Evoked pain analgesia in chronic pelvic pain patients using respiratory-gated auricular vagal afferent nerve stimulation

Respiratory-gated Auricular Vagal Afferent Nerve Stimulation (RAVANS) effects on autonomic outflow in hypertension

Transcutaneous stimulation of the auricular branch of the vagus nerve (ABVN) has been proposed as a non-invasive alternative to vagus nerve stimulation (VNS). However, its cardiovagal effects are inconsistent across studies, likely due to inhomogeneity in the stimulation parameters. Here, we evaluate respiratory-gated ABVN stimulation (Respiratory-gated Auricular Vagal Afferent Nerve Stimulation, RAVANS), where the stimuli are delivered in 1 s bursts during the exhalation phase of respiration, thus mimicking the breathing-induced modulation of cardiac vagal activity. In this study, we present preliminary results from an ongoing single-arm, open label trial investigating the effects of different intensities of RAVANS in hypertensive subjects. We found that a mid-intensity RAVANS stimulation (rated as a 5 on a 0-10 scale) increases the cardiovagal tone and reduces the sympathetic tone during a paced breathing task. The present results could contribute to optimize RAVANS as a non-invasive, low-cost therapeutic intervention for hypertension.

Do the psychological effects of vagus nerve stimulation partially mediate vagal pain modulation?

There is preclinical and clinical evidence that vagus nerve stimulation modulates both pain and mood state. Mechanistic studies show brainstem circuitry involved in pain modulation by vagus nerve stimulation, but little is known about possible indirect descending effects of altered mood state on pain perception. This possibility is important, since previous studies have shown that mood state affects pain, particularly the affective dimension (pain unpleasantness). To date, human studies investigating the effects of vagus nerve stimulation on pain perception have not reliably measured psychological factors to determine their role in altered pain perception elicited by vagus nerve stimulation. Thus, it remains unclear how much of a role psychological factors play in vagal pain modulation. Here, we present a rationale for including psychological measures in future vagus nerve stimulation studies on pain.

Challenges and opportunities for brainstem neuroimaging with ultrahigh field MRI

The human brainstem plays a central role in connecting the cerebrum, the cerebellum and the spinal cord to one another, hosting relay nuclei for afferent and efferent signaling, and providing source nuclei for several neuromodulatory systems that impact central nervous system function. While the investigation of the brainstem with functional or structural magnetic resonance imaging has been hampered for years due to this brain structure's physiological and anatomical characteristics, the field has seen significant advances in recent years thanks to the broader adoption of ultrahigh-field (UHF) MRI scanning. In the present review, we focus on the advantages offered by UHF in the context of brainstem imaging, as well as the challenges posed by the investigation of this complex brain structure in terms of data acquisition and analysis. We also illustrate how UHF MRI can shed new light on the neuroanatomy and neurophysiology underlying different brainstem-based circuitries, such as the central autonomic network and neurotransmitter/neuromodulator systems, discuss existing and foreseeable clinical applications to better understand diseases such as chronic pain and Parkinson's disease, and explore promising future directions for further improvements in brainstem imaging using UHF MRI techniques.

Pharmacological and other treatment modalities for esophageal pain

Treatment of esophageal pain remains a major challenge for the clinician. Although many patients have heartburn and may respond to proton pump inhibitors, there in an unmet need for other treatment modalities in patients where there are no obvious pathological findings. Although analgesics are the mainstay in esophageal pain treatment, many patients are nonresponders to these drugs. The current concise review focuses on other systems affecting pain processing, where better understanding may serve as a framework for therapy. These are the parasympathetic nervous system, exercise, and personality profiles. Finally, treatment with analgesics for functional chest pain remains a challenge, and an overview of treatment with antidepressive drugs is provided.

Ravages of Diabetes on Gastrointestinal Sensory-Motor Function: Implications for Pathophysiology and Treatment

Symptoms related to functional and sensory abnormalities are frequently encountered in patients with diabetes mellitus. Most symptoms are associated with impaired gastric and intestinal function. In this review, we discuss basic concepts of sensory-motor dysfunction and how they relate to clinical findings and gastrointestinal abnormalities that are commonly seen in diabetes. In addition, we review techniques that are available for investigating the autonomic nervous system, neuroimaging and neurophysiology of sensory-motor function. Such technological advances, while not readily available in the clinical setting, may facilitate stratification and individualization of therapy in diabetic patients in the future. Unraveling the structural, mechanical, and sensory remodeling in diabetes disease is based on a multidisciplinary approach that can bridge the knowledge from a variety of scientific disciplines. The final goal is to increase the understanding of the damage to GI structures and to sensory processing of symptoms, in order to assist clinicians with developing an optimal mechanics based treatment.

Management of chronic visceral pain

Despite marked differences in underlying pathophysiology, the current management of visceral pain largely follows the guidelines derived from the somatic pain literature. The effective management of patients with chronic visceral pain should be multifaceted, including both pharmacological and psychological interventions, thereby providing a mechanism-orientated approach to treatment. Patients can frequently become disenfranchised, and subsequently disengaged, with healthcare providers leading to repeated consultations. Thus, a key aspect of management is to break this cycle by validating patients' symptoms, adopting an empathic approach and taking time to educate patients. To optimize treatment and outcomes in chronic visceral pain we need to move away from approaches exclusively based on dealing with peripheral nociceptive input toward more holistic strategies, taking into account alterations in central pain processing.

The heart side of brain neuromodulation

Neuromodulation refers to invasive, minimally invasive or non-invasive techniques to stimulate discrete cortical or subcortical brain regions with therapeutic purposes in otherwise intractable patients: for example, thousands of advanced Parkinsonian patients, as well as patients with tremor or dystonia, benefited by deep brain stimulation (DBS) procedures (neural targets: basal ganglia nuclei). A new era for DBS is currently opening for patients with drug-resistant depression, obsessive-compulsive disorders, severe epilepsy, migraine and chronic pain (neural targets: basal ganglia and other subcortical nuclei or associative fibres). Vagal nerve stimulation (VNS) has shown clinical benefits in patients with pharmacoresistant epilepsy and depression. Non-invasive brain stimulation neuromodulatory techniques such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) are also being increasingly investigated for their therapeutic potential in several neurological and psychiatric disorders. In this review, we first address the most common neural targets of each of the mentioned brain stimulation techniques, and the known mechanisms of their neuromodulatory action on stimulated brain networks. Then, we discuss how DBS, VNS, rTMS and tDCS could impact on the function of brainstem centres controlling vital functions, critically reviewing their acute and long-term effects on brain sympathetic outflow controlling heart function and blood pressure. Finally, as there is clear experimental evidence in animals that brain stimulation can affect autonomic and heart functions, we will try to give a critical perspective on how it may enhance our understanding of the cortical/subcortical mechanisms of autonomic cardiovascular regulation, and also if it might find a place among therapeutic opportunities in patients with otherwise intractable autonomic dysfunctions.

Vagal tone: effects on sensitivity, motility, and inflammation

The vagus nerve (VN) is a key element of the autonomic nervous system. As a mixed nerve, the VN contributes to the bidirectional interactions between the brain and the gut, i.e., the brain-gut axis. In particular, after integration in the central autonomic network of peripheral sensations such as inflammation and pain via vagal and spinal afferents, an efferent response through modulation of preganglionic parasympathetic neurons of the dorsal motor nucleus of the vagus and/or preganglionic sympathetic neurons of the spinal cord is able to modulate gastrointestinal nociception, motility, and inflammation. A low vagal tone, as assessed by heart rate variability, a marker of the sympatho-vagal balance, is observed in functional digestive disorders and inflammatory bowel diseases. To restore a normal vagal tone appears as a goal in such diseases. Among the therapeutic tools, such as drugs targeting the cholinergic system and/or complementary medicine (hypnosis, meditation…), deep breathing, physical exercise, VN stimulation (VNS), either invasive or non-invasive, appears as innovative. There is new evidence in the current issue of this Journal supporting the role of VNS in the modulation of gastrointestinal functions.

Modulation of vagal tone enhances gastroduodenal motility and reduces somatic pain sensitivity

BACKGROUND

The parasympathetic nervous system, whose main neural substrate is the vagus nerve, exerts a fundamental antinociceptive role and influences gastrointestinal sensori-motor function. Our research question was to whether combined electrical and physiological modulation of vagal tone, using transcutaneous electrical vagal nerve stimulation (t-VNS) and deep slow breathing (DSB) respectively, could increase musculoskeletal pain thresholds and enhance gastroduodenal motility in healthy subjects.

METHODS

Eighteen healthy subjects were randomized to a subject-blinded, sham-controlled, cross-over study with an active protocol including stimulation of auricular branch of the vagus nerve, and breathing at full inspiratory capacity and forced full expiration. Recording of cardiac derived parameters including cardiac vagal tone, moderate pain thresholds to muscle, and bone pressure algometry, conditioned pain modulation using a cold pressor test and a liquid meal ultrasonographic gastroduodenal motility test were performed.

KEY RESULTS

Cardiac vagal tone increased during active treatment with t-VNS and DSB compared to sham (p = 0.009). In comparison to sham, thresholds to bone pain increased (p = 0.001), frequency of antral contractions increased (p = 0.004) and gastroduodenal motility index increased (p = 0.016) with active treatment. However, no effect on muscle pain thresholds and conditioned pain modulation was seen.

CONCLUSIONS & INFERENCES

This experimental study suggests that this noninvasive approach with combined electrical and physiological modulation of vagal tone enhances gastroduodenal motility and reduces somatic pain sensitivity. These findings warrant further investigation in patients with disorders characterized with chronic pain and gastrointestinal dysmotility such as functional dyspepsia and irritable bowel syndrome.

Autonomic Testing in Women with Chronic Pelvic Pain

PURPOSE

We determined whether abnormal autonomic nervous system innervation of the bladder underlies IC (interstitial cystitis)/BPS (bladder pain syndrome) differently than other chronic pelvic pain.

MATERIALS AND METHODS

In this institutional review board approved protocol 39 healthy controls and 134 subjects were enrolled, including 36 with IC/BPS, 14 with myofascial pelvic pain and 42 with IC/BPS plus myofascial pelvic pain. Three subjects were excluded from study. Autonomic nervous system evaluations included deep breathing, the Valsalva maneuver, and the tilt table and sudomotor tests. The latter evaluates autonomic neuropathy. A modified validated composite autonomic laboratory score was applied.

RESULTS

Median age in the IC/BPS group was 47.5 years (range 21 to 78), greater than in healthy controls (34 years, range 20 to 75, p = 0.006), the myofascial pelvic pain group (33 years, range 22 to 56, p = 0.004) and the IC/BPS plus myofascial pelvic pain group (38 years, range 18 to 64, p = 0.03). Body mass index did not significantly differ but the myofascial pelvic pain and IC/BPS plus myofascial pelvic pain groups had a higher body mass index than healthy controls (p = 0.05 and 0.03, respectively). Cardiovascular and adrenergic indexes did not differ. The tilt table test showed more orthostatic intolerance in all chronic pelvic pain groups. Tilt table test diagnoses (orthostatic hypotension, postural tachycardia syndrome and reflex syncope) were rare. Baseline heart rate was higher in all chronic pelvic pain groups (p = 0.004). Compared to healthy controls all myofascial pelvic pain groups showed significantly more clear-cut autonomic neuropathy, defined as a sweat score of 3 or greater (vs IC/BPS plus myofascial pelvic pain p = 0.007 and vs myofascial pelvic pain p = 0.03).

CONCLUSIONS

Some chronic pelvic pain types show autonomic neuropathy and some show vagal withdrawal. In all types orthostatic intolerance likely reflects central sensitization and perhaps catastrophizing. Some of these findings suggest novel therapeutic targets.

The hippocampus and TNF: Common links between chronic pain and depression

Major depression and chronic pain are significant health problems that seriously impact the quality of life of affected individuals. These diseases that individually are difficult to treat often co-exist, thereby compounding the patient's disability and impairment as well as the challenge of successful treatment. The development of efficacious treatments for these comorbid disorders requires a more comprehensive understanding of their linked associations through common neuromodulators, such as tumor necrosis factor-α (TNFα), and various neurotransmitters, as well as common neuroanatomical pathways and structures, including the hippocampal brain region. This review discusses the interaction between depression and chronic pain, emphasizing the fundamental role of the hippocampus in the development and maintenance of both disorders. The focus of this review addresses the hypothesis that hippocampal expressed TNFα serves as a therapeutic target for management of chronic pain and major depressive disorder (MDD).

Surgically implanted and non-invasive vagus nerve stimulation: a review of efficacy, safety and tolerability

Vagus nerve stimulation (VNS) is effective in refractory epilepsy and depression and is being investigated in heart failure, headache, gastric motility disorders and asthma. The first VNS device required surgical implantation of electrodes and a stimulator. Adverse events (AEs) are generally associated with implantation or continuous on-off stimulation. Infection is the most serious implantation-associated AE. Bradycardia and asystole have also been described during implantation, as has vocal cord paresis, which can last up to 6 months and depends on surgical skill and experience. The most frequent stimulation-associated AEs include voice alteration, paresthesia, cough, headache, dyspnea, pharyngitis and pain, which may require a decrease in stimulation strength or intermittent or permanent device deactivation. Newer non-invasive VNS delivery systems do not require surgery and permit patient-administered stimulation on demand. These non-invasive VNS systems improve the safety and tolerability of VNS, making it more accessible and facilitating further investigations across a wider range of uses.

Non-invasive Access to the Vagus Nerve Central Projections via Electrical Stimulation of the External Ear: fMRI Evidence in Humans

BACKGROUND

Tract-tracing studies in cats and rats demonstrated that the auricular branch of the vagus nerve (ABVN) projects to the nucleus tractus solitarii (NTS); it has remained unclear as to whether or not the ABVN projects to the NTS in humans.

OBJECTIVE

To ascertain whether non-invasive electrical stimulation of the cymba conchae, a region of the external ear exclusively innervated by the ABVN, activates the NTS and the "classical" central vagal projections in humans.

METHODS

Twelve healthy adults underwent two fMRI scans in the same session. Electrical stimulation (continuous 0.25ms pulses, 25Hz) was applied to the earlobe (control, scan #1) and left cymba conchae (scan #2). Statistical analyses were performed with FSL. Two region-of-interest analyses were performed to test the effects of cymba conchae stimulation (compared to baseline and control, earlobe, stimulation) on the central vagal projections (corrected; brainstem P < 0.01, forebrain P < 0.05), followed by a whole-brain analysis (corrected, P < 0.05).

RESULTS

Cymba conchae stimulation, compared to earlobe (control) stimulation, produced significant activation of the "classical" central vagal projections, e.g., widespread activity in the ipsilateral NTS, bilateral spinal trigeminal nucleus, dorsal raphe, locus coeruleus, and contralateral parabrachial area, amygdala, and nucleus accumbens. Bilateral activation of the paracentral lobule was also observed. Deactivations were observed bilaterally in the hippocampus and hypothalamus.

CONCLUSION

These findings provide evidence in humans that the central projections of the ABVN are consistent with the "classical" central vagal projections and can be accessed non-invasively via the external ear.

Electrical stimulation of the vagus nerve dermatome in the external ear is protective in rat cerebral ischemia

BACKGROUND

Although cervical vagus nerve stimulation is effective for reducing infarct volume in rats, it is not feasible for acute human stroke as it requires surgical incision of the neck. We hypothesized that stimulation of the dermatome in the external ear innervated by the vagus nerve (auricular vagus nerve stimulation; aVNS) reduces infarct volume after transient focal ischemia in rats.

METHODS

Animals were randomized to active aVNS or sham stimulation. For aVNS, electrical stimulation of the left cavum concha (1 h duration) using percutaneous needles was initiated 30 min after induction of ischemia. Behavioral and tissue outcome were measured 24 h after induction of ischemia. In a separate experimental dataset, c-Fos immunohistochemistry was performed to identify the brain regions activated after the stimulation.

RESULTS

Stimulation of the left cavum concha resulted in bilateral c-Fos staining in the nuclei tractus solitarii and the loci coerulei in all animals. There was no c-Fos staining in any part of the brainstem in sham control animals. The mean infarct volume (SD) as calculated by indirect method was 44.20 ± 7.58% in controls and 31.65 ± 9.67% in treated animals (P < 0.0001). The effect of aVNS on tissue outcome was associated with better neurological scores at 24 h after ischemia (P < 0.0001).

CONCLUSIONS

Electric stimulation of the vagus nerve dermatome in the external ear activates brainstem afferent vagal nuclei and reduces infarct volume in rats. This finding has potential to facilitate the development of treatments that leverage the brain's endogenous neuroprotective pathways at the setting of acute ischemic stroke.

Systematic review of endometriosis pain assessment: how to choose a scale?

BACKGROUND

Numerous studies concerning endometriosis and pain have been reported. However, there is no consensus on the best method to evaluate pain in endometriosis and many scales have been used. Moreover, there are only a few descriptions of minimal clinically important differences after treatment (MCID) to evaluate variations in pain. In our study, we aim to identify pain scales used in endometriosis pain treatment, to address their strong and weak points and to define which would be the ideal scale to help clinicians and researchers to evaluate endometriosis-related pain.

METHODS

A search of the MEDLINE and EMBASE databases was carried out for publications in English, French or Portuguese from 1980 to December 2012, for the words: endometriosis, treatment, pain. Studies were selected if they studied an endometriosis treatment and a pain scale was specified. A quantitative and a qualitative analysis of each scale was performed to define strong and weak points of each scale (systematic registration number: CRD42013005336).

RESULTS

A total of 736 publications were identified. After excluding duplications and applying inclusion criteria 258 studies remained. We found that the visual analog scale (VAS) is the most frequently used scale. Both VAS and the numerical rating scale (NRS) show a good balance between strong and weak points in comparison with others such as the Biberoglu and Behrman scale. Concerning MCID, only VAS, NRS and Brief Pain Inventory scales have reported MCID and, among these, only VAS MCID has been studied in endometriosis patients (VAS MCID = 10 mm). Adding the Clinical Global Impression score (CGI) to the pain scale allows calculation of the MCID.

CONCLUSIONS

When using pain scales their strengths and weaknesses must be known and included in the analysis. VAS is the most frequently used pain scale and, together with NRS, seems the best adapted for endometriosis pain measurement. The use of VAS or NRS for each type of typical pain related to endometriosis (dysmenorrhea, deep dyspareunia and non-menstrual chronic pelvic pain), combined with the CGI and a quality-of-life scale will provide both clinicians and researchers with tools to evaluate treatment response.

Transcutaneous vagal nerve stimulation may elicit anti- and pro-nociceptive effects under experimentally-induced pain - a crossover placebo-controlled investigation

Vagal nerve stimulation is a promising method for the treatment of pain. The aim was to investigate the effect of non-invasive transcutaneous vagal nerve stimulation (TVNS) on the experimental pain threshold (PT) and to compare it with placebo. PT of standardized electrical stimulation was measured in 22 healthy male volunteers during two study sessions. TVNS was applied to the auricular concha bilaterally for 35min using 2Hz/100Hz bursts with the intensity, which was individually maximal but non-painful. During the placebo session, the volunteers received no stimulation. PT, heart rate and blood pressure were registered as outcome measures. There were no differences in PT values between TVNS and placebo conditions in the group analysis. Fifteen volunteers (responders) reacted with an increase in PT during TVNS (p<0.01 vs. baseline) but not during the placebo session. Another six participants reported decreased PT during and after TVNS (p<0.05 vs. baseline), but not during the placebo session. Heart rate and blood pressure did not change during the study. Transcutaneous vagal nerve stimulation may produce both anti- and pro-nociceptive effects in healthy volunteers. The individual sensitivity and TVNS parameters might play a role.

Non-invasive vagus nerve stimulation in healthy humans reduces sympathetic nerve activity

BACKGROUND

Vagus nerve stimulation (VNS) is currently used to treat refractory epilepsy and is being investigated as a potential therapy for a range of conditions, including heart failure, tinnitus, obesity and Alzheimer's disease. However, the invasive nature and expense limits the use of VNS in patient populations and hinders the exploration of the mechanisms involved.

OBJECTIVE

We investigated a non-invasive method of VNS through electrical stimulation of the auricular branch of the vagus nerve distributed to the skin of the ear--transcutaneous VNS (tVNS) and measured the autonomic effects.

METHODS

The effects of tVNS parameters on autonomic function in 48 healthy participants were investigated using heart rate variability (HRV) and microneurography. tVNS was performed using a transcutaneous electrical nerve stimulation (TENS) machine and modified surface electrodes. Participants visited the laboratory once and received either active (200 μs, 30 Hz; n = 34) or sham (n = 14) stimulation.

RESULTS

Active tVNS significantly increased HRV in healthy participants (P = 0.026) indicating a shift in cardiac autonomic function toward parasympathetic predominance. Microneurographic recordings revealed a significant decrease in frequency (P = 0.0001) and incidence (P = 0.0002) of muscle sympathetic nerve activity during tVNS.

CONCLUSION

tVNS can increase HRV and reduce sympathetic nerve outflow, which is desirable in conditions characterized by enhanced sympathetic nerve activity, such as heart failure. tVNS can therefore influence human physiology and provide a simple and inexpensive alternative to invasive VNS.

Psychophysiological responses to visceral and somatic pain in functional chest pain identify clinically relevant pain clusters

BACKGROUND

Despite chronic pain being a feature of functional chest pain (FCP) its experience is variable. The factors responsible for this variability remain unresolved. We aimed to address these knowledge gaps, hypothesizing that the psychophysiological profiles of FCP patients will be distinct from healthy subjects.

METHODS

20 Rome III defined FCP patients (nine males, mean age 38.7 years, range 28-59 years) and 20 healthy age-, sex-, and ethnicity-matched controls (nine males, mean 38.2 years, range 24-49) had anxiety, depression, and personality traits measured. Subjects had sympathetic and parasympathetic nervous system parameters measured at baseline and continuously thereafter. Subjects received standardized somatic (nail bed pressure) and visceral (esophageal balloon distension) stimuli to pain tolerance. Venous blood was sampled for cortisol at baseline, post somatic pain and post visceral pain.

KEY RESULTS

Patients had higher neuroticism, state and trait anxiety, and depression scores but lower extroversion scores vs controls (all p < 0.005). Patients tolerated less somatic (p < 0.0001) and visceral stimulus (p = 0.009) and had a higher cortisol at baseline, and following pain (all p < 0.001). At baseline, patients had a higher sympathetic tone (p = 0.04), whereas in response to pain they increased their parasympathetic tone (p ≤ 0.008). The amalgamating the data, we identified two psychophysiologically distinct 'pain clusters'. Patients were overrepresented in the cluster characterized by high neuroticism, trait anxiety, baseline cortisol, pain hypersensitivity, and parasympathetic response to pain (all p < 0.03).

CONCLUSIONS & INFERENCES

In future, such delineations in FCP populations may facilitate individualization of treatment based on psychophysiological profiling.

New directions in the treatment of pelvic pain

SUMMARY The treatment of chronic pelvic pain in both females and males is a challenge for pain clinicians. Standard therapies are multimodal in nature with use of behavioral, medical and procedural therapeutics. In recent years, our understanding of the neurobiology of this disorder has improved and novel approaches have focused on neuromodulatory options, novel pharmacology and complementary/alternative medicine options. This review briefly examines newly employed therapeutic options, while restating currently utilized options. The current state-of-the-art treatment includes focal therapies for identified pathologies and empiric trials of other options for care when precise sources of the chronic pelvic pain are ill defined.

Vagal sensory evoked potentials disappear under the neuromuscular block - an experimental study

BACKGROUND

Transcutaneous vagal nerve stimulation is a promising treatment modality in patients suffering mood disorders and chronic pain, however, the mechanisms are still to be elucidated. A recently developed technique of EEG responses to electrical stimulation of the inner side of the tragus suggests that these responses are far field potentials, generated in the vagal system - Vagal Sensory Evoked Potentials (VSEP).

OBJECTIVE

To reproduce the VSEP technique free from myogenic artifacts.

METHODS

Fourteen ASA I-II patients scheduled for elective surgery in standardized Total Intravenous Anesthesia (TIVA) were enrolled. Transcutaneous electrical stimulation was applied to the inner side of the right tragus. Averaged EEG responses were recorded from the electrode positions C4-F4 and T4-O2 before and after induction of TIVA, during the maximal effect of the non-depolarizing muscle relaxing agent, cis-atracurium (C-AR) and after recovery from C-AR under TIVA.

RESULTS

Typical response curves with P1, N1 and P2 peaks could be reproduced in all patients before and after anesthesia induction. The response curves disappeared during the C-AR action and re-appeared after recovery from C-AR under TIVA.

CONCLUSION

The disappearance of the scalp responses to electrical tragus stimulation under the neuromuscular block suggests a muscular origin of these potentials.