High-Density Multichannel Electrode Array Improves the Accuracy of Cutaneous Electrogastrography Across Subjects With Wide-Ranging BMI

Abstract

Introduction: The cutaneous electrogastrogram (EGG) is a noninvasive technique for measuring gastric myoelectric activity. The size, position and shape of the stomach vary considerably depending on body mass index, fed/fasting state and age (Lamart et al, 2013). In this study, we assessed how the placement of EGG electrodes can influence the ability to detect normal gastric slow waves. Methods: Eleven asymptomatic subjects (8M/3F, age 21—77 years) with an average BMI of 26 (range 21.8—36.3) were enrolled. Subjects were excluded if they had any active foregut symptoms on the PAGI—SYM questionnaire. We placed 100 EGG electrodes in a uniform 10x10 grid (2cm x 2cm spacing) on the abdominal wall extending inferiorly from the sternum at the top with reference and ground electrodes on the subject's right side. The locations of the umbilicus and xiphoid relative to the array were documented as anatomical references. After 30 minutes of fasting recording, each subject consumed a standardized meal and the study was continued for 90 minutes. The signal—to—noise ratio (SNR) for each electrode pair was calculated, defined as the average power between 0.04 Hz and 0.06 Hz divided by the average power in all other frequencies between 0.02 Hz and 0.20 Hz. We calculated the percentage of normal gastric slow waves, i.e., 2—4 cpm activity. The results from the highest SNR electrode pair were compared to those from the traditional single—channel EGG placement: one electrode halfway between the xiphoid and umbilicus and the second electrode placed 4—6 cm to the subject's left. Results: Using the highest SNR electrode pair, the percentage of normal slow waves was 92 ± 8%, and all 11 subjects were over the 70% threshold that defines normal. When using the traditional EGG electrode placement, however, this value dropped significantly to 68 ± 16%, and 6/11 subjects fell below 70% (see Table 1; Figure 1). Statistical significance of p = 4.4 x 10—5 was determined by a two—sided t—test for the null hypothesis that the two related samples have identical average values. This effect was particularly pronounced for the high BMI subjects.1235_A Figure 1. Improved detection of gastric slow wave frequency with a high—density EGG array versus traditional lead placement.Conclusion: Standardization of cutaneous lead placement for EGG may be confounded by anatomical variability in stomach location coupled with an increased sensitivity to lead placement due to low signal amplitude. The results from this study suggest that multiple electrodes or a priori stomach localization can improve accurate detection of the gastric slow wave.1235_B Figure 2. Determination of normal gastric slow wave based on traditional EGG location versus highest EGG SNR location with a high density array.