Chapter 15 (page 74)

The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 15 (page 74)

Dooley et al. (l985), commenting on the contradictory results of previous investigators, pointed out that the motility of the upper gastrointestinal tract during fasting was not a static one and marked variations were seen during the various phases of the interdigestive motility complex (IDMC). It was conceivable that the pylorus could show cyclic variation with the different phases of the complex. Consequently pyloric pressure was monitored continuously for 300 minutes at a time, in 6 healthy fasting adult subjects. A perfused catheter system was used with 2 "antral" and 2 duodenal side openings. A Dent (l976) sleeve, 4.5 cm in length and with an outer diameter of 6.0mm, was incorporated in the multilumen tube assembly between the duodenal and antral ports, and placed in the pylorus under fluroscopic control, with measurements obtained in the supine position. The pylorus was assessed for the possible presence of an elevated basal pressure zone, using baseline duodenal pressure as a reference. Pyloric pressure was also analyzed for each separate phase of the IDMC, and the frequency and amplitude of its phasic contractions were determined.

Dooley et al. (l985) found that basal pyloric pressure in the fasting state showed no elevation above baseline duodenal pressure during phase III of the IDMC. In phases I and II, basal pyloric pressures varied in different subjects, being elevated in some but not in others. Subjects studied on separate days often showed different patterns of activity, and it appeared that duodenal acidification gradually increased basal pyloric pressure. The pylorus also showed phasic activity, which was maximal in phase III. The exact significance of this activity was not clear. The sleeve device did not allow any firm conclusions to be drawn on the phasic activity of the pylorus in relation to that of the "antrum" on the one hand, and that of the duodenum on the other.

Using a system of perfused catheters and a pull-through technique, Gaffney et al. (l987) found that the presence of a high pressure zone at the pylorus was very variable. Of 170 records made, a high pressure zone was present in 53 percent while no change in pressure was found in 47 percent. The subject's position had no effect on the presence of a high pressure zone, which refuted the premise of Kaye et al. (l976) that the zone of elevated pressure found by Fisher and Cohen (l973) might be artifactual. In addition the pylorus showed no response to duodenal acidification. It was concluded that the evidence weighed heavily against the presence of a tonic sphincter at the pylorus.

Houghton et al. (l988) investigated the normal patterns of pressure activity in the "antrum", pylorus and duodenum and their relationship to changes in "antral" and duodenal pH, under fasting conditions and after ingestion of chocolate milk. By this procedure the relationship between motor events and transpyloric flow of acid gastric secretions could be determined. An eleven-channel intraluminal probe was used, incorporating a sleeve sensor 4.5 cm in length positioned across the pylorus. The maximum diameter of the manometric assembly was 6.5 mm. The "short pyloric sphincter" was identified by continuous measurements of transmucosal electrical potential difference (Chap. 6). The sleeve sensor in the pylorus consistently registered a higher basal pressure from the pylorus than from the adjacent "antral" and duodenal ports. However, it was conceded that the recording of pyloric tone might depend on the width of the manometric probe in relation to the pyloric aperture; the higher basal pressure might be an artifact. The most common fasting motor pattern consisted of regular co-ordinated contractions, most of which involved the "antrum" and duodenum, and showed evidence of propagation with transient reductions in duodenal pH. Ingestion of milk changed the motor pattern to one which was composed of pressure waves confined to the pylorus with few waves in the "terminal antrum" or proximal duodenum. These isolated pyloric pressure waves were gradually replaced by propagated "antroduodenal" contractions occurring at a regular frequency. The liquid component of a mixed meal emptied rapidly in an exponential manner, whereas the solid remained in the gastric fornix until 80 per cent of the liquid had emptied, and then emptied in a linear manner; the onset of solid emptying was associated with an increase in the frequency of antral pressure waves.

Discussion

Gaffney (l987) pointed out that the results of pyloric manometric studies conflict, some showing evidence of a sphincter at the pylorus, and others not. As examples of the former, the following may be mentioned:

Brink et al. (l965) demonstrated a narrow (1.1cm to 1.6cm) zone of raised intraluminal pressure at the gastroduodenal junction in canines. Isenberg and Csendes (l972) found the dog pylorus to be tonically contracted, the sphincter length being 1.8 cm. Fisher and Cohen (l973) recorded a pyloric high pressure zone, 1.5 cm in length, in humans; to them it had the characteristics of a true sphincter, but it was acknowledged that it could simply be a manifestation of the normal configuration of the pyloric channel. Valenzuela et al. (l976) found that the basal pyloric sphincter pressure was elevated in normal human subjects lying on the right side; they looked upon the pyloric ring as a sphincter in the usually accepted sense. Using a sleeve sensor, Houghton et al. (l988) consistently registered a higher basal pressure from the pylorus than from the adjacent antral and duodenal ports. This was ascribed to the pyloric sphincter, but it was acknowledged that it might be artefactual.

These findings were not accepted universally. Kaye et al. (l976) pointed out that the results of Fisher and Cohen (l973) could have been influenced by the fact that subjects were examined in the right lateral decubitus position; in this position there could be angulation of catheters with increased resistance to flow and consequent increase in intraluminal pressure. Valenzuela et al. (l976) similarly examined patients lying on their right side. However, Gaffney et al. (l987) found that the subject's position had no effect on the presence of a high pressure zone, refuting the premise of Kaye et al. (l976).

It is doubtful if the findings of Brink et al. (l965) and of Isenberg and Csendes (l972) can be regarded as physiological, as each experimental animal had both a gastrostomy and a duodenostomy, which might have influenced the results.