High-Resolution Electrogastrogram: A Novel, Noninvasive Method for Determining Gastric Slow-Wave Direction and Speed

Multi-day, multi-sensor ambulatory monitoring of gastric electrical activity

OBJECTIVE

Bioelectrial signals known as slow waves play a key role in coordinating gastric motility. Slow wave dysrhythmias have been associated with a number of functional motility disorders. However, there have been limited human recordings obtained in the consious state or over an extended period of time. This study aimed to evaluate a robust ambulatory recording platform.

APPROACH

A commercially available multi-sensor recording system (Shimmer3, ShimmerSensing) was applied to acquire slow wave information from the stomach of six humans and four pigs. First, acute experiments were conducted in pigs to verify the accuracy of the recording module by comparing to a standard widely employed electrophysiological mapping system (ActiveTwo, BioSemi). Then, patients with medically refractory gastroparesis undergoing temporary gastric stimulator implantation were enrolled and gastric slow waves were recorded from mucosally-implanted electrodes for 5 d continuously. Accelerometer data was also collected to exclude data segments containing excessive patient motion artefact.

MAIN RESULTS

Slow wave signals and activation times from the Shimmer3 module were closely comparable to a standard electrophysiological mapping system. Slow waves were able to be recorded continuously for 5 d in human subjects. Over the 5 d, slow wave frequency was 2.8  ±  0.6 cpm and amplitude was 0.2  ±  0.3 mV.

SIGNIFICANCE

A commercial multi-sensor recording module was validated for recording electrophysiological slow waves for 5 d, including in ambulatory patients. Multiple modules could be used simultaneously in the future to track the spatio-temporal propagation of slow waves. This framework can now allow for patho-electrophysiological studies to be undertaken to allow symptom correlation with dysrhythmic slow wave events.

Colonic Electromechanical Abnormalities Underlying Post-operative Ileus: A Systematic and Critical Review

Post-operative ileus (POI) is an inevitable consequence of major abdominal surgery, and may be prolonged in up to 30% of patients. Ileus is commonly presumed to result from paralysis of the GI tract, though there is little direct evidence to support this view. The aim of this review is to systematically search and critically review the literature investigating post-operative colonic electrical and mechanical activity. MEDLINE and Embase databases were systematically searched for articles investigating post-operative colonic motor or electrical activity in human patients. Nineteen original articles investigating post-operative colonic motor or electrical activity were identified. Most studies have used low-resolution techniques, with intermittent recordings of colonic motility. Numerous studies have shown that colonic electrical and motor activity does not cease routinely following surgery, but is of abnormal character for 3–6 days following laparotomy. One recent high-resolution manometry study identified hyperactive cyclic motor patterns occurring in the distal colon on the first post-operative day. Low-resolution studies have shown colonic slow waves are not inhibited by surgery, and are present even in the immediate post-operative period. Recovery of normal motility appears to occur in a proximal to distal direction and is temporally correlated with the clinical return of bowel function. No studies have investigated motility specifically in prolonged POI. Future studies should use high-resolution techniques to accurately characterise abnormalities in electrical and mechanical function underlying POI, and correlate these changes with clinical recovery of bowel function.

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.

Noninvasive Magnetogastrography Detects Erythromycin-Induced Effects on the Gastric Slow Wave

OBJECTIVE

The prokinetic action of erythromycin is clinically useful under conditions associated with gastrointestinal hypomotility. Although erythromycin is known to affect the electrogastrogram, no studies have examined the effects that erythromycin has on gastric slow wave magnetic fields.

METHODS

In this study, gastric slow wave activity was assessed simultaneously using noninvasive magnetogastrogram (MGG), electrogastrogram, and mucosal electromyogram recordings. Recordings were obtained for 30 min prior to and 60 min after intravenous administration of erythromycin at dosages of 3 and 6 mg/kg.

RESULTS

MGG recordings showed significant changes in the percentage power distribution of gastric signal after infusion of both 3 and 6 mg/kg erythromycin at t = 1-5 min that persisted for t = 30-40 min after infusion. These changes agree with the changes observed in the electromyogram. We did not observe any statistically significant difference in MGG amplitude before or after injection of either 3 or 6 mg/kg erythromycin. Both 3 and 6 mg/kg erythromycin infusion showed retrograde propagation with a statistically significant decrease in slow wave propagation velocity 11-20 min after infusion. Propagation velocity started returning toward baseline values after approximately 21-30 min for the 3 mg/kg dosage and after 31-40 min for a dosage of 6 mg/kg.

CONCLUSION

Our results showed that the magnetic signatures were sensitive to disruptions in normal slow wave activity induced by pharmacological and prokinetic agents such as erythromycin.

SIGNIFICANCE

This study shows that repeatable noninvasive bio-electro-magnetic techniques can objectively characterize gastric dysrhythmias and may quantify treatment efficacy in patients with functional gastric disorders.

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.

Artifact Rejection Methodology Enables Continuous, Noninvasive Measurement of Gastric Myoelectric Activity in Ambulatory Subjects

The increasing prevalence of functional and motility gastrointestinal (GI) disorders is at odds with bottlenecks in their diagnosis, treatment, and follow-up. Lack of noninvasive approaches means that only specialized centers can perform objective assessment procedures. Abnormal GI muscular activity, which is coordinated by electrical slow-waves, may play a key role in symptoms. As such, the electrogastrogram (EGG), a noninvasive means to continuously monitor gastric electrical activity, can be used to inform diagnoses over broader populations. However, it is seldom used due to technical issues: inconsistent results from single-channel measurements and signal artifacts that make interpretation difficult and limit prolonged monitoring. Here, we overcome these limitations with a wearable multi-channel system and artifact removal signal processing methods. Our approach yields an increase of 0.56 in the mean correlation coefficient between EGG and the clinical "gold standard", gastric manometry, across 11 subjects (p < 0.001). We also demonstrate this system's usage for ambulatory monitoring, which reveals myoelectric dynamics in response to meals akin to gastric emptying patterns and circadian-related oscillations. Our approach is noninvasive, easy to administer, and has promise to widen the scope of populations with GI disorders for which clinicians can screen patients, diagnose disorders, and refine treatments objectively.

A Combined Methodology to Eliminate Artifacts in Multichannel Electrogastrogram Based on Independent Component Analysis and Ensemble Empirical Mode Decomposition

Cutaneous measurements of electrogastrogram (EGG) signals are heavily contaminated by artifacts due to cardiac activity, breathing, motion artifacts, and electrode drifts whose effective elimination remains an open problem. A common methodology is proposed by combining independent component analysis (ICA) and ensemble empirical mode decomposition (EEMD) to denoise gastric slow-wave signals in multichannel EGG data. Sixteen electrodes are fixed over the upper abdomen to measure the EGG signals under three gastric conditions, namely, preprandial, postprandial immediately, and postprandial 2 h after food for three healthy subjects and a subject with a gastric disorder. Instantaneous frequencies of intrinsic mode functions that are obtained by applying the EEMD technique are analyzed to individually identify and remove each of the artifacts. A critical investigation on the proposed ICA-EEMD method reveals its ability to provide a higher attenuation of artifacts and lower distortion than those obtained by the ICA-EMD method and conventional techniques, like bandpass and adaptive filtering. Characteristic changes in the slow-wave frequencies across the three gastric conditions could be determined from the denoised signals for all the cases. The results therefore encourage the use of the EEMD-based technique for denoising gastric signals to be used in clinical practice.

Progress in Mathematical Modeling of Gastrointestinal Slow Wave Abnormalities

Gastrointestinal (GI) motility is regulated in part by electrophysiological events called slow waves, which are generated by the interstitial cells of Cajal (ICC). Slow waves propagate by a process of "entrainment," which occurs over a decreasing gradient of intrinsic frequencies in the antegrade direction across much of the GI tract. Abnormal initiation and conduction of slow waves have been demonstrated in, and linked to, a number of GI motility disorders. A range of mathematical models have been developed to study abnormal slow waves and applied to propose novel methods for non-invasive detection and therapy. This review provides a general outline of GI slow wave abnormalities and their recent classification using multi-electrode (high-resolution) mapping methods, with a particular emphasis on the spatial patterns of these abnormal activities. The recently-developed mathematical models are introduced in order of their biophysical scale from cellular to whole-organ levels. The modeling techniques, main findings from the simulations, and potential future directions arising from notable studies are discussed.

Assessment of slow wave propagation in multichannel electrogastrography by using noise-assisted multivariate empirical mode decomposition and cross-covariance analysis

Electrogastrography (EGG) is a noninvasive technique for recording the myoelectrical activity of the stomach. An electrogastrographic signal recorded by using a four-channel system with electrodes placed on the surface of the skin is a mixture of a low-frequency gastric pacesetter potential known as a slow wave, electrical activity from other organs, and random noise. The aim of this work was to investigate the possibility of detecting the propagation of the gastric slow wave from multichannel EGG data. Noise-assisted multivariate empirical mode decomposition (NA-MEMD) and cross-covariance analysis (CCA) are proposed as new detection tools. NA-MEMD was applied to attenuate the noise and extract the EGG signal from four channels, while CCA was performed to assess the time shift between the EGG signal channels. Validation of the method was performed using synthetic EGG signals and the methodology was tested on four young, healthy adults. After validation, the proposed method was applied for two kinds of human EGG data: 10-min (short) EGG data from the preprandial phase and 90-120-min (long) EGG data from the preprandial phase as well as the postprandial phase. The results obtained for both synthetic and human EGG data confirm that the proposed method could be a useful tool for assessing the propagation of slow waves. The time shift calculation from the preprandial phase of the EGG examination yielded more consistent results than the postprandial phase. The mean value of the slow wave time lag between neighbouring channels for synthetic data was found to be 4.99±0.47 s. In addition, it was confirmed that the proposed method, that is, NA-MEMD and CCA together, are robust to noise.