Manometry at the Gastroduodenal Junction #

Atkinson et al. (l957) stated that although the pyloric sphincter was a well-defined anatomical structure, there was doubt whether it functioned physiologically as a sphincter in the sense that it closed the stomach off from the duodenum. Using a system of small air-filled balloons and air-filled, open-tipped tubes, these authors investigated intraluminal pressure profiles in the pyloro-duodenal region in normal subjects as well as in patients with active duodenal ulceration and with non-ulcer dyspepsia. Measurements were taken in the fasting stomach and in stomachs containing a mixture of food and barium sulphate. In no instance could a band of increased pressure be obtained anywhere in the region of the duodenal cap, pyloric canal or pyloric "antrum". While phasic pressure waves were recorded in the pyloric region on many occasions, and while it was possible to correlate radiologically visible peristaltic waves inthe corpus and "antrum" with the pressure records, no convincing evidence of independent contractions at the gastroduodenal junction (i.e. the pyloric ring) was found. It was concluded that the diameter of the pyloric ring was more than 7.0 mm most of the time, whether the stomach was empty or not. These authors could not demonstrate a physiological sphincter in the sense of a tonically contracted muscular ring which kept the lumen tightly closed and which relaxed intermittently to allow gastric contents to pass into the duodenum.

The phasic pressure waves recorded on the gastric side of the ring were deemed capable of causing partial or complete obliteration of the lumen. Each contraction was found to be intermittent and brief, and involved a segment 3.0 to 4.0 cm in length. It probably reduced the bore of the pyloric canal and closed it momentarily. (Comment: "Pyloric canal" was equated with the pyloric aperture). Atkinson et al. (l957) concluded that the pylorus was normally relaxed; there was no evidence that it acted antagonistically to peristaltic or other phasic pressure waves.

Andersson and Grossman (l965), using a system of small (5.0 to 10 mm diameter) water- filled balloons, recorded intraluminal pressures of the pyloro-duodenal region in normal, fasting, supine human subjects. As a balloon was withdrawn from the duodenum through the pylorus, a change in pressure occurred only rarely. During 7 of 130 withdrawals, i.e. in approximately 5 percent of instances, a transient pressure peak of variable magnitude occurred when the balloon passed the "sphincter". It was concluded that the pyloric sphincter was usually not detectable by pressure measurements and that these measurements could not be used as a means of identifying the pylorus. The luminal diameter of the resting pylorus in supine subjects appeared to be greater than 10.0 mm.

Brink et al. (l965) measured intraluminal pressures of the gastroduodenal region in canines. Having performed a gastrostomy and duodenostomy in each animal, cannulae were inserted into the stomach and duodenum through which water-filled, open-tipped tubes and small balloons were introduced into the lumen. As the pressure-detecting units were withdrawn, an increase in resting pressure occurred when the gastroduodenal junctional zone was reached. The magnitude of the change in pressure varied with the cross-sectional diameter of the detecting instrument. With the open-tip tube, elevation of pressure occurred in the junctional zone in 15 of 25 tests on 5 dogs. The mean length of the zone of increased pressure varied from 1.1cm to 1.6 cm. With balloons an increase in pressure was detected more often. The frequency with which they were able to demonstrate a high pressure zone rose as the size of the balloon sensor was increased. With a 7.0 mm diameter balloon, a rise in pressure was seen in 97 percent of 58 observations. Instillation of acid into the duodenum caused an increase in the pressure peaks of the junctional zone, with a simultaneous increase in amplitude of duodenal contractions (type I pressure waves) and a cessation of motor activity in the "antrum". It was concluded that there was a narrow zone of raised pressure at the gastroduodenal junction in fasting dogs, in which the diameter of the lumen was less than 7 mm most of the time.

Carlson et al. (l966) investigated motor action of the canine gastroduodenal junction by means of combined cineradiographic, manometric and electrical studies. Small intraluminal water-filled balloons were positioned in the first part of the duodenum and within 3.0 to 4.0 cm of the pyloric ring on the gastric side, i.e. in the "terminal antrum". The balloons were connected to external strain gauge transducers by means of cannulae. When a Type II contraction (Chap. 13) reached a point 3.0 to 4.0 cm from the pyloric ring, the terminal antrum and pyloric canal distal to it contracted simultaneously, or almost simultaneously, in a segmental way; such vigorous terminal antral contractions (TAC) caused sharp elevations in intraluminal pressures. The pyloric canal almost always contracted with the terminal antrum. (Comment: "Pyloric canal" was equated with the pyloric aperture). The mean duration of TAC was 3.1 seconds, the mean time interval between completion of cycles 12.7 seconds, and the mean rate 4.8 per minute.

Isenberg and Csendes (l972), using open-tipped perfused tubes as pressure sensors, measured intraluminal pressures in canines prepared with gastric and duodenal cannulas. The sensors were moved in 1.0 cm increments back and forth across the pylorus. Mean resting pyloric pressure when the sensors were moved from the stomach to duodenum was 14.8 cm H²0; when they were moved from duodenum to stomach, it was 8.9 cm H²0. Intravenous infusion of cholecystokinin octapeptide produced an increase in pyloric pressure. Mean sphincter length was 1.8 cm. It was concluded that the dog pylorus was tonically contracted and that the resting tone was increased by octapeptide of cholecystokinin. 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. 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:

1. 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

2. 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. 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. Many authors failed to find evidence of a tonically contracted ring structure at the pylorus. Atkinson et al. (l957) were unable to demonstrate independent contraction of the pyloric ring; they found that the pylorus was normally relaxed and did not act antagonistically to phasic pressure waves. Andersson and Grossman (l965), Kaye et al. (l976), McShane et al. (l980), White et al. (l98l), Dooley et al. (l985) and Gaffney et al. (l987) found no convincing manometric evidence of a zone of tonically elevated basal pressure at the pylorus. McShane et al. (l980) stated that the pyloric sphincter remained patent under fasting conditions. Apart from a brief closure during contraction, the pylorus was always open, according to White et al. (l98l). Kelly (l983) and Gaffney et al. (l987) concluded that the evidence weighed heavily against the presence of a tonic sphincter at the pylorus.

Winans (l976) attributed the divergent results of manometric studies to differences in methodology and differences in position of the subjects examined. Whereas the human pylorus was easily identifiable as a gross anatomic structure, it eluded identification as a functioning sphincter. Winans (l976) called this a "sphincteric paradox", and referred to the pylorus as being "fickle". Adding to the confusion is the lack of agreement on the definition of a sphincter (Chap. 2) and its relation to a high pressure zone.

In determining the manometric features of the pylorus, none of the authors quoted, with the exception of Keet et al. (l978), referred to or took note of the muscular anatomy of the region as determined by Cunningham (l906), Forssell (l913) and Torgersen (l942) (Chap. 3). According to this concept the pyloric ring consists of an aboral thickening of the cylinder, and constitutes an inherent part of the cylinder both anatomically and functionally. The closest any of the authors came to the concept of a sphincteric cylinder at the pylorus, was the recognition of the "terminal antrum" as a functional unit by Carlson, Code and Nelson (l966), Code and Carlson (l968) and Shepard (l97l). However, the terminal antrum had not been defined in terms of muscular anatomy, whereas the sphincteric cylinder had.

The sphincteric mechanism at the pylorus will probably prove to be less paradoxical once the muscular component of the pyloric ring (the right pyloric loop) is no longer regarded as a separate structure, but is acknowledged to be an inherent part (i.e. the aboral end) of the pyloric sphincteric cylinder.

References #

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