13 - Radiographic Examination of Normal Motility

Radiographic Examination of Normal Motility #

Introduction #

In radiographic studies of the upper gastrointestinal tract, only the contrast material in the lumen is visible, the actual walls of the tract being invisible.

The contrast material usually consists of one or more of the following:

  1. Insoluble, non-absorbable barium sulphate in fluid suspension. Where such a suspension is used, it represents the luminal contents, and being radio-opaque, is visualized as an image of positive contrast. In the "conventional" radiographic study a low density barium suspension is used with a specific gravity of 2.004 and a viscosity approximately four times that of water. The consistency approximates that of thick soup but may, if required, be increased to that of a paste. Commercial preparations contain additives regulating consistency and taste.

  2. Water soluble, absorbable iodine-containing solutions, also providing images of positive contrast, but with lower radio-opacity than barium.

  3. Air, which may be swallowed or introduced via tubes, providing negative contrast.

  4. Carbondioxide gas, affording an intraluminal, negative contrast agent. The gas is liberated in the lumen by swallowed, commercially available gas-producing granules or powders.

In the "conventional" radiographic study, barium sulphate with or without the addition of air or gas is used, affording clear and sharply defined images of the contrast column in the lumen. As pharmacologically active substances are not usually administered, normally occurring, physiological movements of the contrast column may be studied. While the rate of flow of a fluid contrast agent depends to a large extent on its viscosity, we noted no naked eye differences in the type or range of movements, whether "conventional" fluid barium suspension, barium paste or a watery iodine solution was used as contrast agent. (Comment: The "range" of movement seen radiologically roughly corresponds to the amplitude as determined at manometry).

The comparatively large volume of barium used in the conventional radiographic study (much less being used in the double-contrast method) may obscure some of the intraluminal features, confirming the dictum that "barium reveals but also conceals". Consequently use is made of compression techniques, by which some of the suspension is pressed away, to reveal the macroscopic mucosal folds and other intraluminal features.

In the double-contrast radiographic study, a coating of the luminal surface of the mucosa is obtained by swallowing a small volume of a micropulverized, dense, more viscous barium preparation; positioning the patient ensures equal allround coating. The parenteral administration of an antimuscarinic pharmacological agent causes temporary paralysis of the muscular walls with expansion of the lumen; this is enchanced by introducing a large volume of carbondioxide gas into the lumen. Under these circumstances naked-eye movements are no longer discernible; moreover, distension of the lumen with stretching of the walls effaces the macroscopic mucosal folds. The micropulverized barium enters minute furrows between the areae gastricae on the inner surface of the mucosa, thus rendering the areae gastricae, or surface mucosal pattern, visible (Fig. 13.1). In the present investigation, whenever motility patterns were studied, the conventional barium examination was used.

Fig. 13.1. Double contrast study with gas distended lumen. Fine, reticular pattern indicates areae gastricae or surface mucosal pattern

Validation Studies #

It is regarded as axiomatic in radiology that a temporary, circumferential, physiological narrowing of the barium column in the lumen of a hollow muscular tube is due to contraction of the walls of the tube. This supposition has not always been accepted universally. It has been argued, especially in physiology, that a barium column may appear to be narrowed in cases of incomplete filling of the lumen. Alternatively, even with complete filling, a passive "falling together" of the walls (as opposed to active contraction) may narrow the column. Whether these objections are valid or not may be determined by combining alternative modes of investigation, e.g. manometry, with radiological imaging procedures.

In the present context intraluminal pressure profiles and specially devised living anatomical studies have been done in an effort to validate the radiological observations.

Intraluminal Pressure Profiles #

While investigating mucosal fold movements in the distal 3.0 to 4.0 cm of the stomach, i.e. within the confines of the anatomical pyloric sphincteric cylinder, as well as in the duodenum, intraluminal pressure studies were combined with radiological imaging procedures in 11 normal subjects (Keet et al l978) (Chap. 15). These investigations may, at the same time, be utilized to determine the relationship between intraluminal pressures and radiologically demonstrable, physiological movements of the circumference of the barium column in these regions. (In this context "movements" do not imply propulsion or retropulsion of contents).

Ethical Considerations. All subjects taking part were informed, volunteer, adult, male ambulatory outpatients who had been referred for an upper gastro-intestinal radiographic study because of vague abdominal symptoms. None had had any significant clinical signs at the preliminary clinical examination. Only patients in whom no organic lesion could be demonstrated in the oesophagus, stomach and duodenum at the radiological examination were admitted to the study; it was cleared by the Ethical Committee.

Patients, Materials and Methods #

Pressure recordings were obtained by means of an air-filled system and a miniature balloon, placed on the immediate oral side of the pyloric aperture (i.e. in the lumen of the pyloric sphincteric cylinder) in 5 subjects, and in the second or third parts of the duodenum in 6 other subjects.

A pressure sensitive system usually used for cardiovascular physiology, with some modifications, was employed. It consisted of a monitor (Statham SP1400) (Statham Instruments Inc., Los Angeles), a miniature transducer (Statham P37B), a recorder (Statham SP2006) and a catheter, 125 cm in length, with an outside diameter of 2.0mm. A miniature balloon 38 mm in length and 8.0 mm in diameter, covered the 6 endholes of the catheter. The volume of air introduced into the balloon to achieve zero pressure was 0.8 ml. After an overnight fast the balloon was manipulated into position under TV screening, with the subject in the erect position. Four mouthfulls of a fluid barium suspension were swallowed to delineate the lumen and for purposes of localization. In the absence of visible motor activity the diameter of the pyloric sphincteric cylinder was approximately eight times the diameter of the balloon (visible because of its air content), and the diameter of the duodenum three times that of the balloon. Artifacts such as subject movement, coughing and pressure increases produced during compression procedures were identified and excluded. Pressure increases were correlated with motility of the barium column as viewed radiographically, and vice versa.

Results in Stomach #

In the pyloric sphincteric cylinder the base line of the curve represented intraluminal pressure while the cylinder was distended, in the absence of radiologically visible motor activity (Fig. 15.1). The following two distinct waves of pressure increase were noted manometrically:

  1. Irregularly occurring, nonrhythmic contractions, causing intraluminal pressure increases varying from 9.0 to 34 mm Hg (the majority being in the range of 12 to 25 mm Hg). These waves lasted for 5 to 21 seconds (the majority being in the 6 to 10 second range) (Fig. 15.1), occurred repeatedly in all subjects and conform to Type II contractions (Code and Carlson l968; Shepard l97l).

  2. In two of the subjects compound waves, consisting of a rise in base line pressure of 3.0 to 5.0mm 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 recorded; these conform to Type III waves (Shepard l97l).

Simultaneous radiological TV monitoring showed that both waves of pressure increase were associated with a concentric narrowing of the barium column characteristically occurring in this situation (see below). The higher the amplitude of the pressure wave, the greater the luminal narrowing appeared to be radiologically.

Conclusion #

It was concluded that the narrowing of the barium column was due to active contraction of the walls.

Results in Duodenum #

In the second and third parts of the duodenum the base line again represented intraluminal pressure in the absence of radiologically visible motor activity. Two waves of pressure increase were noted manometrically:

  1. Nonrhythmic, simple, brief monophasic waves, causing intraluminal pressure increases of 4.0 to 35 mm Hg (the majority being in the 7.0 to 34 mm Hg range), and lasting 2 to 8 seconds (Fig. 13.2). These waves occurred repeatedly in all subjects and conform to Type I duodenal waves (Foulk et al. l954; Vantrappen et al. l965; Friedman et al l965); it was suggested that they should be designated phasic waves (Texter l968).

  2. In two of the subjects nonrhythmic, complex waves consisting of a rise in base line pressure of 3.0 to 4.0 mm Hg and lasting from 40 seconds to 2½ minutes, with superadded peaks of l9 to 23 mm Hg lasting for 5 to 6 seconds, were seen occasionally. These conform to Type III duodenal waves (Foulk et al. l954; Vantrappen et al. l965; Friedman et al. l965); it was suggested that they should be designated tonic waves (Texter l968).

During both types of waves radiologically visible, circumferential narrowing of the luminal barium column occurred simultaneously with the increases in pressure (see also Chap. 15).

Fig. 13.2. Four monophasic duodenal pressure waves. Each was associated with a radiologically visible contraction. During each wave mucosal folds changed in direction to become longitudinal. Base line indicates intraluminal pressure in absence of motor activity. Ten-second marker on zero line

Conclusion #

It was concluded that the narrowing of the intraluminal barium column was due to active contraction of the walls.

Living Anatomical Studies #

The living anatomy was investigated in a number of patients who had to undergo cholecystectomy during the ordinary course of events (Keet and Heydenrych l982). The investigation was designed to determine the spatial relationship between the barium column in the lumen and the walls.

Ethical Considerations. The study was undertaken in informed, adult, white, volunteer patients who had been admitted to hospital with definite indications for cholecystectomy. All aspects of the procedure had been considered carefully beforehand by ourselves, our peers and the Head of the Department of Surgery; no objections were raised. The Ethical Committee indicated that it could find no objection to the procedure.

Patients, materials and methods #

Six patients were examined. On completion of the cholecystectomy, and before closure of the abdomen, the stomach and duodenum were shown to be normal by means of direct inspection and palpation. Two fine, flexible stainless metal wires, similar to the wires used in the leads of myocardial pacemakers, were attached to the serosal surface of the pyloric region of the stomach and first part of the duodenum by means of superficial, interrupted, absorbable sutures (Fig. 13.3). One wire was attached to the lesser and the other to the greater curvature, the free "duodenal" ends of both wires being brought to the surface (as in the case of a postoperative T-tube) through the cholecystectomy incision, which was subsequently closed in the usual way.

Approximately 8 days later, on the day before discharge, each patient had a limited radiographic study as follows: after an overnight fast 4 to 5 mouthfulls of the usual liquid barium suspension was swallowed in the erect position, so as to outline the horizontal part of the gastric lumen and to extend well up into the vertical part. The space between the metal wires on the serosal surfaces and the luminal barium indicated the thickness of the wall; during the motor quiescent stage it was approximately 4.0 to 5.0 mm. After emptying into the duodenum had commenced, gastric contractions were studied by means of radiographic TV monitoring and appropriate radiographs.

Fig. 13.3. Radiograph showing living anatomy. Two fine, flexible metal wires (retouched) are attached to serosal surfaces of lesser and greater curvatures. The space between the wires and intraluminal barium indicates the cylindrical muscular contraction

Results #

Narrow, circumferential indentations of the barium column appeared in the body of the stomach and proceeded to move in a caudal direction. Opposite the indentations the fine, flexible wires remained in their original position, showing that these indentations were due to contraction waves in the walls and not "falling together" of the walls. At a point 3.0 to 4.0 cm orally to the pyloric ring each wave became stationary, at the same time initiating a concentric, cylindrical narrowing of the barium column in the remaining part of the stomach, as far as and including the area of the ring. Again the wires were seen to remain in their original position. During a contraction the space between the wires and the luminal barium widened to approximately 8.0 to 10.0 mm all round, indicating an active, tube-like or cylindrical contraction of the muscular walls, 3.0 to 4.0 cm in length (Fig. 13.3). After a second or two of maximal contraction, the walls relaxed and the cycle was repeated.

On completion of the radiological examination the wires were removed by gentle traction on their external ends. None of the patients suffered any discomfort or untoward sequelae; recovery was normal.

Conclusion #

It is concluded that the narrowing of the intraluminal barium column was not due to a passive falling together of the walls, as the fine, flexible wires on the serosal surface remained in their original positions. The narrowing of the column was due to active contraction of the walls between the serosa and the barium containing lumen. (Endoscopic ultrasonography confirms that "peristaltic" contraction of the wall produces wall thickening, as mentioned in Chapter 10).

Motor Divisions of Stomach #

According to Code and Carlson (l968) the stomach has 3 functional regions corresponding to its anatomic divisions, namely the fundus, corpus and pyloric antrum, which, in their view, is the region stretching from the incisura angularis to the pylorus. (Comment: While the concept of these "anatomical" divisions appears to be widely accepted, it is shown in Chapters 2 and 3 that the division is of an arbitrary nature and not based on anatomical facts). In terms of motor activity Code and Carlson (l968) divided the antrum into two segments of varying length. The caudal portion participates in a simultaneous segmental contraction called the terminal antral contraction (TAC), previously described by Carlson, Code and Nelson (l966). The cephalad portion of the antrum, according to these authors, is not usually involved in TAC; however, at times TAC involves only the distal one to two centimeters of the antrum, and at other times almost the entire antrum. During TAC a simultaneous contraction of the terminal segment of the antrum occurs, a phenomenon which corresponds to antral systole previously described by Golden (l937). The cephalad and terminal (or caudal) segments of the antrum, together with the pylorus (also called the pyloric canal or pyloric sphincter) constitute a functional motor unit according to Code and Carlson (1968); the separate parts vary in their dimensions but contract in a co-ordinated way. The pyloric canal closes vigorously with contraction of the terminal antrum. (Comment: According to these authors the pyloric ring constitutes the pyloric sphincter. The pyloric canal is equated with the aperture).

Ruch and Patton (l973) state that morphologically, histologically and functionally the stomach is divided into 3 parts, viz. the fundus, corpus and pyloric antrum or pars pylorus, a narrower, more muscular, non-acid secreting region. The fundus and corpus together form a somewhat bulbous, thin-walled storage and secretory chamber, while food is fragmented and mixed with digestive juices in the "antrum". There is no structural discontinuity between these regions, which are only modifications of a basic pattern.

From the point of view of motility, other authors divided the stomach into two parts, namely a proximal one third and a distal two thirds (Kelly l98l; Funch-Jensen l987). The division was said to be based not on the usually accepted anatomical considerations, but on the type of smooth muscle activity. During swallowing the proximal part of the stomach relaxes, which allows filling without a significant increase in pressure. It acts as a receptacle and determines to a large extent the emptying of liquids. The distal two thirds shows active peristalsis which propagate luminal contents towards the pylorus, thereby effecting the emptying of solids.

In terms of motor function, based on the muscular anatomy, radiologically visible contraction patterns, manometrically recordable pressure waves and myoelectric activity, it is our view that the stomach should be divided into three parts namely (1) the fornix, (2) the corpus and sinus and (3) the distal 3.0 to 4.0 cm (Keet l957) (Fig. 13.4).

Fig. 13.4. In terms of motor activity the stomach should be divided into three parts. 1., fornix; 2., corpus and sinus; 3., distal 3-4 cm

Fornix #

This region roughly encompasses the proximal one sixth of the stomach. The muscular coat is at its thinnest in this region and consists of outer longitudinal, middle circular and inner oblique fibres. The entire cardiac mucosal zone as well as the upper part of the oxyntic zone are located in this region. During radiographic examinations this part of the stomach is seen to be capable of slow expansion and contraction (depending on the degree of filling), but no other intrinsic motility, such as peristaltic activity, is discernible. This correlates well with manometric findings, in which it has been shown that motor activity in the fornix consists almost entirely of slow, low amplitude phasic changes in pressure or tone (Lind et al. l961; Code and Carlson l968; Granger et al. l985). It has also been found that myoelectric activity is absent in the fornix (Kelly and Code l97l; Koch et al. l987).

Corpus and Sinus #

This region extends from the base of the fornix as far as an imaginary line 3.0 to 4.0 cm orally to the pyloric aperture. The muscular coat in its proximal part again consists of outer longitudinal, middle circular and inner oblique fibres, while the oblique layer terminates in its distal part. The major part of the oxyntic mucosal zone as well as the proximal part of the pyloric mucosal zone are located in this region. (The extent of the pyloric mucosal zone is discussed in Chap. 5).

During radiological examinations narrow, annular constricting waves, moving in a caudal direction (i.e. peristaltic waves) are seen in this part. They commence as shallow circumferential indentations of the barium column in the corpus, some distance above the incisura angularis, and may or may not become deeper as they proceed. This agrees with manometric and other physiological findings, where it has been shown that peristaltic contractions originate in the orad part of the corpus and migrate towards the pylorus (Smith et al. l957; Rhodes et al. l966; Carlson et al. l966; Granger et al. l985; Koch et al. l987). On the basis of intraluminal pressure changes, these peristaltic waves are divided into Type I waves (producing pressure increases of less than 5.0 cm of water) and Type II waves (producing pressure increases of more than 5.0 cm of water) (Code et al. l952; Smith et al. l957; Carlson et al. l966). The two types are essentially similar, being simple, monophasic waves, differing only in amplitude (Code and Carlson l968). It was surmised that the main function of Type I waves was mixing (with a secondary function of propulsion) and the main function of Type II waves propulsion (and secondarily mixing).

While both Type I and Type II waves are of a peristaltic nature, a third type namely Type III waves, may occur. These are complex waves, characterized by a rise in base-line pressure on which either Type I or Type II waves are superimposed. They are seldom present and of little consequence in the stomach (Code et al. l952). Radiologically Type III waves are usually not recognizable in the stomach.

The frequency of barium-induced peristaltic (i.e. Type I and Type II) waves in this part of the stomach, as seen radiologically, is approximately 3 per minute in man and 5 per minute in dogs (Smith et al l957; Rhodes et al. l966; Carlson et al. l966). Underlying myoelectric activity occurring here consists of slow waves (also known as basic electrical rhythm, pacesetter potential or electrical control activity) and spike activity (spike bursts, action potential or electrical response activity) (Chap. 16). Slow waves originate on the greater curvature in the upper part of the corpus, where spontaneous depolarizations occur at a frequency of 3 cycles per minute in man (Kwong et al. l970; Couturier et al. l972; Funch-Jensen l987), and 5 cycles per minute in canines (Weber and Kohatsu l970; Kelly et al. l97l). Contraction occurs when spike activity is superimposed on slow waves.

Distal 3-4 cm #

The muscular coat is at its thickest in this part of the stomach and consists of outer longitudinal and inner circular fibres. The thickening of the circular musculature commences almost imperceptibly 3.0 to 4.0 cm from the pylorus, increases gradually in an aboral direction and ends abruptly in the muscular ring (i.e. the muscular component of the pyloric ring) which surrounds the aperture. There is no structural discontinuity between the musculature of this region and that of the more proximal part of the stomach on its oral side (the sinus). Aborally the circular musculature of the ring is sharply demarcated from that of the duodenum by a fibrous septum (Chap. 3).

The musculature of the distal 3.0 to 4.0 cm of the stomach forms the pyloric sphincteric cylinder, as described by Cunningham (l906), the circular musculature of which consists of a system of rings or loops according to Forssell (l913), Cole (l928) and Torgersen (l942) (Chap. 3). It was shown that the loops deviate from the lesser curvature, where they meet in a muscle torus or knot, to encircle the greater curvature in a fan-like shape. The right muscular loop forms the peripheral part of the pyloric ring (Chap. 11). The greater curvature part of the left loop (which is less well-developed than the right) is situated 3.0 to 4.0 cm orally to the right loop and corresponds to the sulcus intermedius; the circular loops are connected by intervening circular as well as by the overlying longitudinal fibres.

The interior of this part of the stomach is lined by pyloric mucosa. However, the pyloric mucosal zone is not limited to this region, but extends orally into the more proximal part of the stomach (i.e. the sinus) for a variable distance (Chap. 5).

Myoelectric activity in the distal 3.0 cm of the stomach differs from that in the corpus and sinus in that a marked velocity increase in basic electrical rhythm occurs here (Chap. 16). This is associated with a "rapid spread of peristalsis" or a "nearly simultaneous contraction" of this part of the stomach, responsible for its behaviour as a motor unit (Chap. 16).

Do Gastric Peristaltic Waves Progress as far as the Pyloric Aperture? #

In a consideration of motility patterns of the distal 3.0 to 4.0 cm of the stomach, it is necessary to determine if gastric peristaltic waves normally proceed as far as the pyloric aperture.

Golden (l937) stated that each narrow peristaltic wave proceeding down the stomach terminated in "antral systole", i.e. a segmental or concentric contraction of the entire canalis egestorius described by Forssell (l913), which corresponds to the pyloric sphincteric cylinder.

Other authors differed. During simultaneous cineradiographic and kymographic studies in man, Smith et al. (l957) found that both Type I and Type II waves invariably progressed over the antrum toward the pylorus in a peristaltic manner. In some cases the pylorus failed to relax as barium was driven towards it (which implied that the waves proceeded as far as the pylorus); in other cases the wave faded just proximal to the pylorus.

Rhodes et al. (l966) stated that propulsive contractions arose near the incisura angularis and progressed smoothly towards the pylorus (from which it is concluded that they reached the pylorus).

Carlson et al. (l966), during simultaneous cineradiograpic, pressure and electrical studies in dogs, found that Type I waves passed in a continuous, peristaltic manner to the pyloric ring. Type II waves behaved differently; when such a wave reached a point 3.0 to 4.0 cm from the pyloric ring, the terminal segment of the antrum and the pyloric canal contracted in a segmental, simultaneous way. The contraction, designated a terminal antral contraction (TAC), was followed by relaxation. An antral cycle was the time from completion of one antral contraction wave to completion of the next. The pyloric canal almost always contracted with the terminal antrum. (Comment: Pyloric canal was equated with the pyloric aperture). Sometimes the pyloric canal would narrow early in the cycle but not completely close, so that movement of the contents through it into the duodenum occurred while the "antrum" was contracting. Simultaneous contraction of the terminal antrum and pyloric canal had an important effect on luminal contents; when contraction occurred, most of the contents were forcefully regurgitated into the proximal antrum (retropulsion) instead of being propelled into the duodenum (propulsion). Thus Type II contractions had a dual action, viz. propulsion into the duodenum and retropulsion into the stomach. Each TAC correlated with a sharp increase in intraluminal pressure. The mean rate of TAC's was 4.8 per minute in dogs.

Carlson et al. (1966) found that over the proximal antrum a definite interval always occurred between the detection of basal electrical rhythm (BER) at successively distal electrodes. As the BER complex reached the terminal antrum, its rate of conduction increased several fold and it was detected simultaneously, or nearly simultaneously, at successive electrodes, providing the pattern for TAC. The pyloric canal was closed during TAC and the rest phase following on TAC; it was open during peristalsis before the onset of TAC.

Edwards and Rowlands (l968) described Type I waves as shallow, annular, moving constrictions that progressed along the body of the stomach towards the pylorus. Type II waves were a deeper version of the former. As these constrictions approached the distal 4.0 cm of the stomach, instead of continuing in a sequential manner to the pylorus, they ended in a simultaneous, concentric contraction of the entire 4.0 cm long segment.

According to Code and Carlson (l968) three patterns of peristaltic activity are to be observed in this region: (1) some peristaltic contractions diminish in amplitude as they progress into the terminal antrum, where they simply fade away; (2) some contractions pass with increasing vigour over the entire antrum to end abruptly at the pylorus; (3) most peristaltic contractions end with segmental, simultaneous contraction of the terminal antrum and pyloric canal, closing the pylorus. Cineradiography showed that TAC and the contraction that closed the pyloric canal started simultaneously, but the pyloric canal usually closed earlier in the sequence than the rest of the "antrum"; it remained closed throughout the continuation of the terminal antral contraction. Sometimes the pyloric canal narrowed early in the cycle, without closing completely, so that intraluminal contents moved through it into the duodenum while the antrum was contracting.

The maximum rhythmic frequency of TAC's corresponded to the rhythmic frequency of gastric peristaltic contractions, namely 4 to 5 per minute in dogs and 3 per minute in man. The frequency of Type I or Type II contractions corresponded to the frequency of the basic electrical rhythm (BER).

Discussion #

With the exception of Golden (l937) and Edwards and Rowlands (l968), the authors mentioned above did not base the concentric, segmental, simultaneous contraction of what they called the terminal antrum (TAC) on any unique characteristic or specialization of the musculature of the wall of this part of the stomach. Yet Forssell (l913), Cole (l928) and Torgersen (l942) had stated previously that the forms of movement in this region depended on the specialized muscular build which had been described by themselves as well as by Cunningham (l906) (Chap. 3). It comes as some surprise to note that in investigations of gastric motility in human subjects, the above anatomical findings have been almost universally ignored. Only Golden (l937) stated that as far as motility was concerned, the canalis egestorius of Forssell (l913) was the most important part of the stomach; unfortunately he equated the term "antrum" with "canalis egestorius". Forssell (1913) had been adamant that "antrum" had no basis in anatomical fact, whereas canalis egestorius was a well defined anatomical entity.

Contraction Patterns of Distal 3-4 cm of Stomach #

Details of the contractions of the distal 3.0 to 4.0 cm of the stomach, as seen radiologically, have been documented (Keet l957, l962). While the descriptions remain valid, room exists for minor modifications and further clarification. Moreover, in the previous descriptions only maximal (or complete) contractions, i.e. those bisecting the lumen, were considered; in the present investigation the more shallow (or incomplete) contractions will also be dealt with. Consequently the following additional studies have been done.

Radiological Studies #

Patients and Methods #

The contractions were studied in (1) the group of 100 adult, ambulatory outpatients mentioned in Chap. 12; (2) a group of 20 patients in whom previous endoscopic examinations had proved the oesophagus, stomach and duodenum to be normal. (These patients had been referred for radiographic studies to confirm the absence of hiatus hernia).

Each patient had a conventional upper gastrointestinal barium study, the contractions being observed in both the erect and supine positions. As people generally have meals in a sitting position, studies were also performed with the subject sitting in 5 of the 20 endoscopically normal cases. Localized "spot" exposures were done occasionally for record purposes.

Ethical Considerations. As the contractions were studied during the ordinary course of events, the examinations were not prolonged to any appreciable extent, which means that any possible extra radiation to the patient was negligible.

Results #

Irrespective of the position of the patient, definite "patterns" of contraction occurred.

In all 120 cases a stage was awaited in which the duodenal cap was filled, in which the normal division between the stomach and duodenum (the pyloric ring) was clearly visible, and in which the pyloric region as well as the duodenal bulb were free of contractions, i.e. a motor quiescent phase (Fig. 11.1, 11.2). Measurements at this stage showed that the width of the normal indentation between the stomach and duodenum (the pyloric ring) on the lesser curvature, was more or less equal to the width on the greater curvature (Fig. 13.5) (see also Fig. 11.1 and 11.2). At this stage it is also seen that the pyloric aperture is patent, that it contains barium and that its diameter can be measured.

Fig. 13.5. Normal pyloric ring (arrow) in motor quiescent phase. Width of ring on lesser curvature more or less equal to that on greater curvature. Note patent pyloric aperture with diameter of 9 mm, containing barium

After a variable interval peristaltic contractions commenced in the gastric corpus in all cases. These narrow, annular waves were seen to proceed along the body of the stomach in a caudal direction as far as a point 3.0 to 4.0 cm proximal to the pyloric aperture. At this point each caudally travelling peristaltic wave came to a halt, i.e. it failed to advance any further, and ended in a concentric or cylindrical contraction of the entire distal 3.0 to 4.0 cm of the stomach (Fig. 13.6).

Fig. 13.6. Point at which peristaltic wave stops (curved arrows). Pyloric aperture (straight arrow). The region between the curved and straight arrows is distal 3-4 cm of stomach.

A caudally travelling peristaltic wave was never seen to proceed as far as the pyloric aperture.

The degree (or range) of contraction (which would probably correspond to amplitude in manometry) of the distal 3.0 to 4.0 cm long cylinder varied. During a single examination various degrees of contraction might be seen, e.g. feeble or incomplete contractions might occur in the early stages of the examination (Fig. 13.7), followed by maximal or complete contractions in which the lumen was bisected, later on (see also Chapter 12). During an examination contractions might become shallower for various (and sometimes unknown) reasons. For instance, not uncommonly contractions became very shallow, or even disappeared temporarily, after the patient had been supine and re-assumed the erect position. As a rule, however, once maximal contractions started, they occurred fairly regularly.

Fig. 13.7. Incomplete cylindrical (or "systolic") contraction (arrows) of distal 3-4 cm of stomach.

Maximal or Complete Contractions

Each maximal (or complete) cylindrical contraction of the distal 3.0 to 4.0 cm of the stomach was initiated by a peristaltic wave.

In all normal cases the contractions conformed to a definite pattern. The details may best be visualized if attention is focussed on the "black" regions of contraction surrounding the barium filled lumen. With this purpose in mind, sketches of radiographs taken at various stages have been made. The details of a typical maximal contraction may be described as follows:

When the peristaltic wave comes to a halt 3.0 to 4.0 cm orally to the pyloric ring, a widening of the indentation of the ring on the lesser curvature side occurs (Fig. 13.8). On the greater curvature a loculus of gastric lumen begins to form between the ring and the indentation of the arrested peristaltic wave (Fig. 13.8). While the peristaltic wave remains stationary, its indentation widens progressively. Simultaneously the indentation of the ring on the greater curvature also widens. The widening of these indentations can only be due to muscular contraction, and the effect is to compress the loculus so that it becomes smaller and resembles what can be called a pseudodiverticulum (Fig. 13.9).

Fig. 13.8. Sketch of commencing normal contraction showing widening of pyloric ring on lesser curvature side. D.B., duodenal bulb; L.O.C., loculus of gastric lumen; M.C., muscular contraction; P.W., stationary peristaltic wave; C.M.P., circular muscularis propria

Meanwhile the indentation on the lesser curvature enlarges further and merges imperceptibly with the impression of the original peristaltic wave which remained stationary at this point (Fig. 13.9). The effect of this is to cause a single, wide region of contraction on the lesser curvature, as opposed to two separate contractions on the greater curvature. The contracted region at this stage resembles an inverted V, with the apex on the lesser curvature and the two limbs radiating to and surrounding the greater curvature.

Fig. 13.9. Sketch of continuing normal contraction. D.B., duodenal bulb; P.D., pseudodiverticulum; M.C., muscular contraction; P.W.; stationary peristaltic wave

Finally, a simultaneous widening of the two legs or loops of the inverted V occurs, causing the disappearance of the pseudodiverticulum. This results in a triangular region of tight contraction (Fig. 13.10). The pyloric canal is now fully formed and runs through the contracted region as a thin channel containing one or more barium-lined longitudinal mucosal furrows.

Fig. 13.10. Sketch of maximal contraction. D.B., duodenal bulb; P.C., pyloric canal; M.C., muscular contraction

The events on the lesser and greater curvatures, together with the narrowing of the lumen, occur simultaneously in one smooth, integrated, uninterrupted movement.

This then constitutes a maximal contraction of the distal 2.0 to 3.0 cm of the stomach. It occurred in all normal cases. After two to three seconds the contraction relaxed, the lumen reassumed its "resting" diameter, and the process was repeated, showing it to be of cyclical nature. A "pyloric cycle" denotes the time from commencement of one contraction to the commencement of the next.

Frequency

The frequency of pyloric cycles per minute was determined as follows: In 50 of the subjects a stage was awaited in which maximal contractions occurred regularly. At the commencement of one of these contractions an assistant with a stopwatch would be told to "start!". At the end of 30 seconds the assistant would exclaim "stop!". The number of cyclical contractions per 30 second period per subject would be counted, from which the average number of contractions per minute per subject could be established. This proved to be approximately three and a half cycles of contraction per minute. (Because of various factors, e.g. the delay in responding to "start" and "stop", the correct figure is estimated to be somewhat less and probably between 3 and 3Æ cyles per minute).

Amplitude

A maximal contraction wave was associated with a sharp increase in intraluminal pressure, ranging up to 34 mm Hg (vide supra: See also Chapter 15).

Anatomical Correlates

An attempt was made to correlate details of the contractions of the distal 3.0 to 4.0 cm of the stomach, as revealed by radiology, with the muscular anatomy as described by Cunningham (l906), Forsell (l913), Cole (l928) and Torgersen (l942). The findings, which were analyzed in 320 cases (Keet l957), can be described as follows:

From the validation studies it is concluded that dynamic narrowing of the barium- containing lumen, as seen during a maximal contraction, is caused by muscular contraction of the walls. In order to visualize the shape and extent of muscular contraction, the method of focussing on the "black" areas of contraction surrounding the "white" barium-filled lumen is used. Using this perspective, it appears that the arrival of a peristaltic wave at a point 3.0 to 4.0 proximal to the pyloric aperture, initiates contraction of the various divisions of the pyloric sphincteric cylinder; normally this progresses uninterruptedly to culminate in a tight, maximal contraction of the entire cylinder.

One of the first events to occur, namely widening of the pyloric ring on the lesser curvature side (Fig. 13.8), tallies with commencing contraction of the pyloric muscle torus or knot, which is located in this situation. (This is also evident on the radiograph shown in Fig. 13.6).

Commencing formation of a gastric loculus on the greater curvature side (Fig. 13.8) tallies with early contraction and approximation of the right and left pyloric loops (the latter is adjacent to the stationary peristaltic wave on the greater curvature).

On the lesser curvature the indentation caused by continuing contraction of the muscle torus fuses with that of the stationary peristaltic wave, to cause a single region of contraction (Fig. 13.9). At this stage the right and left pyloric loops radiate in a fan-like shape from the muscle torus to surround the greater curvature, where two contraction rings are seen. The rings compress the gastric loculus, resulting in the formation of a physiological pseudodiverticulum (Fig. 13.9) (see also Fig. 13.11).

Fig. 13.11. Radiograph of normal, physiological pseudodiverticulum. Note single area of contraction on lesser curvature and two loops on greater curvature

Continuing contraction of the muscle torus and the two loops further compresses the pseudodiverticulum, causing its disappearance and resulting in a single, cylindrical region of tight contraction (Fig. 13.10). The compressed lumen at this stage is not more than 2-3 mm in diameter; it extends through the centre of the maximally contracted cylinder as a thin tube, often containing one or more longitudinal mucosal furrows (see Fig. 13.15B).

It is probable that narrowing of the lumen is brought about by contraction of the circular, and approximation of the loops by contraction of the longitudinal muscle fibres of the sphincteric cylinder.

Pyloric Aperture (or Orifice) and Pyloric Canal

Torgersen (l942) stated categorically that a distinction should be made between the terms "pyloric aperture or orifice" and "pyloric canal". In his view "pyloric orifice" denotes the central aperture in the pyloric ring at times when the sphincteric cylinder is relaxed or expanded (Fig. 13.12A). In adults it is approximately 5.0 to 10.0 mm in diameter and 4.7 mm in width (the width being equal to that of the ring (Chap. 11). "Pyloric canal" denotes the thin channel, 2.0 to 3.0 mm in diameter and 2.0 to 3.0 cm in length, which is formed during maximal contraction of the sphincteric cylinder (Fig. 13.12B). The pyloric canal, in other words, is a functional entity which is fully formed only during maximal contraction of the cylinder. Should "pyloric canal" be used for both entities, it is clear that the pyloric canal could be both short and long in the same subject, depending on the stage of contraction of the cylinder. Torgersen advised that these terms should be used with special care. In the present context the terms "pyloric aperture" and "pyloric canal" are used according to his guidelines.

Closure of Pyloric Aperture as a Function of Maximal Contraction of the Sphincteric Cylinder

An attempt to correlate closure and opening of the pyloric aperture, as seen at radiology, with the muscular anatomy as described by Cunningham (l906), Forssell (l913) and Torgersen (l942), has been made (Keet l962).

The findings showed that in each pyloric cycle, at a stage when the sphincteric cylinder is relaxed (i.e. expanded), the aperture is seen to contain barium or air, i.e. it is patent, and its diameter can be measured (Fig 13.12A). When contraction of the cylinder commences, the diameter of the aperture may widen or narrow marginally (see later). With continuing contraction of the cylinder the diameter of the aperture decreases, and with maximal contraction, at a stage when the pyloric canal is fully formed, the aperture is closed (Fig. 13.12B). This process of dynamic muscular closing of the aperture is seen regularly during maximal, cyclical contraction of the sphincteric cylinder; it was not seen during incomplete contraction of the cylinder. It is one mechanism by which the aperture is closed and should be differentiated from mucosal closure and from passive closure (see later).

A
B
Fig. 13.12. A Pyloric sphincteric cylinder expanded. Pyloric aperture (arrow) widely patent. B Maximal contraction of sphincteric cylinder with formation of pyloric canal (arrows). Pyloric aperture closed

Contractions of Pyloric Sphincteric Cylinder in Mixed Solid and Liquid Meals

From time to time a patient would arrive after having had a full breakfast. As a general rule these patients would be asked to come back at another time. However, in 20 of these patients it was decided to examine gastric contractions in the presence of a mixed solid and liquid meal. Each was asked to swallow four mouthfuls of barium suspension. In all cases typical pyloric cycles with maximal contraction of the sphincteric cylinder were seen. The impression was that contractions occurred at a more regular rate than in liquid "meals". Also, the range of movement appeared to be greater, with a greater degree of expansion and tight contraction during formation of the pyloric canal.

It was concluded that the character or nature of the contractions was the same in liquid and mixed solid and liquid meals. However, the rate of contraction was more regular, and contractions appeared to be more vigorous, in the latter.

Interplay Between Left and Right Loops

Radiologically it appears if contractions of the left and right pyloric loops start simultaneously. However, the degree or intensity of contraction of the two loops appears to vary. During a pyloric cycle the left loop (which is adjacent to the stationary peristaltic wave) may contract maximally, bisecting the lumen (Fig. 13.13). At this stage the right loop may be incompletely contracted, surrounding a central aperture (the patent pyloric aperture). Under these circumstances liquid contents flows into the duodenum. Propulsion into the duodenum is enhanced if contraction of the entire sphincteric cylinder now ensues.

Fig. 13.13. Left pyloric loop (arrow) tightly contracted, almost bisecting lumen. Right loop (i.e. muscular part of pyloric ring) not contracted and aperture patent

This process is well seen during gastric emptying of liquid barium, as illustrated in the following representative case:

Case J.V., male aged 35 years. A motor quiescent stage was awaited in which the stomach and duodenal bulb were filled; as often happens in the absence of motor activity, filling of the remainder of the duodenum was in abeyance. The pyloric sphincteric cylinder was relaxed; the aperture was patent, measuring 10.0 mm in diameter (Fig 13.14A). When gastric motor activity resumed, a stage was awaited at which the first peristaltic wave became stationary, immediately prior to contraction of the cylinder (Fig 13.14B). Immediate filling of the remainder of the duodenum ensued. The pyloric aperture widened marginally, now measuring 12.0 mm in diameter.

A
B
Fig. 13.14. A,B. Case J.V. A Motor quiescent phase. Pyloric sphincteric cylinder relaxed. Pyloric aperture patent. Duodenal bulb filled. B Peristaltic wave stationary and commencing contraction of left pyloric loop (arrow). Filling of remainder of duodenum. Marginal widening of aperture.

This and similar cases show that gastric emptying of liquid barium may be associated with arrival of a peristaltic wave at the commencement of the sphincteric cylinder. Arrival of a peristaltic wave here may also be associated with marginal further widening of the already patent pyloric aperture.

On the other hand the right loop may be fully contracted, closing the pyloric aperture, while the left loop is incompletely contracted, surrounding a central aperture. In this instance contraction of the sphincteric cylinder is associated with orad movement of barium, i.e. retropulsion. (An example of retropulsion is to be described in Case G.O., under "Mucosal Movements"). Ultimately, towards the end of each pyloric cycle, both loops as well as the intervening region become tightly contracted, resulting in formation of the pyloric canal and closure of the gastric outlet (Fig 13.12B, 13.15B).

A
B
Fig. 13.15 A,B. Double contrast study. A Sphincteric cylinder relaxed. Pyloric aperture filled with gas and patent. B. Sphincteric cylinder contracted, resulting in formation of pyloric canal and closure of gastric outlet. Note longitudinal mucosal folds in pyloric canal

The cases quoted are not exceptions but are examples of numerous other normal cases. No attempt was made to analyze contractions of the loops statistically. Studies of gastric emptying were not pursued in greater detail as the investigation is primarily concerned with the anatomy and movements of the sphincteric cylinder.

Ehrlein (l980) described a technique for simultaneous recording of motility and radiography in unanaesthetized dogs. Antral and duodenal contractions were recorded with chronically implanted strain gauge transducers, the external diameter of the pylorus was measured with induction coils, and radiography was used to measure gastric emptying, the internal pyloric diameter, and the volume of the "antrum". The right pyloric loop was called the distal pyloric loop (DPL) or pyloric sphincter, and the left loop the proximal pyloric loop (PPL); the latter is not as prominent in dogs as it is in man and certain other vertebrates. The distal 2.5 cm of the antrum was referred to as the terminal antrum. (Ehrlein's terminal antrum, located between the DPL and PPL, corresponds to the pyloric sphincteric cylinder located between the right and left pyloric loops).

Using the above methodology in a number of elegant studies, Ehrlein et al. (l984), Ehrlein and Akkermans (l984) and Keinke et al. (l984), found the mean frequency of terminal antral contractions to be 5.1 per minute in dogs. The velocity of each gastric contraction wave was found to increase during propagation from the proximal part of the antrum to the pyloric sphincter; during progression from the middle to the terminal antrum it increased from 0.9 to 1.5 cm per second. Detailed analysis of transducer recordings revealed a time lag between contraction maxima of the canine terminal antrum and the distal pyloric loop; contraction maxima at a site 2.5 cm orally to the sphincter occurred approximately 2.2 seconds before contraction maxima of the sphincter.
According to Ehrlein (l984), it was doubtful whether this sequence should be interpreted as a systolic contraction of the terminal antrum (as the case appeared to be in radiography), or as a rapidly progressing peristaltic wave, causing sequential contraction of the terminal antrum and pyloric sphincter. The final result of the contraction was complete obliteration of the antral lumen in the last 2.0 to 3.0 cm of the stomach.
(Although different terminology is used, the same final result was found in radiology).

In a study of gastric evacuation of mashed potatoes, Keinke and Ehrlein (l983) found that the external diameter of the pylorus increased and decreased in sequence with antral contraction waves. Simultaneous injection of fat (oleic acid) into the duodenum caused inhibition of antral contractions with delay in gastric emptying. When the contraction wave travelled over the proximal antrum, the terminal antrum and pylorus began to relax. When the wave reached the middle of the antrum the pylorus was relaxed, the ingesta being partly propelled through the pylorus into the duodenum and partly retropelled through the central opening of the peristaltic constriction into the proximal antrum. When the gastric wave moved with increasing velocity over the terminal antrum, the pyloric sphincter began to contract; this enhanced retropulsion of ingesta.

Ehrlein et al. (l984) showed that the "antral wave" could be differentiated into phases of propagation, of evacuation and retropulsion, and of enhanced retropulsion and grinding. Two factors were of importance for regulating flow of chyme into the duodenum, namely the depth of antral constriction waves and the degree of pyloric relaxation; a deep, constricting antral wave produced a strong propagative force, whereas a shallow constriction reduced forward flow and enhanced retropulsion. The depth of the antral wave depended in large measure on the viscosity of gastric contents (Pröve and Ehrlein l982).

Mucosal Movements #

One of the functions of the stomach is to ensure transit and evacuation of chyme, which is achieved by pressure gradients and motor movements. As indicated above, the movements of the muscularis externa have been studied and analyzed in some detail. The investigation of possible movements of the inner mucosal layer, on the other hand, has been almost universally omitted in physiological and gastro-intestinal motility studies (Chap. 2). This comes as a surprise, as the mucosa is in near contact with ingested solids, liquids and the products of gastric digestion; only a layer of gastric mucus separates it from the luminal contents. It seems reasonable to expect that the height and direction of mucosal folds may have some bearing on the transit of contents, even if this were of a purely mechanical nature.

For many years mucosal folds of the stomach were thought to be of little significance as far as motility was concerned. The fundamental work of Forssell (l923, l939) has received scant attention outside radiology, and it is an enigma of the medical literature that little or no mention is made of these findings in other disciplines. Briefly, Forssell's findings may be stated to be as follows:

Two independent but co-ordinated mechanisms of movement exist in the gastro-intestinal tract, including the stomach, namely (1) movements of the muscularis externa, and (2) movements of the mucosal coat, brought about by contractions of the muscularis mucosae.

A certain contraction of the outer muscular tube is necessary for the formation of macroscopic mucosal folds. The variability of the fold pattern is also dependent on the hydrodynamic action of the fluid content of the submucosa, which in turn depends on the degree of filling of the blood vessels; the mass of mucous membrane, and consequently the volume of its folds, is regulated by the varying vascularity in the submucosa.

In addition Forssell showed that the surface of the mucosa, or mucosal relief pattern, may vary from moment to moment; these movements are independent of, but co-ordinated with the contractions of the muscularis externa. Especially in the small intestine, but also in the stomach, various active contractile shapes, in some of which the mucosa "grips" particles of food, may be discerned. These consist of digestion chambers, blocking or filtering devices, re-absorption reservoirs and smooth or corrugated transporting tubes. In this way each region may best meet the varying demands placed on it from moment to moment, namely digestion, storage, absorption and transport respectively. One moment the mucosa may be occupied with one task, the next with another. Forsell called the inherent ability of the mucosa to move "mucosal autoplastik", providing a working relief pattern. It also determined to a large extent the number, position and form of the folds. While the coarser breakdown of food particles is effected by contractions of the muscularis externa, the finer dispersion occurs through changes in the relief pattern of the mucosa, which may enhance or counteract effects of contraction of the muscular walls. The special contractile organ of the mucous membrane is the muscularis mucosae; being attached to the mucosa and being incorporated in the submucosa, it is able to displace the former in different directions.

While elaborating on Forssell's work, Golden (l937), during radiological examinations, observed that in some cases the mucosal folds in the "antrum" ran irregularly transverse to the long axis, but when "antral systole" occurred they changed in direction and came to lie parallel to the long axis. It was surmized that during this process the mucosa also moved in an oral direction; otherwise, if this failed to occur, the folds would be exaggerated and jammed toward the pylorus during contraction of the canalis, tending to cause obstruction. The change in direction of folds only occurred during complete contractions of the canalis which expelled gastric contents.

Brooks et al. (l948), while investigating the gastric mucosa in canines, confirmed Forssell's view that the gastric mucosa was capable of independent movements. However, contraction of the muscularis externa also produced changes in the mucosal pattern. No clear picture of co-ordinated movements between the muscularis externa and muscularis mucosae emerged from their study.

Evidence of co-ordinated movements in the small bowel was furnished by Deucher (l951), who noted at operations that mucosal folds were transverse to the long axis in distended regions, and longitudinal in contracted segments of the bowel.

In radiological and experimental anatomical studies of mucosal fold movements Keet (l974, l978) found that normally, transverse or oblique mucosal folds could be demonstrated in the pyloric sphincteric cylinder while the latter was distended or relaxed (Fig. 13.16). (Comment: The terms "transverse" and "oblique" indicate the direction in relation to the long axis. Folds which appear transverse on the two- dimensional radiographic image are in reality circular, surrounding the tube-like lumen. Oblique folds are of a spiral nature).

Fig. 13.16. Pyloric sphincteric cylinder partially distended. All its mucosal folds are transverse (i.e. circular)

During contraction of the sphincteric cylinder the folds changed in direction, becoming progressively more longitudinal, and with maximum contraction only longitudinal folds were present in the fully contracted pyloric canal (Fig. 13.17). This was a regular occurrence in all our normal cases, including those described here, and appears to be one of the best examples of co-ordinated movements between the muscularis externa and mucosa (muscularis mucosae) occurring in the gastro-intestinal tract.

Fig. 13.17. Sphincteric cylinder contracted (arrows). The folds have changed in direction to become longitudinal. RPL, right pyloric loop; LPL, left pyloric loop. Note pseudodiverticulum between loops

In some of our normal cases not only a change in direction, but also a cephalad movement of the folds occurred during contraction of the sphincteric cylinder. The following is an example:

Case Report

Case G.O., 35 year old male. During the radiological examination a stage was awaited in which the pyloric shincteric cylinder was relaxed and distended with barium, while the part of the stomach on its oral side (Forssell's sinus) was also relaxed but filled with air. At this stage the mucosal folds in the cylinder were circular. During contraction of the cylinder the folds changed to longitudinal, at the same time moving in an orad direction and jutting into the sinus, forming a lobulated, intraluminal defect which had not been present previously (Fig. 13.18). Not only the folds were forced in an orad direction, but some of the barium in the cylinder was squirted orally to enter the sinus. The process may also be described as follows: During contraction of the pyloric sphincteric cylinder retropulsion of its mucosal folds, as well as some of its barium contents, occurred through the partially contracted left pyloric loop. During this contraction no barium was seen to enter the duodenum, indicating closure of the pyloric aperture, due to contraction of the right pyloric loop.

Fig. 13.18. Case G.O. Contraction of sphincteric cylinder and its right loop, closing the pyloric aperture (straight arrow). Retropulsion of mucosal folds (curved arrows) and barium (open arrow)

Further evidence that the mucosa of the cylinder may move in an orad direction during its contraction is seen in Chap. 36, cases 36.1 and 36.2. In these cases broad-based, sessile mucosal polyps in the inactive, relaxed cylinder, moved orally during contraction of the cylinder. The orad movement of the mucosa, while occurring normally, is not easily demonstrable during the conventional barium studies, but retropulsion of barium during contraction of the cylinder can often be shown; this should not be mistaken for duodenogastric reflux (Chap. 27).

Further evidence of co-ordinated movements between the muscularis externa and mucosa in the small bowel was presented by Sloan (l957). A correlation was found between the direction of the mucosal folds on the one hand, and the degree of distension or contraction of the walls on the other. During life longitudinal folds were seen to be associated with peristaltic activity. This feature could not be reproduced in anatomical specimens fixed in formalin.

Closure of Pyloric Aperture by Mucosal Folds

When the pyloric sphincteric cylinder is filled but inactive, its mucosal folds run in a circular or oblique direction; this was a regular feature seen in all our normal cases (Fig. 13.16). With the appropriate radiological double contrast or graduated compression techniques, these folds are seen to converge on the aperture (Fig. 13.19) or to surround it in an iris-like way, similar to the shutter leaves of a camera. At this stage barium is not seen to leave the stomach, and consequently its diameter cannot be measured; in other words, the aperture is plugged or closed. Not infrequently one of the radiolucent folds may extend for a distance of 3.0 or 4.0 mm through the aperture as far as the base of the duodenal bulb; extension of a single fold through the pylorus is considered to be normal (Torgersen l942), and does not constitute prolapse of gastric mucosa into the duodenum (Keet l952).

Fig. 13.19. Double contrast. Pyloric mucosal folds converge on aperture (arrow), causing mucosal closure

On the duodenal side, under these circumstances, a similar convergence of mucosal folds toward the pyloric aperture is evident.

On radiological evidence it is concluded that, at times when the pyloric sphincteric cylinder is filled but inactive, the aperture may be plugged by both gastric and duodenal mucosal folds converging on it, or it may be closed in a shutter-like way by oblique mucosal folds on the gastric side.

In a series of fresh partial gastrectomy specimens (removed because of gastric or duodenal ulceration), Williams (l962) demonstrated mucosal closure of the pylorus. These specimens, consisting of the distal half of the stomach and the first one or two centimeters of the duodenum, retained their pliability for some hours after operation. When barium was poured into such a gastric "bag" it did not always run out of the pylorus. In 8 of 40 specimens, the pylorus was watertight to a pressure of 4.0 to 10.0 cm of barium suspension with a specific gravity of 1.2. Williams (l962) called it a watertight, physiologically closed pylorus; viewed from the duodenal side, bulging, pliable gastric mucosal folds were seen to occlude the aperture. A probe 5.0 mm in diameter could be passed into the stomach, withdrawn and the pylorus remained watertight. When the probe reached a diameter of 10.0 mm it met the resistance of the muscular ring. Transverse anatomical sections of fresh specimens also showed the muscular ring to have a diameter of 10.0 mm, the opening being occluded by mucosal folds. In one of the cases nylon threads were tied to the mucosa on the gastric side of the pylorus. Pulling towards the fornix pulled the mucosal "plug" out of the ring into the stomach, causing the barium suspension to run out, i.e. the pylorus opened. When tension on the threads was released the mucosa returned, closing the pylorus.

It is concluded that radiological observations as well as experimental anatomical investigations show that the pyloric aperture may be closed by mucosal "plugging" or mucosal occlusion. This is seen during stages when the adjacent part of the stomach, i.e. the pyloric sphincteric cylinder, is filled but inactive. (A small collection of barium situated centrally at the base of the bulb may sometimes fill the hollow of the closed pyloric aperture; this we have called the duodenal "tail". In cases of pyloric carcinoma it may appear to be uninvolved, as described in Chapter 33).

Types of Closure of the Pyloric Aperture

Radiologically the following types of closure of the aperture may be recognized:

  1. Dynamic closure due to muscular contraction of the sphincteric cylinder

    From the above it is concluded that, when the sphincteric cylinder is relaxed or expanded, the aperture is patent. Maximal contraction of the cylinder, with formation of the pyloric canal, closes the aperture.

    During contraction of the cylinder there may be an interplay between its right pyloric loop (surrounding the aperture) and its left loop. Should the former close first, retropulsion of contents may occur. Should the left loop close first, propulsion may occur.

    Permanent, partial contraction of the sphincteric cylinder (which is regarded as a type of pylorospasm, as described in Chapter 20), may "fix" the aperture in a patent position, midway between maximal patency and maximal closure.

  2. Closure due to converging mucosal folds.

    When the pyloric sphincteric cylinder is relaxed, its mucosal folds are circular. The folds may converge on the aperture or close it in an iris-like way.

  3. Descent or sagging of filled stomach.

    The pyloric aperture in the filled stomach may be patent (Fig. 13.20). A sudden descent or sagging of the stomach may cause apparent elongation of the aperture with passive narrowing of its diameter (Fig. 13.21).

Gastric hypotonicity with delayed emptying in the erect position, is often ascribed to pylorospasm, by which is meant spasm of the pyloric ring with closure of the aperture. However, there is reason to believe that the aperture is patent in these cases (Chap. 19).

Fig. 13.20. The stomach is filled, the sphincteric cylinder expanded, and the aperture patent

Fig. 13.21. Sagging of stomach causes elongation and apparent narrowing of the aperture

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