Twenty-Four Hour Ambulatory Simultaneous Impedance and pH Monitoring: A Multicenter Report of Normal Values From 60 Healthy Volunteers

Medical University of South Carolina, Charleston, South Carolina, United States
The American Journal of Gastroenterology (Impact Factor: 10.76). 06/2004; 99(6):1037-43. DOI: 10.1111/j.1572-0241.2004.04172.x
Source: PubMed


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.
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.
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.
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.

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    • "Supine reflux from the stomach into the oesophagus is rare in normal human subjects [20,26] probably because lower oesophageal sphincter relaxations are uncommon during sleep [33]. By contrast, reflux from the duodenum into the stomach is a normal, physiological, postprandial event and it also occurs nocturnally [29]. "
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    • "MII-pH data should at least include the type (acid, weakly acidic, weakly alkaline) and number of reflux episodes, bolus exposure index (%), bolus clearance time, acid exposure time (%), acid clearance time, total number of symptoms subdivided into symptom type, and symptom association. Normal ranges for MII-pH monitoring in children and adults have been reported (Table 3) [24,25,26]. Recently, normal values for preterm infants were suggested [24]. "
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    • "GERD is defined as esophageal acid exposure >5% in 24 hour pH monitoring [17] or the number of total reflux episodes greater than 73 in MII monitoring [18]. "
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