title: Liquid-containing Refluxes and Acid Refluxes May Be Less Frequent in the Japanese Population Than in Other Populations: Normal Values of 24- hour Esophageal Impedance and pH Monitoring.
abstract: OBJECTIVE
  Twenty-four-hour esophageal impedance and pH monitoring allows detection of all types of reflux episodes and is considered the best technique for identifying gastroesophageal refluxes. However, normative data for the Japanese population are lacking. This multicenter study aimed to establish the normal range of 24-hour esophageal impedance and pH data both in the distal and the proximal esophagus in Japanese subjects.
  
  
  METHODS
  Forty-two healthy volunteers (25 men and 17 women) with a mean ± standard deviation age of 33.3 ± 12.4 years (range: 22-72 years) underwent a combined 24-hour esophageal impedance and pH monitoring. According to the physical and pH properties, distal or proximal esophageal reflux events were categorized.
  
  
  RESULTS
  Median 45 reflux events occurred in 24 hours, and the 95th percentile was 85 events. Unlike previous reports, liquid-containing reflux events are median 25/24 hours with the 95th percentile of 62/24 hours. Acidic reflux events were median 11/24 hours with the 95th percentile of 39/24 hours. Non-acidic gas reflux events were median 15/24 hours with the 95th percentile of 39/24 hours. Proximal reflux events accounted for 80% of the total reflux events and were mainly non-acidic gas refluxes. About 19% of liquid and mixed refluxes reached the proximal esophagus.
  
  
  CONCLUSIONS
  Unlike previous studies, liquid-containing and acidic reflux events may be less frequent in the Japanese population. Non-acidic gas reflux events may be frequent and a cause of frequent proximal reflux events. This study provides important normative data for 24-hour impedance and pH monitoring in both the distal and the proximal esophagus in the Japanese population.
authors.affiliation: Department of Gastroenterology and Hepatology, Gunma University Hospital, Maebashi, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Kawamura
authors.affiliation: Department of Gastroenterology, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Yukie
authors.initials: Y
authors.lastname: Kohata
authors.affiliation: Department of Gastroenterology, Nippon Medical School, Graduate School of Medicine, Tokyo, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kawami
authors.affiliation: Department of Medical Education, Yokohama City University School of Medicine, Yokohama, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Iida
authors.affiliation: Department of Gastroenterology and Hepatology, Gunma University Hospital, Maebashi, Japan.
authors.forename: Akiyo
authors.initials: A
authors.lastname: Kawada
authors.affiliation: Department of Gastroenterology and Hepatology, Gunma University Hospital, Maebashi, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Hosaka
authors.affiliation: Department of Gastroenterology and Hepatology, Gunma University Hospital, Maebashi, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Shimoyama
authors.affiliation: Department of Gastroenterology and Hepatology, Gunma University Hospital, Maebashi, Japan.
authors.forename: Shiko
authors.initials: S
authors.lastname: Kuribayashi
authors.affiliation: Department of Gastroenterology, Osaka University Graduate School of Medicine, Osaka, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Fujiwara
authors.affiliation: Department of Gastroenterology, Nippon Medical School, Graduate School of Medicine, Tokyo, Japan.
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Iwakiri
authors.affiliation: Office of Postgraduate Medical Education, Yokohama City University Hospital, Yokohama, Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Inamori
authors.affiliation: Department of Gastroenterology and Hepatology, Gunma University Hospital, Maebashi, Japan.
authors.forename: Motoyasu
authors.initials: M
authors.lastname: Kusano
authors.affiliation: Kurokawa general hospital, Miyagi, Japan.
authors.forename: Micho
authors.initials: M
authors.lastname: Hongo
keywords: 24-hour esophageal impedance and pH monitoring; Gastroesophageal reflux; Japanese population; Normal values; Proximal reflux