Esophageal acid exposure in healthy adults in Taiwan: experience with pH step-up method by dual-channel pH-metry

Esophageal acid exposure is common in normal subjects. The aim of this study was to investigate proximal and distal esophageal acid exposure in asymptomatic volunteers using dual-channel esophageal pH-metry with probe positioning by pH step-up. A total of 21 healthy subjects (9 male; mean age, 51 years) underwent 24-hour ambulatory esophageal pH recording with the pH step-up method using a two-channel pH probe, a portable digital data recorder, and computerized data analysis. All reflux episodes, episodes longer than 5 minutes, longest reflux episode, duration of acidity (pH <4), and percentage of time with acidity were analyzed. The 95th percentile for reflux parameters assessed in the distal/proximal esophagus were: total reflux episodes, 100/34; episodes greater than 5 minutes, 2.9/0; longest reflux episode, 16.6/2.95 minutes; duration of acidity, 87.95/15.5 minutes; and percentage of time with acidity, 7.0%/1.3%. Proximal and distal acid exposure were well correlated. Results showed that neither gender nor age influenced reflux parameters and that asymptomatic volunteers might experience some gastroesophageal reflux.     

Accurate positioning of the 24-hour pH monitoring catheter： Agreement between manometry and pH step-up method in two patient positions

AIM： TO investigate the agreement between esophageal manometry and pH step-up method in two different patient positions. METHODS： Eighteen subjects were included in the study. First, the distance from the nose to the proximal border of the lower esophageal sphincter （LES） was measured manometrically. Then a different investigator, who was blinded to the results of the first study, measured the same distance using the pH step-up method, with the patient in both upright and supine positions. An assessment of agreement between the two techniques was performed. RESULTS： In the supine position, the measurement of only one subject was outside the range accepted for correct positioning （~〈 3 cm distal or proximal to the LES）. In the upright position, errors in measurement were recognized in five subjects. Bland-Airman plots revealed good agreement between measurements obtained manometrically and by the pH-step up method with the patient in the supine position. CONCLUSION： In the case of nonavailability of manometric detection device, the pH step-up method can facilitate the positioning of the 24 h pH monitoring catheter with the patient in the supine position. Thisshould increase the use of pH-metry in clinical practice for subjects with suspected gastroesophageal reflux disease if our results are supported by further studies.     

Effect of hyoscine N-butylbromide on gastroesophageal reflux in normal subjects and patients with gastroesophageal reflux disease

OBJECTIVES: Recent studies have shown that atropine reduces gastroesophageal reflux in normal subjects and patients with gastroesophageal reflux. The aim of the study has been to assess the effects of an atropine derivative, hyoscine N-butylbromide in normal subjects and patients with gastroesophageal reflux disease by recording esophageal and gastric pH-metry for a 24-h period. METHODS: Ten normal subjects and 10 patients with gastroesophageal reflux disease were evaluated. PH-metry was performed using two glass pH flexible probes with distal incorporated electrodes. The two catheters were introduced nasally under fluoroscopy. One probe was positioned in the gastric body; the other was placed 5 cm above the lower esophageal sphincter which had been evaluated manometrically before the study. Recording lasted without interruption for 48 h. Patients and normal subjects were assigned to receive hyoscine N-butylbromide (10 mg p.o. t.i.d.) for 24 h followed by a placebo for another 24 h or vice versa in a random manner. The pH was analyzed for a total number of acid refluxes and percentage of the period with pH <4 in the esophagus and the mean gastric pH in 24 h, before and after treatment with hyoscine N-butylbromide. RESULTS: The number of reflux episodes was significantly greater with hyoscine N-butylbromide in comparison with a placebo in patients with gastroesophageal reflux disease and normal subjects (p < 0.02). The percentage of time with pH <4, was also significantly greater in patients with gastroesophageal reflux disease and in controls (p < 0.05). The mean 24-h gastric pH after hyoscine N-butylbromide was not different from placebo in gastroesophageal reflux disease and controls. CONCLUSIONS: Hyoscine N-butylbromide, an anticholinergic agent, increases the total number of esophageal acid refluxes in patients with gastroesophageal reflux disease and in controls, therefore it is not recommended in the treatment of gastroesophageal reflux disease.     

Utility of esophageal biopsy in the diagnosis of nonerosive reflux disease

This study evaluated the accuracy of esophageal biopsy for the diagnosis of nonerosive reflux disease (NERD) in adults. Thirty-five patients with reflux symptoms and a normal endoscopy were prospectively evaluated using esophageal biopsies, 24-h ambulatory pH monitoring and symptomatic response 4 weeks after an increase in antireflux therapy. Biopsies were scored for the total number of typical histologic reflux features seen. Patients were considered to have NERD if both pH-metry was positive and step-up therapy was successful. Biopsies were then compared to this predefined gold standard. Biopsy was most sensitive (62%) but poorly specific (27%) when one or more histologic reflux features were seen. A threshold of three or more histologic features improved the specificity (91%) but reduced sensitivity (31%). Response to step-up therapy was associated with 100% sensitivity and 100% negative predictive value when compared to biopsy and pH-metry as an alternate combined gold standard. In conclusion, biopsy is insensitive in diagnosing NERD but reasonably specific if three or more typical histologic reflux features are present.     

24-H pharyngeal pH monitoring in healthy volunteers: a normative study

BACKGROUND: Gastropharyngeal reflux has been associated with disorders of the upper and lower airways. It may be shown by pharyngeal pH-metry, but reports on normality in healthy volunteers are scarce. No definite consensus has been reached considering the upper limit of normality (ULN). The aim of the present study was therefore to quantify the occurrence of pharyngeal acid exposure (pH < 4) in healthy volunteers and, further, to examine its relation to acid exposure of the oesophagus and oesophageal motility and its occurrence in relation to age, sex, and body position. METHODS: Forty healthy volunteers underwent ambulatory 24-h pH-metry, using antimony electrodes positioned 2 cm above the upper oesophageal sphincter and 5 cm above the lower oesophageal sphincter on the basis of manometry. Technical artefacts were excluded before calculation of all results. RESULTS: Gastropharyngeal reflux occurred in most healthy volunteers without any significant relation to age, sex, or body weight. Pharyngeal acid reflux occurred mainly in the upright position. The ULN for pharyngeal acid exposure time was assessed to 0.9% (0.2% after exclusion of mealtimes). The ULN for the number of acid events in the pharynx was 18 (6.1). The corresponding ULNs for the oesophagus were 7% and 84. CONCLUSION: Gastropharyngeal reflux may be effectively monitored by ambulatory pH-metry. The present study provides reference limits, a prerequisite for evaluating the pathophysiologic importance of the phenomenon.     

24-H Pharyngeal pH Monitoring in Healthy Volunteers: A Normative Study

Background: Gastropharyngeal reflux has been associated with disorders of the upper and lower airways. It may be shown by pharyngeal pH-metry, but reports on normality in healthy volunteers are scarce. No definite consensus has been reached considering the upper limit of normality (ULN). The aim of the present study was therefore to quantify the occurrence of pharyngeal acid exposure (pH &lt; 4) in healthy volunteers and, further, to examine its relation to acid exposure of the oesophagus and oesophageal motility and its occurrence in relation to age, sex, and body position. Methods: Forty healthy volunteers underwent ambulatory 24-h pH-metry, using antimony electrodes positioned 2 cm above the upper oesophageal sphincter and 5 cm above the lower oesophageal sphincter on the basis of manometry. Technical artefacts were excluded before calculation of all results. Results: Gastropharyngeal reflux occurred in most healthy volunteers without any significant relation to age, sex, or body weight. Pharyngeal acid reflux occurred mainly in the upright position. The ULN for pharyngeal acid exposure time was assessed to 0.9% (0.2% after exclusion of mealtimes). The ULN for the number of acid events in the pharynx was 18 (6.1). The corresponding ULNs for the oesophagus were 7% and 84. Conclusion: Gastropharyngeal reflux may be effectively monitored by ambulatory pH-metry. The present study provides reference limits, a prerequisite for evaluating the pathophysiologic importance of the phenomenon.     

24-hour oesophageal two-level pH monitoring in healthy children and adolescents

Two-level pH recording in the oesophagus was performed for 24 h in 28 healthy schoolchildren between 9.3 and 17.3 years of age, to obtain reference values for reflux studies. The pH probes were placed 5 and 15 cm above the lower oesophageal sphincter by means of the manometric technique. A standardized acid-free diet was given on the day of recording. A drop in pH to 4.0 or below was regarded as reflux. The normal upper limit of total reflux time was 1.0% at the lower oesophageal level. Mean reflux time was about three times shorter at the upper level than at the lower, which indicates the importance of exact positioning of the pH probe.     

Gastroesophageal pH step-up inaccurately locates proximal border of lower esophageal sphincter

Limiting the widespread use of 24-hr pH monitoring is the necessity of manometrically placing the pH probe 5 cm above the proximal lower esophageal sphincter (LES) border. Therefore, we prospectively compared LES localization by gastroesophageal pH step-up with manometry in 71 patients and 14 asymptomatic volunteers. The gastroesophageal pH step-up significantly correlated with the proximal LES border in patients (r=0.53, P<0.0001) and volunteers (r=0.91, P<0.0001). Based on previously published criteria, the pH step-up value was considered acceptably accurate if it was within ±3 cm (6 cm total span) of the manometrically determined proximal LES border. In 58% of patients and 29% of volunteers the pH step-up occurred outside this accuracy range. Esophagitis (P=0.015) and abnormal reflux parameters (P=0.002) were variables contributing to this error. Subsequent analysis found that the pH step-up overestimated the proximal LES border and occurred at the midportion of the sphincter. The pH step-up still inaccurately located the mid LES in 34% of patients. Therefore, manometry should remain the standard for accurate LES localization prior to placing the pH probe.     

The relationship between oesophageal and gastric pH during 24-hours pH-metry in patients diagnosed with atypical chest pain

Gastric secretion is the only source of hydrochloric acid influencing oesophageal and extraesophageal symptoms in patients with gastroesophageal reflux disease (GERD). The aim of this study was to determine the relationships between gastric and oesophageal pH estimated by 24-hours pH-metry. PATIENTS AND METHODS: We studied 93 men suffering from atypical chest pain. In all endoscopy with mucosa biopsy and simultaneous gastric and oesophageal 24-hours pH-metry using two-channel antimony probe with 15 cm distance of measurement ducts were performed. Results: Among studied patients 24 (26%) had pathological gastroesophageal acid reflux in pH-metry (above 4.5% of monitoring time with oesophageal pH<4). This patients group had higher percentage of monitoring time with gastric pH<4. but only with borderline statistical significance. We did not not find significant differences in values of gastric and oesophageal pH-metry parameters between patients group divided in relation to presence of endoscopic and histologic features of oesophagitis. We found only some significant, but weak correlations between gastric and oesophageal pH. CONCLUSION: Only weak relationship occurring between gastric and oesophageal pH suggests more important role of some other factors in pathogenesis of gastroesophageal reflux and oesophageal mucosa injury.     

Pattern of acid reflux in patients with reflux esophagitis 'resistant' to H2-receptor antagonists

Ambulatory 24-h esophageal pH monitoring was carried out in 54 patients with erosive/ulcerative reflux esophagitis before a 12- to 24-week treatment with either ranitidine, 150 to 300 mg twice daily, or famotidine, 20 to 40 mg twice daily. After this period, 21 patients continued to present endoscopic evidence of esophagitis. Patients who did not respond to the therapy showed a more severe pretreatment pattern of acid reflux than those who healed, with regard to both median percentage time of reflux (16.2% versus 11.0%, respectively, p less than 0.05) and median number of reflux episodes (88.0 versus 55.0; p less than 0.05). Ambulatory 24-h esophageal pH-metry is therefore to be recommended in all patients with acid reflux symptoms, even in those who already show endoscopic lesions of the esophageal mucosa, since this test is a valid prognostic indicator of response to treatment.     

Twenty-four hour ambulatory simultaneous impedance and pH monitoring: a multicenter report of normal values from 60 healthy volunteers

OBJECTIVES: 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.     

Esophageal 24-h pH monitoring: is prior manometry necessary for correct positioning of the electrode?

In 24-h esophageal pH monitoring, the electrode is usually positioned 5 cm above the manometrically localized esophagogastric junction. In order to replace esophageal manometry for this purpose, we tested whether the esophagogastric junction can be identified correctly by fluoroscopy or the determination of the pH-step between stomach and esophagus, compared with esophageal manometry. The distance from the nares to the esophagogastric junction was determined three times with each of the three methods in 46 patients and 14 volunteers. Fluoroscopy assumed the esophagogastric junction 1.23 +/- 0.23 cm (mean +/- SE) lower than the peak pressure point determined at manometry, pH-step only 0.45 +/- 0.16 cm. With pH-step, only one subject had a difference of more than 3 cm to the manometrically defined esophagogastric junction, whether gastroesophageal reflux disease (as proven by pH monitoring) was present or not. We conclude that the esophagogastric junction can usually be identified with sufficient accuracy by the measurement of the pH-step between stomach and esophagus. Fluoroscopy is far less accurate than pH-step, and should not be used.     

Esophageal motility and 24-h pH profiles of patients with heterotopic gastric mucosa in the cervical esophagus

BackgroundHeterotopic gastric mucosa occurs as a flat island of red mucosa in the proximal third of the esophagus where it gives rise to the cervical inlet patch. The aims of this study were to investigate the esophageal motility pattern and 24-h pH profiles of patients with cervical inlet patch.MethodsThirty patients (16 women, mean age: 44.9 years, range: 23–72) diagnosed as having heterotopic gastric mucosa in the cervical esophagus with upper gastrointestinal symptoms had undergone esophageal motility testing and 24-h pH monitorisation with a double-channel pH probe.ResultsManometric investigation was abnormal in 7 patients (non-specific esophageal motor disorder in 4 patients, esophageal hypomotility in 1 patient, and hypotensive LES in 2 patients). Pathological acid reflux (pH < 4) was found in 9 (30%) of 30 heterotopic gastric mucosa patients during pH monitorisation from the distal probe. Pathological acid reflux in the proximal esophagus (percentage of total time of pH < 4) was seen in four of these nine patients. Only four of the 30 patients (13.3%) presented with “acid independent episodes” during the 24-h esophageal pH monitorisation.ConclusionManometric investigation and 24-h pH monitorisation revealed that some of the patients with HGM have signs of esophageal motor dysfunction and “acid independent episodes” from the patches. These abnormalities may be responsible for some of the symptoms of HGM patients.     

The role of esophageal motility in gastroesophageal reflux disease: Technique and clinical results of ambulatory 24-hour Mano/-pH-Metry

The interplay between esophageal motility and gastroesophageal reflux (GER) was investigated with a new ambulatory system of 24-h monitoring of intraesophageal pressures and pH (MP24). The technique allows for simultaneous digital recordings and off-line data analysis. Both computer-aided and visual analyses were used, and algorithms for intercorrelation of mano- and pH-metry were developed. In a group of normal volunteers the physiological response of esophageal motility on GER was defined. In unselected patients suffering from GER disease, the esophageal motility prior to and during GER events was analyzed. In healthy people, most GER episodes occurred spontaneously and were cleared from the distal esophagus by peristaltic contractions. In GER patients, reflux episodes were often preceded by irregular contractions; during GER, esophageal motility was less often peristaltic compared with controls. Therefore, we conclude that MP24 gives relevant information in GER disease which might help in selecting patients for medical or surgical therapy.     

Influence of spontaneous sleep positions on nighttime recumbent reflux in patients with gastroesophageal reflux disease

OBJECTIVE: Body position has been shown to influence postprandial and fasting gastroesophageal reflux (GER) in patients and normal volunteers when they are assigned to lie in a prescribed position. No published studies have evaluated the effect of spontaneous sleeping positions on recumbent reflux in patients with GER. METHODS: Ten patients, three female and seven male (mean age 47.6 yr, range 30-67 yr) with abnormal recumbent esophageal pH <4 on 24-h pH-metry participated. A standardized high fat dinner (6 PM) and a bedtime snack (10 PM) were administered to all patients. GER during spontaneous sleep positions was assessed with a single channel pH probe placed 5 cm above the lower esophageal sphincter (LES) and with a position sensor taped to the sternum. Data were recorded with a portable digital data logger (Microdigitrapper-S, Synectics Medical) and analyzed for recumbent percent time pH <4 and esophageal acid clearance time in each of four sleeping positions. Time elapsed between change in sleeping position and GER episodes was also calculated. RESULTS: Right lateral decubitus was associated with greater percent time pH <4 (p < 0.003) and longer esophageal acid clearance (p < 0.05) compared to the left, supine, and prone. GER episodes were more frequent in the supine position (p < 0.04) and occurred within 1 min after change in sleeping position 28% of the time. CONCLUSIONS: The left lateral decubitus position is preferred in patients with nocturnal GER. Measures to aid patients in sleeping in this position should be developed.     

Pattern of Acid Reflux in Patients with Reflux Esophagitis ‘Resistant’ to H2-Receptor Antagonists

Ambulatory 24-h esophageal pH monitoring was carried out in 54 patients with erosive/ulcerative reflux esophagitis before a 12- to 24-week treatment with either ranitidine, 150 to 300 mg twice daily, or famotidine, 20 to 40 mg twice daily. After this period, 21 patients continued to present endoscopic evidence of esophagitis. Patients who did not respond to the therapy showed a more severe pretreatment pattern of acid reflux than those who healed, with regard to both median percentage time of reflux (16.2% versus 11.0%, respectively, p < 0.05) and median number of reflux episodes (88.0 versus 55.0; p < 0.05). Ambulatory 24-h esophageal pH-metry is therefore to be recommended in all patients with acid reflux symptoms, even in those who already show endoscopic lesions of the esophageal mucosa, since this test is a valid prognostic indicator of response to treatment.     

Is There a Relationship Between the pH and Volume of Saliva and Esophageal pH-metry Results?

There are several implications in the buffer capacity and in the protective role of saliva in gastroesophageal reflux disease (GERD) and other digestive disorders. The lack of knowledge about the production and quality of saliva and the fact that saliva plays an important role in digestive homeostasis motivated the authors to study the relationship between reflux measured by esophageal pH-metry and the pH and volume of saliva in individuals with GERD and its laryngopharyngeal manifestations (LPR). The study was designed as a randomized clinical trial. The studied population consisted of 39 adults with GERD and LPR confirmed by a positive 24-hour double-probe esophageal pH-metry. Unstimulated whole saliva was collected and its pH and volume were compared to pH-metry results. Patients were divided into four groups according to the number of distal episodes of reflux and two groups according to the presence or absence of proximal reflux. A highly significant difference was found between the groups with distal reflux when comparing salivary volume alone and salivary volume/salivary pH. The same occurred for the presence or absence of proximal reflux. These results suggest a direct correlation between salivary volume and “salivary pH × volume” with the number of distal and proximal episodes of reflux on the esophageal pH-metry. If larger studies confirm this finding, in the future it might be possible to diagnose GERD and LPR through a simple “spit test,” avoiding more costly and invasive procedures.     

Comparison of Simultaneous Esophageal pH Monitoring and Scintigraphy in Infants with Gastroesophageal Reflux

Twenty-nine infants under 1 yr of age were studied by simultaneous esophageal pH monitoring and scintigraphy for evaluation of gastroesophageal reflux (GER). Scintigraphy and pH monitoring were performed for 120 min after infants ingested their usual volume of formula. The number of reflux episodes during six 20-min intervals, as determined by both tests, were recorded. Esophageal pH monitoring was continued for 18–24 h. Sixteen of 29 patients exhibited GER by pH monitoring during the 2-h study. Gastroesophageal reflux occurred in seven of 29 during the first hour and 13 of 29 during the second hour. The mean time of first reflux episode detected by pH monitoring following the feeding was 82.4 ± 49.3 min. In comparison, 28 of 29 patients had GER by scintigraphy during the 2 h. All 28 exhibited GER during the first hour, whereas only 22 of 29 patients exhibited GER during the second hour. The mean time of first episode of reflux by scintigraphy was 3.1 ± 2.7 min. Forty-five percent of all reflux episodes detected by scintigraphy occurred during the first 20 min and 80% were detected during the first hour. In contrast, only 17% of reflux episodes were seen by pH monitoring during the first 20 min and 35% during the first hour; 65% of reflux episodes detected by pH monitoring were during the second hour. There was no correlation between the total number of reflux episodes detected by scintigraphy and 2-h esophageal pH monitoring during the 2-h study period ( r = 0.326; p > 0.1). Overall, to detect reflux, scintigraphy was a more sensitive method than esophageal pH monitoring under the conditions of this study. Scintigraphy selectively detected reflux during the first 60 min postprandially whereas pH monitoring was more likely to detect reflux beyond the first postprandial hour. These observations help to explain the lack of correlation between the two tests.     

Significantly Reduced Acid Detection at 10 Centimeters Compared to 5 Centimeters above Lower Esophageal Sphincter in Patients with Acid Reflux

Ambulatory pH monitoring of the esophagus is carried out by positioning a pH sensor 5 cm above the lower esophageal sphincter (LES). There are several techniques to locate the LES, and each method has a different margin of error. This work used dual pH sensors to monitor simultaneously at two different levels (5 and 10 cm above the LES) in order to establish the possible magnitude of error that could arise from inaccurate placement of a pH probe. Thirty-four patients with symptoms of gastroesophageal reflux (GER) were studied. They were grouped as 20 patients with pathological reflux (GER group) and 14 patients with physiological reflux, based on a reflux score derived by Johnson and DeMeester for distal esophageal pH monitoring. When the reflux scores were compared, the difference between the two monitoring levels was statistically significant in the GER group ( p < 0.001) but not in the physiological reflux group ( p = 0.09). In the GER group, the difference in the Johnson and DeMeester score accounted for a change in clinical diagnosis in nine of the 20 patients if the pH probe was placed at 10 cm above the upper margin of LES. Proximal reflux episodes (10 cm above LES) were preceded by distal reflux episodes (5 cm above LES) in 97% (878/901) of cases. Accurate probe placement is essential in the diagnosis of GER.     

Comparison of stationary vs ambulatory 24-hour pH monitoring systems in diagnosis og gastroesophageal reflux disease

Twenty-four-hour intraesophageal pH monitoring is presently considered the most reliable diagnostic test for gastroesophageal reflux. Prolonged esophageal pH measurements can be obtained in hospitalized patients with a stationary technique and in ambulant outpatients by means of a portable device; however, there have been no studies that have examined whether the two approaches provide a similar diagnostic accuracy. We performed a prospective study to compare stationary and ambulatory pH-metry in the diagnosis of gastroesophageal reflux. Seventy-seven control subjects and 178 patients with proven gastroesophageal reflux disease were randomized to either ambulant or static pH-metry, which was performed with standard pH electrodes, sensors, and recorders. Reflux events (intraesophageal pH<4.0) analyzed were: number of episodes; total, upright, and supine reflux time; number of episodes lasting >5 min; and duration of the longest episode. A composite score of all reflux events according to DeMeester was also calculated. The limits of normality were defined as the 95th percentiles of the control groups. Both controls and patients assigned to either pH monitoring method were comparable. Of 255 studies attempted, 243 (95%) were completed successfully. The results showed similar median values of reflux events for the two control groups and for the two patients groups. Percent total reflux time provided a good separation between normal and abnormal reflux, with a sensitivity of 0.92 for static pH-metry and 0.68 for the ambulant procedure (respective 95th percentiles, 3.4 and 4.6). The lower sensitivity of ambulatory pH-metry compared to the stationary method could not be attributed to the higher normal limit in the former; circumstantial evidence suggests that dietary restrictions by the patients to minimize symptoms during home monitoring were probably responsible of this relatively high false negative rate. In conclusion, the results confirm the accuracy of stationary pH monitoring in the diagnosis of gastroesophageal reflux and show that the ambulatory procedure is less reliable; its sensitivity could probably be improved by strict dietary standardization.Supported in part by grants 87/1132, 89/631 and 90/505 from FISSS, Spanish Ministry of Health.A preliminary communication of this work was presented at the 3rd International Polydisciplinary Congress of the OESO, Paris, June 1990.