Ambulatory long-term pH monitoring in pigs -: Establishment of an easy technique and determination of normal and pathological values in a reflux model

Background: pH monitoring has been established as the "gold standard" in the diagnosis of gastroesophageal reflux. Evaluation of experimental antireflux therapy should therefore also include this technique, but a suitable technique in an experimental model did not exist so far. The aim of our study was to establish a reliable method for the evaluation of an experimental reflux model in pigs. Methods: A total of 33 German Landrace pigs with an average body weight of 56 (50.2-67.2) kg were included. pH monitoring was performed before and after open cardiomyotomy in each animal. All manipulations were performed under general anesthesia. After manometric localization of the gastroesophageal high-pressure zone, a standard pH probe was inserted into the pharynx through a small needle-punctured canal on the side of the animal's snout and placed under endoscopic guidance with the proximal sensor 3 cm above the lower esophageal sphincter (LES) and the distal sensor in the stomach for reference. The harness to carry the pH recorder on the animal's back consisted of a modified belly strap that enabled the animal to move around without limitation. For analysis the same threshold levels were defined as in humans. Gastroesophageal reflux was induced by cardiomyotomy. Results: The placement of the standard pH probe was possible in all cases. Inserting the probe on the side of the snout left the animals free to nuzzle, which complies with the normal habits of pigs, without breaking the probes and without being compromised in their natural behavior. Repeated punctures for multiple measurements were easily feasible. We performed up to three examinations in each individual animal. Recording was performed for 48 h. A mean number of 67.3 (+/-9.7) acidic refluxes were registered. The mean number of long acidic refluxes was 3.2 ( 0.75). For an average total time of 75.5 (+/-14.3) min the pH was below 4 accounting for a fraction time pH below 4 of 3.5% (+/-0.68%). Following cardiomyotomy the number of acidic refluxes increased significantly to 166.1 (+/-21.8) and the number of long refluxes to 17.74 (+/-3.35). The total time of pH below 4 increased to 371.3 (+/- 62) min so that the fraction time pH below 4 was 14.5% (p = 0.0006). Conclusion: pH monitoring should be mandatory in any investigation of antireflux therapy. Our method is easy and secure to perform. It is suitable for other gastrointestinal investigations (Bilitec, long-term manometry) that could be carried out using the same technique. The described data represent the basis for other investigations of experimental antireflux therapy.