title: Effects of posture on the physiology of gastric emptying: a magnetic resonance imaging study.
abstract: OBJECTIVE
  Gastric contents empty from the stomach despite frequent changes in body position. The mechanism that maintains gastric emptying independent of position is poorly understood. The aim of this study was to determine the effects of body position on gastric emptying and motor function.
  
  
  METHODS
  Twelve volunteers were investigated in seated position (SP) and upside-down position (UDP) after ingestion of 300 ml water. Magnetic resonance imaging provided a non-invasive assessment of gastric emptying and volumes, intragastric distribution and peristaltic function.
  
  
  RESULTS
  A marked difference in distal/proximal intragastric distribution between UDP and SP was present (7% versus 40%; p < 0.01). Gastric-emptying time was similar but emptying pattern was linear in UDP and exponential in SP. Peristalsis was slower in UDP than SP (2.75 versus 2.96 min-1; p < 0.01), but no correlation was found between peristaltic frequency and the rate of gastric emptying in either position. Postprandial volume response (gastric relaxation) was greater in UDP than SP (280 versus 250 ml; p < 0.05). A correlation was found between gastric relaxation and gastric-emptying time in SP (r2=0.46) but not in UDP.
  
  
  CONCLUSIONS
  The stomach maintains the rate of gastric emptying despite radical changes in body position and intragastric distribution of gastric contents. In SP, hydrostatic pressure (modulated by gastric tone) dictates the gastric emptying. In UDP, gastric emptying also appears to be mediated by continuous adaptation of gastric tone. These findings provide support for the hypothesis that the mechanism of gastric emptying resembles a "pressure pump" rather than a "peristaltic pump".
authors.affiliation: Institute for Biomedical Engineering, University and ETH Zurich, Switzerland. steingoetter@biomed.ee.ethz.ch
authors.forename: Andreas
authors.initials: A
authors.lastname: Steingoetter
authors.forename: Mark
authors.initials: M
authors.lastname: Fox
authors.forename: Reto
authors.initials: R
authors.lastname: Treier
authors.forename: Dominik
authors.initials: D
authors.lastname: Weishaupt
authors.forename: Borut
authors.initials: B
authors.lastname: Marincek
authors.forename: Peter
authors.initials: P
authors.lastname: Boesiger
authors.forename: Michael
authors.initials: M
authors.lastname: Fried
authors.forename: Werner
authors.initials: W
authors.lastname: Schwizer
mesh_terms: D000328:Adult; D005260:Female; D005746:Gastric Emptying / Q000502:physiology*; D006801:Humans; D006874:Hydrostatic Pressure; D008279:Magnetic Resonance Imaging; D008297:Male; D010528:Peristalsis / Q000502:physiology; D011187:Posture / Q000502:physiology*