title: Regional differences in gastric acidity and antacid distribution: is a single pH electrode sufficient?
abstract: Accurate measurement of intragastric acidity has both clinical and investigational importance in studying gastric pathophysiology.
  
  
  OBJECTIVE
  The aims of this study were fourfold: (1) to investigate whether regional differences in intragastric acidity exist; (2) to determine intragastric acidity after a standard antacid was administered in both the fasting and fed states; (3) to monitor gastric emptying of and anatomic distribution of radiolabeled antacid during fasting and postprandial periods; and (4) to determine whether the regional effects of ingested antacid correlated with the anatomic distribution of the antacid.
  
  
  METHODS
  Eight normal male volunteers were studied after fluoroscopically guided nasogastric placement of a tube assembly containing four pH electrodes, with one electrode in each quartile of the stomach. Simultaneous pH readings were made from the four electrodes while fasting, after administration of fasting antacid (30 ml, 79 mEq buffering capacity), postprandially, and after postprandial antacid ingestion. All subjects repeated the protocol on a separate day, five of them using radiolabeled antacid. Gastric emptying and gastric distribution over time of radiolabeled antacid were determined for comparison to regional intragastric acidity.
  
  
  RESULTS
  Intragastric acidity varied regionally over 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 in a distal to proximal (antrum to cardia) sequence. Radiolabeled antacid distribution paralleled intragastric pH and hydrogen ion concentration in the fasting state, with 82% of the antacid localizing in the distal half of the stomach within the first minute after antacid ingestion. Postprandially, the greatest initial and most prolonged antacid buffering effect occurred proximally, correlating with the presence of radiolabeled antacid. Postprandial antacid remained in the stomach for a longer time (T1/2 = 93.1 +/- 23.4 min) compared with fasting antacid (T1/2 = 23.6 +/- 11.1 min).
  
  
  CONCLUSIONS
  Measurement of acidity in the four quartiles of the stomach demonstrated regional variation in response to both food and a standard antacid. A single pH electrode does not detect regional intragastric pH differences.
authors.affiliation: Department of Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Fisher
authors.forename: D J
authors.initials: DJ
authors.lastname: Sher
authors.forename: D
authors.initials: D
authors.lastname: Donahue
authors.forename: L C
authors.initials: LC
authors.lastname: Knight
authors.forename: A
authors.initials: A
authors.lastname: Maurer
authors.forename: J L
authors.initials: JL
authors.lastname: Urbain
authors.forename: B
authors.initials: B
authors.lastname: Krevsky
mesh_terms: D000328:Adult; D000863:Antacids / Q000493:pharmacokinetics*; D004566:Electrodes; D005215:Fasting / Q000502:physiology; D005745:Gastric Acidity Determination / Q000295:instrumentation; D005746:Gastric Emptying / Q000502:physiology; D005753:Gastric Mucosa / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007205:Indium Radioisotopes; D008297:Male; D019518:Postprandial Period / Q000502:physiology; D012016:Reference Values; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D000863:Antacids; D007205:Indium Radioisotopes