Advances in heart rate variability signal analysis: joint position statement by the e-Cardiology ESC Working Group and the European Heart Rhythm Association co-endorsed by the Asia Pacific Heart Rhythm Society

Photoplethysmography-based HRV analysis and machine learning for real-time stress quantification in mental health applications

Prolonged exposure to high-stress environments can lead to mental illnesses such as anxiety disorders, depression, and posttraumatic stress disorder. Here, a wearable device utilizing photoplethysmography (PPG) technology is developed to noninvasively measure physiological signals and analyze heart rate variability (HRV) parameters. Traditional normative HRV databases typically do not account for responses induced by specific stressors such as cognitive tasks. Therefore, machine learning is used to build a more dynamic stress assessment model. Machine learning can capture complex nonlinear relationships among HRV parameters during stress-inducing tasks, adapts to individual stress response variations, and provides real-time stress level predictions. Furthermore, machine learning models can integrate temporal patterns in HRV data to achieve nuanced stress level assessment. This study examines the feasibility of PPG signals and validates the developed stress model. The RR intervals derived from PPG signals were highly positively correlated with those from electrocardiography signals (correlation coefficient = 0.9920, R-squared = 0.9837); this confirms the usability of PPG signals for HRV analysis. The stress model is constructed via the open-source Swell dataset. In the experiments, participants complete the Depression Anxiety Stress Scales-21-Chinese (DASS-21-C) questionnaire to quantify levels of depression, anxiety, and stress over a week. Baseline and stress-state PPG data are collected, converted into HRV values, and input into the model for stress quantification. The Stroop test is used to elicit stress responses. After the experiment, the DASS-21-C stress scores were compared with the model's baseline, stress state, and combined scores. The highest correlation was observed between the model's baseline score and the DASS-21-C stress score (correlation coefficient = 0.92, R-squared =  0.8457), supporting the model's psychological significance in quantifying everyday stress. HRV parameter changes across experimental phases are discussed as well as sex differences in stress responses. In the future, this device may be applied in clinical scenarios for further validation and could be integrated with additional physiological indicators for broader application in daily health management and stress warning systems.

Reliability of short-term measurement of heart rate variability on rest in individuals with temporomandibular disorder

Individuals with temporomandibular disorder (TMD) experience autonomic dysfunction, which disrupts the balance between the sympathetic and parasympathetic nervous systems. This imbalance can result in altered heart rate variability (HRV) and other physiological disturbances. However, it is important to note that, to date, no research has investigated the inter- and intra-rater reliability of HRV measurements in individuals with TMD. The objective of this investigation was to analyze the intra- and inter-examiner reliability of HRV captured by a polar heart rate monitor in individuals with TMD. The RR interval, the time elapsed between two successive R-waves of the QRS signal on the electrocardiogram (RRi), were recorded during a 10 min period in a supine position using a portable heart rate monitor (Polar® V800 model). The data were transferred into Kubios® HRV standard analysis software and analyzed within the stable sessions containing 5 min sequential RRi. The intraclass correlation coefficient (ICC) ranged from 0.907 to 0.998 according to the intra-examiner analysis by Examiner 1 and 0.875 to 0.998 according to the intra-examiner by Examiner 2. The inter-examiner ICC ranged from 0.796 to 0.996. The coefficient of variation was up to 9.60 for Examiner 1 intra-examiner analysis, 11.95 for Examiner 2 intra-examiner analysis and 14.88 for inter-examiner analysis. The HRV analysis captured by a Polar cardio frequency meter presented adequate reliability when considering different times and examiners. Intra-examiner reliability showed ICC values ranging from 0.842 to 0.999, and inter-examiner reliability ranged from 0.796 to 0.994. Bland-Altman plots indicated good agreement with minimal bias. Coefficients of variation were below 10% for most variables.

Enhancing psychological skills and well-being in sport through an app-based blended intervention: a randomized controlled pilot study

BACKGROUND

Mental preparation is a fundamental aspect of athletic performance. We present here an experiment aimed at evaluating the effectiveness of a blended intervention to promote mindfulness and self-confidence and a reduction of anxiety among professional athletes.

METHODS

The intervention, delivered through an application for smartphones, included eight weekly modules with variable and progressive training and relaxation exercises. Meetings with the athletes took place every 2 weeks. The study involved 41 tennis players who were randomly assigned to either the intervention or the control group. Data were analyzed via repeated measures ANOVA.

RESULTS

The results showed a significant change in self-confidence, arousal control, anxiety, awareness and refocusing in the experimental group and no significant change in the control group.

CONCLUSION

The blended intervention showed good results in only 8 weeks, thus again emphasizing the effectiveness of breathing and relaxation techniques opening the door for future studies and interventions that can use new technologies to promote athletes' well-being and performance.

TRIAL REGISTRATION

Current Controlled Trials NCT06212986, 01/18/2024 - Retrospectively registered.

Prevalence of Sleep Apnea in Patients with Syncope of Unclear Cause: SINCOSAS Study

Background and Objectives: The association between syncope and sleep apnea (SA) has been scarcely investigated. Dysfunction of the autonomic nervous system (ANS) may represent a shared pathophysiological mechanism. This study aimed to determine the prevalence of SA in patients with syncope of unclear cause (SUC), identify potential associated factors, and evaluate nocturnal heart rate variability (HRV) as a marker of ANS function. Materials and Methods: A prospective cohort study was conducted in adult patients diagnosed with SUC. Nocturnal cardiorespiratory polygraphy was performed to detect the presence of SA. A range of variables potentially associated with SA was collected. Both SA diagnosis and HRV parameters were assessed using the Embletta® MPR polygraph system. Results: A total of 156 patients were enrolled (57% male), with a mean age of 64 years and a mean body mass index of 27.5 kg/m2 (range: 24.8-32.2). Hypertension was present in 46% of the cohort. The overall prevalence of SA was 78.2% (95% CI: 71.7-84.4%), with 28.7% classified as severe. Age (OR = 1.04; 95% CI: 1.01-1.07) and BMI (OR = 1.17; 95% CI: 1.06-1.28) were independent predictors of SA. Mean RR interval was significantly lower in patients with SA compared to those without (942 ms vs. 995 ms; p = 0.04). No significant differences in HRV parameters were observed between the two groups. Conclusions: This study found a high prevalence (nearly 78%) of SA among adult patients with SUC, particularly in individuals over 50 years of age and those who were overweight. However, this association could not be predicted based on clinical variables alone. No significant differences in nocturnal HRV were detected between patients with SUC with and without SA.

The role of cardiovascular response as a predictor of neurologic disability in children with brain injury - a pilot study

OBJECTIVE

We aimed to assess medium-to long-term neurological outcomes in children with severe acute brain injury (ABI) and to identify cardiovascular predictors associated with unfavorable outcomes, such as heart rate (HR), blood pressure (BP), and heart rate variability (HRV). HRV refers to the oscillations in the intervals between consecutive heartbeats, reflecting the dynamic interplay between sympathetic and parasympathetic impulses to the heart. It provides a non-invasive indicator of autonomic nervous system (ANS) activity.

DESIGN

Prospective observational cohort.

SETTING

Tertiary academic pediatric intensive care unit (PICU).

PATIENTS

Children >27 days and <18 years old admitted to the PICU after severe ABI who survived to PICU discharge. Children suspected of being brain dead at PICU admission or with cardiac arrythmias were excluded.

INTERVENTIONS

None.

MEASURE

ments: Physiological variables, neurological data, chemistry and hematologic tests and medication were collected within the initial 12 h following admission to the PICU. Linear and nonlinear indices of HRV obtained from electrocardiogram (ECG) Holter recordings, computerized tomography (CT) and PICU scores, as well as survival rates within the PICU, were evaluated. The primary outcome measure was global functional outcome as measured by the Pediatrics Glasgow Outcome Scale Extended (GOSE-Peds) at 3 and 12 months after injury. These data were taken by reviewing the medical records. The outcome was dichotomized into favorable and unfavorable based on predefined cutoffs. None to mild disability (GOSE-E PEDS category ≤2) was categorized as favorable outcome, whereas moderate to severe disability was categorized as unfavorable (GOSE-E PEDS category ≥3).

MAIN RESULTS

Thirty-one children with ABI were eligible for the study. Twenty-four were male (77.4 %) and they had the median age of 11.3 years old (IQR 5.6-14.3). Twenty-two (71.0 %) patients had traumatic brain injury (TBI) and five (16.1 %) cerebral hemorrhage. Sixteen children (51.6 %) had a favorable outcome at 3 months and twenty-one (67.7 %) at 12 months. The presence of tachycardia or bradycardia was not related to the prognosis. Patients with systolic arterial blood pressure (SBP) above the 95th percentile in the first 12 h after admission to the PICU exhibited a significantly better neurological outcome [15 (68.2 %) vs. 9 (31.8 %), p = 0.006] at 3 months, and [20 (83.3 %) vs. 4 (16.7 %), p = 0.002] at 12 months. Calculated HRV values were higher, both on admission and 12 h after admission, in patients with a favorable prognosis at 3 and 12 months. However, these results were statistically significant only for RMSSD, LF, TP, and Poincaré SD1 and SD2 at 12 h after admission and for outcomes at 3 months. Patients with LF > 70.0 ms2 at 12 h after admission had a significantly better outcome at 12 months [11.0 (91.7 %) vs 1.0 (8.3 %), p = 0.046]. 87.5 % of patients with SDNN >35.0 ms and 70.5 % of patients with RMSSD >3.2 ms, at 12 h after admission, showed a statistically significative better outcome at 3 months. Patients who had a more unfavorable prognosis spent significantly more time on mechanical ventilation and had a longer length of stay (LOS) in the PICU.

CONCLUSIONS

This study suggests that elevated early SBP and HRV indices-particularly LF power measured 12 h after PICU admission-may serve as independent, non-invasive predictors of long-term neurological outcomes in children with severe ABI. These findings support the role of early autonomic activation as a marker of favorable prognosis and underscore the potential value of incorporating cardiovascular and autonomic monitoring into prognostic models and individualized neuroprotective strategies in pediatric neurocritical care.

Sex hormones correlate with heart rate variability in healthy women and this correlation is conserved in women with well-controlled type 2 diabetes mellitus

SUBJECTS AND METHODS

In this study, four groups of women were designated according to their health status (control or T2DM) and fertility status (premenopausal or postmenopausal). Five serum sex hormones were measured (estradiol, progesterone, testosterone, LH and FSH), and time-domain and frequency-domain HRV indices were determined during three conditions: supine position, active standing, and rhythmic breathing. For the complete sample (n=118), bivariate Pearson correlations and linear multiple regressions were used to analyze the relationship between sex hormones, HRV indices, and other independent variables, such as glycemia and age. A p-value <0.05 was considered as significant.

RESULTS

There were no differences in sex hormones or HRV indices when comparing the healthy and T2DM groups. All bivariate Pearson correlations were significant between sex hormones and HRV indices; estradiol, progesterone, and testosterone have positive correlations; meanwhile, LH and FSH were negative in the time-domain (SDNN, RMSSD, pNN20) and frequency domain (PLF and PHF) indices. Regression models adjusted for mean heartbeat intervals confirmed an association between all sex hormones and HRV indices. Estradiol maintained significance in the regression models for specific HRV indices during supine and active standing conditions even after adjusting for age and glucose levels.

CONCLUSIONS

All sex hormones correlate with HRV indices. Regression analysis confirms that this correlation is independent from the mean heartbeat interval. However, in regression models adjusted for age and glucose levels, only estradiol was found to be significant, and should be considered an important variable related to cardiovascular and autonomic balance in T2DM women and may provide crucial information to improve cardiovascular risk algorithms.

Circadian rhythm modulation in heart rate variability as potential biomarkers for major depressive disorder: A machine learning approach

Major depressive disorder (MDD) is associated with reduced heart rate variability (HRV), but its link to circadian rhythm modulation (CRM) of HRV is unclear. Given that depression disrupts circadian rhythms, assessing HRV fluctuations may better capture the CRM and the related autonomic nervous system (ANS) alterations, potentially enhancing our understanding of the pathophysiological mechanisms of MDD. This study aimed to explore the relationship between CRM of HRV and MDD, and to identify potential biomarkers for MDD using machine learning (ML). A total of 165 MDD patients and 60 healthy controls (HCs) were enrolled in the study, with each participant completing 24-h Holter electrocardiogram (ECG) monitoring and psychological scale assessments prior to receiving antidepressant treatment. The circadian rhythm of HRV was quantified using a cosine regression model, and seven typical ML models were employed to distinguish MDD from HCs. MDD patients exhibited a significant decrease in average diurnal HRV indices, particularly during night-time, along with reductions in the parameter M of HRV circadian rhythms compared to HCs. Depression severity was negatively associated with the parameters M of RMSSD, PNN50, HF, while positively associated with the parameter M of LF/HF ratio. Furthermore, the gradient boosting machine (GBM) model demonstrated the best performance in classifying MDD (accuracy 0.823, AUC 0.868), and a final GBM model was developed with 12 selected features. This study provides new insights into the relationship between circadian rhythm abnormalities and MDD, highlighting the potential of using CRM of HRV as novel biomarkers for MDD pathophysiology and clinical applications.

The use of heart rate variability, oxygen saturation, and anthropometric data with machine learning to predict the presence and severity of obstructive sleep apnea

Introduction

Obstructive sleep apnea (OSA) is a prevalent sleep disorder with a high rate of undiagnosed patients, primarily due to the complexity of its diagnosis made by polysomnography (PSG). Considering the severe comorbidities associated with OSA, especially in the cardiovascular system, the development of early screening tools for this disease is imperative. Heart rate variability (HRV) is a simple and non-invasive approach used as a probe to evaluate cardiac autonomic modulation, with a variety of newly developed indices lacking studies with OSA patients.

Objectives

We aimed to evaluate numerous HRV indices, derived from linear but mainly nonlinear indices, combined or not with oxygen saturation indices, for detecting the presence and severity of OSA using machine learning models.

Methods

ECG waveforms were collected from 291 PSG recordings to calculate 34 HRV indices. Minimum oxygen saturation value during sleep (SatMin), the percentage of total sleep time the patient spent with oxygen saturation below 90% (T90), and patient anthropometric data were also considered as inputs to the models. The Apnea-Hypopnea Index (AHI) was used to categorize into severity classes of OSA (normal, mild, moderate, severe) to train multiclass or binary (normal-to-mild and moderate-to-severe) classification models, using the Random Forest (RF) algorithm. Since the OSA severity groups were unbalanced, we used the Synthetic Minority Over-sampling Technique (SMOTE) to oversample the minority classes.

Results

Multiclass models achieved a mean area under the ROC curve (AUROC) of 0.92 and 0.86 in classifying normal individuals and severe OSA patients, respectively, when using all attributes. When the groups were dichotomized into normal-to-mild OSA vs. moderate-to-severe OSA, an AUROC of 0.83 was obtained. As revealed by RF, the importance of features indicates that all feature modalities (HRV, SpO2, and anthropometric variables) contribute to the top 10 ranks.

Conclusion

The present study demonstrates the feasibility of using classification models to detect the presence and severity of OSA using these indices. Our findings have the potential to contribute to the development of rapid screening tools aimed at assisting individuals affected by this condition, to expedite diagnosis and initiate timely treatment.

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.

Heartbeat signature for predicting motor and non-motor involvement among nonparkinsonian LRRK2 G2019S mutation carriers

PURPOSE

Increased beat-to-beat heart rate variability (HRV) is a feature of patients with Parkinson's disease (PD) who carry the G2019S mutation in the LRRK2 gene (LRRK2-PD). Since LRRK2 mutations have incomplete penetrance, HRV changes preceding PD conversion would likely be observed only in a subset of LRRK2 non-manifesting carriers (NMC). We aimed to assess HRV in a subgroup of NMC with distinctive characteristics of LRRK2-PD, identified through clustering analysis.

METHODS

HRV measures derived from 300 normal heartbeat intervals extracted from the electrocardiograms of 25 NMC, 32 related non-carriers (RNC), 27 unrelated healthy controls, and 14 patients with LRRK2-PD were analyzed. Clinical symptoms were evaluated using questionnaires and scales, and three NMC subgroups were identified using a k-means cluster analysis on the basis of the deceleration capacity of heart rate (DC) and Rényi entropy. Standard and advanced HRV measures were compared using multiple regression analysis, controlling for age, sex, and mean heart rate.

RESULTS

Beat-to-beat HRV markers were significantly increased in a subgroup of seven NMC (NMC2, 28%) compared with RNC and controls. Increased irregularity and DC were also verified in the NMC2 compared with controls, and were typical traits in both the NMC2 and RNC. Overall, the HRV profile of NMC2 was comparable to that of patients with LRRK2-PD. NMC2 further exhibited greater motor and non-motor traits than the other NMC, RNC, and controls.

CONCLUSIONS

Our results confirmed that HRV characteristics of LRRK2-PD are also found in a subset of NMC displaying clinical traits of LRRK2-PD. Further research is needed to clarify whether higher HRV represents a LRRK2-PD prodromal manifestation.

Modelling the time-resolved modulations of cardiac activity in rats: A study on pharmacological autonomic stimulation

Assessing cardiac dynamics over time is essential for understanding cardiovascular health and its parallel patterns of activity with the brain. We present a methodology to estimate the time-resolved sympathetic and parasympathetic modulations of cardiac dynamics, specifically tailored for the rat heart. To evaluate the performance of our method, we study a dataset comprising spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. These rats were administered dobutamine to elicit autonomic dynamics. The results obtained from our method demonstrated accurate time-resolved depiction of sympathetic reactivity induced by dobutamine administration. These responses closely resembled the expected autonomic alterations observed during physical exercise conditions, albeit emulated pharmacologically. We further compared our method with standard measures of low-frequency (LF) and high-frequency (HF) components, which are commonly used, although debated, for sympathetic and parasympathetic activity estimation. The comparisons with LF and HF measures further confirmed the effectiveness of our method in better capturing autonomic changes in rat cardiac dynamics. Our findings highlight the potential of our adapted method for time-resolved analysis in future clinical and translational studies involving rodent models. The validation of our approach in animal models opens new avenues for investigating the relationship between ongoing changes in cardiac activity and parallel changes in brain dynamics. Such investigations are crucial for advancing our understanding of the brain-heart connection, particularly in cases involving neurodegeneration, brain injuries and cardiovascular conditions. KEY POINTS: We developed a method for time-resolved estimation of sympathetic and parasympathetic modulations in rat cardiac dynamics, validated against standard low-frequency and high-frequency measures. We used a cohort of spontaneously hypertensive rats and Wistar-Kyoto rats, with dobutamine administration to induce autonomic responses. Our method accurately depicted time-resolved sympathetic reactivity similar to autonomic changes during physical exercise. Our findings suggest potential for future clinical and translational studies on the brain-heart connection, particularly in cardiovascular conditions.

Assessing the clinical reliability of short-term heart rate variability: insights from controlled dual-environment and dual-position measurements

Heart rate variability (HRV) is a widely recognized biomarker for autonomic nervous system regulation, applicable in clinical and athletic settings to monitor health and recovery. Despite its extensive use, HRV measurement reliability is influenced by numerous factors, necessitating controlled conditions for accurate assessments. This study investigates the reliability of short-term HRV measurements in various settings and positions, aiming to establish consistent protocols for HRV monitoring and interpretation. We assessed morning HRV in 34 healthy, physically active adults across supine and standing positions, at home and in the laboratory, over a 24-hour period. Environment significantly impacted standing HRV. Home measurements exhibited slightly lower variance compared to lab settings, underscoring the importance of environment control. Our findings confirm the high reliability of HRV measurements, indicating their robustness in capturing autonomic changes, provided a rigorous methodology is employed. Here we show that effective and reliable HRV assessment is possible across various conditions, contingent upon strict management of confounding factors. This research supports the utility of HRV as a non-invasive diagnostic tool, emphasizing its importance in health management and potential in broadening applications to diverse populations. Future studies are encouraged to expand these assessments to include varied demographic and clinical profiles, enhancing HRV integration into routine health evaluations.

The autonomous nervous system and the cholinergic anti-inflammatory reflex in postoperative neurocognitive disorders

PURPOSE OF REVIEW

Postoperative delirium (POD) is a common and serious complication after surgery. It is associated with postoperative neurocognitive disorder (PNCD). The vagal cholinergic anti-inflammatory pathway (CAP) has been hypothesized to play a role in POD/PNCD and may be a target for interventions such as transcutaneous auricular stimulation (taVNS). We aim to review associations of heart rate variability (HRV) as an indicator of vagal function with POD and postoperative immune reaction as well as taVNS as a potential preventive intervention for POD.

RECENT FINDINGS

Autonomous nervous system (ANS) dysfunction was a common finding in studies analysing HRV in POD and postoperative cognitive dysfunction, but results were heterogeneous. There was no evidence from HRV analysis that vagal activity prevents overshooting postoperative immune activation, but HRV may help to identify patients at risk for postoperative infections. Animal studies and preliminary trials suggest that taVNS may be used to prevent POD/PNCD.

SUMMARY

Our review provides no evidence that CAP suppression is associated with POD/PNCD. Future studies should consider that high vagal tone may also mediate immunosuppression in surgical patients, yielding an increased risk for postoperative infections. Although taVNS is a promising approach to prevent POD/POCD, future studies should take these concerns into account.

Comprehensive linear and nonlinear heart rate variability normative data in children

BACKGROUND

The autonomic nervous system (ANS) is critical in regulating involuntary bodily functions, including heart rate. Heart rate variability (HRV) reflects the complex interplay between the ANS and humoral factors, making it a valuable noninvasive tool for assessing autonomic function. While HRV has been extensively studied in adults, normative data for HRV in children, primarily based on long-term rhythm recordings, are limited.

OBJECTIVE

This study aimed to establish comprehensive normative data for HRV in children.

METHODS

In this retrospective study, we examined 24-h Holter monitors of children aged 1 day to 18 years, divided into six age groups, at Nemours Children's Health in Orlando, Florida, spanning the years 2013-2023. HRV analysis encompassed time-domain, frequency-domain, and nonlinear indices.

RESULTS

Holter data for a total of 247 patients in six age groups were included. An age-related uptrend was observed in all time- and frequency-domain variables except the normalized unit of low-frequency power. Entropy analysis revealed contradictory results among different entropy techniques. Sample and approximate entropy analyses were consistent and showed less complexity and more predictability of HRV with decreasing heart rate, while Shannon entropy analysis showed the opposite. Fractal detrended fluctuation analysis exhibited significant decreases across the age groups, suggestive of diminishing self-similarity of HRV patterns.

CONCLUSION

Control of heart rate and HRV is a highly complex process and requires further study for a better understanding. It seems that no single parameter can fully elucidate the entire process. A combination of time-domain, frequency-domain, and nonlinear indices may be necessary to explain HRV behavior in the growing body.

Cholesterol, triglycerides, HDL, and nitric oxide as determinants of resting heart rate variability in non-hospitalized mild post-COVID individuals: a cross-sectional study

BACKGROUND

The association between plasma lipids, nitric oxide (NO) and cardiovascular risk has been well documented in the literature, however, the association between these outcomes and heart rate variability (HRV) in COVID-19 remains incipient as there is no scientific evidence that has investigated this outcome.

OBJECTIVE

Investigate whether metabolic outcomes may be associated with cardiac autonomic behavior arising from short-term HRV variables in non-hospitalized mild post-COVID individuals.

METHODS

This is a cross-sectional study. Individuals of both sexes, aged ≥ 18 years, who tested positive for SARS-CoV-2 according to the RT-PCR test, without the need for hospitalization, were included. The HRV was collected in the supine position for at least 10 min for later analysis in the Kubios software. Metabolic outcomes [high density lipoprotein (HDL) (mg/dL), cholesterol (mg/dL), triglycerides (mg/dL) and NO (µmol/L)] were collected through a blood sample.

RESULTS

Seventy-three individuals were included (post-COVID = 32; control = 41). HRV was worse in the post-COVID group when compared to the control group (p < 0.05). Cholesterol, HDL, triglycerides and NO showed significant correlations with HRV indices. Regression models indicated that cholesterol and triglycerides, as well as NO, explain up to 30.3% of the variations in certain HRV indices, suggesting an impact of metabolic outcomes on autonomic modulation.

CONCLUSION

There is a relationship between plasma lipids, NO and HRV in non-hospitalized individuals with mild COVID-19. Metabolic outcomes are associated and explain between 16.6% and 30.30% of certain variables of resting HRV in post-COVID individuals.

CLINICAL TRIAL NUMBER

Not applicable.

Test-Retest Reliability and Concurrent Validity of Photoplethysmography Finger Sensor to Collect Measures of Heart Rate Variability

The purpose of the current study was to determine the test-retest reliability and concurrent validity of a photoplethysmography (PPG) finger sensor when collecting heart rate variability (HRV) metrics in reference to electrocardiography (ECG) and heart rate monitor (HRM) devices. Five minutes of R-R interval data were collected from 45 participants (23 females; age: 23.13 ± 4.45 yrs; body mass index: 25.39 ± 4.13 kg/m2) in the supine and seated positions in testing sessions 48 h apart. Moderate-to-excellent test-retest reliability of the HRV data collected from the PPG sensor was identified (ICC2,1 = 0.60-0.93). Additionally, similar standard errors of the mean, coefficient of variation, and minimal detectable change metrics were observed across all devices. Statistically significant (p < 0.05) differences were identified in the HRV data between the PPG sensor and ECG and HRM devices; however, these differences were interpreted as trivial-to-small (g = 0.00-0.59). Further, the PPG sensor tended to only overestimate HRV metrics by <0.5 ms and near perfect relationships (r = 0.91-1.00) and very large-to-near perfect agreement (CCC = 0.81-1.00) were identified between collection methods. The PPG sensor demonstrated adequate test-retest reliability and concurrent validity in both the supine and seated resting positions.

Relationship between heart rate variability and echocardiography indices of cardiac function in healthy individuals

PURPOSE

This study evaluated the relationship between HRV and echocardiography indices of cardiac function.

METHODS

Healthy individuals (N = 30) aged 33 ± 10 years old, underwent short-term resting HRV assessment and transthoracic echocardiography with speckle tracking analysis. Time domain - (i.e. R-R interval, root mean square of successive RR interval difference (RMSSD), standard deviation of normal RR intervals (SDNN) and frequency domain-measures of HRV (i.e. high-frequency power (HF), low-frequency power (LF), high-frequency normalised (HFnorm) and low-frequency normalised (LFnorm)). Echocardiography indices of cardiac function included; Left ventricular ejection fraction (LVEF), left- and right-ventricular global longitudinal strain (LV-GLS, and RV GLS), left atrial strain: left atrial reservoir (LAres), left atrial conduit (LAcon) and left atrial contraction (LACT).

RESULTS

The mean values for HRV time-domain measures were: R-R (991 ± 176 ms), SDNN (50.9 ± 21.5 ms), and RMSSD (46.8 ± 29.4 ms); and frequency-domain: LF (727 ± 606 ms2), HF (415 ± 35 ms2), LFnorm (56 ± 19.4) and HFnorm (36.5 ± 18.8). Mean values for indices of cardiac function were LVEF (59.9% ± 2.8%), LV-GLS (19.2% ± 1.4%), RV-GLS (21.7% ± 2.7%), LAres (36.8% ± 6.99%), LAcon (26.2% ± 6.95%) and LACT (12.3% ± 3.56%). There was a significant negative relationship between HF and LV-GLS (r = -0.47, p = 0.01) and RMSSD and LVEF (r = -0.39, p = 0.03) respectively.

CONCLUSION

Heart rate variability measures such as high frequency power and RMSSD are associated with left ventricle systolic function in healthy individuals.

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.

Impact of COVID-19 on heart rate variability in post-COVID individuals compared to a control group

This study investigated the impact of mild COVID-19 on HRV in groups stratified by time after infection and to compare to a healthy group of the same age without previous virus infection and without need of hospitalization. This is a cross-sectional study. We divided the sample into four groups: control group (CG) (n = 31), group 1 (G1): ≤6 weeks (n = 34), group 2 (G2): 2-6 months (n = 30), group 3 (G3): 7-12 months (n = 35) after infection. For HRV analysis, we used the indices of linear (time and frequency domain) and non-linear analysis. For comparisons between groups, ANOVA one way test or Kruskal-Wallis was used according to the data distribution. The effect size was calculated based on Cohen's d or η2. Simple and multiple linear regressions were performed to investigate the interaction between clinical outcomes and HRV parameters. A total of 130 individuals were included. Groups G1 and G2 showed less parasympathetic modulation when compared to CG (p < 0.05), while G3 showed an increase in parasympathetic modulation when compared to G1 (p < 0.05). Moderate to large effect sizes were found according to Cohen d or η2. The multiple linear regression models identified age and infection duration as significant predictors for RMSSD (adjusted R2 = 0.227) and SD1 (adjusted R2 = 0.242), while age was significant for SDNN (adjusted R2 = 0.213). BMI, hypertension, and dyslipidemia were non-significant in all models. For HF (n.u.), infection duration was consistently significant, with stress emerging as a predictor in Model 2 (adjusted R2 = 0.143). The recovery time since diagnosis and age influences recovery from HRV, suggesting a transient effect of the disease on the autonomic nervous system.

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.

Auxiliary identification of depression patients using interpretable machine learning models based on heart rate variability: a retrospective study

OBJECTIVE

Depression has emerged as a global public health concern with high incidence and disability rates, which are timely imperative to identify and intervene in clinical practice. The objective of this study was to explore the association between heart rate variability (HRV) and depression, with the aim of establishing and validating machine learning models for the auxiliary diagnosis of depression.

METHODS

The data of 465 outpatients from the Affiliated Hospital of Southwest Medical University were selected for the study. The study population was then randomly divided into training and test sets in a 7:3 ratio. Logistic regression (LR), support vector machine (SVM), random forest (RF) and eXtreme gradient boosting (XGBoost) algorithm models were used to construct risk prediction models in the training set, and the model performance was verified in the test set. The four models were evaluated by the area under the receiver operating characteristic curve (ROC), calibration curve and the decision curve analysis (DCA). Furthermore, we employed the SHapley Additive exPlanations (SHAP) method to illustrate the effects of the features attributed to the model.

RESULTS

There were 237 people in the depressed group and 228 in the non-depressed group. In the training set (n = 325) and test set (n = 140), the area under of the curve(AUC) values of the XGBoost model are 0.92 [95% confidence interval (CI) 0.888,0.95] and 0.82 (95% CI 0.754,0.892)] respectively, which are higher than the other three models. The XGBoost model has excellent predictive efficacy and clinical utility. The SHAP method was ranked according to the importance of the degree of influence on the model, with age, heart rate, Standard deviation of the NN intervals (SDNN), two nonlinear parameters of HRV and sex considered to be the top 6 predictors.

CONCLUSION

We provided a feasibility study of HRV as a potential biomarker for depression. The proposed model based on HRV provides clinicians with a quantitative auxiliary diagnostic tool, which is assist to improving the accuracy and efficiency of depression diagnosis, and can also be utilized for the monitoring and prevention of depression.

Vagus nerve stimulation for epilepsy: A narrative review of factors predictive of response

Vagus nerve stimulation (VNS) is an established therapy for drug-resistant epilepsy. However, there is a lack of reliable predictors of VNS response in clinical use. The identification of factors predictive of VNS response is important for patient selection and stratification as well as tailored stimulation programming. We conducted a narrative review of the existing literature on prognostic markers for VNS response using clinical, demographic, biochemical, and modality-specific information such as from electroencephalography (EEG), magnetoencephalography, and magnetic resonance imaging (MRI). No individual marker demonstrated sufficient predictive power for individual patients, although several have been suggested, with some promising initial findings. Combining markers from underresearched modalities such as T1-weighted MRI morphometrics and EEG may provide better strategies for treatment optimization.

L-Arginine Supplementation Did Not Impact the Rapid Recovery of Cardiovascular and Autonomic Function Following Exercise in Physically Active Healthy Males: A Triple-Blind Randomised Placebo-Controlled Crossover Trial

BACKGROUND AND AIMS

Post-exercise recovery strategies include massage, low-intensity active exercise, thermal contrast, hydration, and nutritional and herbal approaches. These strategies aim to accelerate recovery, enhance performance, and optimise the physical training process. L-arginine (L-ARG) is the physiological precursor of nitric oxide (NO), a crucial mediator of vasodilation and the inhibition of platelet aggregation. A previous study reported that L-ARG supplementation could significantly reduce the systolic blood pressure (SBP) and diastolic blood pressure (DBP). This study aimed to investigate the effects of L-ARG on autonomic and cardiovascular recovery immediately following submaximal exercise.

METHODS AND RESULTS

Thirty-two healthy individuals were subjected to two experimental protocols. The first protocol included 60 min of rest, a treadmill warm-up, and load increments until reaching 80% of their maximum HR. Before this protocol, the subjects consumed 3 g of starch (placebo protocol). The second protocol was identical, but the subjects consumed 3 g of L-ARG. Heart rate recovery (HRR), heart rate variability (HRV), and blood pressure (BP) responses were assessed. No significant differences in HRR were found (p = 0.944) regarding the root mean square of successive differences in the RR interval (RMSSD30) of HRV (p = 0.562) or in the BP responses (mean arterial pressure (MAP), p = 0.687; pulse pressure (PP), p = 0.929) between the protocols.

CONCLUSIONS

L-ARG supplementation did not significantly alter immediate post-exercise autonomic recovery in healthy males.

Cardiovascular responses as predictors of mortality in children with acute brain injury

BACKGROUND

Investigate the utility of cardiovascular responses such as heart rate (HR), blood pressure (BP), and heart rate variability (HRV) in the prognosis of children with acute acquired brain injury (ABI).

METHODS

Children under 18 years with severe acute acquired brain injury (ABI) who survived at least 12 h after PICU admission were included in a prospective observational cohort in a tertiary academic PICU. Physiological variables, neurological data, laboratory tests (chemistry and hematology), and medications were recorded within 12 h of admission. Linear and nonlinear HRV indices, CT scans, PICU scores, and survival rates were evaluated.

RESULTS

Seventy-two children, median age 10.7 years (IQR 4.1-13.6), were eligible for the study; 28 (38.9%) were diagnosed with brain death (BD). Tachycardia, SBP and MBP < 5th percentile, and MBP and DBP> 99th percentile were significantly associated with mortality. Poincaré SD1/SD2 was significantly associated with mortality after adjusting for age, sex and ongoing medication.

CONCLUSION

Tachycardia, systolic hypotension and median hypo and hypertension were associated to mortality in children with severe ABI. While further validation through larger, multicenter studies is necessary, the Poincaré SD1/SD2 ratio has shown promise as a prognostic tool for predicting mortality in children with severe ABI.

IMPACT STATEMENT

This study explores cardiovascular changes, including heart rate and blood pressure, and linear/nonlinear HRV measures using ECG at 1000 Hz, and compare them with other prognostic factors like brain tomography and PICU scores. Tachycardia, hypo/hypertension in the early hours after admission are linked to early mortality in children with severe traumatic and non-traumatic brain injury. Linear/non-linear measures of HRV were also related to survival. Higher HRV values indicating better survival chances. We identified Poincaré SD1/SD2 ratio as a promising tool for predicting mortality in children with severe ABI.

Inter- and intra-examiner reliability of short-term measurement of heart rate variability on rest in patients hospitalized with COVID-19

Measures reflecting cardiac sympathovagal activity, particularly those associated with heart rate variability (HRV), are widely recognized and utilized in both scientific and clinical contexts. This study aimed to assess the inter- and intra-examiner reliability of short-term HRV parameters in patients hospitalized with coronavirus disease 2019 (COVID-19). A total of 103 patients (both sexes) diagnosed with COVID-19 were included in the study. HRV was analyzed using both linear and nonlinear methods. Reliability was evaluated through intraclass correlation coefficient (ICC2.1), minimum detectable change (MDC), standard error of measurement (SEM), and coefficient of variation (CV). According to Fleiss' criteria, excellent reliability was demonstrated, with ICC values ranging from 0.970 to 0.999 for Examiner 1, and from 0.956 to 0.999, for Examiner 2. In the inter-examiner analysis, the ICCs of HRV parameters ranged from 0.972 to 0.999. SEM values for intra-examiner reliability for Examiner 1 ranged from 0.02 to 5.64, with MDC values from 0.05 to 15.64, and CV (%) from 0.28 to 8.04. For Examiner 2, SEM values ranged from 0.02 to 8.18, MDC values from 0.05 to 22.68, and CV (%) from 0.24 to 8.14. For inter-examiner reliability, SEM values ranged from 0.02 to 6.17, MDC from 0.06 to 17.11, and CV (%) from 0.34 to 9.81. Across all analyses, CVs for HRV parameters remained below 10%. Considering different time points and different examiners, short-term resting HRV measurements in patients hospitalized with COVID-19, as evaluated using a portable heart rate device, exhibit high reliability.

Treating heart failure by targeting the vagus nerve

Increased sympathetic and reduced parasympathetic nerve activity is associated with disease progression and poor outcomes in patients with chronic heart failure. The demonstration that markers of autonomic imbalance and vagal dysfunction, such as reduced heart rate variability and baroreflex sensitivity, hold prognostic value in patients with chronic heart failure despite modern therapies encourages the research for neuromodulation strategies targeting the vagus nerve. However, the approaches tested so far have yielded inconclusive results. This review aims to summarize the current knowledge about the role of the parasympathetic nervous system in chronic heart failure, describing the pathophysiological background, the methods of assessment, and the rationale, limits, and future perspectives of parasympathetic stimulation either by drugs or bioelectronic devices.

Heart rate variability in chronic ischemic stroke: analysis during the sleep-wake cycle

BACKGROUND

 Alterations of the autonomic nervous system (ANS) in the chronic stage of ischemic stroke (IS) are not well understood. Heart rate variability (HRV) provides a noninvasive approach to assess autonomic function.

OBJECTIVE

 To compare the HRV parameters during the sleep-wake cycle between patients with IS in the chronic stage and healthy subjects.

METHODS

 We conducted a retrospective transversal study based on clinical records and 24-hour electrocardiogram (EKG) monitoring registries of 179 patients with a confirmed IS diagnosis and 184 age- and sex-matched healthy subjects. Circadian variation was calculated according to the variation of the total autonomic activity (VTAI) and the parasympathetic activity (VPAI) indexes. Comparisons were performed using nonparametric tests. Multivariable analyses were performed with canonical discriminant analysis (CDA) and a three-way analysis of variance (ANOVA). Statistical significance was established with a confidence level of 95%.

RESULTS

 During waking hours, the healthy group exhibited higher variability in the time domain and frequency domain parameters: standard deviation of NN intervals (SDNN, p < 0.001) and of the average NN intervals (SDANN, p < 0.001), as well as low-frequency (LF) band (p < 0.001). During sleep, the difference was higher in the high-frequency (HF) band (p < 0.001), and lower in the low-/high-frequency ratio (LF/HF, p < 0.001). Both VPAI and VTAI showed less significant difference in IS patients (p < 0.001).

CONCLUSION

 There was diminished heart vagal activity among IS patients, as measured through HRV. During sleep, this is likely caused by an imbalance in the sympathetic and parasympathetic systems shifting through the sleep phases. These imbalances could persist over time in patients with IS, lasting months after the initial injury.

Emotional Awareness Is Correlated With Ambulatory Heart Rate Variability: A Replication and Extension

OBJECTIVE

In healthy volunteers, a positive association has previously been observed between emotional awareness (EA), the ability to identify and describe emotional experiences in oneself and others, and resting heart rate variability (HRV), which is dominated by vagus nerve activity. The current study aimed to investigate the EA-HRV association across multiple assessments in a "real-world" ambulatory context in patients with long QT syndrome (LQTS) who are at genetic risk for sudden cardiac death.

METHODS

Participants (157 LQTS patients; Mean Age = 35.1, SD Age = 10.4; 115 women) completed the levels of emotional awareness scale (LEAS) on one occasion, which served as our measure of EA. In an ecological momentary assessment study involving 10 assessments per day over 3 days, multiple 5-minute ECG assessments (mean = 24.6, SD = 5.1) were obtained in each patient using a Holter monitor, from which high-frequency HRV (HF-HRV) was computed on each occasion.

RESULTS

There was a significant positive association between LEAS scores and HF-HRV controlling for biobehavioral covariates. We also detected a similar inverse relation between EA and mean heart rate.

CONCLUSION

These findings suggest that, in patients with a well-defined genetic risk for ventricular arrhythmia and sudden death, the ability to experience emotions in a complex and differentiated way covaries with greater parasympathetic influences on the heart. These findings are consistent with the overlapping neural substrates of EA and HRV and their common contribution to adaptive emotional responding, consistent with the Neurovisceral Integration Model.

Autonomic reactivity to mental stress is associated with cardiovascular mortality

Aims

The mechanisms linking acute psychological stress to cardiovascular disease (CVD) mortality are incompletely understood. We studied the relationship of electrocardiographic measures of autonomic dysfunction during acute mental stress provocation and CVD death.

Methods and results

In a pooled cohort of 765 participants with stable CVD from two related studies, we collected Holter data during standardized laboratory-based mental stress testing with a speech task and followed them for events. We assessed autonomic function using low-frequency (LF) heart rate variability (HRV) in 5-min intervals before, during, and after stress induction, and specifically examined changes from rest to stress. We employed cause-specific survival models to examine its association with CVD and all-cause mortality, controlling for demographic and CVD risk factors. The mean (SD) age was 58 (10) years, 35% were women, and 44% self-identified as Black. After a median follow-up of 5.6 years, 37 (5%) died from CVD causes. A stress-induced LF HRV decrease (67% of sample), vs. increase, was associated with a hazard ratio (HR) of 3.48 (95% confidence interval-3.25, 3.73) for CVD mortality. Low rest LF HRV (bottom quartile) was also independently associated with CVD mortality, HR = 1.75 (1.58, 1.94), vs. normal rest LF HRV (upper three quartiles). The combination of stress-induced LF HRV decrease and low rest LF HRV was associated with HR = 5.73 (5.33, 6.15) vs. the normal stress/rest LF HRV reference. We found similar results with HF HRV.

Conclusion

Stress-induced LF HRV decrease and low rest LF HRV are both independently and additively associated with a higher CVD mortality risk. Additional research is needed to assess whether targeting autonomic dysfunction may improve CVD outcomes.

Impact of applying different levels of threshold-based artifact correction on the processing of heart rate variability data in individuals with temporomandibular disorder

Although heart rate variability (HRV) is a valid method to evaluate the behavior of the autonomic nervous system in individuals with temporomandibular disorder (TMD), the measurement can easily be biased by factors involving the analysis methodology, such as the removal of artifacts. Therefore, the objective of this investigation is to evaluate the impact of using different levels of threshold-based artifact correction to process HRV data in individuals with TMD. This cross-sectional observational study. Adults aged 18 to 55 years old with a diagnosis of myogenic TMD, score ≥ 50 on the Fonseca Anamnestic Index (FAI) and pain ≥ 3 on the Numerical Pain Scale (NPS) participated. The HRV was registered in the supine position (short-term) using a Polar S810i. Kubios software was used for HRV analysis using all filters. One-way ANOVA with Tukey-Kramer post-hoc was used to test the differences in HRV using the different Kubios Software artifact correction filters. The effect size was calculated based on the Cohen d. The very strong filter was statistically different (p < 0.05) compared to the no filter in all overview and time domain variables. In the frequency domain, the variables VLF, LF, HF and Total Power showed statistical differences (p < 0.05) when using the very strong filter. The same occurred with the variables SD1, SD2 and DFA α2 of the non-linear analysis (p < 0.05). The most restrictive filter of the Kubios software (very strong) significantly impacts the quantification of HRV parameters in individuals with TMD.

Heart Rate Variability and Interoception in Periodic Limb Movements in Sleep: Interference with Psychiatric Disorders?

Periodic limb movements in sleep (PLMS) are a prevalent disorder characterized by rhythmic, involuntary movements of the lower limbs, such as dorsiflexion of the ankle and extension of the big toe, occurring in periodic intervals during sleep. These movements are often linked to disrupted autonomic nervous system (ANS) activity and altered interoception. Interoception involves perceiving internal bodily states, like heartbeat, breathing, hunger, and temperature, and plays a crucial role in maintaining homeostasis and the mind-body connection. This review explores the complex relationships between PLMS, heart rate variability (HRV), ANS dysregulation, and their impact on psychiatric disorders. By synthesizing the existing literature, it provides insights into how ANS dysregulation and altered interoceptive processes, alongside PLMS, contribute to psychiatric conditions. The review highlights the potential for integrated diagnostic and therapeutic approaches and presents a cause-and-effect model illustrating the mutual influence of psychiatric disorders, ANS dysregulation, PLMS, and interoception.

Music therapy with adult burn patients in the intensive care unit: short-term analysis of electrophysiological signals during music-assisted relaxation

Burn patients often face elevated pain, anxiety, and depression levels. Music therapy adds to integrative care in burn patients, but research including electrophysiological measures is limited. This study reports electrophysiological signals analysis during Music-Assisted Relaxation (MAR) with burn patients in the Intensive Care Unit (ICU). This study is a sub-analysis of an ongoing trial of music therapy with burn patients in the ICU. Electroencephalogram (EEG), electrocardiogram (ECG), and electromyogram (EMG) were recorded during MAR with nine burn patients. Additionally, background pain levels (VAS) and anxiety and depression levels (HADS) were assessed. EEG oscillation power showed statistically significant changes in the delta (p < 0.05), theta (p = 0.01), beta (p < 0.05), and alpha (p = 0.05) bands during music therapy. Heart rate variability tachograms high-frequencies increased (p = 0.014), and low-frequencies decreased (p = 0.046). Facial EMG mean frequency decreased (p = 0.01). VAS and HADS scores decreased - 0.76 (p = 0.4) and - 3.375 points (p = 0.37) respectively. Our results indicate parasympathetic system activity, attention shifts, reduced muscle tone, and a relaxed state of mind during MAR. This hints at potential mechanisms of music therapy but needs to be confirmed in larger studies. Electrophysiological changes during music therapy highlight its clinical relevance as a complementary treatment for ICU burn patients.Trial registration: Clinicaltrials.gov (NCT04571255). Registered September 24th, 2020. https//classic.clinicaltrials.gov/ct2/show/NCT04571255.

Lifelong longitudinal assessment of the contribution of multi-fractal fluctuations to heart rate and heart rate variability in aging mice: role of the sinoatrial node and autonomic nervous system

Aging is a major risk factor for sinoatrial node (SAN) dysfunction, which can impair heart rate (HR) control and heart rate variability (HRV). HR and HRV are determined by intrinsic SAN function and its regulation by the autonomic nervous system (ANS). The purpose of this study was to use multi-scale multi-fractal detrended fluctuation analysis (MSMFDFA; a complexity-based approach to analyze multi-fractal dynamics) to longitudinally assess changes in multi-fractal HRV properties and SAN function in ECG time series recorded repeatedly across the full adult lifespan in mice. ECGs were recorded in anesthetized mice in baseline conditions and after autonomic nervous system blockade every three months beginning at 6 months of age until the end of life. MSMFDFA was used to assess HRV and SAN function every three months between 6 and 27 months of age. Intrinsic HR (i.e. HR during ANS blockade) remained relatively stable until 15 months of age, and then progressively declined until study endpoint at 27 months of age. MSMFDFA revealed sudden and rapid changes in multi-fractal properties of the ECG RR interval time series in aging mice. In particular, multi-fractal spectrum width (MFSW, a measure of multi-fractality) was relatively stable between 6 months and 15 months of age and then progressively increased at 27 months of age. These changes in MFSW were evident in baseline conditions and during ANS blockade. Thus, intrinsic SAN function declines progressively during aging and is manifested by age-associated changes in multi-fractal HRV across the lifespan in mice, which can be accurately quantified by MSMFDFA.

Fructose-1,6-bisphosphate reverses hypotensive effect caused by L-kynurenine in Wistar male rats

Hypotension is one of the main characteristics of the systemic inflammation, basically caused by endothelial dysfunction. Studies have shown that the amino acid L-kynurenine (KYN) causes vasodilation in mammals, leading to hypotensive shock. In hypotensive shock, when activated by the KYN, the voltage-gated potassium channel encoded by the family KCNQ (Kv7) gene can cause vasodilation. Fructose-1,6-bisphosphate (FBP) it is being considered in studies an anti-inflammatory, antioxidant, immunomodulator, and a modulator of some ion channels (Ca2+, Na+, and K+). We analyzed the effects of KYN and FBP on mean blood pressure (MBP), systolic and diastolic (DBP) blood pressure, and heart rate variability (HRV) in Wistar rats. Results demonstrated that the administration of KYN significant decreased MBP, DBP, and increased HRV. Importantly, the FBP treatment reversed the KYN effects on MBP, DBP, and HRV. Molecular Docking Simulations suggested that KYN and FBP present a very close estimated free energy of binding and the same position into structure of KCNQ4. Our results did demonstrate that FBP blunted the decrease in BP, provoked by KYN. Results raise new hypotheses for future and studies in the treatment of hypotension resulting from inflammation.

Remote fitness assessment in younger and middle-aged to older adults: a comparison between laboratory- and videoconference-based assessment of selected measures of physical and cognitive fitness

BACKGROUND

Digital technologies can play an important role in improving the limited accessibility of healthcare services in rural regions (e.g., via remote assessment). However, whether remote fitness assessments (RFA) of selected physical and cognitive fitness parameters are feasible both in younger and older persons and whether they can reproduce laboratory tests needs yet to be established. Thus, this study aimed to address this knowledge gap by investigating the feasibility, and reproducibility of RFA in younger and middle-aged to older adults (MOA).

METHODS

A total of 31 younger adults and 32 MOAs participated in this study. At an interval of seven days, laboratory-based and remote assessments (via videoconferencing software) were conducted which included the quantification of the following parameters: (i) measurement of heart rate variability [HRV]; followed by (ii) cognitive testing to examine the level of attention, executive functions (oral Trail Making Test [A and B]), working memory, verbal short-term memory (digit span memory test and word list test (immediate recall)) and episodic memory (word list test (delayed recall)); followed by (iii) physical fitness assessments including performance tests of balance (balance test), functional strength ability of the lower limbs (5-time-sit-to-stand-test) and endurance capacity (3-min step test). Parameters of absolute and relative reliability were determined to assess the reproducibility of the laboratory-based and remote assessments.

RESULTS

The selected physical and cognitive fitness parameters showed moderate to excellent relative reliability (intraclass correlation coefficient [ICC] = 0.52-0.95). The parameters of absolute reliability (Bland-Altman plot and standard error of measurement [SEM]) provide evidence for good reproducibility of HRV parameters and measures of physical fitness, whereas measures of cognitive fitness showed moderate to good reproducibility. On a descriptive level, the absolute and relative reliability of the selected measures of physical and cognitive fitness did not vary as a function of participants' age.

CONCLUSION

Our results suggest that RFA of selected measures of physical and cognitive fitness is feasible and reproduces corresponding laboratory results to a moderate to excellent level in both younger adults and MOA. Data showed that the reproducibility of laboratory-based and remote assessments is not influenced by the age of the participants. These findings support the use of digital technologies to improve the accessibility of healthcare services (e.g., in remote areas). However, as the reproducibility varies considerably across the different parameters, further studies are needed to evaluate the effects of an optimised standardisation of the remote assessments and confounding factors.

Robust and time-resolved estimation of cardiac sympathetic and parasympathetic indices

The time-resolved analysis of heart rate (HR) and heart rate variability (HRV) is crucial for the evaluation of the dynamic changes of autonomic activity under different clinical and behavioral conditions. Standard HRV analysis is performed in the frequency domain because the sympathetic activations tend to increase low-frequency HRV oscillations, while the parasympathetic ones increase high-frequency HRV oscillations. However, a strict separation of HRV in frequency bands may cause biased estimations, especially in the low frequency range. To overcome this limitation, we propose a robust estimator that combines HR and HRV dynamics, based on the correlation of the Poincaré plot descriptors of interbeat intervals from the electrocardiogram. To validate our method, we used electrocardiograms gathered from open databases where standardized paradigms were applied to elicit changes in autonomic activity. Our proposal outperforms the standard spectral approach for the estimation of low- and high-frequency fluctuations in HRV, and its performance is comparable to newer methods. Our method constitutes a valuable, robust, time-resolved, and cost-effective tool for a better understanding of autonomic activity through HR and HRV in healthy state and potentially for pathological conditions.

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.

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.

Rationale and Design of PURE: A Randomized Controlled Trial to Evaluate Peritoneal Ultrafiltration with PolyCore™ in Refractory Congestive Heart Failure

INTRODUCTION

Peritoneal ultrafiltration (PUF) has been proposed as an additional therapeutic option for refractory congestive heart failure (RCHF) patients. Despite promising observational studies and/or case report results, limited clinical trial data exist, and so far, PUF solutions remain only indicated for chronic kidney diseases. In this article, we described a multicenter, randomized, controlled, unblinded, adaptive design clinical trial, about to start, investigating the effects of PolyCore™, an innovative PUF solution, in the treatment of RCHF patients.

METHODS

The Peritoneal Ultrafiltration in Cardiorenal Syndrome (PURE) study is a phase II, multicenter, randomized, controlled, unblinded, adaptive design clinical trial that aims to evaluate the safety and efficacy of PUF, using PolyCore™ as the investigational solution, in the treatment of RCHF patients who present with prominent right ventricular failure due to afterload mismatch, functional tricuspid regurgitation and enlarged cava vein consequent to intravascular fluid overload. Approximately 84 patients will be randomized 1:1 either to continue with their prescribed guideline-directed medical therapy or to add the PUF treatment on top of it. The primary objective is to evaluate if PUF treatment has an impact on the composite endpoint of the patient's mortality or worsening of the patient's condition such as hospitalization for cardiovascular causes, increasing the initial daily dose of loop diuretic or worsening of renal function. Statistical analysis for the primary endpoint will be standard survival analysis to estimate the failure rate at month 7 for each group via Kaplan-Meier curves. Sensitivity analysis and various secondary analyses, including a multiple events analysis, will be conducted to evaluate the robustness of the primary endpoint results. Safety will be evaluated for up to 12 months.

CONCLUSION

The PURE study was designed to evaluate the safety and efficacy of peritoneal ultrafiltration with PolyCore™ on top of guideline-directed medical therapy in patients with RCHF, assuming a combined clinical endpoint of mortality or worsening patients' condition. If successful, the treatment should allow for an improvement of the RCHF symptoms, decreasing hospitalization rate of patients.

Heart rate variability and mortality in critically ill COVID-19 pneumonia patients

Background

Heart rate variability (HRV) has prognostic value for predicting mortality in both cardiovascular and sepsis patients. Decreased HRV has been associated with increased mortality and morbidity. However, the prognostic significance of HRV in critically ill patients COVID-19 pneumonia still remains unknown. The current study aimed to (1) evaluate prognostic utility of HRV parameters on outcomes in patients with severe COVID-19 pneumonia and (2) assess the correlation between HRV parameters and inflammatory markers.

Methods

Consecutive critically ill patients with COVID-19 pneumonia admitted to a tertiary referral intensive care unit from October 2021 to June 2022 in Bangkok, Thailand were enrolled. HRV parameters over the 24 h following intensive care unit admission were recorded using telemetry and analyzed using the Holter program (Philips Holter 2010 Plus/1810 Series). Receiver-operating characteristic (ROC) curve analysis was used to determine optimum threshold cutoffs of various HRV parameters. Formal comparisons of in-hospital mortality between patients with and without a decrease in HRV were performed using Cox regression after adjusting for potential confounders.

Results

A total of 65 patients were enrolled in the study. Patients were classified into two groups: survivors (n = 44, 68 %) and non-survivors (n = 21, 32 %). The standard deviation of normal-to-normal intervals (SDNN) was significantly lower in non-survivors than in survivors (70.30 vs. 105.95; p = 0.03). The SDNN predicted in-hospital mortality with an area under the ROC curve of 0.67 (95 % CI 0.55-0.79). At a cutoff of 70 ms, the SDNN showed a sensitivity and specificity of 0.48 and 0.86. The low SDNN group (<70 ms) demonstrated higher median ferritin, IL-6, and hs-C-reactive protein levels than did the normal SDNN group, although such differences did not reach statistical significance (1139.0 vs. 508.4; p = 0.137 and 91.2 vs. 64.4; p = 0.352, respectively). After adjusting for potential confounders in the multivariable model, the adjusted hazard ratio for in-hospital mortality in those with SDNN <70 ms was 3.70 (95 % CI 1.34-10.24).

Conclusion

A decrease in SDNN, a commonly used HRV parameter, was associated with mortality and inflammatory biomarkers in critically ill patients with COVID-19 pneumonia.

Autonomic Nervous System and Sarcopenia in Elderly Patients: Insights from Long-Term Heart Rate Variability Monitoring in a Hospital Setting

Background

Emerging evidence suggests a link between muscle health and the autonomic nervous system, but research is scarce. This study examines the connection between long-term heart rate variability (HRV) measured autonomic function and sarcopenia in the elderly, focusing on muscle mass and strength.

Patients and Methods

This retrospective cross-sectional study comprised 132 elderly hospitalized patients. Sarcopenia was defined according to the European Working Group on Sarcopenia in Older People (EWGSOP2) criteria, involving reduced muscle mass and strength. HRV was assessed using standard deviation of NN intervals (SDNN), with values below 100 milliseconds indicating reduced HRV. Multivariate logistic regression and Pearson's correlation analyses were conducted to explore the associations between sarcopenia, muscle metrics, and HRV parameters.

Results

Among elderly hospitalized patients, 45.45% had reduced HRV, with sarcopenia patients showing a fivefold higher risk (OR: 5.042; p = 0.034). Grip strength and SARC-CalF scores were independent factors associated with reduced HRV. Moderate correlations were noted between grip strength and HRV indices, particularly with SDNN (r = 0.393, p = 0.001) and the triangular index (r = 0.385, p < 0.001), while a weaker correlation was found with very low frequency power (VLF) (r = 0.283, p = 0.006). No significant correlations were identified between HRV and muscle mass. Regression analyses revealed significant independent associations between HRV parameters and the decline in muscle strength and the onset of sarcopenia.

Conclusion

Reduced HRV is closely linked to sarcopenia and diminished muscle strength in the elderly, with the triangular index and SDNN as key indicators, highlighting HRV's potential in muscle health assessment.

Update: factors influencing heart rate variability-a narrative review

Objective

Heart rate variability (HRV) is an important non-invasive marker for the assessment of an organism's autonomic physiological regulatory pathways. Lower HRV has been shown to correlate with increased mortality. HRV is influenced by various factors or diseases. The aim of this narrative review is to describe the current state of knowledge on factors influencing HRV and their significance for interpretation.

Methods

The narrative review only included reviews, meta-analyses, and cohort studies which were published until 2021. HRV confounders were grouped into four categories (non-influenceable physiological factors, diseases, influenceable lifestyle factors and external factors).

Results

The review found that HRV was decreased not only in non-influenceable physiological factors (e.g., age, gender, ethnicity) but also in connection with various number of acute and chronic diseases (e.g., psychiatric diseases, myocardial infarction, heart failure), influenceable lifestyle factors (e.g., alcohol abuse, overweight, physical activity), and external factors (e.g., heat, noise, shift work, harmful- and hazardous substances).

Conclusion

In order to improve the quality of HRV studies and to ensure accurate interpretation, it is recommended that confounders be taken into account in future diagnostic measurements or measurements in the workplace (e.g., as part of health promotion measures) in order to counteract data bias.

Increased heart rate fragmentation in those with Williams-Beuren syndrome suggests nonautonomic mechanistic contributors to sudden death risk

Williams-Beuren syndrome (WBS) is a rare genetic condition caused by a chromosomal microdeletion at 7q11.23. It is a multisystem disorder characterized by distinct facies, intellectual disability, and supravalvar aortic stenosis (SVAS). Those with WBS are at increased risk of sudden death, but mechanisms underlying this remain poorly understood. We recently demonstrated autonomic abnormalities in those with WBS that are associated with increased susceptibility to arrhythmia and sudden cardiac death (SCD). A recently introduced method for heart rate variability (HRV) analysis called "heart rate fragmentation" (HRF) correlates with adverse cardiovascular events (CVEs) and death in studies where heart rate variability (HRV) failed to identify high-risk subjects. Some argue that HRF quantifies nonautonomic cardiovascular modulators. We, therefore, sought to apply HRF analysis to a WBS cohort to determine 1) if those with WBS show differences in HRF compared with healthy controls and 2) if HRF helps characterize HRV abnormalities in those with WBS. Similar to studies of those with coronary artery disease (CAD) and atherosclerosis, we found significantly higher HRF (4 out of 7 metrics) in those with WBS compared with healthy controls. Multivariable analyses showed a weak-to-moderate association between HRF and HRV, suggesting that HRF may reflect HRV characteristics not fully captured by traditional HRV metrics (autonomic markers). We also introduce a new metric inspired by HRF methodology, significant acute rate drop (SARD), which may detect vagal activity more directly. HRF and SARD may improve on traditional HRV measures to identify those at greatest risk for SCD both in those with WBS and in other populations.NEW & NOTEWORTHY This work is the first to apply heart rate fragmentation analyses to individuals with Williams syndrome and posits that the heart rate fragmentation parameter W3 may enable detection and investigation of phenomena underlying the proarrhythmic short-long-short RR interval sequences paradigm known to precede ventricular fibrillation and ventricular tachycardia. It also forwards a novel method for quantifying sinus arrhythmia and sinus pauses that likely correlate with parasympathetic activity.

Sepsis-induced inflammatory demyelination in medullary visceral zone and cholinergic anti-inflammatory pathway: Insights from a Rat's model study

Background

Our previous studies have demonstrated that the activated Cholinergic Anti-inflammatory Pathway (CAP) effectively suppresses systemic inflammation and immunity in early sepsis. Some parameters of Heart Rate Variability (HRV) could be used to reflect the regulatory activity of CAP. However, in the early stages of severe sepsis of some patients, the inflammatory storm can still result in multiple organs dysfunction and even death, suggesting they lose CAP's modulation ability. Since CAP is part of the vagus nerve and is directly innervated by the Medullary Visceral Zone (MVZ), we can reasonably concluded that pathological changes induced by MVZ's neuroinflammation should be responsible for CAP's dysfunction in modulating systemic inflammation in early sepsis.

Methods

We conducted two independent septic experiments, the sepsis model rats were prepared by cecum ligation and puncture (CLP) method. In the first experiment, A total of 64 adult male Sprague-Dawley rats were included. Under the condition of sepsis and CAP's pharmacological activation or blockade, we investigated the MVZ's pathological changes, the functional state of key neurons including catecholaminergic and cholinergic neurons, key genes' expression such as Oligodendrocyte Transcription Factor 2 (Olig-2) mRNA, glial fibrillary acidic protein (GFAP) mRNA, and matrix metalloprotein (MMP) -9 mRNA, and CAP's activities reflected by HRV. The second experiment involved in 56 rats, through central anti-inflammation by feeding with 10 mg/ml minocycline sucrose solution as the only water source, or right vagus transection excepting for central anti-inflammation as a mean of the CAP's functional cancel, we confirmed that the neuroinflammation in MVZ affected systemic inflammation through CAP in sepsis.

Results

In the first experiment, cholinergic and catecholaminergic neurons showed significant apoptosis with reduced expressions of TH, but the expression of CHAT remained relatively unaffected in MVZ in sepsis. HRV parameters representing the tone of the vagus nerve, such as SDNN, RMSSD, HF, SD1, and SD2, did not show significant differences among the three Septic Groups, although they all decreased significantly compared to the Control Group. The expressions of GFAP mRNA and MMP-9 mRNA were up-regulated, while the expression of Olig-2 mRNA was down-regulated in the Septic Groups. Intervention of CAP had a significant effect on cholinergic and catecholaminergic neurons' apoptosis, as well as the expressions of TH/CHAT and these key genes, but had little effect on HRV in sepsis. In the second experiment, the levels of TNF-α, IL-6, in serum and MVZ were significantly increased in sepsis. Central anti-inflammatory treatment reversed these changes. However, right vagotomy abolished the central anti-inflammatory effect.

Conclusions

Our study uncovered that MVZ's neuroinflammation may play a crucial role in the uncontrolled systemic inflammation through inflammatory demyelination in MVZ, which disrupts CAP's modulation on the systemic inflammation in early sepsis.

Can heart rate variability demonstrate progression of mindfulness through two-week repeated practice?

Mindfulness could benefit on mental and physical health. Through repeated practice, progression of mindfulness could be found. Except for self-report questionnaires, heart rate variability (HRV) is a potential biomarker to demonstrate the effects of mindfulness. However, few studies focus on the changes in HRV which may vary through repeated practice. This study aims to explore whether HRV could demonstrate progression of mindfulness through repeated practice. 20 experienced practitioners and 26 novices were enrolled to practice two-week mindfulness and completed the Five Facet Mindfulness Questionnaire pre and post the training. ECG signals were collected by holter monitors, covering baseline to training and 9 HRV metrics were extracted. The results indicate that the experienced group showed significantly increased parasympathetic activity during mindfulness training and the effects were stable through repeated practice, while the novice group showed high cognitive load, with inconspicuous but probably progressive effects. The findings indicate that HRV could demonstrate progression of mindfulness through repeated practice, suggesting the possibility of assessing mindfulness based on HRV.

Measures of the coupling between fluctuating brain network organization and heartbeat dynamics

In recent years, there has been an increasing interest in studying brain-heart interactions. Methodological advancements have been proposed to investigate how the brain and the heart communicate, leading to new insights into some neural functions. However, most frameworks look at the interaction of only one brain region with heartbeat dynamics, overlooking that the brain has functional networks that change dynamically in response to internal and external demands. We propose a new framework for assessing the functional interplay between cortical networks and cardiac dynamics from noninvasive electrophysiological recordings. We focused on fluctuating network metrics obtained from connectivity matrices of EEG data. Specifically, we quantified the coupling between cardiac sympathetic-vagal activity and brain network metrics of clustering, efficiency, assortativity, and modularity. We validate our proposal using open-source datasets: one that involves emotion elicitation in healthy individuals, and another with resting-state data from patients with Parkinson's disease. Our results suggest that the connection between cortical network segregation and cardiac dynamics may offer valuable insights into the affective state of healthy participants, and alterations in the network physiology of Parkinson's disease. By considering multiple network properties, this framework may offer a more comprehensive understanding of brain-heart interactions. Our findings hold promise in the development of biomarkers for diagnostic and cognitive/motor function evaluation.

Benefits From Different Modes of Slow and Deep Breathing on Vagal Modulation

Slow and deep breathing (SDB) is a relaxation technique that can increase vagal activity. Respiratory sinus arrhythmia (RSA) serves as an index of vagal function usually quantified by the high-frequency power of heart rate variability (HRV). However, the low breathing rate during SDB results in deviations when estimating RSA by HRV. Besides, the impact of the inspiration-expiration (I: E) ratio and guidelines ways (fixed breathing rate or intelligent guidance) on SDB is not yet clear. In our study, 30 healthy people (mean age = 26.5 years, 17 females) participated in three SDB modes, including 6 breaths per minute (bpm) with an I:E ratio of 1:1/ 1:2, and intelligent guidance mode (I:E ratio of 1:2 with guiding to gradually lower breathing rate to 6 bpm). Parameters derived from HRV, multimodal coupling analysis (MMCA), Poincaré plot, and detrended fluctuation analysis were introduced to examine the effects of SDB exercises. Besides, multiple machine learning methods were applied to classify breathing patterns (spontaneous breathing vs. SDB) after feature selection by max-relevance and min-redundancy. All vagal-activity markers, especially MMCA-derived RSA, statistically increased during SDB. Among all SDB modes, breathing at 6 bpm with a 1:1 I:E ratio activated the vagal function the most statistically, while the intelligent guidance mode had more indicators that still significantly increased after training, including SDRR and MMCA-derived RSA, etc. About the classification of breathing patterns, the Naive Bayes classifier has the highest accuracy (92.2%) with input features including LFn, CPercent, pNN50, [Formula: see text], SDRatio, [Formula: see text], and LF. Our study proposed a system that can be applied to medical devices for automatic SDB identification and real-time feedback on the training effect. We demonstrated that breathing at 6 bpm with an I:E ratio of 1:1 performed best during the training phase, while intelligent guidance mode had a more long-lasting effect.

Stress-Induced Autonomic Dysfunction is Associated With Mental Stress-Induced Myocardial Ischemia in Patients With Coronary Artery Disease

BACKGROUND

Mental stress-induced myocardial ischemia (MSIMI) is associated with adverse cardiovascular outcomes in individuals with coronary artery disease, but the mechanisms underlying this phenomenon are unknown. We examined the relationship between stress-induced autonomic dysfunction, measured by low heart rate variability (HRV) in response to stress, and MSIMI in patients with stable coronary artery disease. We hypothesized that stress-induced autonomic dysfunction is associated with higher odds of MSIMI.

METHODS

In 735 participants with stable coronary artery disease, we measured high- and low-frequency HRV in 5-minute intervals before and during a standardized laboratory-based speech stressor using Holter monitoring. HRV at rest and stress were categorized into low HRV (first quartile) versus high HRV (second to fourth quartiles); the low category was used as an indicator of autonomic dysfunction. Multivariable logistic regression models were used to examine the association of autonomic dysfunction with MSIMI.

RESULTS

The mean age was 58 (SD, ±10) years, 35% were women, 44% were Black participants, and 16% developed MSIMI. Compared with high HRV during stress, low HRV during stress (both high and low frequencies) was associated with higher odds of MSIMI after adjusting for demographic and clinical factors (odds ratio for high-frequency HRV, 2.1 [95% CI, 1.3-3.3]; odds ratio for low-frequency HRV, 2.1 [95% CI, 1.3-3.3]). Low-frequency HRV at rest was also associated with MSIMI but with slightly reduced effect estimates.

CONCLUSIONS

In individuals with coronary artery disease, mental stress-induced autonomic dysfunction may be a mechanism implicated in the causal pathway of MSIMI.