Isopower mapping of the electrogastrogram (EGG)

Electrogastrograms (EGGs) were recorded simultaneously at 14 locations of the epigastric abdominal surface of the human. EGGs were spectrally analyzed by the maximal entropy method (MEM). Spectral frequencies were classified into five groups: I cycle per minute (cpm) (-2.4 cpm), 3 (2.5-4.9), 6 (5.0-7.4), 8 (7.5-9.9), and 10 (10.0-12.9). The maximal power peak (Z(i)) in each spectral group at a certain electrode location (X(i), Y-i) was used as a representative (Z(i) = [X(i), Y-i]). Horizontal line through the symphysis pubis was designated Y, and a line along the right thoraco-abdominal border was designated X,. Thereafter, the usual geographic contour map program was used, and the isopower EGGs were determined and the maximal power spots were obtained for five spectral groups. The maximal power spots or foci for the 1 cpm group distributed evenly over the supra- and infraumbilical areas on a retouched and superimposed map. The distribution of the 3 cpm group spots was restricted mainly to the epigastric area. The epigastric 3 cpm spots may reflect the gastric electrical activity because of their location. The distribution of the 6 cpm group spots was essentially similar to that of the 3 cpm group. The spots of the 8 and 10 cpm groups were evenly distributed over the abdominal surface, similar to that of 1 cpm group. The infraumbilical 3 and 6 cpm spots may reflect colonic activity.