Computer simulation of the impact of different dimensions of the stomach on the validity of electrogastrograms.
Mintchev MP. Bowes KL.
Department of Surgery, University of Alberta, Edmonton, Canada. email@example.com
The impact of the dimensions of the stomach on cutaneous recordings of gastric electrical activity (GEA) has not been adequately studied. The stomach was represented as a truncated conoid in a spherical coordinate system. The gastric electric field was modelled using a previously described methodology. Electrical potentials were calculated from sets of points simulating standard cutaneous recordings. The frequency of the signals was maintained at 3 cycles min-1 (period of repetition: 20 s), while the velocity of propagation of the depolarisation waves was reduced relative to the reduction in gastric dimensions. The signals were digitally contaminated with a random artificial artefact with a constant amplitude range of 0.2 mV, while the dimensions of the conoid (the circumferential radii and the length of the central axis) were decreased by factors of 1.5, two, four, six and eight. Simulated EGG signals were evaluated quantitatively. Simulated EGG records contaminated with random signals recorded from stomachs with decreasing dimensions exhibited non-linearly increasing standard deviations (p < 0.001). Randomly contaminated EGGs calculated from stomachs with dimensions reduced four, six and eight times were abnormal according to previously established quantitative criteria. Computer modelling indicated that gastric dimensions can significantly influence the validity of EGGs. These findings could be particularly important in a paediatric electrogastrography.
Comparative quantification of gastric electrical activity and electrogastrograms.
Mintchev MP. Bowes KL.
Department of Surgery, University of Alberta, Canada.
The aim of this study was to compare quantitatively the variability of gastric electrical activity (GEA) recorded from asymptomatic patients with implanted serosal electrodes and patients with implanted and cutaneous electrodes. Three pairs of electrodes were inserted into the gastric wall in six patients undergoing laparotomy for other reasons. Normal GEA was assessed visually once patients were tolerating a normal diet. Mean frequency (MF) values of the GEA signal in successive 256 s intervals were obtained. Standard deviations of the MF values for each separate channel of each patient were calculated. Probability density functions (pdfs) of these values were also obtained and compared. 36 1 h simultaneous recordings were made for three patients with implanted and cutaneous electrodes. The recordings were assessed both visually and with computer. A fast Hartley transform was used to obtain the dominant MF values in 256 s time intervals. These values were statistically evaluated for each channel. Normal internal GEA had a mean frequency of 2.5-3.75 cycles min-1 (cpm) and a standard deviation range of 0-0.45 cpm. Bell-shaped pdfs with coinciding maxima were observed in all these recordings, indicating normal electrical coupling. In the comparative 36 h study, using the above definitions of normality, different cutaneous recordings were found to reflect GEA with a sensitivity of 94% and a specificity of 79%.