Conclusion

This study has replicated the effects of taVNS on WM performance reported in previous studies. However, the synergistic effects of combined taVNS and SPB warrant further research.

Features of the Effects of Serotonin and Dopamine on Changes in Heart Rate Variability in Non-Linear Rats under Conditions of Acute Stress

Changes in indicators of heart rate variability after a single injection of serotonin (200 μg/kg) or dopamine (60 μg/kg) were analyzed in male non-linear rats at rest and during acute stress. At rest, administration of serotonin is accompanied by an increase in the role of the vasomotor center in the formation of heart rate variability; administration of dopamine causes a moderate weakening of HF waves. In both cases, no sharp shifts in the sympathetic-parasympathetic relations are seen, but a more variable rhythm is formed under the effect of serotonin. Under conditions of acute stress, the increase in HR after injection of serotonin is half as much as in the control series, a trend towards weakening of the power of VLF- and even LF-waves is observed. After dopamine injection, a sharp increase in HR and strain index and a decrease in the power of waves of all spectral ranges and the centralization index are observed at the beginning of stress, but by the 30th min, tachycardia becomes moderate, the powers of all waves are restored; HF waves dominate in the spectrum, but potentiation of VLF- and LF-waves and growth of the centralization index are not observed in contrast to the control series. In general, serotonin and dopamine exhibit stress-limiting properties and moderate activation of sympathoadrenal influences and the suprasegmental level of regulation under stress conditions, but after dopamine injection we observed increased reactivity at the beginning of stress and less variable HR. Therefore, serotonin has more pronounced stress limiting effects, which can be revealed by heart rate variability analysis.

Adhésion et implémentation d’un programme de cohérence cardiaque visant à réduire l’anxiété de patients opérés pour une carcinose péritonéale : étude pilote randomisée

Objectif : Évaluer l’implémentation d’une pratique quotidienne de cohérence cardiaque chez des patients opérés pour une carcinose péritonéale.

Matériel et méthode : Étude pilote monocentrique, ouverte, contrôlée, randomisée non comparative, incluant 20 patients en soins courants vs 40 patients formés à la cohérence cardiaque avec biofeedback et guide respiratoire pour une pratique au domicile enregistrée.

Résultats attendus : Adhésion satisfaisante au programme, pouvant caractériser les éléments favorisant son implémentation avant et après chirurgie et évaluation de son impact sur l’anxiété.

Perspectives : Efficacité à déterminer pour transférer ce soin de support.

Ten-Second Heart Rate Variability, Its Changes Over Time, and the Development of Hypertension

BACKGROUND

The role of ultrashort-term heart rate variability (HRV) and its temporal changes in incident hypertension are unknown. We aimed to investigate the association between 10-second HRV, its changes, and incident hypertension in adults aged <40 years and older.

METHODS

This cohort study included 232 587 Koreans (mean age 37.6 years) without hypertension. Hypertension was defined according to the 2017 American College of Cardiology and American Heart Association hypertension guidelines. HRV, including the root mean square of successive RR interval differences and the SD of normal-to-normal RR intervals, was estimated using standard 12-lead, 10-second electrocardiography.

RESULTS

During a median follow-up of 3.8 years, 40 268 hypertension cases were identified (incidence rates: 36.1 and 67.9 per 1000 person-years for young and older participants, respectively). An inverse association was observed between HRV and hypertension risk, in a dose-dependent manner. The multivariable-adjusted hazard ratios (95% CIs) for hypertension comparing the first to the fifth quintiles of root mean square of successive RR interval difference and SD of normal-to-normal RR interval were 1.58 (1.52-1.63) and 1.35 (1.30-1.39), respectively. These associations were stronger in young adults than in older adults. In a subsample of 150 301 participants, compared with stable HRV, an increase in HRV over time was also inversely associated with incident hypertension.

CONCLUSIONS

A higher HRV and its increase over time on a 10-second electrocardiography were associated with a lower risk of hypertension. Our findings indicate that autonomic function, estimated using 10-second standard electrocardiography, plays a role in predicting hypertension, with a stronger effect in young adults.

Investigating the effect of cholinergic and adrenergic blocking agents on maternal-fetal heart rates and their interactions in mice fetuses

This study examines the role of autonomic control of maternal and fetal heart rate variability (MHRV and FHRV) and their heartbeats phase coupling prevalence (CP_heartbeat) in mice. The subjects are divided into three groups: control with saline, cholinergic blockade with atropine, and β-adrenergic blockade with propranolol. Electrocardiogram signals of 27 anesthetized pregnant mice and 48 fetuses were measured for 20 min (drugs were administered after 10 min). For the coupling analysis, different maternal heartbeats were considered for one fetal beat. Results show that saline infusion did not produce any significant changes in MHRV and FHRV, as well as CP_heartbeat. Atropine increased maternal HR (MHR) and decreased MHRV significantly without any considerable effect on fetal HR (FHR) and FHRV. Propranolol infusion did not produce any significant changes in MHR and MHRV, but significantly decreased FHR and increased FHRV. Moreover, atropine had led to a decrease in CP_heartbeat when considering two and three maternal beats, and an increase for four beats; while propranolol resulted in a decrease for two heartbeats, but an increase for four and five beats. The proposed approach is useful for assessing the impact of maternal autonomic modulation activity on fetal distress and obstetric complications prevalent in pregnant mothers.

Summary: Autonomic development of fetal mice is analyzed through electrocardiography. Saline infusion does not alter maternal and fetal heart rate variation and coupling significantly. Atropine increases maternal heart rate, while propranolol lowers fetal heart rate.

Heart rate variability biofeedback in chronic disease management: A systematic review

BACKGROUND

Heart rate variability biofeedback (HRVB) is a non-pharmacological intervention used in the management of chronic diseases.

METHOD

A systematic search was performed according to eligibility criteria including adult chronic patients, HRVB as main treatment with or without control conditions, and psychophysiological outcomes as dependent variables.

RESULTS

In total, 29 articles were included. Reported results showed the feasibility of HRVB in chronic patients without adverse effects. Significant positive effects were found in various patient profiles on hypertension and cardiovascular prognosis, inflammatory state, asthma disorders, depression and anxiety, sleep disturbances, cognitive performance and pain, which could be associated with improved quality of life. Improvements in clinical outcomes co-occurred with improvements in heart rate variability, suggesting possible regulatory effect of HRVB on autonomic function.

CONCLUSIONS

HRVB could be effective in managing patients with chronic diseases. Further investigations are required to confirm these results and recommend the most effective method.

Physiological Sympathetic Activation Reduces Systemic Inflammation: Role of Baroreflex and Chemoreflex

Baroreflex and chemoreflex act through the autonomic nervous system, which is involved with the neural regulation of inflammation. The present study reports the effects of reflex physiological sympathetic activation in endotoxemic rats using bilateral carotid occlusion (BCO), a physiological approach involving the baroreflex and chemoreflex mechanisms and the influence of the baroreceptors and peripheral chemoreceptors in the cardiovascular and systemic inflammatory responses. After lipopolysaccharide (LPS) administration, the arterial pressure was recorded during 360 min in unanesthetized rats, and serial blood samples were collected to analyze the plasma cytokine levels. BCO elicited the reflex activation of the sympathetic nervous system, providing the following outcomes: (I) increased the power of the low-frequency band in the spectrum of the systolic arterial pressure during the BCO period; (II) reduced the levels of pro-inflammatory cytokines in plasma, including the tumor necrosis factor (TNF) and the interleukin (IL)-1β; (III) increased the plasma levels of anti-inflammatory cytokine IL-10, 90 min after LPS administration. Moreover, selective baroreceptor or chemoreceptor denervation deactivated mechanosensitive and chemical sensors, respectively, and decreased the release of the LPS-induced cytokine but did not alter the BCO modulatory effects. These results show, for the first time, that physiological reflex activation of the sympathetic circuit decreases the inflammatory response in endotoxemic rats and suggest a novel function for the baroreceptors as immunosensors during the systemic inflammation.

Exposures influencing the developing central autonomic nervous system

Autonomic nervous system function is critical for transition from in-utero to ex-utero life and is associated with neurodevelopmental and neuropsychiatric outcomes later in life. Adverse prenatal and neonatal conditions and exposures can impair or alter ANS development and, as a result, may also impact long-term neurodevelopmental outcomes. The objective of this article is to provide a broad overview of the impact of factors that are known to influence autonomic development during the fetal and early neonatal period, including maternal mood and stress during and after pregnancy, fetal growth restriction, congenital heart disease, toxic exposures, and preterm birth. We touch briefly on the typical development of the ANS, then delve into both in-utero and ex-utero maternal and fetal factors that may impact developmental trajectory of the ANS and, thus, have implications in transition and in long-term developmental outcomes. While many types of exposures and conditions have been shown to impact development of the autonomic nervous system, there is still much to be learned about the mechanisms underlying these influences. In the future, more advanced neuromonitoring tools will be required to better understand autonomic development and its influence on long-term neurodevelopmental and neuropsychological function, especially during the fetal period.

Blood Pressure Variability and Optimal Cerebral Perfusion Pressure-New Therapeutic Targets in Traumatic Brain Injury

BACKGROUND

Optimal cerebral perfusion pressure (CPPopt) is an autoregulatory-oriented target in the neurointensive care (NIC) of patients with traumatic brain injury (TBI), and deviation from CPPopt is associated with poor outcome. We recently found that blood pressure variability (BPV) is associated with deviation from CPPopt.

OBJECTIVE

To evaluate BPV and other variables related to deviation from CPPopt and to evaluate challenges and strategies for autoregulatory-oriented treatment in TBI.

METHODS

Data including arterial blood pressure and intracranial pressure (ICP) from 362 TBI patients treated at the NIC unit, Uppsala University Hospital, Sweden, between 2008 and 2016, were retrospectively analyzed day 2 to 5.

RESULTS

Higher BPV was a strong predictor of both CPP deviation below and above CPPopt after multiple regression analyses. There was no other explanatory variable for CPP deviation above CPPopt, whereas also higher ICP and worse autoregulation (higher pressure reactivity index) were associated with CPP deviation below CPPopt. A higher BPV was, in turn, explained by older age, lower ICP, higher mean arterial blood pressure, and higher slow arterial blood pressure amplitude (0.018-0.067 Hz).

CONCLUSION

BPV was strongly associated with deviation from CPPopt. High age is a risk factor for high BPV and hence CPP insults. Our treatment protocol is focused on avoiding CPP below 60 mm Hg. It is possible that a more restrictive upper level could generate more stable blood pressure and less deviation from CPPopt.

Effects of Cardiac Sympathetic Neurodegeneration and PPARγ Activation on Rhesus Macaque Whole Blood miRNA and mRNA Expression Profiles

Degeneration of sympathetic innervation of the heart occurs in numerous diseases, including diabetes, idiopathic REM sleep disorder, and Parkinson's disease (PD). In PD, cardiac sympathetic denervation occurs in 80-90% of patients and can begin before the onset of motor symptoms. Today, there are no disease-modifying therapies for cardiac sympathetic neurodegeneration, and biomarkers are limited to radioimaging techniques. Analysis of expression levels of coding mRNA and noncoding RNAs, such as microRNAs (miRNAs), can uncover pathways involved in disease, leading to the discovery of biomarkers, pathological mechanisms, and potential drug targets. Whole blood in particular is a clinically relevant source of biomarkers, as blood sampling is inexpensive and simple to perform. Our research group has previously developed a nonhuman primate model of cardiac sympathetic denervation by intravenous administration of the catecholaminergic neurotoxin 6-hydroxydopamine (6-OHDA). In this rhesus macaque (Macaca mulatta) model, imaging with positron emission tomography showed that oral administration of the peroxisome proliferator-activated receptor gamma (PPARγ) agonist pioglitazone (n = 5; 5 mg/kg daily) significantly decreased cardiac inflammation and oxidative stress compared to placebo (n = 5). Here, we report our analysis of miRNA and mRNA expression levels over time in the whole blood of these monkeys. Differential expression of three miRNAs was induced by 6-OHDA (mml-miR-16-2-3p, mml-miR-133d-3p, and mml-miR-1262-5p) and two miRNAs by pioglitazone (mml-miR-204-5p and mml-miR-146b-5p) at 12 weeks posttoxin, while expression of mRNAs involved in inflammatory cytokines and receptors was not significantly affected. Overall, this study contributes to the characterization of rhesus coding and noncoding RNA profiles in normal and disease-like conditions, which may facilitate the identification and clinical translation of biomarkers of cardiac neurodegeneration and neuroprotection.

Adapted physical activity and cardiac coherence in hematologic patients (APACCHE): study protocol for a randomized controlled trial

Background

Hematologic malignancies and their treatments are recognized for their significant long-term adverse effects on health-related quality of life. As a part of cancer treatment, physical exercise is known to improve physical functioning, but there are still questions regarding its impact on psychological and emotional functioning. Nonetheless, heart rate variability biofeedback (HRVB) is recognized for its positive effects on autonomic nervous system balance and emotional self-regulation. The Adapted Physical Activity and Cardiac Coherence in Hematologic Patients (APACCHE) protocol is a randomized, controlled superiority trial designed to evaluate the effects of HRBV training combined with an adaptive physical activity (APA) program compared to APA alone on the post-treatment quality of life of adult hematologic patients.

Methods

Seventy patients aged 18–70 years, with various forms of hematological malignancies, in post-treatment remission within six months prior to beginning the study and who have been prescribed APA by a hematologist, will be randomly allocated in a 1:1 ratio to two 12-week treatment groups: HRVB + APA versus APA alone. APA sessions will consist of aerobic and resistance training for 1-h twice weekly. The HRVB training will consist of controlled breathing exercises with biofeedback of heart rate variability for 10 sessions and will include a daily home-based practice. The primary outcome will be to evaluate health-related quality of life (QLQ-C30, SF-36). The secondary outcomes will be to evaluate fatigue (MFI-20); anxiety and depression (HADS); clinical status with blood pressure, progression-free survival, overall survival, and body mass index; heart rate variability level and cardiac coherence score. All of these assessments will be evaluated initially (T1), 6 weeks after (T2), at the end of the 12 weeks (T3), and then at a 12-week post-intervention follow-up (T4).

Discussion

To our knowledge, this is the first protocol to investigate the additional value of HRVB on physical exercise. In addition, there has been no study previously published about HRVB in hematologic patients. We hypothesize that overall quality of life and psychological and physical functioning will be improved, potentially offering a better understanding of supportive cancer care in hematology and inferring new perspectives in psychophysiological research in cancer.

Trial registration

Current randomized controlled trial was registered 29 November 2017 on Clinical Trials.gov (NCT number: NCT03356171).

The Association between Nutritional Markers and Heart Rate Variability Indices in Patients Undergoing Chronic Hemodialysis

The associations between nutritional markers and heart rate variability (HRV) are poorly addressed. This study aimed to evaluate whether malnutrition is associated with the altered autonomic nervous system (ANS) function. This cross-sectional study was conducted enrolling 175 patients (100 women, mean age 65.1 ± 12.9 years) receiving chronic hemodialysis in a teaching hospital from June to August 2010. We performed HRV measurements before and during the index hemodialysis and compared these HRV values between two groups categorized by the individual nutritional marker. By using the multivariate generalized estimating equation with adjustment, we exhibited the independent associations between HRV and poor nutritional status defined by serum albumin < 3.8 g/dL, total cholesterol < 100 mg/dL, body mass index < 23 kg/m², bodyweight loss within six months > 10%, bodyweight loss within three months > 5%, and normalized protein catabolic rate < 1.1 g/kg BW/day. The current study disclosed ANS impairment in hemodialysis patients with poor nutritional status. The impaired ANS function might be a potential mechanism linking malnutrition to subsequent adverse prognoses in hemodialysis patients. Further investigations are warranted to confirm these findings and clarify the causal association among this complex issue.

Hypothesis: Pulmonary Afferent Activity Patterns During Slow, Deep Breathing Contribute to the Neural Induction of Physiological Relaxation

Control of respiration provides a powerful voluntary portal to entrain and modulate central autonomic networks. Slowing and deepening breathing as a relaxation technique has shown promise in a variety of cardiorespiratory and stress-related disorders, but few studies have investigated the physiological mechanisms conferring its benefits. Recent evidence suggests that breathing at a frequency near 0.1 Hz (6 breaths per minute) promotes behavioral relaxation and baroreflex resonance effects that maximize heart rate variability. Breathing around this frequency appears to elicit resonant and coherent features in neuro-mechanical interactions that optimize physiological function. Here we explore the neurophysiology of slow, deep breathing and propose that coincident features of respiratory and baroreceptor afferent activity cycling at 0.1 Hz entrain central autonomic networks. An important role is assigned to the preferential recruitment of slowly-adapting pulmonary afferents (SARs) during prolonged inhalations. These afferents project to discrete areas in the brainstem within the nucleus of the solitary tract (NTS) and initiate inhibitory actions on downstream targets. Conversely, deep exhalations terminate SAR activity and activate arterial baroreceptors via increases in blood pressure to stimulate, through NTS projections, parasympathetic outflow to the heart. Reciprocal SAR and baroreceptor afferent-evoked actions combine to enhance sympathetic activity during inhalation and parasympathetic activity during exhalation, respectively. This leads to pronounced heart rate variability in phase with the respiratory cycle (respiratory sinus arrhythmia) and improved ventilation-perfusion matching. NTS relay neurons project extensively to areas of the central autonomic network to encode important features of the breathing pattern that may modulate anxiety, arousal, and attention. In our model, pronounced respiratory rhythms during slow, deep breathing also support expression of slow cortical rhythms to induce a functional state of alert relaxation, and, via nasal respiration-based actions on olfactory signaling, recruit hippocampal pathways to boost memory consolidation. Collectively, we assert that the neurophysiological processes recruited during slow, deep breathing enhance the cognitive and behavioral therapeutic outcomes obtained through various mind-body practices. Future studies are required to better understand the physio-behavioral processes involved, including in animal models that control for confounding factors such as expectancy biases.

Assessment of Ultra-Short Heart Variability Indices Derived by Smartphone Accelerometers for Stress Detection

Body acceleration due to heartbeat-induced reaction forces can be measured as mobile phone accelerometer (m-ACC) signals. Our aim was to test the feasibility of using m-ACC to detect changes induced by stress by ultra-short heart rate variability (USV) indices (standard deviation of normal-to-normal interval—SDNN and root mean square of successive differences—RMSSD). Sixteen healthy volunteers were recruited; m-ACC was recorded while in supine position, during spontaneous breathing at rest conditions (REST) and during one minute of mental stress (MS) induced by arithmetic serial subtraction task, simultaneous with conventional electrocardiogram (ECG). Beat occurrences were extracted from both ECG and m-ACC and used to compute USV indices using 60, 30 and 10 s durations, both for REST and MS. A feasibility of 93.8% in the beat-to-beat m-ACC heart rate series extraction was reached. In both ECG and m-ACC series, compared to REST, in MS the mean beat duration was reduced by 15% and RMSSD decreased by 38%. These results show that short term recordings (up to 10 s) of cardiac activity using smartphone’s accelerometers are able to capture the decrease in parasympathetic tone, in agreement with the induced stimulus.

Autonomic Disturbances in Acute Cerebrovascular Disease

Autonomic disturbances often occur in patients with acute cerebrovascular disease due to damage of the central autonomic network. We summarize the structures of the central autonomic network and the clinical tests used to evaluate the functions of the autonomic nervous system. We review the clinical and experimental findings as well as management strategies of post-stroke autonomic disturbances including electrocardiographic changes, cardiac arrhythmias, myocardial damage, thermoregulatory dysfunction, gastrointestinal dysfunction, urinary incontinence, sexual disorders, and hyperglycemia. The occurrence of autonomic disturbances has been associated with poor outcomes in stroke patients. Autonomic nervous system modulation appears to be an emerging therapeutic strategy for stroke management in addition to treatments for sensorimotor dysfunction.

Dynamic resting state fMRI analysis in mice reveals a set of Quasi-Periodic Patterns and illustrates their relationship with the global signal

Time-resolved 'dynamic' over whole-period 'static' analysis of low frequency (LF) blood-oxygen level dependent (BOLD) fluctuations provides many additional insights into the macroscale organization and dynamics of neural activity. Although there has been considerable advancement in the development of mouse resting state fMRI (rsfMRI), very little remains known about its dynamic repertoire. Here, we report for the first time the detection of a set of recurring spatiotemporal Quasi-Periodic Patterns (QPPs) in mice, which show spatial similarity with known resting state networks. Furthermore, we establish a close relationship between several of these patterns and the global signal. We acquired high temporal rsfMRI scans under conditions of low (LA) and high (HA) medetomidine-isoflurane anesthesia. We then employed the algorithm developed by Majeed et al. (2011), previously applied in rats and humans, which detects and averages recurring spatiotemporal patterns in the LF BOLD signal. One type of observed patterns in mice was highly similar to those originally observed in rats, displaying propagation from lateral to medial cortical regions, which suggestively pertain to a mouse Task-Positive like network (TPN) and Default Mode like network (DMN). Other QPPs showed more widespread or striatal involvement and were no longer detected after global signal regression (GSR). This was further supported by diminished detection of subcortical dynamics after GSR, with cortical dynamics predominating. Observed QPPs were both qualitatively and quantitatively determined to be consistent across both anesthesia conditions, with GSR producing the same outcome. Under LA, QPPs were consistently detected at both group and single subject level. Under HA, consistency and pattern occurrence rate decreased, whilst cortical contribution to the patterns diminished. These findings confirm the robustness of QPPs across species and demonstrate a new approach to study mouse LF BOLD spatiotemporal dynamics and mechanisms underlying functional connectivity. The observed impact of GSR on QPPs might help better comprehend its controversial role in conventional resting state studies. Finally, consistent detection of QPPs at single subject level under LA promises a step forward towards more reliable mouse rsfMRI and further confirms the importance of selecting an optimal anesthesia regime.

A method for assessment of the dynamic response of the arterial baroreflex

AIM

The baroreflex is a key mechanism in cardiovascular regulation, and alterations in baroreceptor function are seen in many diseases, including heart failure, obesity and hypertension. We propose a new method for analysing baroreceptor function from continuous blood pressure (BP) and heart rate (HR) in both health and disease.

METHODS

Forty-eight-hour data series of BP and HR were collected with telemetry. Sprague Dawley rats on standard chow (n = 11) served as controls, while rats on a high-fat, high-fructose (HFHC) diet (n = 6) constituted the obese-hypertensive model. A third group of rats underwent autonomic blockade (n = 6). An autoregressive-moving-average with exogenous inputs (ARMAX) model was applied to the data and compared with the α-coefficient.

RESULTS

Autonomic blockade caused a significant reduction in the strength of the baroreflex as estimated by ARMAX [ARMAX- baroreflex sensitivity (BRS)] -0.03 ± 0.01 vs. -0.19 ± 0.04 bpm heartbeat^-1) . Both methods showed a ~50% reduction in BRS in the obese-hypertensive group compared with control (body weight 531 ± 27 vs. 458 ± 19 g, P < 0.05; mean arterial pressure 119 ± 3 vs. 102 ± 1 mmHg, P < 0.05; ARMAX-BRS -0.08 ± 0.01 vs. -0.15 ± 0.01 bpm heartbeat^-1 , P < 0.05; α-coefficient BRS 0.51 ± 0.07 vs. 0.89 ± 0.07 ms mmHg^-1 , P < 0.05). The ARMAX method additionally showed the open-loop gain of the baroreflex to be reduced by ~50% in the obese-hypertensive group (-2.3 ± 0.3 vs. -4.1 ± 0.3 bpm, P < 0.05), while the rate constant was similar between groups.

CONCLUSION

The ARMAX model represents an efficient method for estimating several aspects of the baroreflex. The open-loop gain of the baroreflex was attenuated in obese-hypertensive rats compared with control, while the time response was similar. The algorithm can be applied to other species including humans.

The physiological effects of slow breathing in the healthy human

Slow breathing practices have been adopted in the modern world across the globe due to their claimed health benefits. This has piqued the interest of researchers and clinicians who have initiated investigations into the physiological (and psychological) effects of slow breathing techniques and attempted to uncover the underlying mechanisms. The aim of this article is to provide a comprehensive overview of normal respiratory physiology and the documented physiological effects of slow breathing techniques according to research in healthy humans. The review focuses on the physiological implications to the respiratory, cardiovascular, cardiorespiratory and autonomic nervous systems, with particular focus on diaphragm activity, ventilation efficiency, haemodynamics, heart rate variability, cardiorespiratory coupling, respiratory sinus arrhythmia and sympathovagal balance. The review ends with a brief discussion of the potential clinical implications of slow breathing techniques. This is a topic that warrants further research, understanding and discussion.

Slow breathing techniques have been used in asthma but are there effects in healthy individuals?http://ow.ly/gCPO30eQOPZ

Heart rate variability during hemodialysis is an indicator for long-term vascular access survival in uremic patients

BACKGROUND

Vascular access (VA) is the lifeline of hemodialysis patients. Although the autonomic nervous system might be associated with VA failure (VAF), it has never been addressed in previous studies. This study aimed to evaluate the predictive values of the heart rate variability (HRV) indices for long-term VA outcomes.

METHODS

This retrospective study was conducted using a prospectively established cohort enrolling 175 adult chronic hemodialysis patients (100 women, mean age 65.1 ± 12.9 years) from June 2010 to August 2010. Each participant received a series of HRV measurements at enrollment. After a 60-month follow-up period, we retrospectively reviewed all events and therapeutic procedures of the VAs which existed at the enrollment and during the follow-up period.

RESULTS

During the 60-month follow-up period, 37 (26.8%) had VAF but 138 (73.2%) didn't. The values of most HRV indices were statistically increased during hemodialysis since initiation in the non-VAF group, but not in the VAF group. Among all participants, the independent indicators for VAF included higher normalized high-frequency (nHF) activity [hazard ratio (HR) 1.04, p = 0.005], lower low-frequency/high-frequency (LF/HF) ratio (HR 0.80, p = 0.015), experience of urokinase therapy (HR 11.18, p = 0.002), percutaneous transluminal angioplasty (HR 2.88, p = 0.003) and surgical thrombectomy (HR 2.36, p = 0.035), as well as higher baseline serum creatinine (HR 1.07, p = 0.027) and potassium level (HR 1.58, p = 0.037). In subgroup analysis, a lower sympathetic activity indicated by lower LF/HF ratio was an independent indicator for VAF (HR 0.61, p = 0.03) for tunneled cuffed catheter, but conversely played a protective role against VAF (HR 1.27, p = 0.002) for arteriovenous fistula.

CONCLUSIONS

HRV is a useful tool for predicting long-term VAF among hemodialysis patients.

Respiratory modulation of human autonomic function: long-term neuroplasticity in space

KEY POINTS

We studied healthy astronauts before, during and after the Neurolab Space Shuttle mission with controlled breathing and apnoea, to identify autonomic changes that might contribute to postflight orthostatic intolerance. Measurements included the electrocardiogram, finger photoplethysmographic arterial pressure, respiratory carbon dioxide levels, tidal volume and peroneal nerve muscle sympathetic activity. Arterial pressure fell and then rose in space, and drifted back to preflight levels after return to Earth. Vagal metrics changed in opposite directions: vagal baroreflex gain and two indices of vagal fluctuations rose and then fell in space, and descended to preflight levels upon return to Earth. Sympathetic burst frequencies (but not areas) were greater than preflight in space and on landing day, and astronauts' abilities to modulate both burst areas and frequencies during apnoea were sharply diminished. Spaceflight triggers long-term neuroplastic changes reflected by reciptocal sympathetic and vagal motoneurone responsiveness to breathing changes.

ABSTRACT

We studied six healthy astronauts five times, on Earth, in space on the first and 12th or 13th day of the 16 day Neurolab Space Shuttle mission, on landing day, and 5-6 days later. Astronauts followed a fixed protocol comprising controlled and random frequency breathing and apnoea, conceived to perturb their autonomic function and identify changes, if any, provoked by microgravity exposure. We recorded the electrocardiogram, finger photoplethysmographic arterial pressure, tidal carbon dioxide concentrations and volumes, and peroneal nerve muscle sympathetic activity on Earth (in the supine position) and in space. (Sympathetic nerve recordings were made during three sessions: preflight, late mission and landing day.) Arterial pressure changed systematically from preflight levels: pressure fell during early microgravity exposure, rose as microgravity exposure continued, and drifted back to preflight levels after return to Earth. Vagal metrics changed in opposite directions: vagal baroreflex gain and two indices of vagal fluctuations (root mean square of successive normal R-R intervals; and proportion of successive normal R-R intervals greater than 50 ms, divided by the total number of normal R-R intervals) rose significantly during early microgravity exposure, fell as microgravity exposure continued, and descended to preflight levels upon return to Earth. Sympathetic mechanisms also changed. Burst frequencies (but not areas) during fixed frequency breathing were greater than preflight in space and on landing day, but their control during apnoea was sharply altered: astronauts increased their burst frequencies from already high levels, but they could not modulate either burst areas or frequencies appropriately. Space travel provokes long-lasting sympathetic and vagal neuroplastic changes in healthy humans.

Impact of metabolic syndrome and its components on heart rate variability during hemodialysis: a cross-sectional study

Background

Both uremia and metabolic syndrome (MetS) affect heart rate variability (HRV) which is a risk factor of poor prognoses. The aim of this study was to evaluate the impact of MetS on HRV among chronic hemodialysis patients.

Methods

This cross-sectional study was carried out in a teaching hospital in Northern Taiwan from June to August, 2010. Adult patients on chronic hemodialysis without active medical conditions were enrolled. HRV were measured for 4 times on the index hemodialysis day (HRV-0, -1, -2, and -3 at before, initial, middle, and late phases of hemodialysis, respectively), and the baseline demographic data and clinical parameters during the hemodialysis session were documented. Then we evaluated the impacts of MetS and its five components on HRV.

Results

One hundred and seventy-five patients (100 women, mean age 65.1 ± 12.9 years) were enrolled and included those with MetS (n = 91, 52 %) and without MetS (n = 84, 48 %). The patients with MetS(+) had significantly lower very low frequency, total power, and variance in HRV-0, total power and variance in HRV-2, and variance in HRV-3. (all p ≦ 0.05) When using the individual components of MetS to evaluate the impacts on HRV indices, the fasting plasma glucose (FPG) criterion significantly affected most indices of HRV while other four components including “waist circumference”, “triglycerides”, “blood pressure”, and “high-density lipoprotein” criteria exhibited little impacts on HRV. FPG criterion carried the most powerful influence on cardiac ANS, which was even higher than that of MetS. The HRV of patients with FPG(+) increased initially during the hemodialysis, but turned to decrease dramatically at the late phase of hemodialysis.

Conclusions

The impact of FPG(+) outstood the influence of uremic autonomic dysfunction, and FPG criterion was the most important one among all the components of MetS to influence HRV. These results underscored the importance of interpretation and management for abnormal glucose metabolism.

Assessment of cardiac autonomic tone in conscious rats

Cardiac autonomic tone can be assessed either by estimating separately vagal and sympathetic tones or by evaluating the net effect of their interaction, the so-called sympathovagal balance (SVB). To compare the most commonly used methods in rats, telemetric recordings of the electrocardiogram were performed in normotensive WKY rats, and in groups of spontaneously hypertensive (SHR) rats that were either untreated or chronically treated with the cholinesterase inhibitor, pyridostigmine, to enhance vagal tone. Cardiac autonomic blockers were administered alone and in combination, so that heart rate (HR) could be measured (1) under resting conditions, (2) with either autonomic branch blocked, and (3) with both branches blocked (which provided intrinsic HR, iHR). SVB was assessed as the ratio of resting HR to iHR. This calculation pointed to a sympathetic predominance in untreated SHRs and even more so in WKY rats, and to a marked vagal predominance in pyridostigmine-treated SHRs. By contrast, the ratio between low and high frequency components (LF/HF) of RR interval spectra did not significantly differ between the groups. Each autonomic tone was quantified as the HR change induced by its selective blocker or as the difference between iHR and HR after blockade of its counterpart. Both pharmacological methods indicated vagal enhancement in treated SHRs, but provided opposite results in terms of vagal vs. sympathetic predominance. These data seriously question the use of the LF/HF ratio as an index of SVB, and the possibility to reliably estimate vagal and sympathetic tones separately through current pharmacological approaches in conscious rats.

Heart rate variability is an indicator for intradialytic hypotension among chronic hemodialysis patients

BACKGROUND

Intradialytic hypotension (IDH) carries adverse impact. Heart rate variability (HRV) represents autonomic cardiac regulation which influences intradialytic blood pressure. We aimed to evaluate the association between IDH and HRV.

METHODS

This prospective study was carried out in a teaching hospital in Taiwan from June to August 2010. Adult patients on chronic hemodialysis without active medical conditions were enrolled and received HRV measurements for 4 times (before and during an index hemodialysis session). Patients were categorized by the changes of systolic blood pressure during the index hemodialysis into Group 1 (elevation >20 mmHg), Group 2 (decrease >20 mmHg), and Group 3 (others). Then we compared HRV indices among the three groups, and determined the indicators for IDH.

RESULTS

One hundred and seventy-one patients (96 women, mean age 64.9 years) were enrolled and categorized into Group 1 (n = 47, 27.5 %), Group 2 (n = 45, 26.3 %) and Group 3 (n = 79, 46.2 %). Comparing with Group 1 and/or Group 3, Group 2 had significantly higher blood pressure at hemodialysis initiation (most p < 0.001) and statistically lower levels of HRV indices including variance, total power, very low-frequency, low-frequency and high-frequency since the middle phase of the hemodialysis. By logistic regression method, higher systemic blood pressure [odds ratio (OR) 1.048; p < 0.001], heart rate (OR 1.093; p = 0.021), low-frequency/high-frequency ratio (OR 1.715; p = 0.022), as well as lower variance (OR 0.639; p = 0.048) at hemodialysis initiation were independently associated with intradialytic blood pressure changes.

CONCLUSIONS

HRV is a useful indicator for IDH among hemodialysis patients.

Modulation of Cardiac Autonomic Dysfunction in Ischemic Stroke following Ayurveda (Indian System of Medicine) Treatment

Objectives. Cardiac autonomic dysfunction in stroke has implications on morbidity and mortality. Ayurveda (Indian system of medicine) describes stroke as pakshaghata. We intended to study the effect of Ayurveda therapies on the cardiac autonomic dysfunction. Methods. Fifty patients of ischemic stroke (middle cerebral artery territory) (mean age 39.26 ± 9.88 years; male 43, female 7) were recruited within one month of ictus. All patients received standard allopathic medications as advised by neurologist. In addition, patients were randomized to receive physiotherapy (Group I) or Ayurveda treatment (Group II) for 14 days. Continuous electrocardiogram and finger arterial pressure were recorded for 15 min before and after treatments and analyzed offline to obtain heart rate and blood pressure variability and baroreflex sensitivity (BRS). Results were analysed by RMANOVA. Results. Patients in Group II showed statistically significant improvement in cardiac autonomic parameters. The standard deviation of normal to normal intervals,and total and low frequency powers were significantly enhanced (F = 8.16, P = 0.007, F = 9.73, P = 0.004, F = 13.51, and P = 0.001, resp.). The BRS too increased following the treatment period (F = 10.129, P = 0.004). Conclusions. The current study is the first to report a positive modulation of cardiac autonomic activity after adjuvant Ayurveda treatment in ischemic stroke. Further long term studies are warranted.

Everything Hertz: methodological issues in short-term frequency-domain HRV

Frequency analysis of the electrocardiographic RR interval is a common method of quantifying autonomic outflow by measuring the beat-to-beat modulation of the heart (heart rate variability; HRV). This review identifies a series of problems with the methods of doing so—the interpretation of low-frequency spectral power, the multiple use of equivalent normalized low frequency (LFnu), high frequency (HFnu) and ratio (LF/HF) terms, and the lack of control over extraneous variables, and reviews research in the calendar year 2012 to determine their prevalence and severity. Results support the mathematical equivalency of ratio units across studies, a reliance on those variables to explain autonomic outflow, and insufficient control of critical experimental variables. Research measurement of HRV has a substantial need for general methodological improvement.

Progesterone and mental rotation task: is there any effect?

Mental rotation task (MRT) incorporates elements of spatial abilities, important in many professions, with people of both genders involved. Importantly, these are the areas where spatial tasks might be performed for long time periods; thus adverse effects of mental fatigue are highly unwanted. Substantial variation of MRT performance in relation to estrogen levels has been observed in many studies, whereas the role of progesterone remains elusive. Here we aimed to elucidate the effect of progesterone level on the long-duration (1.5 hours) performance of MRT. We included three groups of subjects: a group of males as a control, a group of females in their follicular phase (low progesterone) and a group of females in their luteal phase (high progesterone), MRT accuracy and response time, subjective fatigue ratings and cardiovascular measures together with 17 β -estradiol and progesterone concentrations were analyzed. We found that subjective ratings of fatigue increased, performance accuracy increased, and mean response times decreased during the task in all groups. Females in luteal phase were significantly slower not only than men, but also than females in their follicular phase. An increase in subjective fatigue ratings was positively related to progesterone level-at higher progesterone levels, females felt more tired.

A novel approach to the design of an artificial bionic baroreflex

This paper presents a computationally efficient method to design an artificial bionic baroreflex. This work is built upon a physiology-based mathematical model of autonomic-cardiac regulation describing the regulation of heart rate and blood pressure as well as a system identification technique to identify a subject-specific mathematical model for each subject. The control strategy to regulate blood pressure is developed based upon the in-vivo baroreflex mechanism. A unique strength of the proposed method is its capability to determine the modulating baroreflex functions on the sympathetic and parasympathetic nerve activities. This method can be used in the treatment of individuals with baroreflex failure through overriding the corresponding nerves to properly regulate blood pressure. In fact, nerve overriding causes heart rate and arterial stiffness to adjust such that blood pressure reaches a proper range to provide enough oxygenated-blood to the critical organs.

Autonomic-cardiorespiratory regulation: a physiology-based mathematical model

This paper presents a novel physiology-based mathematical model of autonomic-cardiorespiratory regulation described by a set of three nonlinear, coupled differential equations. We improved our previously proposed autonomic-cardiac regulation model by considering neuromechanical and mechanical coupling of cardiovascular and respiration systems including lung stretch-receptor reflex and venous return variation. We also introduced a differential equation describing respiration rate regulation which mainly originates in the medullary respiratory center. The results of simulation experiments suggest that the venous return variation generates a higher perturbation on heart rate and blood pressure than lung stretch-receptor reflex. The proposed model is also powerful in determining and removing direct respiratory impacts on parasympathetic activation tone to accurately extract parasympathetic activity caused by emotional states and environmental conditions.

Power spectral analysis of heart rate variability in cynomolgus monkeys in safety pharmacology studies: comparative study with beagle dogs

INTRODUCTION

Power spectral analysis of heart rate variability is a tool known to provide information of interest on the autonomic control of heart rate in human. However, its use and its conditions of application and interpretation for safety purposes are not well defined for cardiovascular safety pharmacology studies. Likewise, data of power spectral analysis of heart rate variability in cynomolgus monkeys, a species often appropriate for use as second non rodent species in preclinical safety programmes, are not available. This study was designed to evaluate the relevance of this biomarker in this non human primate species, and to compare results with those from beagle dogs under the conditions of safety evaluation studies.

METHODS

Power spectral analysis of heart rate variability was performed on data collected in both species by telemetry following a standard design for cardiovascular safety pharmacology studies. Various pharmacological agents were tested in order to compare the profile of responses in both species after modifying the autonomic nervous balance.

RESULTS

Heart rate variability in cynomolgus monkeys is mainly driven by the parasympathetic nervous system as in beagle dogs although vagal tone is less than in dogs. Power spectral analysis of heart rate variability allows detection of interaction with the autonomic nervous system in both species in all investigated situations, i.e. sympatholytic/sympathomimetic and parasympatholytic/parasympathomimetic drug induced effects. However, due to species difference in the autonomic control of heart rate, cynomolgus monkeys are likely to be more sensitive than beagle dogs for assessment of sympatholytic properties.

DISCUSSION

This study confirms that power spectral analysis of heart rate variability from data derived from ECG recordings in telemetry studies is applicable in cardiovascular safety pharmacology studies and may provide relevant information about possible interaction with the autonomic nervous system when new drug entities are evaluated in either species. However, interspecies differences in autonomic control must be taken into account when interpreting possible drug effects.

Association between heart rate variability and fluctuations in resting-state functional connectivity

Functional connectivity has been observed to fluctuate across the course of a resting state scan, though the origins and functional relevance of this phenomenon remain to be shown. The present study explores the link between endogenous dynamics of functional connectivity and autonomic state in an eyes-closed resting condition. Using a sliding window analysis on resting state fMRI data from 35 young, healthy male subjects, we examined how heart rate variability (HRV) covaries with temporal changes in whole-brain functional connectivity with seed regions previously described to mediate effects of vigilance and arousal (amygdala and dorsal anterior cingulate cortex; dACC). We identified a set of regions, including brainstem, thalamus, putamen, and dorsolateral prefrontal cortex, that became more strongly coupled with the dACC and amygdala seeds during states of elevated HRV. Effects differed between high and low frequency components of HRV, suggesting specific contributions of parasympathetic and sympathetic tone on individual connections. Furthermore, dynamics of functional connectivity could be separated from those primarily related to BOLD signal fluctuations. The present results contribute novel information about the neural basis of transient changes of autonomic nervous system states, and suggest physiological and psychological components of the recently observed non-stationarity in resting state functional connectivity.

Linear and nonlinear measures of fetal heart rate patterns evaluated on very short fetal magnetocardiograms

We analyzed the effectiveness of linear short- and long-term variability time domain parameters, an index of sympatho-vagal balance (SDNN/RMSSD) and entropy in differentiating fetal heart rate patterns (fHRPs) on the fetal heart rate (fHR) series of 5, 3 and 2 min duration reconstructed from 46 fetal magnetocardiograms. Gestational age (GA) varied from 21 to 38 weeks. FHRPs were classified based on the fHR standard deviation. In sleep states, we observed that vagal influence increased with GA, and entropy significantly increased (decreased) with GA (SDNN/RMSSD), demonstrating that a prevalence of vagal activity with autonomous nervous system maturation may be associated with increased sleep state complexity. In active wakefulness, we observed a significant negative (positive) correlation of short-term (long-term) variability parameters with SDNN/RMSSD. ANOVA statistics demonstrated that long-term irregularity and standard deviation of normal-to-normal beat intervals (SDNN) best differentiated among fHRPs. Our results confirm that short- and long-term variability parameters are useful to differentiate between quiet and active states, and that entropy improves the characterization of sleep states. All measures differentiated fHRPs more effectively on very short HR series, as a result of the fMCG high temporal resolution and of the intrinsic timescales of the events that originate the different fHRPs.

Heart rate variability changes at 2400 m altitude predicts acute mountain sickness on further ascent at 3000-4300 m altitudes

OBJECTIVE

If the body fails to acclimatize at high altitude, acute mountain sickness (AMS) may result. For the early detection of AMS, changes in cardiac autonomic function measured by heart rate variability (HRV) may be more sensitive than clinical symptoms alone. The purpose of this study was to ascertain if the changes in HRV during ascent are related to AMS.

METHODS

We followed Lake Louise Score (LLS), arterial oxygen saturation at rest (R-SpO(2)) and exercise (Ex-SpO(2)) and HRV parameters daily in 36 different healthy climbers ascending from 2400 m to 6300 m altitudes during five different expeditions.

RESULTS

After an ascent to 2400 m, root mean square successive differences, high-frequency power (HF(2 min)) of HRV were 17-51% and Ex-SpO(2) was 3% lower in those climbers who suffered from AMS at 3000 to 4300 m than in those only developing AMS later (≥5000 m) or not at all (all p < 0.01). At the altitude of 2400 m RMSSD(2 min) ≤ 30 ms and Ex-SpO(2) ≤ 91% both had 92% sensitivity for AMS if ascent continued without extra acclimatization days.

CONCLUSIONS

Changes in supine HRV parameters at 2400 m were related to AMS at 3000-4300 m Thus, analyses of HRV could offer potential markers for identifying the climbers at risk for AMS.

Sympathetic activation and baroreflex function during intradialytic hypertensive episodes

Background

The mechanisms of intradialytic increases in blood pressure are not well defined. The present study was undertaken to assess the role of autonomic nervous system activation during intradialytic hypertensive episodes.

Methodology/Principal Findings

Continuous interbeat intervals (IBI) and systolic blood pressure (SBP) were monitored during hemodialysis in 108 chronic patients. Intradialytic hypertensive episodes defined as a period of at least 10 mmHg increase in SBP between the beginning and the end of a dialysis session or hypertension resistant to ultrafiltration occurring during or immediately after the dialysis procedure, were detected in 62 out of 113 hemodialysis sessions. SBP variability, IBI variability and baroreceptor sensitivity (BRS) in the low (LF) and high (HF) frequency ranges were assessed using the complex demodulation technique (CDM). Intradialytic hypertensive episodes were associated with an increased (n = 45) or decreased (n = 17) heart rate. The maximal blood pressure was similar in both groups. In patients with increased heart rate the increase in blood pressure was associated with marked increases in SBP and IBI variability, with suppressed BRS indices and enhanced sympatho-vagal balance. In contrast, in those with decreased heart rate, there were no significant changes in the above parameters. End-of- dialysis blood pressure in all sessions associated with hypertensive episode was significantly higher than in those without such episodes. In logistic regression analysis, predialysis BRS in the low frequency range was found to be the main predictor of intradialytic hypertension.

Conclusion/Significance

Our data point to sympathetic overactivity with feed-forward blood pressure enhancement as an important mechanism of intradialytic hypertension in a significant proportion of patients. The triggers of increased sympathetic activity during hemodialysis remain to be determined. Intradialytic hypertensive episodes are associated with higher end-of- dialysis blood pressure, suggesting that intradialytic hypertension may play a role in generation of interdialytic hypertension.

Single atom substitution in mouse protein kinase G eliminates oxidant sensing to cause hypertension

Blood pressure regulation is crucial for the maintenance of health, and hypertension is a risk factor for myocardial infarction, heart failure, stroke and renal disease. Nitric oxide (NO) and prostacyclin trigger well-defined vasodilator pathways; however, substantial vasorelaxation in response to agents such as acetylcholine persists when the synthesis of these molecules is prevented. This remaining vasorelaxation activity, termed endothelium-derived hyperpolarizing factor (EDHF), is more prevalent in resistance than in conduit blood vessels and is considered a major mechanism for blood pressure control. Hydrogen peroxide (H2O2) has been shown to be a major component of EDHF in several vascular beds in multiple species, including in humans. H2O2 causes the formation of a disulfide bond between the two α subunits of protein kinase G I-α (PKGI-α), which activates the kinase independently of the NO-cyclic guanosine monophosphate (cGMP) pathway and is coupled to vasodilation. To test the importance of PKGI-α oxidation in the EDHF mechanism and blood pressure control in vivo, we generated a knock-in mouse expressing only a C42S 'redox-dead' version of PKGI-α. This amino acid substitution, a single-atom change (an oxygen atom replacing a sulfur atom), blocked the vasodilatory action of H2O2 on resistance vessels and resulted in hypertension in vivo.

A systematic approach to local stability analysis of cardiovascular baroreflex

This paper presents a novel systematic approach to the stability analysis of the cardiovascular (CV) baroreflex. The proposed approach determines the equilibrium state and the system stability in its neighbourhood with computational efficiency, once the parameters of the CV baroreflex model are specified for an individual. We first propose a linearization-based analytical method for determining the equilibrium state of the CV baroreflex. We then present a Lyapunov-based systematic approach to analyze the system stability in the neighbourhood of the equilibrium state. The results of simulation experiments suggest that the performance of the proposed approach is encouraging: it was able to accurately determine the equilibrium state and quantify the stability of the CV baroreflex. The proposed approach is also powerful in exploring the relationship between the CV baroreflex stability and its parameter configurations.

Baroreflex sensitivity and sympatho-vagal balance during intradialytic hypotensive episodes

OBJECTIVES

The role of the baroreflex function in the pathogenesis of hemodialysis-associated hypotension is controversial. Complex demodulation technique (CDM), providing continuous assessment of the amplitude of cardiovascular oscillation over time, is particularly suitable to assess dynamic changes in autonomic nervous system and baroreceptor sensitivity (BRS) during dialysis. In the present study, CDM was used to determine the effects of dialysis treatment on BRS and to characterize BRS changes during acute intradialytic hypotension.

METHODS

Continuous beat-to-beat blood pressure and interbeat intervals (IBIs) were monitored in 93 chronic patients without (n = 70) and with (n = 26) hypotension during 96 dialysis sessions. The amplitudes of SBP and DBP, IBIs, and BRS change in the low-frequency (around center frequency of 0.09 Hz) and high-frequency (around center frequency of 0.30 Hz) ranges were followed during the whole dialysis session.

RESULTS

Hemodialysis treatment was associated with increased low-frequency BRS, especially in sessions without hypotension. Hypotensive episodes were associated with significant increases in both low-frequency BRS and high-frequency BRS, mainly in patients with severe hypotension. The magnitude of the increase in baroreflex indices was proportional to the decrease in blood pressure. Low-frequency IBI/high-frequency IBI ratio, a marker of sympatho-vagal balance, did not significantly change during hypotension.

CONCLUSION

Our study shows that the baroreflex mechanism is preserved and adequately activated during intradialytic hypotension. Other factors, such as ischemic heart disease, left ventricular dysfunction, and inadequate arteriolar tone, rather than failure of baroreflex function, are more likely to be responsible for dialysis-induced hypotension.