Cardiac and Peripheral Autonomic Responses to Orthostatic Stress During Transcutaneous Vagus Nerve Stimulation in Healthy Subjects

The Intestine in Acute and Long COVID: Pathophysiological Insights and Key Lessons

Post-Acute Sequelae of SARS-CoV-2 infection (PASC), commonly known as Long COVID, represents a significant and complex health challenge with a wide range of symptoms affecting multiple organ systems. This review examines the emerging evidence suggesting a critical role of the gut and gut-brain axis in the pathophysiology of Long COVID. It explores how changes in the gut microbiome, disruption of gut barrier integrity, and the persistence of SARS-CoV-2 antigens within the gastrointestinal tract may contribute to the prolonged and varied symptoms seen in Long COVID, including chronic inflammation and neuropsychiatric disturbances. The review also summarizes key insights gained about Long COVID, highlighting its multifactorial nature, which involves immune dysregulation, microvascular damage, and autonomic nervous system dysfunction, with the gut playing a central role in these processes. While progress has been made in understanding these mechanisms, current evidence remains inconclusive. The challenges of establishing causality, standardizing research methodologies, and addressing individual variations in the microbiome are discussed, emphasizing the need for further longitudinal studies and more comprehensive approaches to enhance our understanding of these complex interactions. This review underscores the importance of personalized approaches in developing effective diagnostic and therapeutic strategies for Long COVID, while also acknowledging the significant gaps in our current understanding. Future research should aim to further unravel the complex interplay between the gut and Long COVID, ultimately improving outcomes for those affected by this condition.

Impact of optimized transcutaneous auricular vagus nerve stimulation on cardiac autonomic profile in healthy subjects and heart failure patients

Objective.To determine the optimal frequency and site of stimulation for transcutaneous vagus nerve stimulation (tVNS) to induce acute changes in the autonomic profile (heart rate (HR), heart rate variability (HRV)) in healthy subjects (HS) and patients with heart failure (HF).Approach.We designed three single-blind, randomized, cross-over studies: (1) to compare the acute effect of left tVNS at 25 Hz and 10 Hz (n= 29, age 60 ± 7 years), (2) to compare the acute effect of left and right tVNS at the best frequency identified in study 1 (n= 28 age 61 ± 7 years), and (3) to compare the acute effect of the identified optimal stimulation protocol with sham stimulation in HS and HF patients (n= 30, age 59 ± 5 years, andn= 32, age 63 ± 7 years, respectively).Main results.In study 1, left tragus stimulation at 25 Hz was more effective than stimulation at 10 Hz in decreasing HR (-1.0 ± 1.2 bpm,p< 0.001 and -0.5 ± 1.6 bpm, respectively) and inducing vagal effects (significant increase in RMSSD, and HF power). In study 2, the HR reduction was greater with left than right tragus stimulation (-0.9 ± 1.5 bpm,p< 0.01 and -0.3 ± 1.4 bpm, respectively). In study 3 in HS, left tVNS at 25 Hz significantly reduced HR, whereas sham stimulation did not (-1.1 ± 1.2 bpm,p< 0.01 and -0.2 ± 2.9 bpm, respectively). In HF patients, both active and sham stimulation produced negligible effects.Significance.Left tVNS at 25 Hz is effective in acute modulation of cardiovascular autonomic control (HR, HRV) in HS but not in HF patients (NCT05789147).

Refractory Autonomic Instability in Mild Traumatic Brain Injury: A Case Report

Although the specific relationship between concussion and the autonomic nervous system (ANS) has not been fully elucidated, it is generally understood that the pathologic response after a traumatic brain injury (TBI) is linked with systolic cardiac dysfunction. In this case, we present a patient with multiple concussion injuries over a five-year period who exhibited severe cardiac and autonomic dysfunction, in addition to prolonged impairments in vestibular function, oculomotor function, cognitive function, and headaches. The patient is a 28-year-old male with a past medical history of multiple concussions, with the first concussion occurring due to a skiing accident in January 2015. He initially presented in October 2016 after sustaining a concussion due to a motor vehicle accident (MVA) without loss of consciousness (LOC) two weeks prior. In July 2017, the patient was involved in another MVA with a positive head strike and without LOC, causing his third concussion. After each of his first three concussions, he displayed various symptoms that eventually resolved. In October 2020, the patient suffered a syncopal ground-level fall with several minutes of LOC due to dehydration and lightheadedness, leading to his fourth concussion. His fourth concussion resulted in chronic autonomic dysfunction with resting tachycardia refractory to medical management, and he eventually underwent a cardiac ablation. Although the patient underwent a cardiac ablation, his tachycardia and dysautonomia still cause dysfunction in his daily life. With millions of people living with the sequelae of TBI, the recognition and treatment of autonomic dysfunction should be a continued focus in brain injury research.

Cardiovascular effects of auricular stimulation -a systematic review and meta-analysis of randomized controlled clinical trials

Background

The number of randomized controlled trials using auricular stimulation (AS) such as transauricular vagus nerve stimulation, or other auricular electrostimulation or auricular acupuncture or acupressure, in experimental and clinical settings, has increased markedly over the last three decades. This systematic review focusses on cardiovascular effects of auricular stimulation.

Methods and analysis

The following databases were searched: MEDLINE (PubMed), EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), ISI Web of Science, and Scopus Database. RCTs were reviewed that had been published in English and European languages. Data collection and analysis was conducted by two reviewers independently. Quality and risk assessment of included studies was performed and the meta-analysis of the effect of the most frequently assessed biomarkers.

Results

Altogether, 78 trials were included. 38 studies assessed heart rate (HR), 19 studies analyzed heart rate variability (HRV), 31 studies analyzed blood pressure (BP) and 7 studies were identified that measured oxygen saturation (O2), 2 studies on baroreflex sensitivity and 2 studies on skin conductance were evaluated in this review. 26 studies contained continuous data and were eligible for meta-analysis, 50 trials reported non continuous data and were evaluated descriptively. The overall quality of the studies was moderate to low. AS leads to a significant reduction of HR, the changes though were not considered an adverse reaction. Furthermore, when looking at HRV, AS was able to reduce the LF/HF ratio significantly compared to control procedures. No other cardiovascular parameters (blood pressure, oxygen saturation, baroreflex sensitivity) were changed significantly. AS produced only minor side effects in all trials.

Conclusion

AS can lead to clinically safe reduction of HR and changes in the LF/HF ratio of the HRV, which is presumably via an increase in vagal activity. More research is needed to clarify whether AS can be used to modulate tachycardia or indications with autonomic imbalance.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=231885 PROSPERO, ID CRD42021231885.

Management of auricular transcutaneous neuromodulation and electro-acupuncture of the vagus nerve for chronic migraine: a systematic review

Background

Migraine is a type of primary headache that is accompanied by symptoms such as nausea, vomiting, or sensitivity to light and sound.

Objective

The aim of this study was to conduct a systematic review on the effectiveness of non-invasive neuromodulation, auricular transcutaneous vagus nerve stimulation (at-VNS), and electro-ear acupuncture of the vagus nerve in patients with migraine headaches.

Methods

Six databases were searched from inception to 15 June 2022 for clinical trials, in which at least one group received any form of non-invasive neuromodulation of the vagus nerve for managing migraine with outcomes collected on pain intensity and related disability. Data, including participants, interventions, blinding strategy, outcomes, and results, were extracted by two reviewers. The methodological quality was assessed with the PEDro scale, ROB, and Oxford scale.

Results

The search identified 1,117 publications with nine trials eligible for inclusion in the review. The methodological quality scores ranged from 6 to 8 (mean: 7.3, SD: 0.8) points. Low-quality evidence suggests some positive clinical effects for the treatment of chronic migraine with 1 Hz with at-VNS and ear-electro-acupuncture compared with the control group at post-treatment. Some of the studies provided evidence of the relationship between chronic migraine and a possible positive effect as a treatment with at-VNS and the neurophysiological effects using fMRI. Six of the studies provided evidence using fMRI of the relationship between chronic migraine and a possible positive effect as a treatment with at-VNS and the neurophysiological effects. Regarding all included studies, the level of evidence with the Oxford scale was level 1 (11.17%), six studies were graded as level 2 (66.66%), and two studies were graded as level 3 (22.2%). With the PEDro score, five studies got a low methodological score < 5 and only four got a score superior to 5, being highly methodological quality studies. For ROB, most of the studies were high risk and only a few of them received a low risk of bias. The pain intensity, migraine attacks, frequency, and duration were measured by three studies with positive results at post-treatment. And only 7% reported adverse events using at-VNS. All studies reported results at a post-treatment period in their respective main outcomes. And all studies with fMRI provided strong evidence of the relationship between the Locus Coeruleus, Frontal Cortex, and other superior brain areas with the auricular branch of the Vagus nerve with at-VNS.

Conclusion

Some positive effects regarding the effect of non-invasive neuromodulation, auricular transcutaneous vagus nerve stimulation (at-VNS), and electro-ear acupuncture of the vagus nerve on migraine is reported in the current literature, but there are not enough data to obtain strong conclusions.

Systematic review registration

This systematic review was registered in the PROSPERO database (registration number: CRD42021265126).

Prefrontal cortex oxygenation and autonomic nervous system activity under transcutaneous auricular vagus nerve stimulation in adolescents

INTRODUCTION

The Neurovisceral Integration Model (NIM) proposes a complex interplay of visceral and neural structures that are crucial for adaptive responses to environmental demands. The aim of the present study was to investigate this circuitry using experimental manipulation via transcutaneous auricular vagus nerve stimulation (tVNS), measures of peripheral autonomic nervous system (ANS) activity and prefrontal cortex (PFC) oxygenation, quantified using functional near-infrared spectroscopy (fNIRS).

METHODS

In a sample of n = 30 adolescents (age 14-17 years), tVNS versus sham stimulation was applied each during a 15-minute stimulation phase in a within-subject-cross-randomized-design. Mean oxygenation of the PFC and functional connectivity were assessed using fNIRS. Additionally, heart rate variability (HRV), heart rate (HR), electrodermal activity (EDA), and saliva alpha-amylase (sAA) were assessed to quantify peripheral ANS activity.

RESULTS

Using linear mixed-effects models, HRV increased (p < .0001) and HR (p < .0001) decreased during tVNS compared to sham. No effect on EDA or sAA was observed. PFC oxygenation increased over time under tVNS compared to sham (p = .017). The relative increase in HRV and decrease in HR was associated with increased oxygenation of the PFC (HR: p < .0001; HRV: p = .007). Exploratory analyses illustrated, that under tVNS, PFC connectivity increased compared to sham.

CONCLUSION

The present study supports the NIM by showing that tVNS influences ANS activity and that relative changes in PFC oxygenation contribute to these effects. Implications of these findings and directions for further research are discussed.

Orthostatic intolerance: a handicap of aging or physical deconditioning?

Despite several studies that have been investigated physical inactivity and age-related effects on orthostatic tolerance, impaired hemodynamics and postural balance responses to orthostatic stress are incorrectly attributed to aging or sedentarism alone. The isolated effects from aging and sedentarism should be investigated through comparative studies between senior athletes and age-matched controls, and physical activity assessments on aging follow-up studies. On the other hand, bed rest and space flight studies mimic accelerated physical inactivity or disuse, which is not the same physiological decline provoked by aging alone. Thus, the elementary question is: could orthostatic intolerance be attributed to aging or physical inactivity? The main purpose of this review is to provide an overview of possible mechanisms underlying orthostatic tolerance contrasting the paradigm of aging and/or physical inactivity. The key points of this review are the following: (1) to counterpoint all relevant literature on physiological aspects of orthostatic tolerance; (2) to explore the mechanistic aspects underneath the cerebrovascular, cardiorespiratory, and postural determinants of orthostatic tolerance; and (3) examine non-pharmacological interventions with the potential to counterbalance the physical inactivity and aging effects. To date, the orthostatic intolerance cannot be attributed exclusively with aging since physical inactivity plays an important role in postural balance, neurovascular and cardiorespiratory responses to orthostatic stress. These physiological determinates should be interpreted within an integrative approach of orthostatic tolerance, that considers the interdependence between physiological systems in a closed-loop model. Based on this multisystem approach, acute and chronic countermeasures may combat aging and sedentarism effects on orthostatic tolerance.

“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.

Dysautonomia following breast surgery: Disproportionate response to post-operative hematoma

Background

Up to 10% of patients undergoing breast surgery suffer from bleeding complications. Some experience severe hypotension and bradycardia of unclear etiology. Similar to the vasovagal hyperstimulation provoked by abdominal insufflation during laparoscopic surgery, we hypothesize that chest wall stretch from postoperative breast hematoma may mechanically stretch the vagus nerve, triggering dysautonomia disproportionate to the degree of blood loss.

Methods

A single-institution retrospective review of patients requiring reoperation for hematoma evacuation following breast surgery between 2011 and 2021 was performed. The relationship between hematoma volume and hemodynamic instability, as well as hematoma volume and vasovagal symptoms, was measured.

Results

Sixteen patients were identified. Average hematoma volume was 353 mL, and average minimum mean arterial pressure was 64 mm Hg (range: 34–102 mm Hg). Fifty-six percent of patients reported symptoms including dizziness, somnolence, and/or syncope. Accounting for body surface area, patients with larger hematomas had similar minimum mean arterial pressures compared to those with smaller hematomas, 55 and 73 mm Hg, respectively (P = .0943). However, patients in the large hematoma group experienced over 3 times as many vasovagal symptoms, 88% and 25%, respectively (P = .0095).

Conclusion

Patients with large hematomas reported significantly more vagal symptoms compared to those with small hematomas despite similar mean arterial pressures. In addition, the trend of lower mean arterial pressures and heart rates more closely resembles vagal hyperstimulation than hypovolemic shock. Early hematoma evacuation to relieve vagal nerve stretch and parasympatholytics to reverse dysautonomia are targeted interventions to consider in this patient population rather than fluids, vasopressors, and blood products that are used in cases of hemodynamic instability due to hypovolemia alone.

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.

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.

Effects of transcutaneous auricular vagus nerve stimulation on cardiovascular autonomic control in health and disease

Autonomic nervous system (ANS) dysfunction is a well-known feature of cardiovascular diseases (CVDs). Studies on heart rate variability (HRV), a non-invasive method useful in investigating the status of cardiovascular autonomic control, have shown that a predominance of sympathetic modulation not only contributes to the progression of CVDs but has a pivotal role in their onset. Current therapies focus more on inhibition of sympathetic activity, but the presence of drug-resistant conditions and the invasiveness of some surgical procedures are an obstacle to complete therapeutic success. On the other hand, targeting the parasympathetic branch of the autonomic nervous system through invasive vagus nerve stimulation (VNS) has shown interesting results as alternative therapeutic approach for CVDs. However, the invasiveness and cost of the surgical procedure limit the clinical applicability of VNS and hinder the research on the physiological pathway involved. Transcutaneous stimulation of the auricular branch of the vagus nerve (tVNS) seems to represent an important non-invasive alternative with effects comparable to those of VNS with surgical implant. Thus, in the present narrative review, we illustrate the main studies on tVNS performed in healthy subjects and in three key examples of CVDs, namely heart failure, hypertension and atrial fibrillation, highlighting the neuromodulatory effects of this technique.

Does transcutaneous auricular vagus nerve stimulation affect vagally mediated heart rate variability? A living and interactive Bayesian meta-analysis

Non-invasive brain stimulation techniques, such as transcutaneous auricular vagus nerve stimulation (taVNS), have considerable potential for clinical use. Beneficial effects of taVNS have been demonstrated on symptoms in patients with mental or neurological disorders as well as transdiagnostic dimensions, including mood and motivation. However, since taVNS research is still an emerging field, the underlying neurophysiological processes are not yet fully understood, and the replicability of findings on biomarkers of taVNS effects has been questioned. The objective of this analysis was to synthesize the current evidence concerning the effects of taVNS on vagally mediated heart rate variability (vmHRV), a candidate biomarker that has, so far, received most attention in the field. We performed a living Bayesian random effects meta-analysis. To keep the synthesis of evidence transparent and up to date as new studies are being published, we developed a Shiny web app that regularly incorporates new results and enables users to modify study selection criteria to evaluate the robustness of the inference across potential confounds. Our analysis focuses on 16 single-blind studies comparing taVNS versus sham in healthy participants. The meta-analysis provides strong evidence for the null hypothesis (g = 0.014, CI_shortest = [-0.103, 0.132], BF₀₁ = 24.678), indicating that acute taVNS does not alter vmHRV compared to sham. To conclude, there is no support for the hypothesis that vmHRV is a robust biomarker for acute taVNS. By increasing transparency and timeliness, the concept of living meta-analyses can lead to transformational benefits in emerging fields such as non-invasive brain stimulation.

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.

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.

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.

Targeting the Autonomic Nervous System for Risk Stratification, Outcome Prediction and Neuromodulation in Ischemic Stroke

Ischemic stroke is a worldwide major cause of mortality and disability and has high costs in terms of health-related quality of life and expectancy as well as of social healthcare resources. In recent years, starting from the bidirectional relationship between autonomic nervous system (ANS) dysfunction and acute ischemic stroke (AIS), researchers have identified prognostic factors for risk stratification, prognosis of mid-term outcomes and response to recanalization therapy. In particular, the evaluation of the ANS function through the analysis of heart rate variability (HRV) appears to be a promising non-invasive and reliable tool for the management of patients with AIS. Furthermore, preclinical molecular studies on the pathophysiological mechanisms underlying the onset and progression of stroke damage have shown an extensive overlap with the activity of the vagus nerve. Evidence from the application of vagus nerve stimulation (VNS) on animal models of AIS and on patients with chronic ischemic stroke has highlighted the surprising therapeutic possibilities of neuromodulation. Preclinical molecular studies highlighted that the neuroprotective action of VNS results from anti-inflammatory, antioxidant and antiapoptotic mechanisms mediated by α7 nicotinic acetylcholine receptor. Given the proven safety of non-invasive VNS in the subacute phase, the ease of its use and its possible beneficial effect in hemorrhagic stroke as well, human studies with transcutaneous VNS should be less challenging than protocols that involve invasive VNS and could be the proof of concept that neuromodulation represents the very first therapeutic approach in the ultra-early management of stroke.

The Instant Effects of Continuous Transcutaneous Auricular Vagus Nerve Stimulation at Acupoints on the Functional Connectivity of Amygdala in Migraine without Aura: A Preliminary Study

Background

A growing body of evidence suggests that both auricular acupuncture and transcutaneous auricular vagus nerve stimulation (taVNS) can induce antinociception and relieve symptoms of migraine. However, their instant effects and central treatment mechanism remain unclear. Many studies proved that the amygdalae play a vital role not only in emotion modulation but also in pain processing. In this study, we investigated the modulation effects of continuous taVNS at acupoints on the FC of the bilateral amygdalae in MwoA.

Methods

Thirty episodic migraineurs were recruited for the single-blind, crossover functional magnetic resonance imaging (fMRI) study. Each participant attended two kinds of eight-minute stimulations, taVNS and sham-taVNS (staVNS), separated by seven days in random order. Finally, 27 of them were included in the analysis of seed-to-voxel FC with the left/right amygdala as seeds.

Results

Compared with staVNS, the FC decreased during taVNS between the left amygdala and left middle frontal gyrus (MFG), left dorsolateral superior frontal gyrus, right supplementary motor area (SMA), bilateral paracentral lobules, bilateral postcingulum gyrus, and right frontal superior medial gyrus, so did the FC of the right amygdala and left MFG. A significant positive correlation was observed between the FC of the left amygdala and right SMA and the frequency/total time of migraine attacks during the preceding four weeks.

Conclusion

Continuous taVNS at acupoints can modulate the FC between the bilateral amygdalae and pain-related brain regions in MwoA, involving the limbic system, default mode network, and pain matrix, with obvious differences between the left amygdala and the right amygdala. The taVNS may produce treatment effects by modulating the abnormal FC of the amygdala and pain networks, possibly having the same central mechanism as auricular acupuncture.

Noradrenergic Regulation of Cognitive Flexibility: No Effects of Stress, Transcutaneous Vagus Nerve Stimulation, and Atomoxetine on Task-switching in Humans

Cognitive flexibility allows us to adaptively switch between different responsibilities in important domains of our daily life. Previous work has elucidated the neurochemical basis underlying the ability to switch responses to a previously nonreinforced exemplar and to switch between attentional sets. However, the role of neuromodulators in task switching, the ability to rapidly switch between two or more cognitive tasks afforded by the same stimuli, is still poorly understood. We attempted to fill this gap by manipulating norepinephrine levels using stress manipulation (Study 1a, n = 48; between-group design), transcutaneous vagus nerve stimulation at two different intensities (Study 1b, n = 48; sham-controlled between-group design), and pharmacological manipulation (Study 2, n = 24; double-blind crossover design), all of which increased salivary cortisol measures. Participants repeatedly switched between two cognitive tasks (classifying a digit as high/low [Task 1] or as odd/even [Task 2]), depending on the preceding cue. On each trial, a cue indicated the task to be performed. The cue-stimulus interval was varied to manipulate the time to prepare for the switch. Participants showed typical switch costs, which decreased with the time available for preparation. None of the manipulations modulated the size of the switch costs or the preparation effect, as supported by frequentist and Bayesian model comparisons. Task-switching performance reflects a complex mix of cognitive control and bottom-up dynamics of task-set representations. Our findings suggest that norepinephrine does not affect either of these aspects of cognitive flexibility.

Autonomic Control of the Heart and Its Clinical Impact. A Personal Perspective

This essay covers several aspects of the autonomic control of the heart, all relevant to cardiovascular pathophysiology with a direct impact on clinical outcomes. Ischemic heart disease, heart failure, channelopathies, and life-threatening arrhythmias are in the picture. Beginning with an overview on some of the events that marked the oscillations in the medical interest for the autonomic nervous system, our text explores specific areas, including experimental and clinical work focused on understanding the different roles of tonic and reflex sympathetic and vagal activity. The role of the baroreceptors, not just for the direct control of circulation but also because of the clinical value of interpreting alterations (spontaneous or induced) in their function, is discussed. The importance of the autonomic nervous system for gaining insights on risk stratification and for providing specific antiarrhythmic protection is also considered. Examples are the interventions to decrease sympathetic activity and/or to increase vagal activity. The non-invasive analysis of the RR and QT intervals provides additional information. The three of us have collaborated in several studies and each of us contributes with very specific and independent areas of expertise. Here, we have focused on those areas to which we have directly contributed and hence speak with personal experience. This is not an attempt to provide a neutral and general overview on the autonomic nervous system; rather, it represents our effort to share and provide the readers with our own personal views matured after many years of research in this field.

Tethering role of the autonomic nervous system on cardioventilatory coupling

Hypovolemia and intermittent positive pressure ventilation are conditions that frequently characterize the state of critical illness, but their interaction and resulting cardioventilatory coupling is poorly understood even in healthy humans. We explored heart rate variability, baroreflex activity, and their interaction in an experimental protocol involving twelve mildly hypovolemic healthy subjects during spontaneous breathing and noninvasive positive-pressure ventilation. In seven subjects, an echocardiographic assessment was also performed. Correction of hypovolemia, raising cardiac preload, produced an increase in high-frequency spectral power density of heart rate, left low-frequency spectral power density unchanged but enhanced baroreflex sensitivity. Cardioventilatory coupling was affected by both central blood volume and ventilatory mode and was mainly entrained by the respiratory oscillation. In conclusion, the autonomic nervous system and baroreflex have a significant role in compensating the hemodynamic perturbation due to changes of volemia and ventilatory-induced fluctuations of venous return. They exert an integrative function on the adaptive pattern of cardioventilatory coupling.

Stimulus frequency modulates brainstem response to respiratory-gated transcutaneous auricular vagus nerve stimulation

BACKGROUND

The therapeutic potential of transcutaneous auricular VNS (taVNS) is currently being explored for numerous clinical applications. However, optimized response for different clinical indications may depend on specific neuromodulation parameters, and systematic assessments of their influence are still needed to optimize this promising approach.

HYPOTHESIS

We proposed that stimulation frequency would have a significant effect on nucleus tractus solitarii (NTS) functional MRI (fMRI) response to respiratory-gated taVNS (RAVANS).

METHODS

Brainstem fMRI response to auricular RAVANS (cymba conchae) was assessed for four different stimulation frequencies (2, 10, 25, 100 Hz). Sham (no current) stimulation was used to control for respiration effects on fMRI signal.

RESULTS

Our findings demonstrated that RAVANS delivered at 100 Hz evoked the strongest brainstem response, localized to a cluster in the left (ipsilateral) medulla and consistent with purported NTS. A co-localized, although weaker, response was found for 2 Hz RAVANS. Furthermore, RAVANS delivered at 100 Hz also evoked stronger fMRI responses for important monoamine neurotransmitter source nuclei (LC, noradrenergic; MR, DR, serotonergic) and pain/homeostatic regulation nuclei (i.e. PAG).

CONCLUSION

Our fMRI results support previous localization of taVNS afference to pontomedullary aspect of NTS in the human brainstem, and demonstrate the significant influence of the stimulation frequency on brainstem fMRI response.

Evaluation of Fatigue in Cancer Patients in An Area Affected by The Great East Japan Earthquake

Objective:

The objective of this study is to evaluate fatigue in cancer outpatients receiving chemotherapy using an objective system and to clarify the type of nursing support needed after a disaster.

Methods:

Based on the diagnostic criteria for chronic fatigue syndrome, the degree of subjective fatigue, autonomic function, and amount of physical activity were measured in cancer outpatients undergoing chemotherapy from an area affected by the Great East Japan Earthquake.

Results:

The study participants were ten adults (8 men [80.0%] and 2 women [20.0%]). Significant differences were seen in subjective physical fatigue (P = 0.347), mental fatigue (P = 0.128), comprehensive fatigue (P = 0.621), and comprehensive evaluations (P = 0.293); however, no significant differences were seen in the results for changes over time for any survey item. The balance between sympathetic and parasympathetic nerve function changed statistically significant with time (log low frequency [LF] [P = 0.039] and log LF/high frequency [HF] [P = 0.021]). In all participants, autonomic nervous function was enhanced in the sympathetic nervous system, and the sympathetic nervous system was dominant. Significant differences were observed between the three measurements for mean diurnal activity (P = 0.027), total sleep time (P = 0.011), sleep efficiency (P = 0.019), awakening (P = 0.032), and naps (P = 0.037).

Conclusions:

In the event of a disaster, in addition to self-care support for side effects caused by anticancer drugs, patients' physical and mental conditions are assessed in terms of fatigue using objective indicators, and then, appropriate nursing support is provided. The nurse grasps objective facts behind the patient's subjective data and systematically recommends adjustments to the patient's daily life. In addition, by providing appropriate information to patients, patient education specific to each patient is provided.