The Gastroscan-IAM Impedance/pH Monitor
A.S. Artemiev 1*, I.A. Ilin1, L.V. Kononenko1, A.G. Mikheev1, L.E. Mishulin1, T.V. Nikitina1, B.V. Rakitin1,
M.M. Trifonov1, S.I. Shchukin2, G.A. Yakovlev1
1Scientific-Manufacturing Company Іstок-Sistema. Fryazino, Moscow Region, Russua; E-mail: firstname.lastname@example.org
2Bauman Moscow State Technical University, Moscow, Russia.
* To whom correspondence should be addressed.
Technical and functional characteristics of the Gastroscan-IAM impedance/pH monitoring system, the first Russian medical device for 24-h impedance/pH-metry of the esophagus, are presented. Such monitoring is a new and most informative method for diagnosis of gastroesophageal reflux disease (GERD), the symptoms of which are experienced daily in 4-10% of the population.
Gastroesophageal reflux disease (GERD) is a widespread disease of the gastrointestinal tract (GIT). This disease is associated with reverse transport of the stomach content into the esophagus (gastroesophageal reflux, GER). GERD symptoms (heartburn, belch, etc.) occur regularly in 4-10% population. About 2-5% patients with GERD suffer from ulcers, hemorrhage, strictures, or Barrett's esophagus .
GERD is now diagnosed using 24h pH-metry of the esophagus (Fig. Ia) [l, 2]. GER pH is usually less than 4, while the normal pH value for the esophagus is essentially neutral, about pH 6.5. Esophagus pH < 4 is assumed to be the symptom of GER. In Russia, the main apparatus for 24h pH-metry of GIT is the portable acidogastromonitor AGM-24 MP (Gastroscan 24) available from Istok-Sistema .
Weakly acidic and weakly alkaline duodenogastroesophageal refluxes should be identified to provide adequate diagnosis and therapy of GERD. Impedance/pH-metry of the esophagus can be used to detect such pathology [l, 3. 4] (Fig. 1b).
Detection of GER using impedance/pH metry is based on the following facts :
- electric conductivity of liquid reflux content is greater than the conductivity of the esophagus walls; thus, liquid reflux content decreases impedance of the esophagus (Fig. 2);
- electric conductivity of gas bubbles is lower than the conductivity of the esophagus walls;
- impedance electrodes form several channels for impedance monitoring (Fig. 3), thereby providing differentiation between reflux and swallowing.
Reflux pH is monitored using pH sensors situated between the impedance electrodes. The first domestic impedance/pH monitor implementing the new method of GERD diagnosis was developed in 2012 .
Fig. 1. Digrams оf sensor location in esophagus (LES, lower esophageal sphincter): a) 24h pH-metry; b) 24h impedance/pH-metry
Fig. 2. Esophagus impedance: 1) reflux content is absent, impedance is high; 2) liquid reflux content is present, impedance is low
Fig. 3. Diagram of impedance channel formation from impedance electrodes
Impedance/pH Monitor IAM-01 Gastroscan-IAM
The apparatus for impedance/pH monitoring of the esophagus (Fig. 4) has three main components:
- ZpH-probe (2-mm plastic tube) with 8 cylindrical impedance electrodes (diameter 2 mm: height, 4 mm) 20 mm apart and 3 pH electrodes made of antimony. The detection unit is connected using 11 electric microwires. The probe is inserted transnasally into the esophagus and stomach (Fig. 1b). A silver-chloride reference electrode is attached to the skin. A few types of ZpH-probes with different positions of impedance and pH-eleclrodes are available;
- portable monitoring unit with autonomous power source providing a monitoring cyclogram, measurement of impedance and pH, 24h storage of monitoring results, and a test protocol (occurrence of food ingestion, drug intake, heartburn, etc.) on a microSD card. The pH values are displayed on a LED indicator;
- a PC with GastroScan software for storage and processing of test results.
The developed impedance/pH monitor provides the same range of measurements as its foreign analogs. This determined the basic specifications of this apparatus.
Basic Specifications of Gastroscan-IAM Impedance/pH Monitoring System
Time of continuous operation: 24 h
Number of impedance channels: 7
Frequency: 1 kHz
Periodicity of impedance monitoring per channel: 25 msec
Impedance range: 100-10000 Ω
Number of pH channels: 3
pH monitoring periodicity: 1 sec
pH range: 0.8-9.2
pH buffer-mediated calibration: 1.2 and 9.2
Dimensions: 83 x 167 x 32 mm
Weight: 350 g
Power source: 2 AA batteries
ZpH-sensor use: ≥30 per day
PC system: Windows XP/7
The apparatus can work with standard pH-probes and provides standard analysis of acidograms.
Clinical tests of Gastroscan-IAM apparatuses were carried out in leading gastroenterological centers of Russia: Sechenov Moscow Medical University (Vasilenko clinics of internal diseases) and Research Institute of Gaslroentcrology.
The impedance/pH monitor IAM-01 Gastroscan-IAM was certified in 2012. The user manual of the apparatus was compiled [6,7].
Fig. 4. Gastroscan-IAM portable monitor with ZpH-probe
Examples of impedance/pH-grams obtained on the Gastroscan-IAM
Еxamples of the impedance/pH graphs in typical situations are shown below . Arrangement of the sensors is as in Fig. 1b. Fig. 5-7 on the upper three graphs (top to bottom) show the evolution of pH: in the upper part of the esophagus, the lower part of the esophagus and stomach. Esophageal impedance graphs at seven different levels are on the lower chart. The bottom graph shows the impedance at the level of 2 cm above the lower esophageal sphincter (LES). Graphs above show the impedance at levels 5, 8, 10, 13, 16 and 18 cm above the LES respectively.
A typical picture of acid GER is shown in Fig. 5. There is an impedance drop (i.e. liquid reflux), which begins in lower impedance channels (1) and extends up into the esophagus. Simultaneously, the pH falls at the lower part of the esophagus (2). These impedance graphs show that reflux reaches 5th impedance sensor (6th impedance electrode), i.e., the height of the reflux is at least 15 cm above the LES. Then there is an increase of impedance to the initial level (3), reflecting the return of the refluxate into the stomach. Duration of the reflux is about 2 minutes, but pathologic esophageal acidification (see middle pH graph) persists after the returning of the liquid back into the stomach.
Fig. 5. Impedance/pH-gram of acid GER
Impedance/pH graph of mixed GER, consisting of liquid and gas, is shown on Fig. 6. Such a reflux is characterized by sharp impedance jumps to the upper limit of measurement. Presented reflux is very high, as it goes through all the impedance sensors and reaches the upper pH sensor, which is located at a height of 23 cm above the LES. Gas bubbles brought acidic contents of the stomach into the throat. Such a high reflux causes extraesophageal manifestations of GERD: chronic cough, asthma, pharyngitis, laryngitis, stomatitis etc. Duration of the reflux is about 40 seconds, and the esophagus is almost immediately cleared from the acid.
Fig. 6. Impedance/pH-grams of acid mixed (liquid and gas) GER
Fig . 7 is another example — high weakly acidic GER of a patient on antisecretory therapy, which reduced gastric acidity to pH = 6. Impedance graphs show the upward movement of the refluxate in the esophagus and its return into the stomach, and on the pH-graphs only the minor variations of pH (within the normal range) are visible. Reflux duration is about 30 seconds. In this episode, the patient marked the emergence of non-productive cough with the keyboard on the recording unit. Thus, the impedance/pH monitoring revealed that the cause of the symptom is namely a weakly acidic GER, which could not be detected by conventional pH-metry.
Fig. 7. Impedance/pH-gram of weakly acidic GER
GastroScan Software package
GastroScan software package is shipped with the device. It allows to store the examinations in the database, to represent them in the form of graphs on the computer screen and print these graphs, to perform the calculations of various parameters of the functional condition of the digestive systems of patients, generate and print the final report of the examination, include the graphs that were selected by physician into reports .
A detection of GER episodes is the most difficult part of the impedance/pH-grams analysis. Stendard here is the visual detection of an experienced specialist. However, it is very time-consuming way. Because there is need to detect events about a few seconds, the 24h study session have to be stretched on a computer screen to 200...500 m. Therefore a variety of automatic and semi-automatic methods for the detection of GER are being developed.
The GastroScan software package has algorithm for automatic GER detection. However, sometimes GER episodes are skipped or false detected (when the episode of normal functioning of the esophagus treated as GER). Therefore, the program includes the ability to quickly revise the results of the automatic analysis and correct it exclude some time spans, such such as periods of meals and noisy areas, from the analysis remove false positives and add skipped episodes of GER.
Preliminary automatic analysis impedance/pH-grams with subsequent manual adjustment is currently the main stream mode for Gastroscan-IAM, as for its foreign counterparts.
In the final study report reflux statistic is displayed, namelythe following parameters :
1) the patient's body position: standing (upright) or lying down (supine);
2) reflux acidity: acid, weakly acidic or weakly alkaline;
3) reflux consistency: liquid, gas or mixed;
4) reflux duration time of esophagus clear from esophageal refluxate;
5) reflux height.
Clinical Perspectives of impedance pH-metry
Impedance/pH monitoring is currently more laborious method than conventional pH monitoring, but more informative one. Experience with the Gastroscan-IAM [6, 7] and foreign experience [3, 4] allow us to formulate the main indications for impedance/pH-metry:
1) the ineffectiveness of antisecretory therapy of GERD (heartburn persistence and/or symptoms of reflux esophagitis of patients receiving drugs that reduce stomach acid);
2) atypical forms and manifestations of extraesophageal GERD: chronic cough, asthma, pharyngitis, laryngitis etc.;
3) GERD symptoms of patients with known or suspected stomach hypo- or anacidity: gastrectomy, atrophic gastritis, elderly patients;
4) evaluation of the effectiveness of the treatment of GERD, including surgical.
Contraindications to the impedance/pH monitoring: conditions when a transnasal probe introduction is impossible (acute diseases of the nose and throat, esophageal varices, tumors, and diverticula of the pharynx and esophagus, etc.).
As can be seen from the above, the esophagus impedance/pH monitoring has a fairly wide range of applications, and we could expect it to be included into Russian standards for gastroenterological office equippment and healthcare standards for GERD treatment, similarly to foreign standards .
The first domestic monitor for 24h impedance/pH-metry of the esophagus was developed in Research and Production Enterprise Istok-Systema (Fryazino).
As for technical specifications and functionality, Gastroscan-IAM is similar to foreign counterparts, which began to be introduced into the medical practice in leading clinics of the United States and European Union.
Using of the Gastroscan-IAM allows Russian gastroenterologists to carry out the scientific research and to provide medical care of Gastroenterology profile at the modern world level.
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Original of the article in Russian: Артемьев А.С., Ильин И.А., Кононенко Л.В. и др. Импедансоацидомонитор «Гастроскан-ИАМ» // Медицинская техника. 2013. № 6 (282). С. 10–14.