The AGM-03 Microprocessor Acidogastrometer
L.E. Mishulin, M.M. Trifonov, and A.V. Fedichkin
Intragastric pH-metry is one of the most effective methods for diagnosis of the state of upper segments of the gastrointestinal tract (GIT) [1,2,4]. The first commercially manufactured acidogastrometer, AGMI-01, was developed at the State Scientific-Manufacturing Company Istok-Sistema (Fryazino) under the supervision of Academician N. D. Devyatkov [3]. This acidogastrometer found wide application in clinical practice. A modification of this device (AGM-01) is still used in some medicoprophylactic institutions.
The development of microprocessor technologies has made it possible to improve the functional capabilities of acidogastrometers. The AGM-03 acidogastrometer was developed on the basis of modern microprocessor technology taking into account the accumulated experience in measurement of GIT acidity. The AGM-03 device is intended for use in small hospitals and en-doscopic departments. It can be used for measuring basal and stimulated acidity in the GIT; performing acid, alkaline, and other tests; selecting optimum drug therapy. In addition, it can be used for topographical intra-endoscopic pH-metry. The main function of the device is to reveal acid-dependent pathologies of the GIT.
The AGM-03 acidogastrometer is rather inexpensive in comparison with other devices used for examination of acidogenic and antacid functions of the GIT and available from the Istok-Sistema, the leading domestic manufacturer of devices and probes for intragastric pH-metry.
The AGM-03 acidogastrometer is based on modern microprocessor technology. An advanced system of menus and prompts displayed on the indicator is very useful in performing medical examination of the GIT. The general view of the device is shown in Fig. 1.
The AGM-03 acidogastrometer is compatible with all pH-probcs available from Istok-Sistema [5]. A pH-probe converts the measured acidity into electric signal detected by a sensor. The AGM-03 device in combination with appropriate probes can be used for examination of both adult and pediatric patients. The number of electric signal sensors (electrodes) on a pH-probe varies from 1 to 5. To increase the accuracy of measurements, the device and the selected probe are calibrated using buffer solutions. According to the design and manufacturing technique, pH-probes can be divided into the following groups: pH-probe with cutaneous AgCI reference electrode; pH-probe with distal AgCl reference electrode; pH-probe with calomel reference electrode. The selected type of pH-probe is entered into the memory of the AGM-03. It is taken into account in calibration of the device. During measurements, the device corrects automatically the obtained data according to the type of pH-probe and the results of calibration. The measurement range of the device is pH 1.1-9.2; maximum permissible absolute error of measure-meat, ± 0.5 pH; dimensions. 160 x 200 x 100 mm; weight, 1 kg.
Fig. 1. General view of the AGM-03 microprocessor acidogastrometer
Fig. 2. Structural diagram of secondary converter
In addition to pH-probes (number and type of probes arc optional), the AGM-03 device is complete with a temperature-controlled calibration set, a cable Tor testing. a connecting extension cable (used, in particular. in endoscopic examinations), standard tilers, and online documentation.
The AGM-03 acidogastrometer consists of a special-purpose bipolar DC millivoltmeter and several devices for acquisition, storage, and primary analysis of measured data (values of pH at the sites of sensors). The AGM-03 device includes the following structural units (Fig. 2):
- 5-channel analog-to-digital converter (ADC);
- galvanic decoupling;
- liquid-crystal display and keyboard;
- microcomputer;
- permanent memory device for storage of parameters.
During examination, the pH-probe connected to the AGM-03 device (immediately or via an extension cable) is inserted into the GIT. The signals from five sensors are applied to the input of ADC (ADC has 5 input channels). The digitized output signal of the ADC is applied to microcomputer via galvanic decoupling. The galvanic decoupling provides required electrical safely.
The microcomputer provides input of user commands, data output on the liquid-crystal display, data reading from ADC, and data storage. A six-pushbutton film keyboard attached to the device is used for data input. The time chart of the device operation is formed using a timer.
The permanent memory device is used for storage of parameters in case of power-down.
The power source transforms the supply-line voltage of 220 V into the operating voltage of 5 V.
Algorithm of Software Operation
One of the advantages of the AGM-03 is that it provides preliminary calibration of the selected probe and continuous comparison of the daia obtained with the calibration data.
The pH-probe is calibrated using buffer solutions with known pH. For each solution, the output voltage of each sensor of the probe is measured. The characteristic of the pH-probe is determined from these dala using the method of piecewise-linear interpolation. The results arc stored in the permanent memory of parameters. These results are used in the examination, when the acidity is measured, and the resulting data are indicated on the display.
The software provides a number of additional services, including comparison of the results of various examinations performed using probes of different types, monitoring of EMF of all electrodes of the pH-probe (in mV), and the device performance check.
Conclusion
The AGM-03 acidogastrometer has successfully passed all medical and engineering tests. The results obtained using ihe AGM-03 device are in good agreement with the results obtained using other instrumental methods of measurement, esophagogastroduodenoscopy, X-ray examination, and three-hour pH-metry. The results of examination correlate well wiih the clinical symptoms of diagnosed diseases. The AGM-03 acidogastrometer has been certified and adopted by the Ministry of Health of the Russian Federation for serial production. The experience in the use of the AGM-03 shows that it may be expected to be the most widely used acidogastrometer in domestic clinical practice.
1. Yu. Ya. Leya, pH-Metry of the Stomach [in Russian], Leningrad (1987).
2. E. Yu. Linar, Normal and Pathological Acidifiable Function of Stomach [in Russian], Riga (1968).
3. Yu. M. Pantsyrev, A. G. Samusev, S. A. Chernyakevich, et al., Elektron. Prom., 2, 36-38 (1988)
4. V. N. Chernov, A. N. Chebotarev, and A. M. Donskov, Gastroenterology [in Russian], Rostov-on-Don (1997).
5. G. A. Yakovlev, Med. Tekh., No. 4, 16-21 (2000).
Оригинал статьи на русском языке: Мишулин Л.Е., Трифонов М.М., Федичкин А.В. Микропроцессорный ацидогастрометр АГМ-03 // Медицинская техника. 2001. № 6. С. 44–45.
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