title: The effect of posture on gastroesophageal reflux event frequency and composition during fasting.
abstract: OBJECTIVE
  To examine the influence of three postures (upright and left and right recumbent) on gastroesophageal reflux event (RE) frequency and composition and a possible mechanism for the observations.
  
  
  METHODS
  A) Forty fasting patients with (E+, n = 20) and without (E-, n =20) esophagitis were studied. Simultaneous manometry and pH monitoring were conducted in the left and right recumbent (10 min each) as well as the upright posture (20 min). RE were classified by the pH probe and/or the manometry catheter as acid or gas RE. B) In 23 patients referred for UGI series, radiographs were taken in the left and right recumbent and upright postures after barium and Fizzies.
  
  
  RESULTS
  A) Upright RE were similar in frequency in E+ and E- patients (2.6 +/- 0.5 vs 3.05 +/- 0.6). However, E+ patients had more recumbent RE (16.3 +/- 3 vs 0.65 +/- 0.2, p = 0.0001) than E- patients; moreover, the left recumbent posture had more recumbent RE than the right (10.9 +/- 2 vs 5.3 +/- 1, p < 0.02). Moving from recumbent to the upright posture had an opposite effect on RE in the two groups; RE decreased sixfold in E+ patients (16.3 +/- 3 vs 2.6 +/- 0.5, p = 0.0001) but increased fourfold in E- patients (0.65 +/- 0.2 vs 3.05 +/- 0.6, p = 0.0001). In examining RE composition in the E+ patients, RE were twofold more likely to be gas in the left recumbent posture (7.6 +/- 2 vs 3.3 +/- 1, p < 0.1); in direct contrast, RE were eightfold more likely to be acid in the right recumbent posture (4.7 +/- 1 vs 0.6 +/- 0.5, p = 0.0001). As expected from this observation, acid exposure was greater in the right than left posture (52 +/- 8 vs 15 +/- 6%, p < 0.0001). Although RE were too infrequent in E- patients to reach statistical significance, the effect of posture on the composition of the few RE that did occur mirrored that of the E+ patients. B) In 17/23 (74%) radiographs in the right recumbent posture, the EG junction was submerged in a barium pool below the air-barium interface in the stomach. In contrast, this occurred in 0/23 patients in the left recumbent and 1/23 patients in the upright postures because the EG junction was in the air above the barium pool.
  
  
  CONCLUSIONS
  Posture has an influence on RE frequency and composition while fasting, and the latter is likely due to whether the EG junction is submerged below liquid gastric contents or in the air above the liquid gastric contents.
authors.affiliation: Department of Medicine, Walter Reed Army Medical Center, Washington DC, USA.
authors.forename: S S
authors.initials: SS
authors.lastname: Shay
authors.forename: D L
authors.initials: DL
authors.lastname: Conwell
authors.forename: V
authors.initials: V
authors.lastname: Mehindru
authors.forename: B
authors.initials: B
authors.lastname: Hertz
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D016009:Chi-Square Distribution; D004941:Esophagitis / Q000000981:diagnostic imaging / Q000503:physiopathology; D004947:Esophagus / Q000000981:diagnostic imaging / Q000503:physiopathology; D005215:Fasting / Q000502:physiology*; D005260:Female; D005764:Gastroesophageal Reflux / Q000145:classification / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000503:physiopathology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015994:Incidence; D008297:Male; D008365:Manometry / Q000706:statistics & numerical data; D008875:Middle Aged; D011187:Posture / Q000502:physiology*; D011859:Radiography; D018709:Statistics, Nonparametric