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

Abstract

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...

Influence of body parameters on gastric bioelectric and biomagnetic fields in a realistic volume conductor

“…These sensors are coupled to SQUIDs which convert the incident magnetic flux to a voltage that can be digitized and recorded. MGGs have been used to examine uncoupling and the effects of elevated glucose in the gastric slow wave (Bradshaw et al 2003, 2007, 2009). Recent studies from our group have used surface current density (SCD) methods to localize the underlying sources and attempt to calculate propagation direction and velocities from magnetic fields (Bradshaw et al 2009b, Kim et al 2010).…”

Effects of volume conductor and source configuration on simulated magnetogastrograms

“…It is important to accurately measure and simulate MFs generated from GEA as they are known to be weak in nature (Allescher et al 1998, Bradshaw et al 2007, 2009, Richards et al 1996, Saijyo et al 1995). In addition, only the MFs in the direction normal to the coronal plane are typically measured experimentally, and the simulation results have shown that the MFs in this direction are generally much smaller than those in the other two directions (Komuro et al 2008).…”

Noninvasive Biomagnetic Detection of Isolated Ischemic Bowel Segments

“…Correlation between the magnetic and electrical frequencies was determined by calculating the correlation coefficient ( r) value. In addition, we determined the percentage of power distributed (PPD) in the power spectra in frequency ranges defined as bradyenteric (lower than two standard deviations from the mean baseline enteric frequency determined by serosal and magnetic recordings) and tachyenteric (higher than two standard deviations from the mean baseline enteric frequency) [24]. …”