The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 18 (page 84)

Malagelada (l977) described the striking changes undergone by a solid liquid meal in the stomach during the postprandial period. Gastric and duodenal aspiration of a meal of meat labelled with 51Cr and containing water with polyethylene glycol, showed that the volume of solids was decreased by solubilization and partial digestion in the stomach. At the same time, endogenous secretions expanded the liquid phase of the gastric contents. Because of these processes, the gap between the percentage of solids in the stomach and that entering the duodenum gradually disappeared during the postprandial period, and gastric secretions rapidly replaced the water imbibed as the main intragastric liquid. It was thought that the process of retaining solids in the stomach and allowing liquids to empty into the duodenum, would expose the solid nutrients to continuously renewed, fresh gastric juice.

Canine gastric emptying of a digestible solid, an indigestible solid and a liquid was studied by Hinder and Kelly (l977), by quantitating the rate of appearance of gastric markers in the duodenum. Bovine liver tagged with 57Co-cyanocobalamine, 7.0 mm diameter radio-opaque plastic spheres and one percent or 10 percent dextrose tagged with 3H polyethylene glycol (3HPEG) were used for the digestible solid, the indigestible solid and liquid respectively. The rate of gastric emptying of cubed liver was found to be similar, whether the liver was given alone or with solutions of the rapidly emptying one percent dextrose; the rate of emptying was slowed by 10 percent dextrose. Homogenization of the liver speeded emptying. The homogenized liver emptied even faster when dispensed in one percent dextrose, and emptied more slowly when dispersed in 10 percent dextrose, but in both instances the liver emptied at the same rate as the solution with which it was mixed. Indigestible spheres were nearly all retained, whereas the liver and dextrose were emptied. It was concluded that the stomach emptied liquids while solids were retained for reduction to a smaller size, after which they were discharged at the same rate as the liquid then present in the stomach.

Meyer (l979) pointed out that while external gamma counting of food markers to measure gastric emptying should theoretically obviate the need for sampling gastric contents, the method was not entirely free from difficulties. The distribution of radiolabels was not necessarily precise, as labels of the aqueous phase might adhere to the solids, and overlap could contribute to inaccuracies in gamma counting. Even when a radiolabel accurately identified a portion of the solid phase, that portion might empty at rates dependent on the size of its particles. Meyer (l980) nevertheless pointed out that short half-life, low- energy, gamma-emitting nuclide labels were safe for the investigation of gastric emptying processes. The phagocytosis of circulating colloidal nuclides such as 99mTc and 113mIn by the Kupfer cells of the liver of living donor animals had reduced labelling time. Hepatocytes could be labelled with 57Co or 59Fe in donor animals to provide tagged liver. The high chemical affinity of elemental 123I for starch in foods and the chemical conjugation of radioiodine to hemicellulose have also provided methods for labelling food constituents. Having identified some of the artifacts in counting, methods have been instituted to correct them.

Horowitz et al. (l982) in an extensive review, pointed out that major advantages of radionuclide studies of gastric emptying were that they were simple and noninvasive, did not interfere with normal physiological mechanisms in the stomach, and allowed the simultaneous labelling of solid and liquid components of a meal. Methodological problems limiting the specificity and sensitivity of radionuclide tests included factors such as angulation of gamma rays originating within the stomach, causing them to be counted outside the gastric region of interest. Most of these minor problems were capable of correction.

According to Horowitz et al. (l982), emptying of labelled solids was usually linear after an initial lag phase. The lag phase reflected the movement of food from the fundus to the "antrum". Emptying of liquids was generally nonlinear, with a minimal lag period, and could be represented as a monoexponential, volume dependent process. Consequently it appeared that solid and liquid components of a meal were emptied in different ways. The pressure gradient across the gastroduodenal junction, largely controlled by the tone of the fundus, was the major factor controlling the emptying of liquids. The "antropyloric musculature" was of major importance in controlling the emptying of solid food, the end point being the passage of particles less than 1.0mm in size. Both these processes were also controlled from the duodenum by receptors responding to carbohydrate, fat and protein, with resultant slowing of gastric emptying.

Collins et al. (l983) assessed gastric emptying of a mixed solid and liquid meal in normal subjects, using 99mTc sulphur colloid as the solid, and 113mIn-DTPA as the liquid marker. It was shown that large errors in the measurements were possible, due to the variation in tissue attenuation caused by the changing depth of the radionuclide within the stomach. A technique for the correction of attenuation was described, using factors derived from a lateral image of the stomach. Normal solid emptying was found to be slower than liquid emptying and was characterised by a delay or lag period, which was followed by linear emptying; liquid emptying followed a single exponential pattern. Increasing the calorie content of the meal prolonged the lag period of solid and slowed liquid emptying. Whereas previous studies using other radionuclides in normal subjects had shown day-to-day variation in gastric emptying rates within normal subjects, as well as variations in rates between subjects (Heading et al. l976), this study showed that the day-to-day variation in gastric emptying within individual subjects was not significant. On the other hand, statistically significant differences were present in solid and liquid emptying between different subjects and groups.

Camilleri et al. (l985) studied the possible relation between "antral" phasic pressure activity and the emptying of solids and liquids from the normal human stomach after a mixed meal. Simultaneous antral manometry and radioscintigraphy were performed in 14 normal individuals after ingestion of a meal labelled with 99mTc sulphur colloid in cooked egg (solid component) and 111In DTPA (liquid component). Phasic pressure activity was recorded in the "distal antrum", i.e. 1.0 cm proximal to the gastroduodenal junction. During early precipitous emptying of liquids, occurring during the lag phase for solids, there was no relation between liquid emptying and "antral" motility. During the solid-emptying period however, there was a positive correlation between emptying of solids and "antral" motility. In addition, during the solid-emptying phase, a possible association was noted between antral phasic pressure activity and the emptying of liquids. The data are consistent with a role for antral pressure activity in trituration of solid food and a role for the "antrum" in the subsequent propulsion of solids and liquids from the stomach.

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