REGIONAL DIFFERENCES IN GASTRIC-ACIDITY AND ANTACID DISTRIBUTION - ISA SINGLE PH ELECTRODE SUFFICIENT

Accurate measurement of intragastric acidity has both clinical and inv estigational importance in studying gastric pathophysiology. Objective s: The aims of this study were fourfold: (1) to investigate whether re gional differences in intragastric acidity exist; (2) to determine int ragastric acidity after a standard antacid was administered in both th e fasting and fed states; (3) to monitor gastric emptying of and anato mic distribution of radiolabeled antacid during fasting and postprandi al periods; and (4) to determine whether the regional effects of inges ted antacid correlated with the anatomic distribution of the antacid. Methods: Eight normal male volunteers were studied after fluoroscopica lly guided nasogastric placement of a tube assembly containing four pH electrodes, with one electrode in each quartile of the stomach. Simul taneous pH readings were made from the four electrodes while fasting, after administration of fasting antacid (30 ml, 79 mEq buffering capac ity), postprandially, and after postprandial antacid ingestion. All su bjects repeated the protocol on a separate day, five of them using rad iolabeled antacid. Gastric emptying and gastric distribution over time of radiolabeled antacid were determined for comparison to regional in tragastric acidity. Results: Intragastric acidity varied regionally ov er time in response to meals and to fasting and postprandial antacid. In the fasting state, intragastric acidity returned to baseline after antacid ingestion in a proximal to distal (cardia to antrum) sequence, while postprandial antacid resulted in a return to baseline acidity i n a distal to proximal (antrum to cardia) sequence. Radiolabeled antac id distribution paralleled intragastric pH and hydrogen ion concentrat ion in the fasting state, with 82% of the antacid localizing in the di stal half of the stomach within the first minute after antacid ingesti on. Postprandially, the greatest initial and most prolonged antacid bu ffering effect occurred proximally, correlating with the presence of r adiolabeled antacid. Postprandial antacid remained in the stomach for a longer time (T-1/2 = 93.1 +/- 23.4 min) compared with fasting antaci d (T-1/2 = 23.6 +/- 11.1 min). Conclusions: Measurement of acidity in the four quartiles of the stomach demonstrated regional variation in r esponse to both food and a standard antacid. A single pH electrode doe s not detect regional intragastric pH differences.