Chapter 15 (page 73)

The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 15 (page 73)

During combined radiographic and manometric studies Keet et al. (l978) recorded fasting intraluminal pressures in the pyloric sphincteric cylinder by means of an air-filled system and a miniature balloon in 5 normal adult subjects in the erect position (Chap. 13). The following two distinct waves of pressure increase in the pyloric sphincteric cylinder were noted:

Irregularly occurring, nonrhythmic contractions, causing pressure increases varying from 9 to 34 mm Hg (the majority being in the range of 12 to 25 mm Hg). These waves lasted from 5 to 21 seconds (the majority being in the 6 to 10 second range), and occurred repeatedly in all subjects (Fig. 15.1). Simultaneous radiographic TV monitoring showed that each of these waves was associated with a typical maximal contraction of the pyloric sphincteric cylinder (Chap. 13). The waves also conformed to contractions of the "terminal antrum" (TAC) described by Carlson, Code and Nelson (l966), Code and Carlson (l968) and Shepard (l97l), called Type II waves.

Fig. 15.1. Two Type II pressure waves of pyloric sphincteric cylinder. Simultaneous radiography showed typical contraction of cylinder during both waves. Base line indicates intraluminal pressure in absence of radiologically visible motor activity. 10- second marker on zero line

In two of the subjects compound waves, consisting of a rise in base line pressure of 3 to 5 mm Hg and lasting for 10 to 40 seconds, on which were superimposed waves of shorter duration (3 to 5 seconds) and higher amplitude (up to 12 mm Hg) were seen. These conformed to Type III waves (Shepard l97l). (Comment: Radiologically both types of waves were associated with typical contractions of the pyloric sphincteric cylinder. Compound waves are usually ascribed to additional increases in tone. Contractions of the cylinder in the full stomach are usually quite regular, tending to occur at a rate of 3 per minute. The fact that pressure waves occurred irregularly in this investigation, might have been due to the fact that a small volume of liquid barium was used. Houghton et al pointed out that emptying of solids was associated with an increase in frequency of "antral" peristaltic waves; vide infra).

No attempt was made by Keet et al. (l978) to record contractions of the pyloric ring (right pyloric loop) and the sphincteric cylinder separately.

McShane et al. (l980) studied pyloric sphincter pressures in 32 patients under basal conditions, after stimulation with HCl and after posture changes. A single fine perfused catheter, 2.0mm in diameter, with 2 diametrically opposite side openings, was placed in the duodenum at endoscopy; resting pyloric pressures were measured during catheter withdrawal 3 to 5 hours later. In 28 of the 32 patients no rise in pressure occurred in the pyloric region. One patient of the remaining 4 showed a temporary rise in pressure which did not recur at repeat examinations, and in the other 3 there were pressure rises of 3.0, 3.0 and 6.0 mm Hg respectively. It was concluded that it was not possible to demonstrate any significant zone of pressure change at the pylorus in the basal state. Posture changes and instillation of 0.1N HCl into the duodenum did not affect the results. It was thought that the conflicting results previously obtained by Fisher and Cohen (l973) and by Valenzuela et al. (l976) might have been due to the fact that in their investigations the catheter was withdrawn too soon after intubation, at a time when the intubation itself might have affected the sphincter tone. Moreover, the catheters of Fisher and Cohen (l973) had 3 times the diameter of those used by McShane et al. (l980), which could also have affected their results; Brink et al. (l965) had shown previously that the larger the diameter of a pressure detecting unit, the greater were the pressures recorded. They implication was that the zones of elevated pressure recorded by Fisher and Cohen (l973) and by Valenzuela et al (l976), might have been due to muscle excitation and resistance to stretch, and might not have been a true indication of basal pyloric sphincter tone. McShane et al. (l980) concluded that the pyloric sphincter remained patent under fasting conditions, with a luminal diameter greater than 2.0 mm. They supported the concept of the pylorus as a "filter pump", having the ability to filter particles greater than 2.0 mm in diameter, while allowing fluid and chyme to enter the duodenum continuously.

In discussing the uncertainties pertaining to the action of the human pylorus, White et al. (l98l) thought that there had been a failure to obtain adequate pressure recordings from within the lumen. Pull-through techniques would not be applicable if the pylorus were open most of the time. It was necessary to determine the timing of closure of the pylorus with respect to contractions of the "antrum" and duodenal bulb. Consequently continuous records of intraluminal pressures had to be obtained simultaneously from the "antrum", pylorus and duodenal bulb. In order to achieve this end an open-tipped, water- perfused, six-channel catheter assembly with an external diameter of 6.0.mm was used. The middle opening was placed within the pylorus while other pressure channels recorded from the "mid-antrum" and the distal duodenal bulb. Measurements were taken in 15 fasting, normal human subjects in the right recumbent position. It was found that basal pressures in the "antrum", pylorus and duodenal bulb were the same relative to atmospheric pressures; there was no gradient of basal pressure across the pylorus. During withdrawal of the catheters through the pylorus a change in basal pressure did not occur.

White et al. (l98l) recorded a total of 264 "antral", 213 pyloric and 834 duodenal pressure waves. The majority of pyloric contractions were related to an "antral" contraction, and most of these were also associated with a duodenal contraction. In this way a concerted contraction of the whole gastroduodenal region occurred. However, independent contractions of all three areas were also encountered; 70 per cent of duodenal and 36 per cent of pyloric contractions were independent. Powerful contractions of the "antrum" were usually associated with related contractions of the pylorus and duodenum. Less powerful contractions of the "antrum" were usually independent. It was concluded that the human pylorus did not cause a zone of elevated basal pressure; apart from a brief closure during contraction, the pylorus was always open.