Chin Med J (Taipei) 1998;61:S89.

Electrogastrography: Measurement, Analysis and Applications

Jiande Chen, Ph.D.

Lynn Institute for Healthcare Research, Oklahoma City, Oklahoma USA

Abstract

The electrogastrogram is a non-invasive measurement of gastric myoelectrical activity by placing electrodes in the epigastric area of the abdomen. Single or multiple channel EGG recordings may be made based on applications. The electrodes should be placed as close to the stomach as possible and the abdominal skin must be well prepared to reduce the impedance. A number of previous studies have validated the non-invasive technique using intralurninal or serosal electrodes. It is known that the three cycles per min (cpm) waves measured in the EGG is of gastric origin. The dominant frequency of the EGG is the same as that of the gastric slow wave measured from the serosal electrodes. The variation of the slow wave frequency is also reflected in the EGG. Unlike the internal recording, however, the EGG contains not only the gastric signal but various interferences and artifacts, such as respiratory and motion artifacts and electrical interferences from the heart and small bowel. Accordingly, adequate data analysis methods should be applied to extract useful and clinically or physiologically relevant parameters from the EGG. Fortunately, the frequency of the gastric signal (0.5-9.0cpm) is different from that of the respirator artifact and interferences from the heart and small bowel. Therefore, spectral analysis has become a well-accepted standard for the analysis of the EGG. The smoothed power spectral analysis method is used to compute the dominant frequency and power (or amplitude) of the EGG. The running (minute-by-minute) spectral analysis is applied to calculate the percentages of normal gastric slow waves and dysrhythmias as well as the minute-by-minute variation of the slow wave frequency.

Although the EGG is a measurement of the gastric slow wave, its correlation with gastric motility has been investigated. In healthy subjects, the dominant frequency of the EGG is the same as the maximum frequency of the gastric contractions. The relative change of the EGG amplitude reflects the contractivity of the stomach. The power (or amplitude) of the EGG at 3 cpm is significantly higher during gastric contractions than that during motor quiescence. However, there is no one-to-one correlation between the EGG and the mamometric recording. The correlation between the EGG and gastric emptying has also been investigated. Some investigators reported a significant negative correlation between the gastric retention and the percentage of normal slow waves and between the gastric retention and the relative postprandial EGG amplitude. However, cautions should be made in studying the correlation of the EGG with gastric emptying due to the fact that gastric emptying also involves the pylorus and small intestine which are not associated with the EGG at all. It may be more conceivable in stating that the EGG and gastric scintigraphy are complimentary for the assessment of gastric emptying, and that the abnormal EGG may be predictive of delayed gastric emptying.

The EGG can be used to study the electrophysiology of the stomach in-vivo and pathophysiology of gastric motility disorders. This is because the EGG is an accurate measurement of the gastric slow wave and the gastric slow wave regulates gastric motility. Studies have been performed to investigate the effects of various gastrointestinal hormones, and prokinetic and pharmacological agents on the gastric slow wave. Gastric dysrhythmias in the EGG have been recorded in patients with functional dyspepsia, gastroparesis, unexplained nausea and vomiting, motion sickness, early pregnancy and etc. Some of the recent studies include the EGG in childhood and diabetic patients. In conclusion, electrogastrography is an attractive noninvasive method for the studies of gastric slow waves and pathophysiology of gastric motility disorders. However, cautions should be made in the measurement, analysis and interpretation of the data.

[Chin Med J (Taipei) 1998;61:S89.]