Ambulatory 24-hour esophageal pH monitoring

If 24-hour esophageal pH monitoring is to be a useful diagnostic tool, it must reliably discriminate gastroesophageal reflux patients despite daily variations in distal esophageal acid exposure. To address this issue, we studied 53 subjects (14 healthy normals, 14 esophagitis patients, and 25 patients with atypical symptoms) with two ambulatory pH tests performed within 10 days of each other. Intrasubject reproducibility of 12 pH parameters to discriminate the presence of abnormal acid reflux was determined. As a group, the parameters of percent time with pH<4 (total, upright, recumbent) were most reproducible (80%). Therefore, a subject was defined as having gastroesophageal reflux disease if at least one of these three values were abnormal. Intrasubject reproducibility for the diagnosis of reflux disease was 89% for the entire sample. Among subsets, the reproducibility was 93% for the normals and esophagitis patients and 84% for the atypical symptom patients. Total percent time with pH<4 was the single most discriminate pH parameter (85%) and nearly equaled that of the three combined parameters (89%). The intrasubject variability of this parameter was determined by the mean ±2sd of the relative differences between the two test results for all 53 subjects. Total percent time with pH<4 may vary between tests by a factor of 3.2-fold or less (218% higher to 69% lower). We conclude: (1) ambulatory 24-hr esophageal monitoring is a reproducible test for the diagnosis of gastroesophageal reflux disease; and (2) the large intrastudy variability in 24-hr total acid exposure may limit this test's usefulness as a measurement of therapeutic improvement.Supported, in part, by Public Health Services Grant AM 34200-01A1 from NIADDIK.     

Validation of a new method of measuring esophageal acid exposure: comparison with 24-hour pH monitoring

Recently, we developed a disposable acid exposure sensor whose in vitro response to acid below pH 4 is linearly determined by the duration of exposure and the degree of acidity. The aim of the present study was to compare the SR to simultaneous esophageal pH and duodenogastroesophageal reflux (DGER) monitoring (Bilitec) in patients investigated for presumed gastroesophageal reflux disease (GERD). Twenty-six patients (16 men, mean age 46 ± 2 years) with symptoms suggestive of GERD underwent 24-hr ambulatory pH monitoring and SR monitoring at 5 cm proximal to the LES. DGER monitoring was performed in 21 patients. Exposure of the esophagus to acid and to DGER were analyzed. These data were compared to SR. A significant correlation was found between the exposure of the distal esophagus to acid and SR (R = 0.85; P < 0.0001). Similarly, the area below a cutoff pH 4 was significantly correlated to SR (r = 0.81; P < 0.0001). SR was not correlated to DGER (r = 0.16; NS). At a cutoff of 50, the sensitivity and specificity of SR to predict esophageal acid exposure >5% of time were 91% and 93%, respectively conclusion, the response of the acid exposure sensor is strongly correlated with the results of simultaneous esophageal pH monitoring. The sensor seems able to reliably predict pathological esophageal acid exposure. These findings warrant larger studies of the clinical potential of the acid exposure sensor in the diagnosis and quantification of GERD.     

Acid perfusion test and 24-hour esophageal pH monitoring with symptom index

The acid perfusion (Bernstein) test and esophageal pH monitoring are the two most popular tests for identifying esophageal acid sensitivity in difficult cases of reflux disease. Therefore, we prospectively compared these test results in 75 consecutive noncardiac chest pain patients who had both an acid perfusion test and chest pain during 24-hr pH testing. A positive acid perfusion test was defined by the replication of the patient's typical chest pain twice by the acid infusion. Esophageal pH testing identified abnormal amounts of acid reflux and correlated symptoms with acid reflux-the symptom index. Fifteen patients (20%) had a positive acid perfusion test while 45 patients (59%) had a positive symptom index (range 6–100%). Only 9/34 (26%) patients with abnormal reflux had a positive acid perfusion test. Although it had excellent specificity (83–94%), the acid perfusion test had poor sensitivity (32–46%) when compared to the symptom index regardless of the percent positive cutoff level. The best positive predictive value for the acid perfusion test was 87%, but this occurred when the test sensitivity was 32%. Modifying the end point of a positive acid perfusion test to include heartburn improves the sensitivity (52–67%) while markedly compromising specificity and positive predictive value. Thus, esophageal pH monitoring correlating symptoms with acid reflux is superior to the acid perfusion test for identifying an acid sensitive esophagus in patients with noncardiac chest pain.     

Exclusion of meal periods from ambulatory 24-hour pH monitoring May improve diagnosis of esophageal acid reflux

Distal esophageal pH less than 4 is frequently seen during meal ingestion in 24-hr ambulatory pH monitoring for the diagnosis of gastroesophageal reflux disease (GERD). The characteristics of this meal-related apparent reflux without diet restriction was evaluated. Data from normal volunteers (N=21) and consecutive patients (N=66) referred with heartburn and/or chest pain were studied with ambulatory pH monitoring. The median percent times pH<4 in the distal esophagus were significantly greater in symptomatic patients than controls for total 24-hr, upright, and supine periods, and postprandial periods of 30, 60, 90, 120, and 150 min (P values of 0.007–0.03). However, the median percent time pH<4 during the meal periods was the same for patients (4.4%) and for controls (6.6%) withP=0.23. Excluding the meal periods from analysis resulted in greater separation between controls and patients with abnormal acid exposure when compared to the conventional method. Patients should maintain their usual routine without diet restriction during 24-hr ambulatory pH studies in the clinical setting. Furthermore, exclusion of meal periods can eliminate meal-time pH variabilities without affecting postprandial acid exposure and improve the diagnosis of GERD.     

Comparison of stationary vs ambulatory 24-hour pH monitoring recording systems

Twenty-four-hour pH monitoring of the esophagus is frequently performed to assess gastroesophageal reflux. We performed a prospective study to determine if results obtained from stationary and ambulatory pH recording systems are comparable. Two groups of patients were studied. Group I consisted of 12 patients monitored simultaneously by both a stationary and an ambulatory pH recording system, each system having a separate pH and reference electrode. In group II, in order to eliminate electrode variability, 10 patients were monitored simultaneously with both systems and a common single pH and reference electrode. In group I, significant correlations were found in six reflux parameters measured and in the 24-hr composite score (r0.8722). However, in three of the 12 patients, marked discrepancies were noted in the composite score calculated by the stationary and ambulatory recording systems. Small variations in the pH level recorded by different pH electrodes may have accounted for the discrepancies. In group II, where electrode variability was eliminated, a better correlation was noted between all parameters measured (r 0.991), and no discrepancies were noted between calculated composite scores. We concluded that the stationary and ambulatory recording systems tested are comparable in measuring 24-hr esophageal pH.This protocol (WR-1477) was approved by the WRAMC Human Use Committee/Institutional Review Board and supported by Department of Clinical Investigation Funding.The opinions and assertions contained herein are the private ones of the authors and are not to be construed as official policy or reflecting the views of the Department of the Army or the Department of Defense.     

Age- and gender-related differences in 24-hour esophageal pH monitoring of normal subjects

Twenty-four-hour esophageal pH monitoring is currently the most sensitive test for diagnosing gastroesophageal reflux. Little is known, however, about the effect of aging and gender on esophageal acid exposure in asymptomatic individuals. Thirty asymptomatic volunteers underwent 24-hr esophageal pH monitoring. Fifteen were <65 years (eight female, seven male) and 15 were 65 years (seven female, eight male). In this asymptomatic group no significant difference was seen by age, while males were found to have significantly more esophageal acid exposure than females. The need for sex-specific normal 24-hr pH monitoring values is suggested. Thirty percent of these asymptomatic subjects were abnormal by conventional 24-hr pH criteria. The clinical importance of these silent refluxers is unknown.     

Reliability of 24-hour home esophageal ph monitoring in diagnosis of gastroesophageal reflux

Twenty-four-hour home esophageal pH monitoring is proposed in order to study gastroesophageal reflux (GER) so that prolonged use of costly hospital equipment and staff can be curtailed and the diagnostic accuracy of the examination improved. Eighty-six patients affected by GER symptoms and 20 healthy volunteers underwent 24-hr home esophageal pH monitoring, x-rays, and endoscopy of the upper gastrointestinal tract to investigate reliability of outpatient recording. Fifteen more patients consecutively underwent out- and inpatient recording to detect possible differences between these methods in the two daily periods. Outpatient monitoring was well tolerated in 94.7% of the patients; 14.3% of them markedly reduced their routine activities. The range of normality of outpatient recording does not differ from that of inpatients. In the 15 patients who consecutively underwent out-and inpatient monitoring, no significant differences were reported. The sensitivity of 24-hr home esophageal pH recording is 0.85, the specificity 1, the accuracy for negative prediction 0.68, and the accuracy for positive prediction 1. The reliability of 24-hr home esophageal pH monitoring is comparable to inpatient recording. It allows hospital cost reduction and is also better tolerated by patients but has not greatly improved the diagnostic accuracy of the gastroesophageal reflux pH monitoring.Supported by the Ministere Pubblica Istruzione, Rome; and Finanziamenti per studi e ricerche 40%, Com. 06, Cat 12-07 imp. 11515, University of Bologna.     

Simultaneous two-level esophageal 24-hour pH monitoring in patients with mild and severe esophagitis

Simultaneous ambulatory esophageal pH monitoring was performed in 10 patients (group 1) with normal distal acid exposure and in 40 patients (group 2) with pathological distal reflux. The probes were placed 5 and 10 cm above the lower esophageal sphincter to quantify variations of pH values that can be due to a displacement of pH sensor. In group 1 the median percent time with pH<4 for total and upright monitoring periods and composite score were significantly lower at the proximal than the distal level. In group 2 all pH data were significantly lower at the proximal than the distal level. The patients with pathological reflux were subdivided into two subgroups based on endoscopic findings (mild and severe esophagitis). The patients with severe esophagitis showed a proximal acid reduction higher than in patients with mild esophagitis. Nine patients with mild esophagitis showed normal values at 10 cm, but all patients with severe esophagitis had abnormal proximal acid exposure.     

含餐8 h食管pH监测与常规24 h pH监测对胃食管反流病的诊断价值比较

目的探讨含餐8h食管pH监测对胃食管反流病(GERD)的诊断意义,并以常规24hpH监测为标准验证其灵敏度及特异度。方法对2003年3月至2006年9月北京大学人民医院消化科221例患者进行食管测压和pH监测。首先由系统计算24h DeMeester积分,≥14.72分诊断为胃食管反流病。入选患者晚餐开始共计8h的监测数据,同样计算DeMeester积分,相同的标准诊断胃食管反流病。比较两种方法的一致性及积分的相关性。结果221例患者经常规24hpH监测诊断胃食管反流病124例,正常97例,含餐8hpH监测方法诊断胃食管反流病120例,正常101例。含餐8h的灵敏度为93.5%,特异度95.9%,经Kappa及Mc-nemar检验2种方法具有良好的一致性,部分结果的差异不具有显著性。2种检测方式DeMeester积分的相关系数为0.929。结论含餐8小时监测法和24hpH监测法具有良好的一致性,有望用于GERD特别是内镜阴性GERD的诊断。     

Gastroesophageal and laryngopharyngeal reflux detected by 24-hour combined impedance and pH monitoring in healthy Chinese volunteers

OBJECTIVE: To define the normative data of gastroesophageal reflux (GER) and laryngopharyngeal reflux (LPR) in healthy Chinese volunteers. METHODS: Healthy volunteers without gastrointestinal and throat disease and symptoms were enrolled and underwent 24‐hour impedance‐pH monitoring. RESULTS: A total of 37 healthy volunteers completed all the tests (female 54.1%; age 38.0 ± 15.2 years). Of 1862 GER, 49.6% were mixed, 40.9% were liquid and 9.5% were gas. More than half (54.9%) were acid. The median and 95th percentile numbers of GER were 52 and 71, respectively. The number of LPR was eight, of which two were mixed and the others were liquid. Only one episode of reflux was classified as acid LPR. The median and 95th percentile numbers of LPR were 0 and 2, respectively. More liquid reflux were associated with LPR (P = 0.02). Age had no influence on GER and LPR reflux profiles. CONCLUSIONS: Few LPR occurred in healthy Chinese volunteers and they were rarely acid when they reached the larynx. LPR was mostly associated with liquid reflux.     

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 microprocessorbased 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<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.     

Indications for 24-hour gastric pH monitoring with single and multiple probes in clinical research and practice

The methodology of prolonged gastric pH monitoring has not yet been standardized with regard to the number and position of pH probes. Twenty-seven healthy volunteers and 11 patients affected by nonulcer dyspepsia have been submitted to 24-hr ambulatory simultaneous pH monitoring of the distal esophagus, fundus, and antrum. Fundic and antral pH profiles have been compared and causes of pH variations (pH>4) identified. Both in healthy volunteers and dyspeptic patients, percentile curves of fundic and antral pH were statistically different in more than one of the daily periods considered (24-hr, postprandial, interdigestive, nocturnal). Percent time of duodenogastric reflux is significantly higher in the antrum than in the fundus in both groups. Modalities of gastric alkalinization secondary to food or duodenogastric reflux were different for the fundus and for the antrum both in healthy and dyspeptic subjects and between the two groups. These differences suggest that single and multiple pH monitoring of the stomach have different indications, and the position of the probes should vary according to the purpose of the test.     

国产食管pH胶囊与导管式24h食管pH监测的有效性、安全性及耐受性比较

[目的]比较国产食管pH胶囊与导管式24h食管pH监测的有效性、安全性及耐受性。[方法]26例志愿者均先应用导管式24h食管pH监测系统检测食管酸反流,隔1d后再应用国产食管pH胶囊进行食管酸反流检测,48h后送回接收器;监测期间记录工作、饮食、活动、睡眠和不适症状等情况。食管pH胶囊检查结束12d后行胸片检查明确胶囊脱落情况。[结果]与导管式24h食管pH监测方法相比,食管pH胶囊监测方法对食管酸反流检测的敏感性为78.57%,特异性为91.67%,准确性为84.62%;食管pH胶囊监测方法主要不适症状为吞咽疼痛、胸骨后异物感,而导管式24h食管pH监测方法中,咽喉部不适、流涕和恶心较多见。食管pH胶囊监测方法对日常生活、饮食和运动的影响程度较小,生活满意程度较高。当需要重复检查时,更多的志愿者愿意选择应用食管pH胶囊监测方法。12d后食管pH胶囊的脱落率为96.43%。[结论]国产食管pH胶囊与导管式24h食管pH监测2种方法的有效性相当,但食管pH胶囊监测方法较导管式24h食管pH监测耐受性高,安全性好。     

Low reproducibility of 2 x 24-hour continuous esophageal pH monitoring in infants and children: a limiting factor for interventional studies

The aim of this study was to investigate the day-to-day reproducibility of 24-hr esophageal pH monitoring. The procedure was performed continuously for 48 hr in order to enable future studies on dietary challenges, using consecutive 2 × 24 hr pH recording. Furthermore, one objective was to relate the degree of reproducibility to endoscopic evidence of mucosal injury. Upper endoscopy and 2 × 24-hr consecutive pH monitoring were performed in 30 infants and children referred for gastroesophageal reflux disease. The monitoring was performed without dietary or activity restrictions in order to assess reflux parameters in a near-normal physiologic setting. The NASPGHAN criteria for pathological reflux index (RI, % fraction of time with pH < 4.0) were employed. Based upon the NASPGHAN criteria for the RI, 9/30 subjects (30%) had discordant (normal vs pathologic) results at the two recording days, yielding an overall reproducibility of 70%. The limits of agreement for RI at day 2 were 0.2–3.3 times the initially obtained value at day 1. No difference was found in terms of reproducibility between groups with and without esophageal mucosal changes (erythema and esophagitis). No significant difference was noted in the association between pH monitoring and macroscopic esophageal mucosal changes between the two recordings days. In conclusion; a considerable intraindividual variability in reflux parameters was observed between the measurements from day 1 to day 2. This physiologic variability should be taken into consideration when evaluating gastroesophageal reflux disease in infants and children by means of pH monitoring. The day-to-day variability limits the use of simultaneous pH monitoring and dietary challenges as a procedure to identify a possible causative relation between GERD and dietary allergy/intolerance.     

Proximal Sensor Data from Routine Dual-Sensor Esophageal pH Monitoring Is Often Inaccurate

Dual-sensor esophageal pH monitoring is routinely used to diagnose GERD. However, the proximal sensor may not be in proximal esophagus in patients with shortened esophagi. Our objective was to determine how often the proximal sensor was misplaced and to determine the effect on pH monitoring. Superior margins of the upper and lower esophageal sphincters (UES and LES) were determined prospectively in consecutive patients. Dual sensors were placed 20 and 5 cm above the LES with a fixed 15-cm spacing pH catheter. Patients were classified into subgroups based on the actual location of the proximal sensor. In 661 patients, the proximal pH sensor was in the hypopharynx in 9% of patients, within the UES in 36%, and in the proximal esophagus in 55%. Spearman's correlation for acid exposure was very good between the dual sensors when the proximal sensor was in the proximal esophagus (R = 0.76) but was poor when the proximal sensor was misplaced in the hypopharynx (R = 0.28). The proximal sensor was misplaced in 45% of patients undergoing dual-sensor esophageal pH monitoring. It is important to locate the UES by manometry before interpreting the proximal esophageal pH data.     

Ambulatory 24-hr pH monitoring of esophagus,fundus, and antrum

A method for outpatient 24-hr simultaneous recording of pH in the distal esophagus, fundus, and antrum was developed in order to detect acid, alkaline, alkalacid gastroesophageal reflux, and duodenogastric reflux and to study these phenomena in patients complaining of gastroesophageal reflux and dyspepsia related symptoms. Two hundred ninety-four studies were performed in 42 healthy volunteers and 237 patients. Three-probe ambulatory 24-hr esophagogastric pH monitoring applicability, tolerability, and capability to determine a relationship between symptoms which occurred during the tests, gastroesophageal reflux, and duodenogastric reflux episodes were assessed. Eighty-nine percent of the three-probe esophagogastric pH studies were easily performed. The examination was tolerated well by 86.1% of the patients and poorly by 13.9%. A temporal correlation between symptoms and pH activities was recognized in 61.3% when the esophageal tracing was considered (acid gastroesophageal reflux recording) and in 95.6% when the three pH traces were simultaneously interpreted. Alkalacid gastroesophageal reflux and duodenogastric reflux total percentage times were significantly higher in patients complaining of dyspeptic symptoms than in patients only affected by typical gastroesophageal symptoms. Three-probe 24-hr ambulatory esophagogastric pH monitoring is a simple, well-tolerated test that should be routinely adopted for the study of patients complaining of unclear upper gastrointestinal tract symptomatology.     

Correlation of 24-hr esophageal pH patterns with clinical features and endoscopy in gastroesophageal reflux disease

We performed 24-hr ambulatory esophageal pH monitoring in north Indian patients with gastroesophageal reflux disease (GERD) and correlated it with symptom severity and endoscopic abnormalities. Thirty-six consecutive patients with symptomatic GERD and 16 healthy volunteers underwent objective grading of clinical symptoms and endoscopic findings. Total, supine, and upright reflux periods as well as frequency and duration of reflux episodes were determined from the 24-hr pH-metry record using standard software. This was abnormal in 32 patients, who could be categorized into upright refluxers (31.2%), supine refluxers (34.4%), and combined refluxers (34.4%). Supine reflux and upright reflux were distinct entities that did not correlate with each other (r=0.22,P=NS). In upright refluxers, symptoms (P<0.02) and=" endoscopic=" abnormalities=">P<0.005) were=" milder=" than=" in=" combined=" refluxers.=" total=" duration=" of=" acid=" exposure=" correlated=" significantly=" with=" severity=" of=" symptoms=">P<0.001) and=" endoscopic=" esophagitis=">P<0.005). patients=" with=" gerd=" had=" three=" distinct=" patterns=" of=" abnormal=" gastroesophageal=" reflux,=" with=" upright=" refluxers=" having=" milder=" disease=" and=" supine=" and=" combined=" refluxers=" having=" more=" severe=" disease.=" this=" may=" reflect=" differences=" in=" underlying=" mechanisms=" of=">     

Utilising multichannel intraluminal impedance for diagnosing GERD: a review

The diagnosis of gastroesophageal reflux is sometimes challenging, especially when symptoms are unresponsive to high-dose acid suppression. With the advent of new technology it is possible to detect and quantify nonacid or weakly acidic reflux. Multichannel intraluminal impedance (MII), introduced over 10 years ago, is gaining popularity as a reflux detection tool. The ability to detect nonacid or weakly acidic reflux events, aerophagia, and to discern true reflux events from swallows could make it more a powerful tool than pH detection alone. This is a review of the role of MII as it pertains to the diagnosis of GERD and related disorders. Studies done on normal subjects and in GERD reveal that nonacid or weakly acidic reflux occurs frequently. Several studies have been published that document types and frequency or reflux episodes comparing pH to MII. pH electrodes fail to detect the majority of nonacid or weakly acidic reflux events. MII has revealed nonacid reflux to be less common in untreated GERD subjects than in normal subjects. GERD subjects have greater degrees of liquid-type reflux events compared to normal subjects who have more gas-type reflux events. In treated GERD subjects and normal subjects, proton pump inhibitors do not seem to decrease the amount of reflux but render the reflux nonacid or weakly acidic in nature. Recently work evaluating atypical symptoms of GERD with MII has been published.     

24h动态PH监测在支气管哮喘合并胃食管反流病的临床研究

目的探讨24 h动态PH监测在支气管哮喘合并胃食管反流病(GERD)的诊断价值。方法纳入支气管哮喘患者32例(A组),GERD患者40例(B组),支气管哮喘合并GERD患者32例(C组),对3组患者行24 h食管p H监测,记录胃酸反流的总次数,总计、立位、卧位p H4的百分比,并行食管测压。结果C组及B组近段、中段远端的食管体部压力低于A组;A组食管括约肌静息压力、蠕动波传导速度高于C组及B组,反流频数C组低于其他两组;A组酸反流总次数,总计、立位、卧位p H4的百分比和De Meester评分均少于C组及B组。结论 24 h动态PH监测能发现更多的反流时间,卧位p H4百分比及反流频数是重要的参考指标。     

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.