Biomagnetic signatures of uncoupled gastric musculature

Abstract

Gastric slow waves propagate in the electrical syncytium of the healthy stomach, being generated at a rate of approximately three times per minute in a pacemaker region along the greater curvature of the antrum and propagating distally towards the pylorus. Disease states are known to alter the normal gastric slow wave. Recent studies have suggested the use of biomagnetic techniques for assessing parameters of the gastric slow wave that have potential diagnostic significance. We present a study in which the gastric syncytium was uncoupled by mechanical division as we recorded serosal electric potentials along with multichannel biomagnetic signals and cutaneous potentials. By computing the surface current density (SCD) from multichannel biomagnetic recordings, we were able to quantify gastric slow wave propagation as well as the frequency and amplitude of the slow wave and to show that these correlate well with similar parameters from serosal electrodes. We found the dominant slow wave frequency to be an unreliable indicator of gastric uncoupling as uncoupling results in the appearance of multiple slow wave sources at various frequencies in external recordings. The percentage of power distributed in specific frequency ranges exhibited significant postdivision changes. Propagation velocity determined from SCD maps was a weak indicator of uncoupling in this work; we believe that the relatively low spatial resolution of our 19-channel biomagnetometer confounds the characterization of spatial variations in slow wave propagation velocities. Nonetheless, the biomagnetic technique represents a non-invasive method for accurate determination of clinically significant parameters of the gastric slow wave.

Figure 1

Experimental setup illustrating approximate relative position of SQUID sensors and serosal electrodes. SQUID sensors are indicated by circles with vector sensors containing xs. Serosal electrode bipolar pairs have a baseline of 5 mm with a separation of 2 cm. The stomach was mechanically uncoupled by surgical division in the antrum at the approximate location of the indiciated dashed line.

Figure 2

Recordings (A) before and (B) after gastric division in (i) raw and (ii) filtered serosal electrodes and in (i) the multichannel SQUID magnetometer. Recordings from four sequential electrodes demonstrate propagation of spiking activity in unfiltered data (i). In panel (Aii) and (Bii) the spiking activity has been filtered to show only slow waves. Magnetogastrogram signals are mapped to the spatial location of the sensors (Aiii) before and (Biii) after gastric division.

Figure 3

Simultaneous MGG (A and D), serosal EMG (B and E) and EGG (C and F) signals and power spectra obtained during suspension of respiration before (A–C) and after (D–F) gastric division.

Figure 4

Magnetogastrogram signals (A) and AR power spectra (B) recorded during baseline for each of the nine subjects. The dominant gastric slow wave frequency was identified from the power spectra.

Figure 5

Surface current density maps computed over 60 s of data. (A) Predivision SCD reveals a propagation pattern from the subject's left to right across the sensor array. The pattern repeats approximately every 15 s. (B) Postdivision, the pattern retains a periodicity of about 18 s, but the left-right propagation is not evident. The location of the SCD maxima as a function of time is shown below each set of SCD maps. Propagation velocity may be computed from these plots.

Figure 6

(A) The average frequency and (B) the average number of spectral peaks from MGG, serosal EMG and EGG data before (solid) and after (shaded) gastric uncoupling. Although the distal serosal EMG recorded a significant decrease in postdivision dominant frequencies, no decrease was noted in MGG, EGG or the proximal serosal electrodes. However, there was a significant increase in the number of spectral peaks recorded postdivision in the MGG. This finding suggests that MGG records multiple frequencies present during uncoupling.