Importance of tachogram length and period of recording during noninvasive investigation of the autonomic nervous system

Heart Rate Variability Measurement through a Smart Wearable Device: Another Breakthrough for Personal Health Monitoring?

Heart rate variability (HRV) is a measurement of the fluctuation of time between each heartbeat and reflects the function of the autonomic nervous system. HRV is an important indicator for both physical and mental status and for broad-scope diseases. In this review, we discuss how wearable devices can be used to monitor HRV, and we compare the HRV monitoring function among different devices. In addition, we have reviewed the recent progress in HRV tracking with wearable devices and its value in health monitoring and disease diagnosis. Although many challenges remain, we believe HRV tracking with wearable devices is a promising tool that can be used to improve personal health.

Autonomic Responses During Acute Anterior Versus Inferior Myocardial Infarction: A Systematic Review and Meta-Analysis

Autonomic responses elicited by myocardial infarction vary depending on the site of injury, but accurate assessment using heart rate variability during the acute phase is limited. We systematically searched PubMed without language restrictions throughout July 2023. We reviewed studies reporting autonomic indices separately for anterior and inferior infarcts, followed by a meta-analysis of those reporting the standard deviation of the inter-beat interval between normal sinus beats during the initial 24 hours after the onset of symptoms. Six studies were included, comprising 341 patients (165 anterior, 176 inferior infarcts), all with satisfactory scores on the Newcastle-Ottawa quality scale. The estimated average of the standardized mean difference (based on the random-effects model) was -0.722 (95% confidence intervals: -0.943 to -0.501), which differed from zero (z=-6.416, p<0.0001). This finding indicates sympathetic and vagal dominance during acute anterior and inferior infarcts, respectively, with excessive responses likely contributing to early arrhythmogenesis. Despite the amelioration of autonomic dysfunction by revascularization, infarct location should be considered when commencing β-adrenergic receptor blockade, especially after delayed procedures.

Sex differences in estimates of cardiac autonomic function using heart rate variability: effects of dietary capsaicin

PURPOSE

Heart rate variability (HRV) estimates the autonomic nervous system (ANS) influence on the heart and appears sex-specific. Sensory afferents exhibit sex-specificity; although, it is unknown if Capsaicin, an agonist for transient receptor potential vanilloid channel-1 (TRPV₁), alters cardiac ANS activity in a sex-dependent manner, which could be important given the predictive nature of HRV on risk of developing hypertension. Thus, we explored if there was sex-specificity in the effect of capsaicin on estimated cardiac ANS activity.

METHODS

HRV was measured in 38 young males (M: n = 25) and females (F: n = 13), in a blinded-crossover design, after acute ingestion of placebo or capsaicin. Resting HR, RR-interval, root-mean-square of successive differences (RMSSD), natural log-transformed RMSSD (LnRMSSD), standard deviation of n-n intervals (SDNN), number of pairs of successive n-n intervals differing by > 50 ms (NN50), and percent NN50 (PNN50) were obtained using standard techniques.

RESULTS

Significant sex differences were observed in mean HR (M: 59 ± 9.3 vs. F: 65 ± 12 beats/min, p = 0.036, η² = 0.098), minimum HR (M: 47 ± 8.3 vs. F: 56 ± 12 beats/min, p = 0.014, η² = 0.124), and NN50 (M: 177 ± 143 vs. F: 29 ± 17, p < 0.001, η² = 0.249). There was a significant interaction of sex*treatment (p = 0.02, η² = 0.027) for RMSSD, where males increased (78 ± 55 vs. 91 ± 64 ms), and females decreased (105 ± 83 vs. 76 ± 43 ms), placebo vs. capsaicin.

CONCLUSION

This controlled study recapitulates sex differences in HR and HRV, but revealed a sexual dimorphism in the parasympathetic response to capsaicin, perhaps due to differing TRPV₁-afferent sensitivity, highlighting a potential mechanism for differential regulation of hemodynamics, and CVD risk, and should be considered in future studies.

Normalization of Cardiac Function After Bariatric Surgery Is Related to Autonomic Function and Vitamin D

PURPOSE

Subclinical cardiac dysfunction is common in patients with obesity. Bariatric surgery is associated with normalization of subclinical cardiac function in 50% of the patients with obesity. The aim of this study was to identify predictors for a lack of improvement of subclinical cardiac dysfunction 1-year post-bariatric surgery.

METHODS

Patients who were referred for bariatric surgery were enrolled in a longitudinal study. Inclusion criteria were age 35-65 years and BMI ≥ 35 kg/m². Patients with a suspicion of or known cardiovascular disease were excluded. Conventional and advanced echocardiography, Holter monitoring, and blood tests were performed pre- and 1-year post-bariatric surgery. Subclinical cardiac dysfunction was defined as either a reduced left ventricular ejection fraction, decreased global longitudinal strain (GLS), diastolic dysfunction, arrhythmia, or an increased BNP or hs Troponin I.

RESULTS

A total of 99 patients were included of whom 59 patients had cardiac dysfunction at baseline. Seventy-two patients completed the 1-year follow-up after bariatric surgery. There was a significant reduction in weight and cardiovascular risk factors. Parameters of cardiac function, such as GLS, improved. However, in 20 patients cardiac dysfunction persisted. Multivariate analysis identified a decreased heart rate variability (which is a measure of autonomic function), and a decreased vitamin D pre-surgery as predictors for subclinical cardiac dysfunction after bariatric surgery.

CONCLUSION

Although there was an overall improvement of cardiac function 1-year post-bariatric surgery, autonomic dysfunction and a decreased vitamin D pre-bariatric surgery were predictors for a lack of improvement of subclinical cardiac dysfunction.

Using sleep heart rate variability to investigate the sleep quality in children with obstructive sleep apnea

Background

Obstructive sleep apnea (OSA) is associated with impaired sleep quality and autonomic dysfunction. Adenotonsillectomy significantly improves subjective and objective sleep quality in children with OSA. However, the postoperative changes in heart rate variability (HRV) indices (indicators of cardiac autonomic function) and their importance remain inconclusive in childhood OSA. This retrospective case series aimed to investigate the association of sleep HRV indices, total OSA-18 questionnaire score (a subjective indicator of sleep quality) and polysomnographic parameters (objective indicators of sleep quality), and effects of adenotonsillectomy on HRV indices, total OSA-18 questionnaire score and polysomnographic parameters in children with OSA.

Methods

Seventy-six children with OSA were included in baseline analysis, of whom 64 (84%) completed at least 3 months follow-up examinations after adenotonsillectomy and were included in outcome analysis. Associations between baseline variables, and relationships with treatment-related changes were examined.

Results

Multivariable linear regression models in the baseline analysis revealed independent relationships between tonsil size and obstructive apnea-hypopnea index (OAHI), adenoidal-nasopharyngeal ratio and very low frequency (VLF) power of HRV (an indicator of sympathetic activity), and normalized low frequency power (an indicator of sympathetic activity) and OAHI. The outcome analysis showed that adenotonsillectomy significantly improved standard deviation of all normal-to-normal intervals, and high frequency power, QoL (in terms of reduced total OSA-18 questionnaire score), OAHI and hypoxemia. Using a conceptual serial multiple mediation model, % change in OSA-18 questionnaire score and % change in VLF power serially mediated the relationships between change in tonsil size and % change in OAHI.

Conclusions

The improvement in OAHI after adenotonsillectomy was serially mediated by reductions in total OSA-18 questionnaire score and VLF power. These preliminary findings are novel and provide a direction for future research to investigate the effects of VLF power-guided interventions on childhood OSA.

Effects of trunk posture on cardiovascular and autonomic nervous systems: A pilot study

Objective: Although regular and moderate physical activity has been shown to improve the cardiovascular and autonomic nervous systems, little has been done to study the effects of postural changes in the movement on the heart and autonomic nervous system. To uncover changes in cardiac function and autonomic nerves induced by different underlying posture transitions and explore which trunk postures lead to chronic sympathetic activation. Therefore, this study investigated the effects of trunk posture on the cardiovascular and autonomic nervous systems. Methods: Twelve male subjects (age 24.7 ± 1.3) underwent this study. The non-invasive cardiac output NICOM monitoring equipment and the FIRSTBEAT system are used to dynamically monitor seven trunk postures in the sitting position simultaneously (neutral position, posterior extension, forward flexion, left lateral flexion, right lateral flexion, left rotation, right rotation). Each posture was maintained for 3 min, and the interval between each movement was 3 min to ensure that each index returned to the baseline level. Repeated analysis of variance test was used to compare and analyze the differences in human cardiac function, heart rate variability index, and respiratory rate under different postures. Results: Compared with the related indicators of cardiac output in a neutral trunk position: the cardiac index (CI) was significantly reduced in forwarding flexion and left rotation (3.48 ± 0.34 vs. 3.21 ± 0.50; 3.48 ± 0.34 vs. 3.21 ± 0.46, Δ L/(min/m2)) (p = 0.016, p = 0.013), cardiac output decreased significantly (6.49 ± 0.78 vs. 5.93 ± 0.90; 6.49 ± 0.78 vs. 6.00 ± 0.96, Δ L/min) (p = 0.006, p = 0.014), the stroke volume (stroke volume)decreased significantly (87.90 ± 15.10 vs. 81.04 ± 16.35; 87.90 ± 15.10 vs. 79.24 ± 16.83, Δ ml/beat) (p = 0.017, p = 0.0003); heart rate increased significantly in posterior extension (75.08 ± 10.43 vs. 78.42 ± 10.18, Δ beat/min) (p = 0.001); left rotation stroke volume index (SVI) decreased significantly (47.28 ± 7.97 vs. 46.14 ± 8.06, Δ ml/m2) (p = 0.0003); in the analysis of HRV-related indicators, compared with the neutral trunk position, the LF/HF of the posterior extension was significantly increased (1.90 ± 1.38 vs. 3.00 ± 1.17, p = 0.037), and the LF/HF of the forward flexion was significantly increased (1.90 ± 1.38 vs. 2.85 ± 1.41, p = 0.041), and the frequency-domain index LF/HF of right rotation was significantly increased (1.90 ± 1.38 vs. 4.06 ± 2.19, p = 0.008). There was no significant difference in respiratory rate (p > 0.05). Conclusion: A neutral trunk is the best resting position, and deviations from a neutral trunk position can affect the cardiovascular and autonomic nervous systems, resulting in decreased stroke volume, increased heart rate, and relative activation of sympathetic tone.

Effects of a Short-Term Resistance-Training Program on Heart Rate Variability in Children With Cystic Fibrosis-A Randomized Controlled Trial

Background: Cystic fibrosis (CF) affects the autonomic nervous system (ANS) and exercise in healthy children modulates the interaction between sympathetic and parasympathetic activity. This study aimed to evaluate the effects of a short-term resistance exercise program on heart rate variability (HRV) in children and adolescents with CF.

Methods: A randomized controlled trial was carried out in children diagnosed with CF aged 6–18 years. Individuals were divided into two groups: control (CON) and resistance-training (EX). Individuals in the EX group completed an individualized guided resistance program (5-RM—60–80%) for 8 weeks (3 sessions of 60 min/week). Upper and lower limbs exercises (seated bench press, seated lateral row, and leg press) were used. HRV was measured using a Suunto watch with subjects in lying position.

Results: Nineteen subjects (13 boys) were included (CON = 11; and EX = 8). Mean age was 12.2 ± 3.3, FEV₁ (forced expiratory volume in the first second) z-score was 1.72 ± 1.54 and peak oxygen consumption (VO₂peak) 42.7 ± 7.4 mL.Kg^–1.min^–1. Exercise induced significant changes in the frequency-domain variables, including a decrease in LF power (p = 0.001, d = 0.98) and LF/HF ratio (p = 0.020, d = 0.92), and an increase in HF power (p = 0.001, d = −0.97), compared to the CON group. No significant changes were found for time-domain variables, although increases with a moderate effect size were seen for SDNN (p = 0.152, d = −0.41) and RMSSD (p = 0.059, d = −0.49) compared to the CON group.

Conclusion: A short-term resistance exercise-training program was able to modulate HRV in children and adolescents with CF presenting mild to moderate lung function impairment and good physical condition.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier NCT04293926.

Low Heart Rate Variability Predicts Stroke and Other Complications in the First Six Postoperative Months After a Hip Fracture Operation

Background: One-year mortality after hip fractures is underestimated and is reported as 25%. An improved risk stratifying could contribute to a better follow up of these patients. Heart Rate Variability (HRV) is an easy point-of-care investigation and is been used in cardiology, endocrinology, and perioperative care. This observational study intended to explore relevant associations between HRV parameters and 6-months mortality and morbidity after a hip fracture. Methods: One hundred and sixty-five patients admitted to two hospitals were included, and short-time HRV measurements (5 min, and 10 min at the two hospitals, respectively) were obtained. Mortality data were gathered by means of the Norwegian central address register. Patients, close relatives of patients, and in some cases their general physicians or nursery home physicians were interviewed 6 months postoperatively regarding the incidence of pneumonia, cardiac events, or stroke. Results: One and hundred fifty-seven (95.2%) patients were followed up after 6 months post-surgery. Twenty-one (13%) died during this period. Twenty patients (13%) developed pneumonia, eight (5 %) stroke, and four (2%) myocardial infarction. No HRV parameter was associated with 6-month general mortality. However, patients who developed stroke had significantly lower High Frequency Power (HF, p < 0.001) and lower Very Low Frequency Power (VLF, p = 0.003) at inclusion compared to patients without complications. Patients who developed pneumonia had at the inclusion lower root mean square of successive differences (RMSSD, p = 0.044). Patients with a history of coronary heart disease (n = 41) showed a mortality of 7%. Mortality in this group was associated with standard deviation of beat-to-beat intervals (SDNN, p = 0.006), Total Power (TP, p = 0.009), HF (p = 0.026), and Low Frequency Power (LF, p = 0.012). Beta-blocker intake was associated with lower heart rate, but not with differences in HRV parameters. Conclusion: In this exploratory study, we present for the first-time significant associations between different preoperative HRV parameters and stroke, myocardial infarction, and pneumonia during a 6-month period after hip fracture. HRV might be a simple and effective tool to identify patients at risk that would warrant better follow-up.

Wearable Devices Suitable for Monitoring Twenty Four Hour Heart Rate Variability in Military Populations

Heart rate variability (HRV) measurements provide information on the autonomic nervous system and the balance between parasympathetic and sympathetic activity. A high HRV can be advantageous, reflecting the ability of the autonomic nervous system to adapt, whereas a low HRV can be indicative of fatigue, overtraining or health issues. There has been a surge in wearable devices that claim to measure HRV. Some of these include spot measurements, whilst others only record during periods of rest and/or sleep. Few are capable of continuously measuring HRV (≥24 h). We undertook a narrative review of the literature with the aim to determine which currently available wearable devices are capable of measuring continuous, precise HRV measures. The review also aims to evaluate which devices would be suitable in a field setting specific to military populations. The Polar H10 appears to be the most accurate wearable device when compared to criterion measures and even appears to supersede traditional methods during exercise. However, currently, the H10 must be paired with a watch to enable the raw data to be extracted for HRV analysis if users need to avoid using an app (for security or data ownership reasons) which incurs additional cost.

A Critical Review of Ultra-Short-Term Heart Rate Variability Norms Research

Heart rate variability (HRV) is the fluctuation in time between successive heartbeats and is defined by interbeat intervals. Researchers have shown that short-term (∼5-min) and long-term (≥24-h) HRV measurements are associated with adaptability, health, mobilization, and use of limited regulatory resources, and performance. Long-term HRV recordings predict health outcomes heart attack, stroke, and all-cause mortality. Despite the prognostic value of long-term HRV assessment, it has not been broadly integrated into mainstream medical care or personal health monitoring. Although short-term HRV measurement does not require ambulatory monitoring and the cost of long-term assessment, it is underutilized in medical care. Among the diverse reasons for the slow adoption of short-term HRV measurement is its prohibitive time cost (∼5 min). Researchers have addressed this issue by investigating the criterion validity of ultra-short-term (UST) HRV measurements of less than 5-min duration compared with short-term recordings. The criterion validity of a method indicates that a novel measurement procedure produces comparable results to a currently validated measurement tool. We evaluated 28 studies that reported UST HRV features with a minimum of 20 participants; of these 17 did not investigate criterion validity and 8 primarily used correlational and/or group difference criteria. The correlational and group difference criteria were insufficient because they did not control for measurement bias. Only three studies used a limits of agreement (LOA) criterion that specified a priori an acceptable difference between novel and validated values in absolute units. Whereas the selection of rigorous criterion validity methods is essential, researchers also need to address such issues as acceptable measurement bias and control of artifacts. UST measurements are proxies of proxies. They seek to replace short-term values which, in turn, attempt to estimate long-term metrics. Further adoption of UST HRV measurements requires compelling evidence that these metrics can forecast real-world health or performance outcomes. Furthermore, a single false heartbeat can dramatically alter HRV metrics. UST measurement solutions must automatically edit artifactual interbeat interval values otherwise HRV measurements will be invalid. These are the formidable challenges that must be addressed before HRV monitoring can be accepted for widespread use in medicine and personal health care.

Subclinical cardiac dysfunction in obesity patients is linked to autonomic dysfunction: findings from the CARDIOBESE study

Aims

Obesity doubles the lifetime risk of developing heart failure. Current knowledge on the role of obesity in causing cardiac dysfunction is insufficient for optimal risk stratification. The aim of this study was first to estimate the prevalence of subclinical cardiac dysfunction in obesity patients and second to investigate the underlying pathophysiology.

Methods and results

The CARDIOBESE study is a cross‐sectional multicentre study of 100 obesity patients [body mass index (BMI) ≥ 35 kg/m²] without known cardiovascular disease and 50 age‐matched and gender‐matched non‐obese controls (BMI ≤ 30 kg/m²). Echocardiography was performed, blood samples were collected, and a Holter monitor was affixed. Fifty‐nine obesity patients [48 (42–50) years, 70% female] showed subclinical cardiac dysfunction: 57 patients had decreased global longitudinal strain (GLS), and two patients with normal GLS had either diastolic dysfunction or increased brain natriuretic peptide (BNP). Only one non‐obese control had diastolic dysfunction, and none had another sign of cardiac dysfunction. Multivariable logistic analysis identified male gender and standard deviation of all NN intervals (SDNN) index, which is a measure of autonomic dysfunction, as independent significant risk factors for subclinical cardiac dysfunction in obesity patients.

Conclusions

There was a high prevalence (61%) of subclinical cardiac dysfunction in obesity patients without known cardiovascular disease, which appeared to be best identified by GLS. Subclinical cardiac dysfunction in obesity was linked to autonomic dysfunction and male gender, and not to the presence of traditional cardiac risk factors, increased C‐reactive protein, increased BNP, increased high‐sensitivity troponin I, or increased left ventricular mass.

The Acute Effects of Aerobic Exercise on Cognitive Flexibility and Task-Related Heart Rate Variability in Children With ADHD and Healthy Controls

Objective: To investigate cognitive flexibility and task-related heart rate variability following moderately intense aerobic exercise and after watching a video in both children with ADHD and healthy controls. Method: Using a cross-over design, participants completed cognitive assessments following exercise and a physically inactive control condition. Behavioral performance was assessed using the Alternate Uses task. Heart rate variability was recorded via electrocardiography during the cognitive task. Results: The statistical analysis revealed that in comparison with the control condition, both groups showed higher cognitive flexibility following aerobic exercise. Moreover, decreased low frequency and high frequency power was observed in the exercise condition. Conclusion: The findings suggest that exercise elicits similar benefits for cognitive flexibility in children with ADHD and healthy controls, partly due to an increase in arousal induced by parasympathetic withdrawal.

Stressing the accuracy: Wrist-worn wearable sensor validation over different conditions

Wearable sensors are promising instruments for conducting both laboratory and ambulatory research in psychophysiology. However, scholars should be aware of their measurement error and the conditions in which accuracy is achieved. This study aimed to assess the accuracy of a wearable sensor designed for research purposes, the E4 wristband (Empatica, Milan, Italy), in measuring heart rate (HR), heart rate variability (HRV), and skin conductance (SC) over five laboratory conditions widely used in stress reactivity research (seated rest, paced breathing, orthostatic, Stroop, speech task) and two ecological conditions (slow walking, keyboard typing). Forty healthy participants concurrently wore the wristband and two gold standard measurement systems (i.e., electrocardiography and finger SC sensor). The wristband accuracy was determined by evaluating the signal quality and the correlations with and the Bland-Altman plots against gold standard-derived measurements. Moreover, exploratory analyses were performed to assess predictors of measurement error. Mean HR measures showed the best accuracy over all conditions. HRV measures showed satisfactory accuracy in seated rest, paced breathing, and recovery conditions but not in dynamic conditions, including speaking. Accuracy was diminished by wrist movements, cognitive and emotional stress, nonstationarity, and larger wrist circumferences. Wrist SC measures showed neither correlation nor visual resemblance with finger SC signal, suggesting that the two sites may reflect different phenomena. Future studies are needed to assess the responsivity of wrist SC to emotional and cognitive stress. Limitations and implications for laboratory and ambulatory research are discussed.

Large-scale wearable data reveal digital phenotypes for daily-life stress detection

Physiological signals have shown to be reliable indicators of stress in laboratory studies, yet large-scale ambulatory validation is lacking. We present a large-scale cross-sectional study for ambulatory stress detection, consisting of 1002 subjects, containing subjects' demographics, baseline psychological information, and five consecutive days of free-living physiological and contextual measurements, collected through wearable devices and smartphones. This dataset represents a healthy population, showing associations between wearable physiological signals and self-reported daily-life stress. Using a data-driven approach, we identified digital phenotypes characterized by self-reported poor health indicators and high depression, anxiety and stress scores that are associated with blunted physiological responses to stress. These results emphasize the need for large-scale collections of multi-sensor data, to build personalized stress models for precision medicine.

Cardiac autonomic function during postural changes and exercise in people with multiple sclerosis: A cross-sectional study

BACKGROUND

People with multiple sclerosis (PwMS) often develop an autonomic dysfunction (AD), which onset should be assessed early at a subclinical level, as it may interfere with pharmacological treatments and exercise.

OBJECTIVE

To evaluate basal cardiac autonomic tone, its modulations during sit-to-stand, sub-maximal exercise and recovery in PwMS without clinical overt AD and its relationships with fatigue perception.

METHODS

Twenty-three PwMS (55 ± 8 yrs [mean ± SD]; EDSS score 5.7 ± 1.3) and 20 age-matched healthy controls (HC; 55 ± 8yrs) were enrolled. ECG was digitally acquired during:1) sitting at rest (low sympathetic activation); 2) standing (light sympathetic activation); and 3) during light exercise (moderate sympathetic activation) and recovery. Parasympathetic and sympatho-vagal parameters of heart rate (HR) variability in time and frequency domains were calculated from beat series.

RESULTS

HR was slightly but not significantly higher in PwMS compared to HC in all experimental conditions. Parasympathetic indexes were significantly lower (p < 0.05) in PwMS compared to HC during baseline sitting and post-exercise recovery, whereas sympathovagal parameters were similar in both groups. No correlation between autonomic tone and perceived fatigue was observed.

CONCLUSION

Parasympathetic tone appears to be impaired in PwMS basal and post-exercise conditions, but not during postural challenge and exercise. In addition, AD does not affect perceived fatigue.

An Overview of Heart Rate Variability Metrics and Norms

Healthy biological systems exhibit complex patterns of variability that can be described by mathematical chaos. Heart rate variability (HRV) consists of changes in the time intervals between consecutive heartbeats called interbeat intervals (IBIs). A healthy heart is not a metronome. The oscillations of a healthy heart are complex and constantly changing, which allow the cardiovascular system to rapidly adjust to sudden physical and psychological challenges to homeostasis. This article briefly reviews current perspectives on the mechanisms that generate 24 h, short-term (~5 min), and ultra-short-term (<5 min) HRV, the importance of HRV, and its implications for health and performance. The authors provide an overview of widely-used HRV time-domain, frequency-domain, and non-linear metrics. Time-domain indices quantify the amount of HRV observed during monitoring periods that may range from ~2 min to 24 h. Frequency-domain values calculate the absolute or relative amount of signal energy within component bands. Non-linear measurements quantify the unpredictability and complexity of a series of IBIs. The authors survey published normative values for clinical, healthy, and optimal performance populations. They stress the importance of measurement context, including recording period length, subject age, and sex, on baseline HRV values. They caution that 24 h, short-term, and ultra-short-term normative values are not interchangeable. They encourage professionals to supplement published norms with findings from their own specialized populations. Finally, the authors provide an overview of HRV assessment strategies for clinical and optimal performance interventions.

Decreases in heart rate variability are associated with postoperative complications in hip fracture patients

Background

To explore relevant associations between deviations in linear and nonlinear heart rate variability (HRV) scores, and short-term morbidity and mortality in patients undergoing hip-surgery after a fracture.

Methods

165 patients with hip fractures being admitted for surgery at two hospitals were included in a prospective cohort study. A short-term ECG was recorded within 24 hours of arrival. 15 patients had to be excluded due to insufficient quality of the ECG recordings. 150 patients were included in the final analysis. Linear parameters were calculated in time domain: standard deviation of NN intervals (SDNN), root mean square of successive differences (rMSSD); and frequency domain: Total Power (TP), High Frequency Power (HF), Low Frequency Power (LF), Very Low Frequency Power (VLF), and the ratio of LF/HF. Postoperative outcome was evaluated at the time of discharge. This included occurrence of pneumonia, overall infection rate, stroke, myocardial infarction, and all-cause mortality.

Results

Patients experiencing complications had significantly lower rMSSD (p = 0.04), and TP (p = 0.03) preoperatively. Postoperative infections were predicted by decreased VLF preoperatively (p = 0.04). There was a significant association between pneumonia and LF/HF<1 (p = 0.03). The likelihood ratio to develop pneumonia when LF/HF < 1 was 6,1.

Conclusion

HRV seems to reflect the general frailty of the patient with hip fracture and might be used to identify patients in need of increased surveillance or prophylactic treatment.

The Difference Between Exercise-Induced Autonomic and Fitness Changes Measured After 12 and 20 Weeks of Medium-to-High Intensity Military Training

Grant, CC, Mongwe, L, Janse van Rensburg, DC, Fletcher, L, Wood, PS, Terblanche, E, and du Toit, PJ. The difference between exercise-induced autonomic and fitness changes measured after 12 and 20 weeks of medium-to-high intensity military training. J Strength Cond Res 30(9): 2453-2459, 2016-The aim of this study was to compare the physical fitness, based on VO2max and exercise-induced cardiac autonomic changes, measured by heart rate variability (HRV) of 12 weeks with 20 weeks of training in the South African National Defence Force. Recruits (n = 154) participated in a medium-to-high intensity exercise intervention (daily energy expenditure: 8,485 kJ·d). The significant effect on VO2max between weeks 1 and 12 (48.57, SD = 9.25 vs. 53.36, SD = 7.21] did not continue during weeks 12-20 (53.36, SD = 7.21 vs. 53.87, SD = 7.87). No changes in the supine low frequency (LF)/high frequency (HF) (0.48, SD = 0.51 vs. 0.41, SD = 0.64) or the standing LF/HF (4.02, SD = 5.14 vs. 3.91, SD = 5.28), an indicator of autonomic balance and a possible indicator of overtraining syndrome, suggests that overtraining did not take place during weeks 12-20. This was confirmed with further decreases in supine and standing heart rate. However, the power of the vagal-induced variability continued to increase after 12 weeks. Increased vagal influence without concurrent change in autonomic balance may be interpreted as decreased sympathetic cardiac control. It is important to note that although no fitness changes were detected, positive cardiac autonomic conditioning did continue between weeks 12 and 20, as measured by increased vagal-induced HRV and decreased sympathetic influence on cardiac control. Results may be extrapolated to training in the normal population/athletes after a medium-to-high intensity exercise program, as this intervention was a closely monitored and standardized exercise program.

Guidelines for Reporting Articles on Psychiatry and Heart rate variability (GRAPH): recommendations to advance research communication

The number of publications investigating heart rate variability (HRV) in psychiatry and the behavioral sciences has increased markedly in the last decade. In addition to the significant debates surrounding ideal methods to collect and interpret measures of HRV, standardized reporting of methodology in this field is lacking. Commonly cited recommendations were designed well before recent calls to improve research communication and reproducibility across disciplines. In an effort to standardize reporting, we propose the Guidelines for Reporting Articles on Psychiatry and Heart rate variability (GRAPH), a checklist with four domains: participant selection, interbeat interval collection, data preparation and HRV calculation. This paper provides an overview of these four domains and why their standardized reporting is necessary to suitably evaluate HRV research in psychiatry and related disciplines. Adherence to these communication guidelines will help expedite the translation of HRV research into a potential psychiatric biomarker by improving interpretation, reproducibility and future meta-analyses.

A comparison between heart rate and heart rate variability as indicators of cardiac health and fitness

Quantification of cardiac autonomic activity and control via heart rate (HR) and heart rate variability (HRV) is known to provide prognostic information in clinical populations. Issues with regard to standardization and interpretation of HRV data make the use of the more easily accessible HR on its own as an indicator of autonomic cardiac control very appealing. The aim of this study was to investigate the strength of associations between an important cardio vascular health metric such as VO2max and the following: HR, HRV indicators, and HR normalized HRV indicators. A cross sectional descriptive study was done including 145 healthy volunteers aged between 18 and 22 years. HRV was quantified by time domain, frequency domain and Poincaré plot analysis. Indirect VO2max was determined using the Multistage Coopers test. The Pearson correlation coefficient was calculated to quantify the strength of the associations. Both simple linear and multiple stepwise regressions were performed to be able to discriminate between the role of the individual indicators as well as their combined association with VO2max. Only HR, RR interval, and pNN50 showed significant (p < 0.01, p < 0.01, and p = 0.03) correlations with VO2max. Stepwise multiple regression indicated that, when combining all HRV indicators the most important predictor of cardio vascular fitness as represented by VO2max, is HR. HR explains 17% of the variation, while the inclusion of HF (high frequency HRV indicator) added only an additional 3.1% to the coefficient of determination. Results also showed when testing the normalized indicators, HR explained of the largest percentage of the changes in VO2max (16.5%). Thus, HR on its own is the most important predictor of changes in an important cardiac health metric such as VO2max. These results may indicate that during investigation of exercise ability (VO2max) phenomena, quantification of HRV may not add significant value.

The contribution of preintervention blood pressure, VO2max, BMI, autonomic function and gender to exercise-induced changes in heart rate variability

INTRODUCTION

The quantification of heart rate variability (HRV) is a tool to assess the interaction between exercise and autonomic control, as well as the pathophysiology of diseases affecting autonomic function. Little is known about the influence of genetically influenced physiology on exercise-induced changes in autonomic cardiac regulation. It was theorised that preintervention values for blood pressure, VO2max, body mass index (BMI), autonomic function and gender contribute significantly to the exercise-induced changes in HRV.

METHODS

A 12-week, medium-to-high intensity exercise intervention was completed by 183 volunteers (18-22 years). Data were sampled at baseline and after 12 weeks. Standard time domain, frequency domain and Poincaré HRV quantification techniques were implemented. Regression analysis was performed to determine the influences of the predictors (baseline values for low frequency  (LF), high frequency (HF), BMI, VO2max, gender, blood pressure) on the exercise-induced response of the dependent variables (changes in HRV-indicator values).

RESULTS

Parameters found to be significant (p<0.05) predictors of exercise-induced changes were LF, HF and systolic blood pressure in, respectively, 10, 5 and 2 of the 12 regressions performed. The results indicated that the independent variables contribute between 12.83% and 29.82%, depending on the specific HRV indicator, to the exercise-induced changes in the autonomic nervous system.

CONCLUSIONS

Preintervention autonomic status, as represented specifically by LF, is the most important determinant of cardiac autonomic response to an exercise intervention in a healthy study population. Baseline autonomic function could thus be a significant confounder in the outcome of exercise study results.

Heart rate variability assessment of the effect of physical training on autonomic cardiac control

BACKGROUND

The effect of exercise interventions on autonomic nervous system (ANS) control of the heart by heart rate variability (HRV) is often investigated in just one position. It was hypothesized that results of exercise-induced changes on ANS are dependent on body position and that it is possible to distinguish between exercise induced changes in vagal and sympathetic influence by taking measurements in different body positions.

METHODS

One hundred eighty-three (male = 100, female = 83) healthy volunteers, between 18 and 22 years, participated in a prospective twelve week medium to high intensity exercise intervention study with a self-control design. The influence of the exercise intervention was investigated on supine, rising, and standing as well as on the orthostatic response. Time domain, frequency domain and nonlinear (Poincaré) HRV analysis were performed.

RESULTS

The exercise intervention lead to a significant increase (P < 0.05) in vagal influence during supine, rising, and standing. Sympathetic control in the supine position was decreased and increased during rising and standing. In the initial orthostatic response to rising from the supine position, the exercise intervention lead to increased (P < 0.05) vagal withdrawal as well as increased sympathetic control. The orthostatic response measured as the difference between standing and supine indicated only an exercise induced increase in sympathetic control.

CONCLUSIONS

Exercise-induced changes in sympathetic and parasympathetic ANS control differ, depending on posture and period of measurement. Exercise induced changes in parasympathetic and sympathetic outflow, respectively, can be extracted from measurements from supine, through the orthostatic response, to standing, thereby detecting changes in ANS that are otherwise obscured.