title: Twenty-four hour ambulatory simultaneous impedance and pH monitoring: a multicenter report of normal values from 60 healthy volunteers.
abstract: OBJECTIVE
  Impedance monitoring is a new diagnostic method for gastroesophageal reflux disease (GERD) where multiple impedance electrode pairs are placed on a standard pH catheter. It detects reflux of a liquid and/or gas bolus into the esophagus, as well as its distribution, composition, and clearing. The aim of this collaborative study is to define normal values for 24-h ambulatory simultaneous impedance and pH monitoring (24-h Imp-pH), and compare bolus parameters by impedance monitoring to changes in [H(+)] measured by pH monitoring.
  
  
  METHODS
  Sixty normal volunteers without GER symptoms underwent 24-h Imp-pH with impedance measured at six sites (centered at 3, 5, 7, 9, 15, and 17 cm above lower esophageal sphincter) and pH 5 cm above the LES. Reflux detected by impedance was characterized by the pH probe as either acid, weakly acidic, nonacid, or superimposed acid reflux. Proximal reflux was defined as reflux that reached the impedance site 15 cm above the LES.
  
  
  RESULTS
  Reflux frequency was common upright (median-27, 25th and 75th quartile-16, 42), but rare recumbent (median-1; 0, 4). A median of 34% (14%, 49%) of upright reflux reached the proximal esophagus. There was a similar number of mixed composition (liquid + gas; 49%) and liquid-only reflux (51%). Acid reflux was two-fold more common than weakly acidic reflux (p < 0.001). Superimposed acid reflux and nonacid reflux were rare. Acid neutralization to pH 4 took twice as long as volume clearance measured by impedance.
  
  
  CONCLUSIONS
  Combining impedance and pH monitoring improves the detection and characterization of GER. This study characterizes the frequency, duration, and extent of reflux in health and provides normal values for 24-h Imp-pH for future comparison with GERD patients.
authors.affiliation: Department of Gastroenterology, Cleveland Clinic Foundation, OH 44195, USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Shay
authors.forename: Radu
authors.initials: R
authors.lastname: Tutuian
authors.forename: Daniel
authors.initials: D
authors.lastname: Sifrim
authors.forename: Marcelo
authors.initials: M
authors.lastname: Vela
authors.forename: James
authors.initials: J
authors.lastname: Wise
authors.forename: Nagammapudur
authors.initials: N
authors.lastname: Balaji
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.forename: Talal
authors.initials: T
authors.lastname: Adhami
authors.forename: Joseph
authors.initials: J
authors.lastname: Murray
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Peters
authors.forename: Donald
authors.initials: D
authors.lastname: Castell
mesh_terms: D000328:Adult; D015331:Cohort Studies; D017097:Electric Impedance; D004947:Esophagus / Q000378:metabolism*; D005260:Female; D005744:Gastric Acid / Q000378:metabolism*; D005745:Gastric Acidity Determination; D005764:Gastroesophageal Reflux / Q000175:diagnosis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory; D011336:Probability; D011446:Prospective Studies; D012016:Reference Values; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric; D013997:Time Factors