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Esophageal pH monitoring is the current gold standard for diagnosis of Gastroesophageal Reflux Disease (GERD). It provides direct physiologic measurement of acid in the esophagus and is the most objective method to document reflux disease, assess the severity of the disease and monitor the response of the disease to medical or surgical treatment.

[edit] Background

The importance of refluxed gastric contents in the pathogenesis of GERD was emphasized by Winkelstein who introduced the term “peptic esophagitis” and by Bernstein and Baker who reported the symptom of heartburn following instillation of hydrochloric acid in the distal esophagus. Formal measurement of acid in the esophagus was first described in 1960 by Tuttle . He used a glass pH probe to map the gastroesophageal pH gradient, and demonstrateding a sharp gradient in normal subjects and a gradual sloping gradient in patients with esophagitis. Four years later, Miller used an indwelling esophageal pH electrode to continuously measure esophageal and gastric pH for a period up to 12 hours. This technique required that the patient keep their hands immersed in saline to serve as a reference. Prolonged monitoring became feasible in 1974 when Johnson and DeMeester developed a dependable external reference electrode ^[1]. Using this technique to monitor esophageal acid exposure patients for periods up to 24 hours, DeMeester and Johnson were able to identify the most important parameters of esophageal acid exposure and they developed a composite pH score to quantify gastroesophageal reflux. The initial 24 hour pH studies required hospitalization until the introduction of microcircuits in the 1980s that allowed portable esophageal pH monitoring in an outpatient setting.

[edit] Clinical application

Gastroesophageal Reflux Disease (GERD) is a common disease in western countries. In the United States, 7% of the population experiences heartburn daily and 44% at least once a month ^[2]. Heartburn occurs when esophageal mucosa exposes to the acidic gastric content, but the complaint of heartburn is not always a reliable guide to the presence of acid reflux in the esophagus^[3]. Further, only half of the patients with increased esophageal acid exposure will have esophagitis ^[4]. Therefore, the diagnosis of gastroesophageal reflux disease (GERD) on the basis of symptoms or endoscopic findings is problematic. Consequently, measurement of esophageal acid exposure has become the accepted standard for the diagnosis of this disease.

Ambulatory esophageal pH monitoring is now the gold standard for the diagnosis of gastroesophageal reflux disease. In the past, an indwelling nasoesophageal catheter was the only way to measure esophageal acid exposure. This method is associated with nasal and pharyngeal discomfort, rhinorrhea and social embarrassment. Further, patients frequently limited their activity and were more sedentary during the monitored period ^[5]. This may have resulted in less acid reflux and a false negative test.

To avoid these problems, a catheter-free radio telemetric system, called the Bravo pH capsule has been introduced into clinical practice on the basis that it would be better tolerated by the patient and would allow longer monitoring (48 hours or more). This test has shown to have a high sensitivity and specificity in diagnosis of the GERD. A composite pH score of >14 on any of the two 24-hour recordings has a high sensitivity, specificity, and positive and negative predictive values, and an accuracy of 95% ^[6].

[edit] Different techniques

48 Hour Bravo pH monitoring A sample of Bravo pH tracing recorded over 48 hours

Esophageal pH monitoring is being performed using one of the following three techniques:

Single sensor pH monitoring using a pH catheter
Dual sensor pH monitoring using a pH catheter
Wireless pH monitoring using Bravo pH capsule

The duration of the test is 24 hours in the first and second techniques and 48 hours or more for the Bravo capsule.

[edit] pH sensor location and probe placement

In assessment of distal esophageal pH, the sensor is placed 5 cm above upper border of the lower esophageal sphincter (LES) determined by esophageal manometry. To measure proximal esophageal acid exposure the second sensor is placed 1-5 below the lower border of the upper esophageal sphincter (UES).

Bravo pH capsule is placed either transnasally based on manometric measurements or following endoscopy. In transnasal placement capsule is placed 5 cm above upper border of the LES and in endoscopic placement 6 cm above gastroesophageal junction. Transnasal placement of the capsule has the advantage of more accurate placement and consequently more precise pH monitoring and endoscopic placement has the advantage of less degree of patient's discomfort in capsule insertion.

[edit] Components of esophageal pH monitoring

A reflux episode is defined as esophageal pH drop below four. Esophageal pH monitoring is performed for 24 or 48 hours and at the end of recording, patients tracing is analyzed and the results are expressed using six standard components. Of these 6 parameters a pH score called Composite pH Score or DeMeester Score has been calculated, which is a global measure of esophageal acid exposure.

Components of 24-h Esophageal pH Monitoring
Percent total time pH < 4
Percent Upright time pH < 4
Percent Supine time pH < 4
Number of reflux episodes
Number of reflux episodes ≥ 5 min
Longest reflux episode (minutes)

[edit] Multichannel intraluminal impedance (MII) pH monitoring

The widespread prescription of proton pump inhibitors (PPI) by primary care physicians has resulted in a change in pattern of GERD in majority of the patients who use these types of medications. Quite often gastroenterologist and foregut surgeons receive consultations to assess patients with persistent reflux symptoms despite the fact that patients is on acid suppression medications. This is due to the fact that symptoms of these patients are the results of weak acid or non-acid reflux. In 1991 Silny was the first investigator who described Multichannel Intraluminal Impedance (MII), a technique which detects intraesophageal bolus transport. pH Monitoring. This method is based on measuring the resistance to alternating current (i.e., impedance) of the content of the esophageal lumen. MII- pH monitoring was then developed by several clinical investigators, especially by Donald Castell MD who has extensievely studied the role of this technique in the diagnosis of patients with reflux disease ^[7]. The clinical application of this technique is mainly in GERD patients who have persistent symptoms despite medical therapy.

[edit] pH monitoring in extraesophageal reflux disease

Retrograde flow of gastric contents to the upper aerodigestive tract causes a variety of symptoms such as cough, asthma, hoarseness and etc. These respiratory manifestations of the reflux disease commonly called extraesophageal reflux disease (EERD). Distal esophageal pH monitoring has been used as an objective test to establish reflux as the cause of the atypical reflux symptoms but, its role in causally associating patients’ symptoms to GERD is controversial. In an effort to improve diagnostic accuracy of test, a catheter with two pH senors has been used to measure the degree of esophageal acid exposure in both distal and proximal esophagus. The ideal location for pH measurement to confirm the diagnosis of the extraesophageal reflux disease is pharynx and new studies has focused on the development of a new pH sensor which can function in the challenging environment of the pharynx^[8].

[edit] See also

[edit] References

^ Johnson LF, Demeester TR. Twenty-four-hour pH monitoring of the distal esophagus. A quantitative measure of gastroesophageal reflux. Am J Gastroenterol 1974;62(4):325-32.
^ Talley NJ, Zinsmeister AR, and Schleck CD et al., Dyspepsia and dyspepsia subgroups: a population-based study, Gastroenterology 102 (1992), pp. 1259–1268.
^ Tefera L, Fein M and Ritter MP et al., Can the combination of symptoms and endoscopy confirm the presence of gastroesophageal reflux disease?, Am Surg 63 (1997), pp. 933–936
^ DeMeester TR, Peters JH, Bremner CG, Chandrasoma P. Biology of gastroesophageal reflux disease: pathophysiology relating to medical and surgical treatment. Annu Rev Med 1999;50:469-506.
^ Fass R, Hell R, Sampliner RE, et al. Effect of ambulatory 24-hour esophageal pH monitoring on reflux-provoking activities. Digestive Diseases & Sciences 1999; 44(11):2263-9.
^ Ayazi S, Lipham JC, Portale G et al. Bravo catheter-free pH monitoring: normal values, concordance, optimal diagnostic thresholds, and accuracy, Clin Gastroenterol Hepatol 7 (2009), pp. 60–67
^ Tutuian R, Vela MF, Shay SS, Castell DO. Multichannel intraluminal impedance in esophageal function testing and gastroesophageal reflux monitoring. J Clin Gastroenterol 2003;37:206–215
^ Ayazi S, Lipham JC, Hagen JA, et al. A new technique for measurement of pharyngeal pH: normal values and discriminating pH threshold. J Gastrointest Surg. 2009 Aug;13(8):1422-9.

[0] Johnson LF, Demeester TR. Twenty-four-hour pH monitoring of the distal esophagus. A quantitative measure of gastroesophageal reflux. Am J Gastroenterol 1974;62(4):325-32.

[1] Talley NJ, Zinsmeister AR, and Schleck CD et al., Dyspepsia and dyspepsia subgroups: a population-based study, Gastroenterology 102 (1992), pp. 1259–1268.

[2] Tefera L, Fein M and Ritter MP et al., Can the combination of symptoms and endoscopy confirm the presence of gastroesophageal reflux disease?, Am Surg 63 (1997), pp. 933–936

[3] DeMeester TR, Peters JH, Bremner CG, Chandrasoma P. Biology of gastroesophageal reflux disease: pathophysiology relating to medical and surgical treatment. Annu Rev Med 1999;50:469-506.

[4] Fass R, Hell R, Sampliner RE, et al. Effect of ambulatory 24-hour esophageal pH monitoring on reflux-provoking activities. Digestive Diseases & Sciences 1999; 44(11):2263-9.

[5] Ayazi S, Lipham JC, Portale G et al. Bravo catheter-free pH monitoring: normal values, concordance, optimal diagnostic thresholds, and accuracy, Clin Gastroenterol Hepatol 7 (2009), pp. 60–67

[6] Tutuian R, Vela MF, Shay SS, Castell DO. Multichannel intraluminal impedance in esophageal function testing and gastroesophageal reflux monitoring. J Clin Gastroenterol 2003;37:206–215

[7] Ayazi S, Lipham JC, Hagen JA, et al. A new technique for measurement of pharyngeal pH: normal values and discriminating pH threshold. J Gastrointest Surg. 2009 Aug;13(8):1422-9.

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