Pitfalls of assessment of autonomic function by heart rate variability

Pre-movement muscle co-contraction associated with motor performance deterioration under high reward conditions

Reward usually enhances task performance, but exceptionally large rewards can impede performance due to psychological pressure. In this study, we investigated motor activity changes in high-reward situations and identified indicators for performance decline. Fourteen healthy adults practiced a velocity-dependent right-hand motor task for three days, followed by a test day with varying monetary reward for each trial. Participants were divided into low performers (LPs) and high performers (HPs) according to whether success rate decreased or increased, respectively, on the highest reward trials compared to lower reward trials. Both LPs and HPs demonstrated increased hand velocity during higher reward trials, but only LPs exhibited a significant increase in velocity variance. There was also a negative correlation between the pre-movement co-contraction index (CCI) of the biceps and triceps muscles and success rate on the highest reward trials. This correlation was confirmed in a second experiment with 12 newly recruited participants, suggesting that pre-movement CCI is a marker for performance decline caused by high reward. These findings suggest that interventions to reduce pre-movement CCI such as biofeedback training could be useful for preventing the paradoxical decline in motor performance associated with high rewards.

A comprehensive evaluation of linear and non-linear HRV parameters between paced breathing and stressful mental state

Background

Heart rate variability (HRV) is a crucial metric that provides valuable insight into the balance between relaxation and stress. Previous research has shown that most HRV parameters improve during periods of mental relaxation, while decreasing during tasks involving cognitive workload. Although a comprehensive analysis of both linear and non-linear HRV parameters has been carried out in existing literature, there still exists a need for further research in this area. Additionally, limited knowledge exists regarding how specific interventions may influence the interpretation of these parameters and how the different parameters correlate under different interventions. This study aims to address these gaps by conducting a thorough comparison of different linear and non-linear HRV parameters under mentally relaxed versus stressful states.

Methodology

Participants were randomly and equally divided among two between-subjects groups: relaxed-stress (RS) (N = 22) and stress-relaxed (SR) (N = 22). In the RS group, a paced breathing task was given for 5 min to create relaxation, and was followed by a 5-min time-based mental calculation task to create stress. In the SR group, the order of the stress and relaxed tasks was reversed. There was a washout period of 15 min after the first task in both groups.

Results

Of the 37 HRV parameters, 33 differed significantly between the two interventions. The majority of the parameters exhibited an improving and degrading tendency of HRV parameters in the relaxed and stressed states, respectively. The correlation of the majority of HRV parameters decreases during stress, while prominent time domain and geometric domain parameters stand out in the correlation.

Conclusion

Overall, HRV parameters can be reliably used to assess a person's relaxed and stressed mental states during paced breathing and mental arithmetic task respectively. Furthermore, non-linear HRV parameters provide accurate estimators of the mental state, in addition to the commonly used linear parameters.

Effects of Postural Resonance on Skin Sympathetic Nerve Activity and Blood Pressure: A Pilot Study Evaluating Vascular Tone Baroreflex Stimulation Through Biofeedback

Heart rate and vascular tension baroreflex exhibit resonance characteristics at approximately 0.1 and 0.03 Hz. In this study, we aimed to induce postural resonance (PR) through rhythmic postural adjustments. To assess the viability of this technique, we investigated the acute impacts of postural resonance on blood pressure, sympathetic nerve activity, and mood. Fifteen healthy study participants, consisting of 8 males and 7 females, were selected for this self-controlled study. Skin sympathetic nerve activity was continuously monitored during both the intervention and stress test on the experimental day. After PR intervention, the diastolic blood pressure and mean arterial pressure in the PR group exhibited significant reductions compared to the CON group (P = 0.032, CON = 71.67 ± 2.348, PR = 64.08 ± 2.35; P = 0.041, CON = 75.00 ± 2.17, PR = 81.67 ± 2.17). After PR intervention both left brachial ankle pulse wave velocity and right brachial ankle pulse wave velocity exhibited a significant reduction compared to pre-intervention levels (from 1115.86 ± 150.08 to 1048.43 ± 127.40 cm/s, p < 0.001; 1103.86 ± 144.35 to 1060.43 ± 121.35 cm/s, p = 0.018). PR intervention also led to a significant decrease in burst frequency and duration (P = 0.049; CON = 8.96 ± 1.17, PR = 5.51 ± 1.17) and a noteworthy decrease in burst amplitude and burst threshold during the cold-pressor test (P = 0.002; P = 0.002). Additionally, VAS scores exhibited a substantial increase following PR (P = 0.035, CON = 28.4 ± 4.49, PR = 42.17 ± 4.10). PR can induce resonance effects within the cardiovascular system, resulting in the effective reduction of blood pressure, skin sympathetic nerve activity and pulse wave velocity, and decreased burst amplitude and burst threshold of the sympathetic nerve during the cold-pressor test.

Modification of heart rate variability induced by focal muscle vibration in patients with severe acquired brain injury

BACKGROUND/PURPOSE

Heart rate variability (HRV) is a biomarker of autonomic nervous system (ANS) reaction in persons with severe acquired brain injury (sABI) who undergo a rehabilitation treatment, such as focal muscle vibration (FMV).This study aims to evaluate if and how FMV can modulate HRV and to compare potential differences in FMV modulation in HRV between patients with sABI and healthy controls.

METHODS

Ten patients with sABI and seven healthy controls have been recruited. Each individual underwent the same stimulation protocol (four consecutive trains of vibration of 5 minutes each with a 1-minute pause). HRV was analyzed through the ratio of frequency domain heart-rate variability (LF/HF).

RESULTS

In the control group, after performing FMV, a significant LF/HF difference was observed in the in the second vibration session compared to the POST phase. Patients with SABI treated on the affected side showed a statistically significant LF/HF difference in the PRE compared to the first vibration session.

CONCLUSION

These preliminary results suggest that FMV may modify the cardiac ANS activity in patients with sABI.

Case-control study of heart rate variability and sleep apnea in childhood sickle cell disease

Obstructive sleep apnea (OSA) is common in sickle cell disease (SCD) despite the absence of overweight, suggesting a specific pathophysiology. We previously showed that otherwise healthy children with increased pharyngeal compliance, a main endotype of OSA, exhibited decreased sympathetic modulation. Our objective was to assess whether modifications of heart rate variability (HRV) and compliance are associated in SCD. Cases (children with SCD, African or Caribbean ethnicity) and controls (otherwise healthy children, same ethnicity), aged 4-18 years, were selected from our database of children referred for OSA and matched for sex, age, and obstructive apnea-hypopnoea index (OAHI) score. The children underwent polysomnography and acoustic pharyngometry (to compute compliance). HRV analyses were performed from 5 min ECG recordings in wakeful, NREM, and REM sleep states and from the whole night. Twenty-one pairs were analysed (median age 10.5 years, 24 girls). Children with SCD had lower BMI z-scores and more tonsil hypertrophy than control children. Children with SCD and OSA (OAHI ≥2/hour) were characterised by lower compliance than children with SCD without OSA. An inverse relationship between compliance and SD2 (HRV from whole night, inversely related to sympathetic modulation) was evidenced (negative relationship in SCD: R = -0.63, p = 0.002 vs. positive relationship in controls R = 0.59, p = 0.006). In conclusion, while the decrease in sympathetic modulation in control children may contribute to increasing pharyngeal compliance, its decrease seems protective in children with sickle cell disease, which underlines the specificity of OSAS pathophysiology in SCD that could be due to sickle cell disease related smooth muscle dystonia.

Association of Autonomic Symptom Burden with Sudden Sensorineural Hearing Loss

OBJECTIVE

To investigate the autonomic symptom burden in patients with sudden sensorineural hearing loss (SSNHL) and its association with the severity and prognosis.

STUDY DESIGN

Observational prospective study.

SETTING

Tertiary academic medical center.

METHODS

Patients diagnosed with SSNHL at a single medical center completed the COMPASS 31 questionnaire, which assesses dysautonomia across 6 domains with 31 questions. A total COMPASS 31 score was calculated by summing the scores from each weighted domain. The treatment outcome was evaluated by the percentage of recovery, calculated as the hearing gain in pure tone average (PTA) after treatment divided by the pretreatment PTA difference between the 2 ears. We defined poor recovery as a percentage of recovery <80%.

RESULTS

A total of 63 SSNHL patients were included. The mean COMPASS 31 score was 23.4 (SD 14). Patients with poor recovery had significantly higher COMPASS 31 scores than those with good recovery (mean 26.4 [SD 14.4] vs 16.9 [SD 10.4]; 95% confidence interval [CI] 2-17). There was a negative association between COMPASS 31 score and both hearing gain (r = -.323, 95% CI -0.082 to -0.529) and percentage of recovery (r = -.365, 95% CI -0.129 to -0.562). Multivariate analyses of independent factors indicate that patients with higher COMPASS 31 scores had a greater risk for poor recovery (OR 1.06 [95% CI 1.003-1.117]).

CONCLUSION

This study highlights the association between autonomic symptom burden and poor hearing outcomes in SSNHL patients. The findings underscore the importance of evaluating autonomic function during the treatment of SSNHL.

Physiological Responses to Organizational Stressors Among Police Managers

Police officers demonstrate increased risk of physical and mental health conditions due to repeated and prolonged exposure to stressful occupational conditions. Occupational stress is broken into two types: operational stress, related to the content of field duties (e.g., physical demands); and organizational stress, related to cultural and structural contexts (e.g., interpersonal relationships). Applied police research focuses on physiological activation in operational tasks as a mechanism explaining health risk and non-optimal performance outcomes. However, recent survey-based studies indicate numerous organizational stressors associated with self-reported mental health symptoms. The question of whether organizational stressors elicit significant physiological activity remains unknown. The current proof-of-concept field study tests the hypothesis that police managers will display significant physiological reactivity before, during, and after engaging in reality-based scenarios representative of stressful police management tasks developed from evidence-based pedagogical approaches. A sample of 25 training police managers (7 female, M = 16 +/- 5.3 years of experience) completed 5 reality-based scenarios, including resolving a heated conflict between colleagues, delivering negative feedback to a subordinate, and critical incident command. Significant increases in heart rate relative to rest were observed during all tasks, and in anticipation of several tasks. Greater increases in reactive heart rate were associated with longer recovery times. Sex differences and relationships between objective biological and subjective psychological measures of stress are discussed. The current findings demonstrate significant physiological responses to organizational stressors similar to levels observed during operational tasks, despite the absence of physical or aerobic exertion. Implications for police health and training are discussed.

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.

Non-invasive parameters of autonomic function using beat-to-beat cardiovascular variations and arterial stiffness in hypertensive individuals: a systematic review

PURPOSE

Non-invasive, beat-to-beat variations in physiological indices provide an opportunity for more accessible assessment of autonomic dysfunction. The potential association between the changes in these parameters and arterial stiffness in hypertension remains poorly understood. This systematic review aims to investigate the association between non-invasive indicators of autonomic function based on beat-to-beat cardiovascular signals with arterial stiffness in individuals with hypertension.

METHODS

Four electronic databases were searched from inception to June 2022. Studies that investigated non-invasive parameters of arterial stiffness and autonomic function using beat-to-beat cardiovascular signals over a period of > 5min were included. Study quality was assessed using the STROBE criteria. Two authors screened the titles, abstracts, and full texts independently.

RESULTS

Nineteen studies met the inclusion criteria. A comprehensive overview of experimental design for assessing autonomic function in terms of baroreflex sensitivity and beat-to-beat cardiovascular variabilities, as well as arterial stiffness, was presented. Alterations in non-invasive indicators of autonomic function, which included baroreflex sensitivity, beat-to-beat cardiovascular variabilities and hemodynamic changes in response to autonomic challenges, as well as arterial stiffness, were identified in individuals with hypertension. A mixed result was found in terms of the association between non-invasive quantitative autonomic indices and arterial stiffness in hypertensive individuals. Nine out of 12 studies which quantified baroreflex sensitivity revealed a significant association with arterial stiffness parameters. Three studies estimated beat-to-beat heart rate variability and only one study reported a significant relationship with arterial stiffness indices. Three out of five studies which studied beat-to-beat blood pressure variability showed a significant association with arterial structural changes. One study revealed that hemodynamic changes in response to autonomic challenges were significantly correlated with arterial stiffness parameters.

CONCLUSIONS

The current review demonstrated alteration in autonomic function, which encompasses both the sympathetic and parasympathetic modulation of sinus node function and vasomotor tone (derived from beat-to-beat cardiovascular signals) in hypertension, and a significant association between some of these parameters with arterial stiffness. By employing non-invasive measurements to monitor changes in autonomic function and arterial remodeling in individuals with hypertension, we would be able to enhance our ability to identify individuals at high risk of cardiovascular disease. Understanding the intricate relationships among these cardiovascular variability measures and arterial stiffness could contribute toward better individualized treatment for hypertension in the future.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO ID: CRD42022336703. Date of registration: 12/06/2022.

Cardiorespiratory coupling is associated with exercise capacity in athletes: A cross-sectional study

PURPOSE

To determine the association between exercise capacity based on peak oxygen uptake (VO2peak) and resting cardiorespiratory coupling (CRC) levels in athletes and non-athletes' subjects.

METHODS

A cross-sectional study was carried out in 42 apparently healthy male subjects, aged between 20 and 40 years old. The participants were allocated into athletes (n = 21) and non-athletes (n = 21) groups. Resting electrocardiogram and respiratory movement (RESP) were simultaneously acquired during 15 min in supine position and quiet breathing. The beat-to-beat heart period (HP) and RESP series were determined from the recorded signals. Traditional analysis of HP based on frequency domain indexes was performed considering the high-frequency (0.15 - 0.45 Hz) components. To compute the CRC, the linear association between HP and RESP series was determined via squared coherence function and directionality of interaction was investigated through the causal extension of this approach. The exercise capacity was assessed through incremental cardiopulmonary exercise testing in order to determine the VO2peak.

RESULTS

Traditional analysis of HP based on high-frequency index was not correlated with exercise capacity in the athletes (r = -0.1, p = 0.5) and non-athletes (r = -0.1, p = 0.3) cohorts. However, resting CRC values was associated with exercise capacity in athletes (r = 0.4, p = 0.03), but not in the non-athletes group (r = -0.2, p = 0.3).

CONCLUSION

These results suggest that improved resting values of CRC is associated with higher exercise capacity (VO2peak) in endurance athletes. Moreover, frequency domain of HP was not sensitive to identifying this relationship, probably because effects of training on parasympathetic modulation might be affected by respiratory dynamics, and this influence has a directionality (i.e., from RESP to HP).

Effectiveness of spinal manipulation in influencing the autonomic nervous system - a systematic review and meta-analysis

BACKGROUND

Spinal manipulation (SM) has been hypothesized to influence the autonomic nervous system (ANS). Further, it has been proposed that the effects may vary depending on the segment manipulated. The aim of this systematic review was to synthesize the current level of evidence for SM in influencing the ANS in healthy and/or symptomatic population.

METHODS

Various databases (n = 8) were searched (inception till May 2023) and 14 trials (n = 618 participants) were included in the review. Two authors independently screened, extracted and assessed the risk of bias in included studies. The data were synthesized using standard mean differences and meta-analysis for the primary outcome measures. The Grading of Recommendations, Assessment, Development and Evaluation (GRADE) was used for assessing the quality of the body of evidence for each outcome of interest.

RESULTS

Overall, there was low quality evidence that SM did not influence any measure of ANS including heart rate variability (HRV), oxy-hemoglobin, blood pressure, epinephrine and nor-epinephrine. However, there was low quality evidence that cervical spine manipulation may influence high frequency parameter of HRV, indicating its influence on the parasympathetic nervous system.

CONCLUSION

When compared with control or sham interventions, SM did not alter the ANS. Due to invalid methodologies and the low quality of included studies, findings must be interpreted with great caution. Future studies are needed which employ rigorous data collection processes to verify the true physiological implications of SM on ANS.

A History of Suicide Attempt Is Associated with Increased Sympathetic Activation in Bipolar Disorder

OBJECTIVE

Suicide risk in bipolar disorder (BD) is estimated to be up to 20 times higher than in the general population. While there is a large body of evidence suggesting that increased sympathetic activation is associated with disease and death, there is a paucity of research on the role of autonomic nervous system (ANS) dysfunction in patients with BD who have attempted suicide.

METHODS

Fifty-three participants with BD used a wearable device to assess the association between history of suicide attempt, current suicidal ideation, and ANS dysfunction, including measures of heart rate variability (HRV) and respiratory rate. Data were analyzed in a series of unadjusted and adjusted bivariate models of association controlling for relevant variables.

RESULTS

A history of suicide attempts was significantly associated with an increase in respiratory rate (p < 0.01). These results remained significant after adjusting for age, BMI, and current mood state. There was no association between current suicidal ideation and heart rate or respiratory rate. In the frequency domain, HRV parameters suggest reduced parasympathetic (i.e., vagal) activity in participants with a history of suicide attempts and in those with current suicidality, suggesting changes in sympathicovagal balance in BD.

CONCLUSIONS

Our results suggest that changes in the ANS in patients with BD and a history of suicide attempt are not restricted to pure vagally mediated HRV parameters, but rather signal a general ANS dysregulation. This ANS imbalance may be contributing to illness burden and cardiovascular disease. Further research on the relationship between ANS and suicidality in BD is needed.

Heart Rate Variability to Automatically Identify Hyperbaric States Considering Respiratory Component

This study's primary objective was to identify individuals whose physiological responses deviated from the rest of the study population by automatically monitoring atmospheric pressure levels to which they are exposed and using parameters derived from their heart rate variability (HRV). To achieve this, 28 volunteers were placed in a dry hyperbaric chamber, where they experienced varying pressures from 1 to 5 atmospheres, with five sequential stops lasting five minutes each at different atmospheric pressures. The HRV was dissected into two components: the respiratory component, which is linked to respiration; and the residual component, which is influenced by factors beyond respiration. Nine parameters were assessed, including the respiratory rate, four classic HRV temporal parameters, and four frequency parameters. A k-nearest neighbors classifier based on cosine distance successfully identified the atmospheric pressures to which the subjects were exposed to. The classifier achieved an 88.5% accuracy rate in distinguishing between the 5 atm and 3 atm stages using only four features: respiratory rate, heart rate, and two frequency parameters associated with the subjects' sympathetic responses. Furthermore, the study identified 6 out of 28 subjects as having atypical responses across all pressure levels when compared to the majority. Interestingly, two of these subjects stood out in terms of gender and having less prior diving experience, but they still exhibited normal responses to immersion. This suggests the potential for establishing distinct safety protocols for divers based on their previous experience and gender.

Similar Patterns of Dysautonomia in Myalgic Encephalomyelitis/Chronic Fatigue and Post-COVID-19 Syndromes

BACKGROUND

There is a considerable overlap between the clinical presentation of post-COVID-19 condition (PCC) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Many of their common symptoms can be linked to dysregulation of the autonomic nervous system (dysautonomia). This study aimed to objectively assess autonomic function in a general group of patients with PCC and in a group of patients with ME/CFS whose disease was not related to COVID-19. We hypothesize that the similarity in the chronic symptoms of patients with PCC and ME/CFS extends to objective autonomic nervous system abnormalities.

METHODS

Synchronous recordings of an electrocardiogram and continuous dynamics of blood pressure in the digital artery using the Penaz method were obtained using the spiroarteriocardiorhythmography method in 34 patients diagnosed with ME/CFS, in whom the onset of the disease was not associated with COVID-19, 29 patients meeting the PCC definition and 32 healthy controls. Heart rate variability (HRV) and systolic and diastolic blood pressure variability (BPV) were assessed at rest and in tests with fixed respiratory rates. Indicators of baroreflex regulation (baroreflex effectiveness index and baroreflex sensitivity) were additionally determined at rest.

RESULTS

The total power and power of low-frequency and high-frequency of RR interval variability at rest as well as baroreflex sensitivity were significantly lower both in PCC and ME/CFS patients compared to healthy controls. Several diagnostic prediction models for ME/CFS were developed based on HRV parameters. During slow breathing, the HRV parameters returned to normal in PCC but not in ME/CFS patients. The correlation analysis revealed a close relationship of HRV, BPV parameters and baroreflex sensitivity with fatigue, but not with HADS depressive/anxiety symptoms in the ME/CFS and PCC patients.

CONCLUSIONS

A similar pattern of HRV and baroreflex failure with signs of a pathological acceleration of age-dependent dysautonomia was identified in the ME/CFS and PCC patients. The clinical, diagnostic and therapeutic implications of these findings are discussed, in light of previously described relationships between inflammation, vascular pathology, atherosclerotic cardiovascular disease and autonomic dysfunction.

Practice effects of a breathing technique on pilots' cognitive and stress associated heart rate variability during flight operations

Commercial pilots endure multiple stressors in their daily and occupational lives which are detrimental to psychological well-being and cognitive functioning. The Quick coherence technique (QCT) is an effective intervention tool to improve stress resilience and psychophysiological balance based on a five-minute paced breathing exercise with heart rate variability (HRV) biofeedback. The current research reports on the application of QCT training within an international airline to improve commercial pilots' psychological health and support cognitive functions. Forty-four commercial pilots volunteered in a one-month training programme to practise self-regulated QCT in day-to-day life and flight operations. Pilots' stress index, HRV time-domain and frequency-domain parameters were collected to examine the influence of QCT practice on the stress resilience process. The results demonstrated that the QCT improved psychophysiological indicators associated with stress resilience and cognitive functions, in both day-to-day life and flight operation settings. HRV fluctuations, as measured through changes in RMSSD and LF/HF, revealed that the resilience processes were primarily controlled by the sympathetic nervous system activities that are important in promoting pilots' energy mobilization and cognitive functions, thus QCT has huge potential in facilitating flight performance and aviation safety. These findings provide scientific evidence for implementing QCT as an effective mental support programme and controlled rest strategy to improve pilots' psychological health, stress management, and operational performance.

Autonomic Small-Fiber Pathology in Patients With Fibromyalgia

In this clinical and skin biopsy study, we aimed to investigate whether fibromyalgia-associated small-fiber pathology (SFP), consisting of an intraepidermal nerve fiber loss, implies damage of dermal autonomic nerve fibers and how this damage is associated with autonomic symptoms that patients with fibromyalgia syndrome experience. Using skin biopsy, we investigated intraepidermal nerve fiber density, piloerector muscle, and sweat gland nerve fiber density (SGNFD) in 138 participants, that is, 58 patients with fibromyalgia syndrome, 48 healthy subjects, and 32 patients with small-fiber neuropathy. In patients with fibromyalgia-associated SFP, we also investigated how the different skin biopsy variables correlated with autonomic symptoms, as assessed with the Composite Autonomic Symptom Score 31 questionnaire. We found that in patients with fibromyalgia-associated SFP, the piloerector muscle and SGNFD were lower than that in healthy subjects. However, the autonomic small-fiber damage had no correlation with autonomic symptoms severity. In patients with SFP, the intraepidermal, piloerector muscle, and SGNFD were higher than that in patients with small-fiber neuropathy. Our clinical and skin biopsy study shows that patients with fibromyalgia have a reduction of dermal autonomic small fibers paralleling the intraepidermal nerve fiber loss, thus indicating that SFP also implies autonomic small nerve fiber damage. However, the autonomic small-fiber damage we found had no correlation with the severity of autonomic symptoms, and thus its clinical impact is still undetermined. PERSPECTIVE: In patients with fibromyalgia, SFP also affects autonomic fibers. These novel data provide additional insights into the pathophysiology of fibromyalgia syndrome, highlighting the complex role of small-fiber damage in the clinical picture of fibromyalgia.

Autonomic Cardioregulatory Function Does Not Correlate With Symptom Improvement After Concussion in Children and Adolescents

Although there is significant variability in the manifestations of persisting post-concussive symptoms (PPCS), autonomic dysfunction has been reported to contribute to PPCS and could serve as a biomarker of recovery. The objective of this study was to evaluate cardiac autonomic reflexes and autonomic function after concussion injury comparing those with prolonged concussion symptoms to those without. This is a case-control study where a non-referred population of concussed children or adolescent participants were enrolled from the Emergency Department (ED) of the Stollery Children's Hospital, a tertiary pediatric hospital in Edmonton, Alberta, Canada. Children and adolescents 8 through <18 years of age who presented with mild traumatic brain injury were diagnosed with concussion. Our study reported concussion symptoms and standardized clinical cardiac autonomic reflex testing at 4 and 12 weeks after injury. Our findings showed that 28 participants with concussion completed the 4-week follow-up questionnaires, and that 17 (61%) were diagnosed with PPCS. Difficulty concentrating, fatigue, noise sensitivity, light sensitivity, and headache were most commonly reported at baseline among those who were later diagnosed with PPCS. The mean change in heart rate (HR) with head-up tilt was 44.2 bpm (standard deviation [SD] 9.1) in the non-PPCS group and 46.6 bpm (SD 14.1) in the PPCS group at 4 weeks and was not significant in the unadjusted (p = 0.2) or adjusted analysis for age and female sex (p = 0.2). Overall, 70% (19/27) had significant orthostatic tachycardia >40 bpm, but PPCS and non-PPCS groups were similar. Similar results were observed among 23 participants at 12-week follow-up. The median maximum decrease in systolic blood pressure (SBP) with head-up tilt was -26.9 mm Hg (interquartile range [IQR] -32.6, -22.3) in the non-PPCS group and -25.1 mm Hg (IQR -32.2, -18.2) in the PPCS group, and was not significantly different in the unadjusted (p = 0.8) or adjusted (p = 0.8) analysis. Overall, 19 of 26 participants (73%) demonstrated orthostatic hypotension (SBP change >20 mm Hg) with no significant difference between the PPCS and non-PPCS groups. Similar results were observed at 12-week follow-up. In conclusion, cardiac autonomic reflex responses are abnormal in most children and adolescents with a concussion injury at 4- and 12-week follow-up and may reflect ongoing autonomic dysfunction. However, autonomic function did not differentiate PPCS, indicating that reported symptoms are not sensitive to autonomic abnormalities.

Putting back respiration into respiratory sinus arrhythmia or high-frequency heart rate variability: Implications for interpretation, respiratory rhythmicity, and health

Research on respiratory sinus arrhythmia, or high-frequency heart rate variability (its frequency-domain equivalent), has been popular in psychology and the behavioral sciences for some time. It is typically interpreted as an indicator of cardiac vagal activity. However, as research has shown for decades, the respiratory pattern can influence the amplitude of these noninvasive measures substantially, without necessarily reflecting changes in tonic cardiac vagal activity. Although changes in respiration are systematically associated with experiential and behavioral states, this potential confound in the interpretation of RSA, or HF-HRV, is rarely considered. Interpretations of within-individual changes in these parameters are therefore only conclusive if undertaken relative to the breathing pattern. The interpretation of absolute levels of these parameters between individuals is additionally burdened with the problem of residual inspiratory cardiac vagal activity in humans. Furthermore, multiple demographic, anthropometric, life-style, health, and medication variables can act as relevant third variables that might explain associations of RSA or HF-HRV with experiential and behavioral variables. Because vagal activity measured by these parameters only represents the portion of cardiac vagal outflow that is modulated by the respiratory rhythm, alternative interpretations beyond cardiac vagal activity should be considered. Accumulating research shows that activity of multiple populations of neurons in the brain and the periphery, and with that organ activity and function, are modulated rhythmically by respiratory activity. Thus, observable health benefits ascribed to the cardiac vagal system through RSA or HF-HRV may actually reflect beneficial effects of respiratory modulation. Respiratory rhythmicity may ultimately provide the mechanism that integrates central, autonomic, and visceral activities.

The Clinical Relevance of Autonomic Dysfunction, Cerebral Hemodynamics, and Sleep Interactions in Individuals Living With SCI

A myriad of physiological impairments is seen in individuals after a spinal cord injury (SCI). These include altered autonomic function, cerebral hemodynamics, and sleep. These physiological systems are interconnected and likely insidiously interact leading to secondary complications. These impairments negatively influence quality of life. A comprehensive review of these systems, and their interplay, may improve clinical treatment and the rehabilitation plan of individuals living with SCI. Thus, these physiological measures should receive more clinical consideration. This special communication introduces the under investigated autonomic dysfunction, cerebral hemodynamics, and sleep disorders in people with SCI to stakeholders involved in SCI rehabilitation. We also discuss the linkage between autonomic dysfunction, cerebral hemodynamics, and sleep disorders and some secondary outcomes are discussed. Recent evidence is synthesized to make clinical recommendations on the assessment and potential management of important autonomic, cerebral hemodynamics, and sleep-related dysfunction in people with SCI. Finally, a few recommendations for clinicians and researchers are provided.

Comprehensive viewpoints on heart rate variability at high altitude

OBJECTIVES

Hypoxia is a physiological state characterized by reduced oxygen levels in organs and tissues. It is a common clinicopathological process and a major cause of health problems in highland areas.  Heart rate variability (HRV) is a measure of the balance in autonomic innervation to the heart. It provides valuable information on the regulation of the cardiovascular system by neurohumoral factors, and changes in HRV reflect the complex interactions between multiple systems. In this review, we provide a comprehensive overview of the relationship between high-altitude hypoxia and HRV. We summarize the different mechanisms of diseases caused by hypoxia and explore the changes in HRV across various systems. Additionally, we discuss relevant pharmaceutical interventions. Overall, this review aims to provide research ideas and assistance for in-depth studies on HRV. By understanding the intricate relationship between high-altitude hypoxia and HRV, we can gain insights into the underlying mechanisms and potential therapeutic approaches to mitigate the effects of hypoxia on cardiovascular and other systems.

METHODS

The relevant literature was collected systematically from scientific database, including PubMed, Web of Science, China National Knowledge Infrastructure (CNKI), Baidu Scholar, as well as other literature sources, such as classic books of hypoxia.

RESULTS

There is a close relationship between heart rate variability and high-altitude hypoxia. Heart rate variability is an indicator that evaluates the impact of hypoxia on the cardiovascular system and other related systems. By improving the observation of HRV, we can estimate the progress of cardiovascular diseases and predict the impact on other systems related to cardiovascular health. At the same time, changes in heart rate variability can be used to observe the efficacy of preventive drugs for altitude related diseases.

CONCLUSIONS

HRV can be used to assess autonomic nervous function under various systemic conditions, and can be used to predict and monitor diseases caused by hypoxia at high altitude. Investigating the correlation between high altitude hypoxia and heart rate variability can help make HRV more rapid, accurate, and effective for the diagnosis of plateau-related diseases.

Impact of CPAP Therapy on the Autonomic Nervous System

Obstructive sleep apnea (OSA) is a significant risk factor for cardiovascular disease (CVD) with increasing prevalence. An important mechanism of CVD development is a dysregulation of the autonomic nervous system (ANS). This prospective and controlled cohort study aimed to investigate ANS function in OSA including the response to long-term continuous positive airway pressure (CPAP) therapy by analyzing 24 h Holter electrocardiogram and 24 h Holter ambulatory blood pressure recording parameters. The study enrolled 57 patients who were newly diagnosed with severe OSA. After 6 months of CPAP therapy, 37 patients had a good therapy adherence (usage of CPAP device >4 h per night), and their data were analyzed. The difference in nocturnal diastolic blood pressure values before and after CPAP therapy reached statistical significance (76 (68-84) vs. 74 (63-80) mmHg, p = 0.0439). Lower nocturnal values after CPAP therapy of SDNN (101.5 vs. 95 ms, p = 0.0492) and RMSSD (29.5 vs. 26 ms, p = 0.0193) were found. An increase in diurnal spectral power (1742 vs. 2112 ms2, p = 0.0282) and a decrease in nocturnal spectral power (3256 vs. 2124 ms2, p = 0.0097), nocturnal VLF band (2493 vs. 1485.4 ms2, p = 0.0176), nocturnal LF band (638.7 vs. 473 ms2, p = 0.0097), and nocturnal HF band (234.9 vs. 135.7 ms2, p = 0.0319) was found. The results showed an imbalance of the ANS with a sympathetic predominance, especially during the night hours and in those with arterial hypertension. The impact of CPAP therapy on the improvement in ANS parameters was more pronounced at night, in men, and those with arterial hypertension.

Comparison of the effects of dexmedetomidine and propofol on the cardiovascular autonomic nervous system during spinal anesthesia: preliminary randomized controlled observational study

Spinal anesthesia induces sympatholysis and is usually combined with dexmedetomidine or propofol which induce different hemodynamic changes. The purpose of this study was to compare the effect on autonomic nervous system between dexmedetomidine and propofol combined with spinal anesthesia. Patients aged 20-65 undergoing elective surgery under spinal anesthesia were randomly assigned to dexmedetomidine or propofol group. Heart rate variability (HRV) and hemodynamic variables were measured at four time points: T0, baseline; T1, 10 min after spinal anesthesia; T2, 10 min after sedative administration; and T3, 20 min after sedative administration. In 59 patients, dexmedetomidine and propofol groups had significantly different hemodynamic changes over time (time × group effect P < 0.001). The dexmedetomidine group had slower heart rate at T2 (P = 0.001) and higher blood pressures at T2 and T3 (P < 0.001) than the propofol group. Overall HRV dynamics showed a significant change over time from T0 to T3, but both groups exhibited similar trends. Compared to the baseline data within the group, the low frequency (LF) decreased in both groups but the decrease occurred at T2 in the propofol group and at T3 in the dexmedetomidine group. The high frequency (HF) increased at T2 and T3 only in the dexmedetomidine group. The LF/HF ratio decreased in the dexmedetomidine group at T3. Dexmedetomidine showed slower heart rate and higher blood pressure than propofol when combined with spinal anesthesia, however, dexmedetomidine and propofol exhibited similar trends in HRV dynamics. Compared with the baseline within each group, both agents decreased LF, but only dexmedetomidine increased HF and decreased in the LF/HF ratio significantly.

Assessment of the human response to acute mental stress-An overview and a multimodal study

Numerous vital signs are reported in association with stress response assessment, but their application varies widely. This work provides an overview over methods for stress induction and strain assessment, and presents a multimodal experimental study to identify the most important vital signs for effective assessment of the response to acute mental stress. We induced acute mental stress in 65 healthy participants with the Mannheim Multicomponent Stress Test and acquired self-assessment measures (Likert scale, Self-Assessment Manikin), salivary α-amylase and cortisol concentrations as well as 60 vital signs from biosignals, such as heart rate variability parameters, QT variability parameters, skin conductance level, and breath rate. By means of statistical testing and a self-optimizing logistic regression, we identified the most important biosignal vital signs. Fifteen biosignal vital signs related to ventricular repolarization variability, blood pressure, skin conductance, and respiration showed significant results. The logistic regression converged with QT variability index, left ventricular work index, earlobe pulse arrival time, skin conductance level, rise time and number of skin conductance responses, breath rate, and breath rate variability (F1 = 0.82). Self-assessment measures indicated successful stress induction. α-amylase and cortisol showed effect sizes of -0.78 and 0.55, respectively. In summary, the hypothalamic-pituitary-adrenocortical axis and sympathetic nervous system were successfully activated. Our findings facilitate a coherent and integrative understanding of the assessment of the stress response and help to align applications and future research concerning acute mental stress.

Wearable sensors for prediction of intraamniotic infection in women with preterm premature rupture of membranes: a prospective proof of principle study

PURPOSE

To evaluate the use of wearable sensors for prediction of intraamniotic infection in pregnant women with PPROM.

MATERIALS AND METHODS

In a prospective proof of principle study, we included 50 patients diagnosed with PPROM at the University Hospital Zurich between November 2017 and May 2020. Patients were instructed to wear a bracelet during the night, which measures physiological parameters including wrist skin temperature, heart rate, heart rate variability, and breathing rate. A two-way repeated measures ANOVA was performed to evaluate the difference over time of both the wearable device measured parameters and standard clinical monitoring values, such as body temperature, pulse, leucocytes, and C-reactive protein, between women with and without intraamniotic infection.

RESULTS

Altogether, 23 patients (46%) were diagnosed with intraamniotic infection. Regarding the physiological parameters measured with the bracelet, we observed a significant difference in breathing rate (19 vs 16 per min, P < .01) and heart rate (72 vs 67 beats per min, P = .03) in women with intraamniotic infection compared to those without during the 3 days prior to birth. In parallel to these changes standard clinical monitoring values were significantly different in the intraamniotic infection group compared to women without infection in the 3 days preceding birth.

CONCLUSION

Our results suggest that wearable sensors are a promising, noninvasive, patient friendly approach to support the early detection of intraamniotic infection in women with PPROM. However, confirmation of our findings in larger studies is required before implementing this technique in standard clinical management.

Telemetric long-term assessment of autonomic function in experimental heart failure

Despite medical advances in the treatment of heart failure (HF), mortality remains high. It has been shown that alterations of the autonomic-nervous-system (ANS) are associated with HF progression and increased mortality. Preclinical models are required to evaluate the effectiveness of novel treatments modulating the autonomic imbalance. However, there are neither standard models nor diagnostic methods established to measure sympathetic and parasympathetic outflow continuously. Digital technologies might be a reliable tool for continuous assessment of autonomic function within experimental HF models. Telemetry devices and pacemakers were implanted in beagle dogs (n = 6). HF was induced by ventricular pacing. Cardiac hemodynamics, plasma catecholamines and parameter describing the ANS ((heart rate variability (HRV), deceleration capacity (DC), and baroreflex sensitivity (BRS)) were continuously measured at baseline, during HF conditions and during recovery phase. The pacing regime led to the expected depression in cardiac hemodynamics. Telemetric assessment of the ANS function showed a significant decrease in Total power, DC, and Heart rate recovery, whereas BRS was not significantly affected. In contrast, plasma catecholamines, revealing sympathetic activity, showed only a significant increase in the recovery phase. A precise diagnostic of the ANS in the context of HF is becoming increasingly important in experimental models. Up to now, these models have shown many limitations. Here we present the continuous assessment of the autonomic function in the progression of HF. We could demonstrate the advantage of highly resolved ANS measurement by HR and BP derived parameters due to early detection of an autonomic imbalance in the progression of HF.

Multifractal foundations of biomarker discovery for heart disease and stroke

Any reliable biomarker has to be specific, generalizable, and reproducible across individuals and contexts. The exact values of such a biomarker must represent similar health states in different individuals and at different times within the same individual to result in the minimum possible false-positive and false-negative rates. The application of standard cut-off points and risk scores across populations hinges upon the assumption of such generalizability. Such generalizability, in turn, hinges upon this condition that the phenomenon investigated by current statistical methods is ergodic, i.e., its statistical measures converge over individuals and time within the finite limit of observations. However, emerging evidence indicates that biological processes abound with nonergodicity, threatening this generalizability. Here, we present a solution for how to make generalizable inferences by deriving ergodic descriptions of nonergodic phenomena. For this aim, we proposed capturing the origin of ergodicity-breaking in many biological processes: cascade dynamics. To assess our hypotheses, we embraced the challenge of identifying reliable biomarkers for heart disease and stroke, which, despite being the leading cause of death worldwide and decades of research, lacks reliable biomarkers and risk stratification tools. We showed that raw R-R interval data and its common descriptors based on mean and variance are nonergodic and non-specific. On the other hand, the cascade-dynamical descriptors, the Hurst exponent encoding linear temporal correlations, and multifractal nonlinearity encoding nonlinear interactions across scales described the nonergodic heart rate variability more ergodically and were specific. This study inaugurates applying the critical concept of ergodicity in discovering and applying digital biomarkers of health and disease.

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

AIMS

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Heart Rate Variability in Psychiatric Disorders: A Systematic Review

Introduction

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

Methods

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

Results

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

Conclusion

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

Effects of An Isotonic Medinilla Speciosa During and After Exercise

Maintaining an adequate fluid balance is crucial during extended physical activity. It is currently unknown how drinking an isotonic medinilla speciosa beverage affects the autonomic regulation of heart function during and after exercise. The purpose of this study is to examine how drinking isotonic beverages affects heart rate variability (HRV) during and after intense exercise. A maximal exercise test to assess protocol loading, a control group, and an experimental group were all carried out by twenty-one young man (19.3 ± 1.2 years) over the course of three distinct protocols, with a 48-hour break in between each stage. The protocol called for 10 minutes of rest with the subject lying down, 90 minutes of treadmill work at 70% of one's maximum oxygen uptake, and 60 minutes of rest in the dorsal decubitus position. In the control group, no rehydration beverages could be consumed. No matter the level of hydration, alterations in the sympathetic nervous system (SNS) and the parasympathetic nervous system (PSNS) were seen, showing an increase in the former and a reduction in the latter. Hydration with isotonic solutions during recovery causes considerable alterations in cardiac autonomic regulation, hastening the recovery of the linear HRV index. Exercise-induced HRV was not significantly impacted by isotonic hydration, however it does speed up the recovery of linear indices after exercise.

Heart rate variability (HRV) as a way to understand associations between the autonomic nervous system (ANS) and affective states: A critical review of the literature

Evidence suggests affective disorders such as depression and bipolar disorder are characterised by dysregulated autonomic nervous system (ANS) activity. These findings suggest ANS dysregulation may be involved in the pathogenesis of affective disorders. Different affective states are characterised by different ANS activity patterns (i.e., an increase or decrease in sympathetic or parasympathetic activity). To understand how ANS abnormalities are involved in the development of affective disorders, it is important to understand how affective states correlate with ANS activity before their onset. Using heart rate variability (HRV) as a tool to measure ANS activity, this review aimed to look at associations between affective states and HRV in non-clinical populations (i.e., in those without medical and psychiatric disorders). Searches on PubMed and Google Scholar were completed using the following search terms: heart rate variability, autonomic nervous system, sympathetic nervous system, parasympathetic nervous system, affective state, mood and emotion in all possible combinations. All but one of the studies examined (N = 13), demonstrated significant associations between affect and HRV. Findings suggest negative affect, encompassing both diffused longer-term experiences (i.e., mood) as well as more focused short-term experiences (i.e., emotions), may be associated with a reduction in parasympathetic activity as measured through HRV parameters known to quantify parasympathetic activity (e.g., high frequency (HF)-HRV). HRV measures typically linked to reduction in parasympathetic activity appear to be linked to negative affective states in non-clinical populations. However, given the complex and possibly non-linear relationship between HRV and parasympathetic activity, further studies need to clarify specificity of these findings. Future studies should investigate the potential utility of HRV measures as biomarkers for monitoring changes in affective states and for early detection of onset and relapse of depression in patients with affective disorders.

Probiotic and intra-nasal oxytocin combination therapy on autonomic function and gut-brain axis signaling in young children and teens with autism spectrum disorder

Autonomic dysfunction has been widely studied in individuals with autism spectral disorder (ASD); however, the autonomic response to probiotic and oxytocin (OT) combination intervention has not yet been explored. We conducted the present study that includes 35 individuals with ASD aged 3-20 years to explore autonomic responses to daily Lactobacillus plantarum probiotic supplementation and OT nasal spray treatment both alone and in combination. We identified significant improvements in autonomic indices from subjects receiving combination treatment relative to those receiving placebo. Parameters that were observed to improve following combination treatment are time domain metrics of heart rate variability (HRV), including the root mean square of successive differences between normal heartbeats (RMSSD), standard deviation of normal-to-normal R-R intervals (SDNN), and proportion of the number of pairs of adjacent NN intervals that differ by more than 50ms (pNN50, p < 0.05). Furthermore, individuals that received either probiotics or OT alone demonstrated fewer changes in RMSSD, pNN50, and SDNN. Several parameters that demonstrated significant improvements in combination therapy were found to be correlated with baseline levels of OT (LF power: r = -0.86, p = 0.024; mean HR: r = 0.89, p = 0.012). Additionally, Social Responsiveness Scale (SRS) raw total scores (mean HR, r = 0.86, p = 0.024) and Aberrant Behavior Checklist (ABC) raw total scores (mean HR r = 0.94, p = 0.017) were correlated with mean heart rate (HR) and HRV-derived parameters. These results provide further evidence of synergy of probiotic and OT combination and help us gain a better understanding of the role of the gut-brain axis in ASD phenotypes and pathogenesis.

Abnormal heart rate variability and its application in predicting treatment efficacy in patients with chronic migraine: An exploratory study

AIM

This study aimed to investigate the extent of autonomic nervous system dysfunction in patients with chronic migraine using heart rate variability analysis. In addition, we explored the potential association between heart rate variability and treatment outcomes in patients receiving preventive treatment.

METHODS

In this cross-sectional and prospective study, we compared heart rate variability profiles in 81 preventive-naïve chronic migraine patients and 58 healthy controls. In addition, treatment responses of patients, who received a 12-week treatment with flunarizine, were assessed in relation to baseline heart rate variability.

RESULTS

We observed that chronic migraine patients had a reduced heart rate variability, signifying autonomic dysfunction in comparison to healthy controls. Furthermore, patients presenting normal heart rate variability, characterized by a standard deviation exceeding 30 milliseconds in normal-to-normal RR intervals, experienced a superior response to flunarizine treatment. This improvement was exemplified by a significantly larger reduction in monthly headache days for patients with higher heart rate variability compared to those with lower heart rate variability: -9.7 (5.9) vs. -6.2 (6.0) days (p = .026).

CONCLUSIONS

Autonomic dysfunction occurs in chronic migraine as evaluated by heart rate variability. A preserved function is associated with a better treatment outcome to flunarizine.Trial registration: Neurologic Signatures of Chronic Pain Disorders, NCT02747940. Registered 22 April 2016, https://clinicaltrials.gov/ct2/show/NCT02747940.

Cardioautonomic lability assessed by heart rate variability changes in Royal Canadian Mounted Police cadets during the cadet training program

Objective

The current study examined variations in cardioautonomic lability during the Royal Canadian Mounted Police (RCMP) Cadet Training Program (CTP) between cadets starting their training who did or did not screen positive for one or more mental health disorders (i.e., posttraumatic stress disorder [PTSD], major depressive disorder [MDD], social anxiety disorder [SAD], generalized anxiety disorder [GAD], panic disorder [PD], alcohol use disorder [AUD]).

Methods

Electrocardiogram (ECG) signals integrated into Hexoskin garments were used to record ECG and heart rate Over the 26-week CTP. There were 31 heart rate variability (HRV) parameters calculated using Kubios Premium HRV analysis software. Mann-Whitney U-tests were used to perform groupwise comparisons of participant raw values and HRV during the CTP.

Results

A total of 157 cadets (79% male) were screened for any mental disorder using self-report surveys and then grouped by positive and negative screening. Analyses indicated a statistically significant (p < 0.05) decrease in low frequency (LF): High Frequency (HF) variability during CTP, but only for cadets who endorsed clinically significant anxiety symptoms on the GAD-7 at the start of their training. There were no other statistically significant groupwise differences.

Conclusion

The results indicate the participants have excellent cardiac health overall and suggest potentially important differences between groups, such that cadets who endorsed clinically significant anxiety symptoms on the GAD-7 showed less variability in the LF:HF ratio over the course of the CTP. The relatively lower variability suggests decreased parasympathetic tone in those without clinically significant anxiety symptoms. The results also have important implications for future investigations of cardioautonomic dysfunction and chronic hypothalamic pituitary adrenal (HPA) axis deviations in policing populations with anxiety disorders; specifically, cardioautonomic inflexibility related to cardiovascular morbidity and mortality. In any case, the current results provide an important baseline for future cardiac research with cadets and serving officers.

Reduced heart rate variability during mania in a repeated naturalistic observational study

Background

Bipolar disorder (BD) is a chronic recurrent mood disorder associated with autonomic nervous system (ANS) dysfunction, indexed by heart rate variability (HRV). Changes in HRV between mood states are sparsely studied longitudinally. We aimed to compare HRV of hospitalized manic individuals with their own euthymic selves in a naturalistic observational study.

Methods

34 individuals were included, of which 16 were lost to follow-up. Ultimately 15 patients provided reliable heart rate data in both a manic and euthymic state, using photoplethysmography (PPG) sensor wristbands overnight. We calculated HRV measures Root Mean Square of Successive Differences (RMSSD), High-frequency (HF: 0.15-0.40 Hz), Low-frequency (LF: 0.40-0.15 Hz), Very low-frequency (VLF: 0.0033-0.04 Hz), Total power and Sample Entropy in 5-min night-time resting samples. We compared HRV measures by mood state within individuals using paired t-tests and linear regression to control for age and sex.

Results

HRV was lower in the manic state when compared to the euthymic state for all HRV metrics (p ≤ 0.02), with large to medium effect sizes (g = 1.24 to 0.65). HRV changes were not significantly affected by age or sex.

Conclusion

This longitudinal study provides evidence of lower HRV in manic states compared to euthymia, indicating an association between ANS dysregulation and changes in bipolar mood state. This corroborates previous cross-sectional studies, although the association may be less clear or reversed in hypomanic states. Further investigation in larger longitudinal samples is warranted.

Electrodermal activity and heart rate variability for detection of peripheral abnormalities in type 2 diabetes: A review

Modern medicine exhibits an upward trend towards non-invasive methods for early detection of disease and long-term monitoring of patients' health. Diabetes mellitus and its complications are a promising area for implementation of new medical diagnostic devices. One of the most serious complications of diabetes is diabetic foot ulcer. The main causes responsible for diabetic foot ulcer are ischemia caused by peripheral artery disease and diabetic neuropathy caused by polyol pathway-induced oxidative stress. Autonomic neuropathy impairs function of sweat glands, which can be measured by electrodermal activity. On the other hand, autonomic neuropathy leads to changes in heart rate variability, which is used to assess autonomic regulation of the sinoatrial node. Both methods are enough sensitive to detect pathological changes caused by autonomic neuropathy and are promising screening methods for early diagnosis of diabetic neuropathy, which could prevent the onset of diabetic ulcer.

Transcutaneous auricular branch vagal nerve stimulation as a non-invasive add-on therapeutic approach for pain in systemic sclerosis

OBJECTIVE

Systemic sclerosis (SSc) is an autoimmune disease with health-related quality of life (HRQoL) high impairment. Pain is of paramount importance to be targeted by therapeutical approaches. Our study aim was to perform an add-on device-based non-invasive neuromodulatory treatment through transcutaneous auricular vagal nerve stimulation (tVNS) in patients with SSc, assessing its effects on pain as primary endpoint and on inflammation, cardiovascular autonomic control and HRQoL.

METHODS

Thirty-two patients with SSc were enrolled based on reported pain assessed through Numeric Rating Scale (NRS). Twenty-one (90% with limited cutaneous SSc) completed a randomised, cross-over, patient-blind trial, in which interventional and active control were used in random order for 4 weeks, interspersed with 4 weeks washout. NRS, Patient-Reported Outcomes Measurement Information System-29 (PROMIS-29) Item4 for pain interference, heart rate variability (HRV), serum cytokines and HRQoL questionnaires (Health Assessment Questionnaire, Patient Health Questionnaire-9, University of California, Los Angeles Gastrointestinal Tract, Pittsburgh Sleep Quality Index) were assessed at baseline, at T1 (after 1 month of tVNS or active control), at T2 (after washout) and at T3 (after 1 month of active control or tVNS). T-test for paired data and Wilcoxon signed-rank test for non-normally distributed parameters were performed to compare the effect of tVNS and active control.

RESULTS

NRS pain was significantly reduced by tVNS and not by active control (Mean±SD: -27.7%±21.3% vs -7.7%±26.3%, p=0.002). Interleukin-6 was downregulated in tVNS versus active control (p=0.029). No significant differences were observed in tVNS versus active control for PROMIS-29 Item4, QoL scales and HRV with both spectral and symbolic analyses.

CONCLUSION

tVNS demonstrated to be a safe and non-invasive add-on tool to reduce pain in SSc.

Effect of cognitive processing therapy on markers of cardiovascular risk in posttraumatic stress disorder patients: A randomized clinical trial

OBJECTIVE

Posttraumatic stress disorder (PTSD) is associated with elevated risk of coronary heart disease (CHD); however, the effects of PTSD treatment on CHD biomarkers is unknown. This study examined whether cognitive processing therapy (CPT) improves 24-hourheart rate variability (HRV), a predictor of CHD mortality.

METHODS

Individuals between the ages of 40 and 65 years with PTSD (n = 112) were randomized to receive 12 sessions of CPT or a Waiting List (WL) intervention comprised of 6 weekly telephone checks of emotional status. The primary outcome variable was 24-hour HRV estimated from the standard deviation of all normal R-R intervals (SDNN); secondary outcomes were the root mean square of successive differences between heart beats (RMSSD), low-frequency HRV (LF-HRV) and high-frequency HRV (HF-HRV). Secondary outcomes also included 24-hour urinary catecholamine excretion, plasma C-reactive protein (CRP), and flow-mediated dilation (FMD) of the brachial artery. For outcomes, linear mixed longitudinal models were used to estimate mean differences (Mdiff).

RESULTS

Participants randomized to the CPT group did not show improved SDNN (Mdiff = 9.8; 95%CI, -2.7 to 22.3; p = 0.12), the primary outcome variable, but showed improved RMSSD (Mdiff = 3.8; 95% CI, 0.5 to 7.1; p = 0.02), LF- HRV (Mdiff =0.3; 95% CI, 0.1 to 0.5; p = 0.01), and HF-HRV (Mdiff = 0.3; 95% CI, 0.0 to 0.6; p = 0.03) compared to WL. There were no differences between groups in catecholamine excretion, FMD, or inflammatory markers.

CONCLUSION

Treating PTSD may not only improve quality of life but may also help ameliorate heightened CHD risk characteristics of PTSD.

Heart rate variability during auricular acupressure at the left sympathetic point on healthy volunteers: a pilot study

Introduction

This research is a pilot, single-blinded study investigating heart rate variability (HRV) during auricular acupressure at the left sympathetic point (AH7) in healthy volunteers.

Methods

There were 120 healthy volunteers with hemodynamic indexes (heart rate, blood pressure) within normal ranges, randomly divided into two groups AG and SG (in each group having a gender ratio 1:1, aged 20-29), to receive either auricular acupressure using ear seed (AG) or sham method using adhesive patches without seed (SG) at the left sympathetic point while lying in a supine position. Acupressure intervention lasted 25 min, and HRV was recorded by a photoplethysmography device-namely, Kyto HRM-2511B and Elite appliance.

Results

Auricular acupressure at the left Sympathetic point (AG) led to a significant reduction in heart rate (HR) (p < 0.05) and a considerable increase in HRV parameters demonstrated by HF (High-frequency power) (p < 0.05), compared to sham auricular acupressure (SG). However, no significant changes in LF (Low-frequency power) and RR (Respiratory rate) (p > 0.05) were observed in both groups during the process.

Conclusion

These findings suggest that auricular acupressure at the left sympathetic point may activate the parasympathetic nervous system while a healthy person is lying relaxed.

Is Thoracic Kyphosis Relevant to Pain, Autonomic Nervous System Function, Disability, and Cervical Sensorimotor Control in Patients with Chronic Nonspecific Neck Pain?

There is great interest in thoracic kyphosis, as it is thought to be a contributor to neck pain, neck disability, and sensorimotor control measures; however, this has not been completely investigated in treatment or case control studies. This case control design investigated participants with non-specific chronic neck pain. Eighty participants with a defined hyper-kyphosis (>55°) were compared to eighty matched participants with normal thoracic kyphosis (<55°). Participants were matched for age and neck pain duration. Hyper-kyphosis was further categorized into two distinct types: postural kyphosis (PK) and Scheuermann's kyphosis (SK). Posture measures included formetric thoracic kyphosis and the craniovertebral angle (CVA) to assess forward head posture. Sensorimotor control was assessed by the following measures: smooth pursuit neck torsion test (SPNT), overall stability index (OSI), and left and right rotation repositioning accuracy. A measure of autonomic nervous system function included the amplitude and latency of skin sympathetic response (SSR). Differences in variable measures were examined using the Student's t-test to compare the means of continuous variables between the two groups. One-way ANOVA was used to compare mean values in the three groups: postural kyphosis, Scheuermann's kyphosis, and normal kyphosis group. Pearson correlation was used to evaluate the relationship between participant's thoracic kyphosis magnitude (in each group separately and as an entire population) and their CVA, SPNT, OSI, head repositioning accuracy, and SSR latency and amplitude. Hyper-kyphosis participants had a significantly greater neck disability index compared to the normal kyphosis group (p < 0.001) with the SK group having greatest disability (p < 0.001). Statistically significant differences between the two kyphosis groups and the normal kyphosis group for all the sensorimotor measured variables were identified with the SK group having the most decreased efficiency of the measures in the hyper-kyphosis group, including: SPNT, OSI, and left and right rotation repositioning accuracy. In addition, there was a significant difference in neurophysiological findings for SSR amplitude (entire sample of kyphosis vs. normal kyphosis, p < 0.001), but there was no significant difference for SSR latency (p = 0.07). The CVA was significantly greater in the hyper-kyphosis group (p < 0.001). The magnitude of the thoracic kyphosis correlated with worsening CVA (with the SK group having the smallest CVA; p < 0.001) and the magnitude of the decreased efficiency of the sensorimotor control measures and the amplitude and latency of the SSR. The PK group, overall, showed the greatest correlations between thoracic kyphosis and measured variables. Participants with hyper-thoracic kyphosis exhibited abnormal sensorimotor control and autonomic nervous system dysfunction compared to those with normal thoracic kyphosis.

The effect of cranial techniques on the heart rate variability response to psychological stress test in firefighter cadets

Heart rate variability (HRV) is a simple tool to monitor cardiovascular stress. The proper function of the cardiovascular system is a problem among firefighters. Physical activity has health benefits correlated with psychological stress. Physically active people should be more resilient to psychological stress, but this has not always been demonstrated. The aim of this study was to determine whether cranial techniques would have an effect on HRV parameters. Osteopathy in the cranium reduces stress and improves cardiovascular function. Fifty-seven firefighter cadets aged 18-24 years (21.63 ± 1.41) participated in the study. All subjects had their heart rate variability measured and were randomly assigned either to the cranial techniques (CS) group, with therapy performed once a week for 5 weeks), or to the control group (CO). After 5 weeks, heart rate variability was measured again in both groups. In the Friedman test, in the CS group there was a statistically significant effect of cranial techniques on Heart Rate (HR) and Low Frequency (LF), but not on High Frequency (HF); in the CO group, a statistically significant difference was observed for HR, HF and LF. In the Nemenyi test, in the CS group there was a statistically significant difference for HR and LF and in the CO group for HR, HF and LF. After applying hierarchical clustering with Euclidean measure and the complete method, dendrograms were drawn up showing similarities for HR, HF and LF values. The cranial techniques and touch might exert a beneficial effect on HRV. Both factors can be used in stressful situations to lower HRV.

Assessing effectiveness of heart rate variability biofeedback to mitigate mental health symptoms: a pilot study

Introduction: The increasing burden on mental health has become a worldwide concern especially due to its substantial negative social and economic impact. The implementation of prevention actions and psychological interventions is crucial to mitigate these consequences, and evidence supporting its effectiveness would facilitate a more assertive response. Heart rate variability biofeedback (HRV-BF) has been proposed as a potential intervention to improve mental wellbeing through mechanisms in autonomic functioning. The aim of this study is to propose and evaluate the validity of an objective procedure to assess the effectiveness of a HRV-BF protocol in mitigating mental health symptoms in a sample of frontline HCWs (healthcare workers) who worked in the COVID-19 pandemic. Methods: A prospective experimental study applying a HRV-BF protocol was conducted with 21 frontline healthcare workers in 5 weekly sessions. For PRE-POST intervention comparisons, two different approaches were used to evaluate mental health status: applying (a) gold-standard psychometric questionnaires and (b) electrophysiological multiparametric models for chronic and acute stress assessment. Results: After HRV-BF intervention, psychometric questionnaires showed a reduction in mental health symptoms and stress perception. The electrophysiological multiparametric also showed a reduction in chronic stress levels, while the acute stress levels were similar in PRE and POST conditions. A significant reduction in respiratory rate and an increase in some heart rate variability parameters, such as SDNN, LFn, and LF/HF ratio, were also observed after intervention. Conclusion: Our findings suggest that a 5-session HRV-BF protocol is an effective intervention for reducing stress and other mental health symptoms among frontline HCWs who worked during the COVID-19 pandemic. The electrophysiological multiparametric models provide relevant information about the current mental health state, being useful for objectively evaluating the effectiveness of stress-reducing interventions. Further research could replicate the proposed procedure to confirm its feasibility for different samples and specific interventions.

Short-term high-salt consumption does not influence resting or exercising heart rate variability but increases MCP-1 concentration in healthy young adults

High salt consumption increases blood pressure (BP) and cardiovascular disease risk by altering autonomic function and increasing inflammation. However, it is unclear whether salt manipulation alters resting and exercising heart rate variability (HRV), a noninvasive measure of autonomic function, in healthy young adults. The purpose of this investigation was to determine whether short-term high-salt intake 1) alters HRV at rest, during exercise, or exercise recovery and 2) increases the circulating concentration of the inflammatory biomarker monocyte chemoattractant protein 1 (MCP-1). With the use of a randomized, placebo-controlled, crossover study, 20 participants (8 females; 24 ± 4 yr old, 110 ± 10/64 ± 8 mmHg) consumed salt (3,900 mg sodium) or placebo capsules for 10 days each separated by ≥2 wk. We assessed HRV during 10 min of baseline rest, 50 min of cycling (60% V̇o2peak), and recovery. We quantified HRV using the standard deviation of normal-to-normal RR intervals, the root mean square of successive differences (RMSSD), and additional time and frequency domain metrics of HRV. Plasma samples were collected to assess MCP-1 concentration. No main effect of high salt or condition × time interaction was observed for HRV metrics. However, acute exercise reduced HRV (e.g., RMSSD time: P < 0.001, condition: P = 0.877, interaction: P = 0.422). High salt elevated plasma MCP-1 (72.4 ± 12.5 vs. 78.14 ± 14.7 pg/mL; P = 0.010). Irrespective of condition, MCP-1 was moderately associated (P values < 0.05) with systolic (r = 0.32) and mean BP (r = 0.33). Short-term high-salt consumption does not affect HRV; however, it increases circulating MCP-1, which may influence BP in young adults.

Effects of sleep fragmentation and partial sleep restriction on heart rate variability during night

We developed a cross-over study design with two interventions in randomized order to compare the effects of sleep fragmentation and partial sleep restriction on cardiac autonomic tone. Twenty male subjects (40.6 ± 7.5 years old) underwent overnight polysomnography during 2 weeks, each week containing one undisturbed baseline night, one intervention night (either sleep restriction with 5 h of sleep or sleep fragmentation with awakening every hour) and two undisturbed recovery nights. Parameters of heart rate variability (HRV) were used to assess cardiac autonomic modulation during the nights. Sleep restriction showed significant higher heart rate (p = 0.018) and lower HRV-pNN50 (p = 0.012) during sleep stage N1 and lower HRV-SDNN (p = 0.009) during wakefulness compared to the respective baseline. For HR and SDNN there were recovery effects. There was no significant difference comparing fragmentation night and its baseline. Comparing both intervention nights, sleep restriction had lower HRV high frequency (HF) components in stage N1 (p = 0.018) and stage N2 (p = 0.012), lower HRV low frequency (LF) (p = 0.007) regarding the entire night and lower SDNN (p = 0.033) during WASO during sleep. Sleep restriction increases sympathetic tone and decreases vagal tone during night causing increased autonomic stress, while fragmented sleep does not affect cardiac autonomic parameters in our sample.

Embodying Consciousness through Interoception and a Balanced Time Perspective

This review presents current research and scientific knowledge in body mind sciences through the lens of interoception, as a representative of the body; and time perspective, as the representative of the mind. This intertwining dichotomy has been a subject of discourse in many fields, all having the common denominator of consciousness. Our aim is to expand on the congruities of these seemingly deconstructed worlds-of science and philosophy, of the body and the mind, to show that the place of consciousness lies in the zone between these two. Being aware of the body in the present moment. We introduce interoception and time perspective, focusing on how interoceptive signals are depicted in autonomic nervous system (ANS) regulation, and how this relates to the concept of a balanced time perspective (BTP), a highly adaptive psychological characteristic. Time perspective and interoception are also reviewed in the case of clinical conditions. We assess findings on interoceptive pathways in the body, finding convergence with balanced time perspective through the neuroanatomical lens. We conclude with findings that both dysregulated interoceptive states and a time perspective disbalance are recognized as defining features of mental disorders, proposing prospective practical therapeutic approaches, as well as implications for further research in the field.

Medetomidine/midazolam/fentanyl narcosis alters cardiac autonomic tone leading to conduction disorders and arrhythmias in mice

Arrhythmias are critical contributors to cardiovascular morbidity and mortality. Therapies are mainly symptomatic and often insufficient, emphasizing the need for basic research to unveil the mechanisms underlying arrhythmias and to enable better and ideally causal therapies. In translational approaches, mice are commonly used to study arrhythmia mechanisms in vivo. Experimental electrophysiology studies in mice are performed under anesthesia with medetomidine/midazolam/fentanyl (MMF) and isoflurane/fentanyl (IF) as commonly used regimens. Despite evidence of adverse effects of individual components on cardiac function, few data are available regarding the specific effects of these regimens on cardiac electrophysiology in mice. Here we present a study investigating the effects of MMF and IF narcosis on cardiac electrophysiology in vivo in C57BL/6N wild-type mice. Telemetry transmitters were implanted in a group of mice, which served as controls for baseline parameters without narcosis. In two other groups of mice, electrocardiogram and invasive electrophysiology studies were performed under narcosis (with either MMF or IF). Basic electrocardiogram parameters, heart rate variability parameters, sinus node and atrioventricular node function, and susceptibility to arrhythmias were assessed. Experimental data suggest a remarkable influence of MMF on cardiac electrophysiology compared with IF and awake animals. While IF only moderately reduced heart rate, MMF led to significant bradycardia, spontaneous arrhythmias, heart rate variability alterations as well as sinus and AV node dysfunction, and increased inducibility of ventricular arrhythmias. On the basis of these observed effects, we suggest avoiding MMF in mice, specifically when studying cardiac electrophysiology, but also whenever a regular heartbeat is required for reliable results, such as in heart failure or imaging research.

The connection between heart rate variability (HRV), neurological health, and cognition: A literature review

The heart and brain have bi-directional influences on each other, including autonomic regulation and hemodynamic connections. Heart rate variability (HRV) measures variation in beat-to-beat intervals. New findings about disorganized sinus rhythm (erratic rhythm, quantified as heart rate fragmentation, HRF) are discussed and suggest overestimation of autonomic activities in HRV changes, especially during aging or cardiovascular events. When excluding HRF, HRV is regulated via the central autonomic network (CAN). HRV acts as a proxy of autonomic activity and is associated with executive functions, decision-making, and emotional regulation in our health and wellbeing. Abnormal changes of HRV (e.g., decreased vagal functioning) are observed in various neurological conditions including mild cognitive impairments, dementia, mild traumatic brain injury, migraine, COVID-19, stroke, epilepsy, and psychological conditions (e.g., anxiety, stress, and schizophrenia). Efforts are needed to improve the dynamic and intriguing heart-brain interactions.

Adding Core Muscle Contraction to Wrist-Ankle Rhythmical Skeletal Muscle Tension Increases Respiratory Sinus Arrhythmia and Low-Frequency Power

Paced breathing and rhythmical skeletal muscle tension (RSMT) at an individual's resonance frequency [~ 6 breaths or contractions per min (cpm)] can stimulate the arterial and vascular tone baroreflexes. Lehrer (Appl Psychophysiol Biofeedback 1-10, 2022, https://doi.org/10.1007/s10484-022-09535-5 ) has explained that the stimulation rate is important, not the modality. Early RSMT protocols differed in the muscles recruited and whether legs were crossed or uncrossed (in France et al. Clin Physiol Funct Imaging 26: 21-25, 2006, https://doi.org/10.1111/j.1475-097X.2005.00642.x ; Leher et al. Biol Psychol 81: 24-30, 2009, https://doi.org/10.1016/j.biopsycho.2009.01.003 ; Vaschillo et al. Psychophysiology, 48: 927-936, 2011, https://doi.org/10.1111/j.1469-8986.2010.01156.x ). Whereas core muscle RSMT with crossed legs and wrist-ankle RSMT with uncrossed legs produced resonance effects, researchers have not directly compared the effect of these exercises on respiratory sinus arrhythmia (RSA) and low-frequency (LF) power. The current within-subjects experiment investigated whether crossing the legs and recruiting core muscles enhances wrist-ankle RSMT effects on RSA and LF power. We trained 35 participants to complete 6-cpm wrist-ankle RSMT (ankles uncrossed), 6-cpm wrist-core-ankle RSMT (ankles crossed), and a control condition in which participants sat quietly (ankles uncrossed) without performing RSMT. We predicted that 6-cpm wrist-core-ankle RSMT would produce greater heart rate (HR), HR Max-HR Min, and LF power than the other conditions. The experimental findings supported our predictions. Both RSMT conditions produced greater HR, HR Max-HR Min, and LF power than the control condition. Wrist-core-ankle yielded greater HR and HR Max-HR Min than wrist-ankle RSMT. Future research should compare wrist-ankle and wrist-core-ankle RSMT with legs crossed. The practical implication for HRV biofeedback training is that wrist-core-ankle RSMT with legs crossed may more powerfully stimulate the baroreflex than wrist-ankle RSMT with legs uncrossed.

A Pilot Study of a Three-Session Heart Rate Variability Biofeedback Intervention for Veterans with Posttraumatic Stress Disorder

Many veterans do not complete traditional trauma treatments; others may continue to struggle with posttraumatic stress disorder (PTSD) even after completing a full course of therapy (Blasé et al., in Int J Environ Res Public Health 18(7):Article 3329, https://doi.org/10.3390/ijerph18073329 , 2016). Heart rate variability (HRV) biofeedback (HRVB) is a non-invasive, non-pharmacological, breathing-based cardiorespiratory training technique that can reduce trauma symptoms and improve HRV parameters. Prior studies have demonstrated HRVB is well-tolerated by veterans with PTSD symptoms (Tan et al., in Appl Psychophysiol Biofeedback 36(1):27-35, 10.1007/s10484-010-9141-y, 2011; Schuman and Killian, in Appl Psychophysiol Biofeedback 44(1):9-20, https://doi.org/10.1007/s10484-018-9415-3 , 2019). This randomized wait-list controlled pilot study tested a short mobile app-adapted HRVB intervention in combination with treatment as usual for veterans with military-related PTSD to determine if further investigation was warranted. We assessed veterans' military-related PTSD symptoms, depression symptoms, and HRV time and frequency domain measures at baseline, after three clinical sessions, and one month later. This study combined clinical training and home biofeedback with a smartphone app and sensor to reinforce training and validate adherence. In the intervention group, depression and SDNN significantly improved, and we observed marginally significant improvements for PTSD Cluster B (intrusion) symptoms, whereas no significant improvements were observed in the control group. In addition, the brief protocol was acceptable to veterans with PTSD with over 83% of participants completing the study. However, adherence to home practice was low. Findings suggest brief HRVB interventions can decrease comorbid depression and improve overall autonomic function in veterans with PTSD; however, additional research on home biofeedback is necessary to determine the best strategies to increase adherence and which veterans would benefit from brief HRVB interventions.

Autonomic nervous system assessment using heart rate variability

The role of the autonomic nervous system in the onset of supraventricular and ventricular arrhythmias is well established. It can be analysed by the spontaneous behaviour of the heart rate with ambulatory ECG recordings, through heart rate variability measurements. Input of heart rate variability parameters into artificial intelligence models to make predictions regarding the detection or forecast of rhythm disorders is becoming routine and neuromodulation techniques are now increasingly used for their treatment. All this warrants a reappraisal of the use of heart rate variability for autonomic nervous system assessment.Measurements performed over long periods such as 24H-variance, total power, deceleration capacity, and turbulence are suitable for estimating the individual basal autonomic status. Spectral measurements performed over short periods provide information on the dynamics of systems that disrupt this basal balance and may be part of the triggers of arrhythmias, as well as premature atrial or ventricular beats. All heart rate variability measurements essentially reflect the modulations of the parasympathetic nervous system which are superimposed on the impulses of the adrenergic system. Although heart rate variability parameters have been shown to be useful for risk stratification in patients with myocardial infarction and patients with heart failure, they are not part of the criteria for prophylactic implantation of an intracardiac defibrillator, because of their high variability and the improved treatment of myocardial infarction. Graphical methods such as Poincaré plots allow quick screening of atrial fibrillation and are set to play an important role in the e-cardiology networks. Although mathematical and computational techniques allow manipulation of the ECG signal to extract information and permit their use in predictive models for individual cardiac risk stratification, their explicability remains difficult and making inferences about the activity of the ANS from these models must remain cautious.