Sobakin M.A., Smirnov I.P., Mishin L.N. Electrogastrography. IRE transactions on bio-medical electronics. 1962, April. P. 129-132.
M. A. Sobakin*, M.D., I. P. Smirnov* and L. N. Mishin*
* Institute for Medical Equipment, Staroje Shosse Russia. 10a, Moscow, Russia.
Inquiries of contemporary theoretical and practical medicine requires from the experimenters and clinical physicians, on one side, a more exact approach to the study of the individual physiological functions of man and animals, and on the other side, a carrying out of studies which account for the activity of the organism as a whole. Such unity of analytic and synthetic methods was demonstrated by classical studies of the secretory processes of the digestive tract conducted by our native schools as well as by many investigators abroad.
Much less developed is the branch of the physiology and pathology of digestion which concerns itself with the motor functions of the stomach. Particularly limited is our knowledge of the peristaltic action during digestion. The study of the complicated dynamics of the changes in the motor functions of the stomach after the reception of food has been impeded up to now mainly by the imperfect experimental and clinical methods of investigation that are used.
One of the objective methods of study of the dynamic activity of the stomach is the method of electrogastrography.
Electrophysiological analysis of the function of internal organs, having more than justified its usefulness during cardiological studies, has such great potential possibilities that it can be utilized successfully in solving the more complicated problems encountered in the graphical studies of the motor functions of the stomach during digestion. The infrequent use of electrogastrographics for the registration of the peristaltic action during digestion is first of all explained by the lack of sufficiently effective methods that can be used to tap the bio-electric currents. An equally important difficulty encountered in the study of the relatively slow fluctuations of the bio-electric potentials of the stomach walls, which vary in step with the rhythm of peristalsis, is the unavailability of sufficiently stable, sensitive, and especially, sufficiently selective electrical registering equipment.
In all previous investigations, the registration of bioelectric currents during digestion was done by making use of electrodes (one or two) which were led through the stomach cavity and therefore made contact with the mucous membrane; however, this contact was not direct since it was made through a constantly changing layer of food (Kogan, Heinrichsdorf and Mironenko, 1938; Aleshina, 1953; Johnson and Leing, 1940; Shuster and Shmucker, 1950; Ingraim and Richard, 1953; Morton and Martin, 1953; Morton, 1954; Goodman, Kolher, Katz, and Dangler, 1955; and others). The unreliability of the contact, when making use of this method, made it difficult to get a highly accurate recording. In addition, the use of the given registration method of bio-electric currents on humans must inevitably be accompanied by a process of probing. This causes a reflex change in the activity of the vomiting center and of the center of the motor activity of the stomach (which is functionally related to the vomiting center).
W. Alvarez (1922), and T. Garrison and B. Phillips (1932), tried to record electrical signals of the stomach from the surface of the body. These attempts were made only under the conditions of physiological starvation, on an empty stomach, and were proved to be successful only in special cases: Either when the people were very thin and had a relatively thin front abdominal wall, or during pyloric stenosis at which time the contractions of the,stomach are significantly intensified.
The method we have developed to tap bio-electric voltages from the surface of the body, and also the corresponding equipment (the electrogastrograph) permits the study of the digestive motor action of the stomach of practically all healthy and ill people and is not restricted to special pathological cases.
The magnitude of the alternating bio-electric potentials of the stomach measured from the surface of the body, and also their spectral composition, demand a number of specific properties from the gastrographic amplifier. The amplitude of the bio-electric potentials of people with a normal stomach is usually of the order of 250 to 350 tv. For different pathological conditions considerable variations of the cited magnitude can be observed, increases up to millivolts, and decreases down to 10 Vv. The sensitivity of the amplifier must permit the registration of the minimal bio-electric potentials and therefore must not be below 10 vv/mm. The frequency spectrum of the bioelectric voltages of the stomach and of its surrounding organs and systems is quite wide. Besides the potentials produced during peristaltic contraction, there are very lowfrequency components (one cycle in several hours) caused by the functions of the secretory mechanism, as well as high components (1 cps and higher) caused, in all probability, by the functions of the intramural and extramural nervous system.
In electrogastrographic studies the problem was to register bio-electric potentials of the motor functions of the stomach and, therefore, the registration of the above mentioned componetnts was undesirable. Thus the operating frequency band and the shape of the frequency response curve of the gastrographic amplifier had to insure an undistorted registration of the desired peristaltic potentials and also a total suppression of low- as well as highfrequency components.
These conditions are satisfied if the frequency range of the amplifier is between 0.05 and 0.2 cps and if its frequency response curve has a steep slope toward the highand low-frequency ranges.
The attenuation of the high frequencies also lowers the interference caused by bio-electric potentials of the heart, the amplitudes of which are considerably higher than those of the stomach, and totally eliminates line interference.
The scheme devised by us made it possible to construct a special device which permitted the registration of bioelectric potentials of the stomach without the use of probing. The one-channel portable electrogastrograph EGS-3 (Fig. 1) made by the All-Union Scientific Research Institute of Medical Instrumentation and Equipment (Moscow) consists of five units: the amplifier, regulator for the anode voltage, regulator for the filament voltage, rectifier and filter for the anode voltage, and the ink writing device with the paper drive mechanism. The amplifier of the electrogastrograph consists of a four-stage differential circuit. Capacitive coupling is used between the first three stages and dc coupling for the last stage. The discrimination factor, that is the ratio of the amplification factor of the antiphase signal to the amplification factor of the inphase signal, is 2000.
The paper drive, for the ink recording of electrogastrograms, moves at a rate of 10 mm/minute. To tap the bioelectric potential of the stomach muscles of the person under study, the nonpolarizable active electrode is laid along the central line of the abdomen. This positioning is done while viewing an X-ray projection of the antral section of the stomach. The passive electrode is laid on the right leg of the subject. Such positioning of the electrodes (epigastric region right leg) requires the elimination of currents produced by the heart muscle since the same isopotential line passes through both places where the electrodes are located (Fig. 2).
Before the studies, the healthy or ill patient receives a special meal which usually has the following composition: A small portion of Barium (mainly to control the positioning of the electrode), 100 to 150 grams of white bread, and a glass of sweet tea. The clearest rhythmic action of the stomach is registered in the interval between 30 minutes to 2 hours after the patient begins to eat the special meal.
The clinical physiological part of our work in electrogastrography was carried out on 26 healthy and 52 ill subjects. A total of 600 recordings were made. Under our guidance, Dr. L. G. Krasilnikov, up to the present time, has collected clinical data on electrogastrography on 164 ill subjects and has normal electrogastrograms of 31 healthy subjects. In addition, using our method, A. S. Belousov, has recorded electrogastrograms of 30 healthy subjects.
Recording of bio-electric currents from the surface of the body of a healthy person, during the normally proceeding digestive process, show oscillations of a frequency of 3 ± 0.3 cycles per minute (Fig. 3). The same rhythm is repeated during the direct electrogastrographic registration from the mucous membrane which is free of food from the stomach (Fig. 4). The amplitude of the electrical oscillations in the great majority of cases reaches a magnitude of 250 Vv. In single cases the potential oscillations on electrogastrograms can reach magnitudes of 0.5 or even 1 mv. On the average, however, the absolute magnitude of bio-electric potential oscillations, recorded from the surface of the body of healthy persons during the period of digestion, does not exceed 0.3 mv.
To check Alvarez's conviction that currents of the stomach's muscle activity can only be registered from the surface of the body if the people were very thin, electrogastrograms of several people who had a heavy layer of fat under their skin were recorded. Fig. 5 shows the result of such a recording. The woman recorded was of average height, but weighed 96 kg. Even though the average amplitude of the electrical oscillations is lower in this recording, one still can clearly distinguish the characteristic rhythm of peristaltic activity of the stomach. Thus, the method and equipment we have developed permits the recording of electric oscillations of the stomach from the surface of the body, not only of normal subjects but also of ill persons with a hypertrophic layer of fat.
The clinical electrogastrographic studies were continued on people suffering from ulcer and cancer.
When the ulcer is localized in the region of the small curvature of the stomach, no noticeable deviation from the norm was obtained. The rhythm of the voltage oscillations remains at three cycles per minute; the amplitude, on the average, approaches the magnitude of 0.25 mv.
It is known that during stenosis of the pyloric walls one observes in the compensating period a hypertrophy of the muscles of the stomach wall and an intensification of peristaltic activity. It is natural to expect an increase of bio-electric activity in the stomach wall of the patients showing stenotic symptoms in the region of the pyloric sphincter. Indeed, the oscillation of stomach potentials synchronous with the rhythm of peristaltic activity were almost two times larger than those of normal activity. Fig. 6 shows an electrogastrogram of patient E who has difficulties in transferring the contents of the stomach into the intestine due to changes in the paunch after a chronic ulceration in the region of the bulb of the duodenum.
Exactly the same changes in the amplitude of the potential oscillations occurred in patients who had difficulties in expelling the contents of the stomach due to other reasons. Fig. 7 shows the so called ulcus-tumor which occurs in the pyloric region.
A completely different aspect of electrogastrograms which were taken during the period of decompensating activity by the motor system of the stomach was obtained from patients suffering from stomach cancer. Thus, for instance, patient L who had a massive swelling localized in the central third of the stomach, had an electrogastrogram with the following characteristics (Fig. 8). In addition to the oscillation having the usual rhythm, the period of which is approximately 20 sec, there appears a faster oscillation which alternates with the slower oscillations. If we compare the breakdown of the motor action of the stomach with these changes in the electrogastrogram, then obviously, in the given case, it is completely permissible to use the term poikiloperistalsis which is used by some physicians, i.e., a peristalsis with an intermittent rhythm. In addition the electrogastrogram given in the figure shows some decrease in electrical activity of the stomach wall-the amplitudes of the potential oscillations lie at the lower boundaries of the norm.
Clinical approbation of the electrogastrographic method and equipment discussed here has shown it to be completely suitable for objective pathophysiological studies of the displacements of the motor system of the stomach during digestion.
The principles used for the electrogastrographic registration of the peristaltic action of the stomach can be used to study the functions of all other internal organs which have smooth muscle tissues.
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