Chapter 15 (page 72)

The Pyloric Sphincteric Cylinder in Health and Disease

Go to chapter: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39
Chapter 15 (page 72)

Fisher and Cohen (l973) used infused open-tipped catheters for their manometric studies of the gastroduodenal junction in 28 normal, fasting human subjects. All measurements were made with the subject lying on the right side. At the duodenogastric junction a high pressure zone approximately 1.5 cm in length was recorded. The pressure here varied from 2.5 to 11.7 mm Hg above the intra-abdominal pressure, with a mean magnitude of 5.0 mm Hg. During duodenal acidification with 0.1N HCl the pyloric pressure increased from its basal level of 5.0mm Hg to 25.0 mm Hg, an increase occurring in all l7 subjects tested. Intraduodenal olive oil also significantly increased pyloric pressure. An "antral" peristaltic contraction was associated with a brief drop in pyloric pressure, followed by a sequential contraction of the pylorus and the duodenum. This motor behaviour did not occur consistently and could be recorded in several subjects only.

Fisher and Cohen (l973) concluded that the human pylorus had the physiological characteristics of a true gastrointestinal sphincter, since (1) it was distinguised by a zone of elevated pressure which relaxed with "antral" peristalsis; (2) the high pressure zone contracted in response to physiological duodenal stimuli, and (3) an increase in pyloric pressure was associated with a diminution in reflux of duodenal contents into the stomach. Compared with other gastrointestinal sphincters, the high pressure zone was narrow and had a low resting magnitude, which might explain the failure of previous studies to recognize it. They considered their perfused catheters to be more sensitive than balloon sensors which had been used in some previous investigations. Although the presence of a high pressure zone at the gastroduodenal junction implied sphincteric properties, these authors pointed out that an alternative explanation might be that the high pressure zone was simply a manifestation of the anatomical configuration of the "pyloric channel". In that case the findings would not be of any functional significance.

Kaye et al. (l976) did not agree with Fisher and Cohen (l973) that perfused catheters were more sensitive than balloon sensors. As each sensor in a perfused catheter assembly had of necessity a restricted radial disposition, an important limitation was imposed on sphincteric assessment. In their opinion balloon sensors were less accurate, but not less sensitive than perfused catheters. For these reasons they used a circumferentially sensitive pressure sensor, consisting of a silastic diaphragm around a fluid-filled chamber containing a miniature transducer. The overall circumference was 6.0mm, the device being both accurate and sensitive to pressure around the whole circumference. Pressures were recorded in 8 healthy, fasting human subjects lying in the supine position. Transient phasic pressure rises were occasionally observed at the gastroduodenal junction (as indicated by a change in electrical potential difference as described in Chap. 6), but in no instance was a zone of tonically elevated pressure demonstrated convincingly. The most striking evidence for a pyloric high pressure zone in any of the 8 subjects was a sustained rise of only 1.0 or 2.0 mm Hg, corresponding to a 26mV change in potential difference.

Because the miniature transducer assembly was not suitable for the introduction of solutions into the duodenum, additional studies were done with a six-lumen, open-tipped, continuously perfused catheter system similar to that of Fisher and Cohen (l973), its overall diameter being 5.4 mm. Ten healthy, fasting, supine human subjects were studied, firstly in the basal state, subsequently during infusion of 0.1N HCl into the duodenum and lastly after instillation of olive oil into the duodenum. During the basal withdrawal studies a pressure elevation was seen in 1 of 3 pressure-transmitting catheters in 2 of the 10 subjects. Such tonic elevations of pressure were seen more frequently during intraduodenal infusion of HCl and installation of olive oil, but in only one subject was a rise of pressure noted in all 3 leads; this was quite small and occurred over a distance of only 0.5 cm. These elevations were felt to be due to mucosal apposition of the catheter orifice as it traversed the narrowest part of the gastroduodenal region. It was also shown that the right lateral position, as used by Fisher and Cohen (l973), could cause 90 degree angulation at the gastroduodenal junction with increased resistance to flow and therefore an increase in intraluminal pressure.

With both types of assembly, Kaye et al. (l976) recorded phasic elevations in most subjects from both duodenum and "antrum". The "antral" motor activity was usually most prominent at, and immediately proximal to the gastroduodenal junction. These authors concluded that they were unable to demonstrate a zone of tonically elevated pressure at the gastroduodenal junction in healthy subjects, despite the use of accurate and sensitive manometric systems. They inferred that the pylorus was open for most of the time in fasting, healthy young individuals. This conclusion was considered to be consistent with endoscopic observations, which showed that the pylorus was usually not completely closed except during the terminal phase of "antral" contractions (Chap. 14).

Valenzuela et al. (l976) assessed pyloric sphincter pressures in normal, fasting human subjects as well as in patients with gastric ulcer and duodenal ulcer. All individuals were examined in the right recumbent position by means of an open-tipped, water-perfused catheter assembly. Intra-duodenal pressure was used as a zero reference and pyloric pressure was measured as a zone of sustained elevated pressure without considering peak phasic contractions. Basal pyloric sphincter pressure was found to be 10.2 ± 1.2 mm Hg. During perfusion of acid into the duodenum the pressure was almost doubled, to 20.2 ± 1.8mm Hg. This was prevented by the prior administration of atropine. Metoclopramide increased pyloric sphincter pressure in normal subjects as well as in patients with gastric ulcer and duodenal ulcer.

While comparing the findings of Fisher and Cohen (l973) with those of Kaye et al. (l976), Winans (l976) was moved to conclude that the pylorus was "fickle". Whereas Fisher and Cohen (l973) presented evidence to show that it was a true sphincter in the anatomical and physiological sense, the findings of Kaye et al. (l976) cast doubt upon the legitimacy of that claim. Could the divergent experimental results be reconciled? Winans (l976) thought that an explanation might be found in differences in methodology. The right decubitus study position of Fisher and Cohen (l973), for instance, might have narrowed the pyloric lumen mechanically, producing an artifactual high pressure zone. Other seemingly minor but potentially important methodological differences were possible.