Biophysical characterization of the underappreciated and important relationship between heart rate variability and heart rate

Holter study of heart rate variability in children and adolescents with long QT syndrome

OBJECTIVES

This study aimed to retrospectively assess cardiac autonomic activity in children with LQTS, considering genotype, symptoms, sex, age, and beta-blocker therapy (BB) and compare it to healthy controls.

METHODS

Heart rate variability (HRV), using power spectrum analysis, was analyzed in 575 Holter recordings from 116 children with LQTS and in 69 healthy children. The data were categorized into four age-groups and four heart rate (HR) ranges.

RESULTS

In LQT1 and LQT2, increasing HR corresponded to significantly lower low (LF) and high frequency (HF) compared to controls. Total power (PTOT) was lower in all LQT1 age-groups compared to controls at HR 120-140 bpm (1-15 years: p < .01; 15-18 years: p = .03). At HR 80-100, LQT1 patients aged 1-10 years had lower HF than LQT2 patients (1-5 years: p = .05; 5-10 years: p = .02), and LQT2 patients aged 15-18 years had lower HF than LQT1 patients (p < .01). Symptomatic patients aged 10-15 years had lower PTOT at HR 100-120 bpm than asymptomatic patients (p = .04). LQT1 girls aged 10-15 and 15-18 years had a lower PTOT (10-15 years: p = .04; 15-18 years: p = .02) than boys.

CONCLUSION

This study shows a correlation between HR and changes in HRV parameters. At higher HRs, LQTS patients generally had lower HRV values than controls, suggesting an abnormal autonomic response. These results may strengthen the link between physical activity and arrhythmias in LQTS.

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.

Intra-Individual Relationship between Heart Rate Variability and the Underlying Heart Rate in Children and Adolescents

Background/Objective: The relationship between heart rate and heart rate variability (HRV) indices has been repeatedly studied in adults but limited data are available on the relationship in paediatric populations. Methods: Continuous 12-lead electrocardiograms were recorded in 1016 healthy children and adolescents (534 females) aged 4 to 19 years during postural manoeuvres with rapid changes between 10-min positions of supine → sitting → standing → supine → standing → sitting → supine. In each position, the averaged RR interval was measured together with four HRV indices, namely the SDNN, RMSSD, quasi-normalised high-frequency components (qnHF), and the proportions of low- and high-frequency components (LF/HF). In each subject, the slope of the linear regression between the repeated HRV measurements and the corresponding RR interval averages was calculated. Results: The intra-subject regression slopes, including their confidence intervals, were related to the age and sex of the subjects. The SDNN/RR, RMSSD/RR, and qnHF/RR slopes were significantly steeper (p < 0.001) and the (LF/HF)/RR slopes were significantly shallower (p < 0.001) in younger children compared to older children and adolescents. Conclusions: The study suggests that sympathetic and vagal influences on heart rate are present in both younger and older children. With advancing age, the sympatho-vagal balance gradually develops and allows the vagal control to suppress the sympathetic drive towards higher heart rates seen in younger age children.

Characterization of heart rate variability in end-stage renal disease patients after kidney transplantation with recurrence quantification analysis

Heart rate variability (HRV) is a noninvasive approach to studying the autonomic modulation of heart rate in experimental settings, such as active standing sympathetic stimulation. It is known that patients with end-stage renal disease during active standing have few changes in HRV dynamics, which are improved after hemodialysis. However, it is unknown whether the response to active standing is recovered after definitive treatment with kidney transplantation. This work aims to assess the change in HRV dynamics in the supine position and active standing through time and frequency-based metrics, as well as recurrence plot quantitative analysis (RQA). We studied HRV dynamics by obtaining 5-minute electrocardiographic recordings from kidney transplant recipients who underwent an active standing test. The mean duration of heartbeats and their standard deviation diminished in active standing, compared with the supine position. Also, the low-frequency component of HRV and the presence of diagonal and vertical structures in RQA were predominant. A larger estimated glomerular filtration rate was significantly correlated with broader HRV in the supine position and during active standing. The narrower HRV during active standing may indicate a sympathetic response to external stimuli, which is expected in a functional cardiovascular system, and may be influenced by renal function.

Heart Rate Variability, Deceleration Capacity of Heart Rate, and Death: A Veteran Twins Study

BACKGROUND

Autonomic function can be measured noninvasively using heart rate variability (HRV), which indexes overall sympathovagal balance. Deceleration capacity (DC) of heart rate is a more specific metric of vagal modulation. Higher values of these measures have been associated with reduced mortality risk primarily in patients with cardiovascular disease, but their significance in community samples is less clear.

METHODS AND RESULTS

This prospective twin study followed 501 members from the VET (Vietnam Era Twin) registry. At baseline, frequency domain HRV and DC were measured from 24-hour Holter ECGs. During an average 12-year follow-up, all-cause death was assessed via the National Death Index. Multivariable Cox frailty models with random effect for twin pair were used to examine the hazard ratios of death per 1-SD increase in log-transformed autonomic metrics. Both in the overall sample and comparing twins within pairs, higher values of low-frequency HRV and DC were significantly associated with lower hazards of all-cause death. In within-pair analysis, after adjusting for baseline factors, there was a 22% and 27% lower hazard of death per 1-SD increment in low-frequency HRV and DC, respectively. Higher low-frequency HRV and DC, measured during both daytime and nighttime, were associated with decreased hazard of death, but daytime measures showed numerically stronger associations. Results did not substantially vary by zygosity.

CONCLUSIONS

Autonomic inflexibility, and especially vagal withdrawal, are important mechanistic pathways of general mortality risk, independent of familial and genetic factors.

Post-exercise heart rate recovery and its speed are associated with resting-reactivity cardiovagal modulation in healthy women

The present study sought to expand upon prior investigations of the relationship between post-exercise heart rate recovery (HRR) and cardiovagal resting-reactivity modulation. HRR from 1st to 5th min after maximal exercise test was correlated with a cardiovagal index of heart rate variability (SD1) at resting (supine and orthostatic positions) and its reactivity after the orthostatic stress test in 34 healthy women. Statistical analysis employed non-parametric tests with a p-value set at 5%. HRR, ∆%HRR, and coefficient of HRR (CHRR) at the 3rd and 5th min correlated with SD1 and SD1n (normalized units) in the supine position (rs = 0.36 to 0.47; p =  < 0.01). From the 1st to 5th min, HRR, ∆%HRR, and CHRR correlated with SD1 and SD1n in the orthostatic position (rs = 0.29 to 0.47; p =  ≤ 0.01 to 0.05), except for HRR at 5th min with SD1n (p = 0.06). Following the orthostatic stress test, HRR at 3rd and HRR, %∆HRR at 5th min correlated with ∆absSD1 (rs = 0.28 to 0.35; p = 0.02 to 0.05). All HRR measurements at 1st min correlated with ∆absSD1n (rs = 0.32 to 0.38; p = 0.01 to 0.03), and the CHRR at 1st min correlated with ∆%SD1(rs = 0.37; p = 0.01). After the sample was divided into high and low cardiovagal modulation subgroups, the subgroup with high modulation at rest (supine and orthostatic) and higher cardiovagal reactivity (reduction) showed faster HRR (p =  ≤ 0.01 to 0.05; ES:0.37 to 0.50). HRR throughout the 1st to 5th min positively correlates with cardiovagal modulation in the orthostatic position, and the 3rd and 5th min positively correlate with cardiovagal modulation in both postures at rest. Faster HRR following the maximal exercise test is associated with high resting-reactivity cardiovagal modulation in healthy women.

A framework for the interpretation of heart rate variability applied to transcutaneous auricular vagus nerve stimulation and osteopathic manipulation

Reports on autonomic responses to transcutaneous auricular vagus nerve stimulation (taVNS) and osteopathic manipulative techniques have been equivocal, partly due to inconsistent interpretation of heart rate variability (HRV). We developed a mechanistic framework for the interpretation of HRV based on a model of sinus node automaticity that considers autonomic effects on Phase 3 repolarization and Phase 4 depolarization of the sinoatrial action potential. The model was applied to HRV parameters calculated from ECG recordings (healthy adult humans, both genders) before (30 min), during (15 min), and after (30 min) a time control intervention (rest, n = 23), taVNS (10 Hz, 300 μs, 1-2 mA, cymba concha, left ear, n = 12), or occipitoatlantal decompression (OA-D, n = 14). The experimental protocol was repeated on 3 consecutive days. The model simulation revealed that low frequency (LF) HRV best predicts sympathetic tone when calculated from heart rate time series, while high frequency (HF) HRV best predicts parasympathetic tone when calculated from heart period time series. Applying our model to the HRV responses to taVNS and OA-D, revealed that taVNS increases cardiac parasympathetic tone, while OA-D elicits a mild decrease in cardiac sympathetic tone.

Is reduced heart rate variability associated with functional somatic disorders? A cross-sectional population-based study; DanFunD

OBJECTIVES

It has been hypothesised that functional somatic disorders (FSD) could be initiated by sympathetic predominance in the autonomic nervous system as measured by low heart rate variability (HRV). Earlier studies on the association between HRV and FSD are small case-control studies hampered by selection bias and do not consider the great overlap between the various FSDs. The aim of the present study is to assess any associations between HRV and various FSDs and whether chronic stress confounds such an association.

DESIGN

A cross-sectional general population-based study.

SETTING

The Danish Study of Functional Somatic Disorders conducted 2013-2015 in 10 municipalities in the western part of Greater Copenhagen, Denmark.

PARTICIPANTS

A total of 6891 men and women aged 18-72 years were included in the analyses after exclusion of 602 persons with missing HRV data. Various delimitations of FSD (chronic fatigue, chronic widespread pain, irritable bowel and bodily distress syndrome) were identified by validated questionnaires and diagnostic interviews. HRV parameters in time and frequency domains were calculated from successive beat-to-beat heart rate (HR) data using the 'E-motion' HR monitor device during 7 min of supine rest. Chronic stress was assessed by Cohen's self-perceived stress scale.

OUTCOME MEASURES

Logistic regression analyses were used to calculate possible associations between the various delimitations of FSD and HRV adjusting for chronic stress.

RESULTS

Persons with FSD had a slightly higher mean HR and lower HRV as measured by time domain parameters, whereas associations with frequency domain parameters were not consistent. Adjusting for chronic stress attenuated associations slightly.

CONCLUSION

The study supports a sympathetic predominance in persons with FSD, which could not be entirely explained by chronic stress. However, it is not possible to conclude whether the association is a causal factor to or a consequence of FSD.

Resting heart rate causally affects the brain cortical structure: Mendelian randomization study

Resting heart rate (RHR) has been linked to impaired cortical structure in observational studies. However, the extent to which this association is potentially causal has not been determined. Using genetic data, this study aimed to reveal the causal effect of RHR on brain cortical structure. A Two-Sample Mendelian randomization (MR) analysis was conducted. Sensitivity analyses, weighted median, MR Pleiotropy residual sum and outlier, and MR-Egger regression were conducted to evaluate heterogeneity and pleiotropy. A causal relationship between RHR and cortical structures was identified by MR analysis. On the global scale, elevated RHR was found to decrease global surface area (SA; P < 0.0125). On a regional scale, the elevated RHR significantly decreased the SA of pars triangularis without global weighted (P = 1.58 × 10-4) and the thickness (TH) of the paracentral with global weighted (P = 3.56 × 10-5), whereas it increased the TH of banks of the superior temporal sulcus in the presence of global weighted (P = 1.04 × 10-4). MR study provided evidence that RHR might be causally linked to brain cortical structure, which offers a different way to understand the heart-brain axis theory.

Interplay of heart rate variability and resting heart rate on mortality in type 2 diabetes

AIMS

Heart rate variability (HRV) and resting heart rate (RHR) are usually analyzed and interpreted separately. We aimed to assess the interplay of HRV and RHR on mortality in type 2 diabetes.

METHODS

The study included 7,529 participants from the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial. HRV metrics included standard deviation of all normal-to-normal intervals (SDNN) and root mean square of successive differences between normal-to-normal intervals (rMSSD). Abnormal values were defined based on <25th percentile for HRV and >75th percentile for RHR. Interactions of HRV status and RHR status were tested on multiplicative and additive scales. Results were validated in a subset of patients with type 2 diabetes (n = 745) from the Multi-Ethnic Study of Atherosclerosis.

RESULTS

Low SDNN was associated with increased all-cause mortality in the high RHR group (HR 1.60; 95% CI 1.29-1.97), but not in the normal RHR group. Compared with those who had neither low SDNN nor high RHR, the presence of either low SDNN or high RHR was not significantly associated with an increased risk of all-cause mortality. In contrast, the combination of low SDNN and high RHR was associated with a significantly increased risk of all-cause mortality (HR 1.68; 95% CI 1.43-1.97). Significant multiplicative and additive interactions were found between HRV status and RHR status on risk of all-cause mortality (all Pinteraction < 0.05). Similar findings were observed for cardiovascular mortality, in analyses using rMSSD, and in the Multi-Ethnic Study of Atherosclerosis.

CONCLUSIONS

The association between HRV and mortality risk is modified by RHR levels. Furthermore, low HRV and high RHR have interdependent and synergistic associations with mortality risk.

Cardiovascular autonomic nervous function in children conceived by assisted reproductive technology with frozen or fresh embryo transfer

As a result of epigenetic changes, children conceived by assisted reproduction may be at risk of premature cardiovascular aging with notably increased blood pressures. Their cardiovascular autonomic nervous function is unknown. Therefore, this study investigated the cardiovascular autonomic nervous function in 8-12-yr-old children (51% girls) conceived naturally (n = 33) or by assisted reproduction with frozen (n = 34) or fresh (n = 38) embryo transfer by evaluating heart rate variability, during rest; from provocation maneuvers; and from baroreflex function. Heart rate and blood pressure response to provocation maneuvers and baroreflex function were comparable between children conceived naturally or by assisted reproduction. The mean RR-interval and high-frequency component of heart rate variability were lower in children conceived by assisted reproduction than in children conceived naturally. Children conceived by fresh embryo transfer had ∼17% lower heart rate-corrected standard deviation of normal-to-normal R-R intervals; ∼22% lower heart rate-corrected square root of the mean of the squared difference between successive R-R intervals; and ∼37% higher low-frequency/high-frequency ratio than naturally conceived children. Children conceived by assisted reproduction still had lower heart rate variability and vagal modulation than naturally conceived children after adjustment for confounders. Thus, these results raise the possibility of sympathetic predominance in children conceived by assisted reproduction. Therefore, it is important to reproduce these results in larger and older cohorts as sympathetic predominance relates with cardiovascular and metabolic diseases.NEW & NOTEWORTHY We observed that children conceived by assisted reproductive technology (both frozen and fresh embryo transfer) had lowered heart rate variability during rest as compared with children conceived naturally. During physiological stress maneuvers, however, the cardiovascular autonomic nervous regulation was comparable between children conceived by assisted reproductive technologies and naturally. Our findings highlight the potential that lowered heart rate variability during rest in children conceived by assisted reproductive technologies may precede premature hypertension.

Dissecting the heterogeneity of "in the wild" stress from multimodal sensor data

Stress is associated with numerous chronic health conditions, both mental and physical. However, the heterogeneity of these associations at the individual level is poorly understood. While data generated from individuals in their day-to-day lives "in the wild" may best represent the heterogeneity of stress, gathering these data and separating signals from noise is challenging. In this work, we report findings from a major data collection effort using Digital Health Technologies (DHTs) and frontline healthcare workers. We provide insights into stress "in the wild", by using robust methods for its identification from multimodal data and quantifying its heterogeneity. Here we analyze data from the Stress and Recovery in Frontline COVID-19 Workers study following 365 frontline healthcare workers for 4-6 months using wearable devices and smartphone app-based measures. Causal discovery is used to learn how the causal structure governing an individual's self-reported symptoms and physiological features from DHTs differs between non-stress and potential stress states. Our methods uncover robust representations of potential stress states across a population of frontline healthcare workers. These representations reveal high levels of inter- and intra-individual heterogeneity in stress. We leverage multiple stress definitions that span different modalities (from subjective to physiological) to obtain a comprehensive view of stress, as these differing definitions rarely align in time. We show that these different stress definitions can be robustly represented as changes in the underlying causal structure on and off stress for individuals. This study is an important step toward better understanding potential underlying processes generating stress in individuals.

Optimizing support vector machines and autoregressive integrated moving average methods for heart rate variability data correction

Heart rate variability (HRV) is the variation in time between successive heartbeats and can be used as an indirect measure of autonomic nervous system (ANS) activity. During physical exercise, movement of the measuring device can cause artifacts in the HRV data, severely affecting the analysis of the HRV data. Current methods used for data artifact correction perform insufficiently when HRV is measured during exercise. In this paper we propose the use of autoregressive integrated moving average (ARIMA) and support vector regression (SVR) for HRV data artifact correction. Since both methods are only trained on previous data points, they can be applied not only for correction (i.e., gap filling), but also prediction (i.e., forecasting future values). Our paper describes:•why HRV is difficult to predict and why ARIMA and SVR might be valuable options.•finding the best hyperparameters for using ARIMA and SVR to correct HRV data, including which criterion to use for choosing the best model.•which correction method should be used given the data at hand.

Heart rate variability and cardiovascular risk factors in patients with rheumatoid arthritis: A longitudinal study

BACKGROUND

It is established that the risk of cardiovascular disease (CVD) is increased in patients with Rheumatoid Arthritis (RA). Heart rate variability (HRV) is a method for evaluating the activity in the cardiac autonomic nervous system. Our aim was to assess the longitudinal development of HRV in patients with RA and compare with healthy controls. Furthermore, we wanted to investigate associations between HRV, inflammatory disease activity and cardiovascular complications in patients with RA over time.

METHOD

HRV was assessed with frequency-domain analysis at baseline and after five years in 50 patients with early RA, all being younger than 60 years. HRV indices were age-adjusted based on the estimated age-dependency in 100 age and sex matched healthy controls. Additionally, clinical data including serological markers, disease activity, and blood pressure were collected from the patients. Eleven years after inclusion CVD was assessed.

RESULTS

At baseline, patients with RA presented with lower HRV compared to controls during deep breathing (6 breaths/min), paced normal breathing (12 breaths/min) and after passive tilt to the upright position. No significant change in HRV was observed at the five-year follow-up. A significant negative correlation was found between HRV parameters and systolic blood pressure (SBP) at baseline. A significant positive correlation was found between heart rate and inflammatory markers at baseline but not after five years. Nine patients had developed CVD after 11 years, but no significant association was found with baseline HRV data.

CONCLUSION

This study showed that patients with RA have autonomic imbalance both at an early stage of the disease and after five years, despite anti-rheumatic medication, but no correlation between HRV and inflammation markers were observed. Reduced HRV was also significantly negatively correlated with increased SBP. Hypertension is a common finding in patients with RA. Thus, significant decline of HRV could be a useful early marker for development of hypertension in patients with RA.

Immediate and sustained increases in the activity of vagal preganglionic neurons during exercise and after exercise training

AIMS

The brain controls the heart by dynamic recruitment and withdrawal of cardiac parasympathetic (vagal) and sympathetic activity. Autonomic control is essential for the development of cardiovascular responses during exercise, however, the patterns of changes in the activity of the two autonomic limbs, and their functional interactions in orchestrating physiological responses during exercise, are not fully understood. The aim of this study was to characterize changes in vagal parasympathetic drive in response to exercise and exercise training by directly recording the electrical activity of vagal preganglionic neurons in experimental animals (rats).

METHODS AND RESULTS

Single unit recordings were made using carbon-fibre microelectrodes from the populations of vagal preganglionic neurons of the nucleus ambiguus (NA) and the dorsal vagal motor nucleus of the brainstem. It was found that (i) vagal preganglionic neurons of the NA and the dorsal vagal motor nucleus are strongly activated during bouts of acute exercise, and (ii) exercise training markedly increases the resting activity of both populations of vagal preganglionic neurons and augments the excitatory responses of NA neurons during exercise.

CONCLUSIONS

These data show that central vagal drive increases during exercise and provide the first direct neurophysiological evidence that exercise training increases vagal tone. The data argue against the notion of exercise-induced central vagal withdrawal during exercise. We propose that robust increases in the activity of vagal preganglionic neurons during bouts of exercise underlie activity-dependent plasticity, leading to higher resting vagal tone that confers multiple health benefits associated with regular exercise.

Impact of daily artificial gravity on autonomic cardiovascular control following 60-day head-down tilt bed rest

Impaired cardiovascular autonomic control following space flight or immobilization may limit the ability to cope with additional hemodynamic stimuli. Head-down tilt bedrest is an established terrestrial analog for space flight and offers the opportunity to test potential countermeasures for autonomic cardiovascular deconditioning. Previous studies revealed a possible benefit of daily artificial gravity on cardiovascular autonomic control following head-down tilt bedrest, but there is a need for efficiency in a long-term study before an artificial gravity facility would be brought to space. We hypothesized that artificial gravity through short-arm centrifugation attenuates functional adaptions of autonomic function during head-down tilt bed rest. 24 healthy persons (8 women, 33.4 ± 9.3 years, 24.3 ± 2.1 kg/m2) participated in the 60-day head-down tilt bed rest (AGBRESA) study. They were assigned to three groups, 30 min/day continuous, or 6(5 min intermittent short-arm centrifugation, or a control group. We assessed autonomic cardiovascular control in the supine position and in 5 minutes 80° head-up tilt position before and immediately after bed rest. We computed heart rate variability (HRV) in the time (rmssd) and frequency domain, blood pressure variability, and baroreflex sensitivity (BRS). RR interval corrected rmssd was reduced supine (p = 0.0358) and during HUT (p = 0.0161). Heart rate variability in the high-frequency band (hf-RRI; p = 0.0004) and BRS (p < 0.0001) decreased, whereas blood pressure variability in the low-frequency band (lf-SBP, p = 0.0008) increased following bedrest in all groups. We did not detect significant interactions between bedrest and interventions. We conclude that up to daily 30 min of artificial gravity on a short-arm centrifuge with 1Gz at the center of mass do not suffice to prevent changes in autonomic cardiovascular control following 60-day of 6° head-down tilt bed rest. Clinical Trial Registration: https://drks.de/search/en/trial/DRKS00015677, identifier, DRKS00015677.

Heart Rate Variability in Psychiatric Disorders: A Systematic Review

Introduction

Heart rate variability (HRV) is a measure of the fluctuation in time interval between consecutive heart beats. Decreased heart rate variability has been shown to have associations with autonomic dysfunction in psychiatric conditions such as depression, substance abuse, anxiety, and schizophrenia, although its use as a prognostic tool remains highly debated. This study aims to review the current literature on heart rate variability as a diagnostic and prognostic tool in psychiatric populations.

Methods

A literature search was conducted using the MEDLINE, EMBASE, Cochrane, and PsycINFO libraries to identify full-text studies involving adult psychiatric populations that reported HRV measurements. From 1647 originally identified, 31 studies were narrowed down through an abstract and full-text screen. Studies were excluded if they enrolled adolescents or children, used animal models, enrolled patients with another primary diagnosis other than psychiatric as outlined by the diagnostic and statistical manual of mental disorders (DSM) V, or if they assessed HRV in the context of treatment rather than diagnosis. Study quality assessment was conducted using a modified Downs and Blacks quality assessment tool for observational rather than interventional studies. Data were reported in four tables: 1) summarizing study characteristics, 2) methods of HRV detection, 3) key findings and statistics, and 4) quality assessment.

Results

There is significant variability between studies in their methodology of recording as well as reporting HRV, which makes it difficult to meaningfully interpret data that is clinically applicable due to the presence of significant bias in existing studies. The presence of an association between HRV and the severity of various psychiatric disorders, however, remains promising.

Conclusion

Future studies should be done to further explore how HRV parameters may be used to enhance the diagnosis and prognosis of several psychiatric disorders.

Comparison of pulmonary vein isolation using cryoballoon, high-power short-duration, and conventional radiofrequency ablation for atrial fibrillation: a propensity score-weighted study

Background

The comparative efficacy, saftey, and heart rate variability (HRV) parameters after pulmonary vein isolation using cryoballoon (Cryo-PVI), high-power short-duration (HPSD-PVI), and conventional radiofrequency ablation (conventional-PVI) for atrial fibrillation (AF) is unclear.

Materials and methods

In this propensity score-weighted, retrospective analysis of a single-center cohort, we analyzed 3,395 patients (26.2% female, 74.5% paroxysmal AF) who underwent AF catheter ablation without an empirical left atrial ablation. Procedural factors, recurrence rates, complication rates, and the post-procedural HRV parameters were compared across the Cryo-PVI (n = 625), HPSD-PVI (n = 748), and conventional-PVI (n = 2,022) groups.

Results

Despite the shortest procedural time in the Cryo-PVI group (74 min for Cryo-PVI vs. 104 min for HPSD-PVI vs. 153 min for conventional-PVI, p < 0.001), the major complication (p = 0.906) and clinical recurrence rates were similar across the three ablation groups (weighted log-rank, p = 0.824). However, the Cryo-PVI group was associated with a significantly lower risk of recurrent AF in patients with paroxysmal AF [weighted hazard ratio (WHR) 0.57, 95% confidence interval (CI) 0.37-0.86], whereas it was associated with a higher risk of recurrent AF in patients with persistent AF (WHR 1.41, 95% CI 1.06-1.89, p for interaction of <0.001) compared with the conventional-PVI group. In the subgroup analysis for the HRV, the Cryo-PVI group had the highest low-frequency-to-high-frequency ratio at 1-year post-procedure, whereas the HPSD-PVI group had the lowest low-frequency-to-high-frequency ratio at 1-year post-procedure (p < 0.001).

Conclusions

The Cryo-PVI group had better rhythm outcomes in patients with paroxysmal AF but worse rhythm outcomes in patients with persistent AF and a higher long-term post-procedural sympathetic nervous activity and sympatho-vagal balance compared with the conventional-PVI group.

Phenotypic but not genetically predicted heart rate variability associated with all-cause mortality

Low heart rate variability (HRV) has been widely reported as a predictor for increased mortality. However, the molecular mechanisms are poorly understood. Therefore, this study aimed to identify novel genetic loci associated with HRV and assess the association of phenotypic HRV and genetically predicted HRV with mortality. In a GWAS of 46,075 European ancestry individuals from UK biobank, we identified 17 independent genome-wide significant genetic variants in 16 loci associated with HRV traits. Notably, eight of these loci (RNF220, GNB4, LINCR-002, KLHL3/HNRNPA0, CHRM2, KCNJ5, MED13L, and C160rf72) have not been reported previously. In a prospective phenotypic relationship between HRV and mortality during a median follow-up of seven years, individuals with lower HRV had higher risk of dying from any cause. Genetically predicted HRV, as determined by the genetic risk scores, was not associated with mortality. To the best of our knowledge, the findings provide novel biological insights into the mechanisms underlying HRV. These results also underline the role of the cardiac autonomic nervous system, as indexed by HRV, in predicting mortality.

Maternal invalidation and child RSA reactivity to frustration interact to predict teacher-reported aggression among at-risk preschoolers

BACKGROUND

Aggression is a transdiagnostic indicator of risk and represents one of the most common reasons children are referred for mental health treatment. Theory and research highlight the impact of maternal invalidation on child aggression and suggest that its influence may vary based on differences in child physiological reactivity. Moreover, the interaction between these risk factors may be particularly pronounced among children of mothers with emotion regulation (ER) difficulties. The current study examined the independent and interactive effects of maternal invalidation and child physiological reactivity to frustration on teacher-reported aggression in an at-risk sample of preschool children.

METHOD

Participants included 77 mothers (Mage = 33.17 years, s.d. = 4.83; 35% racial/ethnic minority) and their children (Mage = 42.48 months; s.d. = 3.78; 56% female; 47% racial/ethnic minority). Groups of mothers with and without clinician-rated ER difficulties reported on maternal invalidation, and child respiratory sinus arrhythmia (RSA) was assessed continuously during a frustration task as an indicator of physiological reactivity. Teachers or daycare providers reported on child aggression.

RESULTS

Results demonstrated positive associations between maternal ER difficulties and both maternal invalidation and child RSA reactivity to frustration. As expected, the interaction between maternal invalidation and child RSA reactivity was significant, such that higher maternal invalidation and greater child RSA reactivity to frustration predicted more aggression in a daycare or preschool setting. Importantly, this effect was demonstrated while controlling for demographic covariates and baseline RSA.

CONCLUSIONS

Findings are in line with diathesis-stress and biosocial models of risk and point to multiple targets for prevention and early intervention.

Physiological reactivity to acute mental stress in essential hypertension-a systematic review

Objective

Exaggerated physiological reactions to acute mental stress (AMS) are associated with hypertension (development) and have been proposed to play an important role in mediating the cardiovascular disease risk with hypertension. A variety of studies compared physiological reactivity to AMS between essential hypertensive (HT) and normotensive (NT) individuals. However, a systematic review of studies across stress-reactive physiological systems including intermediate biological risk factors for cardiovascular diseases is lacking.

Methods

We conducted a systematic literature search (PubMed) for original articles and short reports, published in English language in peer-reviewed journals in November and December 2022. We targeted studies comparing the reactivity between essential HT and NT to AMS in terms of cognitive tasks, public speaking tasks, or the combination of both, in at least one of the predefined stress-reactive physiological systems.

Results

We included a total of 58 publications. The majority of studies investigated physiological reactivity to mental stressors of mild or moderate intensity. Whereas HT seem to exhibit increased reactivity in response to mild or moderate AMS only under certain conditions (i.e., in response to mild mental stressors with specific characteristics, in an early hyperkinetic stage of HT, or with respect to certain stress systems), increased physiological reactivity in HT as compared to NT to AMS of strong intensity was observed across all investigated stress-reactive physiological systems.

Conclusion

Overall, this systematic review supports the proposed and expected generalized physiological hyperreactivity to AMS with essential hypertension, in particular to strong mental stress. Moreover, we discuss potential underlying mechanisms and highlight open questions for future research of importance for the comprehensive understanding of the observed hyperreactivity to AMS in essential hypertension.

Associations between physical activity and autonomic function during deep breathing test: the Swedish CArdioPulmonary bioImage Study (SCAPIS)

PURPOSE

The deep breathing test (DBT) is a sensitive test of cardiovagal function. The aim of this study was to explore associations between physical activity and sedentary time, measured by accelerometer, and autonomic function, using DBT.

METHODS

In the Swedish Cardio-Pulmonary bioImage Study, men and women aged 50-64 were randomly invited from the general population. A total of 4325 subjects who underwent DBT and assessment of physical activity and sedentary time by accelerometery were included. ECG files from 1-min DBT were used to calculate measures of respiratory sinus arrhythmia [RSA; expiration-inspiration (E-I) difference and E/I ratio], heart rate variability [HRV; root mean square of successive differences (RMSSD), standard deviation of heart rates and mean circular resultant]. Low RSA and HRV was defined as the lowest 10% in the population.

RESULTS

For accelerometer-assessed physical activity, there were significant associations between high percentage of sedentary time and low E/I (p < 0.01), and low RMSSD (p < 0.01) in an age- and sex-adjusted model, and between percentage of sedentary time and low RMSSD (p = 0.04) in a risk factor-adjusted model. Low RMSSD was less common in those with a high percentage of moderate to vigorous physical activity (p = 0.04, after risk-factor adjustment). These associations became non-significant when further adjusting for heart rate.

CONCLUSION

We report associations between degree of physical activity and indices of autonomic dysfunction in a large population. The relationships were no longer significant after adjustments for heart rate, indicating that the relationship between physical activity and cardiovagal function partly is accounted for by reduced heart rate.

Autonomic dysfunction is associated with the development of arterial stiffness: the Whitehall II cohort

This study aims to examine the association between baseline level and change of autonomic nervous function with subsequent development of arterial stiffness. Autonomic nervous function was assessed in 4901 participants of the Whitehall II occupational cohort by heart rate variability (HRV) indices and resting heart rate (rHR) three times between 1997 and 2009, while arterial stiffness was assessed by carotid-femoral pulse wave velocity (PWV) measured twice between 2007 and 2013. First, individual HRV/rHR levels and annual changes were estimated. Then, we modelled the development of PWV by HRV/rHR using linear mixed effect models. First, we adjusted for sex and ethnicity (model 1), and then for socioeconomic and lifestyle factors, various clinical measurements, and medications (model 2). A decrease in HRV and unchanged rHR was associated with subsequent higher levels of PWV, but the effect of a change in HRV was less pronounced at higher ages. A typical individual aged 65 years with a SDNN level of 30 ms and a 2% annual decrease in SDNN had 1.32 (0.95; 1.69) higher PWV compared to one with the same age and SDNN level but with a 1% annual decrease in SDNN. Further adjustment had no major effect on the results. People who experience a steeper decline in autonomic nervous function have higher levels of arterial stiffness. The association was stronger in younger people.

Long-term changes in heart rate and electrical remodeling contribute to alternans formation in heart failure: a patient-specific in silico study

Individuals with chronic heart failure (CHF) have an increased risk of ventricular arrhythmias, which has been linked to pathological cellular remodeling and may also be mediated by changes in heart rate. Heart rate typically fluctuates on a timescale ranging from seconds to hours, termed heart rate variability (HRV). This variability is reduced in CHF, and this HRV reduction is associated with a greater risk for arrhythmias. Furthermore, variations in heart rate influence the formation of proarrhythmic alternans, a beat-to-beat alternation in the action potential duration (APD), or intracellular calcium (Ca). In this study, we investigate how long-term changes in heart rate and electrical remodeling associated with CHF influence alternans formation. We measure key statistical properties of the RR-interval sequences from ECGs of individuals with normal sinus rhythm (NSR) and CHF. Patient-specific RR-interval sequences and synthetic sequences (randomly generated to mimicking these statistical properties) are used as the pacing protocol for a discrete time-coupled map model that governs APD and intracellular Ca handling of a single cardiac myocyte, modified to account for pathological electrical remodeling in CHF. Patient-specific simulations show that beat-to-beat differences in APD vary temporally in both populations, with alternans formation more prevalent in CHF. Parameter studies using synthetic sequences demonstrate that increasing the autocorrelation time or mean RR-interval reduces APD alternations, whereas increasing the RR-interval standard deviation leads to higher alternans magnitudes. Importantly, we find that although both the CHF-associated changes in heart rate and electrical remodeling influence alternans formation, variations in heart rate may be more influential.NEW & NOTEWORTHY Using patient-specific data, we show that both the changes in heart rate and electrical remodeling associated with chronic heart failure influence the formation of proarrhythmic alternans in the heart.

cAMP signaling affects age-associated deterioration of pacemaker beating interval dynamics

Sinoatrial node (SAN) beating interval variability (BIV) and the average beating interval (BI) are regulated by a coupled-clock system, driven by Ca2+-calmodulin activated adenylyl cyclase, cAMP, and downstream PKA signaling. Reduced responsiveness of the BI and BIV to submaximal, [X]50, β-adrenergic receptor (β-AR) stimulation, and phosphodiesterase inhibition (PDEI) have been documented in aged SAN tissue, whereas the maximal responses, [X]max, do not differ by age. To determine whether age-associated dysfunction in cAMP signaling leads to altered responsiveness of BI and BIV, we measured cAMP levels and BI in adult (2-4 months n = 27) and aged (22-26 months n = 25) C57/BL6 mouse SAN tissue in control and in response to β-AR or PDEI at X50 and [X]max. Both cAMP and average BI in adult SAN were reduced at X50, whereas cAMP and BI at Xmax did not differ by age. cAMP levels and average BI were correlated both within and between adult and aged SAN. BIV parameters in long- and short-range terms were correlated with cAMP levels for adult SAN. However, due to reduced cAMP within aged tissues at [X]50, these correlations were diminished in advanced age. Thus, cAMP level generated by the coupled clock mechanisms is tightly linked to average BI. Reduced cAMP level at X50 in aged SAN explains the reduced responsiveness of the BI and BIV to β-AR stimulation and PDEI.

Characterisation of the acute hypoxic response using breathing variability parameters: a pilot study in humans

PURPOSE

We aimed to investigate respiratory rate variability (RRV) and tidal volume (V_t) variability during exposure to normobaric hypoxia (i.e., reduction in the fraction of inspired oxygen - FiO₂), and the association of the changes in RRV and V_t variability with the changes in pulse oxygen saturation (SpO₂).

METHODS

Thirty healthy human participants (15 females) were exposed to: (1) 15-min normoxia, (2) 10-min hypoxia simulating 2200m, (3) 10-min hypoxia simulating 4000m, (4) 10-min hypoxia simulating 5000m, (5) 15-min recovery in normoxia. Linear regression modelling was applied with SpO₂ (dependent variable) and the changes in RRV and V_t variability (independent variables), controlling for FiO₂, age, sex, changes in heart rate (HR), changes in HR variability (HRV), and changes in minute ventilation (V_E).

RESULTS

When modelling breathing parameter variability as root-mean-square standard deviation (RMSSD), a significant independent association of the changes in RRV with the changes in SpO₂ was found (B=-4.3e-04, 95% CI=-8.3e-04/-2.1e-05, p=0.04). The changes in V_t variability showed no significant association with the changes in SpO₂ (B=-1.6, 95% CI=-5.5/2.4, p=0.42). When modelling parameters variability as SD, a significant independent association of the changes in RRV with the changes in SpO₂ was found (B=-8.2e-04, 95% CI=-1.5e-03/-9.4e-05, p=0.03). The changes in V_t variability showed no significant association with the changes in SpO₂ (B=1.4, 95% CI=-5.8/8.6, p=0.69).

CONCLUSION

Higher RRV is independently associated with lower SpO₂ during acute hypoxic exposure, while V_t variability parameters are not. Therefore, RRV may be a potentially interesting parameter to characterize individual responses to acute hypoxia.

Day-night patterns in heart rate variability and complexity: differences with age and cardiopulmonary disease

STUDY OBJECTIVES

Heart rate variability (HRV) measures provide valuable insights into physiology; however, gaps remain in understanding circadian patterns in heart rate dynamics. We aimed to explore day-night differences in heart rate dynamics in patients with chronic cardiopulmonary disease compared with healthy controls.

METHODS

Using 24-hour heart rate data from patients with chronic obstructive pulmonary disease (COPD) and/or heart failure (n = 16) and healthy adult controls (older group: ≥50 years, n = 42; younger group: 20-49 years, n = 136), we compared day-night differences in conventional time and frequency domain HRV indices and a multiscale-entropy-based complexity index (CI1-20) of HRV among the 3 groups.

RESULTS

Twenty-four-hour HRV showed significant day-night differences (marked with "△") among younger healthy (mean age: 34.5 years), older healthy (mean age: 61.6 years), and cardiopulmonary patients (mean age: 68.4 years), including change in percentage of adjacent intervals that differ > 50 ms (△pNN50), high frequency (△HF), normalized low frequency (△nLF), ratio (△LF/HF), and △CI1-20. Among these, △LF/HF (2.13 ± 2.35 vs 1.1 ± 2.47 vs -0.35 ± 1.25; P < .001) and △CI1-20 (0.15 ± 0.24 vs 0.02 ± 0.28 vs -0.21 ± 0.27; P < .001) were significant in each pairwise comparison following analysis of variance tests. Average CI1-20 was highest in younger healthy individuals and lowest in cardiopulmonary patients (1.37 ± 0.12 vs 1.01 ± 0.27; P < .001). Younger healthy patients showed a heart rate complexity dipping pattern (night < day), older healthy patients showed nondipping, and cardiopulmonary patients showed reverse dipping (night > day).

CONCLUSIONS

As measures of 24-hour variability, traditional and complexity-based metrics of HRV exhibit large day-night differences in healthy individuals; these differences are blunted, or even reversed, in individuals with cardiopulmonary pathology. Measures of diurnal dynamics may be useful indices of reduced adaptive capacity in patients with cardiopulmonary conditions.

CITATION

Ma Y, Chang M-C, Litrownik D, Wayne PM, Yeh GY. Day-night patterns in heart rate variability and complexity: differences with age and cardiopulmonary disease. J Clin Sleep Med. 2023;19(5):873-882.

Muscle metaboreflex activation during hypercapnia modifies nonlinear heart rhythm dynamics, increasing the complexity of the sinus node autonomic regulation in humans

Muscle metaboreflex activation during hypercapnia leads to enhanced pressive effects that are poorly understood while autonomic responses including baroreflex function are not documented. Thus, we assessed heart rate variability (HRV) that is partly due to autonomic influences on sinus node with linear tools (spectral analysis of instantaneous heart period), baroreflex set point and sensitivity with the heart period-arterial pressure transfer function and sequences methods, and system coupling through the complexity of RR interval dynamics with nonlinear tools (Poincaré plots and approximate entropy (ApEn)). We studied ten healthy young men at rest and then during muscle metaboreflex activation (MMA, postexercise muscle ischemia) and hypercapnia (HCA, PetCO2 =  + 10 mmHg from baseline) separately and combined (MMA + HCA). The strongest pressive responses were observed during MMA + HCA, while baroreflex sensitivity was similarly lowered in the three experimental conditions. HRV was significantly different in MMA + HCA compared to MMA and HCA separately, with the lowest total power spectrum (p < 0.05), including very low frequency (p < 0.05), low frequency (p < 0.05), and high frequency (tendency) power spectra decreases, and the lowest Poincaré plot short-term variability index (SD1): SD1 = 36.2 ms (MMA + HCA) vs. SD1 = 43.1 ms (MMA, p < 0.05) and SD1 = 46.1 ms (HCA, p < 0.05). Moreover, RR interval dynamic complexity was significantly increased only in the MMA + HCA condition (ApEn increased from 1.04 ± 0.04, 1.07 ± 0.02, and 1.05 ± 0.03 to 1.10 ± 0.03, 1.13 ± 0.04, and 1.17 ± 0.03 in MMA, HCA, and MMA + HCA conditions, respectively; p < 0.01). These results suggest that in healthy young men, muscle metaboreflex activation during hypercapnia leads to interactions that reduce parasympathetic influence on the sinus node activity but complexify its dynamics.

The characteristics of elevated blood pressure in abdominal obesity correspond to primary hypertension: a cross-sectional study

BACKGROUND

Obesity-related hypertension and the associated metabolic abnormalities are considered as a distinct hypertensive phenotype. Here we examined how abdominal fat content, as judged by waist:height ratio, influenced blood pressure and hemodynamic profile in normotensive subjects and never-treated hypertensive patients.

METHODS

The 541 participants (20-72 years) underwent physical examination and laboratory analyses and were divided into age and sex-adjusted quartiles of waist:height ratio. Supine hemodynamics were recorded using whole-body impedance cardiography, combined with analyses of radial tonometric pulse wave form and heart rate variability.

RESULTS

Mean waist:height ratios in the quartiles were 0.46, 0.51, 0.55 and 0.62. Radial and aortic blood pressure, systemic vascular resistance, pulse wave velocity, markers of glucose and lipid metabolism, leptin levels and C-reactive protein were higher in quartile 4 when compared with quartiles 1 and 2 (p < 0.05 for all). Cardiac index was lower in quartile 4 versus quartile 1, while no differences were seen in heart rate variability, augmentation index, plasma renin activity, and aldosterone concentration between the quartiles. Linear regression analyses showed independent associations of abdominal obesity with higher aortic systolic and diastolic blood pressure, systemic vascular resistance, and pulse wave velocity (p < 0.05 for waist:height ratio in all regression models).

CONCLUSION

Higher waist:height ratio was associated with elevated blood pressure, systemic vascular resistance, and arterial stiffness, but not with alterations in cardiac sympathovagal modulation or activation of the circulating renin-angiotensin-aldosterone system. Although obesity-related elevation of blood pressure has distinct phenotypic features, these results suggest that its main characteristics correspond those of primary hypertension.

TRIAL REGISTRATION

ClinicalTrails.gov NCT01742702 (date of registration 5th December 2012).

The Validity of Ultra-Short-Term Heart Rate Variability during Cycling Exercise

Ultra-short-term heart rate variability (HRV) has been validated in the resting state, but its validity during exercise is unclear. This study aimed to examine the validity in ultra-short-term HRV during exercise considering the different exercise intensities. HRVs of twenty-nine healthy adults were measured during incremental cycle exercise tests. HRV parameters (Time-, frequency-domain and non-linear) corresponding to each of the 20% (low), 50% (moderate), and 80% (high) peak oxygen uptakes were compared between the different time segments of HRV analysis (180 s (sec) segment vs. 30, 60, 90, and 120-sec segments). Overall, the differences (bias) between ultra-short-term HRVs increased as the time segment became shorter. In moderate- and high-intensity exercises, the differences in ultra-short-term HRV were more significant than in low intensity exercise. Thus, we discovered that the validity of ultra-short-term HRV differed with the duration of the time segment and exercise intensities. However, the ultra-short-term HRV is feasible in the cycling exercise, and we determined some optimal time duration for HRV analysis for across exercise intensities during the incremental cycling exercise.

Performance of heart rate adjusted heart rate variability for risk stratification of sudden cardiac death

PURPOSE

As a non-invasive tool for the assessment of cardiovascular autonomic function, the predictive value of heart rate variability (HRV) for sudden cardiac death (SCD) risk stratification remains unclear. In this study, we investigated the performance of the individualized heart rate (HR) adjusted HRV (HRV_I) for SCD risk stratification in subjects with diverse risks.

METHODS

A total of 11 commonly used HRV metrics were analyzed in 192 subjects, including 88 healthy controls (low risk group), 82 hypertrophic cardiomyopathy (HCM) patients (medium risk group), and 22 SCD victims (high risk group). The relationship between HRV metrics and HR was examined with long-term and short-term analysis. The performance HRV_I was evaluated by area under the receiver operating characteristic curve (AUC) and covariance of variation (CV).

RESULTS

Most of the HRV metrics were exponentially decayed with the increase of HR, while the exponential power coefficients were significantly different among groups. The HRV_I metrics discriminated low, medium and high risk subjects with a median AUC of 0.72[0.11], which was considerably higher than that of the traditional long-term (0.63[0.04]) and short-term (0.58[0.05]) HRV without adjustment. The average CV of the HRV_I metrics was also significantly lower than traditional short-term HRV metrics (0.09 ± 0.02 vs. 0.24 ± 0.13, p < 0.01).

CONCLUSIONS

Subjects with diverse risks of SCD had similar exponential decay relationship between HRV metrics and HR, but with different decaying rates. HRV_I provides reliable and robust estimation for risk stratification of SCD.

Synergy between Membrane Currents Prevents Severe Bradycardia in Mouse Sinoatrial Node Tissue

Bradycardia is initiated by the sinoatrial node (SAN), which is regulated by a coupled-clock system. Due to the clock coupling, reduction in the 'funny' current (I_f), which affects SAN automaticity, can be compensated, thus preventing severe bradycardia. We hypothesize that this fail-safe system is an inherent feature of SAN pacemaker cells and is driven by synergy between I_f and other ion channels. This work aimed to characterize the connection between membrane currents and their underlying mechanisms in SAN cells. SAN tissues were isolated from C57BL mice and Ca²⁺ signaling was measured in pacemaker cells within them. A computational model of SAN cells was used to understand the interactions between cell components. Beat interval (BI) was prolonged by 54 ± 18% (N = 16) and 30 ± 9% (N = 21) in response to I_f blockade, by ivabradine, or sodium current (I_Na) blockade, by tetrodotoxin, respectively. Combined drug application had a synergistic effect, manifested by a BI prolonged by 143 ± 25% (N = 18). A prolongation in the local Ca²⁺ release period, which reports on the level of crosstalk within the coupled-clock system, was measured and correlated with the prolongation in BI. The computational model predicted that I_Na increases in response to I_f blockade and that this connection is mediated by changes in T and L-type Ca²⁺ channels.

The role of the autonomic nervous system in cerebral blood flow regulation in stroke: A review

Stroke is a pathophysiological condition which results in alterations in cerebral blood flow (CBF). The mechanism by which the brain maintains adequate CBF in presence of fluctuating cerebral perfusion pressure (CPP) is known as cerebral autoregulation (CA). Disturbances in CA may be influenced by a number of physiological pathways including the autonomic nervous system (ANS). The cerebrovascular system is innervated by adrenergic and cholinergic nerve fibers. The role of the ANS in regulating CBF is widely disputed owing to several factors including the complexity of the ANS and cerebrovascular interactions, limitations to measurements, variation in methods to assess the ANS in relation to CBF as well as experimental approaches that can or cannot provide insight into the sympathetic control of CBF. CA is known to be impaired in stroke however the number of studies investigating the mechanisms by which this occurs are limited. This literature review will focus on highlighting the assessment of the ANS and CBF via indices derived from the analyses of heart rate variability (HRV), and baroreflex sensitivity (BRS), and providing a summary of both clinical and animal model studies investigating the role of the ANS in influencing CA in stroke. Understanding the mechanisms by which the ANS influences CBF in stroke patients may provide the foundation for novel therapeutic approaches to improve functional outcomes in stroke patients.

Change in heart rate variability during two firefighting work cycles

This study aimed to determine whether the change in heart rate variability from pre to post firefighting is modulated by different work cycles. Thirteen male firefighters underwent two firefighting simulations that comprised two identical 25-min work bouts intercalated by a passive recovery period of either 20 min (T20) or 5 min (T5). The square root of the mean squared differences of successive R-R intervals (RMSSD) and aural temperature were measured at rest before (PRE) and after (POST) firefighting simulations. The decrease in RMSSD was different between firefighting simulations (T20: -10 ± 21.2 ms, T5: -19.9 ± 20.9 ms, interaction, p = 0.02). Post-firefighting aural temperature was greater (p = 0.05) in T5 (37.18 ± 0.53 °C) than in T20 (36.88 ± 0.49 °C). In conclusion, a shorter recovery period of 5 min between firefighting work bouts decreases post-firefighting heart rate variability, possibly attributed to a lower parasympathetic reactivation and a higher absolute value of body temperature.

Heart Rate Variability in Individuals with Down Syndrome: A Scoping Review with Methodological Considerations

Individuals with Down syndrome (DS) present similar heart rate variability (HRV) parameters at rest but different responses to selected movement maneuvers in comparison to individuals without DS, which indicates reduced vagal regulation. The present study undertakes a scoping review of research on HRV in individuals with DS, with special attention paid to the compliance of the studies with standards and methodological paper guidelines for HRV assessment and interpretation. A review was performed using PubMed, Web of Science and CINAHL databases to search for English language publications from 1996 to 2020 with the MESH terms "heart rate variability" and "down syndrome", with the additional inclusion criteria of including only human participants and empirical investigations. From 74 studies, 15 were included in the review. None of the reviewed studies met the recommendations laid out by the standards and guidelines for providing the acquisition of RR intervals and necessary details on HRV analysis. Since authors publishing papers on this research topic do not adhere to the prescribed standards and guidelines when constructing the methodology, results of the research papers on the topic are not directly comparable. Authors need to design the study methodology more robustly by following the aforementioned standards, guidelines and recommendations.

The virtual sinoatrial node: What did computational models tell us about cardiac pacemaking?

Since its discovery, the sinoatrial node (SAN) has represented a fascinating and complex matter of research. Despite over a century of discoveries, a full comprehension of pacemaking has still to be achieved. Experiments often produced conflicting evidence that was used either in support or against alternative theories, originating intense debates. In this context, mathematical descriptions of the phenomena underlying the heartbeat have grown in importance in the last decades since they helped in gaining insights where experimental evaluation could not reach. This review presents the most updated SAN computational models and discusses their contribution to our understanding of cardiac pacemaking. Electrophysiological, structural and pathological aspects - as well as the autonomic control over the SAN - are taken into consideration to reach a holistic view of SAN activity.

Amateur Athlete with Sinus Arrest and Severe Bradycardia Diagnosed through a Heart Rate Monitor: A Six-Year Observation-The Necessity of Shared Decision-Making in Heart Rhythm Therapy Management

Heart rate monitors (HRMs) are used by millions of athletes worldwide to monitor exercise intensity and heart rate (HR) during training. This case report presents a 34-year-old male amateur soccer player with severe bradycardia who accidentally identified numerous pauses of over 4 s (maximum length: 7.3 s) during sleep on his own HRM with a heart rate variability (HRV) function. Simultaneous HRM and Holter ECG recordings were performed in an outpatient clinic, finding consistent 6.3 s sinus arrests (SA) with bradycardia of 33 beats/min. During the patient's hospitalization for a transient ischemic attack, the longest pauses on the Holter ECG were recorded, and he was suggested to undergo pacemaker implantation. He then reduced the volume/intensity of exercise for 4 years. Afterward, he spent 2 years without any regular training due to depression. After these 6 years, another Holter ECG test was performed in our center, not confirming the aforementioned disturbances and showing a tendency to tachycardia. The significant SA was resolved after a period of detraining. The case indicates that considering invasive therapy was unreasonable, and patient-centered care and shared decision-making play a key role in cardiac pacing therapy. In addition, some sports HRM with an HRV function can help diagnose bradyarrhythmia, both in professional and amateur athletes.

Association of the Heart Rate Variability Response to Active Standing with the Severity of Calcific Aortic Valve Disease: Novel Insights of a Neurocardiovascular Pathology

The aim of this work was to obtain insights of the participation of the autonomic nervous system in different stages of calcific aortic valve disease (CAVD) by heart rate variability (HRV) analysis. Studying subjects with no valve impairments and CAVD patients, we also sought to quantify the independent contribution or explanatory capacity of the aortic valve echocardiographic parameters involved in the HRV changes caused by active standing using hierarchical partitioning models to consider other variables or potential confounders. We detected smaller adjustments of the cardiac autonomic response at active standing caused specifically by the aortic valve deterioration. The highest association (i.e., the highest percentage of independent exploratory capacity) was found between the aortic valve area and the active standing changes in the short-term HRV scaling exponent α₁ (4.591%). The valve’s maximum pressure gradient echocardiographic parameter was present in most models assessed (in six out of eight models of HRV indices that included a valve parameter as an independent variable). Overall, our study provides insights with a wider perspective to explore and consider CAVD as a neurocardiovascular pathology. This pathology involves autonomic-driven compensatory mechanisms that seem generated by the aortic valve deterioration.

Heart rate variability and atrial fibrillation in the general population: a longitudinal and Mendelian randomization study

BACKGROUND

Sex differences and causality of the association between heart rate variability (HRV) and atrial fibrillation (AF) in the general population remain unclear.

METHODS

12,334 participants free of AF from the population-based Rotterdam Study were included. Measures of HRV including the standard deviation of normal RR intervals (SDNN), SDNN corrected for heart rate (SDNNc), RR interval differences (RMSSD), RMSSD corrected for heart rate (RMSSDc), and heart rate were assessed at baseline and follow-up examinations. Joint models, adjusted for cardiovascular risk factors, were used to determine the association between longitudinal measures of HRV with new-onset AF. Genetic variants for HRV were used as instrumental variables in a Mendelian randomization (MR) analysis using genome-wide association studies (GWAS) summary-level data.

RESULTS

During a median follow-up of 9.4 years, 1302 incident AF cases occurred among 12,334 participants (mean age 64.8 years, 58.3% women). In joint models, higher SDNN (fully-adjusted hazard ratio (HR), 95% confidence interval (CI) 1.24, 1.04-1.47, p = 0.0213), and higher RMSSD (fully-adjusted HR, 95% CI 1.33, 1.13-1.54, p = 0.0010) were significantly associated with new-onset AF. Sex-stratified analyses showed that the associations were mostly prominent among women. In MR analyses, a genetically determined increase in SDNN (odds ratio (OR), 95% CI 1.60, 1.27-2.02, p = 8.36 × 10^-05), and RMSSD (OR, 95% CI 1.56, 1.31-1.86, p = 6.32 × 10^-07) were significantly associated with an increased odds of AF.

CONCLUSION

Longitudinal measures of uncorrected HRV were significantly associated with new-onset AF, especially among women. MR analyses supported the causal relationship between uncorrected measures of HRV with AF. Our findings indicate that measures to modulate HRV might prevent AF in the general population, in particular in women. AF; atrial fibrillation, GWAS; genome-wide association study, IVW; inverse variance weighted, MR; Mendelian randomization, MR-PRESSO; MR-egger and mendelian randomization pleiotropy residual sum and outlier, RMSSD; root mean square of successive RR interval differences, RMSSDc; root mean square of successive RR interval differences corrected for heart rate, SDNN; standard deviation of normal to normal RR intervals, SDNNc; standard deviation of normal to normal RR intervals corrected for heart rate, WME; weighted median estimator. ^aRotterdam Study n=12,334 ^bHRV GWAS n=53,174 ^cAF GWAS n=1,030,836.

The Mechanism of Cardiac Sympathetic Activity Assessment Methods: Current Knowledge

This review has summarized the methods currently available for cardiac sympathetic assessment in clinical or under research, with emphasis on the principles behind these methodologies. Heart rate variability (HRV) and other methods based on heart rate pattern analysis can reflect the dominance of sympathetic nerve to sinoatrial node function and indirectly show the average activity level of cardiac sympathetic nerve in a period of time. Sympathetic neurotransmitters play a key role of signal transduction after sympathetic nerve discharges. Plasma or local sympathetic neurotransmitter detection can mediately display sympathetic nerve activity. Given cardiac sympathetic nerve innervation, i.e., the distribution of stellate ganglion and its nerve fibers, stellate ganglion activity can be recorded either directly or subcutaneously, or through the surface of the skin using a neurophysiological approach. Stellate ganglion nerve activity (SGNA), subcutaneous nerve activity (SCNA), and skin sympathetic nerve activity (SKNA) can reflect immediate stellate ganglion discharge activity, i.e., cardiac sympathetic nerve activity. These cardiac sympathetic activity assessment methods are all based on the anatomy and physiology of the heart, especially the sympathetic innervation and the sympathetic regulation of the heart. Technological advances, discipline overlapping, and more understanding of the sympathetic innervation and sympathetic regulation of the heart will promote the development of cardiac sympathetic activity assessment methods.

Resting heart rate predicts cardiac autonomic modulation during passive head-up tilt in subjects without cardiovascular diseases

Background Resting heart rate (HR) and its variability (HRV) reflects the cardiac sympathovagal balance that is stimulated by head-up tilting. HRV is influenced by the level of HR, but how much HRV offers additional information about cardiac autonomic tone than HR alone remains unresolved. We examined the relation of resting HR with HRV during head-up tilt. Methods. Hemodynamics of 569 subjects without known cardiovascular diseases and medications with direct cardiovascular effects were recorded using whole-body impedance cardiography, radial pulse wave analysis, and electrocardiography-based HRV analysis during passive head-up tilt. Results. Higher low frequency to the high-frequency ratio (LF/HF) of HRV (reflecting sympathovagal balance) was associated with higher HR in supine (p < .05, both linear regression analysis and variance analysis comparing HR tertiles) and upright postures (p < .001, linear regression analysis). The association of HR with HRV during tilt-testing remained significant when the HR dependence of HRV was mathematically weakened by dividing the HRV power spectra with the fourth power of the average RR-interval. Conclusion. Higher resting HR is related to higher LF/HF both supine and upright, reflecting elevated sympathetic influence on cardiac autonomic modulation. Lower resting HR is associated with lower resting LF/HF, while the differences in LF/HF between the HR tertiles were minor during head-up tilt, suggesting a greater change in cardiac sympathovagal balance in response to upright posture in those with lowest resting HR. Altogether, resting HR well predicts HRV levels during head-up tilt.Trial registration: Clinicaltrialsregister.eu 2006-002065-39, first registered 5 May 2006. ClinicalTrials.gov NCT01742702, first registered 5 December 2012.

Cardiovascular phenotype of long-term anabolic-androgenic steroid abusers compared with strength-trained athletes

Introduction

Abuse of anabolic‐androgenic steroids (AAS) has been linked to a variety of different cardiovascular (CV) side effects, but still the clinical effects of AAS abuse on CV risk are not clear. The aim of this study was to assess the CV phenotype of a large cohort of men with long‐term AAS use compared with strength‐trained athletes without AAS use.

Methods

Fifty one strength‐trained men with ≥3 years of AAS use was compared with twenty one strength‐trained competing athletes. We verified substance abuse and non‐abuse by blood and urine analyses. The participants underwent comprehensive CV evaluation including laboratory analyses, 12‐lead ECG with measurement of QT dispersion, exercise ECG, 24 h ECG with analyses of heart rate variability, signal averaged ECG, basic transthoracic echocardiography, and coronary computed tomography angiography (CCTA).

Results

Hemoglobin levels and hematocrit were higher among the AAS users compared with non‐users (16.8 vs. 15.0 g/dl, and 0.50% vs. 0.44%, respectively, both p < 0.01) and HDL cholesterol significantly lower (0.69 vs. 1.25 mmol/L, p < 0.01). Maximal exercise capacity was 270 and 280 W in the AAS and the non‐user group, respectively (p = 0.04). Echocardiography showed thicker intraventricular septum and left ventricular (LV) posterior wall among AAS users (p < 0.01 for both), while LV ejection fraction was lower (50 vs. 54%, p = 0.02). Seven AAS users (17%) had evidence of coronary artery disease on CCTA. There were no differences in ECG measures between the groups.

Conclusions

A divergent CV phenotype dominated by increased CV risk, accelerated coronary artery disease, and concentric myocardial hypertrophy was revealed among the AAS users.

A Systematic Review of Utilisation of Diurnal Timing Information in Clinical Trial Design for Long QT Syndrome

Diurnal oscillations in human cardiac electrophysiology are thought to be under the control of the endogenous circadian clock. The incidence of arrhythmic events in patients with Long QT syndrome (LQTS) varies diurnally. The diurnal variation in QT interval has previously been identified as a potential for error in clinical trials which utilise ECG measurement. We performed a systematic review of clinical trials for LQTS to identify practice around specification of timing information for point electrocardiogram (ECG) measurements, analysis of continual ECG recordings ≥24 h, and drug delivery. Despite guidelines having been issued around the analysis of 24-h ECG recordings, we identify a lack of usage of detailed time of day information in trial design for LQTS studies, which has the potential to affect the interpretation of the results of drug trials. We identify that, in contrast, clinical trials for QT prolonging drugs demonstrate increased incorporation of time of day information of both QT analysis and drug dosing. We provide a visual portal to allow trial designers and clinicians to better understand timing of common cardiac-targeting drugs, and to bear this concept in mind in the design of future clinical trials.

The mechanistic and prognostic implications of heart rate variability analysis in patients with cirrhosis

Chronic liver damage leads to scarring of the liver tissue and ultimately a systemic illness known as cirrhosis. Patients with cirrhosis exhibit multi-organ dysfunction and high mortality. Reduced heart rate variability (HRV) is a hallmark of cirrhosis, reflecting a state of defective cardiovascular control and physiological network disruption. Several lines of evidence have revealed that decreased HRV holds prognostic information and can predict survival of patients independent of the severity of liver disease. Thus, the aim of this review is to shed light on the mechanistic and prognostic implications of HRV analysis in patients with cirrhosis. Notably, several studies have extensively highlighted the critical role systemic inflammation elicits in conferring the reduction in patients' HRV. It appears that IL-6 is likely to play a central mechanistic role, whereby its levels also correlate with manifestations, such as autonomic neuropathy and hence the partial uncoupling of the cardiac pacemaker from autonomic control. Reduced HRV has also been reported to be highly correlated with the severity of hepatic encephalopathy, potentially through systemic inflammation affecting specific brain regions, involved in both cognitive function and autonomic regulation. In general, the prognostic ability of HRV analysis holds immense potential in improving survival rates for patients with cirrhosis, as it may indeed be added to current prognostic indicators, to ultimately increase the accuracy of selecting the recipient most in need of liver transplantation. However, a network physiology approach in the future is critical to delineate the exact mechanistic basis by which decreased HRV confers poor prognosis.

Low Heart Rate Variability Predicts Poor Overall Survival of Lung Cancer Patients With Brain Metastases

Background

The aim of this prospective study was to evaluate the association between heart rate variability (HRV) and overall survival of lung cancer patients with brain metastases (LCBM).

Methods

Fifty-six LCBM patients were enrolled in this study. Five-minute electrocardiograms were collected before the time to first brain radiotherapy. HRV was analyzed quantitatively by using the time domain parameters, i.e., the standard deviation of all normal-normal intervals (SDNN) and the root mean square of successive differences (RMSSD). Survival time for LCBM patients was defined as from the date of HRV testing to the date of death or the last follow-up.

Results

In the univariate analysis, SDNN ≤ 13 ms (P = 0.003) and RMSSD ≤ 4.8 ms (P = 0.014) significantly predicted poor survival. Multivariate analysis confirmed that RMSSD ≤ 4.8 ms (P = 0.013, hazard ratio = 3.457, 95% confidence interval = 1.303–9.171) was also an independent negative prognostic factor after adjusting for mean heart rate, Karnofsky performance status, and number of brain metastases in LCBM patients.

Conclusion

Decreased RMSSD is independently associated with shorter survival time in LCBM patients. HRV might be a novel predictive biomarker for LCBM prognosis.

Association between circadian variation of heart rate and mortality among critically ill patients: a retrospective cohort study

Background

Heart rate (HR) related parameters, such as HR variability, HR turbulence, resting HR, and nighttime mean HR have been recognized as independent predictors of mortality. However, the influence of circadian changes in HR on mortality remains unclear in intensive care units (ICU). The study is designed to evaluate the relationship between the circadian variation in HR and mortality risk among critically ill patients.

Methods

The present study included 4,760 patients extracted from the Multiparameter Intelligent Monitoring in Intensive Care II database. The nighttime mean HR/daytime mean HR ratio was adopted as the circadian variation in HR. According to the median value of the circadian variation in HR, participants were divided into two groups: group A (≤ 1) and group B (> 1). The outcomes included ICU, hospital, 30-day, and 1-year mortalities. The prognostic value of HR circadian variation was investigated by multivariable logistic regression models and Cox proportional hazards models.

Results

Patients in group B (n = 2,471) had higher mortality than those in group A (n = 2,289). Multivariable models revealed that the higher circadian variation in HR was associated with ICU mortality (odds ratio [OR], 1.393; 95% confidence interval [CI], 1.112–1.745; P = 0.004), hospital mortality (OR, 1.393; 95% CI, 1.112–1.745; P = 0.004), 30-day mortality (hazard ratio, 1.260; 95% CI, 1.064–1.491; P = 0.007), and 1-year mortality (hazard ratio, 1.207; 95% CI, 1.057–1.378; P = 0.005), especially in patients with higher SOFA scores.

Conclusions

The circadian variation in HR might aid in the early identification of critically ill patients at high risk of associated with ICU, hospital, 30-day, and 1-year mortalities.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-022-01586-9.

Recurrence Quantitative Analysis of Wavelet-Based Surrogate Data for Nonlinearity Testing in Heart Rate Variability

Exploring the presence of nonlinearity through surrogate data testing provides insights into the nature of physical and biological systems like those obtained from heart rate variability (HRV). Short-term HRV time series are of great clinical interest to study autonomic impairments manifested in chronic diseases such as the end stage renal disease (ESRD) and the response of patients to treatment with hemodialysis (HD). In contrast to Iterative Amplitude Adjusted Fourier Transform (IAAFT), the Pinned Wavelet Iterative Amplitude Adjusted Fourier Transform (PWIAAFT) surrogates preserve nonstationary behavior in time series, a common characteristic of HRV. We aimed to test synthetic data and HRV time series for the existence of nonlinearity. Recurrence Quantitative Analysis (RQA) indices were used as discriminative statistics in IAAFT and PWIAAFT surrogates of linear stationary and nonstationary processes. HRV time series of healthy subjects and 29 ESRD patients before and after HD were tested in this setting during an active standing test. Contrary to PWIAAFT, linear nonstationary time series may be erroneously regarded as nonlinear according to the IAAFT surrogates. Here, a lower proportion of HRV time series was classified as nonlinear with PWIAAFT, compared to IAAFT, confirming that the nonstationarity condition influences the testing of nonlinear behavior in HRV. A contribution of nonlinearity was found in the HRV data of healthy individuals. A lower proportion of nonlinear time series was also found in ESRD patients, but statistical significance was not found. Although this proportion tends to be lower in ESRD patients, as much as 60% of time series proved to be nonlinear in healthy subjects. Given the important contribution of nonlinearity in HRV data, a nonlinear point of view is required to achieve a broader understanding of cardiovascular physiology.

Autonomic dysfunction in adults following mild traumatic brain injury: A systematic review

BACKGROUND

Increasing evidence suggests autonomic nervous system (ANS) dysfunction may occur following mild traumatic brain injury (mTBI). Measures of heart rate, heart rate variability, blood pressure and baroreceptor sensitivity can be used to evaluate ANS dysfunction following mTBI.

OBJECTIVE

Summarize the evidence for ANS dysfunction in adults following mTBI.

METHODS

A search of Embase, MEDLINE, Cochrane Central Register, PsycINFO, CINAHL and SPORTDiscus databases was conducted. Search topics included: mTBI and ANS. Identified abstracts were independently reviewed by 2 reviewers followed by full text screening. Risk of bias was assessed using a modified SIGN checklist. A structured synthesis was performed.

RESULTS

Thirty-nine studies (combined 1,467 participants diagnosed with mTBI) evaluating ANS function were included. ANS function was evaluated under various conditions including: rest, during exertion, cold pressor test, Valsalva maneuver, using face cooling and eyeball pressure paradigms. Short-term or ultra-short-term recordings were most common. The majority of studies (28/39) were rated as "unacceptable" for quality of evidence.

CONCLUSIONS

Altered parameters of ANS function have been reported in multiple conditions following mTBI, both acutely and in the post-acute/chronic stages of recovery. However, due to methodological limitations, conclusions regarding the severity and timing of ANS dysfunction following mTBI cannot be drawn.