Efficacy of electrical stimulation at frequencies higher than basal rate in canine stomach

Gastric Electrical Stimulation: Role and Clinical Impact on Chronic Nausea and Vomiting

Gastric electrical stimulation (GES) is currently used as an alternative treatment for medically refractory gastroparesis. GES has been initially developed to accelerate gastric motility, in order to relieve the symptoms of the patients. Subsequent studies, unfortunately, failed to demonstrate the acceleration of gastric emptying using high-frequency stimulation – low energy stimulation although the technique has shown a clinical impact with a reduction of nausea and vomiting for patients with gastroparesis. The present review details the clinical efficacy of GES in gastroparesis as well as its putative mechanisms of action.

Low-frequency electrical stimulation promotes the recovery of gastrointestinal motility following gynecological laparoscopy (Review)

The rapid recovery of gastrointestinal transit is critical for clinical recovery following laparoscopic procedures, including gynecological laparoscopies (GLs). Rehabilitation interventions post-surgery may provide significant prevention against early post-operative gastrointestinal motility disorders and maid aid in the acceleration of post-operative recovery in patients undergoing GLs. Among others, low-frequency electrical stimulation (LFES) has been demonstrated to pronouncedly mitigate the symptoms caused by gastrointestinal motility disorders; thus, this has attracted increasing attention over the past decade. The present study aimed to present an overview of the efficacy and application of LFES in gastrointestinal motility recovery following GL procedures.

Strategies to Refine Gastric Stimulation and Pacing Protocols: Experimental and Modeling Approaches

Gastric pacing and stimulation strategies were first proposed in the 1960s to treat motility disorders. However, there has been relatively limited clinical translation of these techniques. Experimental investigations have been critical in advancing our understanding of the control mechanisms that innervate gut function. In this review, we will discuss the use of pacing to modulate the rhythmic slow wave conduction patterns generated by interstitial cells of Cajal in the gastric musculature. In addition, the use of gastric high-frequency stimulation methods that target nerves in the stomach to either inhibit or enhance stomach function will be discussed. Pacing and stimulation protocols to modulate gastric activity, effective parameters and limitations in the existing studies are summarized. Mathematical models are useful to understand complex and dynamic systems. A review of existing mathematical models and techniques that aim to help refine pacing and stimulation protocols are provided. Finally, some future directions and challenges that should be investigated are discussed.

An emerging method to noninvasively measure and identify vagal response markers to enable bioelectronic control of gastroparesis symptoms with gastric electrical stimulation

BACKGROUND

Gastric electrical stimulation (GES) can be a life-changing, device-based treatment option for drug-resistant nausea and vomiting associated with diabetic or idiopathic gastroparesis (GP). Despite over two decades of clinical use, the mechanism of action remains unclear. We hypothesize a vagal mechanism.

NEW METHOD

Here, we describe a noninvasive method to investigate vagal nerve involvement in GES therapy in 66 human subjects through the compound nerve action potential (CNAP).

RESULTS

Of the 66 subjects, 28 had diabetic GP, 35 had idiopathic GP, and 3 had postsurgical GP. Stimulus charge per pulse did not predict treatment efficacy, but did predict a significant increase in total symptom score in type 1 diabetics as GES stimulus charge per pulse increased (p < 0.01), representing a notable side effect and providing a method to identify it. In contrast, the number of significant left and right vagal fiber responses that were recorded directly related to patient symptom improvement. Increased vagal responses correlated with significant decreases in total symptom score (p < 0.05).

COMPARISON WITH EXISTING METHOD(S)

We have developed transcutaneous recording of cervical vagal activity that is synchronized with GES in conscious human subjects, along with methods of discriminating the activity of different nerve fiber groups with respect to conduction speed and treatment response.

CONCLUSIONS

Cutaneous vagal CNAP analysis is a useful technique to unmask relationships among GES parameters, vagal recruitment, efficacy and side-effect management. Our results suggest that CNAP-guided GES optimization will provide the most benefit to patients with idiopathic and type 1 diabetic gastroparesis.

The Effect of Gastric Electrical Stimulation on Small Bowel Motility in Patients With Gastroparesis and Concomitant Pancreatic and Small Bowel Dysfunction: From Animal Model to Human Application

BACKGROUND/AIMS

Patients with gastroparesis often have biliary/pancreatic and small bowel symptoms but the effects of gastric electrical stimulation on small bowel electrical activity of the mid-gut have not been studied. Animal model aim: Establish gastric and upper small bowel/biliary slow wave activity relationships with electrical stimulation. Human study aim: Demonstrate improvement in symptoms associated with proximal small bowel dysmotility in gastric stimulated patients.

MATERIALS AND METHODS

Animal model: In vivo evoked responses of duodenal and Sphincter of Oddi measures recorded during gastric electrical stimulation in a nonsurvival swine model (N = 3). High-resolution electrical slow wave mapping of frequency, amplitude, and their ratio, for duodenal and Sphincter of Oddi electrical activity were recorded. Human study: Patients (N = 8) underwent temporary gastric stimulation with small bowel electrodes. Subjective and objective data was collected before and after temporary gastric stimulation. Symptom scores, gastric emptying times, and mucosal electrograms via low-resolution mapping were recorded.

RESULTS

Animal gastric stimulation resulted in some changes in electrical activity parameters, especially with the highest energies delivered but the changes were not statistically significant. Human study revealed improvement in symptom and illness severity scores, and changes in small bowel mucosal slow wave activity.

CONCLUSIONS

Gastric electrical stimulation in an animal model seems to show nonsignificant effects small bowel slow wave activity and myoelectric signaling, suggesting the existence of intrinsic neural connections. Human data shows more significance, with possible potential for therapeutic use of electrical stimulation in patients with gastroparesis and pancreato-biliary and small bowel symptoms of the mid-gut. This study was limited by the nonsurvival pig model, small sample size, and open label human study.

Minimally-invasive temporary gastric stimulation: A pilot study to predict the outcome of electronic gastric stimulation with the Enterra™ system

INTRODUCTION

Gastroparesis (GP) is defined as delayed gastric emptying (GE) without any obstruction of the pylorus. It can be divided into idiopathic, diabetic, post surgical and rare causes. Electronic gastric stimulation (EGS) - Enterra Medtronic™ - is a part of GP therapy. Although its positive impact has been reported in open label trials, randomized controlled trials failed in demonstrating a positive outcome. The aim of this pilot study was to establish a reliable prediction for permanent gastric stimulation.

PATIENTS AND PROCEDURE

6 female patients underwent laparoscopic implantation of 2 temporary electrodes. The Enterra™ system was connected and taped to the skin. Baseline and postoperative gastroparesis cardinal symptom index (GCSI), a validated index for GP therapy, was assessed. Response to EGS was defined as a 50% decrease of baseline GCSI.

RESULTS

4 of 6 patients responded to temporary EGS. 3 of 4 responders underwent permanent implantation. 1 non-responder received a permanent Enterra™ at another institution. After a median follow up time of 9months the responder group GCSI remained low, whereas the non-responder GCSI had increased. Moreover, the health care system was saved € 30,678.03 by this test stimulation concept.

CONCLUSION

Laparoscopic implantation of a temporary EGS system predicts the outcome of permanent gastric stimulation and is cost-saving.

Electrical therapies for gastrointestinal motility disorders

Gastrointestinal (GI) motility disorders are common in clinical settings, including esophageal motility disorders, gastroesophageal reflux disease, functional dyspepsia, gastroparesis, chronic intestinal pseudo-obstruction, post-operative ileus, irritable bowel syndrome, diarrhea and constipation. While a number of drugs have been developed for treating GI motility disorders, few are currently available. Emerging electrical stimulation methods may provide new treatment options for these GI motility disorders. Areas covered: This review gives an overview of electrical therapies that have been, and are being developed for GI motility disorders, including gastroesophageal reflux, functional dyspepsia, gastroparesis, intestinal motility disorders and constipation. Various methods of gastrointestinal electrical stimulation are introduced. A few methods of nerve stimulation have also been described, including spinal cord stimulation and sacral nerve stimulation. Potentials of electrical therapies for obesity are also discussed. PubMed was searched using keywords and their combinations: electrical stimulation, spinal cord stimulation, sacral nerve stimulation, gastrointestinal motility and functional gastrointestinal diseases. Expert commentary: Electrical stimulation is an area of great interest and has potential for treating GI motility disorders. However, further development in technologies (devices suitable for GI stimulation) and extensive clinical research are needed to advance the field and bring electrical therapies to bedside.

Some Non-FDA Approved Uses for Neuromodulation in Treating Autonomic Nervous System Disorders: A Discussion of the Preliminary Support

INTRODUCTION

Neuromodulation, including cavernous nerve stimulation, gastric electrical stimulation, deep brain stimulation, and vagus nerve stimulation, has been used with success in treating several functional disease conditions. The FDA has approved the use of neuromodulation for a few indications. We discuss in our review article the evidence of using neuromodulation for treating some important disorders involving the autonomic nervous system that are not currently FDA approved.

METHODS

This was a review article that included a systematic online web search for human clinical studies testing the efficacy of neuromodulation in treating erectile dysfunction, gastroparesis, gastroesophageal reflux disease, obesity, asthma, and heart failure. Our review includes all feasibility studies, nonrandomized clinical trials, and randomized controlled trials.

RESULTS

Our systematic literature search found 3, 4, 5, 4, 1, and 4 clinical studies relating to erectile dysfunction, gastroparesis, gastroesophageal reflux disease, obesity, asthma, and heart failure, respectively.

CONCLUSION

This review article shows preliminary support based on clinical studies that neuromodulation can be of benefit for patients with important autonomic nervous system disease conditions that are not currently approved by the FDA. All of these investigational uses are encouraging; further studies are necessary and warranted for all indications discussed in this review before achieving FDA approval.

Acute Slow Wave Responses to High-Frequency Gastric Electrical Stimulation in Patients With Gastroparesis Defined by High-Resolution Mapping

BACKGROUND AND AIMS

High-frequency gastric electrical stimulation (GES) has emerged as a therapy for gastroparesis, but the mechanism(s) of action remain unclear. There is a need to refine stimulation protocols for clinical benefit, but a lack of accurate techniques for assessing mechanisms in clinical trials, such as slow wave modulation, has hindered progress. We thereby aimed to assess acute slow wave responses to GES in gastroparesis patients using high-resolution (HR) (multi-electrode) mapping, across a range of stimulation doses achievable by the Enterra stimulation device (Medtronic Inc., MN, USA).

MATERIALS AND METHODS

Patients with medically refractory gastroparesis (n = 8) undergoing device implantation underwent intraoperative HR mapping (256 electrodes). Baseline recordings were followed by four protocols of increasing stimulation intensity, with washout periods. Slow wave patterns, frequency, velocity, amplitude, and dysrhythmia rates were quantified by investigators blinded to stimulation settings.

RESULTS

There was no difference in slow wave pattern, frequency, velocity, or amplitude between baseline, washout, and stimulation periods (all p > 0.5). Dysrhythmias included ectopic pacemakers, conduction blocks, retrograde propagation, and colliding wavefronts, and dysrhythmia rates were unchanged with stimulation off vs. on (31% vs. 36% duration dysrhythmic; p > 0.5). Symptom scores and gastric emptying were improved at 5.8 month follow-up (p < 0.05).

CONCLUSIONS

High-frequency GES protocols achievable from a current commercial device did not acutely modulate slow wave activity or dysrhythmias. This study advances clinical methods for identifying and assessing therapeutic GES parameters, and can be applied in future studies on higher-energy protocols and devices.

Autonomic Evaluation of Patients With Gastroparesis and Neurostimulation: Comparisons of Direct/Systemic and Indirect/Cardiac Measures

Background

Disorders of nausea, vomiting, abdominal pain, and related problems often are manifestations of gastrointestinal, neuromuscular, and/or autonomic dysfunction. Many of these patients respond to neurostimulation, either gastric electrical stimulation or electroacupuncture. Both of these therapeutic techniques appear to influence the autonomic nervous system which can be evaluated directly by traditional testing and indirectly by heart rate variability.

Methods

We studied patients undergoing gastric neuromodulation by both systemic autonomic testing (39 patients, six males and 33 females, mean age 38 years) and systemic autonomic testing and heart rate variability (35 patients, seven males and 28 females, mean age 37 years) testing before and after gastric neuromodulation. We also performed a pilot study using both systemic autonomic testing and heart rate variability in a small number of patients (five patients, all females, mean age 48.6 years) with diabetic gastroparesis at baseline to compare the two techniques at baseline. Systemic autonomic testing and heart rate variability were performed with standardized techniques and gastric electrical stimulation was performed as previously described with electrodes implanted serosally in the myenteric plexus.

Results

Both systemic autonomic testing and heart rate variability measures were often abnormal at baseline and showed changes after gastric neuromodulation therapy in two groups of symptomatic patients. Pilot data on a small group of similar patients with systemic automatic nervous measures and heart rate variability showed good concordance between the two techniques.

Conclusions

Both traditional direct autonomic measures and indirect measures such as heart rate variability were evaluated, including a pilot study of both methods in the same patient group. Both appear to be useful in evaluation of patients at baseline and after stimulation therapies; however, a future full head-to-head comparison is warranted.

Neuroenteric Stimulation for Gastroparesis

OPINION STATEMENT

Gastroparesis (GP) is a syndrome characterized by delayed gastric emptying in association with symptoms of epigastric pain, nausea, and vomiting in the absence of mechanical obstruction. The prevalence of gastroparesis has been estimated at 24 per 100,000, with women more commonly affected than men. Diabetes appears to be the underlying cause in approximately 25 % of patients, while connective tissue disorders, autoimmune disorders, prior gastric surgery, ischemia, and medications make up a smaller percentage of the remaining identifiable causes. However, the largest group of GP patients falls into the idiopathic category (~50 %); many of these patients likely develop GP as a result of a prior viral infection. Symptoms of gastroparesis develop due to a number of different pathophysiologic processes, including disorders of fundic accommodation, antroduodenal dyscoordination, a weak antral pump, gastric dysrhythmias, abnormal duodenal feedback, and enhanced visceral sensation. Once the diagnosis of GP is made, the clinician has a number of different treatment options. For patients with mild to moderate symptoms, dietary modifications in conjunction with or without prokinetics and antiemetics are often all that is required. However, many patients with severe symptoms who fail to respond to standard therapy may benefit from neuroenteric stimulation (gastric electrical stimulation). This monograph will review the role of the neuroenteric stimulator therapy for gastroparesis, discuss possible mechanisms of action of neuroenteric stimulation, review data from recently published studies on its efficacy, and discuss patient selection and adverse events.

Gastroparesis: a review of current and emerging treatment options

Gastroparesis is a motility disorder of the stomach causing delay in food emptying from the stomach without any evidence of mechanical obstruction. The majority of cases are idiopathic. Patients need to be diagnosed properly by formal testing, and the evaluation of the severity of the gastroparesis may assist in guiding therapy. Initially, dietary modifications are encouraged, which include frequent and small semisolid-based meals. Promotility medications, like erythromycin, and antiemetics, like prochlorperazine, are offered for symptom relief. In patients who are refractory to pharmacologic treatment, more invasive options, such as intrapyloric botulinum toxin injections, placement of a jejunostomy tube, or implantation of a gastric stimulator, can be considered. Hemin therapy and gastric electric stimulation are emerging treatment options that are still at different stages of research. Regenerative medicine and stem cell-based therapies also hold promise for gastroparesis in the near future.

Gastric electrical stimulation for the treatment of obesity: from entrainment to bezoars-a functional review

GROWING WORLDWIDE OBESITY EPIDEMIC HAS PROMPTED THE DEVELOPMENT OF TWO MAIN TREATMENT STREAMS: (a) conservative approaches and (b) invasive techniques. However, only invasive surgical methods have delivered significant and sustainable benefits. Therefore, contemporary research exploration has focused on the development of minimally invasive gastric manipulation methods featuring a safe but reliable and long-term sustainable weight loss effect similar to the one delivered by bariatric surgeries. This antiobesity approach is based on placing external devices in the stomach ranging from electrodes for gastric electrical stimulation to temporary intraluminal bezoars for gastric volume displacement for a predetermined amount of time. The present paper examines the evolution of these techniques from invasively implantable units to completely noninvasive patient-controllable implements, from a functional, rather than from the traditional, parametric point of view. Comparative discussion over the available pilot and clinical studies related to gastric electrical stimulation outlines the promises and the fallacies of this concept as a reliable alternative anti-obesity strategy.

Long term efficacy of gastric electrical stimulation in intractable nausea and vomiting

BACKGROUND

Although the efficacy of gastric electrical stimulation has been reported in short-term studies, there is a lack of data on the long-term improvement of nausea and vomiting by gastric electrical stimulation in patients with delayed or normal gastric emptying.

METHODS

Thirty-one patients were implanted at our centre for medically refractory severe and chronic nausea and/or vomiting. Patients were evaluated at baseline, 6 months then 5 years after implantation (mean follow-up 80±4 months) using a symptomatic and quality of life scores.

KEY RESULTS

Amongst the 31 patients, 4 were lost to follow-up, 6 explanted due to lack of improvement, and 1 patient died. Out of the 20 patients evaluated over 5 years, the quality of life score showed 27% improvement (p<0.01), including nausea (62%; p<0.01), vomiting (111%; p=0.03), satiety (158%; p<0.01), bloating (67%; p<0.01) and epigastric pain (43%; p=0.03). Over 5 years, 15/20 patients reported a 50% improvement with a global satisfaction rated at 64±6%. Therefore, 15/27 patients (56%) were improved by gastric electrical stimulation over 5 years in intention to treat. Improvement of nausea 6 months after implantation was predictive of 5-year success of gastric electrical stimulation (p=0.04). Finally, patients with delayed gastric emptying or with normal gastric emptying rate before surgery were similarly improved over 5 years (60% versus 50% respectively).

CONCLUSION

Gastric electrical stimulation is safe and effective in the long term in patients with medically refractory nausea and vomiting, with an efficacy over 50% beyond 5 years in intention to treat. Gastric emptying measured before implantation did not influence the response rate over 5 years.

Gastric electrical stimulation for gastroparesis

Gastric electrical stimulation (GES) for gastroparesis has been in use for more than a decade. Multiple publications, consisting almost entirely of open label single center studies, reported a beneficial effect on symptoms, quality of life and nutritional status. Some predictors of better response to GES have been lately identified, primarily diabetic etiology and nausea and vomiting as the predominant symptoms. However, individual response to GES remains difficult to predict. The mechanism of action of GES remains poorly understood. Stimulation parameters approved in clinical practice do not regulate gastric slow wave activity and have inconsistent effect on gastric emptying. Despite such limitations, gastric electrical stimulation remains a helpful intervention in some patients with severe gastroparesis who fail to respond to medical therapy.

An endoscopic wireless gastrostimulator (with video)

BACKGROUND

Gastric electric stimulation (GES) at a high-frequency, low-energy setting is an option for treating refractory gastroparesis. The currently available commercial stimulator, the Enterra neurostimulator (Medtronic Inc, Minneapolis, MN), however, requires surgical implantation and is powered by a nonrechargeable battery.

OBJECTIVE

To develop and test a miniature wireless GES device for endoscopic implantation in an experimental model.

DESIGN

In-vivo gastric signals were recorded and measured in a nonsurvival swine model (n = 2; 110-lb animals).

INTERVENTION

An endoscopically placed, wireless GES device was inserted into the stomach through an overtube; the two GES electrodes were endoscopically attached to the gastric mucosa and secured with endoclips to permit stimulation.

MAIN OUTCOME MEASUREMENTS

Stable electrogastrogram measures were observed during GES stimulation.

RESULTS

Electrogastrogram recordings demonstrated that gastric slow waves became more regular and of constant amplitudes when stomach tissues were stimulated, in comparison with no stimulation. The frequency-to-amplitude ratio also changed significantly with stimulation.

LIMITATION

Nonsurvival pig studies.

CONCLUSION

Gastric electric stimulation is feasible by our endoscopically implanted, wireless GES device.

Gastroparesis: concepts, controversies, and challenges

Patients with gastroparesis often present a challenge to the treating physician. Postprandial symptoms with nausea and vomiting may not only lead to nutritional and metabolic consequences, but also cause significant disruptions to social activities that often center around food. While the definition of gastroparesis focuses on impaired gastric emptying, treatment options that affect gastric function are limited and often disappointing. The female predominance, the mostly idiopathic nature of the illness with a common history of abuse, and coexisting anxiety or depression show parallels with other functional disorders of the gastrointestinal tract. These parallels provided the rationale for some initial studies investigating alternative therapies that target the brain rather than the stomach. This emerging shift in medical therapy comes at a time when clinical studies suggest that gastric electrical stimulation may exert its effects by modulating visceral sensory processing rather than altering gastric motility. Physiologic and detailed anatomic investigations also support a more complex picture with different disease mechanisms, ranging from impaired accommodation to apparent visceral hypersensitivity or decreased interstitial cells of Cajal to inflammatory infiltration of myenteric ganglia. Delayed gastric emptying remains the endophenotype defining gastroparesis. However, our treatment options go beyond prokinetics and may allow us to improve the quality of life of affected individuals.

Design, implementation and testing of an implantable impedance-based feedback-controlled neural gastric stimulator

Functional neural gastrointestinal electrical stimulation (NGES) is a methodology of gastric electrical stimulation that can be applied as a possible treatment for disorders such as obesity and gastroparesis. NGES is capable of generating strong lumen-occluding local contractions that can produce retrograde or antegrade movement of gastric content. A feedback-controlled implantable NGES system has been designed, implemented and tested both in laboratory conditions and in an acute animal setting. The feedback system, based on gastric tissue impedance change, is aimed at reducing battery energy requirements and managing the phenomenon of gastric tissue accommodation. Acute animal testing was undertaken in four mongrel dogs (2 M, 2 F, weight 25.53 ± 7.3 kg) that underwent subserosal two-channel electrode implantation. Three force transducers sutured serosally along the gastric axis and a wireless signal acquisition system were utilized to record stimulation-generated contractions and tissue impedance variations respectively. Mechanically induced contractions in the stomach were utilized to indirectly generate a tissue impedance change that was detected by the feedback system. Results showed that increasing or decreasing impedance changes were detected by the implantable stimulator and that therapy can be triggered as a result. The implantable feedback system brings NGES one step closer to long term treatment of burdening gastric motility disorders in humans.

Comparative gastric motility study of Enterra ™ Therapy and neural gastric electrical stimulation in an acute canine model

BACKGROUND

Gastric electrical stimulation (GES) is an avenue for treating gastroparesis and obesity by controlling gastric motility using electrically mediated gastric contractions. Neural gastrointestinal electrical stimulation (NGES) is a GES modality capable of producing strong lumen-occluding local gastric contractions. Conversely, Enterra ™ Therapy, a commercial implantable gastric electrical stimulator, has been utilized to treat symptoms of gastroparesis, but its nominal electrical parameters are not capable of generating lumen-occluding contractions. However, comparative studies between these two stimulation modalities are lacking.

METHODS

Strain gauge transducers complemented by endoscopic monitoring have been utilized to register gastric contractions invoked with NGES and Enterra neurostimulators in four acute dogs. Mucosal and serosal electrode implantations, 'nominal' and 'maximum' electrical parameters, and longitudinal and transverse electrode placements have been tested with each neurostimulator type.

KEY RESULTS

Strong lumen-occluding, circumferential contractions were induced with a wide variety of NGES parameters utilizing both transverse and longitudinal electrode configurations from the serosal side of the stomach. Similarly, local gastric contractions were observed with the Enterra neurostimulator programmed at its 'maximum' electrical parameters but only when utilizing transverse serosal electrode implantation. Under 'maximum' electrical parameters Enterra was not capable of producing registerable gastric contractions with longitudinally implanted serosal electrodes. Mucosal electrode implantations did not result in GES-invoked gastric contractions in both stimulation modalities.

CONCLUSIONS & INFERENCES

Enterra Therapy is capable of producing gastric contractions under 'maximum' parameters and transverse electrode configuration. Neural gastrointestinal electrical stimulation produces stronger, lumen-occluding contractions under a wider range of electrode configurations and parameters.

Gastric electrical stimulation for gastroparesis: a goal greatly pursued, but not yet attained

The lack of an effective medical treatment for gastroparesis has pushed the research of new techniques of gastric electrical stimulation (GES) for nearly half a century of experimentation with a large variety of electrical stimuli delivered to the gastric wall of animals and patients with gastroparesis. Three principal methods are currently available: gastric low-frequency/high-energy GES with long pulse stimulation, high-frequency/low-energy GES with short pulse stimulation and neural sequential GES. The first method aims to reset a regular slow wave rhythm, but has variable effects on contractions and requires devices with large and heavy batteries unsuitable for implantation. High-frequency/low-energy GES, although inadequate to restore a normal gastric electro-mechanical activity, improves dyspeptic symptoms, such as nausea and vomiting, giving patients a better quality of life together with a more satisfactory nutritional status and is suitable for implantation. Unfortunately, the numerous clinical studies using this type of GES, with the exception of two, were not controlled and there is a need for definitive verification of the effectiveness of this technique to justify the cost and the risks of this procedure. The last method, which is neural sequential GES, consists of a microprocessor-controlled sequential activation of a series of annular electrodes along the distal two thirds of the stomach and is able to induce propagated contractions causing forceful emptying of the gastric content. The latter method is the most promising, but has been used only in animals and needs to be tested in patients with gastroparesis before it is regarded as a solution for this disease.

Gastrointestinal system

The functions of the gastrointestinal (GI) tract include digestion, absorption, excretion, and protection. In this review, we focus on the electrical activity of the stomach and small intestine, which underlies the motility of these organs, and where the most detailed systems descriptions and computational models have been based to date. Much of this discussion is also applicable to the rest of the GI tract. This review covers four major spatial scales: cell, tissue, organ, and torso, and discusses the methods of investigation and the challenges associated with each. We begin by describing the origin of the electrical activity in the interstitial cells of Cajal, and its spread to smooth muscle cells. The spread of electrical activity through the stomach and small intestine is then described, followed by the resultant electrical and magnetic activity that may be recorded on the body surface. A number of common and highly symptomatic GI conditions involve abnormal electrical and/or motor activity, which are often termed functional disorders. In the last section of this review we address approaches being used to characterize and diagnose abnormalities in the electrical activity and how these might be applied in the clinical setting. The understanding of electrophysiology and motility of the GI system remains a challenging field, and the review discusses how biophysically based mathematical models can help to bridge gaps in our current knowledge, through integration of otherwise separate concepts.

Implantable functional gastrointestinal neurostimulation

Neural Gastrointestinal Electrical Stimulation (NGES) is a new microprocessor-based method for invoking gastric or colonic contractions by generating multi-channel, high energy, high frequency waveforms. It has been shown that when applied to the lower stomach, NGES offers the possibility for enhancing propulsive peristalsis for the treatment of gastric motor dysfunctions, or for producing retrograde peristalsis for the treatment of obesity. When applied to the colon, NGES can be utilized either for propulsive control in severe constipation or for invoked retrograde contractility. This paper briefly discusses the implementation of an implantable neurostimulator and summarizes the performance of the NGES technique in acute tests on experimental animals and humans, and in chronic tests on animals. These experimental tests indicate that NGES is successful in accelerating gastric emptying of both liquids and solids, and in producing strong, externally-controlled, retrograde contractions.

Efficacy of gastric electrical stimulation in improving functional vomiting in patients with normal gastric emptying

The objective of this study is to evaluate the utility of gastric electrical stimulation (GES) in the subgroup of patients with refractory nausea and vomiting in the presence of normal gastric emptying. Eighteen patients (15 females) underwent GES implantation for dyspeptic symptoms in the presence of normal gastric emptying. Upper gastrointestinal (UGI) symptom score, health-related quality of life (HR-QOL), nutritional status and weight, and medication use (prokinetics and antiemetics) were assessed at baseline and at 1 year after GES placement. Twelve patients (two males) were included in the final analysis. All patients had normal gastric emptying scintigraphy at baseline. After 1 year of GES, there was a significant reduction in the UGI symptom score from 18 to 10 (P = 0.001). The physical component score (PCS) of the HR-QOL was also significantly increased from 25 to 42 (P = 0.04). Gastric emptying actually became slower in 29% of those who repeated the test after 1 year. No adverse events related to GES placement were recorded. Results of our study suggest that GES improves dyspeptic symptoms in patients with medically refractory nausea and vomiting independent of its effect on gastric emptying and could be considered as a potential therapy in this clinical setting.

Gastroparesis and functional dyspepsia: excerpts from the AGA/ANMS meeting

BACKGROUND

Despite the relatively high prevalence of gastroparesis and functional dyspepsia, the aetiology and pathophysiology of these disorders remain incompletely understood. Similarly, the diagnostic and treatment options for these two disorders are relatively limited despite recent advances in our understanding of both disorders.

PURPOSE

This manuscript reviews the advances in the understanding of the epidemiology, pathophysiology, diagnosis, and treatment of gastroparesis and functional dyspepsia as discussed at a recent conference sponsored by the American Gastroenterological Association (AGA) and the American Neurogastroenterology and Motility Society (ANMS). Particular focus is placed on discussing unmet needs and areas for future research.

Stopping mechanism for capsule endoscope using electrical stimulus

An ingestible capsule, which has the ability to stop at certain locations in the small intestine, was designed and implemented to monitor intestinal diseases. The proposed capsule can contract the small intestine by using electrical stimuli; this contraction causes the capsule to stop when the maximum static frictional force (MSFF) is larger than the force of natural peristalsis. In vitro experiments were carried out to verify the feasibility of the capsule, and the results showed that the capsule was successfully stopped in the small intestine. Various electrodes and electrical stimulus parameters were determined on the basis of the MSFF. A moderate increment of the MSFF (12.7 +/- 4.6 gf at 5 V, 10 Hz, and 5 ms) and the maximum increment of the MSFF (56.5 +/- 9.77 gf at 20 V, 10 Hz, and 5 ms) were obtained, and it is sufficient force to stop the capsule.

Effects of electrical stimulation on isolated rodent gastric smooth muscle cells evaluated via a joint computational simulation and experimental approach

Gastric electrical stimulation (GES) involves the delivery of electrical impulses to the stomach for therapeutic purposes. New GES protocols are needed that are optimized for improved motility outcomes and energy efficiency. In this study, a biophysically based smooth muscle cell (SMC) model was modified on the basis of experimental data and employed in conjunction with experimental studies to define the effects of a large range of GES protocols on individual SMCs. For the validation studies, rat gastric SMCs were isolated and subjected to patch-clamp analysis during stimulation. Experimental results were in satisfactory agreement with simulation results. The results define the effects of a wide range of GES parameters (pulse width, amplitude, and pulse-train frequency) on isolated SMCs. The minimum pulse width required to invoke a supramechanical threshold response from SMCs (defined at -30 mV) was 65 ms (at 250-pA amplitude). The minimum amplitude required to invoke this threshold was 75 pA (at 1,000-ms pulse width). The amplitude of the invoked response beyond this threshold was proportional to the stimulation amplitude. A high-frequency train of stimuli (40 Hz; 10 ms, 150 pA) could invoke and maintain the SMC plateau phase while requiring 60% less power and accruing approximately 30% less intracellular Ca(2+) concentration during the plateau phase than a comparable single-pulse protocol could in a demonstrated example. Validated computational simulations are an effective strategy for efficiently identifying effective minimum-energy GES protocols, and pulse-train protocols may also help to reduce the power consumption of future GES devices.

Review article: gastric electrical stimulation for gastroparesis--physiological foundations, technical aspects and clinical implications

BACKGROUND

Application of electrical stimulation to the gut, primarily the stomach, has rapidly advanced in the last two decades, from mostly animal studies to the clinical arena. Most studies focused on the use of electrical stimulation for gastroparesis, the only approved indication for such intervention.

AIM

To review the physiological basis of gastric electrical activity and the technical aspects and clinical outcome of gastric electrical stimulation (GES) for gastroparesis.

METHODS

PubMed search from 1966 to 2009, using gastroparesis and GES as search terms. Areas in focus were systematically reviewed.

RESULTS

The literature consists of open-label studies, mostly from single centres, published in the last decade. Improvement in symptoms, quality of life and nutritional status was reported by most studies. Physiologically, stimulation parameters approved in clinical practice do not regulate gastric slow wave activity and have inconsistent effect on gastric emptying. The mechanism of action of GES is not fully known, but data support modulation of gastric biomechanical activity and afferent neural mechanisms.

CONCLUSIONS

Gastric electrical stimulation is a helpful intervention in recalcitrant gastroparesis. Controlled studies and better understanding of mechanisms of action of electrical stimulation are needed to evaluate further the clinical utility of this intervention and to exploit its therapeutic potential better.

Gastric electrical stimulation with long pulses in humans and animals: can data obtained in animals be replicated in humans?

AIMS

  The aim of this study was to investigate and compare effective parameters for gastric electrical stimulation (GES) to modulate gastric muscle functions in different species.

METHODS

  Four species: Pigs, dogs, rats, and mice implanted with two pairs of electrodes on the serosal surface of the stomach were studied, respectively. Experiment 1 was designed to entrain/pace gastric slow waves and included a series of 5-min periods with long-pulse GES of different pulse widths and frequencies. Experiment 2 was designed to induce gastric dysrhythmia with long-pulse GES of different frequencies. Gastric slow waves were recorded during the entire experiment.

RESULTS

  1) The minimum pulse width for GES to completely entrain the slow waves was similar (100-400 msec) in all four species. 2) With fixed amplitude (4 mA) and pulse width (400 msec), the highest frequency at which slow waves could be paced was similar (about 10-60% higher than the intrinsic slow wave frequency) in all species. 3) With fixed pulse width of 400 msec and amplitude of 6 mA, GES with nine to 18 cycles per min (cpm) was able to induce dysrhythmia in dogs. In addition, there was no significant difference among these frequencies of 9-18 cpm. 4) GES with 400 msec, 6 mA, and 9 cpm was able to induce dysrhythmia in all species. These effective GES parameters in results 1-4 were similar to those used in humans in the literature.

CONCLUSIONS

  There is no significant difference in stimulation parameters when GES is applied to alter gastric slow waves in different animal models. Furthermore, the effective parameters for GES to alter slow waves are similar between the humans and various animal models. These findings suggest that stimulation parameters obtained from animal studies are applicable in humans.

A tissue framework for simulating the effects of gastric electrical stimulation and in vivo validation

Gastric pacing is used to modulate normal or abnormal gastric slow-wave activity for therapeutic purposes. New protocols are required that are optimized for motility outcomes and energy efficiency. A computational tissue model was developed, incorporating smooth muscle and interstitial cell of Cajal layers, to enable predictive simulations of slow-wave entrainment efficacy under different pacing frequencies. Concurrent experimental validation was performed via high-resolution entrainment mapping in a porcine model (bipolar pacing protocol: 2 mA amplitude; 400 ms pulsewidth; 17-s period; midcorpus). Entrained gastric slow-wave activity was found to be anisotropic (circular direction: 8.51 mm x s(-1); longitudinal: 4.58 mm x s(-1)), and the simulation velocities were specified accordingly. Simulated and experimental slow-wave activities demonstrated satisfactory agreement, showing similar propagation patterns and frequencies (3.5-3.6 cycles per minute), and comparable zones of entrainment (ZOEs; 64 cm(2)). The area of ZOE achieved was found to depend on the phase interactions between the native and entrained activities. This model allows the predictions of phase interactions between native and entrained activities, and will be useful for determining optimal frequencies for gastric pacing, including multichannel pacing studies. The model provides a framework for the development of more sophisticated predictive gastric pacing simulations in future.

Effects of dual pulse gastric electrical stimulation on gastric tone and compliance in dogs

BACKGROUND

Gastric electrical stimulation (GES) with short pulses improves nausea and vomiting in patients with gastroparesis, whereas GES with long pulses improves gastric motility.

AIMS

To assess the effects of a novel method of GES using dual pulse (both short and long pulses) on gastric tone, compliance and sympathovagal activity in dogs.

MATERIALS AND METHODS

The study was performed in 7 dogs implanted with a gastric cannula and a pair of gastric serosal electrodes for dual pulse GES. The study was composed of a number of sessions on different days with different stimulation parameters, including variations in the number of short pulses and stimulation amplitude.

RESULTS

(1) Dual pulse GES of one short pulse and one long pulse with various amplitudes inhibited gastric tone (p<0.05) but did not alter sympathetic or vagal activity. (2) Dual pulse GES with five short pulses and one long pulse not only inhibited gastric tone, but also reduced sympathetic activity and increased vagal activity (p<0.05). (3) Dual pulse GES with five short pulses and one long pulse significantly increased gastric compliance.

CONCLUSIONS

Dual pulse GES reduces gastric tone and increases gastric compliance. The variation in the number of short pulse affects the sympathetic and vagal activities, whereas, the increase in stimulation strength enhances its effects on gastric tone.

Methods of gastric electrical stimulation and pacing: a review of their benefits and mechanisms of action in gastroparesis and obesity

Development of gastric electrical stimulation techniques for treatment of gastric dysmotility syndromes and obesity has been a long-standing goal of investigators and clinicians. Depending on stimulus parameters and sites of stimulation, such methods have a range of theoretical benefits including entrainment of intrinsic gastric electrical activity, eliciting propagating contractions and reducing symptomatology in patients with gastroparesis and reducing appetite and food intake in individuals with morbid obesity. Additionally, gastric stimulation parameters have extragastrointestinal effects including alteration of systemic hormonal and autonomic neural activity and modulation of afferent nerve pathways projecting to the central nervous system that may represent important mechanisms of action. Numerous case series and smaller numbers of controlled trials suggest clinical benefits in these two conditions, however better controlled trials are mandated to confirm their efficacy. Current research is focusing on novel stimulation methods to better control symptoms in gastroparesis and promote weight reduction in morbid obesity.

Electrophysiologic, morphologic, and serologic features of chronic unexplained nausea and vomiting: lessons learned from 121 consecutive patients

BACKGROUND

Despite substantive morbidity, unexplained nausea and vomiting has not been evaluated in a systematic manner via surgically obtained biopsies and direct electrophysiology of the gut, and this information has not been correlated with serologic information. We investigated consecutive patients with unexplained and refractory chronic nausea and vomiting to define the presence of morphologic, physiologic, and/or serologic abnormalities.

METHODS

In all, 101 of 121 consecutive patients who experienced chronic nausea and vomiting of unknown etiology evaluated in 1 tertiary referral center over a 10-year period were profiled qualitatively by full-thickness small bowel biopsies with hematoxylin and eosin (H&E) and Smith's Silver stains, quantitatively by intraoperative gastric electrophysiology, and semiquantitatively, when it became available, by serum autoimmune Western blot analysis.

RESULTS

Overall, 79 of 101 patients had abnormal full-thickness biopsy (70 neuropathies and 9 myopathies) and frequent serum autoimmune abnormalities (mean score = 13.2, normal < 3.0). In addition, 96 of 101 patients had abnormal frequency and/or uncoupling on gastric electrophysiology. Patients with small-intestinal myopathy showed a diversity of diagnoses; some patients with neuropathy had abdominal pain that correlated with autoimmune scores on Western blot.

CONCLUSION

Patients with refractory and unexplained nausea and vomiting have a high incidence of both small bowel morphologic abnormalities (primarily neuropathies) and gastric electrophysiologic abnormalities, which are associated commonly with serologic autoimmune activation. Similar histomorphologic, physiologic, and serologic measures should be considered in the diagnostic evaluation of any patient with refractory or unexplained nausea and vomiting.

Pilot acute study of feedback-controlled retrograde peristalsis invoked by neural gastric electrical stimulation

Neural gastric electrical stimulation (NGES) is a new method for invoking gastric contractions under microprocessor control. However, optimization of this technique using feedback mechanisms to minimize power consumption and maximize effectiveness has been lacking. The present pilot study proposes a prototype feedback-controlled neural gastric electric stimulator for the treatment of obesity. Both force-based and inter-electrode impedance-based feedback neurostimulators were implemented and tested. Four mongrel dogs (2 M, 2 F, weight 14.9 +/- 2.3 kg) underwent subserosal implantation of two-channel, 1 cm, bipolar electrode leads and two force transducers in the distal antrum. Two of the dogs were stimulated with a force feedback system utilizing the force transducers, and the other two animals were stimulated utilizing an inter-electrode impedance-based feedback system utilizing the proximal electrode leads. Both feedback systems were able to recognize erythromycin-driven contractions of the stomach and were capable of overriding them with NGES-invoked retrograde contractions which exceeded the magnitudes of the erythromycin-driven contractions by an average of 100.6 +/- 33.5% in all animals. The NGES-invoked contractions blocked the erythromycin-driven contractions past the proximal electrode pair and induced temporary gastroparesis in the vicinity of the distal force transducer despite the continuing erythromycin infusion. The amplitudes of the erythromycin-invoked contractions in the vicinity of the proximal force transducer decreased abruptly by an average of 47.9 +/- 6.3% in all four dogs after triggering-invoked retrograde contractions, regardless of the specific feedback-controlled mechanism. The proposed technique could be helpful for retaining food longer in the stomach, thus inducing early satiety and diminishing food intake.

Manipulation of food intake and weight dynamics using retrograde neural gastric electrical stimulation in a chronic canine model

Neural gastric electrical stimulation (NGES) could be a new technique for treating obesity. However, chronic animal experimentation exploring the efficacy of this therapy is lacking. In this study we investigated the utility of retrograde NGES in a chronic canine model. Nine mongrel dogs (26.8 +/- 5.2 kg) underwent laparoscopic implantation of 2-channel neurostimulator leads in the distal antrum. Five dogs formed a control group and four dogs underwent stimulation. Food intake and weight dynamics were regularly monitored during two separate research protocols, each comprising 2-week baseline, stimulation and washout periods. The stimulation voltage was constant in the first protocol and was ramped in the second. In the first protocol three out of the four stimulated dogs demonstrated significant decrease in food intake (P < 0.05). However, this materialized in a significant weight reduction in one dog only. In the second protocol, all stimulated dogs exhibited significant food intake and weight reduction (P < 0.05) compared to controls. Necropsies and histopathological analysis did not reveal any abnormalities in the stomach, the adjacent organs or around the implant. NGES could be a safe new technique for reducing food intake and weight and, therefore, it might be helpful for treating obesity.

Effects of gastric electrical stimulation with short pulses and long pulses on gastric dysrhythmia and signs induced by vasopressin in dogs

AIMS

This study was to investigate the effect of gastric electrical stimulation (GES) with short pulses, long pulses, short-pulse trains or long-pulse trains on gastric dysrhythmia and motion-sickness signs induced by vasopressin.

METHODS

Seven male beagle dogs implanted with four pairs of electrodes on gastric serosa were studied. The study was performed in six sessions in a randomized order. In session 1 or 2, either saline or vasopressin was infused without GES. In session 3, 4, 5 and 6, GES with short pulses, long pulses, trains of short pulses or trains of long pulses was performed before and during vasopressin infusion. Gastric slow waves and motion-sickness signs were recorded in each session.

RESULTS

(1) Vasopressin induced gastric dysrhythmia and motion sickness-like signs (ANOVA, P < 0.001). (2) GES with short pulses or trains of short pulses was capable of preventing vasopressin-induced emetic response (P < 0.001), but did not normalize gastric dysrhythmia. (3) GES with long pulses or trains of long pulses was able to normalize gastric dysrhythmia induced by vasopressin (P < 0.001), but showed no effects on vasopressin-induced motion-sickness signs.

CONCLUSION

GES with short pulses or trains of short pulses prevents vasopressin-induced emetic response with no improvement in gastric dysrhythmia. GES with long pulses or trains of long pulses normalizes gastric dysrhythmia induced by vasopressin with no effects on signs.

Feedback control of retrograde peristalsis using Neural Gastric Electrical Stimulation

Neural Gastric Electrical Stimulation (NGES) is a new method for invoking gastric contractions under microprocessor control. However, optimization of this technique using feedback mechanisms to minimize power consumption and maximize effectiveness has been lacking. The present work proposes a prototype feedback-controlled neural gastric electrical stimulator for the treatment of obesity. Both a force-based and an interelectrode impedance-based feedback neurostimulator were implemented and tested. Four mongrel dogs (2 M, 2 F, weight 14.9 ++/- 2.3kg) underwent subserosal implantation of 2-channel 1-cm bipolar electrode leads in the distal antrum. Two of the dogs were stimulated with a force-based feedback system and the other two animals were stimulated utilizing an interelectrode impedance-based feedback system. Both feedback systems were able to recognize Erythromycin-driven contractions of the stomach and were capable of overriding them with NGES-invoked retrograde contractions. The proposed technique could be helpful for retaining food longer in the stomach, thus inducing early satiety and diminishing food intake.

Gastric electric stimulation for the treatment of gastroparesis

Gastric electric stimulation is an emerging therapy for refractory gastroparesis. Several methods have been used to electrically stimulate the stomach. Initial studies used gastric electrical pacing, which entrains and paces the gastric slow waves at a slightly higher rate than the patient's normal myoelectric frequency of 3 cycles per minute (cpm). The technique currently practiced uses high-frequency, low-energy stimulation at four times the basal rate (12 cpm). Results from published studies with high-frequency stimulation reveal an improvement in symptoms, primarily of nausea and vomiting, and primarily in patients with diabetic gastroparesis, with only a modest change in gastric emptying. As treatment with gastric electric stimulation evolves, further delineation of its overall effectiveness, the type of patient that will likely respond, optimal electrode placement(s), and stimulus parameters should be explored.

Clinical application prospects of gastric pacing for treating postoperative gastric motility disorders

Similar to the heartbeat, gastric peristalsis is regulated by an electrical rhythm generated by a pacemaker. Thus, electrical dysrhythmia of gastric slow waves will inevitably affect gastric peristalsis and emptying. The recurrence of postoperative gastroparesis is thereby closely related to the abnormalities of electrical dysrhythmia and ectopic pacemakers, resulting in postoperatively persistent gastric motility disorders in some severe cases, despite the use of prokinetic and antiemetic drugs. Recent studies have demonstrated that gastric pacing, analogous to pacing the human heart, is an attractive and promising therapy that is both feasible and safe. Gastric pacing has been shown to be strikingly effective in normalizing gastric dysrhythmia, increasing the activity of the gastric slow wave and thereby prompting gastric dynamia and emptying. Furthermore, the long-term utilization of gastric pacing can (i) relieve patients from clinical symptoms, such as nausea and vomiting; (ii) release patients with severe postoperative gastroparesis from relying on prokinetic drugs and the jejunal feeding tube; (iii) return patients to normal oral nutritional intake and provide a more satisfactory nutritional status and most importantly; and (iv) give patients a better quality of life. Overall, research focused on gastric pacing has demonstrated excellent prospects for clinical application in the treatment of postoperative gastroparesis disorders, especially for those unresponsive to prokinetic drugs.

Gastrointestinal electrical stimulation for treatment of gastrointestinal disorders: gastroparesis, obesity, fecal incontinence, and constipation

Electrical stimulation of the gastrointestinal (GI) tract is an attractive concept. Since these organs have their own natural pacemakers, the electrical signals they generate can be altered by externally delivering electric currents by intramuscular, serosal, or intraluminal electrodes to specific sites in the GI tract. This article reviews the advances in electrical stimulation of the GI tract by describing various methods of GI electrical stimulation and their peripheral and central effects and mechanisms; updating the status of GI electrical stimulation in the clinical settings of gastroparesis, obesity, fecal incontinence, and constipation; and predicting future directions and developments of GI electrical stimulation technology and their areas of possible clinical applications.

Severe gastroparesis: new treatment alternatives

Dopamine antagonists, such as metoclopramide and domperidone, and the motilin receptor agonist erythromycin have been the cornerstones in drug treatment of severe gastroparesis for more than a decade. No new drugs have been approved for treatment of this disorder in this period. Instead, the 5-HT4 agonist cisapride has been withdrawn due to side-effects. The effectiveness of intrapyloric botulinum toxin for gastroparesis remains to be shown. In the last decade, gastric electrical stimulation (GES) with a fully implantable device has evolved as a promising treatment, with significant effects on nausea and vomiting in most patients with severe, drug-refractory diabetic gastroparesis and postsurgical gastroparesis. A proportion of patients with severe idiopathic gastroparesis and patients with idiopathic nausea and vomiting also respond. More research is needed to achieve precise selection of responders/non-responders to GES, and to study the potential benefit of GES in other patient groups suffering from severe nausea or vomiting.