Electrodes for 24 hours pH monitoring--a comparative study

Drift Subtraction for Fast-Scan Cyclic Voltammetry Using Double-Waveform Partial-Least-Squares Regression

Background-subtracted fast-scan cyclic voltammetry (FSCV) provides a method for detecting molecular fluctuations with high spatiotemporal resolution in the brain of awake and behaving animals. The rapid scan rates generate large background currents that are subtracted to reveal changes in analyte concentration. Although these background currents are relatively stable, small changes do occur over time. These changes, referred to as electrochemical drift, result in background-subtraction artifacts that constrain the utility of FSCV, particularly when quantifying chemical changes that gradually occur over long measurement times (minutes). The voltammetric features of electrochemical drift are varied and can span the entire potential window, potentially obscuring the signal from any targeted analyte. We present a straightforward method for extending the duration of a single FSCV recording window. First, we have implemented voltammetric waveforms in pairs that consist of a smaller triangular sweep followed by a conventional voltammetric scan. The initial, abbreviated waveform is used to capture drift information that can serve as a predictor for the contribution of electrochemical drift to the subsequent full voltammetric scan using partial-least-squares regression (PLSR). This double-waveform partial-least-squares regression (DW-PLSR) paradigm permits reliable subtraction of the drift component to the voltammetric data. Here, DW-PLSR is used to improve quantification of adenosine, dopamine, and hydrogen peroxide fluctuations occurring >10 min from the initial background position, both in vitro and in vivo. The results demonstrate that DW-PLSR is a powerful tool for evaluating and interpreting both rapid (seconds) and gradual (minutes) chemical changes captured in FSCV recordings over extended durations.

Enhanced Performance Stability of Iridium Oxide-Based pH Sensors Fabricated on Rough Inkjet-Printed Platinum

Today, electrochemical sensors are used for a broad range of applications. A fundamental challenge is still the achievement of long-term sensor stability by ensuring good adhesion between the deposited sensing layer and the substrate material, e.g., a metal electrode. Until now, the most applied strategy to overcome this problem is to increase the surface roughness of the metal layer by mechanical etching or by electroplating of additional material layers, which both imply an increase in manufacturing steps and thus the final cost of the overall device. Alternatively, to overcome these adhesion problems, we propose the direct printing of a novel platinum nanoparticle ink, which is compatible with low-cost additive digital inkjet and with flexible low-cost substrates. This water-based platinum ink has two unique features: it leads to highly rough surfaces, which promotes the adhesion of deposited sensing material, and it is a highly low-temperature curing ink, compatible with polymeric substrates that cannot withstand high temperatures. Based on this concept, we report about a long-term stable and highly sensitive solid-state pH sensor functionalized by anodic electrodeposited iridium oxide on a rough nanostructured platinum printed layer. The sensors showed an excellent reproducibility with a linear super-Nernstian response (71.3 ± 0.3 mV/pH unit) in a wide pH range (pH 2-11). Long-term stability tests for over 1 year of application demonstrate an excellent mechanical sensor layer stability, which is correlated to the distinct roughness of the printed platinum layer. This novel approach is useful to simplify the fabrication process and with that the sensor costs.

Interchangeable Use of Proton Pump Inhibitors Based on Relative Potency

Although proton pump inhibitors (PPIs) are widely used, their relative potency and ideal dosing regimens remain unclear. We analyzed data from randomized clinical trials that performed pH testing in patients receiving solid-dose PPI formulations (omeprazole, esomeprazole, lansoprazole, pantoprazole, rabeprazole) for a minimum of 5 days. We used omeprazole equivalency and the surrogate biomarker, percentage time pH > 4 over a 24-hour period (pH4time), to compare PPI effectiveness for different PPIs given once, twice, or 3 times daily. We found that increasing strength of once-daily PPIs (9-64 mg omeprazole equivalents) increased pH4time linearly from approximately 10.0 to 15.6 hours; higher doses produced no further increase in pH4time. Increasing the frequency to twice-daily PPI increased pH4time linearly, from approximately 15.8 to 21.0 hours. Three-times daily PPIs performed similarly to twice-daily PPIs. The costs of PPIs varied greatly, but the cost variation was not directly related to potency. We conclude that PPIs can be used interchangeably based on potency. Using twice-daily PPIs is more effective in increasing efficacy increasing once-daily PPI dosage. Omeprazole and lansoprazole (30 mg) and 20 mg of esomeprazole rabeprazole are functionally equivalent.

Ambulatory esophageal pHmetry in healthy dogs with and without the influence of general anesthesia

This research aimed to determine the value of esophageal pH in awake and anesthetized dogs, to evaluate the esophageal pH value in awake dogs, in different body positions, as well as to study the occurrence of gastroesophageal reflux episodes in these positions. Thus, 40 healthy male and female adult dogs with mean body weight of 15.5 ± 4.6 kg were used. Esophageal pHmetry was conducted by inserting a catheter through the oropharynx in 30 dogs (stage 1) anesthetized with acepromazine, propofol and isoflurane, submitted to elective ovariosalpingohysterectomy. In addition, 8-h esophageal pHmetry was carried out transnasally in 10 awake dogs (stage 2), allowed to move and change body positions (lateral and sternal decubitus, and standing position), which were recorded. The mean esophageal pH value was lower (p < 0.01) in the anesthetized dogs (7.3 ± 0.82) than in the awake dogs (8.2 ± 0.3). Only four anesthetized dogs (13.33%) suffered reflux episodes. Reflux was not observed in the awake dogs and no esophageal pH differences were found between the body positions studied. Compared to the alert state, general anesthesia in dogs submitted to the previously mentioned anesthesia protocol causes esophageal pH reduction and predisposes to the occurrence of gastroesophageal reflux episodes. Transnasal pHmetry of 8 h in healthy awake dogs reveals that the esophageal pH value is alkaline and does not vary according to body position. In these animals, decubitus position is not a determining factor for reflux episodes to occur.

Ambulatory oesophageal pH monitoring: a comparison between antimony, ISFET, and glass pH electrodes

BACKGROUND AND AIM

Ambulatory oesophageal pH-impedance monitoring is a widely used test to evaluate patients with reflux symptoms. Several types of pH electrodes are available: antimony, ion sensitive field effect transistor (ISFET), and glass electrodes. These pH electrodes have not been compared directly, and it is uncertain whether these different types of pH electrodes result in similar outcome.

METHODS

In an in-vitro model the response time, sensitivity, and drift of an antimony, ISFET, and glass pH electrode were assessed simultaneously after calibration at 22 degrees C and at 37 degrees C. All measurements were performed at 37 degrees C and repeated five times with new catheters of each type. Fifteen patients with reflux symptoms underwent 24-h pH monitoring off PPI therapy using antimony, ISFET, and glass pH electrodes simultaneously.

RESULTS

After calibration at 22 degrees C, pH electrodes had similar response times, sensitivity and drift. In contrast to glass electrodes, antimony electrodes performed less accurately after calibration at 37 degrees C than after calibration at 22 degrees C. Calibration temperature did not affect ISFET electrodes significantly. During in-vivo experiments, significant differences were found in acid exposure times derived from antimony (4.0+/-0.8%), ISFET (5.7+/-1.1%), and glass pH electrodes (9.0+/-1.7%).

CONCLUSION

In vitro, antimony and glass pH electrodes are affected by different buffer components and temperature, respectively. In vivo, significant higher acid exposure times are obtained with glass electrodes compared with antimony and ISFET pH electrodes. ISFET electrodes produce stable in-vitro measurements and result in the most accurate in-vivo measurements of acid exposure time.

Reflux monitoring: pH-metry, Bilitec and oesophageal impedance measurements

Gastro-oesophageal reflux disease (GERD) is a highly prevalent condition in Western countries leading to millions of outpatient visits per year. GERD symptoms including heartburn, regurgitation and chest pain are caused by reflux of gastric content in the oesophagus even in the absence of endoscopically visible mucosal lesions. Several procedures are used to identify gastro-oesophageal reflux, the clinically widely used are: conventional (catheter-based) pH monitoring, wireless oesophageal pH monitoring (Bravo), bilirubin monitoring (Bilitec), and combined multichannel intraluminal impedance-pH monitoring (MII-pH). Each technique has strengths and limitations of which clinicians and investigators should be aware when deciding which to choose in a particular patient. Important is the ability to quantify gastro-oesophageal reflux and evaluate the relationship between symptoms and reflux episodes. The present review summarises the technical aspects in performing and interpreting esophageal reflux monitoring procedures.

A novel placement method of the Bravo wireless pH monitoring capsule for measuring intragastric pH

PURPOSE

The delivery system of the Bravo capsule was designed for placement on the esophagus. We evaluated the feasibility of our novel placement method of the Bravo capsule using a clip to monitor intragastric pH and to compare the accuracy of the Bravo wireless system to the traditionally used Slimline catheter-Mark III Digitrapper pH monitoring system.

METHODS

The Bravo capsule was placed by clip or conventional delivery system using suction on the gastric wall in 20 fasted subjects. A separate group of ten healthy volunteers underwent simultaneous intragastric pH monitoring for comparison of the two systems with meals.

RESULTS

Early dislodgment rate of the capsules was lower when placed using clipping (20%) than using conventional delivery system (70%) within 48 h after placement. We observed prominent movement of one catheter in the stomach during the study. Post-test calibration drifts of the catheters at pH 7.01 were significantly greater than those of the Bravo capsules (P = 0.02).

CONCLUSION

Our novel clipping method of the Bravo pH capsule placement provided accurate monitoring of intragastric pH with merits of tolerability, acid stability, and fixing position.

Reflux monitoring: current status

Gastroesophageal reflux monitoring is a key investigation in managing gastroesophageal reflux disease. Esophageal pH monitoring is used to quantify esophageal acid exposure and the association of symptoms with acidic reflux episodes. Recently available wireless pH monitoring systems allow reflux monitoring over prolonged periods and increase patient comfort during the procedure. Combined impedance-pH monitoring offers the ability to identify reflux episodes independently of their acid content, an important advantage when evaluating patients with symptoms persisting during acid-suppressive therapy.

pH Testing: the basics

Esophageal pH testing, first described more than 3 decades ago, has become incorporated in the diagnostic armamentarium of most gastroenterologists. Using commercially available sophisticated equipment and software, the procedure is easy to perform and the analysis of the signals is automated. Nevertheless, users of esophageal pH testing must remain aware of the technical pitfalls that may stand in the way of the acquisition of meaningful results. Esophageal pH monitoring provides quantitative information about the exposure of the distal esophagus to acid. The technique makes it also possible, however, to quantify the correlation between symptom episodes and reflux events. In clinical practice, the latter is often more relevant than information on esophageal acid exposure.

Pre-anesthetic meperidine: associated vomiting and gastroesophageal reflux during the subsequent anesthetic in dogs

OBJECTIVE

To determine the effect of meperidine administered prior to anesthesia on the incidence of vomiting before, and gastroesophageal reflux (GER) and regurgitation during, the subsequent period of anesthesia in dogs.

STUDY DESIGN

Randomized, controlled trial.

ANIMALS

A total of 60 healthy dogs, 4.3 +/- 2.3 years old, and weighing 35.5 +/- 13.1 kg.

METHODS

Dogs were admitted to the study if they were healthy, had no history of vomiting, and were scheduled to undergo elective orthopedic surgery. The anesthetic protocol used was standardized to include thiopental and isoflurane in oxygen. Dogs were randomly selected to receive one of the following pre-medications: morphine (0.66 mg kg(-1) IM) with acepromazine (0.044 mg kg(-1) IM), meperidine (8.8 mg kg(-1) IM) with acepromazine (0.044 mg kg(-1) IM) or meperidine alone (8.8 mg kg(-1) IM). A sensor-tipped catheter was placed to measure esophageal pH during anesthesia. Gastro-esophageal reflux was judged to have occurred if there was a decrease in esophageal pH below four or an increase above 7.5.

RESULTS

No dogs vomited after the administration of meperidine, but 50% of dogs vomited after the administration of morphine. When compared with morphine, treatment with meperidine alone or combined with acepromazine before anesthesia was associated with a 55% and 27% reduction in absolute risk of developing GER, respectively. Dogs receiving meperidine alone were significantly less sedate than other dogs in the study, and required more thiopental to induce anesthesia. Arterial blood pressure and heart rate were not significantly different between groups at the start of the measurement period. Cutaneous erythema and swelling were evident in four dogs receiving meperidine.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of meperidine to healthy dogs prior to anesthesia was not associated with vomiting and tended to reduce the occurrence of GER, but produced less sedation when compared with morphine. Meperidine is not a useful addition to the anesthetic protocol if prevention of GER is desired.

Review article: complete gastro-oesophageal reflux monitoring - combined pH and impedance

Gastroesophagel reflux disease (GERD) is a common condition encountered in clinical practice. Over the years there has been a continuous interaction between the understanding of the disease, the diagnostic tools and treatments of GERD. The use of proton pump inhibitor (PPI) trials by primary care physicians as diagnostic tool in patients with symptoms suspected to be due to GERD has led to a shift in the type of patients referred to specialists. Currently, gastrointestinal specialists are frequently asked to evaluate patients with persistent reflux symptoms despite acid suppressive therapy. In these patients symptoms can be associated with reflux (both acid and non-acid) or not associated with reflux. While conventional pH monitoring can quantify esophageal acid exposure and evaluate the association between symptoms and acid reflux, it cannot reliably detect reflux episodes with a pH > 4 (i.e. non-acid reflux). Detecting reflux episodes by changes in intraluminal resistance to alternating current (i.e. impedance), combined multichannel intraluminal impedance and pH (MII-pH) monitoring offers the opportunity to detect both acid and non-acid reflux episodes and to evaluate the relationship between symptoms and reflux. We believe that MII-pH monitoring has become the new ''gold standard'' for clarifying the mechanisms of persistent symptom on PPI therapy.

Slimline vs. glass pH electrodes: what degree of accuracy should we expect?

BACKGROUND

Ambulatory pH monitoring is considered the gold standard for measuring oesophageal acid exposure, however, data comparing antimony and glass electrodes are limited.

AIM

To compare the accuracy of the Slimline antimony pH monitoring system and a conventional glass electrode catheter pH monitoring system during ambulatory conditions.

METHODS

Eighteen subjects (13 males, 23-45 years) underwent simultaneous pH monitoring using the Slimline antimony pH electrode and MIC M3 glass pH electrode pH monitoring systems for 12 h. Acid exposure was analysed and compared by manual extraction of the data onto an excel spreadsheet.

RESULTS

There was no statistical difference in the median per cent time the pH was <4 recorded by the two systems (Slimline, 3%, Glass MIC M3, 2%, P = 0.77) and the correlation was excellent (r = 0.84). The difference in recorded reflux events was also not significantly different between the two systems, with the absolute difference being 23 events (s.d., 26). Point-by-point discrepancy was 28% (s.d., 18%), however, the agreement in terms of reflex events was excellent (Kappa value, 0.89, s.d., 0.09).

CONCLUSION

Despite substantial point-by-point disagreement, the antimony Slimline pH catheter compares favourably to the Glass MIC M3 pH catheter in terms of measuring standard pH parameters.

Influence of metoclopramide on gastroesophageal reflux in anesthetized dogs

OBJECTIVE

To determine the effect of 2 doses of metoclopramide on the incidence of gastroesophageal reflux (GER) in anesthetized dogs.

ANIMALS

52 healthy dogs undergoing elective orthopedic surgery.

PROCEDURE

In this prospective clinical study, dogs were evaluated before and during orthopedic surgery. The anesthetic protocol used was standardized to include administration of acepromazine, morphine, thiopental, and isoflurane. Dogs were randomly selected to receive an infusion of saline (0.9% NaCl) solution, a low dose of metoclopramide, or a high dose of metoclopramide before and during anesthesia. Treatment groups were similar with respect to age, body weight, duration of food withholding before surgery, duration of surgery, and dose of thiopental administered. Dogs were positioned in dorsal recumbency during surgery. A sensor-tipped catheter was inserted to measure esophageal pH during anesthesia. We defined GER as a decrease in esophageal pH to < 4 or an increase to > 7.5 that lasted more than 30 seconds.

RESULTS

The high dose of metoclopramide (bolus loading dose of 1.0 mg/kg, IV, followed by continuous infusion at a rate of 1.0 mg/kg/h) was associated with a 54% reduction in relative risk of developing GER. The low dose did not significantly affect the incidence of GER.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of metoclopramide by bolus and constant rate infusion at doses much higher than commonly used will reduce the incidence but not totally prevent GER in anesthetized dogs undergoing orthopedic surgery.

Comparison of the Bravo wireless and Digitrapper catheter-based pH monitoring systems for measuring esophageal acid exposure

INTRODUCTION

We compared esophageal acid exposure data obtained during simultaneous esophageal pH studies using the Bravo wireless and the Slimline catheter-Mark III Digitrapper pH systems.

METHODS

Twenty-five asymptomatic subjects underwent endoscopy with endoclip placement at the squamocolumnar junction (SCJ) and manometry to localize the lower esophageal sphincter (LES). A Bravo capsule was placed 6 cm above the SCJ and a Slimline catheter 5 cm above the LES. Relative positions were checked fluoroscopically. Synchronized pH data were compared by manual extraction into Excel spreadsheets. An in vivo pH reference was established with swallows of orange juice (pH 3.88).

RESULTS

Median acid exposure time was greater with the Slimline compared to the Bravo system (Slimline, 3.4%; Bravo, 1.76%, p < 0.05) but electrode positions were similar. The dominant source of discrepancy between systems was an offset in recorded pH values around pH 4 as evidenced by the recorded values of the swallowed orange juice. Bench-top testing suggested that this offset was mainly attributable to the software designed to compensate for the difference in electrode recording characteristics between room and body temperature. After adjusting the pH data sets to accurately reflect actual orange juice pH, acid exposure between systems was similar (Slimline, 0.90%; Bravo, 1.15%).

CONCLUSION

The Slimline system on average over-recorded esophageal acid exposure compared to the Bravo system largely because of a flawed software scheme for electrode thermal calibration. Accuracy of pH data sets from both systems can be improved by scrutiny for artifacts and use of an in vivo pH reference.

Effects of preanesthetic administration of morphine on gastroesophageal reflux and regurgitation during anesthesia in dogs

OBJECTIVE

To determine the effect of morphine administered prior to anesthesia on the incidence of gastroesophageal reflux (GER) in dogs during the subsequent anesthetic episode.

ANIMALS

90 dogs (30 dogs/group).

PROCEDURE

The randomized prospective clinical study included healthy dogs with no history of vomiting. Dogs were scheduled to undergo elective orthopedic surgery. Food was withheld for (mean+/-SD) 17.8+/-4.1 hours prior to induction of anesthesia. The anesthetic protocol included acepromazine maleate, thiopental, and isoflurane. Dogs were randomly selected to receive morphine at various dosages (0, 0.22, or 1.10 mg/kg, IM) concurrent with acepromazine administration prior to induction of anesthesia. A sensor-tipped catheter was used to measure esophageal pH, and GER was defined as a decrease in pH to < 4 or an increase to > 7.5.

RESULTS

40 dogs had acidic reflux, and 1 had biliary reflux. Proportions of dogs with GER were 8 of 30 (27%), 15 of 30 (50%), and 18 of 30 (60%) for morphine dosages of 0, 0.22, and 1.10 mg/kg, respectively. Mean duration of GER was 91.4+/-56.8 minutes. There was no significant association between GER and age, weight, vomiting after preanesthetic medication, administration of antimicrobials, or start of surgery.

CONCLUSIONS AND CLINICAL RELEVANCE

Most healthy dogs vomit after a large dose of morphine, but vomiting does not increase the likelihood of GER during the subsequent anesthetic episode. Administration of morphine prior to anesthesia substantially increases the incidence of GER during the subsequent anesthetic episode.

Glass and antimony electrodes for oesophageal pH monitoring in distressed infants: how different are they?

OBJECTIVE

Although antimony electrodes are by far the most popular for performing oesophageal pH monitoring, there are few data comparing the accuracy of glass and antimony electrodes. Therefore, we tested the accuracy of both electrodes in the prediction of oesophagitis.

METHOD

pH monitoring using a glass electrode and an antimony electrode was performed in 60 distressed infants, aged between 1 and 6 months. An upper endoscopy with oesophageal biopsies was also performed in all infants.

RESULTS

A reflux index (percentage of the total time with pH < 4.0) greater than 5% was considered to be abnormal and was found in 40/60 patients. Histological oesophagitis was present in 26/60 infants. The reflux index was > 5% with the glass electrode in 18/26 children with histological oesophagitis and with the antimony electrode in 10/26 children with histological oesophagitis. Histology of the oesophagus was normal in 22/40 children with abnormal pH monitoring. With the glass electrode, the mean reflux index in the group with oesophagitis was significantly higher than in the group with normal histology, although there was an important overlap. With the antimony electrode, the mean reflux indices in the groups with and without oesophagitis were not different. Regarding normal/abnormal, there was discordance in 35% of the pH studies. No reflux index could be related to a clinically useful sensitivity and specificity to predict oesophagitis.

CONCLUSION

The reflux index does not accurately predict oesophagitis. Oesophageal pH monitoring and endoscopy provide complementary information.

Assessment of respiratory symptoms with dual pH monitoring in patients with gastro-oesophageal reflux disease

BACKGROUND

Gastro-oesophageal reflux disease (GORD) is a commonly underestimated aetiological factor in patients with respiratory symptoms. In this study, acid reflux in healthy volunteers and patients with GORD with and without respiratory symptoms was investigated by dual pH monitoring.

METHODS

Thirty healthy volunteers and 43 patients with GORD underwent oesophageal manometry and dual pH monitoring with one probe in the proximal and one in the distal oesophagus. Nineteen of the 43 patients complained of respiratory symptoms.

RESULTS

There were no differences in proximal probe measurements between volunteers and patients without respiratory symptoms. Patients with GORD and respiratory symptoms had a higher prevalence of abnormally high exposure to gastric juice and more reflux episodes in the proximal oesophagus compared with patients with GORD and no respiratory symptoms. Some 17 of 19 patients with GORD and respiratory symptoms showed deteriorated oesophageal body motility.

CONCLUSION

Dual pH monitoring is feasible and well tolerated, and provides an objective means of evaluating patients with GORD and respiratory symptoms. Prolonged exposure of the proximal oesophagus to gastric juice and disorders of oesophageal body motility seem to be responsible for the development of respiratory symptoms.

Ambulatory 24-hour esophageal pH monitoring: why, when, and what to do

The incidence of gastroesophageal reflux disease (GERD) is increasing and if left untreated can lead to significant patient morbidity and even death. The disease results from the abnormal reflux of gastric contents into the distal esophagus causing symptoms in most and subsequent mucosal damage in some. Several investigations can be used to confirm the diagnosis, but most are dependent on the presence of sequelae and complications of the disease. The physiologic test of ambulatory 24-hour esophageal pH monitoring has proved to be the most sensitive and specific diagnostic investigation. It measures increased esophageal exposure to gastric juice by detecting the concentration of hydrogen ions (pH <4) in the distal esophagus. The technique measures gastric juice exposure at a point 5 cm above the manometrically determined upper border of the lower esophageal sphincter. The exposure is measured in components of frequency of reflux episodes, duration of reflux episodes, and accumulated exposure time. The components are integrated into a composite score, which is reproducible, gender and race independent, and correlates with the degree of esophageal epithelial damage determined histologically. The composite score has been shown to be the most reliable measurement of a therapeutic acid suppression regimen or an effective antireflux operation.

Esophageal pH monitoring, indications, and methods

Symptomatic gastroesophageal reflux disease (GERD) is a common problem that affects a substantial proportion of the American population. It is estimated that the symptoms of GERD may afflict 40% to 45% of Americans each month. The diagnosis of GERD can be difficult, as its symptoms vary from typical symptoms like heartburn to atypical symptoms such as hoarseness, coughing, and chest pain. Most patients present with typical symptoms and are diagnosed with GERD if they respond to empiric trials of acid suppression. Many tests are available to help with diagnosing GERD in patients who either present with atypical symptoms or who do not respond to acid suppression; however, each test has its own shortcomings. The only test that directly measures whether acid is refluxing into the esophagus is the pH probe, but this test is uncomfortable for the patient, can be difficult to interpret, and may not be necessary in all cases. This article reviews the indications for pH monitoring, its technique, its advantages and limitations, and its role the diagnosis of GERD.

Ambulatory esophageal pH monitoring: technique, interpretations, and clinical indications

Gastroesophageal reflux disease (GERD) is the most common esophageal disorder and perhaps among the most prevalent conditions seen in the primary care setting. The clinical manifestations of GERD, typical or atypical, such as noncardiac chest pain, respiratory or ear, nose, and throat symptoms, result from the reflux of gastric contents into the esophagus. Thus the clinical spectrum is wide and requires accurate diagnosis. Ambulatory 24-hr esophageal pH monitoring is not useful in all patients suspected to have GERD. This review describes the technique of ambulatory 24-hr esophageal pH monitoring, the interpretation of findings, and clinical applications of this test.

Twenty-four hour pH monitoring in the assessment of esophageal function

Ambulatory 24-hour esophageal pH monitoring is an important test in the management of patients with gastroesophageal reflux disease. It quantifies esophageal acid exposure while patients pursue their everyday activities without restrictions. The test is performed with a compact portable data logger, miniature pH electrode, and computerized data analysis. The pH electrode should be positioned 5 cm above the manometrically defined lower esophageal sphincter. The patient is asked to press a button on the data logger indicating the onset of the symptom in question, which allows symptoms and acid reflux correlation. Twenty-four hour pH monitoring is generally performed after a therapeutic trial of antireflux medications, preferably proton pump inhibitors.

Gastroesophageal reflux in healthy subjects. Significance of endoscopic findings, histology, age, and sex

BACKGROUND

Our aim was to evaluate which specific factors are of importance for the gastroesophageal reflux seen in presumably healthy subjects.

METHODS

We investigated 57 healthy, asymptomatic volunteers with computer-aided medical history interrogation, endoscopy, biopsy specimens from the distal esophagus, manometry, and 24-h ambulatory pH-monitoring.

RESULTS

Eight subjects (14%) claimed intermittent reflux symptoms at the computer interview, but they did not have more acid reflux at pH-monitoring than asymptomatic volunteers. Thirteen subjects (23%) had abnormalities at endoscopy, 3 of whom had an erosion in the distal esophagus, and 12 had hiatus hernia. Subjects with hiatus hernia had increased acid reflux at 24-h pH-monitoring compared with those without hernia. If subjects with hernia were excluded, the degree of acid reflux was similar in all age groups. Men had more acid reflux than women, and these differences persisted if subjects with hernia were excluded. There was no correlation of histologic signs of esophagitis in the distal esophagus, lower esophageal sphincter pressure, smoking habit, or body mass index with reflux of acid to the esophagus.

CONCLUSION

Hiatus hernia is a common finding in healthy subjects, and it predisposes to gastroesophageal acid reflux. Histologic abnormalities are poorly related to acid reflux in healthy volunteers. We found increased acid reflux in healthy men compared with women, but larger studies are needed to confirm these findings. Symptom evaluation is not sufficient to exclude significant gastroesophageal reflux in healthy volunteers, and we suggest that the possibility of esophageal abnormalities should be excluded by endoscopy in comparative studies of gastroesophageal reflux disease.

24-hour recording of intragastric pH in clinical trials: preconditions, methodology, and standardization strategies

At present, intragastric pH recording by stomach probe is the standard method for the assessment of the pharmacodynamic effect of newly developed antisecretory drugs, and it is being used increasingly as a diagnostic method. Intraluminal pH can be measured by a variety of different electrode systems, systematic differences among these systems require international standardization of the method. In clinical trials, some recommendations should be followed to standardize the study conditions to assure that repeated measurements are comparable. Standardization of food and liquid intake and a correct positioning of the stomach probe are of paramount importance in assuring that the data are reliable; but there are other factors that may influence the study results, for example, the daily activities of the study participants and the method of data processing. Furthermore, several technical aspects must be considered to guarantee accurate and reproducible recordings, including the type of pH-sensitive electrode and the method of calibration used. Further efforts should be made to create an international standard for the method to assure more comparable study results.

Esophageal motility and reflux testing. State-of-the-art and clinical role in the twenty-first century

Esophageal function testing has an important place in the investigation of a significant proportion of patients with esophageal disorders. Appropriate application of these tests requires a proper understanding of their capabilities and limitations and careful primary assessment by other modalities. Esophageal manometry is most useful for assessing significant troublesome dysphagia in the absence of organic obstruction. Esophageal pH monitoring is an important adjunct to clinical assessment and endoscopy in the diagnosis of reflux disease. Although it is the gold standard for the measurement of esophageal acid exposure and assessment of the relationship of symptoms to reflux, there are weakness in both of these functions that should be understood when applying the test to the diagnosis of reflux disease.

Effect of an evening dose of regular and effervescent formulations of ranitidine or cimetidine on intragastric pH in healthy volunteers

AIMS

To compare the effects on intragastric acidity of a single evening dose of either standard or effervescent formulations of ranitidine (300 mg) or cimetidine (800 mg).

METHODS

Twelve healthy subjects were studied, using a four-period randomized cross-over design and an ambulatory intragastric pH monitoring technique. The subjects received a standard evening meal at 17.00 hours and one of the H2-receptor antagonist formulations was given at 23.00 hours.

RESULTS

Both effervescent formulations caused a transient rapid increase in intragastric pH, reaching a maximum at about 3 min after ingestion. After both effervescent formulations a significantly higher pH was measured during the first 45 min after ingestion (P < 0.05), compared to the regular formulations. The onset of action of the H2-receptor antagonists was similar for both formulations of ranitidine and the effervescent cimetidine, but tended to be slower for the regular cimetidine (P = 0.06). Nocturnal intragastric pH was significantly increased by all four formulations, but more effectively so by the two ranitidine formulations. The duration of action (taken as time with pH > 4) of both ranitidine formulations was longer than that of both cimetidine formulations (P < 0.002).

CONCLUSIONS

A single evening dose of 300 mg ranitidine produces a stronger decrease of nocturnal gastric acid secretion than 800 mg cimetidine. The effervescent formulations of both drugs offer the advantage of a rapid decrease (within minutes) of intragastric acidity, with preservation of the sustained systemic effect.

Gastric acidity and gastroesophageal reflux patterns in patients with esophagitis

Esophageal pH-metry is the test of choice for diagnosing gastroesophageal reflux. However, although it allows acid refluxes to be distinguished, it is of limited value for identifying alkaline or mixed (acid mixed with alkaline material) refluxes. To evaluate the ability of dual pH-metry to identify alkaline or mixed refluxes, the gastric acidity and gastroesophageal reflux pattern were evaluated simultaneously in 64 patients with mild-moderate esophagitis, in 28 patients with severe or complicated esophagitis, and in 20 healthy subjects. A dual esophageal gastric pH-probe allowed three different types of esophageal reflux to be distinguished: (a) acid refluxes, defined as a drop in esophageal pH to values less than 4 together with a gastric pH less than 4; (b) mixed refluxes, defined as a drop in esophageal pH from baseline to values greater than 4 associated with rises in gastric pH to greater than 4 values; (c) alkaline refluxes, defined as a rise in esophageal pH to greater than 7 associated with a simultaneous increase in gastric pH to greater than 4. Gastric acidity was more significantly reduced in patients with severe or complicated esophagitis than it was in healthy subjects (P less than 0.01). The reflux pattern in both mild-moderate and severe esophagitis was characterized by mainly acid refluxes and a marked increase in the time the esophagus mucosa was exposed to acid (P less than 0.001). Pure alkaline refluxes were rare (less than 1%) in both healthy subjects and esophagitis patients. The number of mixed refluxes was considerably higher in severe esophagitis patients than it was in either mild-moderate esophagitis patients or controls (P less than 0.05). The finding of mixed refluxes in severe or complicated esophagitis suggests that biliary acids and/or pancreatic enzymes are involved in the pathogenesis of severe forms of esophagitis.

Normal 24-hr ambulatory esophageal pH values. Influence of study center, pH electrode, age, and gender

Although the most sensitive and specific test for diagnosing gastroesophageal reflux disease, normal standards for prolonged esophageal pH monitoring are based on small sample sizes with questions raised about the effects of pH electrode, older age, gender, and methods of data analysis on pH variables. Recently three groups have established normal data bases using similar methodology. Multiple regression and nonparametric analyses showed that the values for the six traditional pH parameters were comparable across study centers. Therefore, the groups were combined for a total study population of 110 healthy subjects (47 men, 63 women, mean age 38 years with a range of 20-84 years). Further nonparametric analyses revealed the following: (1) type of pH electrode (antimony vs glass) is not significantly related to parameters of physiologic acid reflux; (2) age is not independently related to pH parameters; (3) men tend to have more physiologic reflux than women; and (4) older men tend to experience longer episodes of reflux than younger men and women. There was a significant effect of gender and a significant interaction between age and gender on the number of episodes greater than 5 min (P = 0.008). Nearly significant differences were found for percentage of total acid exposure time (P = 0.03), total reflux episodes (P = 0.02), and the longest reflux episode (P = 0.02). We believe these normal esophageal pH values can be used confidently as standards in any laboratory, and consideration should be given to developing separate standards for men and women.

Variations in results of simultaneous ambulatory esophageal pH monitoring

Twenty-four-hour esophageal pH monitoring is regarded as the gold standard investigation for gastroesophageal reflux (GER) (1) and the possibility of an "incorrect" answer, false positive or false negative, is only rarely considered (2). However, when a group of infants in this hospital had such pH studies performed on two consecutive days, considerable differences in the results were found (3). This also had been reported from other centers (4-6). It seems likely that most of the differences were due to true "biological" variability in the amount of GER from day to day, but it remains possible that variation in the accuracy of the equipment in detecting acid reflux was also involved.

Interaction of liquid aluminium phosphate and aluminium hydroxide with the gastric acid profile. Influence of food components and timing of meals

AlPO4 is generally perceived as a particularly weak antacid. Its neutralizing capacity, when evaluated with the classical Fordtran test at the pH 3 standard, is several times smaller than that of Al(OH)3, which is considered a particularly potent antacid. This difference of in vitro reactivity of the two antacids is largely due to the fact that the pKa value is considerably lower for AlPO4 than for Al(OH)3. The object of this study was to evaluate in vivo and in vitro the impact of the pKa value of these antacids on their efficacy at low pH values and the modulation of their neutralizing capacity through proteins. Since both preparations display a much closer antacid activity at pH 2, we felt it appropriate to reevaluate the comparative in vivo neutralizing capacity of the two antacids at doses matched with their in vitro reactivity at pH 2. In vivo antacid effects were measured by ambulant pH-metry in 18 healthy volunteers after randomized ingestion of carbohydrate or protein meals. Antacid or placebo medication was given 1 and 3 h after meals. At pH 3.0, the standard milieu of the Fordtran test, preparation A, composed of Al(OH)3 and a small fraction of Mg(OH)2, displayed in vitro a neutralizing capacity of 4.4 mmol/ml, whereas this was 0.18 mmol/ml for preparation B, composed solely of AlPO4 (p less than 0.001). When tested at pH 1, 1.5, and 2, however, the ratio between A and B was below 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nocloprost on gastric functions in man

Previous studies in animals and humans demonstrated that nocloprost, a stable prostaglandin E2 analogue, shows very high gastroprotective potency, relatively weak gastric inhibitory activity, and low systemic bioavailability after oral administration. In this study the effects of nocloprost on gastric acid secretion and intraluminal pH and on gastric emptying and plasma gastrin levels were determined in humans. Nocloprost at doses of 50 and 100 micrograms was ineffective, but at a dose of 200 micrograms it reduced the response to pentagastrin significantly and that to a peptone meal by 30-50% and abolished plasma gastrin response without affecting the rate of gastric emptying. Nocloprost given at a dose of 100 micrograms three times daily 30 min before the major meals (breakfast, lunch, and dinner) did not affect intragastric pH significantly as monitored by continuous intraluminal pH-metry. We conclude that nocloprost does not affect gastric acid secretion or intraluminal pH when applied at a dose (50-100 micrograms) that is gastroprotective and that is proposed for peptic ulcer therapy. A higher dose (200 micrograms) of nocloprost causes moderate gastric acid inhibition and suppression of plasma gastrin release without affecting gastric emptying or causing any side effects.

Comparative study of glass and antimony electrodes for continuous oesophageal pH monitoring

Oesophageal pH monitoring data are influenced by numerous patient or technique related factors, or both. In this study, data recorded with glass microelectrodes or antimony electrodes, both with external cutaneous Ag/AgCl reference electrodes, connected to two different recording devices are compared. Pearson correlation coefficients regarding the reflux index (% of the investigation time with a pH less than 4) ranged from poor to excellent (0.55 to 1.00). Differences in data recorded with glass electrodes are not significantly dependent on the recording device (r:0.93 to 1.00 for the reflux index). The correlation between data simultaneously recorded with antimony electrodes is lower, although not significantly different for the reflux index (0.90). Correlation between data recorded with glass and antimony probes is rather poor (0.55 to 0.70). Therefore data recorded with antimony electrodes cannot be compared with those recorded with glass electrodes. The mean pH recorded with glass electrodes is lower than that with antimony probes.

Development and evaluation in an ex vivo rat model of a technique for the endoscopic assessment of mucosal defense in man

We evaluated, in an ex vivo rat model, two electrodes suitable for use in man for the endoscopic assessment of luminal and juxtamucosal pH in the upper gastrointestinal tract. Luminal and mucosal pH measurements were performed under stereomicroscopic control in the exposed stomach of the anesthetized rat, using 0.5-mm and 1-mm immersion depth electrodes in the presence of various luminal pH values and after pre-exposure to the mucolytic agent N-acetylcysteine. Both electrodes consistently recorded lumen-to-mucosa pH gradients in the gastric corpus and antrum, the neutralizing zone being located over the surface of the mucosa. These gradients were dissipated on mucosal exposure to a highly acid luminal fluid and after pre-treatment with N-acetylcysteine. These studies indicate that these microelectrodes do, indeed, reliably record lumen-to-mucosa pH gradients and suggest that this method may prove a useful tool for the investigation of mucosal protection in man. Discrepancies between the size of the electrode and the depth of the mucus gel layer, which predispose to simultaneous sampling of luminal and mucosal pH, together with a slow response time, may, however, limit the sensitivity of the technique.

The ion sensitive field effect transistor (ISFET) pH electrode: a new sensor for long term ambulatory pH monitoring

Intraluminal pH monitoring in man should be performed with disposable multichannel assemblies that allow recordings at multiple sites and prevent transmission of infection. Currently available glass electrodes are unsuitable for this purpose because of their size and price. We have thus constructed and tested a small, combined ion sensitive field effect transistor (ISFET) pH electrode incorporating an integral reference electrode. In vitro studies showed that both ISFET and glass electrodes (440-M4, Ingold, Switzerland) have a linear response over the pH range 1.3-8.0 and that they are comparable with regard to response time and 24 hour drift. Twenty one hour intragastric pH recordings were performed simultaneously in eight healthy volunteers using a glass electrode and an ISFET electrode, placed no more than 2 mm apart in a combined assembly. This was located in the gastric corpus under fluoroscopic control. The 21 hour pH curves recorded by each electrode type showed identical patterns: an early morning rise in pH with three meal-associated pH peaks lasting for about two to three hours. The means of the 21 hour pH medians were 2.09 and 2.07 as measured by the glass and the ISFET electrodes respectively. Thus, ISFETs are suitable for the construction of inexpensive and hence disposable multichannel pH monitoring assemblies of small diameter. Provided that they can be produced in large numbers with appropriate technical support, ISFETs have the potential to replace glass electrodes for long term monitoring of gastrointestinal luminal acidity.

The novel proton pump inhibitor pantoprazole elevates intragastric pH for a prolonged period when administered under conditions of stimulated gastric acid secretion in the gastric fistula dog

The duration of intragastric pH-elevation upon administration of the novel H+K(+)-ATPase inhibitor pantoprazole and its pharmacodynamic interaction with H2 receptor blockade was assessed in the gastric fistula dog using the intragastric 24 hour pH-metry. Gastric acid secretion was stimulated by s.c. pentagastrin infusion. Group A received i.v. saline (controls), group B once an i.v. bolus of pantoprazole and group C twice the H2-receptor antagonist famotidine. Group D received the doses of famotidine and pantoprazole used in groups B and C. The intragastric pH-elevating effect of pantoprazole was not prolonged but, in fact, significantly shortened by the pretreatment with famotidine. Moreover, this effect depended on the pretreatment-dose of famotidine. The results underline that substituted benzimidazoles like pantoprazole need to be chemically activated in the acidic compartment of the parietal cell to produce a sustained intragastric pH-elevation. With regard to the potential therapeutic implication of these observations it is speculated that pantoprazole may be most effective in patients with high gastric acid secretion but may display reduced duration of intragastric pH-elevation under conditions of low acid secretion when acid blockade is not required.

Antimony and glass pH electrodes can be used interchangeably in 24-hour studies of gastric acidity

Antimony and glass pH electrodes show almost identical experimental errors in continuously measuring buffer solutions at constant temperature over 24 hr. These errors are lower than the nominal quantization error of the instruments and are not properly described by the 24-hr drift determination. The addition of food particles to the solutions can induce severe reading artifacts. The longer response time reported in vitro of antimony electrodes when moving from pH 1 to pH 7 (3.4 sec vs 0.8 sec with glass electrodes) is irrelevant during in vivo pH-metry studies, because we found that the greatest absolute difference between raw fast acquired (4-6 sec) consecutive pH readings of two commonly used devices was 0.7 pH units in circadian profiles obtained from 413 subjects with various clinical conditions. In our in vivo studies, gastric acidity was monitored continuously with two side-by-side minielectrodes, which were variously combined (antimony-glass, A-G; antimony-antimony A1-A2; glass-glass, G1-G2) and applied on groups of 27 subjects matched for clinical condition. The 24-hr pH means and the 24-hr [H+] means calculated from the acidity profiles obtained with the three electrode combinations, lie on the identity line in each group. Using the Bland-Altman technique for assessing measurement agreement, the differences between the 24-hr pH means and the 24-hr [H+] means obtained with the three combined systems are similar (P = .903 and P = 0.824, respectively) and their 95% confidence limits are comprised within the range (+/-) of the reading error of the measuring systems (namely, +/- 0.3 pH units and +/- 12 mmol/liter in terms of [H+]).(ABSTRACT TRUNCATED AT 250 WORDS)

Prolonged ambulatory esophageal pH monitoring in the evaluation of gastroesophageal reflux disease

Gastroesophageal reflux disease is a common problem that frequently presents with atypical complaints including nausea, hiccups, globus sensation, chest pain, hoarseness, coughing, or various pulmonary complaints. Diagnosis may be difficult, as these patients often do not have radiographic or endoscopic evidence of esophagitis. In these difficult cases, prolonged esophageal pH monitoring provides an accurate method of quantitating acid reflux parameters and correlating symptoms with reflux episodes in an outpatient setting. Current equipment is compact, durable, and not difficult to use or extremely expensive. Data analysis, with a particular emphasis on acid-exposure time (total, upright, supine), reliably discriminates between abnormal and normal subjects but it is not a perfect "gold standard" for gastroesophageal reflux disease. Indications for esophageal pH monitoring include: (1) atypical symptoms of acid reflux with normal endoscopy, (2) typical reflux symptoms unresponsive to medical therapy, and (3) the follow-up of reflux disease after either medical or surgical therapy. This test is currently performed primarily by gastroenterologists, but we believe many other groups may find this technology helpful. To meet these expanding applications, test refinements are necessary, particularly easier methods of placing the pH probe and better standards for defining abnormal pH parameters in older patients. The future for esophageal pH monitoring is bright. This technology has the potential to do for the diagnosis of gastroesophageal reflux disease what endoscopy has done for the diagnosis of peptic ulcer disease.

The interpretation of oesophageal pH monitoring data

Continuous monitoring of oesophageal pH is regarded as the gold standard for all reflux investigations. However, since gastro-oesophageal reflux is considered a normal phenomenon which occurs to a certain extent in each individual, the distinction between "normal" and "abnormal" is not always obvious and is not possible to achieve with a single test. Moreover, data depend on technical hardware such as recording devices and electrodes together with such patient characteristics as age, position, activity, and medication. Although much literature on pH monitoring has appeared recently, many investigations have failed to take into account the basic principles that are of major importance for any biomedical test such as reproducibility, sample reliability, and indications. There is a need to standardize the technique in order to compare studies performed in different centres, provided the technique is reproducible.

Smoking and pH response to H2-receptor antagonists

Smoking has been shown to impair the therapeutic effect of H2-receptor antagonists. To evaluate the acid-reducing capacity of H2-receptor antagonists in relation to smoking habits, we tested the effect of ranitidine (Ran) and famotidine (Fam) under physiologic conditions, using ambulatory pH-metry. Intragastric pH was measured over 20 h. Each of 18 healthy volunteers, 9 smokers and 9 nonsmokers, received 40 mg Fam, 300 mg Ran, or placebo in a double-blind, randomized study as a single evening dose. With both drugs 20-h acidity was markedly suppressed. After Fam treatment mean inhibition was 61% in smokers and 76% in nonsmokers and after Ran 51% and 67%, respectively. When areas under the pH curves for each individual were calculated and treatment compared with placebo (= 100%), the response was smaller in smokers than in nonsmokers with either drug (Fam, 153 +/- 21% versus 214 +/- 19%, p less than 0.01; Ran, 176 +/- 21% versus 232 +/- 29%, p less than 0.05) during the first 4 h after drug intake. A similar effect was observed in the morning period from 0600 to 1000 h (Fam, 118 +/- 19% versus 206 +/- 19%, p less than 0.001; Ran, 133 +/- 21% versus 207 +/- 31%, p less than 0.02). During the nighttime there were no significant differences. These findings indicate that smoking impairs the response to both drugs tested.

Does the intraesophageal pH probe accurately detect acid reflux? Simultaneous recording with two pH probes in humans

Little is known about the accuracy of intraesophageal pH monitoring, ie, do false negatives occur? This study was designed based on the assumption that if two pH probes are placed equidistant from a distal acid source, and the probes measure different values, then one probe might miss acid if it were there alone. We performed 24-hr intraesophageal pH monitoring in 10 patients with gastroesophageal reflux disease, simultaneously placing two pediatric pH probes (probes A and B) 5 cm proximal to the LES in such close proximity that one would expect only small differences in the acid exposure measured by the probes. However, the amount of acid exposure measured by probes A and B differed greatly in some instances. Individual probe performance does not alone account for these differences, since, when pH recordings were reviewed, one probe was as likely to miss acid exposure as the other. These differences would result in a change in the clinical diagnosis in two of 10 patients. Variability in the number of episodes was great and occurred even when there was concordance in percent acid exposure. These data raise questions about the absolute accuracy of the pH probe as the gold standard in the measurement of gastroesophageal reflux.

Gastric aspiration versus antimony and glass pH electrodes. A simultaneous comparative in vivo study

To carry out a simultaneous comparison of the 24-h in vivo performance of antimony and glass electrodes and the findings of intermittent gastric aspiration, a triple-probe system with closely adjacent tips was positioned in the gastric corpus of 10 subjects representing different clinical and pharmacologic conditions. We showed that pH values measured with the antimony and the glass units were well correlated to those assessed in gastric aspirates (rs = 0.87; b = 1.079; a = -0.33; and rs = 0.85; b = 1.121; a = -0.38, respectively). A proportional correlation (rs = 0.86; b = 0.97; a = 0.02) was also found between the two intraluminal pH measurements. With regard to the error frequency distributions obtained by comparing the three measuring systems two at a time, the pH pairs differed by no more than 1 pH unit in most cases (greater than 90%). It can be concluded that antimony and glass pH electrodes can be used interchangeably in 24-h intragastric acidity studies in man.

Physiological gastroesophageal reflux and esophageal motor activity studied with a new system for 24-hour recording and automated analysis

Gastroesophageal reflux and esophageal motility were studied for 24 hr in 32 ambulatory healthy volunteers (20-73 years old), using a newly developed system, consisting of a microprocessor-based data recorder and algorithms for fully automated data analysis. Physiological reflux was more extensive than expected on the basis of widely used normal values. The percentage of time with pH less than 4 and the duration of the reflux episodes increased with age. Of the more than 2000 esophageal contractions occurring per day, peristaltic contractions constituted 50.9 +/- 2.0%. Their amplitude was significantly lower between meals than during meals and during the night. The duration of the peristaltic contractions increased with age. Simultaneous contractions constituted 10.4 +/- 1.2% of the esophageal contractions. Their incidence increased with age. We conclude that continuous ambulatory 24-hr recording with automated analysis of esophageal motility and pH profile is feasible, that the upper limits of normal in ambulatory esophageal pH recording are higher than previously accepted, and that age, meals, and body position must be taken into account in the interpretation of both 24-hr esophageal pH and pressure data.

Intragastric and intraoesophageal pH monitoring in duodenal ulcerpatients: effect of the new histamine H2-receptor antagonist ramixotidine

The effect of the new histamine H2-receptor antagonist ramixotidine 750 mg p.o., administered at 22.00 h, on intragastric and intraoesophageal pH monitored from 22.00 h to 08.00 h, was studied in a double-blind cross-over trial in 11 duodenal ulcer patients. Placebo and ramixotidine were given to each patient on 2 consecutive days in a randomized sequence. Three patients were excluded from the intragastric pH analysis as the records on the second study day were technically inadequate. No significant carry-over or sequence effect was noted. Intragastric hydrogen ion activity was significantly lower (p = 0.01) after ramixotidine than after placebo: median (range) 24 (9-100) vs 97 (27-188) mmol/l. The percentage of time with intraoesophageal pH less than 4 was less than 5% in all but three recordings, with a maximum value of 12%, and it was not significantly different after the two treatments.

Is standardization of pressure and pH measurement in the oesophagus possible to accomplish in the future?

The interpretation of the manometric results depends on reliable equipment and the technique used. The use of the Bernstein test and the acid clearing test are discussed. The difficulties in obtaining comparable results from long-term pH-measurement with different pH-probes, the placement of the probe and the problems with the position of the subject and the oral intake before or/and during the investigation are dealt with. It is concluded that standardization of the oesophageal function test within different centers are still a major problem, which will take considerable time to solve.

Assessment of intragastric acidity in man: modern aspects, reproducibility of intragastric pH-monitoring, and pharmacodynamic results obtained with H2-receptor antagonists

Unlike other methods for assessing intragastric pH or total acid output, the reproducibility of ambulatory pH-monitoring is excellent but is critically dependent on the electrode system and the recording device. In three double-blind randomized studies in normal volunteers the effects of different dosage regimens of roxatidine acetate were compared with placebo and ranitidine. Roxatidine acetate, 75 mg twice daily, raised median 24-h gastric pH from 1.6 to 3.2 and median nocturnal pH from 1.5 to 3.0 Roxatidine acetate, 150 mg at bedtime, raised median 24-h pH to 2.4 and nocturnal pH to 5.9. Roxatidine acetate, 150 mg at bedtime, was as effective as ranitidine, 300 mg at night, in raising median nocturnal pH. However, when drugs were taken after the evening meal, 150 mg roxatidine acetate was less potent than 300 mg ranitidine or 300 mg roxatidine acetate.