Neuro-cardiac coupling predicts transcutaneous auricular vagus nerve stimulation effects

Transcutaneous auricular vagus nerve stimulation to acutely reduce emotional vulnerability and improve emotional regulation in borderline personality disorder (tVNS-BPD): study protocol for a randomized, single-blind, sham-controlled trial

BACKGROUND

Borderline personality disorder (BPD) is considered a disorder of emotion regulation resulting from the expression of a biologically determined emotional vulnerability (that is, heightened sensitivity to emotion, increased emotional intensity/reactivity, and a slow return to emotional baseline) combined with exposure to invalidating environments. Vagal tone has been associated with activity in cortical regions involved in emotion regulation and a lower resting state of vagal tone has been observed in BPD patients relative to healthy controls. Non-invasive transcutaneous auricular vagus nerve stimulation (taVNS) has been shown to reduce temper outbursts in adults with Prader-Willi Syndrome, to enhance recognition of emotions in healthy students, and to improve depressive and anxiety symptoms. Furthermore, a single session of taVNS has been shown to acutely alter the recognition of facial expressions of negative valence in adolescents with MDD and increase emotion recognition in controls. However, the effect of taVNS on emotional vulnerability and regulation in individuals diagnosed with BPD has not been investigated. Our aims are to determine if taVNS is effective in acutely reducing emotional vulnerability and improve emotional regulation in BPD patients.

METHODS

Forty-two patients will be randomized to a single session of taVNS or sham-taVNS while going through an affect induction procedure. It will consist of the presentation of one neutral and three negative affect-evoking 4-min-long videos in sequence, each of which is followed by a 4-min post-induction period during which participants will rate the quality and intensity of their current self-reported emotions (post-induction ratings) and the perceived effectiveness in managing their emotions during the video presentation. The rating of the current self-reported emotions will be repeated after every post-induction period (recovery ratings). Mixed models with individuals as random effect will be used to investigate the ratings at each stage of the study, taking into account the repeated measures of the same individuals at baseline, pre-induction, post-induction, and recovery.

DISCUSSION

The study has potential to yield new insights into the role of vagal tone in emotion dysregulation in BPD and offer preliminary data on the effectiveness of taVNS as a possible non-invasive brain stimulation to treat a core symptom of BPD.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05892900. Retrospectively registered on Jun 07, 2023.

The effect of transcutaneous auricular vagus nerve stimulation on cardiovascular function in subarachnoid hemorrhage patients: a safety study

Introduction

Subarachnoid hemorrhage (SAH) is characterized by intense central inflammation, leading to substantial post-hemorrhagic complications such as vasospasm and delayed cerebral ischemia. Given the anti-inflammatory effect of transcutaneous auricular vagus nerve stimulation (taVNS) and its ability to promote brain plasticity, taVNS has emerged as a promising therapeutic option for SAH patients. 3,10,13 However, the effects of taVNS on cardiovascular dynamics in critically ill patients like those with SAH have not yet been investigated. Given the association between cardiac complications and elevated risk of poor clinical outcomes after SAH, it is essential to characterize the cardiovascular effects of taVNS to ensure this approach is safe in this fragile population 5 . Therefore, we assessed the impact of both acute taVNS and repetitive taVNS on cardiovascular function in this study.

Methods

In this randomized clinical trial, 24 SAH patients were assigned to either a taVNS treatment or a Sham treatment group. During their stay in the intensive care unit, we monitored patient electrocardiogram (ECG) readings and vital signs. We compared long-term changes in heart rate, heart rate variability, QT interval, and blood pressure between the two groups. Additionally, we assessed the effects of acute taVNS by comparing cardiovascular metrics before, during, and after the intervention. We also explored rapidly responsive cardiovascular biomarkers in patients exhibiting clinical improvement.

Results

We found that repetitive taVNS did not significantly alter heart rate, corrected QT interval, blood pressure, or intracranial pressure. However, taVNS increased overall heart rate variability and parasympathetic activity from 5-10 days after initial treatment, as compared to the sham treatment. Acutely, taVNS increased heart rate, blood pressure, and peripheral perfusion index without affecting the corrected QT interval, intracranial pressure, or heart rate variability. The acute post-treatment elevation in heart rate was more pronounced in patients who experienced a decrease of more than 1 point in their Modified Rankin Score at the time of discharge.

Conclusions

Our study found that taVNS treatment did not induce adverse cardiovascular effects, such as bradycardia or QT prolongation, supporting its development as a safe immunomodulatory treatment approach for SAH patients. The observed acute increase in heart rate after taVNS treatment may serve as a biomarker for SAH patients who could derive greater benefit from this treatment. Trial registration: NCT04557618.

Expiratory-gated Transcutaneous Auricular Vagus Nerve Stimulation (taVNS) does not Further Augment Heart Rate Variability During Slow Breathing at 0.1 Hz

As cardiac vagal control is a hallmark of good health and self-regulatory capacity, researchers are seeking ways to increase vagally mediated heart rate variability (vmHRV) in an accessible and non-invasive way. Findings with transcutaneous auricular vagus nerve stimulation (taVNS) have been disappointing in this respect, as its effects on vmHRV are inconsistent at best. It has been speculated that combining taVNS with other established ways to increase vmHRV may produce synergistic effects. To test this idea, the present study combined taVNS with slow breathing in a cross-over design. A total of 22 participants took part in two sessions of breathing at 6 breaths/min: once combined with taVNS, and once combined with sham stimulation. Electrical stimulation (100 Hz, 400 µs) was applied during expiration, either to the tragus and cavum conchae (taVNS) or to the earlobe (sham). ECG was recorded during baseline, 20-minutes of stimulation, and the recovery period. Frequentist and Bayesian analyses showed no effect of taVNS (in comparison to sham stimulation) on the root mean square of successive differences between normal heartbeats, mean inter-beat interval, or spectral power of heart rate variability at a breathing frequency of 0.1 Hz. These findings suggest that expiratory-gated taVNS combined with the stimulation parameters examined here does not produce acute effects on vmHRV during slow breathing.

The effect of auricular vagus nerve stimulation on electroencephalography and electromyography measurements in healthy persons

Objectives: Auricular vagus nerve stimulation (VNS) is a non-invasive treatment modality. Opinions that it can be used in the treatment of various clinical problems have gained importance in recent years. In this study, it was aimed to lay the groundwork for the use of the auricular VNS in different ears. Methods: Healthy individuals (n = 90) were divided into three groups: unilateral left (n = 30), unilateral right (n = 30), and bilateral (n = 30) auricular VNS. Electroencephalography (EEG) and electromyography (EMG) measurements were performed before and after auricular VNS (10 Hz, 300 µs, 20 min) for a single session. Results: An increase in wrist extensor muscles activation was detected on the contralateral side of the auricular VNS application side. It has been observed that there is a general decrease in the power of high-frequency waves and an increase in the power of lower-medium frequency waves in various parts of the brain. Conclusion: Our findings suggest that the projection of the auricular VNS in the central nervous system may also affect the corticospinal tracts.

Modifying functional brain networks in focal epilepsy by manual visceral-osteopathic stimulation of the vagus nerve at the abdomen

Non-invasive transcutaneous vagus nerve stimulation elicits similar therapeutic effects as invasive vagus nerve stimulation, offering a potential treatment alternative for a wide range of diseases, including epilepsy. Here, we present a novel, non-invasive stimulation of the vagus nerve, which is performed manually viscero-osteopathically on the abdomen (voVNS). We explore the impact of short-term voVNS on various local and global characteristics of EEG-derived, large-scale evolving functional brain networks from a group of 20 subjects with and without epilepsy. We observe differential voVNS-mediated alterations of these characteristics that can be interpreted as a reconfiguration and modification of networks and their stability and robustness properties. Clearly, future studies are necessary to assess the impact of such a non-pharmaceutical intervention on clinical decision-making in the treatment of epilepsy. However, our findings may add to the current discussion on the importance of the gut-brain axis in health and disease. Clinical Trial Registration: https://drks.de/search/en/trial/DRKS00029914, identifier DRKS00029914.

A systematic review of the effects of transcutaneous auricular vagus nerve stimulation on baroreflex sensitivity and heart rate variability in healthy subjects

PURPOSE

This systematic review aimed to evaluate the effect of transcutaneous auricular vagus nerve stimulation on heart rate variability and baroreflex sensitivity in healthy populations.

METHOD

PubMed, Scopus, the Cochrane Library, Embase, and Web of Science were systematically searched for controlled trials that examined the effects of transcutaneous auricular vagus nerve stimulation on heart rate variability parameters and baroreflex sensitivity in apparently healthy individuals. Two independent researchers screened the search results, extracted the data, and evaluated the quality of the included studies.

RESULTS

From 2458 screened studies, 21 were included. Compared with baseline measures or the comparison group, significant changes in the standard deviation of NN intervals, the root mean square of successive RR intervals, the proportion of consecutive RR intervals that differ by more than 50 ms, high-frequency power, low-frequency to high-frequency ratio, and low-frequency power were found in 86%, 75%, 69%, 47%, 36%, and 25% of the studies evaluating the effects of transcutaneous auricular vagus nerve stimulation on these indices, respectively. Baroreflex sensitivity was evaluated in six studies, of which a significant change was detected in only one. Some studies have shown that the worse the basic autonomic function, the better the response to transcutaneous auricular vagus nerve stimulation.

CONCLUSION

The results were mixed, which may be mainly attributable to the heterogeneity of the study designs and stimulation delivery dosages. Thus, future studies with comparable designs are required to determine the optimal stimulation parameters and clarify the significance of autonomic indices as a reliable marker of neuromodulation responsiveness.

Combined effect of transcutaneous auricular vagus nerve stimulation and 0.1 Hz slow-paced breathing on working memory

Background

Previous research has found that transcutaneous auricular vagus nerve stimulation (taVNS) can improve working memory (WM) performance. It has also been shown that 0.1 Hz slow-paced breathing (SPB, i.e., breathing at a rate of approximately 6 breaths/min) can significantly influence physical state and cognitive function via changes in autonomic afferent activity. In the present study, we investigated the synergistic effects of taVNS and SPB on WM performance.

Methods

A total of 96 healthy people participated in this within-subjects experiment involving four conditions, namely taVNS, SPB, combined taVNS with SPB (taVNS + SPB), and sham. Each participant underwent each intervention for 30 min and WM was compared pre- and post-intervention using the spatial and digit n-back tasks in a random order four times. Permutation-based analysis of variance was used to assess the interaction between time and intervention.

Results

For the spatial 3-back task, a significant interaction between time and intervention was found for the accuracy rate of matching trials (mACC, p = 0.03). Post hoc analysis suggested that both taVNS and taVNS + SPB improved WM performance, however, no significant difference was found in the SPB or sham groups.

Conclusion

This study has replicated the effects of taVNS on WM performance reported in previous studies. However, the synergistic effects of combined taVNS and SPB warrant further research.

Low-intensity transcutaneous auricular vagus nerve stimulation reduces postoperative ileus after laparoscopic radical resection of colorectal cancer: a randomized controlled trial

BACKGROUND

Postoperative ileus (POI) is thought to result from a disrupted sympathetic/parasympathetic balance caused by trauma or surgery. Transcutaneous auricular vagus nerve stimulation (tVNS) is a non-invasive technique involving stimulation of the vagal auricular branch, leading to autonomic regulation and reduced inflammation. Here, the effects of low-intensity transcutaneous auricular vagal stimulation on POI after laparoscopic radical resection of colorectal cancer were investigated.

METHODS

One hundred and thirty-four patients who received scheduled laparoscopic radical resection of colorectal cancer were randomly allocated to the A and B groups. The A group received low-intensity (25 Hz, 50 mA) transcutaneous electrical stimulation of the right auricular branch for 20 minutes prior to anesthesia while the B group did not. The primary outcome was the incidence of POI.

RESULTS

The incidence of POI in the A group was 6.25% and 20% in the B group (P=0.022). Patients in the A group showed more regular bowel sounds after 24, 36, and 48 h than those in the B group (P<0.001).

CONCLUSIONS

Low-intensity transcutaneous auricular vagal stimulation reduced POI after laparoscopic radical resection of colorectal cancer.

Contactless Cardiovascular Assessment by Imaging Photoplethysmography: A Comparison with Wearable Monitoring

Despite the notable recent developments in the field of remote photoplethysmography (rPPG), extracting a reliable pulse rate variability (PRV) signal still remains a challenge. In this study, eight image-based photoplethysmography (iPPG) extraction methods (GRD, AGRD, PCA, ICA, LE, SPE, CHROM, and POS) were compared in terms of pulse rate (PR) and PRV features. The algorithms were made robust for motion and illumination artifacts by using ad hoc pre- and postprocessing steps. Then, they were systematically tested on the public dataset UBFC-RPPG, containing data from 42 subjects sitting in front of a webcam (30 fps) while playing a time-sensitive mathematical game. The performances of the algorithms were evaluated by statistically comparing iPPG-based and finger-PPG-based PR and PRV features in terms of Spearman's correlation coefficient, normalized root mean square error (NRMSE), and Bland-Altman analysis. The study revealed POS and CHROM techniques to be the most robust for PR estimation and the assessment of overall autonomic nervous system (ANS) dynamics by using PRV features in time and frequency domains. Furthermore, we demonstrated that a reliable characterization of the vagal tone is made possible by computing the Poincaré map of PRV series derived from the POS and CHROM methods. This study supports the use of iPPG systems as promising tools to obtain clinically useful and specific information about ANS dynamics.

Effects of non-invasive vagus nerve stimulation on cognitive and autonomic correlates of perseverative cognition

Perseverative cognitions can provoke psychophysiological stress in the absence of an actual stressor and are considered important transdiagnostic vulnerability factors for several (mental) health issues. These stress-related cognitive processes are reflected by both cognitive (assessed by self-reports) and autonomic inflexibility (assessed by heart rate variability; HRV), with a key role attributed to the vagus nerve. Interestingly, modulation of the afferent branches of the vagus can be achieved with transcutaneous auricular vagus nerve stimulation (taVNS), a non-invasive technique that employs a low-intensity electrical current applied to the ear. In a sample of healthy individuals, we investigated the effects of taVNS of the left concha, compared to sham (earlobe) stimulation, on the cognitive and autonomic correlates of perseverative cognition following a psychosocial stress task. Interestingly, taVNS significantly reduced cognitive rigidity, reflected by reduced subjective perseverative thinking after psychosocial stress. Although there were no direct effects on autonomic correlates of perseverative cognition, individual differences in perseverative thinking after the stressor significantly affected the effects of taVNS on HRV. Specifically, more autonomic inflexibility during the stress task (i.e., reduced HRV) was associated with increases in perseverative thinking afterward for the sham condition, but not the active taVNS condition. Additional exploratory analyses revealed no significant moderation of stimulation intensity. Overall, the study findings endorse the association between perseverative cognitions and vagus nerve functioning.

Trigeminal electrical stimulation with ULFTENS of the dorsal anterior mucosal surface of the tongue: Effects on Heart Rate Variability (HRV)

BACKGROUND

Trigeminal electrical stimulation of the dorsal anterior mucosal surface of the tongue has demonstrated its efficacy in a variety of neurological disorders in which anatomical or functional alterations are present. The pathogenesis of such disorders is often linked to altered arousal circuits, and the benefits of tongue stimulation are attributed to the rebalancing of this system. Dental ULFTENS shows efficacy in acting on the muscular, autonomic system and control of the descending pathways that modulate pain. It is administered at the skin level in the area anterior to the tragus and not on the mucosal surface of the tongue. The use of this stimulation technique at the tongue level could have new applications and clinical results if it were able to reduce the activity of arousal circuits.

MATERIAL AND METHOD

A new intraoral device allowed electrical stimulation of the dorsal anterior mucosa of the tongue in 32 healthy young women. The effects on HRV were monitored by photoplethysmographic wave (PPG) and compared with a control group. The HRV parameters studied were RMSSD, HF, LF, LF/HF, REC, DET.

RESULTS

The group of stimulated subjects showed a significant change in some of the HRV parameters that was maintained even in the epoch after the end of electrical stimulation. This effect can be considered as a vagal activation and a change of HRV trend. The control group of unstimulated subjects showed an opposite trend. There were no undesirable or annoying effects of stimulation.

CONCLUSION

Stimulation of the dorsal anterior (trigeminal) mucosal surface of the tongue with ULFTENS applied with an intraoral device was shown to be able to increase HRV.

Ear your heart: transcutaneous auricular vagus nerve stimulation on heart rate variability in healthy young participants

Background

Transcutaneous auricular vagus nerve stimulation (taVNS) stimulating the auricular branch of the vagus nerve along a well-defined neuroanatomical pathway, has promising therapeutic efficacy. Potentially, taVNS can modulate autonomic responses. Specifically, taVNS can induce more consistent parasympathetic activation and may lead to increased heart rate variability (HRV). However, the effects of taVNS on HRV remain inconclusive. Here, we investigated changes in HRV due to brief alteration periods of parasympathetic-vagal cardiac activity produced by taVNS on the cymba as opposed to control administration via the helix.

Materials and Methods

We compared the effect of 10 min of active stimulation (i.e., cymba conchae) to sham stimulation (i.e., helix) on peripheral cardiovascular response, in 28 healthy young adults. HRV was estimated in the time domain and frequency domain during the overall stimulation.

Results

Although active-taVNS and sham-taVNS stimulation did not differ in subjective intensity ratings, the active stimulation of the cymba led to vagally mediated HRV increases in both the time and frequency domains. Differences were significant between active-taVNS and both sham-taVNS and resting conditions in the absence of stimulation for various HRV parameters, but not for the low-frequency index of HRV, where no differences were found between active-taVNS and sham-taVNS conditions.

Conclusion

This work supports the hypothesis that taVNS reliably induces a rapid increase in HRV parameters when auricular stimulation is used to recruit fibers in the cymba compared to stimulation at another site. The results suggest that HRV can be used as a physiological indicator of autonomic tone in taVNS for research and potential therapeutic applications, in line with the established effects of invasive VNS. Knowledge of the physiological effect of taVNS short sessions in modulating cardiovagal processing is essential for enhancing its clinical use.

Event-related transcutaneous vagus nerve stimulation modulates behaviour and pupillary responses during an auditory oddball task

Transcutaneous auricular vagus nerve stimulation (taVNS) is a neuromodulatory technique that is thought to activate the Locus Coeruleus-Noradrenaline (LC-NA) system. Standard taVNS protocols consist of the administration of intermittent or continuous stimulation over long periods. However, there is currently a limited understanding of the temporal dynamics of taVNS modulation of cognitive processes, as well as its mechanisms of action. We argue that novel stimulation approaches, informed by established theories of the LC-NA system, are needed to further our understanding of the neurocognitive underpinnings of taVNS. In this pre-registered study, we tested whether an "event-related" taVNS protocol can modulate the LC-NA system. In a within-subject design (single session) we delivered brief trains of taVNS (3 s) during an auditory oddball paradigm. The taVNS was time-locked to the target stimuli presentation and randomly interleaved with sham stimulation. Response times (RT) and stimuli-driven pupillary diameter (PD) were used as indices of LC-NA activity. Results revealed that active taVNS increased RT to targets, as compared to sham trials. Notably, in line with current theories of LC-NA functioning, taVNS modulation of target-related pupil dilation depended on pre-stimulation PD, an index of baseline LC-NA activity. In particular, active (vs. sham) taVNS was associated with smaller pupil dilation in trials where the baseline PD was small. These results demonstrate, for the first time, the effectiveness of brief event-related taVNS in the modulation of cognitive processes and highlight the importance of using pupil size as an index of tonic and phasic LC-NA activity.

Auricular Vagus Nerve Stimulation Attenuates Lipopolysaccharide-Induced Acute Lung Injury by Inhibiting Neutrophil Infiltration and Neutrophil Extracellular Traps Formation

ABSTRACT

Vagus nerve stimulation has been shown to exert anti-inflammation activities in sepsis. However, surgical implantation of stimulation devices is performed under general anesthesia, which limits its clinical application. Auricular vagus nerve stimulation (AVNS) is a minimal invasive technique that delivers electrical currents to the auricular branch of the vagus nerve. The purpose of this study was to determine the effects of AVNS on systemic inflammation, lung injury, neutrophil infiltration, and neutrophil extracellular traps (NETs) formation in the lung. In a LPS challenge lung-injury mice model, AVNS was applied to bilateral ears. Twelve hours after LPS administration, samples of blood, bronchoalveolar lavage fluid (BALF), and lung tissues were processed for investigations. We found that the treatment with AVNS significantly attenuated histopathological changes and neutrophil infiltration in the lung tissue, inhibited inflammatory cytokine elevations in serum and BALF, and decreased protein concentrations in BALF. Besides, AVNS decreased leukocyte and neutrophil accounts in BALF. Furthermore, colocalization of citrullination of histone H3 and myeloperoxidase expressions (highly specific marker of NETs) was reduced in AVNS mice. In conclusion, AVNS reduced systemic inflammation, attenuated lung edema, and inhibited neutrophil infiltration and NETs formation in the lung in LPS mice.

Current challenges in reliably targeting the noradrenergic locus coeruleus using transcutaneous auricular vagus nerve stimulation (taVNS)

Transcutaneous auricular vagus nerve stimulation (taVNS), as a non-invasive brain stimulation technique may influence the locus coeruleus-norepinephrine system (LC-NE system) via modulation of the Vagus Nerve (VN) which projects to the LC. Few human studies exist examining the effects of taVNS on the LC-NE system and studies to date assessing the ability of taVNS to target the LC yield heterogeneous results. The aim of this review is to present an overview of the current challenges in assessing effects of taVNS on LC function and how translational approaches spanning animal and human research can help in this regard. A particular emphasis of the review discusses how the effects of taVNS may be influenced by changes in structure and function of the LC-NE system across the human lifespan and in disease.

High-resolution computational modeling of the current flow in the outer ear during transcutaneous auricular Vagus Nerve Stimulation (taVNS)

BACKGROUND

Transcutaneous auricular Vagus Nerve Stimulation (taVNS) applies low-intensity electrical current to the ear with the intention of activating the auricular branch of the Vagus nerve. The sensitivity and selectivity of stimulation applied to the ear depends on current flow pattern produced by a given electrode montage (size and placement).

OBJECTIVE

We compare different electrodes designs for taVNS considering both the predicted peak electric fields (sensitivity) and their spatial distribution (selectivity).

METHODS

Based on optimized high-resolution (0.47 mm) T1 and T2 weighted MRI, we developed an anatomical model of the left ear and the surrounding head tissues including brain, CSF/meninges, skull, muscle, blood vessels, fat, cartilage, and skin. The ear was further segmented into 6 regions of interest (ROI) based on various nerve densities: cavum concha, cymba concha, crus of helix, tragus, antitragus, and earlobe. A range of taVNS electrode montages were reproduced spanning varied electrodes sizes and placements over the tragus, cymba concha, earlobe, cavum concha, and crus of helix. Electric field across the ear (from superficial skin to cartilage) for each montage at 1 mA or 2 mA taVNS, assuming an activation threshold of 6.15 V/m, 12.3 V/m or 24.6 V/m was predicted using a Finite element method (FEM). Finally, considering every ROI, we calculated the sensitivity and selectivity of each montage.

RESULTS

Current flow patterns through the ear were highly specific to the electrode montage. Electric field was maximal at the ear regions directly under the electrodes, and for a given total current, increases with decreasing electrode size. Depending on the applied current and nerves threshold, activation may also occur in the regions between multiple anterior surface electrodes. Each considered montage was selective for one or two regions of interest. For example, electrodes across the tragus restricted significant electric field to the tragus. Stimulation across the earlobe restricted significant electric field to the earlobe and the antitragus. Because of this relative selectivity, use of control ear montages in experimental studies, support testing of targeting. Relative targeting was robust across assumptions of activation threshold and tissue properties.

DISCUSSION

Computational models provide additional insight on how details in electrode shape and placement impact sensitivity (how much current is needed) and selectivity (spatial distribution), thereby supporting analysis of existing approaches and optimization of new devices. Our result suggest taVNS current patterns and relative target are robust across individuals, though (variance in) axon morphology was not represented.

Brain plasticity and vagus nerve stimulation

After damage to the central nervous system, caused by traumatic injury or ischemia, plasticity becomes critically important for functional recovery. When this inherent capacity to adapt is limited despite training, external stimulation may support this process. Vagus nerve stimulation (VNS) is an effective method to enhance the effect of motor rehabilitation training on functional recovery. However, the mechanisms by which VNS exerts beneficial effects on cortical plasticity are not completely understood. Experimental work suggests that VNS fosters a neurochemical milieu that facilitates synaptic plasticity and supports reinforcement mechanisms. Animal studies, furthermore, suggest that VNS delivery is time-critical and that optima in the parameter space need to be titrated for effect maximization. Human studies suggest that VNS modifies corticospinal excitability. First studies in stroke patients show positive results for invasive, and also promising findings for non-invasive VNS.

Reassessment of the Effect of Transcutaneous Auricular Vagus Nerve Stimulation Using a Novel Burst Paradigm on Cardiac Autonomic Function in Healthy Young Adults

BACKGROUND

Transcutaneous auricular vagus nerve stimulation (taVNS) may modulate cardiac autonomic function. However, the response rate of the traditional tonic paradigm is low, and the results remain inconsistent. A recent pilot study presented a novel burst paradigm to activate the cardiac parasympathetic system, which might offer a new approach to treat cardiac autonomic function. The present study reassessed the effect of burst taVNS on modulating heart rate variability and explored the difference between burst and traditional tonic paradigms.

MATERIALS AND METHODS

Forty-two young adults were recruited for this study. Each participant underwent three types of taVNS with sham (30 sec of stimulation), tonic (25 Hz, 500 μsec), and burst (five pulses at 500 Hz every 200 msec) paradigms, respectively, with simultaneous electrocardiogram recording. One-way analysis of variance, multivariate analysis of variance, and linear regression were used for analysis. Multiple testing was performed using Bonferroni correction.

RESULTS

Both burst and tonic paradigms induced a significant decrease in heart rate, which continued until poststimulation, and increased cardiac parasympathetic activity. Moreover, two parasympathetic system indicators showed significant increase only in burst taVNS. The response rates during burst (35.7%) and tonic (38.1%) stimulations were both higher than that during sham stimulation (11.9%). The response to taVNS showed parameter specificity with few nonresponders to the tonic paradigm responding to the burst paradigm. The overall response rate increased from 38.1% in tonic taVNS to 54.8% in taVNS using both burst and tonic paradigms. For both burst and tonic responders, baseline cardiac parasympathetic activity was found to be significantly negatively correlated with changes during stimulation.

CONCLUSION

The burst parameter could be used as an alternative strategy for regulating cardiac parasympathetic function by taVNS, which has the potential to be used as a complementary paradigm to traditional tonic taVNS for promoting clinical treatment efficacy.

Electrical vagus nerve stimulation as a prophylaxis for SIRS and postoperative ileus

Abdominal surgery results in an activation of immune cells of the bowel wall and a consecutive cytokine and nitric oxide (NO) release leading to an inflammation of the muscularis externa and a bowel paralysis, the so-called postoperative ileus (POI). In addition to the local inflammation, major surgical trauma can also lead to a variable pronounced systemic inflammation up to its maximum variant, the systemic inflammatory response syndrome (SIRS), with hypotension, capillary leak and a breakdown of the intestinal barrier function followed by multi-organ dysfunction (MODS). Until now, neither for SIRS nor for POI, a prophylaxis or an evidence-based treatment exists. Since the pioneering work from Kevin Tracey and his group in the late 90s characterizing the role of the vagus nerve in inflammation and describing the cholinergic anti-inflammatory pathway (CAIP) for the first time, substantial efforts have been made in the research field of neuro-immune interactions. Today, the anti-inflammatory potential of vagus nerve stimulation is moving more and more into focus resulting in new therapeutic approaches. This review focuses on the role of the CAIP in the development of SIRS and POI. Furthermore, new therapeutic options like transcutaneous vagus nerve stimulation are highlighted.

Transcutaneous Auricular Vagus Nerve Stimulation Combined With Slow Breathing: Speculations on Potential Applications and Technical Considerations

OBJECTIVES

Transcutaneous auricular vagus nerve stimulation (taVNS) is a relatively novel noninvasive neurostimulation method that is believed to mimic the effects of invasive cervical VNS. It has recently been suggested that the effectiveness of taVNS can be enhanced by combining it with controlled slow breathing. Slow breathing modulates the activity of the vagus nerve and is used in behavioral medicine to decrease psychophysiological arousal. Based on studies that examine the effects of taVNS and slow breathing separately, this article speculates on some of the conditions in which this combination treatment may prove effective. Furthermore, based on findings from studies on the optimization of taVNS and slow breathing, this article provides guidance on how to combine taVNS with slow breathing.

MATERIALS AND METHODS

A nonsystematic review.

RESULTS

Both taVNS and slow breathing are considered promising add-on therapeutic approaches for anxiety and depressive disorders, chronic pain, cardiovascular diseases, and insomnia. Therefore, taVNS combined with slow breathing may produce additive or even synergistic beneficial effects in these conditions. Studies on respiratory-gated taVNS during spontaneous breathing suggest that taVNS should be delivered during expiration. Therefore, this article proposes to use taVNS as a breathing pacer to indicate when and for how long to exhale during slow breathing exercises.

CONCLUSIONS

Combining taVNS with slow breathing seems to be a promising hybrid neurostimulation and behavioral intervention.

Electrical stimulation of the external ear acutely activates noradrenergic mechanisms in humans

BACKGROUND

Transcutaneous stimulation of the external ear is thought to recruit afferents of the auricular vagus nerve, providing a means to activate noradrenergic pathways in the central nervous system. Findings from human studies examining the effects of auricular stimulation on noradrenergic biomarkers have been mixed, possibly relating to the limited and variable parameter space explored to date.

OBJECTIVE

We tested the extent to which brief pulse trains applied to locations of auricular innervation (canal and concha) elicit acute pupillary responses (PRs) compared to a sham location (lobe). Pulse amplitude and frequency were varied systematically to examine effects on PR features.

METHODS

Participants (n = 19) underwent testing in three separate experiments, each with stimulation applied to a different external ear location. Perceptual threshold (PT) was measured at the beginning of each experiment. Pulse trains (∼600 ms) consisting of different amplitude (0.0xPT, 0.8xPT, 1.0xPT, 1.5xPT, 2.0xPT) and frequency (25 Hz, 300 Hz) combinations were administered during eye tracking procedures.

RESULTS

Stimulation to all locations elicited PRs which began approximately halfway through the pulse train and peaked shortly after the final pulse (≤1 s). PR size and incidence increased with pulse amplitude and tended to be greatest with canal stimulation. Higher pulse frequency shortened the latency of PR onset and peak dilation. Changes in pupil diameter elicited by pulse trains were weakly associated with baseline pupil diameter.

CONCLUSION

(s): Auricular stimulation elicits acute PRs, providing a basis to synchronize neuromodulator release with task-related neural spiking which preclinical studies show is a critical determinant of therapeutic effects. Further work is needed to dissociate contributions from vagal and non-vagal afferents mediating activation of the biomarker.

Transcranial Auricular Vagus Nerve Stimulation (taVNS) and Ear-EEG: Potential for Closed-Loop Portable Non-invasive Brain Stimulation

No matter how hard we concentrate, our attention fluctuates – a fact that greatly affects our success in completing a current task. Here, we review work from two methods that, in a closed-loop manner, have the potential to ameliorate these fluctuations. Ear-EEG can measure electric brain activity from areas in or around the ear, using small and thus portable hardware. It has been shown to capture the state of attention with high temporal resolution. Transcutaneous auricular vagus nerve stimulation (taVNS) comes with the same advantages (small and light) and critically current research suggests that it is possible to influence ongoing brain activity that has been linked to attention. Following the review of current work on ear-EEG and taVNS we suggest that a combination of the two methods in a closed-loop system could serve as a potential application to modulate attention.

A 1.2nW Analog Electrocardiogram Processor Achieving a 99.63% QRS Complex Detection Sensitivity

An energy-efficient electrocardiogram (ECG) processor for real-time QRS detection is presented. The proposed algorithm is based on the Pan-Tompkins algorithm and it is implemented in the analog domain leveraging ultra-low power analog electronics biased in subthreshold. Operational transconductance amplifiers with ∼100 mV linear range are used in almost all of the processing blocks, while squaring is performed on current signals. Additionally, instead of adaptive thresholding, a fixed-level thresholding is performed, thereby eliminating the need for additional blocks such as memory and threshold update. The processor is designed in 65 nm TSMC CMOS technology and has a footprint of 0.078 mm². When supplied by a 1 V supply, the processor consumes 1.2 nW. Using the recordings in the MIT-BIH database, the processor achieves an average QRS detection sensitivity of 99.63% and positive predictivity of 99.47%.

Auricular Vagus Neuromodulation-A Systematic Review on Quality of Evidence and Clinical Effects

Background: The auricular branch of the vagus nerve runs superficially, which makes it a favorable target for non-invasive stimulation techniques to modulate vagal activity. For this reason, there have been many early-stage clinical trials on a diverse range of conditions. These trials often report conflicting results for the same indication. Methods: Using the Cochrane Risk of Bias tool we conducted a systematic review of auricular vagus nerve stimulation (aVNS) randomized controlled trials (RCTs) to identify the factors that led to these conflicting results. The majority of aVNS studies were assessed as having "some" or "high" risk of bias, which makes it difficult to interpret their results in a broader context. Results: There is evidence of a modest decrease in heart rate during higher stimulation dosages, sometimes at above the level of sensory discomfort. Findings on heart rate variability conflict between studies and are hindered by trial design, including inappropriate washout periods, and multiple methods used to quantify heart rate variability. There is early-stage evidence to suggest aVNS may reduce circulating levels and endotoxin-induced levels of inflammatory markers. Studies on epilepsy reached primary endpoints similar to previous RCTs testing implantable vagus nerve stimulation therapy. Preliminary evidence shows that aVNS ameliorated pathological pain but not evoked pain. Discussion: Based on results of the Cochrane analysis we list common improvements for the reporting of results, which can be implemented immediately to improve the quality of evidence. In the long term, existing data from aVNS studies and salient lessons from drug development highlight the need for direct measures of local neural target engagement. Direct measures of neural activity around the electrode will provide data for the optimization of electrode design, placement, and stimulation waveform parameters to improve on-target engagement and minimize off-target activation. Furthermore, direct measures of target engagement, along with consistent evaluation of blinding success, must be used to improve the design of controls-a major source of concern identified in the Cochrane analysis. The need for direct measures of neural target engagement and consistent evaluation of blinding success is applicable to the development of other paresthesia-inducing neuromodulation therapies and their control designs.

Effects of transcutaneous vagus nerve stimulation (tVNS) on beta and gamma brain oscillations

Physiological and behavioral effects induced through transcutaneous vagus nerve stimulation (tVNS) are under scrutiny in a growing number of studies, yet its mechanisms of action remain poorly understood. One candidate mechanism is a modulation of γ-aminobutyric acid (GABA) transmission through tVNS. Two recent behavioral studies suggest that such a GABAergic effect might occur in a lateralized fashion, i.e., the GABA modulation might be stronger in the left than in the right brain hemisphere after tVNS applied to the left ear. Using magnetoencephalography (MEG), we tested for GABA-associated modulations in resting and event-related brain oscillations and for a lateralization of those effects in a sample of 41 healthy young adults. Our data provide substantial evidence against all hypotheses, i.e., we neither find effects of tVNS on oscillatory power nor a lateralization of effects.

Brain-Heart Interaction During Transcutaneous Auricular Vagus Nerve Stimulation

OBJECTIVES

Transcutaneous auricular vagus nerve stimulation (taVNS) modulates brain activity and heart function. The induced parasympathetic predominance leads to an increase of heart rate variability (HRV). Knowledge on the corresponding cortical activation pattern is, however, scarce. We hypothesized taVNS-induced HRV increases to be related to modulation of cortical activity that regulates the autonomic outflow to the heart.

MATERIALS AND METHODS

In thirteen healthy subjects, we simultaneously recorded 64-channel electroencephalography and electrocardiography during taVNS. Two taVNS stimulation targets were investigated, i.e., the cymba conchae and inner tragus, and compared to active control stimulation in the anatomical vicinity, i.e., at the crus helicis and outer tragus. We used intermitted stimulation bursts of 25 Hz applied at a periodicity of 1 Hz. HRV was estimated with different time-domain methodologies: standard deviation of RR (SDNN), the root mean squares of successive differences (RMSSD), the percentage of RR-intervals with at least 50 ms deviation from the preceding RR-interval (pNN50), and the difference of consecutive RR intervals weighted by their mean (rrHRV).

RESULTS

The stimulation-induced HRV increases corresponded to frequency-specific oscillatory modulation of different cortical areas. All stimulation targets induced power modulations that were proportional to the HRV elevation. The most prominent changes that corresponded to HRV increases across all parameters and stimulation locations were frontal elevations in the theta-band. In the delta-band, there were frontal increases (RMSSD, pNN50, rrHRV, SDNN) and decreases (SDNN) across stimulation sites. In higher frequencies, there was a more divers activity pattern: Outer tragus/crus helicis stimulation increased oscillatory activity with the most prominent changes for the SDNN in frontal (alpha-band, beta-band) and fronto-parietal (gamma-band) areas. During inner tragus/cymba conchae stimulation the predominant pattern was a distributed power decrease, particularly in the fronto-parietal gamma-band.

CONCLUSION

Neuro-cardiac interactions can be modulated by electrical stimulation at different auricular locations. Increased HRV during stimulation is correlated with frequency-specific increases and decreases of oscillatory activity in different brain areas. When applying specific HRV measures, cortical patterns related to parasympathetic (RMSSD, pNN50, rrHRV) and sympathetic (SDNN) modulation can be identified. Thus, cortical oscillations may be used to define stimulation locations and parameters for research and therapeutic purposes.