Current clinical applications of heart rate variability

Non-Contact Vision-Based Techniques of Vital Sign Monitoring: Systematic Review

The development of non-contact techniques for monitoring human vital signs has significant potential to improve patient care in diverse settings. By facilitating easier and more convenient monitoring, these techniques can prevent serious health issues and improve patient outcomes, especially for those unable or unwilling to travel to traditional healthcare environments. This systematic review examines recent advancements in non-contact vital sign monitoring techniques, evaluating publicly available datasets and signal preprocessing methods. Additionally, we identified potential future research directions in this rapidly evolving field.

How to properly evaluate cardiac vagal tone in oncology studies: a state-of-the-art review

Heart rate variability (HRV) analysis provides an assessment of cardiac vagal tone and consequently global cardiac health as well as systemic condition. In systemic diseases such as cancer and during treatments that affect the whole body, like chemotherapy, the vagus nerve activity is low and deregulated. Some studies focus on using HRV to predict mortality in oncology. However, in cancer patients, systemic alterations substantially increase artifacts during HRV measurement, especially atrial ectopic beats. Moreover, HRV may be altered by various factors (duration and time of measurement, breathing, drugs, and other confounding factors) that alter each metric in different ways. The Standard Deviation of all Normal to Normal intervals (SDNN) is the most commonly used metric to evaluate HRV in oncology, but it does not appear to be specific to the cardiac vagal tone. Thus, cardiac vagal activity diagnosis and vital prognosis of cancer patients can be biased. Our review presents the main HRV metrics that can be currently used in oncology studies and their links with vagus nerve and cancer. We present the influence of external factors and the required duration and time of measurement. Considering all these parameters, this review proposes seven key points for an assessment of HRV and cardiac vagal tone in patients with cancer.

Assessment of autonomic nervous system dysfunction associated with peripheral neuropathies in the context of clinical neurophysiology practice

Peripheral neuropathies may involve the small diameter nerve fibers of the autonomic nervous system. In the presence of clinical signs compatible with dysautonomia, it is very difficult to affirm that these signs are really linked to an alteration in postganglionic autonomic innervation, and not to a lesion of the central nervous system or to a direct damage to the tissues and innervated organs. Also, in the context of the investigation of peripheral neuropathies, there is an interest in performing objective and quantitative assessment of distal autonomic innervation. The corresponding autonomic tests are mainly based on the exploration of sudomotor or vasomotor disorders of the limb extremities. In this article, we provide an overview of the various tests available for the study of the autonomic nervous system in clinical practice, including vasomotor reactivity tests, in particular based on laser Doppler techniques, and sudomotor tests, based on axon-reflexes produced by iontophoresis of cholinergic drugs or on the simpler measurement of electrochemical skin conductance by the Sudoscan® device.

Effects of Different Fasting Interventions on Cardiac Autonomic Modulation in Healthy Individuals: A Secondary Outcome Analysis of the EDIF Trial

The impact of a fasting intervention on electrocardiographic (ECG) time intervals and heart rate variability (HRV) is a focus that is scarcely analyzed. The main focus of these secondary outcome data was to describe the impact of a different fasting intervention on ECG and HRV analyses. Twenty-seven healthy individuals participated in this study (11 females, aged 26.3 ± 3.8 years, BMI 24.7 ± 3.4 kg/m2), including a pre-intervention controlled run-in period. Participants were randomized to one of the three fasting cohorts: (I) alternate day fasting (ADF, n = 8), (II) 16/8 fasting (16/8 h of fasting/feasting, n = 11) and (III) 20/4 fasting (20/4 h of fasting/feasting, n = 8). An analysis of baseline ECG parameters and HRV parameters following different fasting interventions demonstrated the safety of these interventions without impacting on heart rate variability parameters during Schellong-1 testing, and revealed comparable preserved autonomic cardiac modulation (ACM) independently of the fasting intervention. In conclusion, different short-term fasting interventions demonstrated no safety ECG-based concerns and showed comparable ACM based on ECG and HRV assessments. Finally, our research topic might strengthen the scientific knowledge of intermittent fasting strategies and indicate potential clinically preventive approaches with respect to occurring metabolic disease and obesity in healthy young subjects.

Practices and Applications of Heart Rate Variability Monitoring in Endurance Athletes

Heart rate variability reflects fluctuations in the changes in consecutive heartbeats, providing insight into cardiac autonomic function and overall physiological state. Endurance athletes typically demonstrate better cardiac autonomic function than non-athletes, with lower resting heart rates and greater variability. The availability and use of heart rate variability metrics has increased in the broader population and may be particularly useful to endurance athletes. The purpose of this review is to characterize current practices and applications of heart rate variability analysis in endurance athletes. Important considerations for heart rate variability analysis will be discussed, including analysis techniques, monitoring tools, the importance of stationarity of data, body position, timing and duration of the recording window, average heart rate, and sex and age differences. Key factors affecting resting heart rate variability will be discussed, including exercise intensity, duration, modality, overall training load, and lifestyle factors. Training applications will be explored, including heart rate variability-guided training and the identification and monitoring of maladaptive states such as overtraining. Lastly, we will examine some alternative uses of heart rate variability, including during exercise, post-exercise, and for physiological forecasting and predicting performance.

Glucose and Fructose Supplementation and Their Acute Effects on Electrocardiographic Time Intervals during Anaerobic Cycling Exercise in Healthy Individuals: A Secondary Outcome Analysis of a Double-Blind Randomized Crossover-Controlled Trial

The impact of glucose and fructose supplementation on acute cardiac effects during cardiopulmonary exercise testing (CPET) is a topic that is rarely investigated. The aim of the presented secondary outcome analysis of a double-blind, randomized crossover-controlled trial was to investigate the impact of glucose (Glu), fructose (Fru), glucose and fructose (GluFru), and sucralose on electrocardiogram (ECG), heart rate variability (HRV), premature ventricular complexes (PVCs), and heart rate turn points (HRTP) during CPET. Fourteen healthy individuals (age 25.4 ± 2.5 years, body mass index (BMI) 23.7 ± 1.7 kg/m2, body mass (BM) of 76.3 ± 12.3 kg) participated in this study, of which 12 were included for analysis. Participants received 1 g/kg BM of Glu, 1 g/kg BM of Fru, 0.5 g/kg BM of GluFru (each), and 0.2 g sucralose dissolved in 300 mL 30 min prior to each exercise session. No relevant clinical pathology or significant inter-individual differences between our participants could be revealed for baseline ECG parameters, such as heart rate (HR) (mean HR 70 ± 16 bpm), PQ interval (146 ± 20 ms), QRS interval (87 ± 16 ms) and the QT (405 ± 39 ms), and QTc interval (431 ± 15 ms). We found preserved cardiac autonomic function by analyzing the acute effects of different Glu, Fru, GluFru, or sucralose supplementation on cardiac autonomic function by Schellong-1 testing. SDNN and RMSSD revealed normal sympathetic and parasympathetic activities displaying a balanced system of cardiac autonomic regulation across our participating subjects with no impact on the metabolism. During CPET performance analyses, HRV values did not indicate significant changes between the ingested drinks within the different time points. Comparing the HRTP of the CPET with endurance testing by variable metabolic conditions, no significant differences were found between the HRTP of the CPET data (170 ± 12 bpm), Glu (171 ± 10 bpm), Fru (171 ± 9 bpm), GluFru (172 ± 9 bpm), and sucralose (170 ± 8 bpm) (p = 0.83). Additionally, the obtained time to reach HRTP did not significantly differ between Glu (202 ± 75 s), Fru (190 ± 88 s), GluFru (210 ± 89 s), and sucralose (190 ± 34 s) (p = 0.59). The significance of this study lies in evaluating the varying metabolic conditions on cardiac autonomic modulation in young healthy individuals. In contrast, our participants showed comparable cardiac autonomic responses determined by ECG and CPET.

The Influence of an Alpha Band Neurofeedback Training in Heart Rate Variability in Athletes

Neurofeedback training is a technique which has seen a widespread use in clinical applications, but has only given its first steps in the sport environment. Therefore, there is still little information about the effects that this technique might have on parameters, which are relevant for athletes' health and performance, such as heart rate variability, which has been linked to physiological recovery. In the sport domain, no studies have tried to understand the effects of neurofeedback training on heart rate variability, even though some studies have compared the effects of doing neurofeedback or heart rate biofeedback training on performance. The main goal of the present study was to understand if alpha-band neurofeedback training could lead to increases in heart rate variability. 30 male student-athletes, divided into two groups, (21.2 ± 2.62 year 2/week protocol and 22.6 ± 1.1 year 3/week protocol) participated in the study, of which three subjects were excluded. Both groups performed a pre-test, a trial session and 12 neurofeedback sessions, which consisted of 25 trials of 60 s of a neurofeedback task, with 5 s rest in-between trials. The total neurofeedback session time for each subject was 300 min in both groups. Throughout the experiment, electroencephalography and heart rate variability signals were recorded. Only the three sessions/week group revealed significant improvements in mean heart rate variability at the end of the 12 neurofeedback sessions (p = 0.05); however, significant interaction was not found when compared with both groups. It is possible to conclude that neurofeedback training of individual alpha band may induce changes in heart rate variability in physically active athletes.

Physician Stress During Electronic Health Record Inbox Work: In Situ Measurement With Wearable Sensors

Background

Increased work through electronic health record (EHR) messaging is frequently cited as a factor of physician burnout. However, studies to date have relied on anecdotal or self-reported measures, which limit the ability to match EHR use patterns with continuous stress patterns throughout the day.

Objective

The aim of this study is to collect EHR use and physiologic stress data through unobtrusive means that provide objective and continuous measures, cluster distinct patterns of EHR inbox work, identify physicians’ daily physiologic stress patterns, and evaluate the association between EHR inbox work patterns and physician physiologic stress.

Methods

Physicians were recruited from 5 medical centers. Participants (N=47) were given wrist-worn devices (Garmin Vivosmart 3) with heart rate sensors to wear for 7 days. The devices measured physiological stress throughout the day based on heart rate variability (HRV). Perceived stress was also measured with self-reports through experience sampling and a one-time survey. From the EHR system logs, the time attributed to different activities was quantified. By using a clustering algorithm, distinct inbox work patterns were identified and their associated stress measures were compared. The effects of EHR use on physician stress were examined using a generalized linear mixed effects model.

Results

Physicians spent an average of 1.08 hours doing EHR inbox work out of an average total EHR time of 3.5 hours. Patient messages accounted for most of the inbox work time (mean 37%, SD 11%). A total of 3 patterns of inbox work emerged: inbox work mostly outside work hours, inbox work mostly during work hours, and inbox work extending after hours that were mostly contiguous to work hours. Across these 3 groups, physiologic stress patterns showed 3 periods in which stress increased: in the first hour of work, early in the afternoon, and in the evening. Physicians in group 1 had the longest average stress duration during work hours (80 out of 243 min of valid HRV data; P=.02), as measured by physiological sensors. Inbox work duration, the rate of EHR window switching (moving from one screen to another), the proportion of inbox work done outside of work hours, inbox work batching, and the day of the week were each independently associated with daily stress duration (marginal R²=15%). Individual-level random effects were significant and explained most of the variation in stress (conditional R²=98%).

Conclusions

This study is among the first to demonstrate associations between electronic inbox work and physiological stress. We identified 3 potentially modifiable factors associated with stress: EHR window switching, inbox work duration, and inbox work outside work hours. Organizations seeking to reduce physician stress may consider system-based changes to reduce EHR window switching or inbox work duration or the incorporation of inbox management time into work hours.

A Persistent Homology Approach to Heart Rate Variability Analysis With an Application to Sleep-Wake Classification

Persistent homology is a recently developed theory in the field of algebraic topology to study shapes of datasets. It is an effective data analysis tool that is robust to noise and has been widely applied. We demonstrate a general pipeline to apply persistent homology to study time series, particularly the instantaneous heart rate time series for the heart rate variability (HRV) analysis. The first step is capturing the shapes of time series from two different aspects—the persistent homologies and hence persistence diagrams of its sub-level set and Taken's lag map. Second, we propose a systematic and computationally efficient approach to summarize persistence diagrams, which we coined persistence statistics. To demonstrate our proposed method, we apply these tools to the HRV analysis and the sleep-wake, REM-NREM (rapid eyeball movement and non rapid eyeball movement) and sleep-REM-NREM classification problems. The proposed algorithm is evaluated on three different datasets via the cross-database validation scheme. The performance of our approach is better than the state-of-the-art algorithms, and the result is consistent throughout different datasets.

Sympathetic nervous system activation and heart failure: Current state of evidence and the pathophysiology in the light of novel biomarkers

Heart failure (HF) is a complex clinical syndrome characterized by the activation of at least several neurohumoral pathways that have a common role in maintaining cardiac output and adequate perfusion pressure of target organs and tissues. The sympathetic nervous system (SNS) is upregulated in HF as evident in dysfunctional baroreceptor and chemoreceptor reflexes, circulating and neuronal catecholamine spillover, attenuated parasympathetic response, and augmented sympathetic outflow to the heart, kidneys and skeletal muscles. When these sympathoexcitatory effects on the cardiovascular system are sustained chronically they initiate the vicious circle of HF progression and become associated with cardiomyocyte apoptosis, maladaptive ventricular and vascular remodeling, arrhythmogenesis, and poor prognosis in patients with HF. These detrimental effects of SNS activity on outcomes in HF warrant adequate diagnostic and treatment modalities. Therefore, this review summarizes basic physiological concepts about the interaction of SNS with the cardiovascular system and highlights key pathophysiological mechanisms of SNS derangement in HF. Finally, special emphasis in this review is placed on the integrative and up-to-date overview of diagnostic modalities such as SNS imaging methods and novel laboratory biomarkers that could aid in the assessment of the degree of SNS activation and provide reliable prognostic information among patients with HF.

The Source of Heart Rhythm Changes Caused by Swallowing

Swallowing can lead to the development of syncope in people who have difficulty swallowing during food intake. It has shown that even spontaneous saliva swallowing can change heart rate variability (HRV). Recently, it has been suggested that changes in heart rate during swallowing may be caused by respiratory activities. In this study, the hypothesis that swallowing induced HRV are caused from breathing changes during swallowing has been tested. For this purpose, electrocardiogram (ECG), chest circumference (respiration) signals and swallowing sounds were recorded simultaneously from 20 subjects. Subjects were asked not to swallow their saliva in the first 4 min of the experiment and to swallow them several times in the next 4 min. To observe respiratory effects on HRV during swallowing, a detailed cardio-respiratory system mathematical model was used. By applying recorded chest circumference signal to the mathematical model, respiration induced HRV changes were obtained. The HRV parameters of with and without swallowing regions of the real (obtained from ECG) and model-HRV (obtained from mathematical model) were compared by paired Student t test. Statistical differences seen in the real-HRV between the swallowing and non-swallowing regions (SDNN, LF power, approximate entropy) were not observed in the model-HRV. Considering that the only factor constituting HRV in the mathematical model is respiration, it was concluded that swallowing changes HRV with a mechanism other than breathing changes.

Entropy-Based Measures of Hypnopompic Heart Rate Variability Contribute to the Automatic Prediction of Cardiovascular Events

Surges in sympathetic activity should be a major contributor to the frequent occurrence of cardiovascular events towards the end of nocturnal sleep. We aimed to investigate whether the analysis of hypnopompic heart rate variability (HRV) could assist in the prediction of cardiovascular disease (CVD). 2217 baseline CVD-free subjects were identified and divided into CVD group and non-CVD group, according to the presence of CVD during a follow-up visit. HRV measures derived from time domain analysis, frequency domain analysis and nonlinear analysis were employed to characterize cardiac functioning. Machine learning models for both long-term and short-term CVD prediction were then constructed, based on hypnopompic HRV metrics and other typical CVD risk factors. CVD was associated with significant alterations in hypnopompic HRV. An accuracy of 81.4% was achieved in short-term prediction of CVD, demonstrating a 10.7% increase compared with long-term prediction. There was a decline of more than 6% in the predictive performance of short-term CVD outcomes without HRV metrics. The complexity of hypnopompic HRV, measured by entropy-based indices, contributed considerably to the prediction and achieved greater importance in the proposed models than conventional HRV measures. Our findings suggest that Hypnopompic HRV assists the prediction of CVD outcomes, especially the occurrence of CVD event within two years.

A healthy dose of chaos: Using fractal frameworks for engineering higher-fidelity biomedical systems

Optimal levels of chaos and fractality are distinctly associated with physiological health and function in natural systems. Chaos is a type of nonlinear dynamics that tends to exhibit seemingly random structures, whereas fractality is a measure of the extent of organization underlying such structures. Growing bodies of work are demonstrating both the importance of chaotic dynamics for proper function of natural systems, as well as the suitability of fractal mathematics for characterizing these systems. Here, we review how measures of fractality that quantify the dose of chaos may reflect the state of health across various biological systems, including: brain, skeletal muscle, eyes and vision, lungs, kidneys, tumours, cell regulation, skin and wound repair, bone, vasculature, and the heart. We compare how reports of either too little or too much chaos and fractal complexity can be damaging to normal biological function, and suggest that aiming for the healthy dose of chaos may be an effective strategy for various biomedical applications. We also discuss rising examples of the implementation of fractal theory in designing novel materials, biomedical devices, diagnostics, and clinical therapies. Finally, we explain important mathematical concepts of fractals and chaos, such as fractal dimension, criticality, bifurcation, and iteration, and how they are related to biology. Overall, we promote the effectiveness of fractals in characterizing natural systems, and suggest moving towards using fractal frameworks as a basis for the research and development of better tools for the future of biomedical engineering.

Risk Stratification of Sudden Cardiac Death in Patients with Heart Failure: An update

Heart failure (HF) is a complex clinical syndrome in which structural/functional myocardial abnormalities result in symptoms and signs of hypoperfusion and/or pulmonary or systemic congestion at rest or during exercise. More than 80% of deaths in patients with HF recognize a cardiovascular cause, with most being either sudden cardiac death (SCD) or death caused by progressive pump failure. Risk stratification of SCD in patients with HF and preserved (HFpEF) or reduced ejection fraction (HFrEF) represents a clinical challenge. This review will give an update of current strategies for SCD risk stratification in both HFrEF and HFpEF.

Integrated genetic and epigenetic prediction of coronary heart disease in the Framingham Heart Study

An improved method for detecting coronary heart disease (CHD) could have substantial clinical impact. Building on the idea that systemic effects of CHD risk factors are a conglomeration of genetic and environmental factors, we use machine learning techniques and integrate genetic, epigenetic and phenotype data from the Framingham Heart Study to build and test a Random Forest classification model for symptomatic CHD. Our classifier was trained on n = 1,545 individuals and consisted of four DNA methylation sites, two SNPs, age and gender. The methylation sites and SNPs were selected during the training phase. The final trained model was then tested on n = 142 individuals. The test data comprised of individuals removed based on relatedness to those in the training dataset. This integrated classifier was capable of classifying symptomatic CHD status of those in the test set with an accuracy, sensitivity and specificity of 78%, 0.75 and 0.80, respectively. In contrast, a model using only conventional CHD risk factors as predictors had an accuracy and sensitivity of only 65% and 0.42, respectively, but with a specificity of 0.89 in the test set. Regression analyses of the methylation signatures illustrate our ability to map these signatures to known risk factors in CHD pathogenesis. These results demonstrate the capability of an integrated approach to effectively model symptomatic CHD status. These results also suggest that future studies of biomaterial collected from longitudinally informative cohorts that are specifically characterized for cardiac disease at follow-up could lead to the introduction of sensitive, readily employable integrated genetic-epigenetic algorithms for predicting onset of future symptomatic CHD.

Evaluation of autonomic functions of patients with multiple system atrophy and Parkinson's disease by head-up tilt test

The aim of this study was to evaluate the autonomic neural function in Parkinson's disease (PD) and multiple system atrophy (MSA) with head-up tilt test and spectral analysis of cardiovascular parameters. This study included 15 patients with MSA, 15 patients with PD, and 29 healthy control (HC) subjects. High frequency power of the RR interval (RR-HF), the ratio of low frequency power of RR interval to RR-HF (RR-LF/HF) and LF power of systolic BP were used to evaluate parasympathetic, cardiac sympathetic and vasomotor sympathetic functions, respectively. Both patients with PD and MSA showed orthostatic hypotension and lower parasympathetic function (RR-HF) at tilt position as compared to HC subjects. Cardiac sympathetic function (RR-LF/HF) was significantly high in patients with PD than MSA at supine position. RR-LF/HF tended to increase in MSA and HC, but decreased in PD by tilting. Consequently, the change of the ratio due to tilting (ΔRR-LF/HF) was significantly lower in patients with PD than in HC subjects. Further analysis showed that compared to mild stage of PD, RR-LF/HF at the supine position was significantly higher in advanced stage. By tilting, it was increased in mild stage and decreased in the advanced stage of PD, causing ΔRR-LF/HF to decrease significantly in the advanced stage. Thus, we demonstrated that spectral analysis of cardiovascular parameters is useful to identify sympathetic and parasympathetic disorders in MSA and PD. High cardiac sympathetic function at the supine position, and its reduction by tilting might be a characteristic feature of PD, especially in the advanced stage.

Reproducibility of 24-h heart rate variability in children

BACKGROUND

Over the last decades, time domain heart rate (HR) variability analysis has been explored in different pediatric clinical settings to obtain information on the cardiac autonomic tone. However, the consistency over time of 24 h time domain HRV measurements in children is not well-known.

METHODS

We investigated the reproducibility of 24 h HRV time-domain indices (1 day apart), from 39 healthy children (9.5 ± 5.3 years, 56.4% girls). The parameters analysed included: standard deviation of all the adjacent NN intervals, standard deviation of the averages of NN intervals (the intervals between normal R-peaks) in all 5-min segments, and square root of the mean of the sum of the squares of the differences between adjacent NN intervals, uncorrected and corrected for HR. Reproducibility between two 24-h ECG recordings was evaluated by intraclass correlation coefficients, standard error of measurement, coefficients of variation and Bland-Altman plots.

RESULTS

For the analyzed time-domain indices, standard deviation of all the adjacent NN intervals corrected for HR showed best reproducibility with the highest intraclass correlation coefficient (0.987), the lowest coefficients of variation (5.5%) and the best level of agreement between two recordings as assessed by Bland-Altman plots.

CONCLUSIONS

Our results indicate that the standard deviation of all the adjacent NN intervals corrected for the HR parameter obtained from 24-h ambulatory recordings in children is consistent and reproducible over time, thus allowing reliable identification of cardiac autonomic tone in this age group.

Effect of emotion regulation training in patients with panic disorder: Evidenced by heart rate variability measures

OBJECTIVE

We aimed to examine the effect of emotion regulation training in patients with panic disorder (PD) by measuring heart rate variability (HRV).

METHODS

Forty-eight patients with PD were randomly divided into emotion regulation group (n=25) and no-regulation group (n=23). Three five-minute ECG recordings were taken in the following states: 1) baseline, 2) while subjects viewed 15 aversive pictures (active stimulus), 3) resting state after aversive pictures (post-stimulus). The emotion regulation group briefly received acceptance technique training for five minutes before performing the experimental task. Spectral analysis measures included a high-frequency (HF; 0.15-0.4 HZ) component, a low-frequency (LF; 0.04-0.15Hz) component, and an LF/HF ratio.

RESULTS

The mean change in LF/HF ratio from baseline to active stimulus was significantly lower in the emotion regulation group than in the no-regulation group (emotion regulation group, 0.13; no-regulation group, 2.31; t=-2.67; P<.05).

CONCLUSION

This suggests that brief emotion acceptance training could decrease aversive stimulus-induced sympathetic hyperactivity in patients with PD.

Comparable accuracy of micro-electromechanical blood flowmetry-based analysis vs. electrocardiography-based analysis in evaluating heart rate variability

BACKGROUND

Because the conventional evaluation of autonomic nervous system (ANS) function inevitably uses long-lasting uncomfortable electrocardiogram (ECG) recording, a more simplified and comfortable analysis system has been sought for this purpose. The feasibility of using a portable micro-electromechanical system (MEMS) blood flowmeter to analyze heart rate variability (HRV) for evaluating ANS function was thus examined.

METHODS AND RESULTS

Measurements of the R-R interval (TRR) derived from an ECG, simultaneously with the pulse wave interval (TPP) derived from a MEMS blood flowmeter, in 8 healthy subjects was performed and resultant HRV variables in time and frequency domains were compared. The TRR- and TPP-derived variables were strongly correlated (coefficients of regression for low frequency (LF), high frequency (HF), and LF/HF of 1.1, 0.66, and 0.35, respectively; corresponding coefficients of determination of 0.92, 0.63, and 0.91, respectively (P<0.01)). In addition, the values of LF, HF, and LF/HF, as analyzed using TPP, changed significantly from the supine to the standing position in another 6 subjects.

CONCLUSIONS

Miniaturized-MEMS blood flowmetry can be used to perform HRV analysis for the evaluation of ANS function, which is as accurate as analysis based on ECG within comparable tolerances. As MEMS blood flowmetry can more easily and comfortably record physiological variables for longer durations than ECG recording, and can further capture skin blood flow information, this device has great potential to be used in a wider area of physiological analyses.

Baseline heart rate variability in children and adolescents with vasovagal syncope

Purpose

This study aimed to evaluate the autonomic imbalance in syncope by comparing the baseline heart rate variability (HRV) between healthy children and those with vasovagal syncope.

Methods

To characterize the autonomic profile in children experiencing vasovagal syncope, we evaluated the HRV of 23 patients aged 7-18 years and 20 healthy children. These children were divided into preadolescent (<12 years) and adolescent groups. The following time-domain indices were calculated: root mean square of the successive differences (RMSSD); standard deviation of all average R-R intervals (SDNN); and frequency domain indices including high frequency (HF), low frequency (LF), normalized high frequency, normalized low frequency, and low frequency to high frequency ratio (LF/HF).

Results

HRV values were significantly different between healthy children and those with syncope. Student t test indicated significantly higher SNDD values (60.46 ms vs. 37.42 ms, P=0.003) and RMSSD (57.90 ms vs. 26.92 ms, P=0.000) in the patient group than in the control group. In the patient group, RMSSD (80.41 ms vs. 45.89 ms, P=0.015) and normalized HF (61.18 ms vs. 43.19 ms, P=0.022) were significantly higher in adolescents, whereas normalized LF (38.81 ms vs. 56.76 ms, P=0.022) and LF/HF ratio (0.76 vs. 1.89, P=0.041) were significantly lower in adolescents. In contrast, the control group did not have significant differences in HRV values between adolescents and preadolescents.

Conclusion

The results of this study indicated that children with syncope had a decreased sympathetic tone and increased vagal tone compared to healthy children. Additionally, more severe autonomic imbalances possibly occur in adolescents than in preadolescents.

Threat-induced autonomic dysregulation in panic disorder evidenced by heart rate variability measures

OBJECTIVE

The objective was to compare autonomic response to threatening stimuli between patients with panic disorder (PD) and healthy volunteers by using 5-min recordings of heart rate variability (HRV).

METHODS

Twenty-seven patients with PD and 20 healthy controls were recruited. The first 5-min measurement of HRV was conducted at resting state. HRV measurement during threatening stimuli was conducted while participants were viewing 15 threatening pictures. Spectral analyses measures included high-frequency (HF; 0.15-0.4 HZ) component, low-frequency (LF; 0.04-0.15 Hz) component and LF/HF ratio.

RESULTS

There was no significant HRV difference between the two groups at the resting state. During threatening stimuli, the PD group had significantly higher LF power and LF/HF ratio and significantly lower HF power than the healthy controls (for all, P<.01). A two-way analysis of variance was employed to determine the effect of group (patient and control) and condition (threatening and resting) on all three HRV measures. The analysis showed a significant main effect of group (F=12.21; P<.01), condition (F=14.21; P<.001) and interaction effect between group and condition (F=4.83; P<.05) on LF/HF ratio.

CONCLUSIONS

The findings from the present study suggest that patients with PD exhibit a sympathetic predominance when faced with threatening stimuli compared with normal control subjects.

Heart rate variability in junior high school students with depression and anxiety in Taiwan

BACKGROUND

The impact of depression and anxiety on heart rate variability (HRV) is not clear in adolescents. We hypothesised that HRV investigation in adolescents may early prevent the mental diseases occurrence.

METHODS

Three hundred and thirty-three seventh grade students participated in this study programme. HRV instrumental analysis and spectral with scale of depression were measured respectively.

RESULTS

It showed that among the participants, the depression score of female was higher than male. The population with lower depression score present with lower high frequency and higher low frequency/high frequency ratio but not statistically significant. Oppositely, participants with higher depression score were increased with heart rate and present with lower standard deviation of heart rate. However, it is also not statistically significant.

CONCLUSION

This study supported the positive relation between HRV and depression, especially in the female gender. Therefore, HRV in depression may be beneficial in the detection and prevention of mental disorder development, even suicide behaviour in teenagers.

Application of alpha/theta neurofeedback and heart rate variability training to young contemporary dancers: state anxiety and creativity

As one in a series on the impact of EEG-neurofeedback in the performing arts, we set out to replicate a previous dance study in which alpha/theta (A/T) neurofeedback and heart rate variability (HRV) biofeedback enhanced performance in competitive ballroom dancers compared with controls. First year contemporary dance conservatoire students were randomised to the same two psychophysiological interventions or a choreology instruction comparison group or a no-training control group. While there was demonstrable neurofeedback learning, there was no impact of the three interventions on dance performance as assessed by four experts. However, HRV training reduced anxiety and the reduction correlated with improved technique and artistry in performance; the anxiety scale items focussed on autonomic functions, especially cardiovascular activity. In line with the putative impact of hypnogogic training on creativity A/T training increased cognitive creativity with the test of unusual uses, but not insight problems. Methodological and theoretical implications are considered.

Heart rate and autonomic response to stress after experimental induction of worry versus relaxation in healthy, high-worry, and generalized anxiety disorder individuals

Generalized anxiety disorder (GAD) is the most commonly occurring anxiety disorder and has been related to cardiovascular morbidity such as cardiac ischemia, sudden cardiac death, and myocardial infarction. Both GAD and its cardinal symptom - worry - have been shown to promote muted physiological reactivity in response to laboratory and ecological stressors. Importantly, no study to date has examined the concurrent and relative contributions of trait and state worry within healthy controls, (non-clinical) high trait-worry controls, and GAD participants. The present study examined heart rate (HR), respiratory sinus arrhythmia (RSA), and salivary alpha-amylase (sAA) responses to laboratory stress during and following the experimental induction of worry versus relaxation in healthy controls (n=42), high trait worriers (n=33) and participants with GAD (n=76). All groups exhibited increased HR and decreased RSA in response to the stressor, with no differences by condition. Baseline sAA significantly moderated HR and RSA reactivity, such that higher sAA predicted greater increases in HR and decreases in RSA. There was a significant group by baseline sAA interaction such that in GAD, higher baseline sAA predicted decreased change in sAA during stress, whereas higher baseline sAA predicted greater sAA change in healthy controls. High-worry controls fell non-significantly between these groups. The present study provides additional evidence for the effect of worry on diminished HR stress response and points to possible suppression of adrenergic sympathetic stress responses in GAD.

Translational applications of evaluating physiologic variability in human endotoxemia

Dysregulation of the inflammatory response is a critical component of many clinically challenging disorders such as sepsis. Inflammation is a biological process designed to lead to healing and recovery, ultimately restoring homeostasis; however, the failure to fully achieve those beneficial results can leave a patient in a dangerous persistent inflammatory state. One of the primary challenges in developing novel therapies in this area is that inflammation is comprised of a complex network of interacting pathways. Here, we discuss our approaches towards addressing this problem through computational systems biology, with a particular focus on how the presence of biological rhythms and the disruption of these rhythms in inflammation may be applied in a translational context. By leveraging the information content embedded in physiologic variability, ranging in scale from oscillations in autonomic activity driving short-term heart rate variability to circadian rhythms in immunomodulatory hormones, there is significant potential to gain insight into the underlying physiology.

Mindfulness as Self-Regulated Attention

Empirical research has demonstrated associations between heart rate variability (HRV) and the regulation of emotion and behavior. Similarly, self-regulation of attention to one’s experience of the present moment in an accepting and nonjudgmental manner is an essential characteristic of mindfulness that promotes emotional and behavioral regulation and psychological well-being. The present study investigated the relationship between mindfulness and HRV. A total of 23 undergraduate psychology students completed a recently developed measure of mindfulness, the mindful breathing exercise (MBE), which assesses the ability to mindfully stay in contact with one’s breath during breathing meditation. Moreover, indices of HRV were measured during a short version of the MBE. As predicted, positive correlations were found between indices of HRV and mindfulness. The findings demonstrate that the ability to mindfully regulate one’s attention is associated with higher HRV, a physiological correlate of physical and psychological health, and therefore support on a physiological level the potential benefit of the implemented mindfulness exercises in mindfulness-based clinical interventions.

Heart rate normalization in the analysis of heart rate variability in congestive heart failure

In this study, the effects of heart rate (HR) normalization in the analysis of the heart rate variability (HRV) were investigated to distinguish 29 patients with congestive heart failure from 54 healthy subjects in the control group. In the analysis performed, the best accuracy performances of optimal combination of standard short-term HRV measures and of HR-normalized short-term HRV measures are compared. A genetic algorithm is used to select the best features from among all possible combinations of these measures. A k-nearest-neighbour (KNN) classifier is used to evaluate the performances of the feature combinations in classifying these two data groups. The results imply that using both min—max and HR normalization improves the performance of the classification. The maximum accuracy is achieved as 93.98 per cent using k = 3 and k = 5 for the KNN classifier with the perfect positive predictivity values.

Analysis of heart rate variability as an index of noncardiac surgical stress

Measurement of heart rate variability (HRV) is useful in assessing the function of the autonomic nervous system and in staging of clinical diseases. The purpose of this study is to assess a feasibility of HRV for evaluating surgical stress during the noncardiac perioperative period. Standard deviation of normal-to-normal RR intervals (SDNN) and HRV triangular index derived from 24-h Holter ECC were measured in 24 patients undergoing digestive surgery. Holter ECG was performed at 1 day before operation, the first day (postoperative day 1: POD1), and the 7th day (POD7) after operation. Indices of HRV were compared with factors influencing surgical stress, such as duration of the operation and amount of blood loss during the operation, and postoperative complications. The SDNN and HRV triangular index decreased significantly on POD1 and recovered on POD7 (P < 0.05). Heart rate variability indices correlated significantly to duration and blood loss of operation (both P < 0.05). In 7 patients with postoperative complications, HRV indices were statistically lower than those in patients without complications on POD1 (P < 0.05). Our results indicate that HRV may provide useful information with respect to surgical stress.

Heart rate variability for evaluating surgical stress and development of postoperative complications

Heart rate variability (HRV) has recently been used to detect autonomic nerve tone, which is affected by various stresses. To test out hypothesis that HRV can determine surgical stress, we examined perioperative HRV in 30 patients with surgical treatment. Relations between HRV and factors of surgical stresses, such as duration of the operation, amount of blood loss at the operation, and developments of complications, were evaluated. Mean heart rate (HR) increased and other HRV indices decreased postoperatively. Most indices correlated significantly to the duration of the operation and amount of blood loss at the operation on postoperative day 1. Only the standard deviation of normal to normal RR intervals (SDNN) and HRV triangular index showed significantly low values in complicated patients. HRV measurement in the perioperative period showed a significant relation to surgical stress. The present results indicated that HRV may provide useful information with respect to surgical stress.

Exercício físico em pacientes dialisados

Pacientes portadores de doença renal crônica (DRC) submetidos a tratamento dialítico apresentam alterações físicas e psicológicas que predispõem ao sedentarismo. Nesta população, a prescrição rotineira de exercícios físicos não é uma prática freqüente, especialmente no nosso país. No entanto, alguns autores têm demonstrado que um programa de exercícios para estes pacientes contribui para o melhor controle da hipertensão arterial, da capacidade funcional, da função cardíaca, da força muscular e, conseqüentemente, da qualidade de vida. Além dos benefícios relacionados ao sistema cardiovascular, a realização do exercício traz benefícios secundários, pois quebra a monotonia do procedimento, melhora aderência e pode aumentar a eficácia da diálise. Na presente revisão, os autores discutem aspectos da realização de exercícios físicos em pacientes portadores de DRC em diálise e apresentam dados iniciais de sua experiência com a aplicação de exercícios supervisionados durante as sessões de hemodiálise.

Combining classical HRV indices with wavelet entropy measures improves to performance in diagnosing congestive heart failure

In this study, best combination of short-term heart rate variability (HRV) measures are sought for to distinguish 29 patients with congestive heart failure (CHF) from 54 healthy subjects in the control group. In the analysis performed, in addition to the standard HRV measures, wavelet entropy measures are also used. A genetic algorithm is used to select the best ones from among all possible combinations of these measures. A k-nearest neighbor classifier is used to evaluate the performance of the feature combinations in classifying these two groups. The results imply that two combinations of all HRV measures, both of which include wavelet entropy measures, have the highest discrimination power in terms of sensitivity and specificity values.

Impact of bariatric surgery--induced weight loss on heart rate variability

Obesity is associated with an increased risk of sudden death that may be due to abnormal cardiac vagal modulation reflected by reduced heart rate variability (HRV). Few studies have been conducted analyzing the effect of bariatric surgery-induced weight loss on HRV assessed by 24-hour Holter monitoring. The aim of this study was to assess weight loss effect after bariatric surgery on HRV and ventricular size and function. Ten morbidly obese patients, 6 women and 4 men aged 24 to 47 years, underwent bariatric surgery. Seven morbidly obese patients without active obesity treatment were used as controls. Twenty-four-hour Holter monitoring and echocardiogram were obtained before and at 6 to 12 months after surgery or at follow-up in control patients. Changes in minimal, maximal, and mean heart rate along with HRV during daytime and nighttime were compared before and after surgery. Baseline characteristics in the control group did not differ significantly from the treatment group. Average weight in the treatment group was 141 +/- 31 kg (mean +/- SD) at baseline and decreased to 101 +/- 18 kg at follow-up, corresponding to a body mass index of 52.3 +/- 7.6 kg/m(2) at baseline and 37.7 +/- 5.3 kg/m(2) at follow-up. There was a decrease in minimal heart rate (48 +/- 10 vs 40 +/- 6 beats per minute, P = .021) and mean heart rate (82 +/- 7 vs 66 +/- 10 beats per minute, P < .001) during the Holter monitoring. Spectral analysis showed a significant enhancement in HRV parameters (high- and low-frequency power) because there was an increase in the standard deviation of normal to normal R-R intervals (116 +/- 25 vs 174 +/- 56 milliseconds, P < .001), the standard deviation of the mean R-R intervals calculated over a 5-minute period (104 +/- 25 vs 148 +/- 45 milliseconds, P < .001), the square root of the mean of the squared differences between adjacent normal R-R intervals (25 +/- 8 vs 50 +/- 20 milliseconds, P < .001), and the percentage of differences between adjacent normal R-R intervals exceeding 50 milliseconds (5% +/- 5% vs 22% +/- 13%, P < .001). Echocardiographic measures remained unchanged when comparing the groups. Weight loss after bariatric surgery enhances HRV and decreases mean and minimal heart rate during Holter monitoring through a better cardiac parasympathetic modulation.

Heart Rate Variability as an Index of Regulated Emotional Responding

The study of individual differences in emotional responding can provide considerable insight into interpersonal dynamics and the etiology of psychopathology. Heart rate variability (HRV) analysis is emerging as an objective measure of regulated emotional responding (generating emotional responses of appropriate timing and magnitude). This review provides a theoretical and empirical rationale for the use of HRV as an index of individual differences in regulated emotional responding. Two major theoretical frameworks that articulate the role of HRV in emotional responding are presented, and relevant empirical literature is reviewed. The case is made that HRV is an accessible research tool that can increase the understanding of emotion in social and psychopathological processes.

Efficacy of signal-averaged electrocardiography in the young orthotopic heart transplant patient to detect allograft rejection

Endomyocardial biopsy is the gold standard survey for cardiac graft rejection. Signal-averaged electrocardiography (SAECG) identifies slowly conducting, diseased myocardium. We sought to determine whether SAECG is a sensitive, noninvasive transplant surveillance method in the young.Ninety-four SAECGs recorded prior to biopsy in 20 young transplant (OHT) patients and those from 15 healthy age-matched controls (CTL) were analyzed. In the OHT group, 56 no-rejection (NOREJ) (ISHLT grades 0 or 1 A) and 37 acute rejection (REJ) (ISHLT grades IB, 2, and 3A) SAECGs were compared, SAECGs were filtered at 40-255 Hz. Total QRS duration (QRSd), duration of terminal low amplitude of QRS under 40 microV (LAS), and root mean square amplitude of terminal 40 msec of QRS (RMS40) were compared.SAECGs were significantly different in CTL vs NOREJ but not in NOREJ vs REJ: QRSd, 81.7 +/- 8, 107.2 +/- 18.4, and 112.3 +/- 21.6 msec, respectively; LAS, (18 +/- 5.8, 23.6 +/- 10.7, and 27 +/- 14.8 msec, respectively; and RMS40, (169.3 +/- 100.4, 68 +/- 48.8, and 57.5 +/- 45.6 microV, respectively. Children following OHT exhibited significant differences in the SAECG compared to controls. Differences between the NOREJ and REJ groups were negligible. Therefore, SAECG may not be effective in detecting OHT rejection in the young.

Loss of lag-response curvilinearity of indices of heart rate variability in congestive heart failure

BACKGROUND

Heart rate variability (HRV) is known to be impaired in patients with congestive heart failure (CHF). Time-domain analysis of ECG signals traditionally relies heavily on linear indices of an essentially non-linear phenomenon. Poincaré plots are commonly used to study non-linear behavior of physiologic signals. Lagged Poincaré plots incorporate autocovariance information and analysis of Poincaré plots for various lags can provide interesting insights into the autonomic control of the heart.

METHODS

Using Poincaré plot analysis, we assessed whether the relation of the lag between heart beats and HRV is altered in CHF. We studied the influence of lag on estimates of Poincaré plot indices for various lengths of beat sequence in a public domain data set (PhysioNet) of 29 subjects with CHF and 54 subjects with normal sinus rhythm.

RESULTS

A curvilinear association was observed between lag and Poincaré plot indices (SD1, SD2, SDLD and SD1/SD2 ratio) in normal subjects even for a small sequence of 50 beats (p value for quadratic term 3 x 10-5, 0.002, 3.5 x 10-5 and 0.0003, respectively). This curvilinearity was lost in patients with CHF even after exploring sequences up to 50,000 beats (p values for quadratic term > 0.5).

CONCLUSION

Since lagged Poincaré plots incorporate autocovariance information, these analyses provide insights into the autonomic control of heart rate that is influenced by the non-linearity of the signal. The differences in lag-response in CHF patients and normal subjects exist even in the face of the treatment received by the CHF patients.

Sympatho-vagal control of heart rate variability in patients treated with suppressive doses of L-thyroxine for thyroid cancer

OBJECTIVE

This study aimed to analyze the autonomic control of heart rate variability (HRV) in subjects receiving chronic l-thyroxine (l-T4) treatment after total thyroidectomy and (131)I therapy for differentiated thyroid carcinoma.

METHODS

Blood pressure (BP) and sympatho-vagal activity (evaluated by power spectral analysis (PSA) of time-domain parameters of HRV) were studied in clinostatism and after orthostatism in 24 healthy controls, and in 12 patients taking l-T4 (125-200 mug/day) to maintain serum TSH levels at <0.01 muIU/ml. The study of HRV by PSA is a non-invasive method of analyzing sympatho-vagal control of HRV by quantifying high-frequency (HF) (0.15-0.4 Hz) and low-frequency (LF) (0.04-0.15 Hz) powers.

RESULTS

Patients on L-T4 treatment had undetectable TSH levels, serum free T4 (fT4) above the normal range or at the upper limit in one case, and normal free tri-iodothyronine (fT3) levels. Heart rate and R-R intervals were not different in the two groups, both in clinostatism and in ortostatism. Systolic and mean BP were higher in patients than in controls and were inversely correlated with actual serum fT4 levels. During clinostatism, thyroid patients showed significantly lower LF power (P = 0.035), LF/(LF + HF) (P = 0.008) and LF/HF (P = 0.01) than controls. When patients moved from lying to standing, there was a significantly different decrease in orthostatic LF power (P = 0.001), LF/(LF + HF) (P = 0.044) and LF/HF (P = 0.047) versus controls.

CONCLUSIONS

Changes in autonomic control of HRV, characterized by decreased sympathetic activity and impaired sympatho-vagal balance with preserved vagal tone, are detectable in patients with hyperthyroxinemia due to suppressive l-T4 therapy and increased systolic and mean, but not diastolic, BP.

Präoperative Bestimmung der Herzfrequenzvariabilität bei Diabetikern zur Einschätzung des Blutdruckverhaltens während der Anästhesieeinleitung

BACKGROUND

In diabetics severe hyopotension can occur during anaesthesia as a consequence of cardiovascular autonomic neuropathy (CAN). A simple approach to recognize CAN is heart rate variability (HRV) measured at rest. The aim of this study was to determine the relationship between pre-operatively measured HRV and blood pressure stability during induction phase of anaesthesia.

PATIENTS AND METHODS

A total of 35 diabetics undergoing an ophthalmosurgical procedure under general anaesthesia were investigated. HRV was examined one day before surgery by the following parameters: coefficient of variation (CV), root mean squared successive difference (RMSSD), and power spectrum. Anaesthesia was induced with thiopental and fentanyl and maintained with enflurane/N(2)O; tracheal intubation was performed after relaxation with vecuronium. Patients who developed a drop in systolic blood pressure below 90 mmHg during anaesthesia induction were assigned to group H (hypotensive), the other patients to group N (normotensive). The groups were compared regarding HRV and other variables.

RESULTS

Of all patients 13 developed hypotension during anaesthesia induction (group H). The groups were comparable regarding the demographic data. Parameters of HRV, with the exception of spectral power in low frequency (LF) band of power spectrum, were significantly lower in group H. The groups differed mainly in relation to spectral power in the mid-frequency (MF) band of the power spectrum, and especially regarding CV. In patients with normal CV incidence of hypotension after anaesthesia induction was 11%, but in patients with abnormally reduced CV, 65% (p=0.002).

CONCLUSION

The results confirm a significant relationship between HRV pre-operatively measured at rest and blood pressure stability during anaesthesia induction in diabetics. Particularly examination of CV, a simple test feasible within few minutes, may be useful in pre-operative risk stratification of these patients. Application of the time consuming traditional test combination to identify CAN seems to be unnecessary.

Quantification of the dynamic behavior over time of narrow-band components present in heart rate variability by means of the instantaneous amplitude and frequency

The statistical properties of the time- and frequency-domain characteristics of heart rate variability are known to vary over time. A method is presented to compute the time-varying spectral contents of the characteristic narrow-band frequency components of heart rate variability by means of the instantaneous amplitude and frequency at an optimal time resolution. The instantaneous frequency may show oscillatory, but also irregular periods in time. An index of the instantaneous bandwidth is computed to discriminate between oscillatory and irregular periods and to correct the instantaneous amplitude and frequency for irregular periods.

Influence of exposure to electromagnetic field on the cardiovascular system

1 We examined whether extremely low frequency electromagnetic fields (ELF-EMF) affect the basal level of cardiovascular parameters and influence of drugs acting on the sympathetic nervous system. 2 Male rats were exposed to sham control and EMF (60 Hz, 20 G) for 1 (MF-1) or 5 days (MF-5). We evaluated the alterations of blood pressure (BP), pulse pressure (PP), heart rate (HR), and the PR interval, QRS interval and QT interval on the electrocardiogram and dysrhythmic ratio in basal level and dysrhythmia induced by beta-adrenoceptor agonists. 3 In terms of the basal levels, there were no statistically significant differences among control, MF-1 and MF-5 in PR interval, QRS interval, mean BP, HR and PP. However, the QT interval, representing ventricular repolarization, was significantly reduced by MF-1 (P < 0.05). 4 (-)-Dobutamine (beta1-adrenoceptor-selective agonist)-induced tachycardia was significantly suppressed by ELF-EMF exposure in MF-1 for the increase in HR (DeltaHR), the decrease in QRS interval (DeltaQRS) and the decrease in QT (DeltaQT) interval. Adrenaline (nonselective beta-receptor agonist)-induced dysrhythmia was also significantly suppressed by ELF-EMF in MF-1 for the number of missing beats, the dysrhythmic ratio, and the increase in BP and PP. 5 These results indicated that 1-day exposure to ELF-EMF (60 Hz, 20 G) could suppress the increase in HR by affecting ventricular repolarization and may have a down-regulatory effect on responses of the cardiovascular system induced by sympathetic agonists.

Strategies for managing the diabetic patient

Diabetes mellitus is now classified as either 'type 1' (failure of endogenous insulin production) or 'type 2' ('insulin resistance') and can be diagnosed if fasting blood glucose is >6.1 mmol/l (110mg/dl) on two separate occasions or there is unequivocal hyperglycaemia with acute metabolic decompensation or obvious symptoms. The prevalence of the disease is rising and may be as great as 12-14% in western populations aged over 40 years. Diabetes is complicated by micro- and macrovascular consequences of chronically elevated blood glucose concentrations, and diabetic patients are over-represented in hospital populations, particularly among patients requiring surgical interventions. It is associated with increased perioperative mortality and morbidity. Evidence is now accumulating that intensive glycaemic monitoring and the administration of insulin infusions to achieve tight glycaemic control are associated with an improvement of both perioperative mortality and morbidity.

Do collaterals affect heart rate variability in patients with acute myocardial infarction?

BACKGROUND

The protective effects and the prognostic importance of collaterals during and after acute myocardial infarction (MI) are under debate and heart rate variability (HRV) is a strong predictor of risk of mortality and arrhythmic events after acute MI. We aimed to examine the effects of collateral circulation on HRV in the early period after acute MI.

METHODS

Sixty-four patients admitted to our clinics who were diagnosed with acute anterior MI and underwent thrombolytic therapy were enrolled in this study. We applied 24 h Holter monitoring for HRV analysis to all patients and compared the patients with and without collaterals to the infarct-related artery.

RESULTS

Mean heart rate, low frequency (LF) (day, night and 24 h) and LF/high frequency (HF) (day, night and 24 h) were higher, SD of all NN intervals (SDNN), root mean square of successive differences (RMSSD), number of NN intervals that differed by more than 50 ms from the adjacent interval divided by the total number of all NN intervals (PNN50) and HF night values were lower in patients without collaterals than in those with collaterals. SDNN was negatively correlated with left anterior descending coronary artery (LAD) stenosis, ventricle score indices and left ventricular ejection fraction (LVEF); LF/HF ratio was positively correlated with ventricle score indices and negatively correlated with LVEF and Thrombolysis in Myocardial Infarction flow grade. Linear regression analysis showed that ventricle score index and coronary collaterals affect HRV and LAD stenosis, ventricle score, LVEF and coronary collaterals affect LF/HF ratio. A SDNN <80 ms increased the development of ventricular arrhythmias in the early period by 4.7 fold, a LF/HF ratio >2.7 increased it by 9.8 fold and a LVEF <35% increased it by 12.8 fold, whereas the presence of well-developed collaterals decreased the arrhythmia development by 2.5 fold.

CONCLUSIONS

The collaterals to the infarct-related artery have great impact on HRV, autonomic nervous system activity and the development of ventricular arrhythmias in patients with acute anterior MI. Our results suggest a protective role of collaterals on myocardial electrophysiology in the early period after acute MI.

Sympathovagal response to orthostatism in overt and in subclinical hyperthyroidism

Heart rate variability (HRV) is a measure of the physiological variation of R-R intervals, reflecting the sympathovagal balance. In both overt and subclinical hyperthyroidism, a relative increase in sympathetic activity has been demonstrated, mainly due to a decrease in vagal activity. The modifications of HRV during orthostatism in normal subjects resemble those seen in hyperthyroidism. We have studied the response of 19 patients with overt hyperthyroidism and 12 with subclinical hyperthyroidism during orthostatism using HRV and compared the results to those of 32 healthy controls. In the three groups, the R-R intervals decreased in the same proportion after orthostatism. The low frequency power (LF)/[LF + high frequency power (HF)] ratio, which reflects the sympathetic tone, also increased in the same proportion in the three groups. However, the mechanisms of the modulation of the sympathovagal balance during orthostatism were different among the three groups. In controls, the relative increase of sympathetic tone after orthostatism was due principally to a decrease in vagal tone (reflected by decreased power in the HF band), while in overt hyperthyroidism, where the power in the HF band was already minimal in the lying position, there was a clear increase in the LF band power during orthostatism. The results were intermediate in the subclinical hyperthyroidism group, reflecting a continuum of effects of the thyroid hormone excess on the autonomic nervous system. Our study shows that despite an apparent normal cardiovascular adaptation to orthostatism in hyperthyroidism, the modulation of the autonomic nervous system is profoundly modified.

Safety of antidepressant drugs in the patient with cardiac disease: a review of the literature

Patients with cardiac disease, specifically ischemic heart disease and heart failure, have a higher frequency of major depressive disorder than patients without cardiac disease. The pathophysiologic reason for this is not completely understood. Previous depression, other debilitating illnesses, and type A personality are risk factors for the development of depression in cardiac patients. Depression has been shown to lower the threshold for ventricular arrhythmias. Therefore, treatment of depression potentially may prolong life in these patients. Antidepressant options that have been evaluated include several of the tricyclic antidepressants, trazodone, bupropion, and several of the selective serotonin reuptake inhibitors. Individual antidepressant drugs vary in their pharmacologic activity and side-effect profiles. Although clinical data are limited, it is important to individualize therapy in order to minimize cardiac adverse effects. Clinicians are encouraged to evaluate patients with cardiac disease for major depressive disorder and to consider antidepressant drug therapy for these patients when appropriate.

Potential of feature selection methods in heart rate variability analysis for the classification of different cardiovascular diseases

In this study heart rate variability (HRV) analysis was applied to characterize patients suffering from coronary heart disease (CHD), dilated cardiomyopathy (DCM) and patients who had survived an acute myocardial infarction (MI). On the basis of several HRV parameters, an optimal discrimination between the different kinds of cardiovascular diseases and between the diseases and healthy controls (HC) was derived by feature selection and linear classification. For each task a small favourable subset of a set of 33 potentially interesting HRV measures was selected with the intention of improving the diagnostic value and facilitating the physiological interpretation of HRV analysis. Time- and frequency-domain parameters as well as parameters from non-linear dynamics were included in the analysis. With the expectation that different diseases are characterized by different phenomena, feature selection was applied for each task separately. Using the features optimal for one task to another task can reveal a loss in performance, but it turned out that one specific parameter set (set1: normalized low frequency LF/P and a non-linear variability measure WPSUM13) was applicable for all tasks, where diseased and healthy subjects have to be distinguished, without significant reduction in performance. This set seems to be a general marker for pathologic changes in HRV and might be used for early detection of heart diseases. The classification between different heart diseases requires another parameter set (set2: meanNN and sdaNN, reflecting the steady state behaviour of the heart rate and long and short term SEAR describing the spectral composition). However, the use of set1 for the separation of different kinds of diseases, where set2 is appropriate, led to significant reduction in performance and vice versa. This observation may be important for future developments of HRV measures especially suitable for the assessment of disease severity.

Joint symbolic dynamic analysis of beat-to-beat interactions of heart rate and systolic blood pressure in normal pregnancy

Pregnancy induces important changes in the autonomic control. Measures of heart rate (HR) variability and systolic blood pressure (SP) variability are sensitive to those changes. The interactions between HR and SP are complex and strongly non-linear. Therefore they cannot be completely described by linear analysis techniques. A study of joint symbolic dynamics is presented as a new short-term non-linear analysis method to investigate the interactions between HR and SP. Continuous, non-invasive 30 min blood pressure recordings (Portapres) of 25 pregnant and 14 non-pregnant women were analysed. Time series of beat-to-beat HR and SP were extracted. Using the concept of joint symbolic dynamics, HR and SP changes were transformed into a bivariate symbol vector. Subsequently, this symbol vector was transformed into a word series (words consisting of three successive symbols), and the probability of occurrence of each word type was calculated and compared between both groups. Significant differences were found in five word types between pregnant and non-pregnant women: w0,4(0.021+/-0.011 against 0.008+/-0.006; p = 0.022), w4,6(0.020+/-0.010 against 0.007+/-0.003; p = 0.001), w3,2(0.004+/-0.003 against 0.007+/-0.003; p = 0.038), W6,5(0.009+/-0.007 against 0.023+/-0.008; p< 0.001) and w3,6(0.011+/-0.007 against 0.023+/-0.008; p = 0.001). Joint symbolic dynamics provides an efficient non-linear representation of HR and SP interactions that offers simple physiological interpretations.

Differential regulation of the oscillations in sympathetic nerve activity and renal blood flow following volume expansion

Renal sympathetic nerve activity (RSNA) and renal blood flow (RBF) both show oscillations at various frequencies but the functional significance and regulation of these oscillations is not well understood. To establish whether the strength of these oscillations is under differential control we measured the frequency spectrum of RSNA and RBF following volume expansion in conscious rabbits. Seven days prior to experiment animals underwent surgery to implant an electrode for recording renal nerve activity and a flow probe for recording RBF. Volume expansion (Haemaccel, 1.5 ml min(-1) kg(-1) for 15 min) resulted in a 25 +/- 5% decrease in mean RSNA, paralleled by an increase in RBF to 60 +/- 12 ml min(-1) from resting levels of 51 +/- 11 ml min(-1). Renal denervated rabbits did not show an increase in RBF with volume expansion. Arterial baroreflexes were unaltered by volume expansion. Spectral analysis of the different frequencies in RSNA showed oscillations in RSNA between 0.2 and 0.4 Hz were selectively decreased following volume expansion (14 +/- 3 to 6 +/- 1% of total power in RSNA at < 3 Hz). A corresponding decrease in the strength of oscillations in RBF at this frequency was also seen (20 +/- 6 to 8 +/- 2%). In contrast, the strength of respiratory (0.8-2.0 Hz) and cardiac (3-6 Hz) related rhythms did not change with volume expansion. These results show that selective changes in the different frequency components of RSNA can occur. We suggest that input from cardiopulmonary receptors and/or other vascular beds, and/or altered vascular resistance after volume expansion can reduce the strength of the 0.3 Hz oscillation independent of changes in arterial baroreflex control of RSNA.