title: Postprandial stomach contents have multiple acid layers.
abstract: OBJECTIVE
  The purpose of this study was to evaluate patterns in gastric pH both fasting and postprandially in different body positions.
  
  
  METHODS
  Ten healthy volunteers were studied. A pH probe was positioned with an electrode 15 cm below the lower esophageal sphincter proximal border then withdrawn 1 cm every 30 seconds to 5 cm above the lower esophageal sphincter. Volunteers were tested on 2 occasions. Initially, they were studied in a semirecumbent position (45 degrees), with the first pull-through after 6 hour fasting. After a meal, a pull-through was repeated 4 consecutive times (approximately 15, 30, 45, and 60 min). On a subsequent day, the positions were changed with each pull-through: upright, supine, right decubitus, and left decubitus. The order of these positions was randomly selected.
  
  
  RESULTS
  The pH step-up is defined as a change in pH from a gastric to an esophageal pH (<4-->>4). No significant difference was found between location of the pH step-up in the fasting and postprandial pull-throughs. An area of lower pH was consistently found within 2 cm distal to the step-up area. Distal to the area of higher gastric pH (median pH at 5), a second acid layer was found. This pattern persisted through the 4 postprandial pull-throughs, irrespective of body position.
  
  
  CONCLUSIONS
  The pH step-up was persistent in the fasting period and for 1 hour postprandially, but did not migrate proximally. Gastric buffering from a meal creates a nonuniform environment with at least 2 acid layers. This pattern is present irrespective of body position. The lack of homogeneity of stomach content postprandially helps to explain the observation of occasional persistent acid gastroesophageal reflux after a meal.
authors.affiliation: Medical University of South Carolina, 96 Jonathan Lucas st, suite 210, Charleston, SC 29425, USA. hila@musc.edu
authors.forename: Amine
authors.initials: A
authors.lastname: Hila
authors.forename: Henda
authors.initials: H
authors.lastname: Bouali
authors.forename: Shuwen
authors.initials: S
authors.lastname: Xue
authors.forename: David
authors.initials: D
authors.lastname: Knuff
authors.forename: Donald O
authors.initials: DO
authors.lastname: Castell
mesh_terms: D000328:Adult; D004943:Esophagogastric Junction / Q000502:physiology; D005215:Fasting / Q000502:physiology*; D005260:Female; D005750:Gastric Juice / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008875:Middle Aged; D019518:Postprandial Period / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D013270:Stomach / Q000502:physiology*