Mechanisms underlying very-low-frequency RR-interval oscillations in humans

Assessment of the long RR intervals using convolutional neural networks in single-lead long-term Holter electrocardiogram recordings

Advancements in medical technology have extended long-term electrocardiogram (ECG) monitoring from the traditional 24 h to 7-14 days, significantly enriching ECG data. However, this poses unprecedented challenges for physicians in analyzing these extensive datasets. While artificial neural networks have shown great potential in the automatic recognition of arrhythmias and are gradually being adopted widely, their effectiveness still requires rigorous evaluation in clinical applications. Although there have been many research on the evaluation of atrial fibrillation recognition performance, systematic evaluation of automatic detection algorithms for prolonged RR interval(RRI) remains lacking. This study aims to comprehensively evaluate these algorithms based on convolutional neural networks (CNN). We collected 480 single-lead long-term dynamic ECG records from our hospital, all from patients with prolonged RRI. Both CNN algorithms and manual analysis methods were used to analyze the ECGs, with manual analysis serving as the gold standard for performance evaluation. Results indicated that the CNN algorithm achieved an average recall rate of 98.41%, an average precision of 98.68%, and an average F1 score of 98.54%. These metrics demonstrate that CNN algorithms can meet the clinical demands for recognizing prolonged RRI, thereby enhancing physicians' confidence, especially when dealing with large volumes of RRI data. AI provides invaluable support for quantitative analysis and significantly improves diagnostic efficiency. This evaluation offers a reliable basis for deploying single-lead intelligent monitoring devices in households, communities, nursing homes, and other settings.

Cardiac Vagal Nerve Activity During Exercise: New insights and future directions

A new paradigm is emerging in which cardiac vagal nerve activity is maintained and increases during exercise. This paradigm challenges decades of studies that have quoted a withdrawal of cardiac vagal activity during exercise. Here, we outline the existing evidence for increased cardiac vagal activity. We also explain why previous indirect methods used to measure vagal activity might have indirectly led to incorrect conclusions about the role of the cardiac vagus during exercise. We will review evidence that vagal control of the sinoatrial node and the ventricles differs and how vagal neurotransmitters other than acetylcholine may regulate cardiac function during exercise. We will also suggest future directions for research to uncover how the cardiac vagus influences cardiac function and the mechanisms behind the increase in cardiac vagal nerve activity during exercise.

Noninvasive assessment of temporal dynamics in sympathetic and parasympathetic baroreflex responses

Objective.The baroreflex maintains cardiovascular stability by modulating heart rate, myocardial contraction, and vascular tone. However, noninvasive assessment of its sympathetic vascular and myocardial branches often overlooks their time-dependent interplay. To address this gap, we developed and implemented a noninvasive method that characterizes these baroreflex dynamics to enhance understanding of autonomic function and improve clinical assessments of cardiovascular regulation.Approach.We analyzed blood pressure and ECG recordings from 55 preoperative patients and 21 participants from the EUROBAVAR dataset. Baroreflex sensitivity (BRS) was calculated using the sequence method for interbeat interval (IBI), myocardial contractility (dP/dtmax), and systemic vascular resistance (SVR), derived through pulse contour analysis at multiple delays relative to beat-to-beat changes in systolic arterial pressure (SAP). Correlations of these BRS estimates with hemodynamic parameters and heart rate variability (HRV) were evaluated at rest and during active standing.Main results.Distinct temporal profiles of BRS for IBI, SVR, and dP/dtmaxwere identified, with significant correlations to HRV and average SVR, CO, and SAP levels at physiologically relevant delays. Orthostatic stress primarily impacted parasympathetic BRS for IBI, while BRS for SVR and dP/dtmaxshowed subtler changes, reflecting unique time-dependent associations.Significance.This approach provides a tool to comprehensively understand the baroreflex function, highlighting the latency-dependent interactions of its branches with their effectors and their adaptability to physiological challenges. Such insights could improve clinical assessments of autonomic dysfunction with altered baroreflex latencies and inform personalized strategies for managing conditions that compromise cardiovascular stability.

An adaptive protocol to assess physiological responses as a function of task demand in speech-in-noise testing

BACKGROUND

Acoustic challenges impose demands on cognitive resources, known as listening effort (LE), which can substantially influence speech perception and communication. Standardized assessment protocols for monitoring LE are lacking, hindering the development of adaptive hearing assistive technology.

NEW METHOD

We employed an adaptive protocol, including a speech-in-noise test and personalized definition of task demand, to assess LE and its physiological correlates. Features extracted from electroencephalogram, galvanic skin response, electrocardiogram, respiration, pupil dilation, and blood volume pulse responses were analyzed as a function of task demand in 21 healthy participants with normal hearing.

RESULTS

Heightened sympathetic response was observed with higher task demand, evidenced by increased heart rate, blood pressure, and breath amplitude. Blood volume amplitude and breath amplitude exhibited higher sensitivity to changes in task demand.

COMPARISON WITH EXISTING METHODS

Notably, galvanic skin response showed higher amplitude during low task demand phases, indicating increased attention and engagement, aligning with findings from electroencephalogram signals and Lacey's attention theory.

CONCLUSIONS

The analysis of a range of physiological signals, spanning cardiovascular, central, and autonomic domains, demonstrated effectiveness in comprehensively examining LE. Future research should explore additional levels and manipulations of task demand, as well as the influence of individual motivation and hearing sensitivity, to further validate these outcomes and enhance the development of adaptive hearing assistive technology.

The autonomic response following taVNS predicts changes in level of consciousness in DoC patients

Advancements in emergency medicine and critical care have significantly improved survival rates for patients with severe acquired brain injuries(sABI), subsequently increasing the prevalence of disorders of consciousness (DoC) such as Unresponsive Wakefulness Syndrome (UWS) and Minimally Conscious State (MCS). However, the assessment of conscious states relies on the observation of behavioral responses, the interpretation of which may vary from evaluator to evaluator, as well as the high rate of misdiagnosis, which together pose significant challenges for clinical diagnosis. The study investigates the utility of transcutaneous auricular vagus nerve stimulation (taVNS) in modulating autonomic responses, as evidenced through heart rate variability (HRV), for distinguishing between healthy individuals and DoC patients and for prognosticating patient outcomes. A prospective randomized clinical trial was conducted from Februry 9, 2022, to February 4, 2024, at Hangzhou Armed Police Hospital in China. Healthy controls (HC) and DoC patients were enrolled in this study. The taVNS was administered to each subject for ten minutes. There electrocardiogram (ECG) signals were recorded for the analysis of HRV both during the stimulation and the ten minutes of rest that preceded and followed the stimulation. Subsequent investigations utilized Support Vector Machine (SVM) modeling, enhanced by a Radial Basis Function (RBF) kernel, to explore potential predictors of patient outcomes. This approach aimed to differentiate HC from DoC and MCS from UWS patients. 26 HC and 36 patients diagnosed with DoC were included in the analysis,. The DoC group consisted of 17 patients with a diagnosis of MCS and 19 with diagnosis of UWS/VS. Significant modulations in HRV parameters (HF, VLF, SampEn) were observed, indicating variations in autonomic response between the control group and DoC patients. Using the VLF, LF, and SampEn features in SVM model, DoC and HC were correctly classified with an accuracy of 86%. Similarly, MCS and UWS were classified with an accuracy of 78%. The SVM modeling achieved an 86% accuracy rate in predicting outcomes three months post-intervention, with a 71% confirmation rate at six months.The results highlight taVNS's potential as a therapeutic modality in managing DoC by demonstrating its impact on autonomic regulation and suggesting pathways for enhancing recovery, which accentuates the significance of exploring brain-heart dynamics in DoC, presenting a novel approach to therapeutic strategies. Trial Registration Information: URL: chictr.org.cn; Unique identifier: ChiCTR2100045161. Date of the first registration: 9th/ April/ 2021.

The impact of long COVID on heart rate variability: a cross-sectional study

BACKGROUND

Long-term COVID-19 (LC), which may affect the autonomic nervous system (ANS), is the term for the symptoms that some patients had for an additional month after contracting the virus. Therefore, during the LC phase, ANS status was evaluated in patients with mild-to-moderate COVID-19 using heart rate variability (HRV), a measurement of ANS function.

METHODS

A cross-sectional research with 173 participants - both positive and negative for COVID-19 - was conducted. Based on self-reports, patients with COVID-19 were classified as to whether they had LC or not. A 5-minute ECG recorder and data detection and response report were used to measure the ANS.

RESULTS

There were notable age differences across the groups (p = 0.034). Patients with LC under 25 years of age had a lower HRV categorized as a very-low-frequency (VLF) domain (p = 0.012). Compared to the group without LC, a higher number of people in the LC group had aberrant autonomic neuroactivity (p = 0.048).

CONCLUSION

Mild-to-moderate patients with COVID-19 in young to middle age may develop autonomic dysfunction one month after infection.

Non-invasive vagus nerve stimulation and exercise capacity in healthy volunteers: a randomized trial

BACKGROUND AND AIMS

Vagal parasympathetic dysfunction is strongly associated with impaired exercise tolerance, indicating that coordinated autonomic control is essential for optimizing exercise performance. This study tested the hypothesis that autonomic neuromodulation by non-invasive transcutaneous vagus nerve stimulation (tVNS) can improve exercise capacity in humans.

METHODS

This single-centre, randomized, double-blind, sham-controlled, crossover trial in 28 healthy volunteers evaluated the effect of bilateral transcutaneous stimulation of vagal auricular innervation, applied for 30 min daily for 7 days, on measures of cardiorespiratory fitness (peak oxygen consumption (VO2peak)) during progressive exercise to exhaustion. Secondary endpoints included peak work rate, cardiorespiratory measures, and the whole blood inflammatory response to lipopolysaccharide ex vivo.

RESULTS

tVNS applied for 30 min daily over 7 consecutive days increased VO2peak by 1.04 mL/kg/min (95% CI: .34-1.73; P = .005), compared with no change after sham stimulation (-0.54 mL/kg/min; 95% CI: -1.52 to .45). No carry-over effect was observed following the 2-week washout period. tVNS increased work rate (by 6 W; 95% CI: 2-10; P = .006), heart rate (by 4 bpm; 95% CI: 1-7; P = .011), and respiratory rate (by 4 breaths/min; 95% CI: 2-6; P < .001) at peak exercise. Analysis of the whole blood transcriptomic response to lipopolysaccharide in serial samples obtained from five participants showed that tVNS reduced the inflammatory response.

CONCLUSIONS

Non-invasive vagal stimulation improves measures of cardiorespiratory fitness and attenuates inflammation, offering an inexpensive, safe, and scalable approach to improve exercise capacity.

Reference ranges of gender- and age-related heart rate variability parameters in Russian children

To obtain reference ranges for heart rate variability (HRV) parameters in healthy children, taking into account their gender and age. The study included the results of testing 22,468 children ranging 5.5-12.5 years of age. The data were grouped by age and gender. The analysis of HRV parameters was carried out according to the standards described in existing guidelines. It was based on a 5-min rhythmogram obtained from a standard 12-lead electrocardiogram (ECG). The following characteristics of the temporal and spectral analyses of HRV were studied: standard deviation of NN intervals (SDNN), power in the low-frequency band of the HRV spectrum (LF), low-frequency power as mean percentage of total power (TP) of HRV spectrum (LF%), power in the high-frequency band of the HRV spectrum (HF), high-frequency power as mean percentage of TP of HRV spectrum (HF%), power in the very-low-frequency band of HRV (VLF), and LF/HF ratio. The values of SDNN, LF, HF, HF% and TP increased with age, reaching a peak at 8 and 9 years of age. It is notable that the values of SDNN, LF and TP were significantly lower in girls in each age group. The values of LF% and LF/HF decreased with age, with a peak decrease at 8 and 9 years of age, followed by a moderate increase or stabilization. The values of LF% and LF/HF did not differ statistically significantly between boys and girls. The VLF parameter exhibited a clear trend of growth with age and had higher values in boys of each age group. The correlation between HRV and heart rate (HR) was statistically significant. The correlation graphs had similar curves in both gender groups and both age groups. The parameters of the total HRV, as well as the activity of the parasympathetic nervous system (PNS), exhibited similar growth trends with age, with a peak increase in their values at 8 and 9 years of age. HR, as well as the activity of the sympathetic nervous system (SNS), decreased with age. Gender differences also followed a consistent pattern: parameters characterizing the activity of the peripheral nervous system were significantly higher in boys than in girls across all age groups.

Cross-Sectional Study Evaluating the Role of Autonomic Nervous System Functional Diagnostics in Differentiating Post-Infectious Syndromes: Post-COVID Syndrome, Chronic Fatigue Syndrome, and Lyme Disease

Background/Objectives: Post-infectious syndromes, including Post-COVID syndrome, Chronic Fatigue Syndrome, and late-stage Lyme disease, are associated with overlapping clinical features and autonomic dysfunction. Despite shared symptoms such as fatigue and orthostatic intolerance, the underlying pathophysiology and specific patterns of autonomic dysfunction may differ. This study aimed to evaluate and compare autonomic nervous system function in these syndromes using multiple diagnostic modalities to identify unique characteristics and improve differentiation between these conditions. Methods: This cross-sectional study included 758 patients, which were divided into four groups: Post-COVID syndrome, Chronic Fatigue Syndrome following Post-COVID syndrome, Chronic Fatigue Syndrome unrelated to COVID-19, and late-stage Lyme disease. Autonomic nervous system function was assessed using cardiovascular reflex tests, the Head-Up Tilt Test, beat-to-beat analysis, five-minute electrocardiogram recordings, 24 h Holter electrocardiogram monitoring, and 24 h ambulatory blood pressure monitoring. Statistical analyses compared parameters across the groups, focusing on patterns of sympathetic and parasympathetic dysfunction. Results: The patients with Lyme disease showed distinct autonomic patterns, including a higher prevalence of orthostatic hypotension (53.4%) and changes in heart rate variability during the Head-Up Tilt Test suggestive of adrenergic failure. Compared to the other groups, patients with Lyme disease exhibited reduced baroreceptor sensitivity and diminished changes in frequency domain heart rate variability parameters during orthostatic stress. Parasympathetic dysfunction was less prevalent in the Lyme disease group, while the Post-COVID syndrome and Chronic Fatigue Syndrome groups showed more pronounced autonomic imbalances. Conclusions: The patients with Post-COVID syndrome, Chronic Fatigue Syndrome, and late-stage Lyme disease exhibited varying degrees and types of autonomic dysfunction. Late-stage Lyme disease is characterized by adrenergic failure and distinct hemodynamic responses, differentiating it from other syndromes. The functional assessment of autonomic nervous system function could aid in understanding and managing these conditions, offering insights for targeted therapeutic interventions.

Heart rate variability metrics and myocardial recovery in heart failure with reduced ejection fraction

PURPOSE

Autonomic dysregulation is observed in heart failure (HF) with reduced ejection fraction (HFrEF). Abnormal heart rate variability (HRV), a measure of such dysregulation, is associated with poor prognosis in HFrEF. It is unknown if novel HRV metrics normalize in the patients with recovered ejection fraction (HFrecEF) compared to persistent HFrEF. The aim of this study was to investigate novel HRV indexes in persistent HFrEF in comparison to HFrecEF METHODS: A standard 10-min electrocardiography measurement was performed in patients categorized in four groups: persistent HFrEF (n = 40), HFrecEF (n = 41), stage A HF (n = 73) and healthy controls (n = 40).

RESULTS

All HRV indexes were significantly different between the four groups. Specifically, novel metrics, such as higher parasympathetic nervous system (PNS) index and lower sympathetic nervous system (SNS) index, were observed in the HFrecEF group compared to the persistent HFrEF group. In multiple logistic regression analysis, higher PNS index (odds ratio [OR] 2.02, 95% confidence interval [CI] 1.17-3.49; p = 0.01) and lower SNS index (OR 0.68, 95% CI 0.52-0.87; p = 0.002) were associated with HFrecEF. Receiver operating characteristic analysis showed that the SNS index had the highest area under the curve (AUC), followed by the PNS index and mean heart rate for the HF phenotype regarding EF recovery (AUC = 0.71, 0.69 and 0.69, respectively).

CONCLUSION

Myocardial functional recovery in HFrEF is associated with improved parasympathetic activity and reduced sympathetic activity, as reflected in the PNS and SNS indexes. These novel metrics can be potentially used to aid in identifying recovered versus non-recovered phenotypes in patients with HFrEF.

Tracking autonomic nervous system activity using surface ECG: Personalized, multiparametric evaluation

We present a concise review of the background, pitfalls, and potential solutions for the noninvasive evaluation and continuous tracking of cardiac autonomic nervous system activity (ANSA), using surface-ECG-accessible parameters, including heart rate (HR), heart-rate variability (HRV), and cardiac repolarization. These parameters have provided insights into the dynamics of cardiac ANSA in controlled experiments and have proved useful in risk assessment with respect to sudden cardiac death and all-cause mortality in some patient populations, as well as in implantable device programming. Yet attempts to translate these parameters from the laboratory environment to ambulatory settings have been hampered by the presence of multiple uncontrolled factors, including changes in blood pressure, body position, physical activity, and respiration frequency. We show that a single-parameter-based, simplified cardiac ANSA evaluation in an uncontrolled ambulatory setting could be inaccurate, and we discuss several approaches to improve accuracy. Discerning cardiac ANSA effects in uncontrolled ambulatory environments requires tracking multiple physiological processes, preferably using multisensor, multiparametric monitoring and controlling some physiological variables (e.g., respiration frequency); data fusion and machine-learning-based analytics are instrumental for developing more accurate personalized ANSA evaluation.

Heart Rate Variability and Heart Failure with Reduced Ejection Fraction: A Systematic Review of Literature

INTRODUCTION

Autonomic impairment is a hallmark of heart failure with reduced ejection fraction (HFrEF). While there have been studies on general values for each index of heart rate variability (HRV) analysis in HFrEF, a systematic review comprehensively examining representative values in HFrEF is lacking.

METHODS

We searched PubMed, Embase, and Cochrane databases to extract studies reporting representative values of HRV metrics in HFrEF.

RESULTS

A total of 470 HFrEF patients from 6 studies were included in the review. In general, time and frequency domains were abnormally lower in HFrEF, portending a worse prognosis. In HFrEF, the mean or median value of the standard deviation of NN interval, root mean square successive difference, pNN50, and low-frequency power/high-frequency power were 40 to 121 msec, 19 to 62 msec, 1.3 to 14%, and 1.00 to 1.73, respectively.

CONCLUSION

In this systematic review, most HRV metrics were found to be calculated from 24- hour Holter recordings and were lower in HFrEF patients with poor prognosis.

Changes in heart rate variability at rest and during exercise in patients after a stroke: a feasibility study

The aim of this study was to evaluate the feasibility of using a biofeedback-enhanced robotics-assisted tilt table (RATT) to investigate time- and intensity-dependent changes in heart rate variability (HRV) at rest and during heart rate-controlled exercise in patients recovering from a stroke. Twelve patients (age 55.3 years ± 15.6 years, 7 women) completed two separate measurement sessions. The first involved familiarization and system identification to determine parameters of a feedback system for automatic control of heart rate (HR). The second comprised 14 min of rest and 21 min of active exercise during which HR was held constant using feedback control to eliminate cardiovascular drift. HR data were collected using a chest-belt HR sensor, and raw RR intervals were employed for HRV analysis during periods of rest (0-7 min and 7-14 min) and exercise (5-13 min and 13-21 min). A biofeedback-enhanced, robotics-assisted tilt table can be successfully employed to perform heart rate-controlled exercises in patients after a stroke. All HRV metrics were substantially lower during exercise compared to rest. In the rest period, HRV values during 0-7 min were lower than during 7-14 min, in line with a slight HR decrease over the entire rest period. During exercise, HRV values during 5-13 min were higher than during 13-21 min, suggesting a time-dependent HRV decrease. All HRV metrics exhibited intensity- and time-dependent changes: higher HRV at rest and decreasing HRV over time. Understanding these HRV characteristics will support the development of heart rate-controlled exercise regimens and protocols for examining HRV changes during exercise in patients.

Noninvasive Assessment of Temporal Dynamics in Sympathetic and Parasympathetic Baroreflex Responses

Background

The baroreflex system is crucial for cardiovascular regulation and autonomic homeostasis. A comprehensive assessment requires understanding the simultaneous temporal dynamics of its multiple functional branches, which traditional methods often overlook.

Objective

To develop and validate a noninvasive method for simultaneously assessing the temporal dynamics of sympathetic and parasympathetic baroreflexes using pulse contour analysis and the sequence method.

Methods

Beat-to-beat blood pressure and ECG recordings were analyzed from 55 preoperative cardiothoracic surgery patients in the supine position and 21 subjects from the EUROBAVAR dataset in both supine and standing positions. Systolic arterial pressure (SAP), interbeat interval (IBI), cardiac output (CO), myocardial contraction (dP/dtmax), and systemic vascular resistance (SVR) were estimated using pulse contour analysis. Baroreflex sensitivity (BRS) was calculated via the sequence method and correlated with hemodynamic and heart rate variability (HRV) parameters.

Results

Parasympathetic BRS for IBI was correlated with the root mean square of successive differences of ECG RR intervals (RMSSD-HRV) at 0-beat delay. Sympathetic BRS for SVR strongly correlated with SVR, CO, and RMSSD-HRV, particularly at 3-beat delay, and was uniquely associated with SAP at 1-beat delay. Sympathetic BRS for dP/dtmax correlated with dP/dtmax at 1-beat delay. In contrast, BRS for CO correlated with CO and SVR at 0- and 3-beat delays. Postural changes mainly affected parasympathetically-mediated BRS for IBI and, to a lesser extent, the sympathetic vascular and myocardial branches.

Conclusions

This method effectively captures multiple baroreflex responses and their temporal dynamics, revealing distinct autonomic mechanisms and the impact of postural changes. Further validation is warranted.

Influence of autonomic nervous dysfunction on eating during hemodialysis sessions: An observational study

Although some studies have indicated that eating during hemodialysis may induce hypotension and cardiovascular events, some patients still consume food during their treatment. This prospective study was conducted to determine whether the need to eat during hemodialysis treatment was related to abnormal glucose metabolism and autonomic nerve dysfunction. Seventy patients were enrolled in this study, and their demographic features and various laboratory parameters were analyzed. At each routine hemodialysis visit, predialysis, intradialysis, and postdialysis blood pressure measurements were systematically conducted. A 24-hour ambulatory electrocardiogram (ECG) was performed during the hemodialysis interval, and heart rate variability (HRV) values were calculated. Additionally, whether the patients ate during the hemodialysis treatments was recorded. Another 20 people who underwent physical examinations during the same period and were matched for sex and age were included in the control group. The HRV values of the hemodialysis patients were generally lower than those of the control group. Univariate analysis revealed significant differences in sex, age, calcium antagonist use, blood calcium levels, insulin levels, diastolic blood pressure (DBP) measurements, and HRV indices between hemodialysis patients who ate and those who did not eat during hemodialysis (P < .05), whereas there were no significant differences in diabetes status or in the hemoglobin, albumin, blood glucose and C-peptide levels (P > .05). Multivariate analysis revealed that low values for very low frequency (VLF) and postdialysis DBP were risk factors for fasting intolerance during hemodialysis treatments. Autonomic dysfunction may affect whether hemodialysis patients tolerate fasting during dialysis. VLF evaluation may provide information that can be used to develop a more reasonable intradialytic nutritional supplementation method.

Publication guidelines for human heart rate and heart rate variability studies in psychophysiology-Part 1: Physiological underpinnings and foundations of measurement

This Committee Report provides methodological, interpretive, and reporting guidance for researchers who use measures of heart rate (HR) and heart rate variability (HRV) in psychophysiological research. We provide brief summaries of best practices in measuring HR and HRV via electrocardiographic and photoplethysmographic signals in laboratory, field (ambulatory), and brain-imaging contexts to address research questions incorporating measures of HR and HRV. The Report emphasizes evidence for the strengths and weaknesses of different recording and derivation methods for measures of HR and HRV. Along with this guidance, the Report reviews what is known about the origin of the heartbeat and its neural control, including factors that produce and influence HRV metrics. The Report concludes with checklists to guide authors in study design and analysis considerations, as well as guidance on the reporting of key methodological details and characteristics of the samples under study. It is expected that rigorous and transparent recording and reporting of HR and HRV measures will strengthen inferences across the many applications of these metrics in psychophysiology. The prior Committee Reports on HR and HRV are several decades old. Since their appearance, technologies for human cardiac and vascular monitoring in laboratory and daily life (i.e., ambulatory) contexts have greatly expanded. This Committee Report was prepared for the Society for Psychophysiological Research to provide updated methodological and interpretive guidance, as well as to summarize best practices for reporting HR and HRV studies in humans.

Cardiorespiratory Effects of Yogic Versus Slow Breathing in Individuals with a Spinal Cord Injury: An Exploratory Cohort Study

Background: An intricate physiological and pathophysiological connection exists between the heart and lungs, which is especially important in individuals with spinal cord injury (SCI). While an exercise intervention may seem the best approach to leverage this relationship, the prior work has shown that, despite numerous health benefits, regular exercise training does not improve cardiorespiratory control in individuals with SCI. Breath training presents an alternative intervention that is uniquely accessible, with yogic breathing directly engaging linked fluctuations in respiration and cardiovascular control. In addition, there is evidence across a range of populations that regular yogic breathing reduces cardiovascular disease risk. It is possible that the chronic decrease in breathing frequency associated with regular yogic breathing, rather than the specific yogic breathing techniques themselves, is the primary contributor to the observed risk reduction. Methods: Therefore, in 12 individuals with traumatic SCI from C4 to T8, the authors compared Unpaced and conventional 0.083 Hz (Slow) paced breathing with various yogic breathing techniques including: (1) inspiratory-expiratory breath holds (i.e., Kumbhaka or "Box Breathing"), (2) extended exhalation (1:2 duty cycle), and (3) expiratory resistance via throat constriction (i.e., Ujjayi). Beat-to-beat heart rate and blood pressure were measured as well as end-tidal CO2 and O2 saturation were measured. Statistical analysis was performed using a one-way repeated-measures analysis of variance with post hoc pairwise t tests corrected for multiple comparisons. Results: As expected, all slow breathing patterns markedly increased respiratory sinus arrhythmia (RSA) compared with Unpaced in all (n = 12) individuals. More importantly, Ujjayi breathing appeared to improve ventilatory efficiency over Unpaced breathing in individuals with SCI by increasing O2 saturation (97.6% vs. 96.1%; p = 0.042) and tended to decrease end-tidal CO2 (32 mmHg vs. 35 mmHg; p = 0.08). While other slow breathing patterns demonstrated similar effects, only Ujjayi improved RSA while increasing heart rate and improving ventilatory efficiency. Conclusions: Hence, slow breathing per se can result in important cardiorespiratory changes, but the yogic breathing practice of Ujjayi, with glottic throat resistance, may hold the greatest promise for improving cardiorespiratory control in individuals with SCI (CTR ID No. NCT05480618).

Heart rate variability: reference values and role for clinical profile and mortality in individuals with heart failure

AIMS

To establish reference values and clinically relevant determinants for measures of heart rate variability (HRV) and to assess their relevance for clinical outcome prediction in individuals with heart failure.

METHODS

Data from the MyoVasc study (NCT04064450; N = 3289), a prospective cohort on chronic heart failure with a highly standardized, 5 h examination, and Holter ECG recording were investigated. HRV markers were selected using a systematic literature screen and a data-driven approach. Reference values were determined from a healthy subsample. Clinical determinants of HRV were investigated via multivariable linear regression analyses, while their relationship with mortality was investigated by multivariable Cox regression analyses.

RESULTS

Holter ECG recordings were available for analysis in 1001 study participants (mean age 64.5 ± 10.5 years; female sex 35.4%). While the most frequently reported HRV markers in literature were from time and frequency domains, the data-driven approach revealed predominantly non-linear HRV measures. Age, sex, dyslipidemia, family history of myocardial infarction or stroke, peripheral artery disease, and heart failure were strongly related to HRV in multivariable models. In a follow-up period of 6.5 years, acceleration capacity [HRperSD 1.53 (95% CI 1.21/1.93), p = 0.0004], deceleration capacity [HRperSD: 0.70 (95% CI 0.55/0.88), p = 0.002], and time lag [HRperSD 1.22 (95% CI 1.03/1.44), p = 0.018] were the strongest predictors of all-cause mortality in individuals with heart failure independently of cardiovascular risk factors, comorbidities, and medication.

CONCLUSION

HRV markers are associated with the cardiovascular clinical profile and are strong and independent predictors of survival in heart failure. This underscores clinical relevance and interventional potential for individuals with heart failure.

CLINICALTRIALS

GOV IDENTIFIER

NCT04064450.

Spectral Power Distribution of Heart Rate Variability in Contiguous Short-Term Intervals

INTRODUCTION

Heart rate variability (HRV) is determined by the variation of consecutive cardiac electrical excitations, usually from RR intervals of an EKG. The sequence of intervals is a time series that yields three HRV parameter categories: time domain, frequency domain, and nonlinear. Parameter estimates are based on widely different EKG sample times: short-term (~5-10 minutes), longer (24 hours), and ultra-short (<5 minutes). Five-minute intervals are useful to evaluate intervention effects that change HRV in a single session by comparing pre-to-post values. This approach relies on knowing the minimal detectible change (MDC) that indicates a real change in clinical and research studies. The specific aims of this pilot study were to (1) evaluate HRV power and its spectral distribution among contiguous five-minute intervals, (2) compare the power distribution in a five-minute interval with a full 45-minute assessment, and (3) provide data to aid estimation of the MDC between pre- and post-interventions during a single session.  Methods: Twelve self-reported healthy young adults participated after signing an approved consent. Participation required subjects who had no history of cardiovascular disease or were taking vasoactive substances. Persons with diabetes were not eligible. While subjects were supine, EKG leads were placed, and EKG was recorded for 45 minutes at 1000 samples/sec. The 45 minutes were divided into nine five-minute contiguous intervals, and the spectral density in each was determined. Total power and spectral percentages within each interval were assessed in the very low (VLF, 0.003-0.04 Hz), low (LF, 0.04-0.15 Hz), and high (HF, 0.15-0.4 Hz) frequency bands. These were compared among intervals and to the full 45-minute sample. The MDC was determined by comparing powers in five-minute intervals separated by 10 minutes. The standard error of the measurement (SEME) for each pair was calculated from the square root of the mean square error (√MSE). MSE was based on a two-factor analysis of variance, and MDC was 2×√2×SEME.

RESULTS

Differences in total power and spectral power distribution among intervals were not statistically significant. The total mean power±SD was 4561±1434 ms². The maximum difference in total power was 7.85%. The mean power for the VLF, LF, and HF bands was respectively 1713±1736 ms², 1574±1072 ms², and 1257±1016 ms². The maximum percentage difference in spectral power across all intervals for VLF, LF, and HF was respectively 3.75%, 8.5%, and 7.4%. The percentage of power in the VLF, LF, and HF bands was respectively 37.9%, 36.1%, and 25.9%. The ratios of spectral to total power for VLF, LF, and HF bands were respectively 0.80±0.07, 1.20±0.11, and 1.22±0.10. MDC percentage values were 21.0±4.9% for the HF band, 25.7±1.4% for the LF band, and 30.4±5.5% for the VLF band.

CONCLUSION

Results offer initial estimates of variations in HRV power in the VLF, LF, and HF bands in contiguous five-minute intervals and estimates of the minimum detectible "real" changes between intervals separated by 10 minutes. The pattern of variation and data are useful in experimental planning in which HRV spectral power changes are assessed subsequent to a short-duration intervention during a single session. MDC values (21.0% in the HF band to 30.4% in the VLF band) provide initial estimates useful for estimating the number of participants needed to evaluate the impact of an intervention on spectral components of HRV.

Vagal predominance correlates with mood state changes of winter-over expeditioners during prolonged Antarctic residence

OBJECTIVE

Winter-over expeditioners in Antarctica are challenged by various environmental and psycho-social stress factors, which may induce psychophysiological changes. The autonomic nervous system (ANS) plays a crucial role in the adaptation process under stress. However, the relationship between ANS activity and the mood states of expeditioners remains largely unexplored. This study aims to uncover the pattern of ANS adjustment under extreme Antarctic environments and provide new insights into the correlations between ANS activity and mood state changes, which may provide scientific data for medical interventions.

METHODS

Fourteen expeditioners at Zhongshan Station participated in this study. The study was conducted during four representative periods: pre-Antarctica, Antarctica-1 (pre-winter), Antarctica-2 (winter), and Antarctica-3 (summer). The heart rate variability (HRV) of the expeditioners was continuously measured for 24 hours to evaluate ANS activity. Plasma levels of catecholamines were tested by ELISA. Mood states were assessed by the Profile of Mood States (POMS) scale.

RESULTS

HRV analysis showed a disturbance of ANS during winter and summer periods. For frequency domain parameters, very low frequency (VLF), low frequency (LF), high frequency (HF), and total power (TP) significantly increased during the second half of the mission. Especially, LF/HF ratio decreased during summer, indicating the predominance of vagal tone. Results of the time domain analysis showed increased heart rate variability during the austral winter and summer. Plasma epinephrine (E) significantly increased during residence in Antarctica. Compared with pre-Antarctica, the vigor, depression, and anger scores of the expeditioners decreased significantly during the austral summer. Notably, the depression score showed a moderate positive correlation with LF/HF, while weak negative correlations with other HRV indicators, including TP, VLF, and LF. Anger score showed a moderate positive correlation with LF/HF and weak negative correlations with the average normal-to-normal (NN) interval, and the root mean square of differences between adjacent RR intervals (RMSSD). Plasma E level weakly correlated with the average NN interval.

CONCLUSION

Prolonged residence in Antarctica increased the ANS activities and shifted the cardiac autonomic modulation towards vagal predominance. The alteration of HRV correlated with mood states and plasma epinephrine levels.

Menstrual Irregularity: A Physiological Adaptation to Cope Perceived Stress

INTRODUCTION

Menstrual cycle characteristics are regulated hormonally and are integrated at the level of the hypothalamus. Stress can affect the hypothalamic-pituitary gonadal axis. The objective of the study was to analyse the stress levels of women and compare their autonomic tone and menstrual characteristics.

METHODOLOGY

A group of 100 apparently healthy, young, female volunteers were included in this pilot cohort study. Subjects were assessed for perceived stress using the Perceived Stress Scale 14 Item (PSS-14) questionnaire, underwent a heart rate variability (HRV) test on the second, 10th, and 21st days of their menstrual cycle, and their menstrual history was recorded. The statistical analysis was done using Statistical Product and Service Solutions (SPSS, version 21.0; IBM SPSS Statistics for Windows, Armonk, NY) software. Metric data were expressed in terms of numerical value and analysed as mean ± SD. Paired Student's T-test was used to compare the HRV data of all three days of the menstrual cycle separately, and p value<0.05 was considered significant. Menstrual irregularity was complained of by 13 subjects (Group A), and the rest (87 subjects) reported regular menses (Group B).

RESULT

The perceived stress scores of Group A were significantly higher than Group B (32.53±5.062 vs 28.057±7.618; p=0.044). On second day, Group A had higher median R-R interval (714.38±106 vs 656.84±73.50 ms; p=0.015) and lower average heart rate (85.85±12.07 vs 92.39±9.98 bpm; p=0.034) than Group B, suggesting parasympathetic dominance. On the 10th day, Group A had a higher standard deviation of heart rate (7.09±1.88 vs 5.97±1.71 bpm; p=0.032) and a very low-frequency band (1105.94±984.12 vs 730.49±557.41 μs2; p=0.046) than Group B, indicating parasympathetic dominance in Group A. On the 21st day, Group A had a higher standard deviation of R-R interval (58.19±20.46 vs 44.85±14.55 ms; p=0.004), root mean square standard deviation (55.71±29.84 vs 31.89±15.99 ms; p<0.001), percentage of R-R differing by 50 ms (19.20±19.58 vs 10.87±10.31%; p=0.020), total power (3,440.23±2722.29 vs 2,068.28±1,322.49 μs2; p=0.004), high-frequency band (1,247.57±1173.54 vs 539.06±HPO438.92 μs2; p<0.001), standard deviation ratio of the Poincaré plot (0.53±0.19 vs 0.39±0.16; p=0.003), normalised HF (44.0±12.9 vs 35.4±10.6; p=0.009), and a lower LF/HF ratio (1.43±0.80 vs 2.11±1.16; p=0.043) and normalised LF (53.9±14.4 vs 64.1±11.9; p=0.006) than Group B, suggesting higher parasympathetic tone of Group A than Group B.

CONCLUSION

Analysing these results, it can be concluded that, in apparently healthy young women, menstrual irregularity is a physiological adaptation to combat perceived stress and maintain parasympathetic dominance.

Physiological stress responses in horses participating in novice endurance rides

Horses participating in endurance events encounter enormous physical challenges. Heart rate (HR) and heart rate variability (HRV) have been reported before and after endurance rides, but these have not been determined during the rides. Moreover, the modulation in HRV and haematology in horses with different ride results (completed a course or disqualified due to irregular gait) have not been elucidated. Therefore, this study aimed to investigate changes in HR, HRV, and haematological parameters during novice endurance rides and to compare these parameters between horses that successfully completed the course (SC) or were disqualified for irregular gait (FTQ-GA). Beat-to-beat (RR) intervals of 16 healthy horses (aged 6-14 years) were recorded before and throughout the approximately 40 km endurance event. Blood samples were taken at the pre-ride inspection and after passing each veterinary inspection. HRV and haematology measures were determined from nine SC and seven FTQ-GA horses. Horses with different ride results demonstrated distinctive physiological stress responses. Increases in PCV, RBC, WBC and neutrophils after completing the ride were found only in SC horses, implying that they were ridden with greater effort than FTQ-GA horses. A reduction in HRV during warm-up, followed by a significant reduction during the first and second riding phases, was observed. HRV returned to baseline at the compulsory rest period of both phases. FTQ-GA horses experienced lower RR intervals, RR triangular index, modified deceleration capacity, very-low-frequency band, and parasympathetic nervous system index, coinciding with higher HR and sympathetic nervous system and stress indices than SC horses. These results indicated that endurance horses revealed a shift toward sympathetic activity during the ride. Lower parasympathetic activity in FTQ-GA horses suggests they were under more stress or discomfort than SC horses in novice endurance rides. These results have welfare implications, indicating the need for additional rest breaks in FTQ-GA horses.

Comparison of daily heart rate and heart rate variability in trained and sedentary aged horses

Athletic horses are usually retired from equestrian competition at an advanced age. Aged horses may then continue to have regular exercise or are sedentary. The comparison of autonomic regulation between sedentary aged horses (SAH) and trained aged horses (TAH) after retirement remains unpublished. This study compared daily heart rate (HR) and heart rate variability between 11 SAH and 11 TAH over 22 h (07.00 h to 05.00 h on an alternate day) and during the day and night. An increase in mean beat-to-beat (RR) intervals (p < 0.01-0.0001) and parasympathetic nervous system (PNS) index (p < 0.05-0.0001), corresponding to the decreased HR and sympathetic nervous system (SNS) index (p < 0.01-0.0001), was observed at night. Compared to SAH, lowered mean HR and SNS index, corresponding to elevated mean RR intervals and very-low-frequency bands, were marked in TAH during the day (p < 0.05 for all variables). Whereas the standard deviation of the RR intervals index was higher in TAH than in SAH during the day and night (p < 0.05 for both periods). It was suggested that aged horses with different physical activities revealed distinct autonomic responses. TAH demonstrated higher HRV than SAH during the day. A decreased HR in TAH is prone to result from a reduced SNS role, leading to a shift toward more PNS activity during the day. More research is warranted to determine to what extent the autonomic regulation is modulated by accompanying higher exercise volume or programmed exercise in aged horses.

Ambulatory electrocardiographic longitudinal monitoring in a canine model for Duchenne muscular dystrophy identifies decreased very low frequency power as a hallmark of impaired heart rate variability

Duchenne muscular dystrophy (DMD) patients exhibit a late left ventricular systolic dysfunction preceded by an occult phase, during which myocardial fibrosis progresses and some early functional impairments can be detected. These latter include electrocardiographic (ECG) and heart rate variability (HRV) abnormalities. This longitudinal study aimed at describing the sequence of ECG and HRV abnormalities, using Holter ECG in the GRMD (Golden retriever muscular dystrophy) dog model, known to develop a DMD-like disease, including cardiomyopathy. Most of the known ECG abnormalities described in DMD patients were also found in GRMD dogs, including increased heart rate, prolonged QT and shortened PR intervals, ventricular arrhythmias, and several of them could be detected months before the decrease of fractional shortening. The HRV was impaired like in DMD patients, one of the earliest evidenced abnormalities being a decrease in the very low frequency (VLF) component of the power spectrum. This decrease was correlated with the further reduction of fractional shortening. Such decreased VLF probably reflects impaired autonomic function and abnormal vasomotor tone. This study provides new insights into the knowledge of the GRMD dog model and DMD cardiomyopathy and emphasizes the interest to monitor the VLF power in DMD patients, still unexplored in this disease, whilst it is highly predictive of deleterious clinical events in many other pathological conditions.

The effects of acute exercise and a nap on heart rate variability and memory in young sedentary adults

Recent evidence suggests that the autonomic nervous system can contribute to memory consolidation during sleep. Whether fluctuations in cardiac autonomic activity during sleep following physical exercise contribute to the process of memory consolidation has not been studied. We assessed the effects of a non-rapid eye movement (NREM) nap following acute exercise on cardiac autonomic regulation assessed with heart rate variability (HRV) to examine if HRV influences memory processes. Fifty-six (59% female) healthy young adults (23.14 ± 3.74 years) were randomly allocated to either the exercise plus nap (ExNap, n = 27) or nap alone (NoExNap, n = 29) groups. The ExNap group performed a 40-minute moderate-intensity cycling, while the NoExNap group was sedentary prior to learning 45 neutral pictures for a later test. Subsequently, participants underwent a 60-minute NREM nap while measuring EKG, followed by a visual recognition test. Our results indicated that heart rate did not significantly differ between the groups (p = .243), whereas vagally mediated HRV indices were lower in the ExNap group compared to the NoExNap group (p < .05). There were no significant differences in sleep variables between the groups (p > .05). Recognition accuracy was significantly higher in the ExNap group than in the NoExNap group (p = .027). In addition, the recognition accuracy of the ExNap group was negatively associated with vagally mediated HRV (p < .05). Pre-nap acute exercise appears to attenuate parasympathetic activity and to alter the relationship between memory and cardiac autonomic activity.

Central autonomic network and early prognosis in patients with disorders of consciousness

The central autonomic network (CAN) plays a crucial role in modulating the autonomic nervous system. Heart rate variability (HRV) is a valuable marker for assessing CAN function in disorders of consciousness (DOC) patients. We used HRV analysis for early prognosis in 58 DOC patients enrolled within ten days of hospitalization. They underwent a five-minute electrocardiogram during baseline and acoustic/visual stimulation. The coma recovery scale-revised (CRS-R) was used to define the patient's consciousness level and categorize the good/bad outcome at three months. The high-frequency Power Spectrum Density and the standard deviation of normal-to-normal peaks in baseline, the sample entropy during the stimulation, and the time from injury features were used in the support vector machine analysis (SVM) for outcome prediction. The SVM predicted the patients' outcome with an accuracy of 96% in the training test and 100% in the validation test, underscoring its potential to provide crucial clinical information about prognosis.

CVRanalysis: a free software for analyzing cardiac, vascular and respiratory interactions

Introduction: Simultaneous beat-to-beat R-R intervals, blood pressure and respiration signals are routinely analyzed for the evaluation of autonomic cardiovascular and cardiorespiratory regulations for research or clinical purposes. The more recognized analyses are i) heart rate variability and cardiac coherence, which provides an evaluation of autonomic nervous system activity and more particularly parasympathetic and sympathetic autonomic arms; ii) blood pressure variability which is mainly linked to sympathetic modulation and myogenic vascular function; iii) baroreflex sensitivity; iv) time-frequency analyses to identify fast modifications of autonomic activity; and more recently, v) time and frequency domain Granger causality analyses were introduced for assessing bidirectional causal links between each considered signal, thus allowing the scrutiny of many physiological regulatory mechanisms. Methods: These analyses are commonly applied in various populations and conditions, including mortality and morbidity predictions, cardiac and respiratory rehabilitation, training and overtraining, diabetes, autonomic status of newborns, anesthesia, or neurophysiological studies. Results: We developed CVRanalysis, a free software to analyze cardiac, vascular and respiratory interactions, with a friendly graphical interface designed to meet laboratory requirements. The main strength of CVRanalysis resides in its wide scope of applications: recordings can arise from beat-to-beat preprocessed data (R-R, systolic, diastolic and mean blood pressure, respiration) or raw data (ECG, continuous blood pressure and respiratory waveforms). It has several tools for beat detection and correction, as well as setting of specific areas or events. In addition to the wide possibility of analyses cited above, the interface is also designed for easy study of large cohorts, including batch mode signal processing to avoid running repetitive operations. Results are displayed as figures or saved in text files that are easily employable in statistical softwares. Conclusion: CVRanalysis is freely available at this website: anslabtools.univ-st-etienne.fr. It has been developed using MATLAB® and works on Windows 64-bit operating systems. The software is a standalone application avoiding to have programming skills and to install MATLAB. The aims of this paper area are to describe the physiological, research and clinical contexts of CVRanalysis, to introduce the methodological approach of the different techniques used, and to show an overview of the software with the aid of screenshots.

The Association Between Physical Activity/Heart Rate Variability Data Obtained Using a Wearable Device and Timed Motor Functional Tests in Patients with Duchenne Muscular Dystrophy: A Pilot Study

Background

Duchenne muscular dystrophy (DMD) is a devastating X-linked muscle disease. Clinical evaluation of DMD uses patient-intensive motor function tests, and the recent development of wearable devices allows the collection of a variety of biometric information, including physical activity.

Objective

In this study, we examined differences in physical activity and heart rate variability (HRV) between patients with DMD and healthy subjects using a wearable device, and investigated any association between these parameters and motor function in patients with DMD.

Methods

Participants were 7 patients with DMD and 8 healthy males, whose physical activity and HRV were provided by a wearable device. These data were used to investigate the relationship between both physical activity and HRV parameters and timed motor functional tests [Time to stand from supine, 10-meter walking time (10MWT), North Star Ambulatory Assessment (NSAA), and 6-minute walking test (6MWT)] in patients with DMD.

Results

Results of 24-hours physical activity, fat burning, total number of steps and active distance, average step rate, average exercise intensity during walking, exercise, degree of forward lean during walking, maximum heart rate, normalized low frequency power (LF norm), and maximum exercise intensity in patients with DMD were lower than those in control subjects. Physical activity and HRV parameters did not correlate with the time to stand from supine. The 10MWT positively correlated with average heart rate, while NSAA negatively correlated with average heart rate, total frequency power (TF), and very low frequency power (VLF) during arousal. The 6MWT negatively correlated with ratio LF/high frequency power (HF).

CONCLUSIONS

Physical activity and HRV indices that differ from those of normal children and that correlate with motor function assessment may serve as digital biomarkers.

A pilot study to assess the origin of the spectral power increases of heart rate variability associated with transient changes in the R-R interval

Spectral analysis of heart rate variability (HRV) is used to assess cardiovascular autonomic function. In the power density spectrum calculated from a time series of the R-R interval (RRI), three main components are distinguished: very-low-frequency (VLF; 0.003-0.04 Hz), low-frequency (LF; 0.04-0.15 Hz), and high-frequency (HF; 0.15-0.4 Hz) components. However, the physiological correlates of these frequency components have yet to be determined. In this study, we conducted spectral analysis of data segments of various lengths (5, 30, 100, and 200 s) of the RRI time series during active standing. Because of the trade-off relationship between time and frequency resolution, the analysis of the RRI data segment shorter than 30 s was needed to identify the temporal relationships between individual transient increases in RRI and the resulting spectral power changes. In contrast, the segment of 200 s was needed to properly evaluate the magnitude of the increase in the VLF power. The results showed that a transient increase in the RRI was tightly associated with simultaneous increases in the powers of the VLF, LF, and HF components. We further found that the simultaneous power increases in these three components were caused by the arterial baroreceptor reflex responding to rapid blood pressure rise.

Effect of Exercise in a Vector-Protected Arena for Preventing African Horse Sickness Transmission on Physiological, Biochemical, and Behavioral Variables of Horses

During an African horse sickness (AHS) outbreak, horses were able to exercise daily in a net-covered arena, yet the physiological responses to exercise in a netted arena was unknown. In a cross-over study design, eight horses performed a 39-minute aerobic exercise in conventional (CA) and vector-protected arenas (VPA). Horses were slower in some gaits and covered less distance in the VPA arena (P < .01). Cortisol release, hematology, and heart rate variability (HRV) were also examined. An interaction between the riding arena and time was observed in hematocrit (P = .0013), hemoglobin (P = .0012), and red blood cell count (P = .0027) and HRV variables, including mean beat-to-beat (RR) intervals (P < .0001), mean heart rate (P < .0001), sympathetic nervous system (SNS) index (P = .0038) and parasympathetic nervous system (PNS) index (P < .0001). Cortisol concentrations increased during exercise and 30 minutes postexercise in both arenas. Hematocrit, hemoglobin, and red blood cell count increased immediately postexercise in horses in VPA while remaining high from immediate post-exercise to 60 minutes postexercise in horses in CA. HRV decreased during exercise and was not different between horses in both arenas, but a higher RR interval and PNS index, corresponding to lower heart rate and SNS index, were detected during 30 to 60 minutes postexercise in horses in the VPA compared to the CA. Riding horses in different arenas impacted hematological and HRV variables. The greater RR intervals and PNS index, coinciding with the lower SNS index and heart rate, indicated parasympathetic dominance post-exercise in horses in VPA compared to CA.

Acute hypoxia elicits prefrontal oxygenation asymmetry in young adults

Significance

Cerebrovascular reactivity can be evaluated by prefrontal cortex (PFC) hemodynamic responses and oxygenation changes secondary to hypoxia using near-infrared spectroscopy (NIRS). However, whether there are hemispheric differences in these NIRS-determined PFC hemodynamic responses and oxygenation changes remains unknown.

Aim

This study was performed to determine whether there are differences in the PFC hemodynamic responses and oxygenation changes secondary to hypoxia between the left and right frontal poles (FPL and FPR, respectively).

Approach

Fifteen young men participated in the study. During conduction of an isocapnic hypoxia protocol with a 10-min hypoxic phase at partial pressure of end-tidal oxygen (PET O 2 ) of 45 Torr, hemodynamic and oxygenation indices comprising oxygenated hemoglobin (oxy-Hb), deoxygenated Hb (deoxy-Hb), total Hb (total-Hb), and tissue oxygen saturation (StO 2 ) over FPL and FPR were measured by NIRS. The heart rate (HR) was evaluated by electrocardiography.

Results

In response to hypoxia, the HR increased, oxy-Hb decreased, deoxy-Hb increased, total-Hb increased above baseline, and StO 2 decreased. There was no difference in the change in total-Hb between FPL and FPR. However, there were greater changes in oxy-Hb, deoxy-Hb, and StO 2 over FPL than over FPR, indicating that PFC oxygenation asymmetry occurs in response to hypoxia. Moreover, the change in total-Hb over FPL was associated with the increase in HR.

Conclusions

NIRS-determined hemodynamic responses and oxygenation changes secondary to hypoxia might not simply reflect the direct effect of hypoxia on cerebral vessels. Although there is no hemispheric difference in the PFC hemodynamic responses to hypoxia as in total-Hb, PFC oxygenation asymmetry occurs in young adults.

Association between depressive symptoms and heart rate variability in older patients admitted for rehabilitation: a cross-sectional study

Heart rate variability (HRV) is associated with depressive symptoms, but this relationship in older inpatients undergoing rehabilitation remains unclear. This study investigated the relationship between HRV and depressive symptoms in older inpatients undergoing rehabilitation. Fifty patients aged ≥65 years were assessed for depressive symptoms using the Geriatric Depression Scale. HRV was assessed by frequency analysis. The relationship between depressive symptoms and HRV indices, age, sex, Short Physical Performance Battery (SPPB) score, Mini-Mental State Examination score was examined using simple linear regression. Next, the predictors from the simple linear regression analysis significant at the 0.15 level were inputted in a multiple regression model. Multiple regression analysis revealed that very low frequency HRV [ β = -2.13, 95% confidence interval (CI) -3.15 to -1.11, P  < 0.05] and SPPB score ( β = -0.30, 95% CI -0.52 to -0.08, P  < 0.05) were negatively associated with depressive symptoms: the lower the HRV and the more severe the mobility impairment, the higher the severity of the depressive symptoms. Very low frequency (VLF) HRV and physical performance, as measured by the SPPB score, were associated with depressive symptoms in older patients undergoing rehabilitation. VLF HRV may serve as a useful biomarker for detecting depressive symptoms in this population.

Heart rate variability in patients with psychiatric disorders from adolescence to adulthood

OBJECTIVE

Age is associated with changes in autonomic nervous system activity. These changes are assessed using heart rate variability(HRV) indicators; however, the effect of age on HRV in patients with psychiatric disorders remains unclear. Our study aimed to explore this effect and determine its variance across different lifespans.

METHOD

Consecutive patients(N = 3315), comprising 1833 patients with psychotic disorders, 1040 with mood disorders, and 442 with anxiety disorders, were recruited. The patients were divided into four age groups: adolescence(10-24 years), early adulthood(25-39 years), middle adulthood(40-59 years), and late adulthood(60+ years). HRV indicators were measured during a 5-min rest period.

RESULTS

The heart rate and HRV indices were higher in the adolescent and early adulthood groups than they were in the middle and late adulthood groups(increased HRV is beneficial for health, while reduced HRV is detrimental). Age and all the HRV indices were negatively correlated(r-values 0.153-0.350, p < 0.001), with these correlation patterns being more evident in the adolescent and early adulthood groups than in the middle and late adulthood groups. Stratified by sex, the low-frequency/high-frequency ratio was higher in men than in women across most age groups(p < 0.05), except the late adulthood group(p = 0.085). Stratified by diagnosis, most HRV variables(except very low-frequency) were lower in the psychotic disorder group than they were in the mood and anxiety disorder groups, especially in middle and late adulthood patients. After adjusting for confounders, the HRV variables were significantly associated with age, while older age was associated with lower HRV.

CONCLUSIONS

These results indicate that the substantial reduction in HRV with age in patients with psychiatric disorders. The association remains significant after correction for sex, heart rate, and diagnoses; this may prove useful to clinical practice and further research.

Experimental Investigation of the Influence of Positive Emotion Dysregulation on Risky Behavior Following Idiographic Emotion Inductions

An experimental paradigm with subjective and objective assessments was used to further explicate the role of positive emotion dysregulation on risky behavior. Participants were 151 community women currently experiencing intimate partner violence and using substances (Mage = 40.81, 43.0% white). Participants were randomly assigned to positive, negative, and neutral idiographic emotion inductions. Subjective (state self-report) and objective (high frequency heart rate variability [hfHRV], skin conductance response, and salivary cortisol) markers of emotion dysregulation were assessed, following which participants completed subjective (state urges for substances) and objective (Balloon Analogue Risk Task) measures of risky behavior. Results showed (a) greater self-reported state emotion dysregulation and lower hfHRV predicted more urges for substances in the positive (versus negative and neutral) emotion induction conditions; and (b) lower hfHRV predicted more behavioral risk-taking propensity in the positive (versus neutral) emotion induction condition. Findings provide additional support for the influence of positive emotion dysregulation on risky behavior.

Using a continuous electrocardiographic patch with heart rhythm analysis in the subacute stage of aneurysmal subarachnoid hemorrhage: The feasibility verification

OBJECTIVE

Continuous cardiac monitoring on patients with aneurysmal subarachnoid hemorrhage (aSAH) is difficult out of intensive care unit (ICU) in the subacute stage. Therefore, we verified the feasibility of a novel electrocardiography (ECG) patch device to record long-term heart rhythm.

METHODS

The ECG patches were applied on aSAH patients during their stay in general ward. Any types of significant arrythmia were identified, and heart rate variability (HRV) measures were calculated in time and frequency domains. We analyzed the correlation between heart rhythm with Hunt and Hess scale and modified Fisher scale as well as the occurrence of secondary complications.

RESULTS

Twenty-six patients used the devices on median day 6 after aSAH onset, with put on and take down time average as 137 s and 45 s, respectively. Mean record time was 221.7 h, and no adverse event presented within the period. Hunt and Hess II/III subgroup had higher percentage of HRV high frequency band than IV/V subgroup (9.1 % vs 3.5 %, p = 0.043), whereas ultra low frequency band presented more in the later subgroup (50.4 % vs 61.4 %, p = 0.035). The very low frequency percentage significantly decreased (p = 0.025) at an average of 3 days prior to the occurrence of secondary complications compared to the days without complications.

CONCLUSION

For aSAH patients in general ward during subacute stage, the ECG patch is a safe and feasible tool. The correlation of long-term heart rhythm with prognosis is worthy to be investigated on larger sample size using this device in the future.

The Role of Heart Rate Variability (HRV) in Different Hypertensive Syndromes

Cardiac innervation by the parasympathetic nervous system (PNS) and the sympathetic nervous system (SNS) modulates the heart rate (HR) (chronotropic activity) and the contraction of the cardiac muscle (inotropic activity). The peripheral vasculature is controlled only by the SNS, which is responsible for peripheral vascular resistance. This also mediates the baroreceptor reflex (BR), which in turn mediates blood pressure (BP). Hypertension (HTN) and the autonomic nervous system (ANS) are closely related, such that derangements can lead to vasomotor impairments and several comorbidities, including obesity, hypertension, resistant hypertension, and chronic kidney disease. Autonomic dysfunction is also associated with functional and structural changes in target organs (heart, brain, kidneys, and blood vessels), increasing cardiovascular risk. Heart rate variability (HRV) is a method of assessing cardiac autonomic modulation. This tool has been used for clinical evaluation and to address the effect of therapeutic interventions. The present review aims (a) to approach the heart rate (HR) as a CV risk factor in hypertensive patients; (b) to analyze the heart rate variability (HRV) as a "tool" to estimate the individual risk stratum for Pre-HTN (P-HTN), Controlled-HTN (C-HTN), Resistant and Refractory HTN (R-HTN and Rf-HTN, respectively), and hypertensive patients with chronic renal disease (HTN+CKD).

Respiratory patterns and baroreflex function in heart failure

Little is known on the effects of respiratory patterns on baroreflex function in heart failure (HF). Patients with HF (n = 30, age 61.6 ± 10 years, mean ± SD) and healthy controls (CNT, n = 10, age 58.9 ± 5.6 years) having their R-R interval (RRI, EKG), systolic arterial blood pressure (SBP, Finapres) and respiratory signal (RSP, Respitrace) monitored, were subjected to three recording sessions: free-breathing, fast- (≥ 12 bpm) and slow- (6 bpm) paced breathing. Baroreflex sensitivity (BRS) and power spectra of RRI, SBP, and RSP signals were calculated. During free-breathing, compared to CNT, HF patients showed a significantly greater modulation of respiratory volumes in the very-low-frequency (< 0.04 Hz) range and their BRS was not significantly different from that of CNT. During fast-paced breathing, when very-low-frequency modulations of respiration were reduced, BRS of HF patients was significantly lower than that of CNT and lower than during free breathing. During slow-paced breathing, BRS became again significantly higher than during fast breathing. In conclusion: (1) in free-breathing HF patients is present a greater modulation of respiratory volumes in the very-low-frequency range; (2) in HF patients modulation of respiration in the very-low and low frequency (around 0.1 Hz) ranges contributes to preserve baroreflex-mediated control of heart rate.

Rules of Heliogeomagnetics Diversely Coordinating Biological Rhythms and Promoting Human Health

This investigation reviews how geomagnetic activity affects the circadian variation in blood pressure (BP) and heart rate (HR) and their variabilities of clinically healthy individuals. A small study in Alta, Norway (latitude of 70.0° N), serves to illustrate the methodology used to outline rules of procedure in exploring heliogeomagnetic effects on human physiology. Volunteers in the Alta study were monitored for at least 2 days between 18 March 2002 and 9 January 2005. Estimates of the circadian characteristics of BP and HR by cosinor and the Maximum Entropy Method (MEM) indicate an increase in the circadian amplitude of systolic (S) BP on geomagnetic-disturbance days compared to quiet days (p = 0.0236). Geomagnetic stimulation was found to be circadian-phase dependent, with stimulation in the evening inducing a 49.2% increase in the circadian amplitude of SBP (p = 0.0003), not observed in relation to stimulation in the morning. In two participants monitored for 7 days, the circadian amplitude of SBP decreased by 23.4% on an extremely disturbed day but increased by 50.3% on moderately disturbed days (p = 0.0044), suggesting a biphasic (hormetic) reaction of the circadian SBP rhythm to geomagnetics. These results indicate a possible role of geomagnetic fluctuations in modulating the circadian system.

Exaggerated postural sway improves orthostatic cardiovascular and cerebrovascular control

Introduction

Healthy individuals with poor cardiovascular control, but who do not experience syncope (fainting), adopt an innate strategy of increased leg movement in the form of postural sway that is thought to counter orthostatic (gravitational) stress on the cardiovascular system. However, the direct effect of sway on cardiovascular hemodynamics and cerebral perfusion is unknown. If sway produces meaningful cardiovascular responses, it could be exploited clinically to prevent an imminent faint.

Methods

Twenty healthy adults were instrumented with cardiovascular (finger plethysmography, echocardiography, electrocardiogram) and cerebrovascular (transcranial Doppler) monitoring. Following supine rest, participants performed a baseline stand (BL) on a force platform, followed by three trials of exaggerated sway (anterior-posterior, AP; mediolateral, ML; square, SQ) in a randomized order.

Results

All exaggerated postural sway conditions improved systolic arterial pressure (SAP, p = 0.001) responses, while blunting orthostatic reductions in stroke volume (SV, p < 0.01) and cerebral blood flow (CBFv, p < 0.05) compared to BL. Markers of sympathetic activation (power of low-frequency oscillations in SAP, p < 0.001) and maximum transvalvular flow velocity (p < 0.001) were reduced during exaggerated sway conditions. Responses were dose-dependent, with improvements in SAP (p < 0.001), SV (p < 0.001) and CBFv (p = 0.009) all positively correlated with total sway path length. Coherence between postural movements and SAP (p < 0.001), SV (p < 0.001) and CBFv (p = 0.003) also improved during exaggerated sway.

Discussion

Exaggerated sway improves cardiovascular and cerebrovascular control and may supplement cardiovascular reflex responses to orthostatic stress. This movement provides a simple means to boost orthostatic cardiovascular control for individuals with syncope, or those with occupations that require prolonged motionless standing.

Correlation between heart rate variability and cerebral autoregulation in septic patients

BACKGROUND

Heart rate variability (HRV) may provide an estimation of the autonomous nervous system (ANS) integrity in critically ill patients. Disturbances of cerebral autoregulation (CAR) may share common pathways of ANS dysfunction.

AIM

To explore whether changes in HRV and CAR index correlate in critically ill septic patients.

METHODS

Prospectively collected data on septic adult (> 18 years) patients admitted into a mixed Intensive Care between February 2016 and August 2019 with a recorded transcranial doppler CAR assessment. CAR was assessed calculating the Pearson's correlation coefficient (i.e. mean flow index, Mxa) between the left middle cerebral artery flow velocity (FV), insonated with a 2-MHz probe, and invasive blood pressure (BP) signal, both recorded simultaneously through a Doppler Box (DWL, Germany). MATLAB software was used for CAR assessment using a validated script; a Mxa >0.3 was considered as impaired CAR. HRV was assessed during the same time period using a specific software (Kubios HRV 3.2.0) and analyzed in both time-domain and frequency domain methods. Correlation between HRV-derived variables and Mxa were assessed using the Spearman's coefficient.

RESULTS

A total of 141 septic patients was studied; median Mxa was 0.35 [0.13-0.60], with 77 (54.6 %) patients having an impaired CAR. Mxa had a significant although weak correlation with HRV time domain (SDNN, r = 0.17, p = 0.04; RMSSD, r = 0.18, p = 0.03; NN50, r = 0.23, p = 0.006; pNN50, r = 0.23, p = 0.007), frequency domain (FFT-HF, r = 0.21; p = 0.01; AR-HF, r = 0.19; p = 0.02), and non-linear domain (SD1, r = 0.18, p = 0.03) parameters. Impaired CAR patients had also all of these HRV-derived parameters higher than those with intact CAR.

CONCLUSIONS

In this exploratory study, a potential association of ANS dysfunction and impaired CAR during sepsis was observed.

Acute Severe Heart Failure Reduces Heart Rate Variability: An Experimental Study in a Porcine Model

There are substantial differences in autonomic nervous system activation among heart (cardiac) failure (CF) patients. The effect of acute CF on autonomic function has not been well explored. The aim of our study was to assess the effect of experimental acute CF on heart rate variability (HRV). Twenty-four female pigs with a mean body weight of 45 kg were used. Acute severe CF was induced by global myocardial hypoxia. In each subject, two 5-min electrocardiogram segments were analyzed and compared: before the induction of myocardial hypoxia and >60 min after the development of severe CF. HRV was assessed by time-domain, frequency-domain and nonlinear analytic methods. The induction of acute CF led to a significant decrease in cardiac output, left ventricular ejection fraction and an increase in heart rate. The development of acute CF was associated with a significant reduction in the standard deviation of intervals between normal beats (50.8 [20.5−88.1] ms versus 5.9 [2.4−11.7] ms, p < 0.001). Uniform HRV reduction was also observed in other time-domain and major nonlinear analytic methods. Similarly, frequency-domain HRV parameters were significantly changed. Acute severe CF induced by global myocardial hypoxia is associated with a significant reduction in HRV.

Improved arterial stiffness after combined aerobic and resistance training: correlation with heart rate variability change in prehypertensive offspring of hypertensive parents

Prehypertensive offspring of hypertensive parents are strongly linked to pathological processes of hypertension in later life. It is observed that young adults with high blood pressure (BP) have increased arterial stiffness, which is linked to autonomic anomalies. The purpose of the present study was to assess the effect of combined resistance and aerobic exercise training on BP, brachial-ankle pulse wave velocity (baP-WV), and heart rate variability (HRV) in prehypertensive young men with hypertensive parents. Thirty prehypertensive males aged 19.6±1.2 years were randomly assigned to either a combined exercise training group (CBT, n=15) or no exercise group (CON, n=15). The CBT group performed combined exercise for 8 weeks, 3 times per week. BP, baP-WV, HRV, peak oxygen consumption (VO_2peak), and muscle strength were measured before and after the exercise intervention. Systolic BP (-5.1 mmHg, 3.9% decrease, P<0.05), diastolic BP (-3.9 mmHg, 6.1% decrease, P<0.01), mean arterial pressure (-4.2 mmHg, 4.7% decrease, P<0.05), baPWV (-0.4 m/sec, 3.5% decrease, P<0.01), standard deviation of all RR intervals (+58.5% increase, P<0.05) and very low frequency (VLF) (+34.6% increase, P<0.01), VO_2peak (+11.7% increase, P<0.01) and one-repetition maximum leg press (+30.3% increase, P<0.01) were significantly improved in the CBT group after 8 weeks of training versus the CON group. Additionally, a reduction in baPWV was associated with an increase in the VLF power of HRV (r=0.72, P<0.01). These findings indicate that the combined training improves BP, arterial stiffness, vagal activity, cardiorespiratory fitness, and lower-body muscle strength in prehypertensive offspring of hypertensive parents.

Methodologic implications for rehabilitation research: Differences in heart rate variability introduced by respiration

BACKGROUND

Heart rate variability is a measure of autonomic activity that is growing in popularity as a research outcome. However, despite its increased use, the known effects of respiration on heart rate variability measures are rarely accounted for in rehabilitation medicine research, leading to potential misinterpretation.

OBJECTIVE

To describe the effect that unpaced and paced breathing introduces to heart rate variability measures in a rehabilitation medicine relevant example of individuals with spinal cord injury.

DESIGN

Cross-sectional comparison of heart rate variability during unpaced and paced breathing (0.25 Hz, 15 breaths per minute) within the same individuals during the same lab session.

SETTING

Academic autonomic physiology laboratory.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Mean low frequency (LF) and high frequency (HF) heart rate variability power, percentage of total power derived from the LF spectrum, LF:HF ratio.

RESULTS

Fifty-nine individuals with spinal cord injury completed laboratory assessments using standardized protocols (NCT02139436). In repeated measures within individuals, mean LF power was significantly higher in unpaced breathing compared to paced breathing (1292 vs. 573 ms2 , p < .001). A Bland-Altman plot demonstrated significant positive proportional bias for LF power when comparing unpaced and paced breathing conditions (R2  = 0.39). Mean HF power was similar between unpaced and paced breathing conditions, although there were wide positive and negative differences between measures, leading to notable uncertainty when respiratory confounders were not accounted for. The percentages of total power derived from the LF spectrum and the mean LF:HF ratio were both significantly higher for unpaced breathing compared to paced breathing (64 vs. 42%, p < .001; and 3.2 vs. 1.1, p < .001, respectively).

CONCLUSION

Respiration has a significant effect on heart rate variability following spinal cord injury, and not accounting for this has serious consequences for accurate interpretation of unpaced data. Future studies of heart rate variability in rehabilitation medicine should accordingly consider paced breathing.

Similarities between maternal and fetal RR interval tachograms and their association with fetal development

An association between maternal and fetal heart rate (HR) has been reported but, so far, little is known about its physiological implication and importance relative to fetal development. Associations between both HRs were investigated previously by performing beat-by-beat coupling analysis and correlation analysis between average maternal and fetal HRs. However, studies reporting on the presence of similarities between maternal and fetal HRs or RR intervals (RRIs) over the short term (e.g., 5-min) at different gestational ages (GAs) are scarce. Here, we demonstrate the presence of similarities in the variations exhibited by maternal and fetal RRl tachograms (RRITs). To quantify the same similarities, a cross-correlation (CC) analysis between resampled maternal and fetal RRITs was conducted; RRITs were obtained from non-invasive electrocardiogram (ECG). The degree of similarity between maternal and fetal RRITs (bmfRRITs) was quantified by calculating four CC coefficients. CC analysis was performed for a total of 330 segments (two 5-min segments from 158 subjects and one 5-min from 14 subjects). To investigate the association of the similarity bmfRRITs with fetal development, the linear correlation between the calculated CC coefficients and GA was calculated. The results from the latter analysis showed that similarities bmfRRITs are common occurrences, they can be negative or positive, and they increase with GA suggesting the presence of a regulation that is associated with proper fetal development. To get an insight into the physiological mechanisms involved in the similarity bmfRRITs, the association of the same similarity with maternal and fetal HR variability (HRV) was investigated by comparing the means of two groups in which one of them had higher CC values compared to the other. The two groups were created by using the data from the 158 subjects where fetal RRI (fRRI) calculation from two 5-min ECG segments was feasible. The results of the comparison showed that the maternal very low frequency (VLF) HRV parameter is potentially associated with the similarity bmfRRITs implying that maternal hormones could be linked to the regulations involved in the similarity bmfRRITs. Our findings in this study reinforce the role of the maternal intrauterine environment on fetal development.

Early Cerebrovascular Autoregulation in Neonates with Congenital Heart Disease

Neonates with congenital heart disease (CHD) display delayed brain development, predisposing them to impaired cerebrovascular autoregulation (CAR) and ischemic brain injury. For this paper, we analyzed the percentage of time with impaired CAR (%time impaired CAR) during the first 72 h after birth, the relation with clinical factors, and survival in 57 neonates with CHD. The primary outcome was a correlation coefficient of cerebral oxygenation (rcSO2) and mean arterial blood pressure (MABP, mmHg) for two hours on a daily basis. The %time impaired CAR ranged from 9.3% of the studied time on day one to 4.6% on day three. Variables associated with more %time impaired CAR were the use of inotropes (day 1, B = 19.5, 95%CI = 10.6-28.3; day 3, B = 11.5, 95%CI = 7.1-16), lower MABP (day 1, B = -0.6, 95%CI = -1.2-0.0), and dextro-transposition of the great arteries (dTGA) (16.2%) compared with other CHD types (2.0-5.0%; day 1, p = 0.022). Survival was not an associated variable. To summarize, impaired CAR was found in CHD neonates in up to 9.3% of the studied time. More evidence is necessary to evaluate an association with inotropes, dTGA, %time impaired CAR, and long-term outcome, further in larger cohorts.

Investigating attentional scope as a novel indicator of emotional state in animals

In humans, contrasting emotional states can lead to a broadening or narrowing of attentional scope. Whether this is also the case in animals has yet to be investigated. If confirmed, measurement of attentional scope has potential as a novel cognitive method of welfare assessment. In this study, we therefore aimed to investigate a test of attentional scope as a measure of emotional state in animals. We did this by inducing four putatively different emotional states in dogs (N = 10), varying in valence (positive, negative) and arousal (high, low), in two different reward contexts (food rewards in Experiment 1, social rewards in Experiment 2) and then assessing dogs' behavioural responses in a test of attentional scope. We also recorded heart rate variability (HRV) parameters as additional confirmatory affective indicators. In Experiment 1, the dogs showed a narrowing of attentional scope after the induction of both positively valenced emotional states. That dogs were in a positive state was supported by the reduced Standard Deviation of normal-to-normal R-R intervals (SDNN) and the reduced Low Frequency (LF) and Very Low Frequency (VLF) HRV. In Experiment 2, when responses to social rewards were examined, we did not detect any statistically significant differences in attentional scope between the emotional states, but dogs had a slightly narrow attentional scope in the negatively valenced emotional states. The LF tended to be reduced in the high arousal positive treatment. In conclusion, our study provides the first indication that emotional states can also alter attentional scope in animals. The results justify further investigation of this approach for use in animal welfare assessment, although additional studies are needed to refine predictions.

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

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

Mild simulator sickness can alter heart rate variability, mental workload, and learning outcomes in a 360° virtual reality application for medical education: a post hoc analysis of a randomized controlled trial

Virtual reality (VR) applications could be beneficial for education, training, and treatment. However, VR may induce symptoms of simulator sickness (SS) such as difficulty focusing, difficulty concentrating, or dizziness that could impair autonomic nervous system function, affect mental workload, and worsen interventional outcomes. In the original randomized controlled trial, which explored the effectiveness of using a 360° VR video versus a two-dimensional VR video to learn history taking and physical examination skills, only the former group participants had SS. Therefore, 28 undergraduate medical students who participated in a 360° VR learning module were included in this post hoc study using a repeated measures design. Data of the Simulator Sickness Questionnaire (SSQ), heart rate variability (HRV) analysis, Task Load Index, and Mini-Clinical Evaluation Exercise were retrospectively reviewed and statistically analyzed. Ten (36%) participants had mild SS (total score > 0 and ≤ 20), and 18 (64%) had no SS symptom. Total SSQ score was positively related to the very low frequency (VLF) band power, physical demand subscale, and frustration subscale, and inversely related to physical examination score. Using multilevel modeling, the VLF power mediated the relationship between total SSQ score and physical examination score. Furthermore, frustration subscale moderated the mediating effects of the VLF power. Our results highlight the importance of documenting SS to evaluate a 360° VR training program. Furthermore, the combination of HRV analysis with mental workload measurement and outcome assessments provided the important clinical value in evaluating the effects of SS in VR applications in medical education.

Effect of Hyperthyroidism Treatments on Heart Rate Variability: A Systematic Review and Meta-Analysis

The reversibility of HRV abnormalities in hyperthyroidism remains contradictory. The design of this study involves conducting a systematic review and meta-analysis on the effect of antithyroid treatments on HRV in hyperthyroidism. PubMed, Cochrane, Embase, and Google Scholar were searched until 4 April 2022. Multiple reviewers selected articles reporting HRV parameters in treated and untreated hyperthyroidism. Independent data extraction by multiple observers was stratified by degree of hyperthyroidism for each HRV parameter: RR intervals, SDNN (standard deviation of RR intervals), RMSSD (square root of the mean difference of successive RR intervals), pNN50 (percentage of RR intervals with >50 ms of variation), total power (TP), LFnu (low-frequency normalized unit) and HFnu (high-frequency), VLF (very low-frequency), and LF/HF ratio. We included 11 studies for a total of 471 treated hyperthyroid patients, 495 untreated hyperthyroid patients, and 781 healthy controls. After treatment, there was an increase in RR, SDNN, RMSSD, pNN50, TP, HFnu, and VLF and a decrease in LFnu and LF/HF ratio (p < 0.01). Overt hyperthyroidism showed similar results, in contrast to subclinical hyperthyroidism. Compared with controls, some HRV parameter abnormalities persist in treated hyperthyroid patients (p < 0.05) with lower SDNN, LFnu, and higher HFnu, without significant difference in other parameters. We showed a partial reversibility of HRV abnormalities following treatment of overt hyperthyroidism. The improvement in HRV may translate the clinical cardiovascular benefits of treatments in hyperthyroidism and may help to follow the evolution of the cardiovascular morbidity.