title: Distal mean nocturnal baseline impedance on pH-impedance monitoring predicts reflux burden and symptomatic outcome in gastro-oesophageal reflux disease.
abstract: Mean nocturnal baseline impedance (MNBI), a novel pH-impedance metric, may be a surrogate marker of reflux burden.
  
  
  
  To assess the predictive value of MNBI on symptomatic outcomes after anti-reflux therapy.
  
  
  
  In this prospective observational cohort study, pH-impedance studies performed over a 5-year period were reviewed. Baseline impedance was extracted from six channels at three stable nocturnal 10-min time periods, and averaged to yield MNBI. Distal and proximal oesophageal MNBI values were calculated by averaging MNBI values at 3, 5, 7 and 9 cm, and 15 and 17 cm respectively. Symptomatic outcomes were measured as changes in global symptom severity (GSS, rated on 100-mm visual analogue scales) on prospective follow-up after medical or surgical anti-reflux therapy. Univariate and multivariate analyses assessed the predictive value of MNBI on symptomatic outcomes.
  
  
  
  Of 266 patients, 135 (50.8%) were tested off proton pump inhibitor (PPI) therapy and formed the study cohort (52.1 ± 1.1 years, 63.7% F). The 59 with elevated acid exposure time (AET) had lower composite and distal MNBI values than those with physiological AET (P < 0.0001), but similar proximal MNBI (P = 0.62). Linear AET negatively correlated with distal MNBI, both individually and collectively (Pearson's r = -0.5, P < 0.001), but not proximal MNBI (Pearson's r = 0, P = 0.72). After prospective follow-up (94 patients were followed up for 3.1 ± 0.2 years), univariate and multivariate regression models showed that distal MNBI, but not proximal MNBI, was independently predictive of linear GSS improvement.
  
  
  
  Distal oesophageal MNBI negatively correlates with AET and, when assessed off PPI therapy, is independently predictive of symptomatic improvement following anti-reflux therapy.
authors.affiliation: Division of Gastroenterology, Washington University School of Medicine, Saint Louis, MO, USA.
authors.forename: A
authors.identifier: 0000-0001-7214-5901
authors.initials: A
authors.lastname: Patel
authors.affiliation: Division of Gastroenterology, Washington University School of Medicine, Saint Louis, MO, USA.
authors.forename: D
authors.initials: D
authors.lastname: Wang
authors.affiliation: Division of Gastroenterology, Washington University School of Medicine, Saint Louis, MO, USA.
authors.forename: N
authors.initials: N
authors.lastname: Sainani
authors.affiliation: Division of Gastroenterology, Washington University School of Medicine, Saint Louis, MO, USA.
authors.forename: G S
authors.initials: GS
authors.lastname: Sayuk
authors.affiliation: Division of Gastroenterology, Washington University School of Medicine, Saint Louis, MO, USA. cprakash@wustl.edu.
authors.forename: C P
authors.initials: CP
authors.lastname: Gyawali
mesh_terms: D017097:Electric Impedance; D050782:Esophageal pH Monitoring / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D005764:Gastroesophageal Reflux / Q000175:diagnosis*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D011446:Prospective Studies