Understanding Pyloric Sphincter Activity Using a Distensibility Technique

Jorge Alberto Arroyo Vazquez, MD¹, Per-Ola Park, MD, Professor¹, Maria Bergstrom, MD, PhD¹, Steven Bligh², Barry P McMahon, PhD². ¹Dept of Surgery, South Alvsborg Hospital & Gothenburg University, ²Trinity Academic Gastroenterology Group, Trinity College & Tallaght Hospital, Dublin, Ireland

Background

Limited data is available to fully describe the function of the pyloric sphincter. It is clear that its primary role is in gastric emptying and the control of stomach contents. Stent treatment of duodenal perforated ulcers has been tried out with good clinical results but stent migration has occurred in a few cases. Our theory is that the stent itself causes an increased pressure in the pyloric sphincter initiating emptying sphincteric actions. The aim of the study was to investigate whether distending the pyloric sphincter with the functional lumen imaging probe (FLIP) would provide a better understanding of the pyloric sphincter physiology. The effect of Neostigmine on the sphincter function was also studied.

Method

Four female pigs (40-50 kg) were acquired for the study which had ethical approval. The pigs were anaesthetised and gastroscoped. The EndoFLIP™ Catheter EF-353 (Crospon, Galway, Ireland) was inserted through the scope and placed in the pylorus. To aid positioning a small volume of 20 to 30 ml was filled into the catheter and probe position was adjusted by viewing the EndoFLIP screen and observing the hourglass shape. It was decided that the optimal position would be when the probes 16 measurement were straddling the pyloric sphincter so that the central measurements represent the narrowest region in the middle. Stepwise volume controlled distensions to balloon fill volumes of 20ml, 30ml, 40ml and 50ml were carried out. The volumes were maintained for 1 min and the complete step protocol was repeated. 1.5mg of neostigmine was then administered intravenously and no measurements were taken for 5 minutes to allow for the effect of the drug to occur. The stepwise volume controlled distensions were then repeated.

Results

The EndoFLIP catheter could successfully be inserted into the pylorus and infused with a liquid volume. Initial distensions clearly indicated that it was easy to locate the probe straddling the pylorus. Patterns of motility observed at all bag volume levels indicated a constant rhythmic opening of the narrowest region in the pyloric sphincter while simultaneous a drop in pressure in the bag was observed, indicating that the movement was specifically of an opening and closing nature and not similar to peristaltic wave movement observed in other parts of the GI tract. Plots of narrowest CSA (Cross Sectional Area) and bag pressure during the 1 minute volume hold period indicated that as volume increased the opening patterns grew larger and the pressure increased, consistent with a valvular region that is relatively compliant. A plot of distensibility at the step volumes before and after neostigmine administration indicates that the pylorus becomes more distensible after the administration.

Conclusion

The FLIP can easily be used through a gastroscope for assessing the pyloric sphincter physiology. The sphincter seems to be compliant; it relaxes more and opens more widely after larger volume distensions. This might influence pyloric actions during stent treatment. Possibly larger and stronger stents induce more emptying activity leading to more stent migration.