Accuracy of measurement of acidogenic function of the stomach by intragastric pH-metry

Abstract

Measurement of acidogenic function of the stomach (AFS) is widely used in modern clinical gastroenterology and functional diagnosis of such acid-dependent diseases as duodenal ulcer (DU), gastric ulcer (GU), etc. [2, 5, 9]. According to the method suggested by E. Yu. Linar [4], intragastric pH is measured simultaneously in acidogenic and neutralizing zones of the stomach. The first antimony pH-sensitive electrode (AE) together with a calomel internal reference electrode (IRE) are placed in the antrum. The second AE is placed in the stomach body. According to Yu. A. Leya, the stomach body, intermedial zone, and pyloric segment are acidogenic, transitory, and neutralizing zones, respectively (Fig. 1) [3]. The transition through intermedial zone, which is no wider than 2-3 mm [3], is accompanied by pH change from 1.0-2.0 in the stomach body to 5.0-7.0 in the antrum. The pH probes developed in 1969-1970 were equipped with two or three AEs (diameter, 7 mm) and a calomel IRE attached to the end of the pH probe (Fig. 1). For three decades (up to the 1990s), these probes were widely used for intragastric pH-metry in several thousands of patients [6, 7, 9]. The following standard electrode positions were used: antrumnstomach body, antrumnstomach bodyncardia, duodenumn antrumnstomach body. Accumulated clinical experience made it possible to assess the AFS state in patients with such acid-dependent diseases as duodenal ulcer, gastric ulcer, etc. It has been shown in recent years [10-12] that accuracy of intragastric pH-metry in two or more stomach segments with different levels of pH is significantly reduced if the first AE is collocated with the IRE in the same GIT segment, whereas the second (third) AE is located in another GIT segment. For example, if the first AE with the IRE is in an acidogenic zone of the stomach body and the second SE is in the esophagus, basal pH measured in the esophagus is 0.8 unit lower than true value (Table 1). This decrease in the esophagus pH is due to the fact that this value of intracavitary basal pH measured in esophagus by the second AE is determined not only by the electromotive force (EMF) between the AE and IRE located in stomach body but also by diffusion potential between esophagus and stomach body. If the stomach is strongly acidic (pH 0.9-1.9), the diffusion potential is about 40 mV, which is equivalent to about 0.8 pH unit. The stepwise decrease in the value of pH measured in the esophagus by the third AE is shown in Fig. 2. It follows from Fig. 2c that displacement of the IRE located near the first AE from the esophagus to stomach body (Fig. 2a) causes a 1.0