Biomagnetic detection of gastric electrical activity in normal and vagotomized rabbits

Bradshaw, Leonard A.; Myers, Andrew G.; Redmond, A. M.; Wikswo, John P.; Richards, W.O.

doi:10.1046/j.1365-2982.2003.00432.x

Cited by 16 publications

(15 citation statements)

References 19 publications

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“…While an overall decrease in the slow wave frequency might suggest bradygastria, the additional changes we observed in the PPD, with signal power shifting into both brady-and tachygastric frequency ranges, suggest that glucagon induces more complicated rhythm disturbances in the gastric syncytium that could involve uncoupling, ectopic pacemakers, conduction pathway blocks, and/or reentry loops, similar to effects observed in diseased myocardium. We have observed similar PPD effects in mechanically uncoupled gastric tissue (2,29) and in vagotomized rabbits (6).…”

Section: Discussionsupporting

confidence: 68%

Noninvasive assessment of the effects of glucagon on the gastric slow wave

Bradshaw¹,

Sims²,

Richards³

2007

American Journal of Physiology-Gastrointestinal and Liver Physi

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Bradshaw LA, Sims JA, Richards WO. Noninvasive assessment of the effects of glucagon on the gastric slow wave. Am J Physiol Gastrointest Liver Physiol 293: G1029-G1038, 2007. First published September 20, 2007; doi:10.1152/ajpgi.00054.2007.-Hyperglycemic effects on the gastric slow wave are not well understood, and no studies have examined the effects that hyperglycemia has on gastric slow wave magnetic fields. We recorded multichannel magnetogastrograms (MGGs) before and after intravenous administration of glucagon and subsequent modest hyperglycemia in 20 normal volunteers. Normal slow waves were evident in baseline MGG recordings from all 20 subjects, but within 15 min after glucagon had been given, we noted significant effects on MGG signals. In addition to an overall decrease in the slow wave frequency from 2.9 Ϯ 0.5 cycles per min (cpm) to 2.2 Ϯ 0.1 cpm (P Ͻ 0.05), we observed significant changes in the number and range of spectral peaks recorded. Furthermore, the propagation velocity determined from surface current density maps computed from the multichannel MGG decreased significantly (7.1 Ϯ 0.8 mm/s to 5.0 Ϯ 0.3 mm/s, P Ͻ 0.05). This is the first study of biomagnetic effects of hyperglycemia in normal subjects. Our results suggest that the analysis of the MGG provides parameter quantification for gastric electrical activity specific to and characteristic of slow wave abnormalities associated with increased serum glucose by injection of glucagon.magnetogastrogram; biomagnetism; electrogastrogram; hyperglycemia HYPERGLYCEMIA ALTERS THE ELECTRICAL slow wave of the stomach (14), and previous electrogastrogram (EGG) studies have demonstrated an increase in gastric slow wave frequency in response to glycemic overload (14, 18). These effects are pronounced in patients with diabetes mellitus, where recent evidence suggests that depletion of interstitial cells of Cajal is associated with this disease (23,28). Interstitial cells of Cajal are the progenitors and propagators of gastrointestinal (GI) slow waves, and their absence is associated with disruptions in gastric and intestinal electrical activities (27,33).Although the EGG is generally capable of describing the frequency dynamics of the gastric slow wave, its sensitivity to the electrical conductivity profile of the abdomen complicates the routine analysis of other clinically relevant parameters such as amplitude and propagation velocity (7,25). The magnetic fields generated by gastric slow wave currents are less influenced by these conductivity differences. As a result, the magnetogastrogram (MGG) allows assessment of gastric slow wave frequency as well as amplitude, propagation velocity, and other relevant spatiotemporal parameters (3,5).Given the ability of the MGG to accurately characterize the gastric slow wave, we hypothesized that MGG recordings would reflect slow wave changes caused by a modest degree of hyperglycemia in normal human subjects. MATERIALS AND METHODSThis study was reviewed and approved by Vanderbilt University's Institutional Review B...

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Section: Discussionsupporting

confidence: 68%

Noninvasive assessment of the effects of glucagon on the gastric slow wave

Bradshaw¹,

Sims²,

Richards³

2007

American Journal of Physiology-Gastrointestinal and Liver Physi

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“…By projecting the magnetic field vector into different directions, we can focus on a particular feature of the signal or a particular signal frequency. We also showed that a single vector magnetometer was capable of reproducing electrical activity recorded by a 24-channel serosal electrode array with excellent fidelity [18]. Moreover, the magnetic field vector projection correlates to the direction of propagation of electrical activity the magnetic field is perpendicular to the direction of current.…”

Section: Biomagnetic Techniques To Assess Normal Geamentioning

confidence: 82%

“…Thus, the vector projection provides a substantial increase in the signal-tonoise ratio and aids in the discrimination of signals from multiple bowel sources. In another study, a single vector magnetometer produced projections that correlated highly with 24 gastric serosal electrodes and reflected spatiotemporal signal changes that occurred following a vagotomy [18]. This observation strongly suggests that additional information is available in the full vector recording of the gastrointestinal magnetic field as opposed to that available in any single component.…”

Section: Biomagnetic Techniques To Assess Gea Dysrhythmiasmentioning

confidence: 94%

Biomagnetic Techniques for Assessing Gastric and Small Bowel Electrical Activity

Bradshaw¹

2004

AIP Conference Proceedings

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Recent advances in electrophysiology of the gastrointestinal tract have emphasized the need for methods of noninvasive assessment of gastric and small intestinal electrical activity (GEA and IE A). While the cutaneous electrogastrogram (EGG) may reveal the frequency dynamics of gastric electrical activity, other parameters important for characterizing the propagating electrical activity are not available from EGG recordings. Recent studies on the electroenterogram (EENG) are promising, but low-conductivity abdominal layers have complicated the identification of small intestinal electrical rhythms in cutaneous recordings. The magnetogastrogram (MGG) and magnetoenterogram (MENG) are able to characterize gastric and intestinal electrical activity noninvasively in terms of its frequency, power and characteristics of its propagation. Superconducting QUantum Interference Device (SQUID) magnetometers are used to detect the minute magnetic fields associated with electrical activity of the gastrointestinal syncytium formed by interstitial cells of Cajal and smooth muscle networks. Changes in GEA and IEA that occur in response to disease or abnormal conditions are reflected in MGG and MENG signals. Magnetic methods for assessing the electrical activity of the stomach and small bowel thus show great clinical promise. GASTROINTESTINAL ELECTRICAL ACTIVITYExtracellular electrode recordings in the stomach and small bowel exhibit spontaneous, omnipresent rhythmic variation that depends on the location of the electrode. The slow wave, also known as electrical control activity or basic electrical rhythm, is present regardless of the contractile status of the tissue and modulates the appearance of smooth muscle contractions. Recently, the interstitial cells of Cajal (ICCs) located within the gastrointestinal musculature have been implicated as the originators and propagators of the slow wave [1][2][3][4][5][6]. ICC cells are connected by gap junctions to smooth muscle cells in the longitudinal and circular muscle layers, and the electrical activity propagates passively through these layers.In the stomach, the slow wave originates at a location along the greater curvature and propagates nearly instantaneously around the circumference of the stomach. The slow wave then spreads aborally as a ring of depolarization at a velocity of about 11 mm/s in humans. The stomach's pacemaker generates a new slow wave as the previous one is terminating in the pylorus [7] at a frequency of about 3 cycles per minute (cpm).

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“…Previous studies showed that the magnetogastrogram records signals with the same waveshape and frequency as slow waves recorded with internal serosal electrodes [15, 16]. In addition, studies show that slow wave propagation can be detected with multichannel magnetometers [17], and magnetogastrograms (MGG) propagation characteristics are altered in disease and by both mechanical and pharmacological uncoupling [18, 19]. …”

Section: Introductionmentioning

confidence: 99%

Characterization of Electrophysiological Propagation by Multichannel Sensors

Bradshaw

Kim

Somarajan

et al. 2016

IEEE Trans. Biomed. Eng.

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Objective The propagation of electrophysiological activity measured by multichannel devices could have significant clinical implications. Gastric slow waves normally propagate along longitudinal paths that are evident in recordings of serosal potentials and transcutaneous magnetic fields. We employed a realistic model of gastric slow wave activity to simulate the transabdominal magnetogastrogram (MGG) recorded in a multichannel biomagnetometer and to determine characteristics of electrophysiological propagation from MGG measurements. Methods Using MGG simulations of slow wave sources in a realistic abdomen (both superficial and deep sources) and in a horizontally-layered volume conductor, we compared two analytic methods (Second Order Blind Identification, SOBI and Surface Current Density, SCD) that allow quantitative characterization of slow wave propagation. We also evaluated the performance of the methods with simulated experimental noise. The methods were also validated in an experimental animal model. Results Mean square errors in position estimates were within 2 cm of the correct position, and average propagation velocities within 2 mm/s of the actual velocities. SOBI propagation analysis outperformed the SCD method for dipoles in the superficial and horizontal layer models with and without additive noise. The SCD method gave better estimates for deep sources, but did not handle additive noise as well as SOBI. Conclusion SOBI-MGG and SCD-MGG were used to quantify slow wave propagation in a realistic abdomen model of gastric electrical activity. Significance These methods could be generalized to any propagating electrophysiological activity detected by multichannel sensor arrays.

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Biomagnetic detection of gastric electrical activity in normal and vagotomized rabbits

Cited by 16 publications

References 19 publications

Noninvasive assessment of the effects of glucagon on the gastric slow wave

Noninvasive assessment of the effects of glucagon on the gastric slow wave

Biomagnetic Techniques for Assessing Gastric and Small Bowel Electrical Activity

Characterization of Electrophysiological Propagation by Multichannel Sensors

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