12 - The Pylorus at Rest: Open or Closed?

The Pylorus at Rest: Open or Closed? #

In considering the mechanism of the pylorus it is of importance to determine, first of all, if the aperture is open or closed at rest. By “at rest” is meant conditions pertaining after an overnight fast, in which the stomach is empty except for normally occurring intraluminal gas, swallowed saliva and gastric secretions; it denotes the motor quiescent phase of the interdigestive myo-electric complex, with absence of radiologically discernible motor activity.

As indicated in Chap. 15, a number of authors held the view that the canine and human pylorus was surrounded by a narrow zone of raised pressure which was tonically contracted "at rest", closing the aperture; with the advent of an “antral” peristaltic wave the aperture relaxed (Brink et al. l965; Isenberg and Csendes l972; Fisher and Cohen l973). Other authors found or inferred that the pylorus was patent under fasting conditions, that it was not surrounded by a zone of elevated basal pressure, and that it did not act antagonistically to oncoming peristaltic waves (Atkinson et al. l957; Andersson and Grossman l965; Kaye et al. l976; McShane et al. l980; White et al. l98l; Gaffney et al. l987).

It can be assumed that an open pyloric aperture will allow the passage of liquids, while a closed pylorus will not. For this reason a fluid barium suspension has been used to determine the patency, or otherwise, of the aperture.

Present Investigations #

Patients and Methods #

A total of 100 adult, ambulatory outpatients were examined radiologically after an overnight fast. All had been referred for routine radiographic studies because of vague abdominal symptoms; patients with definite clinical symptoms and signs such as recurrent epigastric pain, weight loss, vomiting, haematemesis, melaena or a palpable mass, were excluded from the study.

Patients were examined in the erect and supine positions, each being asked to swallow three mouthfuls (45 ml) of a barium suspension in quick succession. The viscosity of the suspension was approximately four times that of water, the specific gravity was 2.004 and the consistency that of thick soup. These features ensured a fluidity which was less than that of water, but probably slightly more than that of chyme.

The state of the pylorus was determined by TV fluoroscopy and radiography, not more than one or two “spot” films being exposed (size of radiation field 14.5 x ll.5 cm). As soon as this had been done, more barium was swallowed (usually with the addition of effervescent salts)), and the conventional barium examination, for which the patient had been referred, was completed. If this revealed an organic lesion, the case was also excluded. In this group of 100 patients, in other words, the upper gastrointestinal tract was considered to be normal clinically as well as radiologically.

Ethical Considerations. In 52 patients the screening time due to the procedure varied from 5 to 15 seconds; in 48 patients it was longer, varying from 25 to 60 seconds. (In all the technique of intermittent screening was used). The anterior and posterior skin doses of x- radiation were measured and found to be negligible. As a small field (14.5 x ll.5 cm) limited to the upper abdomen was involved, it was felt that the extra radiation, received as a result of the procedure, could be discounted.

Results #

In 52 of the 100 patients the swallowed, liquid barium suspension passed rapidly down the oesophagus, traversed the stomach and flowed through the pyloric aperture in one smooth movement, without any delay or hold-up at the pylorus. This occurred in the absence of visible motor movements in the stomach. In many cases the head of barium was in the duodenum while the “tail end” was still in the oesophagus (Fig. 12.1). In all cases the normal, deep annular indentation of the pyloric ring between the stomach and duodenum became clearly visible as soon as the barium had traversed the aperture (Fig. 11.1). The part of the stomach on the immediate oral side of the ring (the pyloric sphincteric cylinder) was expanded without being unduly distended.

The width of the barium column in the pyloric aperture, between the lips of the ring, indicated the diameter of the aperture. It was measured on the films and varied from a minimum of 4.0mm to a maximum of 10.0 mm between subjects, the diameter in the majority being in the 5.0 to 10.0 mm range. (Owing to technical factors minor geometrical magnification occurs during radiographic filming, and the true measurements will be approximately four-fifths of those measured on the films).

In 48 patients there was some delay or hold-up at the ring; in the majority the delay varied from approximately 40 to 90 seconds; in a few it lasted for 2 or 3 minutes. The following are representative cases:

Fig. 12.1. Rapid swallowing in fasting stomach. Barium suspension traverses pyloric aperture, which is patent (arrow). “Tail end” of barium still in oesophagus. Absence of gastric motor movements

Case Reports

  • Case 12.1 J.S., male aged 28 years. Having swallowed 3 mouthfuls of barium suspension, a hold-up lasting 41 seconds occurred at the pyloric ring (counting had started as soon as the barium entered the gastric fornix). For the first 20 seconds of this period no gastric motor movements were seen; the distal 3.0 to 4.0 cm of the stomach was expanded without being unduly distended. At 20 seconds two successive, incomplete, “segmental” or “cylindrical” contractions of this region occurred (see Chap. 13), followed by commencing emptying into the duodenum at 41 seconds (Fig 12.2). (By “incomplete” is meant a minor to moderate degree of narrowing of the lumen, i.e. not bisecting the barium column).
  • Case 12.2 S.A., female aged 28 years. There was a hold-up at the pyloric ring lasting 85 seconds. For the first 30 seconds of this period no gastric contractions were seen. Subsequently two incomplete cylindrical contractions of the distal 3.0 to 4.0 cm occurred, followed by commencing emptying into the duodenum at 85 seconds.
  • Case 12.3 H.A., male aged 61 years. The hold-up at the pyloric ring lasted 128 seconds. At l8 seconds 2 or 3 incomplete contractions occurred, followed by a long period of inactivity. Eventually a few contractions reappeared, associated with emptying at 128 seconds.

Fig. 12.2 A-D. Patient J.S. Initial hold-up at pyloric ring (A, B). Successive, incomplete contractions of pyloric sphincteric cylinder (arrow). Emptying into duodenum (C, D)

Generally speaking a similar sequence of events was seen in the majority of patients in this group, namely a short hold-up at the pyloric ring, followed by 2 or 3 incomplete (or occasionally maximal) contractions of the pyloric sphincteric cylinder and commencing emptying into the duodenum (Fig. 12.3). The degree of dynamic narrowing of the lumen, as seen radiologically, probably corresponds to the amplitude as measured manometrically. This varied greatly among subjects.

Fig. 12.3. The first of two or three maximal contractions of pyloric sphincteric cylinder (arrows) preceding emptying into duodenum

In a minority of subjects in this group the period of hold-up at the pyloric ring was longer, lasting at least 90 seconds and sometimes as long as 2 to 3 minutes. In these patients the stomach invariably had a long, hanging, fish-hook shape, with a sagging greater curvature, which is evidence of hypotonia (Chap. 19). Tilting the table to an angle of 45 degrees, and turning the patient into the left anterior oblique position (i.e. with the right side down), invariably caused immediate emptying into the duodenum even in the absence of visible motor activity.

The following case is an example:

  • Case 12.4 S.M., female aged 50 years. In the erect position there was sagging of the greater curvature, which was located low down in the abdomen opposite the 5th lumbar vertebra; the shape of the stomach was compatible with hypotonicity. The first incomplete contraction of the pyloric sphincteric cylinder was seen at 60 seconds, with another occurring at 100 seconds. Up to 230 seconds no emptying had occurred. The table was then tilted to 45 degrees and the patient turned into the left anterior oblique position. Immediate emptying occurred in this position in the absence of visible contractions of the pyloric region, indicating patency of the pyloric aperture.

Discussion #

It is concluded that the pyloric aperture was open at rest in 52 of 100 normal subjects. Its diameter, as measured on the films, varied from a minimum of 4.0 mm to a maximum of 10.0mm in different subjects.

In the remaining 48 subjects some delay or hold-up occurred at the pyloric ring. In the majority of these the hold-up lasted from 40 to 90 seconds; in a few the hold-up was longer, lasting from 90 seconds to 3 minutes. In this latter subgroup the delay at the pylorus was associated with hypotonicity or sagging of the greater curvature of the stomach. Tilting the table by 45 degrees and turning the patient into the left anterior oblique position, caused immediate gastric emptying in the absence of radiologically visible contractions. It is concluded that visible contractions are not necessary for emptying of liquid barium in this position.

It appears that the delay in emptying in these 48 subjects was either due to hypotonicity of the gastric musculature (Chap. l9), or to closure of the pyloric aperture. Different types of closure of the aperture may occur (Chap. 13); in the present cases the pyloric sphincteric cylinder was expanded, and the radiological features suggest that closure of the aperture was due to converging or spiral (“iris-like”) gastric mucosal folds (Chap. 13).

References #

  1. Andersson S, Grossman MI. Profile of pH, pressure and potential difference at gastroduodenal junction in man. Gastroenterology l965, 49, 364-371.
  2. Atkinson M, Edwards DAW, Honour AJ, et al. Comparison of cardiac and pyloric sphincters. Lancet l957, 273, 918-922.
  3. Brink BM, Schlegel JF, Code CF. The pressure profile of the gastroduodenal junctional zone in dogs. Gut l965, 6, 163-171.
  4. Fisher RS, Cohen S. Physiological characteristics of the human pyloric sphincter. Gastroenterology l973, 64, 67-75.
  5. Gaffney PR, Gleeson DJ, Hall JW, et al. The manometric findings at the human pylorus: the evidence against the presence of a tonic sphincter. Scand J Gastroenterol l987, 22, 525-532.
  6. Isenberg JI, Csendes A. Effect of octapeptide of cholecystokinin on canine pyloric pressure. Amer J Physiol l972, 222, 428-431.
  7. Kaye MD, Mehta SJ, Showalter JP. Manometric studies of the human pylorus. Gastroenterology l976, 70, 477-480.
  8. McShane AJ, O'Morain C, Lennon JR, et al. Atraumatic non-distorting pyloric sphincter pressure studies. Gut l980, 21, 826-828.
  9. White CM, Poxon V, Alexander-Williams J. A study of motility of normal human gastroduodenal region. Dig Dis Sci l98l, 26, 609-617.
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