Plastic pH electrodes for the measurement of gastrointestinal pH.

Plastic electrodes have been developed for measuring pH in the human gastrointestinal tract. The electrodes have a plastic hydrogen ion sensitive membrane sealed to a length of fluid filled PVC tubing. Two recently developed hydrogen ion sensitive ligands have been examined. Their operational characteristics have been described. These electrodes have an electrical response of 52 to 58 mV/pH unit change in the range pH 4-9, with a diminished response outwith this range. They have a low resistance value and a fast response time of one second to reach 90% of their maximum response. The electrodes can be passed down the biopsy channel of an endoscope to obtain mucosal pH readings under direct vision. Readings obtained in this way using plastic electrodes are comparable to those obtained with glass electrodes. Alternatively, these electrodes can be joined to a Crosby capsule, allowing continuous recording of mucosal pH through to the jejunum during jejunal biopsy procedures. These electrodes can be used repeatedly or may be acceptable as inexpensive disposable items for sterile clinical use.     

Esophageal pH monitoring

In the 25 years since it was first described, prolonged esophageal pH monitoring has gained increasing acceptance and popularity as a diagnostic and research technique in GER disease. Some recent developments that have contributed to its attraction include compact portable recorders, computerized analysis, short monitoring periods, the good discriminant value of the simple measurement of percent monitoring time that pH is less than 4, and the symptom index, allowing correlation of symptoms with reflux events. Nevertheless, there remain areas of uncertainty with regard to reproducibility and the conditions of monitoring, in particular whether strict dietary control and controlled activity and posture are necessary. There is no universally accepted normal range of values, but it is now apparent that normal and abnormal GER are not appropriately differentiated by simply defining the upper limit of normal using a formula of the mean plus two standard deviations, so other statistical techniques have emerged. Indications for the technique include atypical symptoms, particularly noncardiac chest pain, respiratory symptoms, and, in young children, apneic attacks and recurrent vomiting associated with failure to thrive. The technique is having an impact on the assessment prior to, during, and after medical and surgical therapy for GER, as well as in helping to unravel the complexities of the pathogenesis of esophagitis.     

Accurate placement of the esophageal pH electrode for 24-hour pH monitoring using a combined pH/manometry probe

OBJECTIVE: Accurate placement of a pH electrode requires manometric localization of the lower esophageal sphincter (LES). Combined manometry/pH devices using water-perfused tubes attached to pH catheters and the use of an electronic "LES locator" have been reported. We investigated whether accurate placement of pH probes can be achieved using such a probe, and whether this may reduce the need for the performance of the usual stepwise pull-back manometry. METHODS: Thirty consecutive patients (15 men, 15 women; median age, 56 yr; interquartile range, 42-68 yr) referred for manometry and pH testing were included in the study. The localization of the LES was determined with standard esophageal manometry. After that, a second 3-mm pH electrode with an internal perfusion port was passed into the stomach. Using this catheter, a single stepwise pull-through manometry was performed and the LES position was noted. LES location, mean pressure, and length obtained with standard manometry were compared to data from the combined pH/manometry catheter. Additionally the time necessary to perform each of the procedures was noted and the patient's discomfort caused by the catheter was evaluated using a standardized questionnaire. RESULTS: The LES location with the pH/manometry probe was proximal to that with standard manometry in 19 patients (63%), the same in nine patients (30%), and distal in two patients (7%). The differences were <2 cm in 29 of 30 (97%) patients. The LES location with the pH/manometry probe required a median of 6.5 min (interquartile range: 3.5-8.5 min) versus a median of 21.5 min (interquartile range: 14.5-26.5 min) for standard manometry (p < 0.0001). In addition, LES evaluation using the combined pH/manometry probe provided accurate data on the resting pressure, as well as overall and intraabdominal length of the LES. All patients tolerated the combination probe better than the standard manometry probe (p < 0.001). CONCLUSIONS: Placement of the esophageal electrode for 24-h esophageal pH monitoring using a combined pH/manometry probe is accurate. The technique is simple, time-saving, and convenient for the patients. Because it is possible to accurately evaluate the LES using this technique, it may even replace conventional manometry before pH probe placement.     

Relation of antral pH to gastrin release and fundal pH in dogs

Summary and conclusions Four dogs were prepared with Heidenhain pouches and cannulas placed in the fundus and antrum. Fasting pouch output was measured for 1 hr. Changes in pH in the fundus and pouch, and pouch acid production were then determined while antral pH was varied by perfusion in increasing and decreasing sequences. Results were virtually identical with ascending and descending antral pH values.With an antral pH below 1.8 no appreciable pouch secretory effect was found, the values being identical with those obtained under fasting conditions. A transition zone was encountered between antral pH 1.8–3.0 in which relatively small and variable amounts of pouch acid were produced. Above an antral pH of 3.0 a significant stimulatory effect was noted that did not increase with further increments of antral pH.Fundal and pouch pH were relatively high and had little relationship to one another when antral pH was less than 1.8. The values fell and became more closely associated at the antral transition zone of pH 1.8–3.0. Above an antral pH of 3.0, fundus and pouch pH decreased and fluctuated in a parallel manner. Pouch pH was consistently below fundal pH.Supported by a grant from Wyeth Laboratories, Inc., Radnor, Pa.     

Alternative method of positioning the pH probe for oesophageal pH monitoring.

The most reliable method of positioning a pH probe for oesophageal pH monitoring is to use manometry to determine the upper margin of the lower oesophageal sphincter and to place the probe 5 cm above this point. Manometry is expensive, however, requires special equipment and training, and is not widely available. An alternative cheaper way of determining the site of the lower oesophageal sphincter has been evaluated. A fine bore nasogastric tube with a latex balloon at its tip was inserted transnasally into the stomach. The balloon was inflated with 10 ml of water and the tube withdrawn until resistance was met. The distance from the nose (in cm) was noted and compared with the upper margin of the lower oesophageal sphincter as determined by oesophageal manometry. The manometric distance agreed closely with the balloon distance minus 1 cm (bias 0.29 cm; 95% CI of bias, 0.03 to 0.55 cm; 2 SD, limits of agreement, 1.58 cm). We conclude that where oesophageal manometry is not available, balloon localisation is a suitably accurate way of identifying the lower oesophageal sphincter.     

pH probe positioning for 24-hour pH-metry by manometry or pH step-up

OBJECTIVES: Before pH measurement, manometry is recommended for precise pH probe positioning. We investigated whether the pH probe could be positioned accurately by the pH difference between the oesophagus and the stomach (pH step-up). METHODS: Dual-channel 24-h pH-metry with probes positioned 5 cm above either the manometrically determined upper lower oesophageal sphincter margin or the pH step-up was performed in healthy volunteers and reflux patients. To determine the pH step-up, the pH probe was pulled back from the stomach until a sudden rise to pH greater than four occurred. Probe position, reflux episodes and the fraction of the time pH was less than four were compared using the Wilcoxon test for difference and the Hodges-Lehman estimate inclusive confidence interval for equivalence. The pH step-up method was evaluated further during proton pump inhibitor therapy and after drug discontinuation. RESULTS: The pH probe was positioned 2 cm and 1 cm closer to the stomach by the pH step-up method in the volunteers and reflux patients, respectively. A small increase in upright reflux episodes but not in supine reflux episodes was registered by the probe positioned by pH step-up. No significant differences in the fraction of the time pH was less than four were obtained between the two probes. The Hodges-Lehman calculation proved equivalence for both methods of probe positioning for 24-h pH-metry. During proton pump inhibitor therapy, no pH step-up was detectable in three volunteers and in one patient. On the first day after discontinuing therapy, the pH step-up method yielded clear-cut results again. CONCLUSION: The pH probe for diagnostic 24-h pH-metry and, with some limitations, also for 24-h pH-metry for therapy control, can be positioned accurately by the pH step-up method.     

Ambulatory esophageal pH testing

Over a 30-month period, 867 esophageal pH studies were conducted in a Canadian teaching hospital; of these, 315 tests were recorded in patients who were first-time referrals having no chest or upper gastrointestinal surgery and taking no medication that would affect the results. Patients were referred by gastroenterologists, general surgeons, ENT surgeons, thoracic surgeons, and a miscellaneous group. Patients were classified based on: pH results [abnormal=% total time pH<4.0 (ie, >6.0%)], manometry (abnormal=LES resting pressure<5 mm Hg and/or abnormal peristalsis), and gender. Fifty-one percent (162/315) of the patient records demonstrated abnormal reflux. Intergroup comparisons of severity of reflux using two-way analysis of variance demonstrated no significant differences (P=0.13). In the 162 patients who refluxed, 70% (N=108) had normal motility studies; however, when the severity of reflux was compared, patients with abnormal motility (N=54) demonstrated significantly more severe reflux (19.8±12.8 vs 16.2±11.3)P=0.02. In those patients with abnormal manometry, no significant differences (P=0.44) in the severity of reflux were found among those with abnormal peristalsis (N=27), low resting pressure (N=17), or a combination of aperistalsis and low LES pressure (N=10). Symptomatic patients with reflux (N=107) demonstrated a significantly greater percent time pH<4.0 than those with asymptomatic reflux (N=55); 18.1±11.5% vs 16.2±12.7%,P=0.04. When the severity of reflux by gender was compared, no significant differences were found [18.3±11.9 (male)N=91 vs 16.2±11.9 (female)N=71,P=0.11]. The results from this study show that: (1) esophageal pH testing is important in subspecialties other than gastroenterology and that the clinical yield is high in all referring groups, (2) esophageal pH testing and manometry are complimentary tests, but that reflux occurs commonly in association with normal manometry, (3) asymptomatic reflux was found in 34% of the patients with abnormal reflux scores, and (4) the severity of reflux in male and female patients is similar.     

Determination of pH turning point with pH mapping of the gastroesophageal junction: an alternative technique to orientate esophageal pH monitoring

Manometric location of the lower esophageal sphincter (LES) has been mandatory before esophageal pH monitoring, despite costs and discomfort related with esophageal manometry. The aims of the study were: (i) to map the pH of the gastroesophageal junction (GEJ) to determine a pH turning point (PTP) and its relation with LES; and (ii) to test the feasibility of this technique to orientate esophageal pH monitoring. We studied 310 adult patients who underwent esophageal manometry and pH monitoring off acid‐suppressive therapy. GEJ pH mapping was carried out by step‐pulling the pH sensor from 5 cm below to 5 cm above LES, and a PTP was determined when pH changed from below to above 4, in centimeters from the nostril. Thirty‐six patients referred only for pH monitoring were studied with pH sensor placed at 5 cm above the PTP. Out of 310 patients, a PTP was found in 293 (94.5%): inside LES in 86.3%, into the stomach in 8.2% and in the esophageal body in 5.5% of patients. The median distance between PTP and place where pH sensor monitored reflux was 8 cm. Among 36 patients who performed pH monitoring without LES manometry, there was no gastric monitoring during reflux testing. In adult patients investigated off acid suppressive therapy, GEJ pH mapping with reflux monitoring 5 cm above the PTP can be an alternative technique to perform esophageal pH monitoring when LES manometry is not available. Additional studies are needed before the widespread use of GEJ pH mapping in the clinical practice.     

Reflux and pH: ''alkaline'' components are not neutralized by gastric pH variations

The ability of the 'alkaline' components of reflux to cause harm in vivo is still open to debate, although these components have been shown in vitro to be capable of damaging the mucosa. The precipitation of bile acids and lysolecithin that occurs at low pH values is the main reason for questioning in vivo mucosal damage. This study was undertaken to determine the composition of gastric aspirates at different original pH values and the degree of solubility of the alkaline components when pH modifications are artificially induced. The samples for chemical analysis were collected from indwelling nasogastric tubes after surgical procedures that did not involve the upper gastrointestinal tract. Bile acid and lysolecithin concentrations were assessed by means of dedicated methods. Thirty-five samples were available for bile acid evaluation and 27 for lysolecithin evaluation. Bile acid and lysolecithin assessments were repeated after pH adjustment at 2, 3.5, 5.5 and 7. For easier assessment of the results, three ranges of the original pH were selected (pH < 2, 2 < or = pH < 5, pH > or = 5). For each pH range, results were pooled together and compared with those in the other pH ranges. Bile acid concentrations were 113+/-48, 339+/-90 and 900+/-303 (mean +/- s.e.m. micromol/L), respectively, in the three groups selected on account of the different original pH values. Differences were significant (p < 0.001). Both taurine- and glycine-conjugated bile acids were represented even at pH < 2. No major differences were observed in bile acid concentration with the artificially induced pH variations. Lysolecithin concentrations were 5.99+/-3.27, 30.80+/-8.43 and 108.37+/-22.17 (mean +/- SEM microg/ml), respectively, in the three groups selected on account of the different original pH ranges. Differences were significant (p < 0.001). No significant differences in lysolecithin concentration were detected with the artificially induced pH variations. In conclusion, both bile acids and lysolecithin are naturally represented in the gastric environment even at very low pH values, although their concentrations decrease on lowering of the naturally occurring pH. Given the concentration variability of bile acids and lysolecithin, further studies are needed to assess the minimal concentration capable of mucosal damage in vivo.