High-Energy Pacing Inhibits Slow Wave Dysrhythmias in the Small Intestine

The motility of the gastrointestinal tract is coordinated in part by rhythmic slow waves, and disrupted slow wave patterns are linked to functional motility disorders. At present, there are no treatment strategies that primarily target slow wave activity. This study assessed the use of pacing to suppress glucagon-induced slow wave dysrhythmias in the small intestine. Slow waves in the jejunum were mapped in vivo using a high-resolution surface-contact electrode array in pigs (n=7). Glucagon was intravenously administered to induce hyperglycemia. Slow wave propagation patterns were categorized into antegrade, retrograde, collision, pacemaker and uncoupled activity. Slow wave characteristics such as period, amplitude and speed were also quantified. Post-glucagon infusion, pacing was applied at 4 mA and 8 mA and the resulting slow waves were quantified spatiotemporally. Antegrade propagation was dominant throughout all stages with a prevalence of 55 ± 38% at baseline. However, glucagon infusion resulted in a substantial and significant increase in uncoupled slow waves from 10 ± 8% to 30 ± 12% (p=0.004) without significantly altering the prevalence of other slow wave patterns. Slow wave frequency, amplitude and speed remained unchanged. Pacing, particularly at 8 mA, significantly suppressed dysrhythmic slow wave patterns and achieved more effective spatial entrainment (85%) compared to 4 mA (46%, p=0.039).This study defined the effect of glucagon on jejunal slow waves and identified uncoupling as a key dysrhythmia signature. Pacing effectively entrained rhythmic activity and suppressed dysrhythmias, highlighting the potential of pacing for gastrointestinal disorders associated with slow wave abnormalities.

Optimization of pacing parameters to entrain slow wave activity in the pig jejunum

Pacing has been proposed as a therapy to restore function in motility disorders associated with electrical dysrhythmias. The spatial response of bioelectrical activity in the small intestine to pacing is poorly understood due to a lack of high-resolution investigations. This study systematically varied pacing parameters to determine the optimal settings for the spatial entrainment of slow wave activity in the jejunum. An electrode array was developed to allow simultaneous pacing and high-resolution mapping of the small intestine. Pacing parameters including pulse-width (50, 100 ms), pulse-amplitude (2, 4, 8 mA) and pacing electrode orientation (antegrade, retrograde, circumferential) were systematically varied and applied to the jejunum (n = 15 pigs). Pulse-amplitudes of 4 mA (p = 0.012) and 8 mA (p = 0.002) were more effective than 2 mA in achieving spatial entrainment while pulse-widths of 50 ms and 100 ms had comparable effects (p = 0.125). A pulse-width of 100 ms and a pulse-amplitude of 4 mA were determined to be most effective for slow wave entrainment when paced in the antegrade or circumferential direction with a success rate of greater than 75%. These settings can be applied in chronic studies to evaluate the long-term efficacy of pacing, a critical aspect in determining its therapeutic potential.

Electromechanical Response of Mesenteric Ischemia Defined Through Simultaneous High-Resolution Bioelectrical and Video Mapping

Intestinal motility is governed in part by bioelectrical slow-waves and spike-bursts. Mesenteric ischemia is a substantial clinical challenge, but its electrophysiological and contractile mechanisms are not well understood. Simultaneous high-resolution bioelectrical and video mapping techniques were used to capture the changes in slow-waves, spike-bursts, and contractile activity during baseline, ischemia, and reperfusion periods. Experiments were performed on anesthetized pigs where intestinal contractions were quantified using surface strain and diameter measurements, while slow-wave and spike-bursts were quantified using frequency and amplitude. Slow-waves entrainment within the ischemic region diminished during ischemia, resulting in irregular slow-wave activity and a reduction in the frequency from 12.4 ± 3.0 cycles-per-minute (cpm) to 2.5 ± 2.7 cpm (p = 0.0006). At the end of the reperfusion period, normal slow-wave entrainment was observed at a frequency of 11.5 ± 2.9 cpm. There was an increase in spike-burst activity between the baseline and ischemia periods (1.1 ± 1.4 cpm to 8.7 ± 3.3 cpm, p = 0.0003) along with a spasm of circumferential contractions. At the end of the reperfusion period, the frequency of spike-bursts decreased to 2.7 ± 1.4 cpm, and contractions subsided. The intestine underwent tonal contraction during ischemia, with the diameter decreasing from 29.3 ± 2.6 mm to 21.2 ± 6.2 mm (p = 0.0020). At the end of the reperfusion period, the intestinal diameter increased to 27.3 ± 3.9 mm. The decrease in slow-wave activity, increase in spike-bursts, and tonal contractions can objectively identify ischemic segments in the intestine. It is anticipated that the use of electrophysiological slow-wave and spike-burst biomarkers, along with contractile measures, could identify mesenteric ischemia in surgical settings and allow an objective biomarker for successful revascularization.

High-Energy Pacing in the Jejunum Elicits Pulsatile Segmental Contractions

OBJECTIVE

Compromised bowel function is associated with a range of motility disorders such as post-operative ileus and chronic intestinal pseudo-obstruction. Disordered or weak motility compromise the efficient movement of luminal contents necessary for digestion and nutrient absorption. This study investigated the potential of high-energy pacing to enhance contractions in the proximal jejunum of the small intestine.

METHODS

Pacing pulse parameters (pulse-width: 100 ms, 200 ms, 400 ms, pulse-amplitude: 4 mA, 6 mA, 8 mA) were systematically varied in the in vivo porcine jejunum (n = 7) and the induced contractile responses were evaluated using a video mapping system. Localized segmental contractions were quantified by measuring the intestinal diameter and thereby computing the strain. The impact of pacing parameters on contractile strain was investigated. Finally, histological studies were conducted on paced tissue to assess for potential tissue damage.

RESULTS

Segmental contractions were successfully induced at all pulse-settings and evaluated across 67 pacing sessions. In response to pacing, the intestine segment at the site of pacing contracted, with diameter reduced by 6-18%. Contractile response significantly increased with increasing pulse-amplitude. However, with increasing pulse-width, the increase in contractile response was significant only between 100 ms and 400 ms. Histology showed no tissue damage occurred when maximal pacing energy (pulse-amplitude = 4-8 mA, pulse-width = 400 ms, 5 minute duration) was applied.

CONCLUSION

High-energy pacing induced periodic segmental contractions in response to pacing pulses and the contractile strain was proportional to the energy applied on the intestine. The ability to enhance motility through pacing may hold promising therapeutic potential for bowel disorders and awaits clinical translation.

SIGNIFICANCE

Small intestine pacing elicits localized segmental contractions which increase in magnitude with increasing pulse settings. This study marks the first adaptation of video mapping techniques to track the pacing response in the small intestine.

Three-Dimensional Fractal Analysis of the Interstitial Cells of Cajal Networks of Gastrointestinal Tissue Specimens

Introduction

Several functional gastrointestinal disorders (FGIDs) have been associated with the degradation or remodeling of the network of interstitial cells of Cajal (ICC). Introducing fractal analysis to the field of gastroenterology as a promising data analytics approach to extract key structural characteristics that may provide insightful features for machine learning applications in disease diagnostics. Fractal geometry has advantages over several physically based parameters (or classical metrics) for analysis of intricate and complex microstructures that could be applied to ICC networks.

Methods

In this study, three fractal structural parameters: Fractal Dimension, Lacunarity, and Succolarity were employed to characterize scale-invariant complexity, heterogeneity, and anisotropy; respectively of three types of gastric ICC network structures from a flat-mount transgenic mouse stomach.

Results

The Fractal Dimension of ICC in the longitudinal muscle layer was found to be significantly lower than ICC in the myenteric plexus and circumferential muscle in the proximal, and distal antrum, respectively (both p < 0.0001). Conversely, the Lacunarity parameters for ICC-LM and ICC-CM were found to be significantly higher than ICC-MP in the proximal and in the distal antrum, respectively (both p < 0.0001). The Succolarity measures of ICC-LM network in the aboral direction were found to be consistently higher in the proximal than in the distal antrum (p < 0.05).

Conclusions

The fractal parameters presented here could go beyond the limitation of classical metrics to provide better understanding of the structural-functional relationship between ICC networks and the conduction of gastric bioelectrical slow waves.

Biotrapping Ureolytic Bacteria on Sand to Improve the Efficiency of Biocementation

Microbially induced calcium carbonate precipitation (MICP) has emerged as a novel technology with the potential to produce building materials through lower-temperature processes. The formation of calcium carbonate bridges in MICP allows the biocementation of aggregate particles to produce biobricks. Current approaches require several pulses of microbes and mineralization media to increase the quantity of calcium carbonate minerals and improve the strength of the material, thus leading to a reduction in sustainability. One potential technique to improve the efficiency of strength development involves trapping the bacteria on the aggregate surfaces using silane coupling agents such as positively charged 3-aminopropyl-methyl-diethoxysilane (APMDES). This treatment traps bacteria on sand through electrostatic interactions that attract negatively charged walls of bacteria to positively charged amine groups. The APMDES treatment promoted an abundant and immediate association of bacteria with sand, increasing the spatial density of ureolytic microbes on sand and promoting efficient initial calcium carbonate precipitation. Though microbial viability was compromised by treatment, urea hydrolysis was minimally affected. Strength was gained much more rapidly for the APMDES-treated sand than for the untreated sand. Three injections of bacteria and biomineralization media using APMDES-treated sand led to the same strength gain as seven injections using untreated sand. The higher strength with APMDES treatment was not explained by increased calcium carbonate accrual in the structure and may be influenced by additional factors such as differences in the microstructure of calcium carbonate bridges between sand particles. Overall, incorporating pretreatment methods, such as amine silane coupling agents, opens a new avenue in biomineralization research by producing materials with an improved efficiency and sustainability.

Neural regulation of slow waves and phasic contractions in the distal stomach: a mathematical model

Objective.Neural regulation of gastric motility occurs partly through the regulation of gastric bioelectrical slow waves (SWs) and phasic contractions. The interaction of the tissues and organs involved in this regulatory process is complex. We sought to infer the relative importance of cellular mechanisms in inhibitory neural regulation of the stomach by enteric neurons and the interaction of inhibitory and excitatory electrical field stimulation.Approach.A novel mathematical model of gastric motility regulation by enteric neurons was developed and scenarios were simulated to determine the mechanisms through which enteric neural influence is exerted. This model was coupled to revised and extended electrophysiological models of gastric SWs and smooth muscle cells (SMCs).Main results.The mathematical model predicted that regulation of contractile apparatus sensitivity to intracellular calcium in the SMC was the major inhibition mechanism of active tension development, and that the effect on SW amplitude depended on the inhibition of non-specific cation currents more than the inhibition of calcium-activated chloride current (kiNSCC= 0.77 vs kiAno1= 0.33). The model predicted that the interaction between inhibitory and excitatory neural regulation, when applied with simultaneous and equal intensity, resulted in an inhibition of contraction amplitude almost equivalent to that of inhibitory stimulation (79% vs 77% decrease), while the effect on frequency was overall excitatory, though less than excitatory stimulation alone (66% vs 47% increase).Significance.The mathematical model predicts the effects of inhibitory and excitatory enteric neural stimulation on gastric motility function, as well as the effects when inhibitory and excitatory enteric neural stimulation interact. Incorporation of the model into organ-level simulations will provide insights regarding pathological mechanisms that underpin gastric functional disorders, and allow forin silicotesting of the effects of clinical neuromodulation protocols for the treatment of these disorders.

Electroanatomical mapping of the stomach with simultaneous biomagnetic measurements

Gastric motility is coordinated by bioelectric slow waves (SWs) and dysrhythmic SW activity has been linked with motility disorders. Magnetogastrography (MGG) is the non-invasive measurement of the biomagnetic fields generated by SWs. Dysrhythmia identification using MGG is currently challenging because source models are not well developed and the impact of anatomical variation is not well understood. A novel method for the quantitative spatial co-registration of serosal SW potentials, MGG, and geometric models of anatomical structures was developed and performed on two anesthetized pigs to verify feasibility. Electrode arrays were localized using electromagnetic transmitting coils. Coil localization error for the volume where the stomach is normally located under the sensor array was assessed in a benchtop experiment, and mean error was 4.2±2.3mm and 3.6±3.3° for a coil orientation parallel to the sensor array and 6.2±5.7mm and 4.5±7.0° for a perpendicular coil orientation. Stomach geometries were reconstructed by fitting a generic stomach to up to 19 localization coils, and SW activation maps were mapped onto the reconstructed geometries using the registered positions of 128 electrodes. Normal proximal-to-distal and ectopic SW propagation patterns were recorded from the serosa and compared against the simultaneous MGG measurements. Correlations between the center-of-gravity of normalized MGG and the mean position of SW activity on the serosa were 0.36 and 0.85 for the ectopic and normal propagation patterns along the proximal-distal stomach axis, respectively. This study presents the first feasible method for the spatial co-registration of MGG, serosal SW measurements, and subject-specific anatomy. This is a significant advancement because these data enable the development and validation of novel non-invasive gastric source characterization methods.

Reconstruction of the human lower esophageal sphincter based on ultra-mill imaging for biomechanical analysis

Introduction: The lower esophageal sphincter (LES) controls the passage into the stomach and prevents reflex of contents into the esophagus. Dysfunctions of this region typically involves impairment of muscular function, leading to diseases including gastro-esophageal reflux disease and achalasia. The main objective of this study was to develop a finite element model from a unique human LES dataset reconstructed from an ultra-mill imaging setup, and then to investigate the effect of anatomical characteristics on intraluminal pressures. Methods: A pipeline was developed to generate a mesh from a set of input images, which were extracted from a unique ultra-mill sectioned human LES. A total of 216 nodal points with cubic Hermite basis function was allocated to reconstruct the LES, including the longitudinal and circumferential muscles. The resultant LES mesh was used in biomechanical simulations, utilizing a previously developed LES mathematical model based on the Visible Human data to calculate intraluminal pressures. Anatomical and functional comparisons were made between the Ultra-mill and Visible human models. Results: Overall, the Ultra-mill model contained lower cavity (1,796 vs. 5,400 mm3) and muscle (1,548 vs. 15,700 mm3) volumes than the Visible Human model. The Ultra-mill model also developed a higher basal pressure (13.8 vs. 14.7 mmHg) and magnitude of pressure (19.8 vs. 18.9 mmHg) during contraction. Out of all the geometric transformations (i.e., uniform enlargement of volume, lengthening along the center-axis, dilation of the diameter, and increasing muscle thickness), the muscle volume was found to be the main contributor of basal and magnitude of pressures. Increases in length also caused proportional increases to pressures, while dilation of diameter had a less influential reverse effect. Discussion: The findings provide information on interindividual variability in LES pressure and demonstrates that anatomy has a large influence on pressures. This model forms the basis of more complex simulations involving food bolus transport and predicting LES dysfunctions.

MRI Derived Simulations of Flow Patterns in the Stomach

A framework to simulate the flow in the stomach using subject-specific motility patterns and geometries was developed. Dynamic 2D magnetic resonance images (MRIs) were obtained. Motility parameters such as contraction speed and occlusion were quantified, and 3D stomach geometries were reconstructed using a semi-automated approach. Computational fluid dynamics (CFD) simulations were performed, and flow patterns were investigated. The stomach of both subjects had distinct anatomical features with computed volumes of 789 mL and 619 mL. For the one subject, the occlusion (i.e., normalized contraction size) was 12% while it was around 25% for the other subject. Contraction speeds were also different (1.9-2.8 mm/s vs 3.0-5.1 mm/s) for each subject. CFD simulations resulted in unsteady laminar flow for both subjects with average velocities of 2.1 and 3.2 mm/s. While antegrade flow was mainly observed in the simulations, a retropulsive jet was also present in both stomachs. The versatile framework developed within this study would allow the generation of CFD models of gastric motility from dynamic MRIs.Clinical Relevance- Subject-specific models of flow patterns informed by gastric motility features can elucidate the impact of contractions and anatomical variations on digestion. Such models can inform therapies to treat gastric dysfunctions and improve their efficacy.

Atrous spatial pyramid pooling and multi-image data fusion for smooth muscle segmentation in upper gastrointestinal sphincters

Gastrointestinal (GI) sphincters provide critical roles in regulating the transport of contents along the GI tract. Dysfunctions of GI sphincters are associated with a range of major digestive disorders. Despite their importance, the microstructures of GI sphincters are not well investigated. While micro-computed tomography (μ-CT) provides detailed 3D images, conventional segmentation methods rely on manual correction, which is both time-consuming and prone to human error. This study proposes a segmentation method using atrous spatial pyramid pooling (ASPP), which helps in capturing different effective fields of view from a given input feature map, thereof providing finer local and global information for a given pixel. Additionally, we explored the use of multi-species data fusion to make the model more generalized. The proposed segmentation network incorporating ASPP and multi-species data fusion improved the segmentation of sphincter muscle images. Specifically, it increased the dice score and Jaccard index by 3.7% and 5.8%, respectively, while reducing the variance compared to conventional methods.Clinical relevance- Techniques developed in this study will inform μ-CT segmentation of human upper GI sphincters for detailed structural analysis of muscular dysfunction.

Evaluation of Pacing Parameters to Induce Contractions in the Small Intestine

Postoperative ileus and chronic intestinal pseudo-obstruction are intestinal motility disorders that can compromise bowel function resulting in a significant reduction in quality of life and prolonged hospital stays. While medication and nutritional support provides relief for some patients, a significant patient population remains untreated. Therefore, alternative treatment options are required. A novel framework that enables small intestine pacing and video mapping of the contractile response was developed. Pacing pulse parameters (pulse-period: 2.7, 10 s, pulse-width: 100, 400 ms, and pulse-amplitude: 4, 6, 8 mA) were systematically varied to investigate the effect of pacing on the small intestine contractility. The contractile response was quantified by computing the strain of the intestinal diameter at the pacing site. The framework was applied in vivo on porcine jejunal loops (n=4) where segmental contractions were induced in response to pacing pulses. Strain increased with increasing pulse-amplitude and pulse-width, while pacing at a period of 2.7 s elicited higher contractile strains compared to pacing at a period of 10 s at all settings (e.g., -0.18 ± 0.06 vs 0.12 ± 0.06 at 8 mA, 400 ms). For a pulse-width of 100 ms, the contractile strain continued to increase with increasing pulse-amplitude, while the induced strain was comparable for all pulse-amplitudes when paced with high pulse-width (400 ms). Therefore, pacing is an effective tool in modulating the intensity of segmental contractions.Clinical Relevance- Different pacing parameters can define contraction intensity and frequency in the small intestine. This is of therapeutic potential for treating motility disorders such as post-operative ileus and chronic intestinal pseudo-obstruction.

Cervical Vagus Nerve Stimulation Disrupts Gastric Slow Wave Activity in Rats

Cervical vagus nerve stimulation (cVNS) is a promising neuromodulation therapy for treating symptoms of disease in peripheral organs. The rat is a common animal model for studying and trialing new applications of cVNS therapy, but the stomach and its activity in rats is less well characterized than other animals, such as pigs. We sought to investigate the effects of acute, in vivo cVNS on gastric bioelectrical activity as an intermediate step to computational modeling of the effects of cVNS on gastric smooth muscle electromechanical coupling. Here we show a method of detecting bioelectrical gastric slow wave events using a non-linear energy operator. The marked events are compared to the underlying bioelectrical slow wave activity.The mean propagation velocity before stimulation was 0.79 ± 0.31 mm s-1, and the mean interval was 17.4 ± 1.4 s. During cVNS, there was a significant increase in velocity (1.02 ± 0.69 mm s-1; p < 0.001), and decrease in interval (15.4 ± 2.9 s; p = 0.0196). At stimulation onset, premature slow waves were induced at an ectopic pacemaker location and waves originating at the ectopic and initial pacemaker sites continued to collide following the cessation of cVNS.This work forms the basis for more thorough investigation of the effects of cVNS on gastric bioelectrical slow wave activity and consequential smooth muscle contractions in rats. A better understanding of the effects of cVNS on gastric function will allow the refinement of cVNS therapy to target the stomach, and avoid off-target effects on the stomach.Clinical relevance- This work presents a signal processing and analysis approach for the investigation of cervical vagus nerve stimulation on gastric bioelectrical activity in rats. Vagus nerve stimulation may enable the control and amelioration of hunger, gastric emptying, or functional gastric disorders.

Diffeomorphic Surface Modeling for MRI-Based Characterization of Gastric Anatomy and Motility

OBJECTIVE

Gastrointestinal magnetic resonance imaging (MRI) provides rich spatiotemporal data about the movement of the food inside the stomach, but does not directly report muscular activity on the stomach wall. Here we describe a novel approach to characterize the motility of the stomach wall that drives the volumetric changes of the ingesta.

METHODS

A neural ordinary differential equation was optimized to model a diffeomorphic flow that ascribed the deformation of the stomach wall to a continuous biomechanical process. Driven by this diffeomorphic flow, the surface of the stomach progressively changes its shape over time, while preserving its topology and manifoldness.

RESULTS

We tested this approach with MRI data collected from 10 rats under a lightly anesthetized condition, and demonstrated accurate characterization of gastric motor events with an error in the order of sub-millimeters. Uniquely, we characterized gastric anatomy and motility with a surface coordinate system common at both individual and group levels. Functional maps were generated to reveal the spatial, temporal, and spectral characteristics of muscle activity and its coordination across different regions. The peristalsis at the distal antrum had a dominant frequency and peak-to-peak amplitude of [Formula: see text] cycles per minute and [Formula: see text] mm, respectively. The relationship between muscle thickness and gastric motility was found to be distinct between two functional regions in the proximal and distal stomach.

CONCLUSION

These results demonstrate the efficacy of using MRI to model gastric anatomy and function.

SIGNIFICANCE

The proposed approach is expected to enable non-invasive and accurate mapping of gastric motility for preclinical and clinical studies.

Computational models of autonomic regulation in gastric motility: Progress, challenges, and future directions

The stomach is extensively innervated by the vagus nerve and the enteric nervous system. The mechanisms through which this innervation affects gastric motility are being unraveled, motivating the first concerted steps towards the incorporation autonomic regulation into computational models of gastric motility. Computational modeling has been valuable in advancing clinical treatment of other organs, such as the heart. However, to date, computational models of gastric motility have made simplifying assumptions about the link between gastric electrophysiology and motility. Advances in experimental neuroscience mean that these assumptions can be reviewed, and detailed models of autonomic regulation can be incorporated into computational models. This review covers these advances, as well as a vision for the utility of computational models of gastric motility. Diseases of the nervous system, such as Parkinson’s disease, can originate from the brain-gut axis and result in pathological gastric motility. Computational models are a valuable tool for understanding the mechanisms of disease and how treatment may affect gastric motility. This review also covers recent advances in experimental neuroscience that are fundamental to the development of physiology-driven computational models. A vision for the future of computational modeling of gastric motility is proposed and modeling approaches employed for existing mathematical models of autonomic regulation of other gastrointestinal organs and other organ systems are discussed.

Stomach Geometry Reconstruction Using Serosal Transmitting Coils and Magnetic Source Localization

OBJECTIVE

Bioelectric slow waves (SWs) are a key regulator of gastrointestinal motility, and disordered SW activity has been linked to motility disorders. There is currently a lack of practical options for the acquisition of the 3D stomach geometry during research studies when medical imaging is challenging. Accurately recording the geometry of the stomach and co-registering electrode and sensor positions would provide context for in-vivo studies and aid the development of non-invasive methods of gastric SW assessment.

METHODS

A stomach geometry reconstruction method based on the localization of transmitting coils placed on the gastric serosa was developed. The positions and orientations of the coils, which represented boundary points and surface-normal vectors, were estimated using a magnetic source localization algorithm. Coil localization results were then used to generate surface models. The reconstruction method was evaluated against four 3D-printed anatomically realistic human stomach models and applied in a proof of concept in-vivo pig study.

RESULTS

Over ten repeated reconstructions, average Hausdorff distance and average surface-normal vector error values were 4.7 ±0.2 mm and 18.7 ±0.7° for the whole stomach, and 3.6 ±0.2 mm and 14.6 ±0.6° for the corpus. Furthermore, mean intra-array localization error was 1.4 ±1.1 mm for the benchtop experiment and 1.7 ±1.6 mm in-vivo.

CONCLUSION AND SIGNIFICANCE

Results demonstrated that the proposed reconstruction method is accurate and feasible. The stomach models generated by this method, when co-registered with electrode and sensor positions, could enable the investigation and validation of novel inverse analysis techniques.

A novel framework for the removal of pacing artifacts from bio-electrical recordings

BACKGROUND

Electroceuticals provide clinical solutions for a range of disorders including Parkinson's disease, cardiac arrythmias and are emerging as a potential treatment option for gastrointestinal disorders. However, pre-clinical investigations are challenged by the large stimulation artifacts registered in bio-electrical recordings.

METHOD

A generalized framework capable of isolating and suppressing stimulation artifacts with minimal intervention was developed. Stimulation artifacts with different pulse-parameters in synthetic and experimental cardiac and gastrointestinal signals were detected using a Hampel filter and reconstructed using 3 methods: i) autoregression, ii) weighted mean, and iii) linear interpolation.

RESULTS

Synthetic stimulation artifacts with amplitudes of 2 mV and 4 mV and pulse-widths of 50 ms, 100 ms, and 200 ms were successfully isolated and the artifact window size remained uninfluenced by the pulse-amplitude, but was influenced by pulse-width (e.g., the autoregression method resulted in an identical Root Mean Square Error (RMSE) of 1.64 mV for artifacts with 200 ms pulse-width and both 2 mV and 4 mV amplitudes). The performance of autoregression (RMSE = 1.45 ± 0.16 mV) and linear interpolation (RMSE = 1.22 ± 0.14 mV) methods were comparable and better than weighted mean (RMSE = 5.54 ± 0.56 mV) for synthetic data. However, for experimental recordings, artifact removal by autoregression was superior to both linear interpolation and weighted mean approaches in gastric, small intestinal and cardiac recordings.

CONCLUSIONS

A novel signal processing framework enabled efficient analysis of bio-electrical recordings with stimulation artifacts. This will allow the bio-electrical events induced by stimulation protocols to be efficiently and systematically evaluated, resulting in improved stimulation therapies.

Spatial response of jejunal pacing defined by a novel high-resolution multi-electrode array

BACKGROUND AND PURPOSE

Gastric pacing has shown preclinical success in modulating bioelectrical slow wave activity and has potential as a novel therapy for functional motility disorders. However, the translation of pacing techniques to the small intestine remains preliminary. This paper presents the first high-resolution framework for simultaneous pacing and response mapping of the small intestine.

METHODS

A novel surface-contact electrode array, capable of simultaneous pacing and high-resolution mapping of the pacing response was developed and applied in vivo on the proximal jejunum of pigs. Pacing parameters including the input energy and pacing electrode orientation were systematically evaluated and the efficacy of pacing was determined by analyzing spatiotemporal characteristics of entrained slow waves. Histological analysis was conducted to determine if the pacing resulted in tissue damage.

RESULTS

A total of 54 studies were conducted on 11 pigs and pacemaker propagation patterns were successfully achieved at both low (2 mA, 50 ms) and high (4 mA, 100 ms) energy levels with the pacing electrodes oriented in the antegrade, retrograde and circumferential directions. The high energy level performed significantly better (p=0.014) in achieving spatial entrainment. Comparable success (greater than 70%) was achieved when pacing in the circumferential and antegrade pacing directions, and no tissue damage was observed at the pacing sites.

CONCLUSION

This study defined the spatial response of small intestine pacing in vivo revealing effective pacing parameters for slow wave entrainment in the jejunum. Intestinal pacing now awaits translation to restore disordered slow wave activity associated with motility disorders.

Systematic review of small intestine pacing parameters for modulation of gut function

BACKGROUND AND PURPOSE

The efficacy of conventional treatments for severe and chronic functional motility disorders remains limited. High-energy pacing is a promising alternative therapy for patients that fail conventional treatment. Pacing primarily regulates gut motility by modulating rhythmic bio-electrical events called slow waves. While the efficacy of this technique has been widely investigated on the stomach, its application in the small intestine is less developed. This systematic review was undertaken to summarize the status of small intestinal pacing and evaluate its efficacy in modulating bowel function through preclinical research studies.

METHODS

The literature was searched using Scopus, PubMed, Ovid, Cochrane, CINAHL, and Google Scholar. Studies investigating electrophysiological, motility, and/or nutrient absorption responses to pacing were included. A critical review of all included studies was conducted comparing study outcomes against experimental protocols.

RESULTS

The inclusion criteria were met by 34 publications. A range of pacing parameters including amplitude, pulse width, pacing direction, and its application to broad regional small intestinal segments were identified and assessed. Out of the 34 studies surveyed, 20/23 studies successfully achieved slow-wave entrainment, 9/11 studies enhanced nutrient absorption and 21/27 studies modulated motility with pacing.

CONCLUSION

Small intestine pacing shows therapeutic potential in treating disorders such as short bowel syndrome and obesity. This systematic review proposes standardized protocols to maximize research outcomes and thereby translate to human studies for clinical validation. The use of novel techniques such as high-resolution electrical, manometric, and optical mapping in future studies will enable a mechanistic understanding of pacing.

Quantification of the Regional Properties of Gastric Motility Using Dynamic Magnetic Resonance Images

Goal: To quantify the regional properties of gastric motility from free-breathing dynamic MRI data. Methods: Free-breathing MRI scans were performed on 10 healthy human subjects. Motion correction was applied to reduce the respiratory effect. A stomach centerline was automatically generated and used as a reference axis. Contractions were quantified and visualized as spatio-temporal contraction maps. Gastric motility properties were reported separately for the lesser and greater curvatures in the proximal and distal regions of the stomach. Results: Motility properties varied in different regions of the stomach. The mean contraction frequencies for the lesser and greater curvatures were both 3.1±0.4 cycles per minute. The contraction speed was significantly higher on the greater curvature than the lesser curvature (3.5±0.7 vs 2.5±0.4 mm/s, p<0.001) while contraction size on both curvatures was comparable (4.9±1.2 vs 5.7±2.4 mm, p = 0.326). The mean gastric motility index was significantly higher in the distal greater curvature (28.13±18.89 mm²/s) compared to the other regions of the stomach (11.16-14.12 mm²/s). Conclusions: The results showed the effectiveness of the proposed method for visualization and quantification of motility patterns from MRI data.

Characterizing Spatial Signatures of Gastric Electrical Activity Using Biomagnetic Source Localization

BACKGROUND

The motility patterns in the gastrointestinal tract are regulated, in part, by bioelectrical events known as slow waves (SWs). Understanding temporal and spatial features of gastric SWs can help reveal the underlying causes of functional motility disorders.

OBJECTIVE

This study investigated the ability of source localization techniques to characterize the spatial signatures of SW activity using simulated and experimental magnetogastrography data.

METHODS

Two SW propagation patterns (antegrade and retrograde) with two rhythms (normogastric and bradygastric) were used to simulate magnetic fields using 4 anatomically realistic stomach and torso geometries. Source localization was performed utilizing the equivalent current dipole (ECD) and the equivalent magnetic dipole (EMD) models.

RESULTS

In the normogastric simulations when compared with the SW activity, the EMD model was capable of identifying the SW propagation in the lateral, antero-posterior, and supero-inferior axes with the median correlation coefficients of 0.66, 0.53, and 0.83, respectively, whereas the ECD model produced lower correlation scores (median: 0.52, 0.44, and 0.44). Moreover, the EMD model resulted in distinct and opposite spatial signatures for the antegrade and retrograde propagation. Similarly, when experimental data was used, the EMD model revealed antegrade-like signatures where the propagation was mostly towards the third quadrant in the supero-inferior (preprandial: 49%, postprandial: 35%) and antero-posterior (preprandial: 49%, postprandial: 50%) axes.

CONCLUSION AND SIGNIFICANCE

The EMD model was able to identify and classify the spatial signatures of SW activities, which can help to inform the interpretation of non-invasive recordings of gastric SWs as a biomarker of functional motility disorders.

Relationship Between Intestinal Slow-waves, Spike-bursts, and Motility, as Defined Through High-resolution Electrical and Video Mapping

Background/Aims

High-resolution extracellular mapping has improved our understanding of bioelectric slow-wave and spike-burst activity in the small intestine. The spatiotemporal correlation of electrophysiology and motility patterns is of critical interest to intestinal function but remains incompletely defined.

Methods

Intestinal jejunum segments from in vivo pigs and rabbits were exteriorized, and simultaneous high-resolution extracellular recordings and video recordings were performed. Contractions were quantified with strain fields, and the frequencies and velocities of motility patterns were calculated. The amplitudes, frequencies, and velocities of slow-wave propagation patterns and spike-bursts were quantified and visualized. In addition, the duration, size and energy of spike-burst patches were quantified.

Results

Slow-wave associated spike-bursts activated periodically at 10.8 ± 4.0 cycles per minute (cpm) in pigs and 10.2 ± 3.2 cpm in rabbits, while independent spike-bursts activated at a frequency of 3.2 ± 1.8 cpm. Independent spike-bursts had higher amplitude and longer duration than slow-wave associated spike-bursts (1.4 ± 0.8 mV vs 0.1 ± 0.1 mV, P < 0.001; 1.8 ± 1.4 seconds vs 0.8 ± 0.3 seconds, P < 0.001 in pigs). Spike-bursts that activated as longitudinal or circumferential patches were associated with contractions in the respective directions. Spontaneous peristaltic contractions were elicited by independent spike-bursts and travelled slower than slow-wave velocity (3.7 ± 0.5 mm/sec vs 10.1 ± 4.7 mm/sec, P = 0.007). Cyclic peristaltic contractions were driven by slow-wave associated spike-bursts and were coupled to slow-wave velocity and frequency in rabbit (14.2 ± 2.3 mm/sec vs 11.5 ± 4.6 mm/sec, P = 0.162; 11.0 ± 0.6 cpm vs 10.8 ± 0.6 cpm, P = 0.970).

Conclusions

Motility patterns were dictated by patterns of spike-burst patches. When spike-bursts were coupled to slow-waves, periodic motility patterns were observed, while when spike-bursts were not coupled to slow-waves, spontaneous aperiodic motility patterns were captured.

The bioelectrical conduction system around the ileocecal junction defined through in vivo high-resolution mapping in rabbits

Coordinated contractions across the small and large intestines via the ileocecal junction (ICJ) are critical to healthy gastrointestinal function and are in part governed by myoelectrical activity. In this study, the spatiotemporal characteristics of the bioelectrical conduction across the ICJ and its adjacent regions were quantified in anesthetized rabbits. High-resolution mapping was applied from the terminal ileum (TI) to the sacculus rotundus (SR), across the ICJ and into the beginning of the large intestine at the cecum ampulla coli (AC). Orally propagating slow wave patterns in the SR did not entrain the TI. However, aborally propagating patterns from the TI were able to entrain the SR. Bioelectrical activity was recorded within the ICJ and AC, revealing complex interactions of slow waves, spike bursts, and bioelectrical quiescence. This suggests the involvement of myogenic coordination when regulating motility between the small and large intestines. Mean slow wave frequency between regions did not vary significantly (13.74-17.16 cycles/min). Slow waves in the SR propagated with significantly faster speeds (18.51 ± 1.57 mm/s) compared with the TI (14.05 ± 2.53 mm/s, P = 0.0113) and AC (9.56 ± 1.56 mm/s, P = 0.0001). Significantly higher amplitudes were observed in both the TI (0.28 ± 0.13 mV, P = 0.0167) and SR (0.24 ± 0.08 mV, P = 0.0159) within the small intestine compared with the large intestine AC (0.03 ± 0.01 mV). We hypothesize that orally propagating slow waves facilitate a motor-brake pattern in the SR to limit outflow into the ICJ, similar to those previously observed in other gastrointestinal regions.NEW & NOTEWORTHY Competing slow wave pacemakers were observed in the terminal ileum and sacculus rotundus. Prevalent oral propagation in the sacculus rotundus toward the terminal ileum potentially acts as a brake mechanism limiting outflow. Slow waves and periods of quiescence at the ileocecal junction suggest that activation may depend on the coregulatory flow and distention pathways. Slow waves and spike bursts in the cecum impart a role in the coordination of motility.

Anatomically Constrained Gastric Slow Wave Localization using Biomagnetic Data

Detection of dysrhythmic gastric slow wave (SW) activity could have significant clinical utility because dysrhyth-mias have been linked to gastric motility disorders. The elec-trogastrogram (EGG) and magnetogastrogram (MGG) enable the non-invasive assessment of SW activity, but most analysis methods can only resolve frequency and velocity. Improved characterization of dysrhythmic propagation patterns from non-invasive measurements is important for the diagnosis of motility disorders and could allow early treatment stratification. In this study, we demonstrate the use of a penalized linear regression framework to localize SW events on the longitudinal stomach axis using simulated MGG data. Priors relating to spatial sparsity, the organization of wavefronts into complete circumferential rings, and the local distribution of depolar-ization and repolarization phases were used to constrain the inverse solution. This method was applied to MGG computed for a single wavefront case and a multiple wavefront case that were constructed from simulated 3 cycle-per-minute normal SW activity. Propagation patterns along the longitudinal stomach axis were identifiable from reconstructed SW activity for both cases. Localization error was 5.7 ± 0.1 mm and 7.7 ± 0.1 mm for each respective case within the distal stomach when the signal-to-noise ratio was 10 dB. Results indicate that penalized linear regression can successfully localize SW events provided the 3D geometry of the stomach and torso were acquired. Clinical Relevance- This method could help to improve the efficiency and accuracy of diagnosing gastric motility disorders from non-invasive measurements.

A generalized framework for pacing artifact removal using a Hampel filter

Cardiac pacing is a clinical therapy widely used for treating irregular heart rhythms. Equivalent techniques for the treatment of gastric functional motility disorders hold great potential. Accurate analysis of pacing studies is often hindered by the stimulus artifacts which are superimposed on the recorded signals. This paper presents a semi-automated artifact detection method using a Hampel filter accompanied by 2 separate artifact reconstruction methods: (i) an auto-regressive model, and (ii) weighted mean to estimate the underlying signal. The developed framework was validated on synthetic and experimental signals containing large periodic pacing artifacts alongside evoked bioelectrical events. The performance of the proposed algorithms was quantified for gastric and cardiac pacing data collected in vivo. A lower mean RMS difference was achieved by the artifact segment reconstructed using the auto-regression ([Formula: see text]), method compared to the weighted mean ([Formula: see text]) method. Therefore, a more accurate artifact reconstruction was provided by the auto-regression approach. Clinical Relevance- The ability to efficiently and accurately isolate evoked bioelectrical events by eliminating large artifacts is a critical advancement for the analysis of paced recordings. The developed framework allows more efficient analysis of preclinical pacing data and thereby contributes to the advancement of pacing as a clinical therapy.

Mathematical Modeling of Gastric Slow Waves During Electrical Field Stimulation

While neural modulation has been trialed as a therapy for functional gastric motility disorders, a computational model that guides stimulation protocol does not exist. In this work, a mathematical model of gastric slow wave activity, which incorporates the effects of neurotransmitter release during electrical field stimulation (EFS), was developed. Slow wave frequency responses due to the release of acetylcholine and slow wave amplitude responses due to the release of nitric oxide were modeled. The model was calibrated using experimental data from literature. A sensitivity analysis was conducted, which showed that the model yielded stable, periodic solutions for EFS frequencies in the range 0-20 Hz. A 25% increase in the input parameter (EFS frequency) from 5 Hz to 6.25 Hz resulted in a 5.2% increase in slow wave frequency and a 3.2 % decrease in slow wave amplitude. Simulated EFS showed that, for stimulation at 15 Hz, with blocking of the nitrergic neurotransmitter pathway the slow wave increased from the no stimulation scenario in frequency by only 2.4x compared to 2.7x when the nitrergic pathway was not blocked. A 21 % reduction in slow wave amplitude occurred when the cholinergic pathway was blocked, compared to a 46% reduction when no neurotransmitter pathways were blocked. Clinical relevance - This mathematical model is a step towards successful computational modeling of the effects ther-apeutic neural stimulation on the stomach. The model is also a tool for understanding of the physiology of neural stimulation.

Reconstruction of the Gastro-esophageal Junction Based on Ultramill Imaging for Biomechanical Analysis

The gastro-esophageal junction (GEJ) regulates the entry of food into the stomach and prevents reflux of acidic gastric contents into the lower esophagus. This is achieved through multiple mechanisms and the maintenance of a localized high-pressure zone. Diseases of the GEJ typically involve impairments to its muscular functions and often are accompanied by symptoms of reflux, heartburn, and dysphagia. This study aimed to develop a finite element-based model from a unique human cadaver GEJ data reconstructed from an ultramill imaging setup. A pipeline was developed to generate a mesh from an input stack of images. The anatomy of the model was compared to an existing Visible Human finite element GEJ model. Biomechanical simulations were also performed on both models using loading steps of differing levels of calcium to model different levels of contraction. It was found that the ultramill GEJ model is shorter than the Visible Human model (31 vs 48.3 mm), as well as producing lower pressure (1.35 vs 4.36 kPa). The model will be used to investigate detailed pressure development in the GEJ during swallowing under realistic loading conditions. Clinical Relevance - The modeling of the GEJ would allow further insights into pressure influencing factors and aid in the development and testing of treatments.

A Computational Model of Biophysical Properties of the Rat Stomach Informed by Comprehensive Analysis of Muscle Anatomy

An anatomically based 3D computational model of the rat stomach was developed using experimental muscle thickness measurements and muscle fiber orientations for the longitudinal muscle (LM) and circular muscle (CM) layers. First, 15 data points corresponding to the measurements were registered on the dorsal and ventral faces of the serosal surface of an averaged 3D rat stomach model. A thickness field representing the varying wall thickness was fitted to the surface and nodal points were projected outwards (for the LM layer) and inwards (for the CM layer) to create 2 new surfaces. In addition, a computational volume mesh was created and fiber orientation in each tetrahedral element was computed using a Laplace-Dirichlet rule-based algorithm and a simulation was performed to validate the model. The stomach model successfully represented the experimental measurements with a thickness in the range of 11.7-52.9 µm and 40.6-276.5 µm in the LM and CM layers, respectively, while the variation across the stomach was in agreement with the reported values. Similarly, the generated fiber orientations matched with the investigated fiber data and successfully resembled the observed properties such as the hairpin-like structure formed by the LM fibers in the fundus. Bioelectrical simulation using the developed model was successfully converged and reflected the properties of normal antegrade activity. In conclusion, a 3D computational model of the rat stomach was successfully developed and tested for in-silico studies. The model will be used in future studies to assess parameters in electrical therapies and to investigate the structure-function relationship in gastric motility. Clinical Relevance - Electrical stimulation is an emerging therapy for functional motility disorders. The 3D model of rat stomach developed in this study could provide accurate assessment of the efficacy of a vast range of stimulation parameters via in-silico studies and could aid in the adaptation of electrical therapies to clinical settings.

Wet-printing of PEDOT:PSS Microelectrodes for Gastric Slow Wave Recording

Bioelectrical slow waves are fundamental to maintaining the normal motility of the gastrointestinal tract. Slow wave abnormalities are associated with several major digestive disorders. High-resolution electrical mapping arrays have been used to investigate pathological slow wave abnormalities. However, conventional electrode substrate materials are opaque with high mechanical modulus, which leads to non-compliance and sub-par contact with the organ, without additional manipulations. Here we developed highly conformal and transparent conducting polymer electrode arrays using the extrusion wet-printing technique. The performance of electrodes for the electrophysiological recording of the gastric slow wave was validated using in a pig model, against a previously validated reference array over 100 s recording window. The conducting polymer electrodes registered comparable frequency to the reference array ( 3.31±0.20 cpm vs. 3.27±0.07 cpm, p = 0.067), with lower amplitude ( 372±237 vs. ), and signal to noise ratio ( 10.92±7.83 vs. [Formula: see text]). Further adjustments to the deposition parameters and contact material will improve the performance of the conducting polymer array for future experimental applications. Clinical Relevance- These conducting polymer electrodes provide better compliance and minimized mechanical mismatch to the gut tissue thus allowing long-term monitoring and stimulation of the gut. This could be potentially extended to other organs as well.

Deciphering Stomach Myoelectrical Slow Wave Conduction Patterns via Confocal Imaging of Gastric Pacemaker Cells and Fractal Geometry

Interstitial Cells of Cajal (ICC) are specialized gastrointestinal (GI) pacemaker cells that generate and actively propagate slow waves of depolarization (SWs) of the muscularis propria. SWs regulate the motility of the GI tract necessary for digestion, absorption of nutrients, and elimination of waste. Within the gastric wall, there are three main inter-connected layers of ICC networks: longitudinal muscle ICC (ICC-LM), myenteric plexus ICC (ICC-MP) & circumferential muscle (ICC-CM). Fractal structural parameters such as Fractal Dimension (FD), Lacunarity and Succolarity, have many advantages over physically-based parameters when it comes to characterizing the complex architectures of ICC networks. The analysis of networks of ICC throughout the proximal and distal murine gastric antrum with the FD and Lacunarity metrics was previously performed. Although the application of Succolarity is relatively nascent compared to the FD and Lacunarity; nevertheless, numerous studies have demonstrated the capability of this fractal measure to extract information from images associated with flow by which neither the FD nor Lacunarity are capable of discerning. In this study, Succolarity analysis of ICC-MP and ICC-CM networks were performed with confocal images taken across the proximal and distal murine antrum. Our findings demonstrated the Succolarity of ICC-MP and ICC-CM varied with directions and antral regions. The Succolarity of ICC-MP did not vary considerably with direction, however, Succolarity was higher in the aboral direction with 0.2113 ±0.1589, and 0.0637 ±0.0822 in the proximal and distal antrum, respectively. The overall Succolarity of ICC-MP was significantly higher than that of ICC-CM in the proximal antrum ( 0.1580±0.1325 vs [Formula: see text]) and in the distal antrum ( 0.0449 ±0.0409 vs [Formula: see text]). Clinical Relevance-Modeling SWs conduction patterns via image analysis of detailed ICC networks help to facilitate an improved understanding of the mechanisms underpinning GI myoelectric activity and the diseases associated with its dysfunction.

Targeted ablation of gastric pacemaker sites to modulate patterns of bioelectrical slow wave activation and propagation in an anesthetized pig model

Gastric motility is coordinated by underlying bioelectrical slow waves. Gastric dysrhythmias occur in gastrointestinal (GI) motility disorders, but there are no validated methods for eliminating dysrhythmias. We hypothesized that targeted ablation could eliminate pacemaker sites in the stomach, including dysrhythmic ectopic pacemaker sites. In vivo high-resolution serosal electrical mapping (16 × 16 electrodes; 6 × 6 cm) was applied to localize normal and ectopic gastric pacemaker sites in 13 anesthetized pigs. Radiofrequency ablation was performed in a square formation surrounding the pacemaker site. Postablation high-resolution mapping revealed that ablation successfully induced localized conduction blocks after 18 min (SD 5). Normal gastric pacemaker sites were eliminated by ablation (n = 6), resulting in the emergence of a new pacemaker site immediately distal to the original site in all cases. Ectopic pacemaker sites were similarly eliminated by ablation in all cases (n = 7), and the surrounding mapped area was then entrained by normal antegrade activity in five of those cases. Histological analysis showed that ablation lesions extended through the entire depth of the muscle layer. Immunohistochemical staining confirmed localized interruption of the interstitial cell of Cajal (ICC) network through the ablation lesions. This study demonstrates that targeted gastric ablation can effectively modulate gastric electrical activation, including eliminating ectopic sites of slow wave activation underlying gastric dysrhythmias, without disrupting surrounding conduction capability or tissue structure. Gastric ablation presents a powerful new research tool for modulating gastric electrical activation and may likely hold therapeutic potential for disorders of gastric function.NEW & NOTEWORTHY This study presents gastric ablation as a novel tool for modulating gastric bioelectrical activation, including eliminating the normal gastric pacemaker site as well as abnormal ectopic pacemaker sites underlying gastric dysrhythmias. Targeted application of radiofrequency ablation was able to eliminate these pacemaker sites without disrupting surrounding conduction capability or tissue structure. Gastric ablation presents a powerful new research tool for modulating gastric electrical activation and may likely hold therapeutic potential for disorders of gastric function.

Comparison of two techniques in posterior lens dislocations: Scleral suture fixation vs. modified Yamane intrascleral lens fixation

PURPOSE

To compare the use of Yamane flanged intrascleral haptic fixation and scleral suture fixation (SSF) techniques in combination with pars plana vitrectomy (PPV) for treatment of posterior lens dislocations.

METHODS

Patients who underwent PPV and scleral fixated IOL implantation due to subluxation/luxation of the crystalline lens/intraocular lens (IOL) were included in this retrospective study. The Yamane group included patients who underwent Yamane flanged intrascleral haptic fixation technique, while the SSF group consisted of patients who underwent conventional SSF. All patients underwent comprehensive ophthalmologic examinations preoperatively and postoperatively. Intraoperative and postoperative complications were recorded.

RESULTS

The Yamane group comprised of 39 eyes of 39 patients, and the SSF group included 35 eyes of 35 patients. Postoperative complications included hyphema (Yamane group: 2/39 (5.1%); SSF group: 0/35 (0%)) IOL decentration (Yamane group: 5/39 (12.8%); SSF group: 0/35 (0%)), corneal edema (Yamane group: 4/39 (10.2%); SSF group: 0/35 (0%)) cystoid macular edema (CME) (Yamane group: 1/39 (2.5%); SSF group: 3/35 (8.5%)) and retinal detachment (Yamane group: 1/39 (2.5%); SSF group: 1/35 (28.5%). The mean surgery time was significantly lower in the Yamane group compared with the SSF group (P<0.001). No cases of hypotony, conjunctival erosion, haptic exposure or endophthalmitis were encountered throughout follow-up.

CONCLUSION

SSF remains a safe and effective technique for management of posterior lens dislocations. The Yamane intrascleral IOL fixation technique is an effective alternative to conventional SSF, which has a relatively steep learning curve. Postoperative complications, including IOL tilt and decentration, may be experienced in the initial cases.

High-Resolution Spatiotemporal Quantification of Intestinal Motility with Free-Form Deformation

OBJECTIVE

To develop a method to quantify strain fields from in vivo intestinal motility recordings that mitigate accumulation of tracking error.

METHODS

The deforming geometry of the intestine in video sequences was modeled by a biquadratic B-spline mesh. Green-Lagrange strain fields were computed to quantify the surface deformations from motility. A nonlinear optimization scheme was applied to mitigate the accumulation of tracking error associated with image registration.

RESULTS

The optimization scheme maintained the RMS strain error under 1% and reduced the rate of strain error by 97% during synthetic tests. The algorithm was applied to map 64 segmental, 12 longitudinal, and 23 propagating circular contractions in the jejunum. Coordinated activity of the two muscle layers could be identified and the strain fields were able to map and quantify the anisotropic contractions of the intestine. Frequency and velocity were also quantified, from which two types of propagating circular contractions were identified: (i) -0:360:04 strain contractions that originated spontaneously and propagated at 31 mm/s in two pigs, and (ii) cyclic propagating contractions of -0:170:02 strain occurred at 11:00:6 cpm and propagated at 164 mm/s in a rabbit.

CONCLUSION

The algorithm simultaneously mapped the circular, longitudinal activity of the intestine with high spatial resolution and quantified anisotropic contractions and relaxations.

SIGNIFICANCE

The proposed algorithm can now be used to define the interactions of muscle layers during motility patterns. It can be integrated with high-resolution bioelectrical recordings to investigate the regulatory mechanisms of motility.

Localized gastric distension disrupts slow-wave entrainment leading to temporary ectopic propagation: a high-resolution electrical mapping study

Gastric distension is known to affect normal slow-wave activity and gastric function, but links between slow-wave dysrhythmias and stomach function are poorly understood. Low-resolution mapping is unable to capture complex spatial properties of gastric dysrhythmias, necessitating the use of high-resolution mapping techniques. Characterizing the nature of these dysrhythmias has implications in the understanding of postprandial function and the development of new mapping devices. In this two-phase study, we developed and implemented a protocol for measuring electrophysiological responses to gastric distension in porcine experiments. In vivo, serosal high-resolution electrical mapping (256 electrodes; 36 cm²) was performed in anaesthetized pigs (n = 11), and slow-wave pattern, velocity, frequency, and amplitude were quantified before, during, and after intragastric distension. Phase I experiments (n = 6) focused on developing and refining the distension mapping methods using a surgically inserted intragastric balloon, with a variety of balloon types and distension protocols. Phase II experiments (n = 5) used barostat-controlled 500-mL isovolumetric distensions of an endoscopically introduced intragastric balloon. Dysrhythmias were consistently induced in all five gastric distensions, using refined distension protocols. Dysrhythmias appeared 23 s (SD = 5 s) after the distension and lasted 129 s (SD = 72 s), which consisted of ectopic propagation originating from the greater curvature in the region of distension. In summary, our results suggest that distension disrupts gastric entrainment, inducing temporary ectopic slow-wave propagation. These results may influence the understanding of the postprandial stomach and electrophysiological effects of gastric interventions.NEW & NOTEWORTHY This study presents the discovery of temporary dysrhythmic ectopic pacemakers in the distal stomach caused by localized gastric distension. Distension-induced dysrhythmias are an interesting physiological phenomenon that can inform the design of new interventional and electrophysiological protocols for both research and the clinic. The observation of distension-induced dysrhythmias also contributes to our understanding of stretch-sensitivity in the gut and may play an important role in normal and abnormal postprandial physiology.

Antral Variation of Murine Gastric Pacemaker Cells Informed by Confocal Imaging and Machine Learning Methods

The Interstitial Cells of Cajal (ICC) are specialized gastrointestinal (GI) pacemaker cells that generate and actively propagate electrophysiological events called slow waves. Slow waves regulate the GI motility necessary for digestion. Several functional GI motility disorders have been associated with depletion in the ICC. In this study, a validated Fast Random Forest (FRF) classification method using Trainable WEKA Segmentation for segmenting the networks of ICC was applied to confocal microscopy images of a whole mount tissue from the distal antrum of a mouse stomach (583 × 3,376 × 133 μm³, parcellated into 24 equal image stacks). The FRF model performance was compared to 6 manually segmented subflelds and produced an area under the receiver-operating characteristic (AUROC) of 0.95. Structural variations of ICC network in the longitudinal muscle (ICC-LM) and myenteric plexus (ICC-MP) were quantified. The average volume of ICC-MP was significantly higher than ICC-LM at any point throughout the antral tissue sampled. There was a pronounced decline of up to 80% in ICC-LM (from 3,705 μm³ to 716 μm³) over a distance of 279.3 μm, that eventually diminished towards the distal antrum. However, an inverse relationship was observed in ICC-MP with an overall increase of up to 157% (from 59,100 μm³ to 151,830 μm³) over a distance of approximately 2 mm that proceeds towards the distal antrum.

A computational model of radiofrequency ablation in the stomach, an emerging therapy for gastric dysrhythmias

Gastric ablation has recently emerged as a promising potential therapy for bioelectrical dysrhythmias that underpin many gastrointestinal disorders. Despite similarities to well-developed cardiac ablation, gastric ablation is in early development and has thus far been limited to temperature-controlled, non-irrigated settings. A computational model of gastric ablation is needed to enable in silico testing and optimization of ablation parameters and techniques. In this study, we developed a computational model of radio-frequency (RF) gastric ablation. Model parameters and boundary conditions were established based on the current in vivo experimental application of serosal gastric ablation with a non-irrigated RF catheter. The Pennes bioheat transfer equation was used to model the thermal component of RF ablation, and Laplace's equation was used to model the Joule heating component. Tissue, blood, and catheter parameters were obtained from literature. The performance of the model was compared to previously established experimental values of temperature measured from various distances from the catheter tip. The model produced temperature estimations that were within 6% of the maximum experimental temperature at 2.5 mm from the catheter, and within 13% of the maximum temperature change at 4.7 mm. This model now provides a computational basis through which to conduct in silico testing of gastric ablation, and can be usefully applied to optimize gastric ablation parameters. In future, the model can be expanded to include irrigation of the catheter tip and power-controlled RF settings.Clinical Relevance- This work presents a computational model of gastric ablation that can now guide the in silico development of effective ablation parameters and therapeutic strategies, expanding the breadth of this promising therapy.

Reconstruction of stomach geometry using magnetic source localization

Routine diagnosis of gastric motility disorders represents a significant problem to current clinical practice. The non-invasive electrogastrogram (EGG) and magnetogastrogram (MGG) enable the assessment of gastric slow wave (SW) dysrhythmias that are associated with motility disorders. However, both modalities lack standardized methods for reliably detecting patterns of SW activity. Subject-specific anatomical information relating to the geometry of the stomach and its position within the torso have the potential to aid the development of relations between SWs and far-fields. In this study, we demonstrated the feasibility of using magnetic source localization to reconstruct the geometry of an anatomically realistic 3D stomach model. The magnetic fields produced by a small (6.35 × 6.35 mm) N35 neodymium magnet sequentially positioned at 64 positions were recorded by an array of 27 magnetometers. Finally, the magnetic dipole approximation and a particle swarm optimizer were used to estimate the position and orientation of the permanent magnet. Median position and orientation errors of 3.8 mm and 7.3° were achieved. The estimated positions were used to construct a surface mesh, and the Hausdorff Distance and Average Hausdorff Distance dissimilarity metrics for the reconstructed and ground-truth models were 11.6 mm and 2.4 mm, respectively. The results indicate that source localization using the magnetic dipole model can successfully reconstruct the geometry of the stomach.

Quantification of Gastric Contractions Using MRI with a Natural Contrast Agent

Gastric motility has an essential role in mixing and the breakdown of ingested food. It can affect the digestion process and the efficacy of the orally administered drugs. There are several methods to image, measure, and quantify gastric motility. MRI has been shown to be a suitable non-invasive method for gastric motility imaging. However, in most studies, gadolinium-based agents have been used as an oral contrast agent, making it less desirable for general usage. In this study, MRI scans were performed on 4 healthy volunteers, where pineapple juice was used as a natural contrast agent for imaging gastric motility. A novel method was developed to automatically estimate a curved centerline of the stomach. The centerline was used as a reference to quantify contraction magnitudes. The results were visualized as contraction magnitude-maps. The mean speed of each contraction wave on the lesser and greater curvatures of the stomach was calculated, and the variation of the speeds in 4 regions of the stomach were quantified. There were 3-4 contraction waves simultaneously present in the stomach for all cases. The mean speed of all contractions was 2.4±0.9 mm/s, and was in agreement with previous gastric motility studies. The propagation speed of the contractions in the greater curvature was higher in comparison to the lesser curvature (2.9±0.8 vs 1.9±0.5 mm/s); however, the speeds were more similar near to the pylorus. This study shows the feasibility of using pineapple juice as a natural oral contrast agent for the MRI measurements of gastric motility. Also, it demonstrated the viability of the proposed method for automatic curved centerline estimation, which enables practical clinical translation.Clinical Relevance- MRI is able to non-invasively provide dynamic images of the contraction patterns of the stomach, providing a novel clinical tool for assessing functional motility disorders. The use of a natural oral contrast agent such as pineapple juice, as opposed to a gadolinium-based contrast agent, makes MRI more widely accessible. Our semi-automated methods for quantifying contraction magnitude and speed will streamline analysis and clinical diagnosis.

Quantification of Gastric Slow Wave Velocity using Bipolar High-Resolution Recordings

OBJECTIVE

Gastric bio-electrical slow waves are, in part, responsible for coordinating motility. High-resolution (HR) in vivo recordings can be used to capture the wavefront velocity of the propagating slow waves. A standard marking-and-grouping approach is typically employed along with manual review. Here, a bipolar velocity estimation (BVE) method was developed, which utilized local directional information to estimate the wavefront velocity in an efficient manner.

METHODS

With this approach, unipolar in vivo HR recordings were used to construct bipolar recordings in different directions. Then, the local directionality of the slow wave was extracted by calculating time delay information. The accuracy of the method was verified using synthetic data and then validated with in vivo HR pig experimental recordings.

RESULTS

Against ventilator noise amplitude of 0% - 70% of the average slow wave amplitude, the direction and speed error increased from 4.4 and 0.9 mm/s to 8.6 and 1.4 mm/s. For signals added with high-frequency noise with signal-to-noise ratios of 60 dB - 12 dB, the error increased from 8.0 and 1.0 mm/s to 9.8 and 1.2 mm/s. For experimental signals, the BVE algorithm resulted in 19.2 1.7 of direction error and 2.0 0.2 mm/s of speed error, when compared to the standard marking-and-grouping method.

CONCLUSION

Gastric slow wave wavefront velocities were estimated rapidly using the BVE algorithm with minimal errors.

SIGNIFICANCE

The BVE algorithm enables the ability to estimate wavefront velocities in HR recordings in an efficient manner.

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.

Transmural recordings of gastrointestinal electrical activity using a spatially-dense microelectrode array

Objective. High-resolution serosal recordings provide detailed information about the bioelectrical conduction patterns in the gastrointestinal (GI) tract. However, equivalent knowledge about the electrical activity through the GI tract wall remains largely unknown. This study aims to capture and quantify the bioelectrical activity across the wall of the GI tract.Approach. A needle-based microelectrode array was used to measure the bioelectrical activity across the GI wallin vivo. Quantitative and qualitative evaluations of transmural slow wave characteristics were carried out in comparison to the serosal slow wave features, through which the period, amplitude, and SNR metrics were quantified and statistically compared.Main results. Identical periods of 4.7 ± 0.3 s with amplitudes of 0.17 ± 0.04 mV versus 0.31 ± 0.1 mV and signal to noise ratios of 5.5 ± 1.3 dB versus 14.4 ± 1.1 dB were observed for transmural and serosal layers, respectively. Four different slow wave morphologies were observed across the transmural layers of the GI wall. Similar amplitudes were observed for all morphology types, and Type 1 and Type 2 were of the highest prevalence, dominating the outer and inner layers. Type 2 was exclusive to the middle layer while Type 4 was primarily observed in the middle layer as well.Significance. This study demonstrates the validity of new methodologies for measuring transmural slow wave activation in the GI wall and can now be applied to investigate the source and origin of GI dysrhythmias leading to dysmotility, and to validate novel therapeutics for GI health and disease.

Effects of magnetogastrography sensor configurations in tracking slow wave propagation

Magnetogastrography (MGG) is a non-invasive method of assessing gastric slow waves (SWs) by recording the resultant magnetic fields. MGG can capture both SW frequency and propagation, and identify SW dysrhythmias that are associated with motility disorders. However, the impact of the restricted spatial coverage and sensor density on SW propagation tracking performance is unknown. This study simulated MGG using multiple anatomically specific torso geometries and two realistic SW propagation patterns to determine the effect of different sensor configurations on tracking SW propagation. The surface current density mapping and center-of-gravity tracking methods were used to compare four magnetometer array configurations: a reference system currently used in GI research and three hypothetical higher density and coverage arrays. SW propagation patterns identified with two hypothetical arrays (with coverage over at least the anterior of the torso) correlated significantly higher with simulated realistic 3 cycle-per-minute SW activity than the reference array (p = 0.016, p = 0.005). Furthermore, results indicated that most of the magnetic fields that contribute to the performance of SW propagation tracking were located on the anterior of the torso as further increasing the coverage did not significantly increase performance. A 30% decrease in sensor spacing within the same spatial coverage of the reference array also significantly increased correlation values by approximately 0.50 when the signal-to-noise ratio was 5 dB. This study provides evidence that higher density and coverage sensor layouts will improve the utility of MGG. Further work is required to investigate optimum sensor configurations across larger anatomical variations and other SW propagation patterns.

Detection of Slow Wave Propagation Direction Using Bipolar High-Resolution Recordings

Gastric motility is in part coordinated by bio-electrical slow waves. The wavefront orientation of the slow wave contains vital physiological information about the motility condition of the gastrointestinal system. Dysmotility was shown to be associated with dysrhythmic propagation of the slow wave. The most commonly used method to detect wavefront orientation is computationally expensive because of the involvement of activation time identification. The information of local directionality contained in bipolar slow wave recordings could be used to detect the wavefront orientation. An algorithm called bipolar direction detection was developed to utilize the information contained in the bipolar slow wave recordings. Bipolar recordings were constructed by subtracting the unipolar in vivo recordings of directional electrode pairs. Then, time delay information was used to detect the wavefront direction. The algorithm was verified using synthetic data and validated using experimental data. Ten high-resolution in vivo slow wave signals from 5 pigs were recorded for a duration of 2 minutes. The performance was compared against the semi-automated approach, resulting in an average angle error of 20° for the experimental data. The algorithm was able to detect slow wave wavefront orientation with minimal errors rapidly.Clinical relevance-The ability to rapidly detect slow wave propagation direction will enable effective analysis of large data sets, through which we can obtain a better understanding of functional motility disorders and help with diagnosis and treatment.

Simulation-based Analysis of Magnetogastrography Sensor Configurations for Characterizing Gastric Slow Wave Dysrhythmias

The routine diagnosis of gastric motility disorders represents a significant problem to current clinical practice. Magnetogastrography (MGG) provides a non-invasive option for assessing gastric slow wave (SW) dysrhythmias that are associated with motility disorders. However, its ability to characterize SW propagation is impaired by the limited spatial coverage of existing superconducting quantum interference devices (SQUIDs). Recently developed optically-pumped magnetometers can potentially substitute SQUIDs and enable subject-specific MGG arrays with greater spatial coverage. This study developed simulations of gastric MGG to determine the distribution of the magnetic fields (MFs) generated by SWs above the torso, and investigated the impact of several realistic dysrhythmic patterns of propagation. The distribution of MFs was found to vary significantly for different patterns of SW propagation, with ectopic dysrhythmia displaying the greatest difference from normal. Notably, some important proportion of the MFs lay outside the coverage of an existing experimental SQUID array used in gastrointestinal research for some simulated SW propagation patterns, such as retrograde activity. Results suggest that MGG measurements should be made over the entire frontal face of the torso to capture all of the strongest MFs generated by SWs.Clinical relevance- This provides a guide for the placement of MGG sensors for the capture of both normal and dysrhythmic gastric slow wave propagation.

A Novel Method for Time-Dependent Numerical Modeling of Gastric Motility Directly from Magnetic Resonance Imaging

Gastric motility has a critical role in disintegration and mixing of the ingested food inside the stomach. Several studies have been conducted to quantify and analyze the effect of the contractions of gastric musculature on the stomach contents. Despite the anatomical variation in stomach shape and motility patterns, previous numerical studies employed generalized geometries of the stomach as the computational domain for simulations. To model realistic gastric muscular contractions, the variation in stomach geometries need to be accounted for in numerical simulations. In the current study, a novel method was developed to utilize the recent advances in magnetic resonance imaging (MRI) technology and computational power expansion to build anatomically and physiologically realistic subject specific models of human gastric motility. In this method, MRI scans of the stomach were used to construct two and three dimensional geometry models of gastric motility. MRI was performed on 4 healthy participants. Using the developed method, dynamic numerical geometry models of gastric motility for each participant were constructed and related geometrical calculations were presented. Different combinations of solid and liquid test meals were consumed prior to the scans. The volume of the stomach ranged between 0.36 - 1.10 L in the fed state. The stomach models had an average length of 184 to 226 mm and a maximum diameter of 65 to 102 mm. Contraction propagation speed calculated from the models and MRI data were in good agreement, measuring around 2 mm/s.Clinical relevance- Clinicians can benefit from the proposed method for diagnostic purposes as the method is semi-automatic and can provide dynamic three-dimensional visualization of gastric motility of patients.

Continuum Based Bioelectrical Simulations using Structurally Realistic Gastrointestinal Pacemaker Cell Networks

Cellular and tissue level bioelectrical activity was simulated over structurally realistic 3D interstitial cell of Cajal (ICC) networks reconstructed from confocal images of a wild type (WT) mouse model with a normal ICC distribution and a Spry4 knockout (KO) mouse model with a mild ICC hyperplasia. First, the ICC pixels within the confocal images were segmented. Then, the segmented images were visually inspected and the 3D surface mesh of the ICC tissue network was created from the 90 slices spanning the myenteric plexus ICC network. After two additional concentric meshes (representing the non-ICC and tissue bath regions) surrounding the ICC region were added, a 3D tetrahedral volume mesh containing the three regions was reconstructed. The electrical propagation through the tissue network was simulated using the bidomain continuum model. The results showed that the ICC network of the WT mouse had a smaller volume than the KO mouse (0.008 vs 0.012 mm³). The simulated bioelectrical activity for both mice showed an isotropic propagation from the initial activation region. Mean velocities of 4.2±1.5 and 4.1±1.3 mm/s were reported for the WT and KO mice, respectively. The velocity in the x-direction was higher than the y-direction for the WT mouse with a percent difference of 14.8%. On the other hand, the velocity in the y-direction was higher for the KO mouse with a percent difference of 9.5%. For both cases, there was no propagation in the z-direction as all the solution points along the same z-depth were simultaneously activated.

Current applications of mathematical models of the interstitial cells of Cajal in the gastrointestinal tract

The interstitial cells of Cajal (ICC) form interconnected networks throughout the gastrointestinal (GI) tract. ICC act as the pacemaker cells that initiate the rhythmic bioelectrical slow waves and intermediary between the GI musculature and nerves, both of which are critical to GI motility. Disruptions to the number of ICC and the integrity of ICC networks have been identified as a key pathophysiological mechanism in a number of clinically challenging GI disorders. The current analyses of ICC generally rely on either functional recordings taken directly from excised tissue or morphological analysis based on images of labeled ICC, where the structural-functional relationship is investigated in an associative manner rather than mechanistically. On the other hand, computational physiology has played a significant role in facilitating our understanding of a number of physiological systems in both health and disease, and investigations in the GI field are beginning to incorporate several mathematical models of the ICC. The main aim of this review is to present the major modeling advances in GI electrophysiology, in order to introduce a multi-scale framework for mathematically quantifying the functional consequences of ICC degradation at both cellular and tissue scales. The outcomes will inform future investigators utilizing modeling techniques in their studies. This article is categorized under: Metabolic Diseases > Computational Models.

Supervised Machine Learning Segmentation and Quantification of Gastric Pacemaker Cells

Interstitial Cells of Cajal (ICC) are specialized pacemaker cells that generate and actively propagate electrophysiological events called slow waves. Slow waves regulate the motility of the gastrointestinal tract necessary for digesting food. Degradation in the ICC network structure has been qualitatively associated to several gastrointestinal motility disorders. ICC network structure can be obtained using confocal microscopy, but the current limitations in imaging and segmentation techniques have hindered an accurate representation of the networks. In this study, supervised machine learning techniques were applied to extract the ICC networks from 3D confocal microscopy images. The results showed that the Fast Random Forest classification method using Trainable WEKA Segmentation outperformed the Decision Table and Naïve Bayes classification methods in sensitivity, accuracy, and F-measure. Using the Fast Random Forest classifier, 12 gastric antrum tissue blocks were segmented and variations in ICC network thickness, density and process width were quantified for the myenteric plexus ICC network (the primary pacemakers). Our findings demonstrated regional variation in ICC network density and thickness along the circumferential and longitudinal axis of the mouse antrum. An inverse relationship was observed in the distal and proximal antrum for density (proximal: 9.8±4.0% vs distal: 7.6±4.6%) and thickness (proximal: 15±3 μm vs distal: 24±10 μm). Limited variation in ICC process width was observed throughout the antrum (5±1 μm).Clinical Relevance- Detailed quantification of regional ICC structural properties will provide insights into the relationship between ICC structure, slow waves and resultant gut motility. This will improve techniques for the diagnosis and treatment of functional GI motility disorders.

Trace Mapping: A New Visualization Technique for Analyzing Gastrointestinal High-Resolution Electrical Mapping Data

Visualization techniques are an important tool for understanding high-resolution mapping data in gastric electrophysiology. Isochronal maps and animations provide excellent depictions of spatial propagation patterns, but fail to capture temporal features of electrical activity. In this work, 'trace mapping' was developed and validated as a method for visualizing high-resolution mapping data. A combination of dots and lines represent events and temporal groups, respectively, creating patterns that can be quickly and efficiently interpreted. This work outlines trace mapping methods and introduces a shape-based pattern recognition method for efficient interpretation of trace maps. These methods provide a new perspective for understanding and evaluating gastric electrophysiology.Clinical Relevance-This work provides new visualization methods that can help clinicians interpret and diagnose gastric electrical abnormalities in patients with functional gastrointestinal disorders.

Transmural Temperature Monitoring to Quantify Thermal Conduction And Lesion Formation During Gastric Ablation, an Emerging Therapy for Gastric Dysrhythmias

Gastric ablation is emerging as a potential therapy for electrical dysrhythmias associated with gastric disorders. Thermal conduction properties of gastric tissue during ablation have not yet been defined, but are necessary for optimizing the technique and translating ablation to clinical therapy. We developed custom needle-based transmural temperature probes to quantify the temperature of gastric tissue during ablation. These probes were applied in vivo in pigs (n=5), during gastric ablation (70 °C, 10 s duration), at distances of 2.5 - 20 mm from the ablation catheter tip. Thermal response of the tissue was non-linear; the maximum temperature increase from baseline (33.3 ± 1.0 °C) was observed at the closest temperature probe to the catheter tip (2.5 mm, 14.9 °C), and temperature change decreased with distance from the catheter tip. Probes positioned between 5 -20 mm from the catheter tip recorded temperature increases of less than 5.6 °C. This study provides methods for monitoring temperature during in vivo ablation, and demonstrates that functional temperature increases from ablation were restricted to within approximately 5 mm of the catheter. These methods can now be applied to optimize effective ablation parameters, and to inform models of gastric ablation.