Isopower maps of the electrogastrogram (EGG) after total gastrectomy or total colectomy.

Isopower or topographic electrogastrograms (EGG) correspond to topographic electroencephalograms. Both project the topographic localizations of the spectral frequencies on the abdominal surface or scalp. This paper compares the pre-operative control isopower EGG maps with those of total gastrectomy or total colectomy. EGGs were recorded simultaneously at 27 locations on the epigastro-abdominal surface. Spectral analysis by the maximal entropy method (MEM) was performed and the ensemble means of pre-prandial and post-prandial spectra were calculated. The spectral frequencies were arbitrarily classified into five groups, 1 cycle per minute (cpm) (0-2.4 cpm), 3 cpm (2.5-4.9 cpm), 6 cpm (5.0-7.4 cpm), 8 cpm (7.5-9.9 cpm) and 10 cpm (10.0-12.9 cpm). Maximal power peaks in each spectral group, and electrode locations which were expressed by x-y coordinates were the indicators for making the isopower EGG maps by using a contour map program. Thereafter, the maximal power spots or foci in each spectral group were determined. The pre-operative maximal power foci of the 1, 8 and 10 cpm groups were distributed rather evenly on the epigastro-abdominal surface. Those of the 3 and 6 cpm groups, mainly concentrated in the epigastric region, were absent in almost all patients who had undergone total gastrectomy. The infra-umbilical foci of the 3 and 6 cpm groups completely disappeared after total colectomy. The infra-umbilical foci of the 3 and 6 cpm groups (2.5-7.4) may reflect the colonic activities and the epigastric 3 cpm foci, the gastric activities. The pre-operative maximal power of the 3 cpm foci decreased significantly after total or sub-total gastrectomy.