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 sp ectral frequencies on the abdominal surface or scalp. This paper compares t he pre-operative control isopower EGG maps with those of total gastrectomy or total colectomy. EGGs were recorded simultaneously at 27 locations on the epigastro-abdomina l surface. Spectral analysis by the maximal entropy method (MEM) was perfor med and the ensemble means of pre-prandial and post-prandial spectra were c alculated. The spectral frequencies were arbitrarily classified into five g roups, 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 p eaks in each spectral group, and electrode locations which were expressed b y x-y coordinates were the indicators for making the isopower EGG maps by u sing a contour map program. Thereafter, the maximal power spots or foci in each spectral group were determined. The pre-operative maximal power foci o f the 1, 8 and 10 cpm groups were distributed rather evenly on the epigastr o-abdominal surface. Those of the 3 and 6 cpm groups, mainly concentrated i n the epigastric region, were absent in almost all patients who had undergo ne total gastrectomy. The infra-umbilical foci of the 3 and 6 cpm groups co mpletely 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 ep igastric 3 cpm foci, the gastric actvities. The pre-operative maximal power of the 3 cpm foci decreased significantly after total or sub-total gastrec tomy.