Longitudinal and circumferential spike patches in the canine small intestine in vivo

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.

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.

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.

Robotic Setup Promises Consistent Effects of Multilocular Gastrointestinal Electrical Stimulation: First Results of a Porcine Study

BACKGROUND

Electrical stimulation (ES) of several gastrointestinal (GI) segments is a promising therapeutic option for multilocular GI dysmotility, but conventional surgical access by laparotomy involves a high degree of tissue trauma. We evaluated a minimally invasive surgical approach using a robotic surgical system to perform electromyographic (EMG) recordings and ES of several porcine GI segments, comparing these data to an open surgical approach by laparotomy.

MATERIALS AND METHODS

In 5 acute porcine experiments, we placed multiple electrodes on the stomach, duodenum, jejunum, ileum, and colon. Three experiments were performed with a median laparotomy and 2 others using a robotic platform. Multichannel EMGs were recorded, and ES was sequentially delivered with 4 ES parameters to the 5 target segments. We calculated pre- and poststimulatory spikes per minute (Spm) and performed a statistical Poisson analysis.

RESULTS

Electrode placement was achieved in all cases without complications. Increased technical and implantation time were required to achieve the robotic electrode placement, but invasiveness was markedly reduced in comparison to the conventional approach. The highest calculated (c)Spm values were found in the poststimulatory period of the small bowel with both the conventional and robotic approaches. Six of the 20 Poisson test results in the open setup reached statistical significance and 12 were significant in the robotic experiments.

CONCLUSIONS

The robotic setup was less invasive, revealed more consistent effects of multilocular ES in several GI segments, and is a promising option for future preclinical and clinical studies of GI motility disorders.

A Framework for Spatiotemporal Analysis of Gastrointestinal Spike Burst Propagation

Gastrointestinal spike bursts are a bioelectrical phenomenon associated with motility. These events when initiated propagate a small distance and abruptly terminate activating a small area defined as a patch. Understanding normal and abnormal propagation patterns of these events may shed light on the root causes of functional motility disorders. This study develops an automated framework for spatiotemporal analysis of spike bursts. High-resolution electrical signals were obtained from the pig intestine, after which intestinal spike bursts were identified and clustered into their propagating wavefronts. Propagation velocity was estimated by fitting a polynomial surface to the activation times. The fit was able to estimate the velocity of spike burst patches covering at least six channels with an average RMSE of 0.4 s. Propagation within patches was visualized by plotting the fit as activation maps and velocity maps. Average velocities were calculated to compare the propagation characteristics of different types of patches. In the future, this framework will be extended to generate amplitude maps and spike burst duration maps. These tools can be used to analyze spike patch propagation and their relationship to motility.

Dynamic slow-wave interactions in the rabbit small intestine defined using high-resolution mapping

BACKGROUND

The motility in the small intestine is governed in part by myogenic bio-electrical events, known as slow waves. High-resolution multi-electrode mapping has improved our understanding of slow-wave propagation in the small intestine but has been applied in a limited number of in vivo animal studies. This study applied high-resolution mapping to investigate slow waves in the rabbit small intestine.

METHODS

A high-resolution flexible printed circuit board array (256 electrodes; 4 mm spacing) was applied in vivo to the rabbit intestine. Extracellular slow-wave activity was acquired sequentially along the length of the intestine.

KEY RESULTS AND CONCLUSIONS

The majority of the slow waves propagated in the antegrade direction (56%) while retrograde patterns were primarily observed in the distal intestine (29%). Colliding slow-wave events were observed across the length of the small intestine (15%). The interaction of competing pacemakers was mapped in spatiotemporal detail. The frequency and velocity of the slow waves were highest in the duodenum compared to ileum (20.0 ± 1.2 cpm vs 10.5 ± 0.9 cpm, P < 0.001; 14.4 ± 3.4 mm/s vs 12.3 ± 3.4 mm/s; P < 0.05).

INFERENCES

In summary, extracellular serosal slow-wave activity was quantified spatiotemporally along the length of the rabbit intestine. In particular, the study provides evidence toward the presence and interaction of slow-wave pacemakers acting along the small intestine and how they may contribute to the slow-wave frequency gradient along the length of the intestine.

Methods for High-Resolution Electrical Mapping in the Gastrointestinal Tract

Over the last two decades, high-resolution (HR) mapping has emerged as a powerful technique to study normal and abnormal bioelectrical events in the gastrointestinal (GI) tract. This technique, adapted from cardiology, involves the use of dense arrays of electrodes to track bioelectrical sequences in fine spatiotemporal detail. HR mapping has now been applied in many significant GI experimental studies informing and clarifying both normal physiology and arrhythmic behaviors in disease states. This review provides a comprehensive and critical analysis of current methodologies for HR electrical mapping in the GI tract, including extracellular measurement principles, electrode design and mapping devices, signal processing and visualization techniques, and translational research strategies. The scope of the review encompasses the broad application of GI HR methods from in vitro tissue studies to in vivo experimental studies, including in humans. Controversies and future directions for GI mapping methodologies are addressed, including emerging opportunities to better inform diagnostics and care in patients with functional gut disorders of diverse etiologies.

Intsy: a low-cost, open-source, wireless multi-channel bioamplifier system

OBJECTIVE

Multi-channel electrical recordings of physiologically generated signals are common to a wide range of biomedical fields. The aim of this work was to develop, validate, and demonstrate the practical utility of a high-quality, low-cost 32/64-channel bioamplifier system with real-time wireless data streaming capability.

APPROACH

The new 'Intsy' system integrates three main off-the-shelf hardware components: (1) Intan RHD2132 bioamplifier; (2) Teensy 3.2 microcontroller; and (3) RN-42 Bluetooth 2.1 module with a custom LabView interface for real-time data streaming and visualization. Practical utility was validated by measuring serosal gastric slow waves and surface EMG on the forearm with various contraction force levels. Quantitative comparisons were made to a gold-standard commercial system (Biosemi ActiveTwo).

MAIN RESULTS

Intsy signal quality was quantitatively comparable to that of the ActiveTwo. Recorded slow wave signals had high SNR (24  ±  2.7 dB) and wavefront propagation was accurately mapped. EMG spike bursts were characterized by high SNR (⩾10 dB) and activation timing was readily identified. Stable data streaming rates achieved were 3.5 kS s^-1 for wireless and 64 kS s^-1 for USB-wired transmission.

SIGNIFICANCE

Intsy has the highest channel count of any existing open-source, wireless-enabled module. The flexibility, portability and low cost ($1300 for the 32-channel version, or $2500 for 64 channels) of this new hardware module reduce the entry barrier for a range of electrophysiological experiments, as are typical in the gastrointestinal (EGG), cardiac (ECG), neural (EEG), and neuromuscular (EMG) domains.

Improved Visualization of Gastrointestinal Slow Wave Propagation Using a Novel Wavefront-Orientation Interpolation Technique

OBJECTIVE

High-resolution mapping of gastrointestinal (GI) slow waves is a valuable technique for research and clinical applications. Interpretation of high-resolution GI mapping data relies on animations of slow wave propagation, but current methods remain as rudimentary, pixelated electrode activation animations. This study aimed to develop improved methods of visualizing high-resolution slow wave recordings that increases ease of interpretation.

METHODS

The novel method of "wavefront-orientation" interpolation was created to account for the planar movement of the slow wave wavefront, negate any need for distance calculations, remain robust in atypical wavefronts (i.e., dysrhythmias), and produce an appropriate interpolation boundary. The wavefront-orientation method determines the orthogonal wavefront direction and calculates interpolated values as the mean slow wave activation-time (AT) of the pair of linearly adjacent electrodes along that direction. Stairstep upsampling increased smoothness and clarity.

RESULTS

Animation accuracy of 17 human high-resolution slow wave recordings (64-256 electrodes) was verified by visual comparison to the prior method showing a clear improvement in wave smoothness that enabled more accurate interpretation of propagation, as confirmed by an assessment of clinical applicability performed by eight GI clinicians. Quantitatively, the new method produced accurate interpolation values compared to experimental data (mean difference 0.02 ± 0.05 s) and was accurate when applied solely to dysrhythmic data (0.02 ± 0.06 s), both within the error in manual AT marking (mean 0.2 s). Mean interpolation processing time was 6.0 s per wave.

CONCLUSION AND SIGNIFICANCE

These novel methods provide a validated visualization platform that will improve analysis of high-resolution GI mapping in research and clinical translation.

The virtual intestine: in silico modeling of small intestinal electrophysiology and motility and the applications

The intestine comprises a long hollow muscular tube organized in anatomically and functionally discrete compartments, which digest and absorb nutrients and water from ingested food. The intestine also plays key roles in the elimination of waste and protection from infection. Critical to all of these functions is the intricate, highly coordinated motion of the intestinal tract, known as motility, which is coregulated by hormonal, neural, electrophysiological and other factors. The Virtual Intestine encapsulates a series of mathematical models of intestinal function in health and disease, with a current focus on motility, and particularly electrophysiology. The Virtual Intestine is being cohesively established across multiple physiological scales, from sub/cellular functions to whole organ levels, facilitating quantitative evaluations that present an integrative in silico framework. The models are also now finding broad physiological applications, including in evaluating hypotheses of slow wave pacemaker mechanisms, smooth muscle electrophysiology, structure-function relationships, and electromechanical coupling. Clinical applications are also beginning to follow, including in the pathophysiology of motility disorders, diagnosing intestinal ischemia, and visualizing colonic dysfunction. These advances illustrate the emerging potential of the Virtual Intestine to effectively address multiscale research challenges in interdisciplinary gastrointestinal sciences.

Mapping and modeling gastrointestinal bioelectricity: from engineering bench to bedside

A key discovery in gastrointestinal motility has been the central role played by interstitial cells of Cajal (ICC) in generating electrical slow waves that coordinate contractions. Multielectrode mapping and multiscale modeling are two emerging interdisciplinary strategies now showing translational promise to investigate ICC function, electrophysiology, and contractions in the human gut.

Automated algorithm for GI spike burst detection and demonstration of efficacy in ischemic small intestine

We present a novel, fully-automated gastrointestinal spike burst detection algorithm. Following pre-processing with SALPA (Wagenaar and Potter, J. Neurosci. Methods 120:113-120, 2002) and a Savitzky-Golay filter to remove unwanted low and high frequency components, candidate spike waveforms are detected utilizing the non-linear energy operator. Candidate waveforms are classified as spikes or artifact by a support vector machine. The new method achieves highly satisfactory performance with >90% sensitivity and positive prediction value. We also demonstrate an application of the new method to detect changes in spike rate and spatial propagation patterns upon induction of mesenteric ischemia in the small intestine. Spike rates were observed to transiently increase 10-20 fold for a duration of ≈600 s, relative to baseline conditions. In ischemic conditions, spike activity propagation patterns included retrograde-longitudinal wavefronts with occasional spontaneous conduction blocks, as well as self-terminating concentric-circumferential wavefronts. Longitudinal and circumferential velocities were 6.8-8.0 cm/s and 18.7 cm/s, respectively.

Experimental and Automated Analysis Techniques for High-resolution Electrical Mapping of Small Intestine Slow Wave Activity

BACKGROUND/AIMS

Small intestine motility is governed by an electrical slow wave activity, and abnormal slow wave events have been associated with intestinal dysmotility. High-resolution (HR) techniques are necessary to analyze slow wave propagation, but progress has been limited by few available electrode options and laborious manual analysis. This study presents novel methods for in vivo HR mapping of small intestine slow wave activity.

METHODS

Recordings were obtained from along the porcine small intestine using flexible printed circuit board arrays (256 electrodes; 4 mm spacing). Filtering options were compared, and analysis was automated through adaptations of the falling-edge variable-threshold (FEVT) algorithm and graphical visualization tools.

RESULTS

A Savitzky-Golay filter was chosen with polynomial-order 9 and window size 1.7 seconds, which maintained 94% of slow wave amplitude, 57% of gradient and achieved a noise correction ratio of 0.083. Optimized FEVT parameters achieved 87% sensitivity and 90% positive-predictive value. Automated activation mapping and animation successfully revealed slow wave propagation patterns, and frequency, velocity, and amplitude were calculated and compared at 5 locations along the intestine (16.4 ± 0.3 cpm, 13.4 ± 1.7 mm/sec, and 43 ± 6 µV, respectively, in the proximal jejunum).

CONCLUSIONS

The methods developed and validated here will greatly assist small intestine HR mapping, and will enable experimental and translational work to evaluate small intestine motility in health and disease.

The gastrointestinal electrical mapping suite (GEMS): software for analyzing and visualizing high-resolution (multi-electrode) recordings in spatiotemporal detail

Background

Gastrointestinal contractions are controlled by an underlying bioelectrical activity. High-resolution spatiotemporal electrical mapping has become an important advance for investigating gastrointestinal electrical behaviors in health and motility disorders. However, research progress has been constrained by the low efficiency of the data analysis tasks. This work introduces a new efficient software package: GEMS (Gastrointestinal Electrical Mapping Suite), for analyzing and visualizing high-resolution multi-electrode gastrointestinal mapping data in spatiotemporal detail.

Results

GEMS incorporates a number of new and previously validated automated analytical and visualization methods into a coherent framework coupled to an intuitive and user-friendly graphical user interface. GEMS is implemented using MATLAB®, which combines sophisticated mathematical operations and GUI compatibility. Recorded slow wave data can be filtered via a range of inbuilt techniques, efficiently analyzed via automated event-detection and cycle clustering algorithms, and high quality isochronal activation maps, velocity field maps, amplitude maps, frequency (time interval) maps and data animations can be rapidly generated. Normal and dysrhythmic activities can be analyzed, including initiation and conduction abnormalities. The software is distributed free to academics via a community user website and forum (http://sites.google.com/site/gimappingsuite).

Conclusions

This software allows for the rapid analysis and generation of critical results from gastrointestinal high-resolution electrical mapping data, including quantitative analysis and graphical outputs for qualitative analysis. The software is designed to be used by non-experts in data and signal processing, and is intended to be used by clinical researchers as well as physiologists and bioengineers. The use and distribution of this software package will greatly accelerate efforts to improve the understanding of the causes and clinical consequences of gastrointestinal electrical disorders, through high-resolution electrical mapping.

A novel laparoscopic device for measuring gastrointestinal slow-wave activity

BACKGROUND

A periodic electrical activity, termed "slow waves", coordinates gastrointestinal contractions. Slow-wave dysrhythmias are thought to contribute to dysmotility syndromes such as postoperative gastroparesis, but the clinical significance of these dysrhythmias remains poorly defined. Electrogastrography (EGG) has been unable to characterize dsyrhythmic activity reliably, and the most accurate method for evaluating slow waves is to record directly from the surface of the target organ. This study presents a novel laparoscopic device for recording serosal slow-wave activity, together with its validation.

METHODS

The novel device consists of a shaft (diameter, 4 mm; length, 300 mm) and a flexible connecting cable. It contains four individual electrodes and is fully shielded. Validation was performed by comparing slow-wave recordings from the laparoscopic device with those from a standard electrode platform in an open-abdomen porcine model. An intraoperative human trial of the device also was performed by recording activity from the gastric antrum of a patient undergoing a laparoscopic cholecystectomy.

RESULTS

Slow-wave amplitudes were similar between the laparoscopic device and the standard recording platform (mean 0.38 ± 0.03 mV vs range 0.36-0.38 ± 0.03 mV) (p = 0.94). The signal-to-noise ratio (SNR) also was similar between the two types of electrodes (13.7 dB vs 12.6 dB). High-quality antral slow-wave recordings were achieved in the intraoperative human trial (amplitude, 0.41 ± 0.04 mV; SNR, 12.6 dB), and an activation map was constructed showing normal aboral slow-wave propagation at a velocity of 6.3 ± 0.9 mm/s.

CONCLUSIONS

The novel laparoscopic device achieves high-quality serosal slow-wave recordings. It is easily deployable and atraumatic. It is anticipated that this device will aid in the clinical investigation of normal and dsyrhythmic slow-wave activity. In particular, it offers new potential for investigating the effect of surgical procedures on slow-wave activity.

Mapping slow waves and spikes in chronically instrumented conscious dogs: automated on-line electrogram analysis

Myoelectric recordings from the gastrointestinal (GI) tract in conscious animals have been limited in duration and site. Recently, we have implanted 24 electrodes and obtained electrograms from these sites simultaneously (200 Hz sampling rate; 1.1 MB/min data stream). An automated electrogram analysis was developed to process this large amount of data. Myoelectrical recordings from the GI tract often consist of slow wave deflections followed by one or more action potentials (=spike deflections) in the same traces. To analyze these signals, a first module separates the signal into one containing only slow waves and a second one containing only spikes. The timings of these waveforms were then detected, in real time, for all 24 electrograms, in a separate slow wave detection module and a separate spike-detection module. Basic statistics such as timing and amplitudes and the number of spikes per slow wave were performed and displayed on-line. In summary, with this online analysis, it is possible to study for long periods of time and under various experimental conditions major components of gastrointestinal motility.

Patterns of electrical propagation in the intact pregnant guinea pig uterus

Previous studies have reported on propagation of individual spikes in isolated segments of the pregnant uterus, but there is no information on patterns of spike propagation in the intact organ. There is also no information on propagation of myometrial burst. The aim of this study was to record, at high resolution, patterns of propagation of electrical activities in the pregnant uterus. Sixteen timed-pregnant guinea pigs were euthanized at term, and their uteruses isolated. Fetuses were removed and replaced by an equal amount of Tyrode. A 240-electrode array was positioned at various locations along the organ, all signals were recorded simultaneously, and the electrical propagations were reconstructed. In the intact pregnant uterus at term, spikes propagated with high velocity in longitudinal (6.8 +/- 2.4 cm/s) and slower velocity in circular direction (2.8 +/- 1.0 cm/s; P < 0.01). Direction of propagation and frequency of activity were highly variable but showed similar patterns at the ovary or cervical end and along the anterior, posterior, and antimesometrial borders. Along mesometrium, spike propagation was sparse and fractionated. Migration of burst (0.6 +/- 0.4 cm/s) was significantly much slower than that of individual spikes (P < 0.001). Initial burst activity was located at variable locations along the ovarial end of the antimesometrial border, while the latest excitation occurred at the cervical end (1.2 +/- 0.9 min). In conclusion, high resolution electrical mapping of the intact pregnant uterus reveals fundamental properties in spatial and temporal patterns of spike and burst propagation that determine the contraction of the organ.

Spontaneous electrical activity in sheep mesenteric lymphatics

BACKGROUND

It has recently become apparent that the lymph pump is an electrical entity that rivals the heart in complexity. Many interesting currents have been demonstrated by voltage clamping isolated lymphatic smooth muscle cells, but until now the role of these currents in the intact syncitium has not been studied.

METHODS AND RESULTS

Intracellular microelectrode recordings were made from smooth muscle of sheep mesenteric lymphatics to investigate the electrophysiological basis of lymphatic pumping. Approximately 50% of the vessels exhibited spontaneous electrical activity, varying from regular oscillations in membrane potential to spike complexes. Spike complexes generally consisted of one or more action potentials superimposed on a slower depolarization or 'plateau' phase and were often preceded by a slow diastolic depolarization or 'pre-potential'. Norepinephrine (5 microM) induced depolarizing events in quiescent preparations. Both agonist-induced oscillations and spike complexes were attenuated or completely abolished by 2-aminoethoxydiphenyl borate (2-APB); 10-100 microM). Cesium (1 mM) reduced the frequency of spontaneous firing by approximately 30% by flattening the pre-potential phase. In addition to having a negative inotropic effect, 10 mM Cs(+) also caused gradual membrane depolarization and prolonged the plateau. 1 microM nifedipine abolished spontaneous events while tetrodotoxin (TTX; 0.5-1 muM) decreased the amplitude and maximum dV/dt of the spike upstroke or stopped activity completely. Spontaneously active segments of lymphatic vessel were inhibited by the chloride channel blocker, anthracene-9-carboxylic acid (9-AC; 250 microM - 1 mM) suggesting that I(Cl(Ca)) plays a significant role in the generation of spontaneous activity in this tissue. Penitrem-A (0.1 microM) did not affect resting membrane potential but increased action potential amplitude and prolonged the plateau, suggesting that calcium-activated potassium current does not make a significant contribution to resting membrane conductance but is important in membrane repolarization following calcium influx during the action potential. In contrast 4-aminopyridine (4-AP; 5 microM) caused significant membrane depolarization, suggesting the existence of an active 4-AP-sensitive current at rest.

CONCLUSIONS

These results demonstrate that the currents found in isolated voltage-clamped cells from sheep mesenteric lymphatics do play a significant role in the shaping of spontaneous electrical activity of the intact syncitium.

Postprandial transduodenal bolus transport is regulated by complex peristaltic sequence

AIM: To study the relationship between the patterns of postprandial peristalsis and transduodenal bolus transport in healthy subjects.

METHODS: Synchronous recording of chyme transport and peristaltic activity was performed during the fasting state and after administration of a test meal using a special catheter device with cascade configuration of impedance electrodes and solid-state pressure transducers. The catheter was placed into the duodenum, where the first channel was located in the first part of the duodenum and the last channel at the duodenojejunal junction. After identification of previously defined chyme transport patterns the associated peristaltic patterns were analyzed.

RESULTS: The interdigestive phase 3 complex was reliably recorded with both techniques. Of 497 analyzed impedance bolus transport events, 110 (22%) were short-spanned propulsive, 307 (62%) long-spanned propulsive, 70 (14%) complex propulsive, and 10 (2%) retrograde transport. Short-spanned chyme transports were predominantly associated with stationary or propagated contractions propagated over short distance. Long-spanned and complex chyme transports were predominantly associated with propulsive peristaltic patterns, which were frequently complex and comprised multiple contractions. Propagated double wave contraction, propagated contraction with a clustered contraction, and propagated cluster of contractions have been identified to be an integralted part of a peristaltic sequence in human duodenum.

CONCLUSION: Combined impedancometry and manometry improves the analysis of the peristaltic patterns that are associated with postprandial transduodenal chyme transport. Postprandial transduodenal bolus transport is regulated by propulsive peristaltic patterns, which are frequently complex but well organized. This finding should be taken into consideration in the analysis of intestinal motility studies.

Modelling slow wave activity in the small intestine

We have developed an anatomically based model to simulate slow wave activity in the small intestine. Geometric data for the human small intestine were obtained from the Visible Human project. These data were used to create a one-dimensional finite element mesh of the entire small intestine using an iterative fitting procedure. The electrically active components of the intestinal walls were modelled using a modified Fitzhugh-Nagumo cell model embedded within a longitudinal smooth muscle layer and a layer containing Interstitial Cells of Cajal. Within these layers, the monodomain equation was used to describe slow wave propagation. To solve the monodomain equation, a high-resolution finite difference grid, with an average spatial resolution of 0.95 mm, was embedded within each finite element. The resulting simulations of intestinal activity agree with the experimental observation that slow wave frequency gradually declines from 12 cycles per minute (cpm) in the duodenum to 8 cpm at the terminal ileum. Furthermore, the simulations demonstrated a decrease in conduction velocity with distance along the small intestine (10.7 cm/s in the duodenum, 5.1cm/s in the jejunum and 1.4 cm/s in the ileum), matching experimental recordings from the canine small intestine. We conclude that the framework presented here is capable of qualitatively simulating normal slow wave activity in an anatomical model of the small intestine.

Mapping slow waves and spikes in chronically instrumented conscious dogs: implantation techniques and recordings

Myoelectric recordings from the intestines in conscious animals have been limited to a few electrode sites with relatively large inter-electrode distances. The aim of this project was to increase the number of recording sites to allow high-resolution reconstruction of the propagation of myoelectrical signals. Sets of six unipolar electrodes, positioned in a 3x2 array, were constructed. A silver ring close to each set served as the reference electrodes. Inter-electrode distances varied from 4 to 8 mm. Electrode sets, to a maximum of 4, were implanted in various configurations allowing recording from 24 sites simultaneously. Four sets of 6 electrodes each were implanted successfully in 11 female Beagles. Implantation sites evaluated were the upper small intestine (n=10), the lower small intestine (n=4) and the stomach (n=3). The implants remained functional for 7.2 months (median; range 1.4-27.3 months). Recorded signals showed slow waves at regular intervals and spike potentials. In addition, when the sets were positioned close together, it was possible to re-construct the propagation of individual slow waves, to determine their direction of propagation and to calculate their propagation velocity. No signs or symptoms of interference with normal GI-function were observed in the tested animals. With this approach, it is possible to implant 24 extracellular electrodes on the serosal surface of the intestines without interfering with its normal physiology. This approach makes it possible to study the electrical activities of the GI system at high resolution in vivo in the conscious animal.

Spatial and temporal mapping of pacemaker activity in interstitial cells of Cajal in mouse ileum in situ

Spontaneous electrical pacemaker activity occurs in tunica muscularis of the gastrointestinal tract and drives phasic contractions. Interstitial cells of Cajal (ICC) are the pacemaker cells that generate and propagate electrical slow waves. We used Ca(2+) imaging to visualize spontaneous rhythmicity in ICC in the myenteric region (ICC-MY) of the murine small intestine. ICC-MY, verified by colabeling with Kit antibody, displayed regular Ca(2+) transients that occurred after electrical slow waves. ICC-MY formed networks, and Ca(2+) transient wave fronts propagated through the ICC-MY networks at approximately 2 mm/s and activated attached longitudinal muscle fibers. Nicardipine blocked Ca(2+) transients in LM but had no visible effect on the transients in ICC-MY. beta-Glycyrrhetinic acid reduced the coherence of propagation, causing single cells to pace independently. Thus, virtually all ICC-MYs are spontaneously active, but normal activity is organized into propagating wave fronts. Inhibitors of dihydropyridine-resistant Ca(2+) entry (Ni(2+) and mibefradil) and elevated external K(+) reduced the coherence and velocity of propagation, eventually blocking all activity. The mitochondrial uncouplers, FCCP, and antimycin and the inositol 1,4,5-trisphosphate receptor-inhibitory drug, 2-aminoethoxydiphenyl borate, abolished rhythmic Ca(2+) transients in ICC-MY. These data show that global Ca(2+) transients in ICC-MYs are a reporter of electrical slow waves in gastrointestinal muscles. Imaging of ICC networks provides a unique multicellular view of pacemaker activity. The activity of ICC-MY is driven by intracellular Ca(2+) handling mechanisms and entrained by voltage-dependent Ca(2+) entry and coupling of cells via gap junctions.

Small intestinal motility

PURPOSE OF REVIEW

In the past year, many studies were published in which new and relevant information on small intestinal motility in humans and laboratory animals was obtained.

RECENT FINDINGS

Although the reported findings are heterogeneous, some themes appear to be particularly interesting and novel. Among these is the association between disordered small intestinal motility and bacterial overgrowth of the small intestine. Studies in patients with portal hypertension, in patients with chronic renal failure, and in a rat model of experimental acute pancreatitis all point in the same direction. Another topic of particular interest is the relation between duodenal motility and glucose absorption; propagated duodenal pressure wave sequences are positively related to glucose absorption. Finally, many studies addressed the mechanisms involved in the regulation of interdigestive and postprandial small intestinal motility. These confirmed the key role of cholecystokinin and provided new information on the role of orexin A and leptin.

SUMMARY

The new information on intestinal motility gathered in the past year provides a greater insight in the pathophysiology of a number of diseases and will stimulate further studies in laboratory animals and in human subjects.