Biomagnetic characterization of spatiotemporal parameters of the gastric slow wave

Abstract

Certain gastric disorders affect spatiotemporal parameters of the gastric slow wave. Whereas the electrogastrogram (EGG) evaluates electric potentials to determine primarily temporal parameters, fundamental physical limitations imposed by the volume conduction properties of the abdomen suggest the evaluation of gastric magnetic fields. We used a multichannel superconducting quantum interference device magnetometer to study the magnetogastrogram (MGG) in 20 normal human subjects before and after a test meal. We computed the frequency and amplitude parameters of the gastric slow wave from MGG. We identified normal gastric slow wave activity with a frequency of 2.6 ± 0.5 cycles per minute (cpm) preprandial and 2.8 ± 0.3 cpm postprandial. In addition to frequency and amplitude, the use of surface current density mapping applied to the multichannel MGG allowed us to visualize the propagating slow wave and compute its propagation velocity (6.6 ± 1.0 mm s )1 preprandial and 7.4 ± 0.4 mm s )1 postprandial). Whereas MGG and EGG signals exhibited strong correlation, there was very little correlation between the MGG and manometry. The MGG not only records frequency dynamics of the gastric slow wave, but also characterizes gastric propagation. The MGG primarily reflects the underlying gastric electrical activity, but not its mechanical activity.

Comparison and Analysis of Inter-Subject Variability of Simulated Magnetic Activity Generated from Gastric Electrical Activity

“…Names and locations of the channels for the SQUID used at Vanderbilt University. 4 The channels labeled 5, 17, 18, 26, and 33 are capable of recording all three components of the magnetic field, whereas the other channels record only the y component of the magnetic field. Anatomically realistic models of three subjects.…”

“…8 First, multiple temporally and spatially varying dipoles were calculated during the GEA simulation. The equivalent dipole sources are calculated from: (4) The dipole sources were then used to compute the magnetic fields that corresponds to the locations of the SQUID channels presented in Bradshaw et al 4 and utilized to record MGGs at Vanderbilt University. The three principal directions of the coordinate system used herein are subject's right-to-left (x), front-to-back (y), and bottom-to-top (z) of the torso (Fig.…”

“…It has been shown that magnetic activity generated from GEA can be reliably recorded by a Superconducting Quantum Interference Device (SQUID). 4,18,19 During a recording, the SQUID does not directly contact the subject, and the results are considered to be more reliable than electrical recordings made with cutaneous electrodes.…”

“…For these subjects, the importance of the activity in the other directions is, however, unknown. The SQUID described in Bradshaw et al, 4 the most frequently used SQUID for magnetic recordings of GEA, has channels at nineteen different locations. At five of the positions the SQUID is able to measure a three-component vector field, while only a single component can be measured at the remaining 14 positions.…”

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

“…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. …”