Current Directions in the Auricular Vagus Nerve Stimulation II - An Engineering Perspective

A multicenter registry study on percutaneous electrical nerve field stimulation for pediatric disorders of gut-brain interaction

OBJECTIVES

Percutaneous electrical nerve field stimulation (PENFS) has demonstrated promise in single-center trials for pediatric abdominal pain-related disorders of gut-brain interaction (DGBI). Our aim was to explore efficacy of PENFS as standard therapy for DGBI in a registry involving multiple pediatric gastroenterology referral centers.

METHODS

This was a multicenter, prospective open-label registry of children (8-18 years) undergoing PENFS for DGBI at seven tertiary care gastroenterology clinics. DGBI subtypes were classified by Rome IV criteria. Parents and patients completed Abdominal Pain Index (API), Nausea Severity Scale (NSS), and Functional Disability Inventory (FDI) questionnaires before, during therapy and at follow-up visits up to 1 year later.

RESULTS

A total of 292 subjects were included. Majority (74%) were female with median (interquartile range [IQR]) age 16.3 (14.0, 17.7) years. Most (68%) met criteria for functional dyspepsia and 61% had failed ≥4 pharmacologic therapies. API, NSS, and FDI scores showed significant declines within 3 weeks of therapy, persisting long-term in a subset. Baseline (n = 288) median (IQR) child-reported API scores decreased from 2.68 (1.84, 3.58) to 1.99 (1.13, 3.27) at 3 weeks (p < 0.001) and 1.81 (0.85, 3.20) at 3 months (n = 75; p < 0.001). NSS scores similarly improved from baseline, persisting at three (n = 74; p < 0.001) and 6 months later (n = 55; p < 0.001). FDI scores displayed similar reductions at 3 months (n = 76; p = 0.01) but not beyond. Parent-reported scores were consistent with child reports.

CONCLUSIONS

This large, comprehensive, multicenter registry highlights efficacy of PENFS for gastrointestinal symptoms and functionality for pediatric DGBI.

Non-invasive Auricular Vagus nerve stimulation for Subarachnoid Hemorrhage (NAVSaH): Protocol for a prospective, triple-blinded, randomized controlled trial

Background

Inflammation has been implicated in driving the morbidity associated with subarachnoid hemorrhage (SAH). Despite understanding the important role of inflammation in morbidity following SAH, there is no current effective way to modulate this deleterious response. There is a critical need for a novel approach to immunomodulation that can be safely, rapidly, and effectively deployed in SAH patients. Vagus nerve stimulation (VNS) provides a non-pharmacologic approach to immunomodulation, with prior studies demonstrating VNS can reduce systemic inflammatory markers, and VNS has had early success treating inflammatory conditions such as arthritis, sepsis, and inflammatory bowel diseases. The aim of the Non-invasive Auricular Vagus nerve stimulation for Subarachnoid Hemorrhage (NAVSaH) trial is to translate the use of non-invasive transcutaneous auricular VNS (taVNS) to spontaneous SAH, with our central hypothesis being that implementing taVNS in the acute period following spontaneous SAH attenuates the expected inflammatory response to hemorrhage and curtails morbidity associated with inflammatory-mediated clinical endpoints.

Materials and methods

The overall objectives for the NAHSaH trial are to 1) Define the impact that taVNS has on SAH-induced inflammatory markers in the plasma and cerebrospinal fluid (CSF), 2) Determine whether taVNS following SAH reduces radiographic vasospasm, and 3) Determine whether taVNS following SAH reduces chronic hydrocephalus. Following presentation to a single enrollment site, enrolled SAH patients are randomly assigned twice daily treatment with either taVNS or sham stimulation for the duration of their intensive care unit stay. Blood and CSF are drawn before initiation of treatment sessions, and then every three days during a patient's hospital stay. Primary endpoints include change in the inflammatory cytokine TNF-α in plasma and cerebrospinal fluid between day 1 and day 13, rate of radiographic vasospasm, and rate of requirement for long-term CSF diversion via a ventricular shunt. Secondary outcomes include exploratory analyses of a panel of additional cytokines, number and type of hospitalized acquired infections, duration of external ventricular drain in days, interventions required for vasospasm, continuous physiology data before, during, and after treatment sessions, hospital length of stay, intensive care unit length of stay, and modified Rankin Scale score (mRS) at admission, discharge, and each at follow-up appointment for up to two years following SAH.

Discussion

Inflammation plays a central role in morbidity following SAH. This NAVSaH trial is innovative because it diverges from the pharmacologic status quo by harnessing a novel non-invasive neuromodulatory approach and its known anti-inflammatory effects to alter the pathophysiology of SAH. The investigation of a new, effective, and rapidly deployable intervention in SAH offers a new route to improve outcomes following SAH.

Trial registration

Clinical Trials Registered, NCT04557618. Registered on September 21, 2020, and the first patient was enrolled on January 4, 2021.

Advancements in non-invasive microwave brain stimulation: A comprehensive survey

This survey provides a comprehensive insight into the world of non-invasive brain stimulation and focuses on the evolving landscape of deep brain stimulation through microwave research. Non-invasive brain stimulation techniques provide new prospects for comprehending and treating neurological disorders. We investigate the methods shaping the future of deep brain stimulation, emphasizing the role of microwave technology in this transformative journey. Specifically, we explore antenna structures and optimization strategies to enhance the efficiency of high-frequency microwave stimulation. These advancements can potentially revolutionize the field by providing a safer and more precise means of modulating neural activity. Furthermore, we address the challenges that researchers currently face in the realm of microwave brain stimulation. From safety concerns to methodological intricacies, this survey outlines the barriers that must be overcome to fully unlock the potential of this technology. This survey serves as a roadmap for advancing research in microwave brain stimulation, pointing out potential directions and innovations that promise to reshape the field.

Recent Advances in Implantable Neural Interfaces for Multimodal Electrical Neuromodulation

Electrical neuromodulation plays a pivotal role in enhancing patient outcomes among individuals suffering from neurological disorders. Implantable neural interfaces are vital components of the electrical neuromodulation system to ensure desirable performance; However, conventional devices are limited to a single function and are constructed with bulky and rigid materials, which often leads to mechanical incompatibility with soft tissue and an inability to adapt to the dynamic and complex 3D structures of biological systems. In addition, current implantable neural interfaces utilized in clinical settings primarily rely on wire-based techniques, which are associated with complications such as increased risk of infection, limited positioning options, and movement restrictions. Here, the state-of-art applications of electrical neuromodulation are presented. Material schemes and device structures that can be employed to develop robust and multifunctional neural interfaces, including flexibility, stretchability, biodegradability, self-healing, self-rolling, or morphing are discussed. Furthermore, multimodal wireless neuromodulation techniques, including optoelectronics, mechano-electrics, magnetoelectrics, inductive coupling, and electrochemically based self-powered devices are reviewed. In the end, future perspectives are given.

Advances in Non-Invasive Neuromodulation: Designing Closed-Loop Devices for Respiratory-Controlled Transcutaneous Vagus Nerve Stimulation

Studies suggest non-invasive transcutaneous auricular vagus nerve stimulation (taVNS) as a potential therapeutic option for various pathological conditions, such as epilepsy and depression. Exhalation-controlled taVNS, which synchronizes stimulation with internal body rhythms, holds promise for enhanced neuromodulation, but there is no closed-loop system in the literature capable of performing such integration in real time. In this context, the objective was to develop real-time signal processing techniques and an integrated closed-loop device with sensors to acquire physiological data. After a conditioning stage, the signal is processed and delivers synchronized electrical stimulation during the patient's expiratory phase. Additional modules were designed for processing, software-controlled selectors, remote and autonomous operation, improved analysis, and graphical visualization. The signal processing method effectively extracted respiratory cycles and successfully attenuated signal noise. Heart rate variability was assessed in real time, using linear statistical evaluation. The prototype feedback stimulator device was physically constructed. Respiratory peak detection achieved an accuracy of 90%, and the real-time processing resulted in a small delay of up to 150 ms in the detection of the expiratory phase. Thus, preliminary results show promising accuracy, indicating the need for additional tests to optimize real-time processing and the application of the prototype in clinical studies.

Vagal nerve stimulation for headache

PURPOSE OF REVIEW

Vagal nerve stimulation (VNS) is emerging as a probable therapeutic option for headache. Several questions remain on the mechanism of action, device parameters, efficacy, duration of treatment and long-term safety. This review aims at describing findings of recent literature pertaining to VNS for headache, to put these findings into the perspective of our current fund of knowledge and future scope of work on the topic.

RECENT FINDINGS

Several studies on functional magnetic resonance imaging patterns following VNS in patients with headache have been published, revealing potential biomarkers of headache and possible treatment effects. A study on post-COVID-19 headache and its management with noninvasive cervical VNS adds to the body of original studies. Meta-analyses and systematic reviews outlining previous work have been published. The collection of these studies adds some data to mechanisms of VNS without adding much insight to differential effects of sub-types of VNS and possible device settings that could prove to be beneficial for headache management.

SUMMARY

Well designed studies are needed to identify mechanisms of action, elicit differential effects of various stimulation parameters, and to demonstrate long-term therapeutic effects and safety of VNS in headache.

Meniere Disease treated with transcutaneous auricular vagus nerve stimulation combined with betahistine Mesylate: A randomized controlled trial

BACKGROUND

Meniere Disease is a clinical condition defined by hearing loss, tinnitus, and aural fullness symptoms, there are currently no any medications approved for its treatment.

OBJECTIVE

To determine whether taVNS as an adjunctive therapy could relieve symptoms and improve the quality of life in patients with Meniere disease.

METHODS

In this Single-center, single blind, randomized trial, participants were assigned to transcutaneous auricular vagus nerve stimulation (taVNS) group and sham taVNS group. The primary outcome measures comprised Tinnitus Handicap Inventory, Dizziness Handicap Inventory, Pure Tone Auditory, Visual analogue scale of aural fullness. Secondary outcome measures comprised the 36-Item Short Form Health Survey, video head impulse test, and the caloric test.

RESULTS

After 12 weeks, the THI (-11.00, 95%CI, -14.87 to -7.13; P < 0.001), DHI (-47.26, 95%CI, -50.23 to -44.29; P < 0.001), VAS of aural fullness (-2.22, 95%CI, -2.95 to -1.49; P<0.01), and Pure Tone Thresholds (-7.07, 95%CI, -9.07 to -5.06; P<0.001) were significantly differed between the two groups. In addition, SF36(14.72, 95%CI, 11.06 to 18.39; P < 0.001), vHIT (RD, 0.26, 95 % CI, -0.44 to -0.08, RR, 0.43, 95 % CI, 0.22 to 0.83, P < 0.01), and the caloric test (RD, -0.24, 95 % CI, -0.43 to -0.04, RR, 0.66, 95 % CI, 0.44 to 0.95, P = 0.02) have significant difference between two group, respectively.

CONCLUSIONS

These findings suggest that taVNS combined with Betahistine Mesylate relieve symptoms and improve the quality of life for patients with Meniere Disease. taVNS can be considered an adjunctive therapy in treatment of Meniere Disease.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT05328895.

Voltammetry in the spleen assesses real-time immunomodulatory norepinephrine release elicited by autonomic neurostimulation

BACKGROUND

The noradrenergic innervation of the spleen is implicated in the autonomic control of inflammation and has been the target of neurostimulation therapies for inflammatory diseases. However, there is no real-time marker of its successful activation, which hinders the development of anti-inflammatory neurostimulation therapies and mechanistic studies in anti-inflammatory neural circuits.

METHODS

In mice, we performed fast-scan cyclic voltammetry (FSCV) in the spleen during intravenous injections of norepinephrine (NE), and during stimulation of the vagus, splanchnic, or splenic nerves. We defined the stimulus-elicited charge generated at the oxidation potential for NE (~ 0.88 V) as the "NE voltammetry signal" and quantified the dependence of the signal on NE dose and intensity of neurostimulation. We correlated the NE voltammetry signal with the anti-inflammatory effect of splenic nerve stimulation (SpNS) in a model of lipopolysaccharide- (LPS) induced endotoxemia, quantified as suppression of TNF release.

RESULTS

The NE voltammetry signal is proportional to the estimated peak NE blood concentration, with 0.1 μg/mL detection threshold. In response to SpNS, the signal increases within seconds, returns to baseline minutes later, and is blocked by interventions that deplete NE or inhibit NE release. The signal is elicited by efferent, but not afferent, electrical or optogenetic vagus nerve stimulation, and by splanchnic nerve stimulation. The magnitude of the signal during SpNS is inversely correlated with subsequent TNF suppression in endotoxemia and explains 40% of the variance in TNF measurements.

CONCLUSIONS

FSCV in the spleen provides a marker for real-time monitoring of anti-inflammatory activation of the splenic innervation during autonomic stimulation.

Clinical Research Progress of the Post-Stroke Upper Limb Motor Function Improvement via Transcutaneous Auricular Vagus Nerve Stimulation

Stroke is a disease with high morbidity and disability, and motor impairment is a common sequela of stroke. Transcutaneous auricular vagus nerve stimulation (taVNS) is a type of non-invasive stimulation, which can effectively improve post-stroke motor dysfunction. This review discusses stimulation parameters, intervention timing, and the development of innovative devices for taVNS. We further summarize the application of taVNS in improving post-stroke upper limb motor function to further promote the clinical research and application of taVNS in the rehabilitation of post-stroke upper limb motor dysfunction.

Literature review of transcutaneous electrical nerve stimulation in peripheral arterial occlusive disease of the lower limbs

The therapeutic challenge in peripheral arterial occlusive disease (PAD) is often to increase walking distance, improve pain or heal a wound when PAD is symptomatic. Walking rehabilitation or surgical revascularization techniques are limited. Others strategies as alternatives and/or complementary treatments are needed. Among alternative options, Transcutaneous Electrical Nerve Stimulations (TENS) could be of interest, both for improved walking distance or pain reduction. The Transcutaneous Electrical Nerve Stimulation (TENS) is a non-pharmacological, mini-invasive technique involving transcutaneous electrical stimulation. However, there are other transcutaneous electrical nerve stimulation techniques based on the principle of vagus nerve stimulation with different mechanistics. Trans-auricular Vagus nerve stimulation (Ta-VNS) is another TENS technique (electrode on the external ear) which relies on the anti-inflammatory pathways of efferent and afferent vagal fibers. We propose here to review the literature of mini-invasive electrical stimulations, whatever the anatomical zone concerned, in PAD.

METHOD

The aim was to evaluate the use of non-invasive transcutaneous electrical stimulation therapies (regardless of location) in PAD of the lower limbs, whatever the disease grade. A review of the literature was carried out via a search of the MEDLINE/PubMed database from 1975 to 2023. The articles were selected via abstracts by checking (1) medical indications: PAD patients with claudication were retained, excluding neurological or venous claudication, PAD whatever the disease grade (intermittent claudication or critical limb ischemia [CLI]) and (2) non invasive electrical stimulations were considered (neuromuscular electrical stimulation and spinal cord stimulation were excluded) whatever the anatomical site. Non-electrical stimuli such as acupuncture and reflexotherapy were excluded.

RESULTS

Only 9 items were selected, including 7 studies with TENS treatment on the calf, one with trans-auricular vagus nerve stimulation and one with electro-acupuncture points of stimulation.

CONCLUSION

Even if the mechanisms involved are different, TENS on the calves or in the external ears show an improvement of walking distance in PAD patients with intermittent claudication. The results of the studies show few positive effects in arteriopathy but we should keep vigilant in the technics used since mechanisms are different and not fully understood. Electro-stimulation of the calf and external ear appears to be an easy-to-use and accessible therapeutic option, especially since some PAD patients are still failing to be released from pain, despite the rise of endovascular interventional techniques.

Role of Vagus Nerve Stimulation in the Treatment of Chronic Pain

Vagus nerve stimulation (VNS) can modulate vagal activity and neuro-immune communication. Human and animal studies have provided growing evidence that VNS can produce analgesic effects in addition to alleviating refractory epilepsy and depression. The vagus nerve (VN) projects to many brain regions related to pain processing, which can be affected by VNS. In addition to neural regulation, the anti-inflammatory property of VNS may also contribute to its pain-inhibitory effects. To date, both invasive and noninvasive VNS devices have been developed, with noninvasive devices including transcutaneous stimulation of auricular VN or carotid VN that are undergoing many clinical trials for chronic pain treatment. This review aimed to provide an update on both preclinical and clinical studies of VNS in the management for chronic pain, including fibromyalgia, abdominal pain, and headaches. We further discuss potential underlying mechanisms for VNS to inhibit chronic pain.

Transcutaneous auricular vagus nerve stimulation as a potential novel treatment for polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine disorder in women of childbearing age. The etiology of PCOS is multifactorial, and current treatments for PCOS are far from satisfactory. Recently, an imbalanced autonomic nervous system (ANS) with sympathetic hyperactivity and reduced parasympathetic nerve activity (vagal tone) has aroused increasing attention in the pathogenesis of PCOS. In this paper, we review an innovative therapy for the treatment of PCOS and related co-morbidities by targeting parasympathetic modulation based on non-invasive transcutaneous auricular vagal nerve stimulation (ta-VNS). In this work, we present the role of the ANS in the development of PCOS and describe a large number of experimental and clinical reports that support the favorable effects of VNS/ta-VNS in treating a variety of symptoms, including obesity, insulin resistance, type 2 diabetes mellitus, inflammation, microbiome dysregulation, cardiovascular disease, and depression, all of which are also commonly present in PCOS patients. We propose a model focusing on ta-VNS that may treat PCOS by (1) regulating energy metabolism via bidirectional vagal signaling; (2) reversing insulin resistance via its antidiabetic effect; (3) activating anti-inflammatory pathways; (4) restoring homeostasis of the microbiota-gut-brain axis; (5) restoring the sympatho-vagal balance to improve CVD outcomes; (6) and modulating mental disorders. ta-VNS is a safe clinical procedure and it might be a promising new treatment approach for PCOS, or at least a supplementary treatment for current therapeutics.

Transcutaneous Auricular Vagus Nerve Stimulation in Pediatric Patients: A Systematic Review of Clinical Treatment Protocols and Stimulation Parameters

BACKGROUND

Noninvasive transcutaneous vagus nerve stimulation (tVNS) has promising therapeutic potential in a wide range of applications across somatic and psychiatric conditions. Compared with invasive vagus nerve stimulation, good safety and tolerability profiles also support the use of tVNS in pediatric patients. Potential neurodevelopment-specific needs, however, raise concerns regarding the age-appropriate adjustment of treatment protocols and applied stimulation parameters.

OBJECTIVE

In this study, we aimed to review registered trials and published studies to synthesize existing tVNS treatment protocols and stimulation parameters applied in pediatric patients.

MATERIALS AND METHODS

A systematic search of electronic data bases (PubMed, Scopus, MEDLINE, Cochrane Library, and PsycINFO) and ClinicalTrials was conducted. Information on patient and study-level characteristics (eg, clinical condition, sample size), the tVNS device (eg, brand name, manufacturer), stimulation settings (eg, pulse width, stimulation intensity), and stimulation protocol (eg, duration, dosage of stimulation) was extracted.

RESULTS

We identified a total of 15 publications (four study protocols) and 15 registered trials applying tVNS in pediatric patients (<18 years of age). Most of these studies did not exclusively address pediatric patients. None of the studies elaborated on neurodevelopmental aspects or justified the applied protocol or stimulation parameters for use in pediatric patients.

CONCLUSIONS

No dedicated pediatric tVNS devices exist. Neither stimulation parameters nor stimulation protocols for tVNS are properly justified in pediatric patients. Evidence on age-dependent stimulation effects of tVNS under a neurodevelopment framework is warranted. We discuss the potential implications of these findings with clinical relevance, address some of the challenges of tVNS research in pediatric populations, and point out key aspects in future device development and research in addition to clinical studies on pediatric populations.

Immediate effects and duration of a short and single application of transcutaneous auricular vagus nerve stimulation on P300 event related potential

Introduction

Transcutaneous auricular vagus nerve stimulation (taVNS) is a neuromodulatory technique that stimulates the auricular branch of the vagus nerve. The modulation of the locus coeruleus-norepinephrine (LC-NE) network is one of the potential working mechanisms of this method. Our aims were 1-to investigate if short and single applications of taVNS can modulate the P300 cognitive event-related potential (ERP) as an indirect marker that reflects NE brain activation under control of the LC, and 2-to evaluate the duration of these changes.

Methods

20 healthy volunteers executed an auditory oddball paradigm to obtain P300 and reaction time (RT) values. Then a 7 min active or sham taVNS period was initiated and simultaneously a new P300 paradigm was performed. We successively repeated the paradigm on 4 occasions with different time intervals up to 56 min after the stimulation onset.

Results

During active taVNS an immediate and significant effect of increasing the amplitude and reducing the latency of P300, as well as a shortening in the RT was observed. This effect was prolonged in time up to 28 min. The values then returned to pre-stimulation levels. Sham stimulation did not generate changes.

Discussion

Our results, demonstrate differential facilitating effects in a concrete time window after taVNS. Literature about the modulatory effect of taVNS over P300 ERP shows a wide spread of results. There is not a standardized system for taVNS and currently the great heterogeneity of stimulation approaches concerning targets and parameters, make it difficult to obtain conclusions about this relationship. Our study was designed optimizing several stimulation settings, such as a customized earbud stimulator, enlarged stimulating surface, simultaneous stimulation over the cymba and cavum conchae, a Delayed Biphasic Pulse Burst and current controlled stimulation that adjusted the output voltage and guaranteed the administration of a preset electrical dose. Under our stimulation conditions, targeting vagal nerve fibers via taVNS modulates the P300 in healthy participants. The optimal settings of modulatory function of taVNS on P300, and their interdependency is insufficiently studied in the literature, but our data provides several easily optimizable parameters, that will produce more robust results in future.

Induced pain affects auricular and body biosignals: From cold stressor to deep breathing

Pain affects every fifth adult worldwide and is a significant health problem. From a physiological perspective, pain is a protective reaction that restricts physical functions and causes responses in physiological systems. These responses are accessible for evaluation via recorded biosignals and can be favorably used as feedback in active pain therapy via auricular vagus nerve stimulation (aVNS). The aim of this study is to assess the significance of diverse parameters of biosignals with respect to their deflection from cold stressor to deep breathing and their suitability for use as biofeedback in aVNS stimulator. Seventy-eight volunteers participated in two cold pressors and one deep breathing test. Three targeted physiological parameters (RR interval of electrocardiogram, cardiac deflection magnitude Z _AC of ear impedance signal, and cardiac deflection magnitude PPG _AC of finger photoplethysmogram) and two reference parameters (systolic and diastolic blood pressures BP _S and BP _D) were derived and monitored. The results show that the cold water decreases the medians of targeted parameters (by 5.6, 9.3%, and 8.0% of RR, Z _AC, and PPG _AC, respectively) and increases the medians of reference parameters (by 7.1% and 6.1% of BP _S and BP _D, respectively), with opposite changes in deep breathing. Increasing pain level from relatively mild to moderate/strong with cold stressor varies the medians of targeted and reference parameters in the range from 0.5% to 6.0% (e.g., 2.9% for RR, Z _AC and 6.0% for BP _D). The physiological footprints of painful cold stressor and relaxing deep breathing were shown for auricular and non-auricular biosignals. The investigated targeted parameters can be used as biofeedback to close the loop in aVNS to personalize the pain therapy and increase its compliance.

Case Report: Auricular vagus nerve stimulation possibly alleviates COVID-19 disease on a high-risk patient

Introduction: SARS-CoV-2 is a highly contagious virus that was identified as the cause of COVID-19 disease in early 2020. The infection is clinically similar to interstitial pneumonia and acute respiratory distress syndrome (ARDS) and often shows cardiovascular damage. Patients with cardiovascular risk factors are more prone to COVID-19 disease and their sequelae. Due to the anti-inflammatory effect and the improvement in pulmonary function, auricular vagus nerve stimulation (aVNS) therapy might alleviate a COVID-19 infection. Patient and Methods: A high-risk patient with cardiovascular diseases and Implantable Cardioverter Defibrillator (ICD), type 2 diabetes and peripheral arterial disease IV, according to Rutherford`s classification, became infected with COVID-19. The patient underwent wound surgery because of an infected necrosis with a methicillin-resistant Staphylococcus aureus (MRSA) of his small toe and was already on aVNS therapy to relieve his leg pain and improve microcirculation. AVNS was performed with the AuriStim device (Multisana GmbH, Austria), which stimulates vagally innervated regions of the auricle by administering electrical stimulation via percutaneous electrodes for 6 weeks. Results: The multimorbid high-risk patient, who was expected to go through a severe course of the COVID-19 disease, showed hardly any symptoms during ongoing aVNS therapy, while other family members, being much younger and healthy suffered from a more serious course with headache, pneumonia and general weakness. Conclusion: The auricular vagus nerve stimulation is a clinically tested and safe procedure and might represent an alternative and effective way of treating COVID-19 disease. Nevertheless, due to several limitations of this case report, randomized controlled studies are needed to evaluate the efficacy of aVNS therapy on COVID-19 disease.

The diversity of neuroimmune circuits controlling lung inflammation

It is becoming increasingly appreciated that the nervous and immune systems communicate bidirectionally to regulate immunological outcomes in a variety of organs including the lung. Activation of neuronal signaling can be induced by inflammation, tissue damage, or pathogens to evoke or reduce immune cell activation in what has been termed a neuroimmune reflex. In the periphery, these reflexes include the cholinergic anti-inflammatory pathway, sympathetic reflex, and sensory nociceptor-immune cell pathways. Continual advances in neuroimmunology in peripheral organ systems have fueled small-scale clinical trials that have yielded encouraging results for a range of immunopathologies such as rheumatoid arthritis. Despite these successes, several limitations should give clinical investigators pause in the application of neural stimulation as a therapeutic for lung inflammation, especially if inflammation arises from a novel pathogen. In this review, the general mechanisms of each reflex, the evidence for these circuits in the control of lung inflammation, and the key knowledge gaps in our understanding of these neuroimmune circuits will be discussed. These limitations can be overcome not only through a better understanding of neuroanatomy but also through a systematic evaluation of stimulation parameters using immune activation in lung tissues as primary readouts. Our rapidly evolving understanding of the nervous and immune systems highlights the importance of communication between these cells in health and disease. This integrative approach has tremendous potential in the development of targeted therapeutics if specific challenges can be overcome.

Vagus Nerve Stimulation: A Personalized Therapeutic Approach for Crohn's and Other Inflammatory Bowel Diseases

Inflammatory bowel diseases, including Crohn's disease and ulcerative colitis, are incurable autoimmune diseases characterized by chronic inflammation of the gastrointestinal tract. There is increasing evidence that inappropriate interaction between the enteric nervous system and central nervous system and/or low activity of the vagus nerve, which connects the enteric and central nervous systems, could play a crucial role in their pathogenesis. Therefore, it has been suggested that appropriate neuroprosthetic stimulation of the vagus nerve could lead to the modulation of the inflammation of the gastrointestinal tract and consequent long-term control of these autoimmune diseases. In the present paper, we provide a comprehensive overview of (1) the cellular and molecular bases of the immune system, (2) the way central and enteric nervous systems interact and contribute to the immune responses, (3) the pathogenesis of the inflammatory bowel disease, and (4) the therapeutic use of vagus nerve stimulation, and in particular, the transcutaneous stimulation of the auricular branch of the vagus nerve. Then, we expose the working hypotheses for the modulation of the molecular processes that are responsible for intestinal inflammation in autoimmune diseases and the way we could develop personalized neuroprosthetic therapeutic devices and procedures in favor of the patients.

A Wirelessly Powered 4-Channel Neurostimulator for Reconstructing Walking Trajectory

A wirelessly powered four-channel neurostimulator was developed for applying selective Functional Electrical Stimulation (FES) to four peripheral nerves to control the ankle and knee joints of a rat. The power of the neurostimulator was wirelessly supplied from a transmitter device, and the four nerves were connected to the receiver device, which controlled the ankle and knee joints in the rat. The receiver device had functions to detect the frequency of the transmitter signal from the transmitter coil. The stimulation site of the nerves was selected according to the frequency of the transmitter signal. The rat toe position was controlled by changing the angles of the ankle and knee joints. The joint angles were controlled by the stimulation current applied to each nerve independently. The stimulation currents were adjusted by the Proportional Integral Differential (PID) and feed-forward control method through a visual feedback control system, and the walking trajectory of a rat's hind leg was reconstructed. This study contributes to controlling the multiple joints of a leg and reconstructing functional motions such as walking using the robotic control technology.

Frequency-dependent depression of the NTS synapse affects the temporal response of the antihypertensive effect of auricular vagus nerve stimulation (aVNS)

OBJECTIVES

Auricular vagus nerve stimulation (aVNS) has recently emerged as a promising neuromodulation modality for blood pressure (BP) reduction due to its ease of use although its efficacy is still limited compared to direct baroreflex stimulation. Previous studies have also indicated that synaptic depression of nucleus tractus solitarius (NTS) in the baroreflex pathway depends on stimulus frequency. However, the nature of this frequency dependence phenomenon on antihypertensive effect has been unknown for aVNS. We aimed to investigate the antihypertensive effect of aVNS considering frequency-dependent depression characteristic in the NTS synapse. We explored NTS activation and BP reduction induced by aVNS and by direct secondary neuron stimulation (DS).

APPROACH

Both protocols were performed with recording of NTS activation and BP response with stimulation for each frequency parameter (2, 4, 20, 50, and 80 Hz).

MAIN RESULTS

The BP recovery time constant was significantly dependent on the frequency of DS and aVNS (DS - 2 Hz: 8.17 ± 4.98; 4 Hz: 9.73 ± 6.3; 20 Hz: 6.61 ± 3.28; 50 Hz: 4.93 ± 1.65; 80 Hz: 4.00 ± 1.43, p < 0.001, Kruskal-Wallis H-test / aVNS - 2 Hz: 4.02 ± 2.55; 4 Hz: 8.13 ± 4.05; 20 Hz: 6.40 ± 3.16; 50 Hz: 5.18 ± 2.37; 80 Hz: 3.13 ± 1.29, p < 0.05, Kruskal-Wallis H-test) despite no significant BP reduction at 2 Hz compared to sham groups (p > 0.05, Mann-Whitney U-test).

SIGNIFICANCE

Our observations suggest that the antihypertensive effect of aVNS is influenced by the characteristics of frequency-dependent synaptic depression in the NTS neuron in terms of the BP recovery time. These findings suggest that the antihypertensive effect of aVNS can be improved with further understanding of the neurological properties of the baroreflex associated with aVNS, which is critical to push this new modality for clinical interpretation.

“The Wandering Nerve Linking Heart and Mind” – The Complementary Role of Transcutaneous Vagus Nerve Stimulation in Modulating Neuro-Cardiovascular and Cognitive Performance

The vagus nerve is the longest nerve in the human body, providing afferent information about visceral sensation, integrity and somatic sensations to the CNS via brainstem nuclei to subcortical and cortical structures. Its efferent arm influences GI motility and secretion, cardiac ionotropy, chonotropy and heart rate variability, blood pressure responses, bronchoconstriction and modulates gag and cough responses via palatine and pharyngeal innervation. Vagus nerve stimulation has been utilized as a successful treatment for intractable epilepsy and treatment-resistant depression, and new non-invasive transcutaneous (t-VNS) devices offer equivalent therapeutic potential as invasive devices without the surgical risks. t-VNS offers exciting potential as a therapeutic intervention in cognitive decline and aging populations, classically affected by reduced cerebral perfusion by modulating both limbic and frontal cortical structures, regulating cerebral perfusion and improving parasympathetic modulation of the cardiovascular system. In this narrative review we summarize the research to date investigating the cognitive effects of VNS therapy, and its effects on neurocardiovascular stability.

Transauricular Vagal Nerve Stimulation at 40 Hz Inhibits Hippocampal P2X7R/NLRP3/Caspase-1 Signaling and Improves Spatial Learning and Memory in 6-Month-Old APP/PS1 Mice

OBJECTIVES

Transauricular vagal nerve stimulation (taVNS) at 40 Hz attenuates hippocampal amyloid load in 6-month-old amyloid precursor protein/presenilin 1 (APP/PS1) transgenic mice, but it is unclear whether 40-Hz taVNS can improve cognition in these mice. Moreover, the underlying mechanisms are still unclear.

MATERIALS AND METHODS

6-month-old C57BL/6 (wild type [WT]) and APP/PS1 mice were subjected to 40-Hz taVNS. Novel Object Recognition and the Morris Water Maze were used to evaluate cognition. Hippocampal amyloid-β (Aβ)1-40, Aβ1-42, pro-interleukin (IL)-1β, and pro-IL-18 were measured using enzyme-linked immunosorbent assays. Hippocampal Aβ42, purinergic 2X7 receptor (P2X7R), nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (NLRP3), Caspase-1, IL-1β, and IL-18 expression were evaluated by western blotting. Histologic assessments including immunofluorescence, immunohistochemistry, Nissl staining, and Congo red staining were used to assess microglial phagocytosis, neuroprotective effects, and Aβ plaque load.

RESULTS

40-Hz taVNS improved spatial memory and learning in 6-month-old APP/PS1 mice but did not affect recognition memory. There were no effects on the cognitive behaviors of 6-month-old WT mice. taVNS at 40 Hz modulated microglia; significantly decreased levels of Aβ1-40, Aβ1-42, pro-IL-1β, and pro-IL-18; inhibited Aβ42, P2X7R, NLRP3, Caspase-1, IL-1β, and IL-18 expression; reduced Aβ deposits; and had neuroprotective effects in the hippocampus of 6-month-old APP/PS1 mice. These changes were not observed in 6-month-old WT mice.

CONCLUSION

Our results show that 40-Hz taVNS inhibits the hippocampal P2X7R/NLRP3/Caspase-1 signaling and improves spatial learning and memory in 6-month-old APP/PS1 mice.

Clinical perspectives on vagus nerve stimulation: present and future

The vagus nerve, the great wanderer, is involved in numerous processes throughout the body and vagus nerve stimulation (VNS) has the potential to modulate many of these functions. This wide-reaching capability has generated much interest across a range of disciplines resulting in several clinical trials and studies into the mechanistic basis of VNS. This review discusses current preclinical and clinical evidence supporting the efficacy of VNS in different diseases and highlights recent advancements. Studies that provide insights into the mechanism of VNS are considered.

Auricular vagus nerve stimulator for closed-loop biofeedback-based operation

Auricular vagus nerve stimulation (aVNS) is a novel neuromodulatory therapy used for treatment of various chronic systemic disorders. Currently, aVNS is non-individualized, disregarding the physiological state of the patient and therefore making it difficult to reach optimum therapeutic outcomes. A closed-loop aVNS system is required to avoid over-stimulation and under-stimulation of patients, leading to personalized and thus improved therapy. This can be achieved by continuous monitoring of individual physiological parameters that serve as a basis for the selection of optimal aVNS settings. In this work we developed a novel aVNS hardware for closed-loop application, which utilizes cardiorespiratory sensing using embedded sensors (and/or external sensors), processes and analyzes the acquired data in real-time, and directly governs settings of aVNS. We show in-lab that aVNS stimulation can be arbitrarily synchronized with respiratory and cardiac phases (as derived from respiration belt, electrocardiography and/or photo plethysmography) while mimicking baroreceptor-related afferent input along the vagus nerve projecting into the brain. Our designed system identified > 90% of all respiratory and cardiac cycles and activated stimulation at the target point with a precision of ± 100 ms despite the intrinsic respiratory and heart rate variability reducing the predictability. The developed system offers a solid basis for future clinical research into closed-loop aVNS in favour of personalized therapy.

Closed-Loop Vagus Nerve Stimulation for the Treatment of Cardiovascular Diseases: State of the Art and Future Directions

The autonomic nervous system exerts a fine beat-to-beat regulation of cardiovascular functions and is consequently involved in the onset and progression of many cardiovascular diseases (CVDs). Selective neuromodulation of the brain-heart axis with advanced neurotechnologies is an emerging approach to corroborate CVDs treatment when classical pharmacological agents show limited effectiveness. The vagus nerve is a major component of the cardiac neuroaxis, and vagus nerve stimulation (VNS) is a promising application to restore autonomic function under various pathological conditions. VNS has led to encouraging results in animal models of CVDs, but its translation to clinical practice has not been equally successful, calling for more investigation to optimize this technique. Herein we reviewed the state of the art of VNS for CVDs and discuss avenues for therapeutic optimization. Firstly, we provided a succinct description of cardiac vagal innervation anatomy and physiology and principles of VNS. Then, we examined the main clinical applications of VNS in CVDs and the related open challenges. Finally, we presented preclinical studies that aim at overcoming VNS limitations through optimization of anatomical targets, development of novel neural interface technologies, and design of efficient VNS closed-loop protocols.

Vagus Nerve Stimulation and Atrial Fibrillation: Revealing the Paradox

BACKGROUND AND OBJECTIVE

The cardiac autonomic nervous system (CANS) plays an important role in the pathophysiology of atrial fibrillation (AF). Cardiovascular disease can cause an imbalance within the CANS, which may contribute to the initiation and maintenance of AF. Increased understanding of neuromodulation of the CANS has resulted in novel emerging therapies to treat cardiac arrhythmias by targeting different circuits of the CANS. Regarding AF, neuromodulation therapies targeting the vagus nerve have yielded promising outcomes. However, targeting the vagus nerve can be both pro-arrhythmogenic and anti-arrhythmogenic. Currently, these opposing effects of vagus nerve stimulation (VNS) have not been clearly described. The aim of this review is therefore to discuss both pro-arrhythmogenic and anti-arrhythmogenic effects of VNS and recent advances in clinical practice and to provide future perspectives for VNS to treat AF.

MATERIALS AND METHODS

A comprehensive review of current literature on VNS and its pro-arrhythmogenic and anti-arrhythmogenic effects on atrial tissue was performed. Both experimental and clinical studies are reviewed and discussed separately.

RESULTS

VNS exhibits both pro-arrhythmogenic and anti-arrhythmogenic effects. The anatomical site and stimulation settings during VNS play a crucial role in determining its effect on cardiac electrophysiology. Since the last decade, there is accumulating evidence from experimental studies and randomized clinical studies that low-level VNS (LLVNS), below the bradycardia threshold, is an effective treatment for AF.

CONCLUSION

LLVNS is a promising novel therapeutic modality to treat AF and further research will further elucidate the underlying anti-arrhythmogenic mechanisms, optimal stimulation settings, and site to apply LLVNS.

Toward Diverse or Standardized: A Systematic Review Identifying Transcutaneous Stimulation of Auricular Branch of the Vagus Nerve in Nomenclature

OBJECTIVES

After 20 years of development, there is confusion in the nomenclature of transcutaneous stimulation of the auricular branch of the vagus nerve (ABVN). We performed a systematic review of transcutaneous stimulation of ABVN in nomenclature.

MATERIALS AND METHODS

A systematic search of the literature was carried out, using the bibliographic search engine PubMed. The search covered articles published up until June 11, 2020. We recorded the full nomenclature and abbreviated nomenclature same or similar to transcutaneous stimulation of ABVN in the selected eligible studies, as well as the time and author information of this nomenclature.

RESULTS

From 261 studies, 67 full nomenclatures and 27 abbreviated nomenclatures were finally screened out, transcutaneous vagus nerve stimulation and tVNS are the most common nomenclature, accounting for 38.38% and 42.06%, respectively. In a total of 97 combinations of full nomenclatures and abbreviations, the most commonly used nomenclature for the combination of transcutaneous vagus nerve stimulation and tVNS, accounting for 30.28%. Interestingly, the combination of full nomenclatures and abbreviations is not always a one-to-one relationship, there are ten abbreviated nomenclatures corresponding to transcutaneous vagus nerve stimulation, and five full nomenclatures corresponding to tVNS. In addition, based on the analysis of the usage habits of nomenclature in 21 teams, it is found that only three teams have fixed habits, while other different teams or the same team do not always use the same nomenclature in their paper.

CONCLUSIONS

The phenomenon of confusion in the nomenclature of transcutaneous stimulation of ABVN is obvious and shows a trend of diversity. The nomenclature of transcutaneous stimulation of ABVN needs to become more standardized in the future.

Arousal States as a Key Source of Variability in Speech Perception and Learning

The human brain exhibits the remarkable ability to categorize speech sounds into distinct, meaningful percepts, even in challenging tasks like learning non-native speech categories in adulthood and hearing speech in noisy listening conditions. In these scenarios, there is substantial variability in perception and behavior, both across individual listeners and individual trials. While there has been extensive work characterizing stimulus-related and contextual factors that contribute to variability, recent advances in neuroscience are beginning to shed light on another potential source of variability that has not been explored in speech processing. Specifically, there are task-independent, moment-to-moment variations in neural activity in broadly-distributed cortical and subcortical networks that affect how a stimulus is perceived on a trial-by-trial basis. In this review, we discuss factors that affect speech sound learning and moment-to-moment variability in perception, particularly arousal states—neurotransmitter-dependent modulations of cortical activity. We propose that a more complete model of speech perception and learning should incorporate subcortically-mediated arousal states that alter behavior in ways that are distinct from, yet complementary to, top-down cognitive modulations. Finally, we discuss a novel neuromodulation technique, transcutaneous auricular vagus nerve stimulation (taVNS), which is particularly well-suited to investigating causal relationships between arousal mechanisms and performance in a variety of perceptual tasks. Together, these approaches provide novel testable hypotheses for explaining variability in classically challenging tasks, including non-native speech sound learning.

Closed-Loop Transcutaneous Auricular Vagal Nerve Stimulation: Current Situation and Future Possibilities

Closed-loop (CL) transcutaneous auricular vagal nerve stimulation (taVNS) was officially proposed in 2020. This work firstly reviewed two existing CL-taVNS forms: motor-activated auricular vagus nerve stimulation (MAAVNS) and respiratory-gated auricular vagal afferent nerve stimulation (RAVANS), and then proposed three future CL-taVNS systems: electroencephalography (EEG)-gated CL-taVNS, electrocardiography (ECG)-gated CL-taVNS, and subcutaneous humoral signals (SHS)-gated CL-taVNS. We also highlighted the mechanisms, targets, technical issues, and patterns of CL-taVNS. By reviewing, proposing, and highlighting, this work might draw a preliminary blueprint for the development of CL-taVNS.

Transcutaneous vagal nerve simulation to reduce a systemic inflammatory response syndrome and the associated intestinal failure: study protocol of a prospective, two-armed, sham-controlled, double-blinded trial in healthy subjects (the NeuroSIRS-Study)

PURPOSE

Surgery initiates pro-inflammatory mediator cascades leading to a variably pronounced sterile inflammation (SIRS). SIRS is associated with intestinal paralysis and breakdown of intestinal barrier and might result in abdominal sepsis. Technological progress led to the development of a neurostimulator for transcutaneous auricular vagal nerve stimulation (taVNS), which is associated with a decline in inflammatory parameters and peristalsis improvement in rodents and healthy subjects via activation of the cholinergic anti-inflammatory pathway. Therefore, taVNS might be a strategy for SIRS prophylaxis.

METHODS

The NeuroSIRS-Study is a prospective, randomized two-armed, sham-controlled, double-blind clinical trial. The study is registered at DRKS00016892 (09.07.2020). A controlled endotoxemia is used as a SIRS-mimicking model. 2 ng/kg bodyweight lipopolysaccharide (LPS) will be administered after taVNS or sham stimulation. The primary objective is a reduction of clinical symptoms of SIRS after taVNS compared to sham stimulation. Effects of taVNS on release of inflammatory cytokines, intestinal function, and vital parameters will be analyzed.

DISCUSSION

TaVNS is well-tolerated, with little to no side effects. Despite not fully mimicking postoperative inflammation, LPS challenge is the most used experimental tool to imitate SIRS and offers standardization and reproducibility. The restriction to healthy male volunteers exerts a certain bias limiting generalizability to the surgical population. Still, this pilot study aims to give first insights into taVNS as a prophylactic treatment in postoperative inflammation to pave the way for further clinical trials in patients at risk for SIRS. This would have major implications for future therapeutic approaches.

Therapeutic applications of transcutaneous auricular vagus nerve stimulation with potential for application in neurodevelopmental or other pediatric disorders

Non-invasive transcutaneous auricular vagus nerve stimulation (taVNS) as a newly developed technique involves stimulating the cutaneous receptive field formed by the auricular branch of the vagus nerve in the outer ear, with resulting activation of vagal connections to central and peripheral nervous systems. Increasing evidence indicates that maladaptive neural plasticity may underlie the pathology of several pediatric neurodevelopmental and psychiatric disorders, such as autism spectrum disorder, attention deficit hyperactivity disorder, disruptive behavioral disorder and stress-related disorder. Vagal stimulation may therefore provide a useful intervention for treating maladaptive neural plasticity. In the current review we summarize the current literature primarily on therapeutic use in adults and discuss the prospects of applying taVNS as a therapeutic intervention in specific pediatric neurodevelopmental and other psychiatric disorders. Furthermore, we also briefly discuss factors that would help optimize taVNS protocols in future clinical applications. We conclude from these initial findings that taVNS may be a promising alternative treatment for pediatric disorders which do not respond to other interventions.

Technical Note: Modulation of fMRI brainstem responses by transcutaneous vagus nerve stimulation

Our increasing knowledge about gut-brain interaction is revolutionising the understanding of the links between digestion, mood, health, and even decision making in our everyday lives. In support of this interaction, the vagus nerve is a crucial pathway transmitting diverse gut-derived signals to the brain to monitor of metabolic status, digestive processes, or immune control to adapt behavioural and autonomic responses. Hence, neuromodulation methods targeting the vagus nerve are currently explored as a treatment option in a number of clinical disorders, including diabetes, chronic pain, and depression. The non-invasive variant of vagus nerve stimulation (VNS), transcutaneous auricular VNS (taVNS), has been implicated in both acute and long-lasting effects by modulating afferent vagus nerve target areas in the brain. The physiology of neither of those effects is, however, well understood, and evidence for neuronal response upon taVNS in vagal afferent projection regions in the brainstem and its downstream targets remain to be established. Therefore, to examine time-dependent effects of taVNS on brainstem neuronal responses in healthy human subjects, we applied taVNS during task-free fMRI in a single-blinded crossover design. During fMRI data acquisition, we either stimulated the left earlobe (sham), or the target zone of the auricular branch of the vagus nerve in the outer ear (cymba conchae, verum) for several minutes, both followed by a short 'stimulation OFF' period. Time-dependent effects were assessed by averaging the BOLD response for consecutive 1-minute periods in an ROI-based analysis of the brainstem. We found a significant response to acute taVNS stimulation, relative to the control condition, in downstream targets of vagal afferents, including the nucleus of the solitary tract, the substantia nigra, and the subthalamic nucleus. Most of these brainstem regions remarkably showed increased activity in response to taVNS, and these effect sustained during the post-stimulation period. These data demonstrate that taVNS activates key brainstem regions, and highlight the potential of this approach to modulate vagal afferent signalling. Furthermore, we show that carry-over effects need to be considered when interpreting fMRI data in the context of general vagal neurophysiology and its modulation by taVNS.

Autonomic modulation of ventricular electrical activity: recent developments and clinical implications

PURPOSE

This review aimed to provide a complete overview of the current stance and recent developments in antiarrhythmic neuromodulatory interventions, focusing on lifethreatening vetricular arrhythmias.

METHODS

Both preclinical studies and clinical studies were assessed to highlight the gaps in knowledge that remain to be answered and the necessary steps required to properly translate these strategies to the clinical setting.

RESULTS

Cardiac autonomic imbalance, characterized by chronic sympathoexcitation and parasympathetic withdrawal, destabilizes cardiac electrophysiology and promotes ventricular arrhythmogenesis. Therefore, neuromodulatory interventions that target the sympatho-vagal imbalance have emerged as promising antiarrhythmic strategies. These strategies are aimed at different parts of the cardiac neuraxis and directly or indirectly restore cardiac autonomic tone. These interventions include pharmacological blockade of sympathetic neurotransmitters and neuropeptides, cardiac sympathetic denervation, thoracic epidural anesthesia, and spinal cord and vagal nerve stimulation.

CONCLUSION

Neuromodulatory strategies have repeatedly been demonstrated to be highly effective and very promising anti-arrhythmic therapies. Nevertheless, there is still much room to gain in our understanding of neurocardiac physiology, refining the current neuromodulatory strategic options and elucidating the chronic effects of many of these strategic options.

Vagus nerve afferent stimulation: Projection into the brain, reflexive physiological, perceptual, and behavioral responses, and clinical relevance

The afferent vagus nerves project to diverse neural networks within the brainstem and forebrain, based on neuroanatomical, neurophysiological, and functional (fMRI) brain imaging evidence. In response to afferent vagal stimulation, multiple homeostatic visceral reflexes are elicited. Physiological stimuli and both invasive and non-invasive electrical stimulation that activate the afferent vagus elicit perceptual and behavioral responses that are of physiological and clinical significance. In the present review, we address these multiple roles of the afferent vagus under normal and pathological conditions, based on both animal and human evidence.

Visualization of Complex Processes in Cardiovascular System during Electrical Auricular Vagus Nerve Stimulation

The analysis of human physiological systems from the point of view of complex systems theory remains a very ambitious task. The complexity of the problem often encourages the use of innovative mathematical methods analyzing the processes that take place in space and time. The main goal of this paper is to visualize the cardiovascular system during auricular vagus nerve stimulation (aVNS) using the matrix differences to evaluate the dynamic signal interfaces by cointegrating the initial signal data into the matrices during each case. Algebraic relationships between RR/JT and JT/QRS cardiac intervals are used not only to track the cardiovascular changes during aVNS but also to characterize individual features of the person during the transit through the therapy. This paper presents the computational techniques that can visualize the complex dynamical processes taking place in the cardiovascular system using the electrical aVNS therapy. Four healthy volunteers participated in two verum and two placebo experiments. We discovered that the body's reaction to the stimulation was very different in each of the cases, but the presented techniques opened new possibilities for a novel interpretation of the dynamics of the cardiovascular system.

Evaluation of different vagus nerve stimulation anatomical targets in the ear by vagus evoked potential responses

BACKGROUND

Electrical auricular vagus nerve stimulation (taVNS) is an emerging therapy. Stimuli are transported to brainstem nuclei, whereby its multiple projections reach to many subcortical and cortical areas, thus allowing the neuromodulation of several systemic physiological processes. We aim to define the best auricular target for taVNS through vagus somatosensory evoked potential (VSEP) elicited stimulating different auricular areas with different electrode sizes.

METHODS

Twenty-six subjects were enrolled. Three stimulation areas were studied: simultaneous cymba and cavum (CC), cymba (C) and earlobe (L); and two electrode sizes: extra-large (X) and small (S). We studied the effect of five combinations (CCX, CCS, CS, LX and LS) on VSEP´s latency and amplitude, and sensory and pain threshold (Pt) using a lineal mixed model regression analysis. We used CS combination, used in a commercial device, as reference model.

RESULTS

Valid VSEP were obtained for CCX, CCS and CS but not in LX and LS. Both CCS and CCX tests showed significant amplitude increases. The same effect was observed in CCX using CCS as reference. Significant increases in Pt were found for CCX and LX. The same effect was observed in CCX using LX as reference.

CONCLUSION

The results suggest that CC and C areas are active targets for taVNS but not for earlobe, as anatomical data support. Considering that amplitude reflects the synchronized electrical activity generated, we conclude the most effective topography is the simultaneous stimulation of cymba and concha. The use of X-sized electrodes increases the amplitudes and makes the stimulation more comfortable.

Bursted auricular vagus nerve stimulation alters heart rate variability in healthy subjects

Objective.Recent research suggests that percutaneous auricular vagus nerve stimulation (pVNS) beneficially modulates the autonomic nervous system (ANS). Bursted pVNS seems to be efficient for nerve excitation. Bursted pVNS effects on cardiac autonomic modulation are not disclosed yet.Approach.For the first time, the present study evaluates the effect of pVNS on cardiac autonomic modulation in healthy subjects (n = 9) using two distinct bursted stimulation patterns (biphasic and triphasic stimulation) and heart rate variability analysis (HRV). Stimulation was delivered via four needle electrodes in vagally innervated regions of the right auricle. Each of the two bursted stimulation patterns was applied twice in randomized order over four consecutive stimulation sessions per subject.Main results.Bursted pVNS did not change heart rate, blood pressure, and inflammatory parameters in study subjects. pVNS significantly increased the standard deviation of heart inter-beat intervals, from 46.39 ± 10.4 ms to 63.46 ± 22.47 ms (p < 0.05), and the total power of HRV, from 1475.7 ± 616.13 ms²to 3190.5 ± 2037.0 ms²(p < 0.05). The high frequency (HF) power, the low frequency (LF) power, and theLF/HFratio did not change during bursted pVNS. Both stimulation patterns did not show any significant differences in cardiac autonomic modulation. Stimulation intensity to reach a tingling sensation was significantly lower in triphasic compared to biphasic stimulation (p< 0.05). Bursted stimulation was well tolerated.Significance.Bursted pVNS seems to affect cardiac autonomic modulation in healthy subjects, with no difference between biphasic and triphasic stimulation, the latter requiring lower stimulation intensities. These findings foster implementation of more efficient pVNS stimulation.

Feasibility study on transcutaneous auricular vagus nerve stimulation using millimeter waves

Objective. Electrical stimulation of the auricular vagus nerve is a non-invasive neuromodulation technique that has been used for various conditions, including depression, epilepsy, headaches, and cerebral ischemia. However, unwanted non-vagal nerve stimulations can occur because of diffused stimulations. The objective of this study is to develop a region-specific non-invasive vagus nerve stimulation (VNS) technique using the millimeter wave (MMW) as a stimulus for the auricular branch of the vagus nerve (ABVN).Approach. A numerical simulation was conducted to ascertain whether the MMW could excite the ABVN in the human outer-ear with a millimeter-scale spatial resolution. Additionally, MMW-induced neuronal responses in seven mice were evaluated. Transcutaneous auricular VNS (ta-VNS) was applied to the cymba conchae innervated by the AVBN using a 60-GHz continuous wave (CW). As a control, the auricle's exterior margin was stimulated and referred to as transcutaneous auricular non-vagus nerve stimulation (ta-nonVNS). During stimulation, the local field potential (LFP) in the nucleus tractus solitarii (NTS), an afferent vagal projection site, was recorded simultaneously.Main results. The ta-VNS with a stimulus level of 13 dBm showed a significant increase in the LFP power in the NTS. The mean increases in power (n = 7) in the gamma high and gamma very high bands were 8.6 ± 2.0% and 18.2 ± 5.9%, respectively. However, the ta-nonVNS with a stimulus level of 13 dBm showed a significant decrease in the LFP power in the NTS. The mean decreases in power in the beta and gamma low bands were 11.0 ± 4.4% and 10.8 ± 2.8%, respectively. These findings suggested that MMW stimulation clearly induced a different response according to the presence of ABVN.Significance. Selective auricular VNS is feasible using the MMW. This study provides the basis for the development of a new clinical treatment option using the stimulation of the ta-VNS with a square millimeter spatial resolution.

Transdermal auricular vagus stimulation for the treatment of postural tachycardia syndrome

Postural Tachycardia Syndrome (POTS) is a chronic disorder characterized by symptoms of orthostatic intolerance such as fatigue, lightheadedness, dizziness, palpitations, dyspnea, chest discomfort and remarkable tachycardia upon standing. Non-invasive transdermal vagal stimulators have been applied for the treatment of epilepsy, anxiety, depression, headache, and chronic pain syndromes. Anti-inflammatory and immunomodulating effects after transdermal vagal stimulation raised interest for applications in other diseases. Patients with sympathetic overactivity, reduced cardiac vagal drive and presence of systemic inflammation like POTS may benefit from tVNS. This article will address crucial methodological aspects of tVNS and provide preliminary results of its acute and chronic use in POTS, with regards to its potential effectiveness on autonomic symptoms reduction and heart rate modulation.

Impact of Transcutaneous Auricular Vagus Nerve Stimulation on Large-Scale Functional Brain Networks: From Local to Global

Transcutaneous auricular vagus nerve stimulation (taVNS) is a novel non-invasive brain stimulation technique considered as a potential supplementary treatment option for a wide range of diseases. Although first promising findings were obtained so far, the exact mode of action of taVNS is not fully understood yet. We recently developed an examination schedule to probe for immediate taVNS-induced modifications of large-scale epileptic brain networks. With this schedule, we observed short-term taVNS to have a topology-modifying, robustness- and stability-enhancing immediate effect on large-scale functional brain networks from subjects with focal epilepsies. We here expand on this study and investigate the impact of short-term taVNS on various local and global characteristics of large-scale evolving functional brain networks from a group of 30 subjects with and without central nervous system diseases. Our findings point to differential, at first glance counterintuitive, taVNS-mediated alterations of local and global topological network characteristics that result in a reconfiguration of networks and a modification of their stability and robustness properties. We propose a model of a stimulation-related stretching and compression of evolving functional brain networks that may help to better understand the mode of action of taVNS.

Wearable wireless power systems for 'ME-BIT' magnetoelectric-powered bio implants

Objective.Compared to biomedical devices with implanted batteries, wirelessly powered technologies can be longer-lasting, less invasive, safer, and can be miniaturized to access difficult-to-reach areas of the body. Magnetic fields are an attractive wireless power transfer modality for such bioelectronic applications because they suffer negligible absorption and reflection in biological tissues. However, current solutions using magnetic fields for mm sized implants either operate at high frequencies (>500 kHz) or require high magnetic field strengths (>10  mT), which restricts the amount of power that can be transferred safely through tissue and limits the development of wearable power transmitter systems. Magnetoelectric (ME) materials have recently been shown to provide a wireless power solution for mm-sized neural stimulators. These ME transducers convert low magnitude (<1 mT) and low-frequency (∼300 kHz) magnetic fields into electric fields that can power custom integrated circuits or stimulate nearby tissue.Approach.Here we demonstrate a battery-powered wearable magnetic field generator that can power a miniaturized MagnetoElectric-powered Bio ImplanT 'ME-BIT' that functions as a neural stimulator. The wearable transmitter weighs less than 0.5  lbs and has an approximate battery life of 37 h.Main results.We demonstrate the ability to power a millimeter-sized prototype 'ME-BIT' at a distance of 4 cm with enough energy to electrically stimulate a rat sciatic nerve. We also find that the system performs well under translational misalignment and identify safe operating ranges according to the specific absorption rate limits set by the IEEE Std 95.1-2019.Significance.These results validate the feasibility of a wearable system that can power miniaturized ME implants that can be used for different neuromodulation applications.

A transient decrease in heart rate with unilateral and bilateral galvanic vestibular stimulation in healthy humans

The study of cardiovascular function with galvanic vestibular stimulation has provided evidence on the neural structures that are involved in the vestibulo-autonomic reflex. This study determined if the effect on heart rate using galvanic vestibular stimulation persists after provoking a sympathetic response and if this response differs when using unilateral or transmastoid (bilateral) stimulation. We analysed heart rate and heart rate variability using unilateral and transmastoid galvanic vestibular stimulation combined with cardiovascular reflex evoked by postural change in 24 healthy human subjects. Three electrode configurations were selected for unilateral stimulation considering the anatomical location of each semicircular canal. We compared recordings performed in seated and standing positions, and with unilateral and transmastoid stimulation. With subjects seated, a significant transient decrease in heart rate was observed with unilateral stimulation. With transmastoid stimulation, heart rate decreased in both seated and standing positions. Average intervals between normal heartbeats recorded with stimulation resemble parasympathetic cardiac function induced by auricular vagal nerve stimulation. Our results indicate that unilateral stimulation does not eliminate the natural heart rate increase caused by orthostatic hypotension. In contrast, transmastoid stimulation provoked a transient reduction in heart rate, even when subjects were standing. These responses should be considered while performing experiments with galvanic vestibular stimulation and subsequent effects in cardiac regulation mechanisms.

Implant- and anesthesia-related factors affecting cardiopulmonary threshold intensities for vagus nerve stimulation

Objective.Vagus nerve stimulation (VNS) is typically delivered at increasing stimulus intensity until a neurological or physiological response is observed ('threshold') for dose calibration, preclinically and therapeutically. Factors affecting VNS thresholds have not been studied systematically. In a rodent model of VNS we measured neural and physiological responses to increasing VNS intensity, determined neurological and physiological thresholds and examined the effect of implant- and anesthesia-related factors on thresholds.Approach.In acute and chronic vagus implants (45 and 20 rats, respectively) VNS was delivered under isoflurane, ketamine-xylazine, or awake conditions. Evoked compound action potentials (CAPs) were recorded and activation of different fiber types was extracted. Elicited physiological responses were registered, including changes in heart rate (HR), breathing rate (BR), and blood pressure (BP). CAP and physiological thresholds were determined.Main results. The threshold for evoking discernable CAPs (>10µV) (CAP threshold) is significantly lower than what elicits 5%-10% drop in heart rate (heart rate threshold, HRT) (25µA ± 1.8 vs. 80µA ± 5.1, respectively; mean ± SEM). Changes in BP and small changes in BR (bradypnea) occur at lowest intensities (70µA ± 8.3), followed by HR changes (80µA ± 5.1) and finally significant changes in BR (apnea) (310μA ± 32.5). HRT and electrode impedance are correlated in chronic (Pearson correlationr= 0.47;p< 0.001) but not in acute implants (r= -0.34;pNS); HRT and impedance both increase with implant age (r= 0.44;p< 0.001 andr= 0.64;p< 0.001, respectively). HRT is lowest when animals are awake (200µA ± 35.5), followed by ketamine-xylazine (640µA ± 151.5), and isoflurane (1000µA ± 139.5). The sequence of physiological responses with increasing VNS intensity is the same in anesthetized and awake animals. Pulsing frequency affects physiological responses but not CAPs.Significance. Implant age, electrode impedance, and type of anesthesia affect VNS thresholds and should be accounted for when calibrating stimulation dose.

Effects of Low-Level Tragus Stimulation on Endothelial Function in Heart Failure With Reduced Ejection Fraction

BACKGROUND

Autonomic dysregulation in heart failure with reduced ejection fraction plays a major role in endothelial dysfunction. Low-level tragus stimulation (LLTS) is a novel, noninvasive method of autonomic modulation.

METHODS AND RESULTS

We enrolled 50 patients with heart failure with reduced ejection fraction (left ventricular ejection fraction of ≤40%) in a randomized, double-blinded, crossover study. On day 1, patients underwent 60 minutes of LLTS with a transcutaneous stimulator (20 Hz, 200 μs pulse width) or sham (ear lobule) stimulation. Macrovascular function was assessed using flow-mediated dilatation in the brachial artery and cutaneous microcirculation with laser speckle contrast imaging in the hand and nail bed. On day 2, patients were crossed over to the other study arm and underwent sham or LLTS; vascular tests were repeated before and after stimulation. Compared with the sham, LLTS improved flow-mediated dilatation by increasing the percent change in the brachial artery diameter (from 5.0 to 7.5, LLTS on day 1, P = .02; and from 4.9 to 7.1, LLTS on day 2, P = .003), compared with no significant change in the sham group (from 4.6 to 4.7, P = .84 on day 1; and from 5.6 to 5.9 on day 2, P = .65). Cutaneous microcirculation in the hand showed no improvement and perfusion of the nail bed showed a trend toward improvement.

CONCLUSIONS

Our study demonstrated the beneficial effects of acute neuromodulation on macrovascular function. Larger studies to validate these findings and understand mechanistic links are warranted.

International Consensus Based Review and Recommendations for Minimum Reporting Standards in Research on Transcutaneous Vagus Nerve Stimulation (Version 2020)

Given its non-invasive nature, there is increasing interest in the use of transcutaneous vagus nerve stimulation (tVNS) across basic, translational and clinical research. Contemporaneously, tVNS can be achieved by stimulating either the auricular branch or the cervical bundle of the vagus nerve, referred to as transcutaneous auricular vagus nerve stimulation(VNS) and transcutaneous cervical VNS, respectively. In order to advance the field in a systematic manner, studies using these technologies need to adequately report sufficient methodological detail to enable comparison of results between studies, replication of studies, as well as enhancing study participant safety. We systematically reviewed the existing tVNS literature to evaluate current reporting practices. Based on this review, and consensus among participating authors, we propose a set of minimal reporting items to guide future tVNS studies. The suggested items address specific technical aspects of the device and stimulation parameters. We also cover general recommendations including inclusion and exclusion criteria for participants, outcome parameters and the detailed reporting of side effects. Furthermore, we review strategies used to identify the optimal stimulation parameters for a given research setting and summarize ongoing developments in animal research with potential implications for the application of tVNS in humans. Finally, we discuss the potential of tVNS in future research as well as the associated challenges across several disciplines in research and clinical practice.

Occipitoatlantal decompression and noninvasive vagus nerve stimulation slow conduction velocity through the atrioventricular node in healthy participants

CONTEXT

Management of atrial fibrillation includes either rhythm control that aims at establishing a sinus rhythm or rate control that aims at lowering the ventricular rate, usually with atrioventricular nodal blocking agents. Another potential strategy for ventricular rate control is to induce a negative dromotropic effect by augmenting cardiac vagal activity, which might be possible through noninvasive and nonpharmacologic techniques. Thus, the hypothesis of this study was that occipitoatlantal decompression (OA-D) and transcutaneous auricular vagus nerve stimulation (taVNS) not only increase cardiac parasympathetic tone as assessed by heart rate variability (HRV), but also slow atrioventricular conduction, assessed by the PQ-interval of the electrocardiogram (EKG) in generally healthy study participants without atrial fibrillation.

OBJECTIVES

To test whether OA-D and/or transcutaneous taVNS, which have been demonstrated to increase cardiac parasympathetic nervous system activity, would also elicit a negative dromotropic effect and prolong atrioventricular conduction.

METHODS

EKGs were recorded in 28 healthy volunteers on three consecutive days during a 30 min baseline recording, a 15 min intervention, and a 30 min recovery period. Participants were randomly assigned to one of three experimental groups that differed in the 15 min intervention. The first group received OA-D for 5 min, followed by 10 min of rest. The second group received 15 min of taVNS. The intervention in the third group that served as a time control group (CTR) consisted of 15 min of rest. The RR- and PQ-intervals were extracted from the EKGs and then used to assess HRV and AV-conduction, respectively.

RESULTS

The OA-D group had nine participants (32.1%), the taVNS group had 10 participants (35.7%), and the CTR group had nine participants (32.1%). The root mean square of successive differences between normal heartbeats (RMSSD), an HRV measure of cardiac parasympathetic modulation, tended to be higher during the recovery period than during the baseline recording in the OA-D group (mean ± standard error of the mean [SEM], 54.6 ± 15.5 vs. 49.8 ± 15.8 ms; p<0.10) and increased significantly in the taVNS group (mean ± SEM, 28.8 ± 5.7 vs. 24.7 ± 4.8 ms; p<0.05), but not in the control group (mean ± SEM, 31.4 ± 4.2 vs. 28.5 ± 3.8 ms; p=0.31). This increase in RMSSD was accompanied by a lengthening of the PQ-interval in the OA-D (mean ± SEM, 170.5 ± 9.6 vs. 166.8 ± 9.7 ms; p<0.05) and taVNS (mean ± SEM, 166.6 ± 6.0 vs. 162.1 ± 5.6 ms; p<0.05) groups, but not in the control group (mean ± SEM, 164.3 ± 9.2 vs. 163.1 ± 9.1 ms; p=0.31). The PQ-intervals during the baseline recordings did not differ on the three study days in any of the three groups, suggesting that the negative dromotropic effect of OA-D and taVNS did not last into the following day.

CONCLUSIONS

The lengthening of the PQ-interval in the OA-D and taVNS groups was accompanied by an increase in RMSSD. This implies that the negative dromotropic effects of OA-D and taVNS are mediated through an increase in cardiac parasympathetic tone. Whether these findings suggest their utility in controlling ventricular rates during persistent atrial fibrillation remains to be determined.

Neuro-cardiac coupling predicts transcutaneous auricular vagus nerve stimulation effects

BACKGROUND

Transcutaneous auricular Vagus Nerve Stimulation (taVNS) is a non-invasive neuromodulation technique that may constitute an effective treatment for a wide range of neurological, psychiatric, and medical conditions. One key challenge in taVNS research is the high interindividual response variability. To gain an understanding of this variability, reliable biomarkers for taVNS responsiveness would be highly desirable. In this study, we investigated physiological candidate biomarkers while systematically varying stimulation conditions and observing physiological state characteristics.

METHODS

Forty-four healthy young adults received taVNS and sham-stimulation. Subjects were pseudo-randomly assigned to stimulation of the left or right ear. Each subject underwent six blocks of stimulation. Across blocks, respiration-locking (inhalation-locked taVNS vs. exhalation-locked taVNS vs. sham) and the electrode location (tragus vs. cymba conchae) were varied. We analyzed heart rate (HR), various heart rate variability (HRV) scores, and neuro-cardiac coupling (NCC), indexed by the relationship between electroencephalographic delta power and heartbeat length.

RESULTS

We observed an effect of taVNS on HR and HRV scores during, but not after stimulation. The direction of the effects was consistent with parasympathetic activation. We did not observe any systematic influence of the stimulation conditions that we varied. However, we found baseline NCC scores to be significant predictors for the individual effect of taVNS on HRV scores.

CONCLUSION

Cardiac effects of taVNS indicate parasympathetic activation. These effects were short lived, which might explain that some previous studies were unable to detect them. We propose NCC as a novel candidate biomarker for responsiveness to taVNS.