E. J. van der Schee

What is measured in electrogastrography

The object of this study was to elucidate what is actually measured in electrogastrography. Comparison of gastric signals simultaneously recorded from serosal and cutaneous electrodes in the conscious dog led to the following findings: 1. In the absence of phasic contractile activity and electrical response activity (ERA), the cutaneous recordings contained a frequency corresponding to the fundamental frequency of the electrical control activity (ECA) of the stomach (about 0.08 Hz). 2. Tachygastrias gave rise to cutaneous signals containing the tachygastric frequency (about 0.25 Hz). 3. The amplitude of the electrogastrogram increased when ERA occurred. It is concluded that both ECA and ERA are reflected in the electrogastrogram. A model is proposed that describes the electrogastrogram as the result of field potentials generated by depolarization and repolarization dipoles.

Electrogastrographic study of gastric myoelectrical activity in patients with unexplained nausea and vomiting.

Using cutaneous electrodes an electrogastrographic study was made of gastric myoelectrical activity in both the fasting and postprandial states in 48 patients with unexplained nausea and vomiting and in 52 control subjects. A gastric emptying study, using a radio-labelled solid phase meal, was carried out in 30 of these 48 patients. A follow up study was done after one year. In 48% of the patients abnormal myoelectrical activity was found which was characterised by: instability of the gastric pacemaker frequency; tachygastrias in both the fasting and postprandial states; the absence of the normal amplitude increase in the postprandial electrogastrogram. This last characteristic was correlated with a delayed gastric emptying of solids. The present study shows that with electrogastrography in a heterogeneous group of patients with unexplained nausea and vomiting a subgroup can be discerned with abnormal myoelectrical activity. Our findings suggests that this abnormal myoelectrical activity is related to these symptoms.

Running spectrum analysis as an aid in the representation and interpretation of electrogastrographic signals.

The recording of gastric myoelectrical activity by means of cutaneous electrodes attached to the external abdominal wall is termed electrogastrography. Respiration and motion artefacts hamper the interpretation of electrogastrographic signals. Running spectrum analysis, using the fast Fourier transform, seems to provide a concise spectral representation of electrogastrographic data. In this paper the concept of running spectrum analysis is presented in detail using test signals consisting of frequency modulated sine waves and actual recordings from dog and man. Especially the visual interpretable representation in appropriate plots is emphasised and discussed. It is demonstrated that tachygastrias with a duration of the order of 30s can easily be recognised in the spectra. In most cases the gastric frequency can be recognised in the spectra. It is concluded, therefore, that running spectrum analysis has to be considered an attractive noninvasive method to study gastric myoelectrical activity in dog and man.

Effects of highly selective vagotomy on gastric myoelectrical activity

Changes in gastric myoelectrical activity following highly selective vagotomy were studied in 12 patients by means of electrogastrography (EGG) using cutaneous electrodes. Measurements were made before, 10 days after, and six months after operation. Eight patients undergoing cholecystectomy served as controls. Preoperatively all controls and patients had normal recordings. In the cholecystectomized patients no significant changes were found postoperatively. Ten days after highly selective vagotomy the normal initial postprandial dip in gastric ECA frequency and the subsequent increase in frequency and power were not seen. Tachygastrias were observed in three patients. Six months after operation the normal frequency and power responses to a test meal had returned, but both the fasting and postprandial ECA frequencies were raised significantly. It is concluded that highly selective vagotomy is associated with abnormalities in myoelectrical activity, in particular in the postprandial state, most of which are reversible with time.

Adaptive filtering of canine electrogastrographic signals. Part 1: system design

The study of the relation between gastric myo-electrical activities recorded from serosal and cutaneous electrodes is hindered by the poor quality of the cutaneous signal. This hindrance could be minimised by suitable filtering of the signal. Since it is not yet clear which aspects of the cutaneous signal constitute valuable information, the filter process should not affect phase, amplitude, frequency and waveform of the gastric component, while noise components should be suppressed strongly. The system design of a modified adaptive filter that meets these requirements is described. The filter was implemented on a digital Nova 2 minicomputer. the filter performance is described and tested.

Electrogastrography : clinical applications

Electrogastrography (EGG) is defined as the recording of myoelectric activity of the smooth muscles of the stomach by means of cutaneous electrodes attached to the epigastric skin. Although the origin of the electrogastrogram is clear, the interpretation of the ‘raw’ electrogastrographic signal is problematic. To overcome this problem, running-spectrum analysis was introduced. After defining the electrogastrographic characteristics of the gastric myoelectric behaviour in healthy subjects, and an attempt had been made to identify the different phases of the interdigestive migrating complex, several patient groups were studied. The abnormal myoelectric activity found was characterized by: 1) unstable gastric frequency; 2) tachygastrias; and 3) abnormal postprandial amplitude behaviour of the gastric frequency. This abnormal myoelectric activity was correlated with nausea and vomiting and a delayed gastric emptying for solids. It was concluded that EGG can be regarded as a powerful non-invasive tool for the ...

Adaptive filtering of canine electrogastrographic signals. Part 2: filter performance

The modified adaptive filter method described in Part 1 was applied to 16 stretches of (cutaneous) electrogastrographic signal of 17·07 min duration. A signal-to-noise ratio improvement of about 8 dB was achieved. The most characteristic feature of the filter method appeared to be that wave-form and phase of the gastric component of the electrogastrographic signal are preserved. It is concluded that the use of the modified adaptive filter forms a valuable tool in the study of the electrogastrographic signal.

Electrogastrography in the dog: waveform analysis by a coherent averaging technique

Electrogastrograms (e.g.g.s) recorded cutaneously in the dog were subjected to waveform analysis by coherent (or ‘triggered’) averaging techniques, to study the relation between e.g.g. waveforms and gastric contractile activity on the one hand, and the position of the cutaneous electrodes used to pick up the e.g.g. on the other. The trigger pulses used were picked up by electrodes applied to the serosal surface of the stomach. To make allowance for the influence of gastric contractions and the related electrical signals on the e.g.g. waveforms a computer program was developed to create a multicategory averager. Instead of adding all signal segments together, each segment was assigned to one of four categories, depending on the magnitude of the corresponding gastric contraction (as recorded by a force transducer applied to the stomach wall). The signal segments in each category were then averaged. The results of the analysis showed that both abdominal electrode position and magnitude of gastric contraction had a clear influence on e.g.g. waveforms. It was also concluded that, depending on the position of the abdominal electrodes, e.g.g. waveforms are related to either corporal or antral regions, or to both regions simultaneously.

Transducer forin vivo measurement of the inner diameter of arteries in laboratory animals

A transducer permitting the measurement of the instantaneous inner diameter of arteriesin vivo is presented. Instantaneous diameter is related to a potential difference induced in the secondary coil of a miniature transformer. A detailed description is given and the transducers performance is evaluated. Variation in artery diameter of 0·005 mm can be detected. The maximum force exerted on the artery wall was found to be 4·5×10−2N leading to an estimated distortion error of less than 0·3% for diameters of about 7 mm. The error of the mean diameter measurementin vivo is about 2% in the range from 6 mm to 8 mm. The transducer has a limited range of linearity. Four different sizes cover the range from 3·5 mm to 10 mm. The transducer was successfully used in quantifying the effect of injected contrast media (in dogs).