Ultrasonography of Pyloric Motility and Gastric Emptying #

Bateman et al (l977) measured the rate of gastric contractions by means of ultrasound pulse-echo scanning. As the procedure was non-invasive, non-ionizing and non- traumatic, it had certain advantages over other modes of examination. After an overnight fast normal subjects seated in the upright position imbibed 500 ml orange cordial warmed to 37ºC. Using a standard, commercially available B-scanner with a 1.5 MHz probe, the fluid in the stomach presented as an echo-free, transonic region. A quantitative display of the movement of the anterior and posterior walls of the "antrum" could be obtained in T-M (time motion) mode, and a permanent photographic record could be made. A continuous A-mode record of the wall movements was obtained simultaneously on video-tape.

In the normal stomach a biphasic response to the liquid meal was seen. Initially the "antral" contraction waves were slow and irregular, but after 7 to 15 min they appeared more frequently at regular 20 second intervals. The temperature of the fluid appeared to be of importance as gastric contraction waves were found to be inhibited at temperatures lower than 37ºC. Intravenous administration of 15 mg or 30 mg propantheline caused cessation of the contractions for periods of up to 3 hours. The method was found to be particularly suited to the measurement of contraction rates.

Holt et al. (l980) used real-time ultrasonic imaging to study contractions in the pyloric "antrum" and body of the stomach in 10 healthy subjects after a liquid test meal of 500 ml warmed orange juice. In 5 subjects scanning was also performed at intervals after a variety of solid and liquid meals. In all cases a real-time ultrasonic scanner containing 4 rotating transducers of 2.5 MHz was used; scans were done with the subject standing or seated upright. Real-time ultrasonic images were recorded on video-casettes and permanent photographic records were obtained.

In the resting state the distended, liquid-filled "antrum" was visualized as a rounded, echo-free or transonic zone. After the liquid meal contraction of the "antrum" was absent or weak for up to 5 minutes, but this was followed by regular contractions occurring with a frequency of 3 per minute, i.e. a contraction every 20 seconds; these were taken to be peristaltic waves. Propantheline 30 mg intravenously abolished the "antral" movements, while metoclopramide 10 mg intravenously enhanced the magnitude and frequency of the contractions. It was said that the images produced by real-time ultrasonic techniques closely resembled those seen during barium screening studies.

King et al. (l984) examined l7 normal subjects using a rotating transducer real-time ultrasound scanner with a 5 MHz probe. Subjects were examined seated in the upright position after an overnight fast and after imbibing 500 ml warmed orange cordial to which 0.5 g of chopped and sieved bran was added. The bran particles suspended in the fluid luminal contents acted as a sonic marker, thus allowing identification of movement through the pylorus. Forward flow indicated movement of particles from the stomach to the duodenum and retrograde flow movement from the duodenum into the stomach.

Images of the bran particles, the "distal or terminal antrum", pylorus and duodenum were obtained. (Comment: The "terminal antrum" was defined as the immediate prepyloric area. More detailed definitions of the terms "antrum" and "terminal antrum" were not given.) The timing and duration of the terminal antral contractions (TACs), proximal duodenal contractions, and periods of forward and retrograde flow through the pylorus in each individual were then compared in order to establish the relationships between them. The duration of a terminal antral contraction was about 4 seconds (mean 3.93 seconds ± 0.8). Pyloric closure invariably occurred as the gastric peristaltic wave reached the pylorus at the midpoint of the terminal antral contraction. Contractions of the first part of the duodenum were seen to occur just after the midpoint of the majority (86 percent) of terminal antral contractions. The vast majority (92 percent) of duodenal contractions occurred immediately after the terminal antral contraction, 5.5 percent occurred simultaneously with it and 2.5 percent were ectopic. Contraction of the first part of the duodenum lasted about 5 seconds (mean 4.93 seconds SD ± 1.75).

Transpyloric fluid movement was reflected by the movement of the bran particles. It occurred as brief episodes when the pylorus was open. Forward flow occurred in 81 percent of the cycles of contraction and lasted about 2 to 4 seconds. The majority of these episodes occurred after relaxation of the terminal antrum, pylorus and duodenum, while 25 percent occurred just before the terminal antral contraction. The discrete episodes of forward flow thus occurred as the terminal antrum, pylorus and duodenum were relaxed at the end or the start or each peristaltic cycle. Occasionally there was no forward flow in spite of terminal antral and duodenal contractions.

Retrograde flow, in episodes lasting up to 5 seconds, occurred in the vast majority of observed cycles of contraction. Most of these episodes were seen just before the terminal antral contraction, with 39 percent following it. A brief period of forward flow often ended abruptly and was sometimes immediately followed by a period of retrograde flow.

Bolondi et al. (l985) measured gastric emptying times in l8 normal subjects and 36 patients with functional dyspepsia, using a high-resolution real-time scanner with a 3.5 MHz linear array transducer. Having measured the transverse diameter and length of the "antrum" before and after a mixed solid-liquid meal, the volume of the "antropyloric" region was calculated and the time taken for its emptying determined. The antrum was taken to be the area extending from the "angle region" to the pylorus. Significantly longer emptying times were observed in patients with functional dyspepsia as compared with normal subjects. It was stated that various phases of antral peristalsis, such as propulsion waves, grinding movements and retropulsion could be studied by means of ultrasonic techniques, but no further particulars of these movements were given. King et al. (l985) used real-time ultrasonic imaging to study the temporal relationships between contractions of the terminal antrum, pylorus and proximal duodenum in 22 normal subjects. The methodology was similar to that of their previous study (King et al. l984). A total of 259 cyclical periods of motor activity were observed during 32 recordings, a general pattern being seen in all.

Terminal antral contractions occurred in 98 percent of the cyclical periods of motor activity. The duration of the terminal antral contraction was relatively constant at about 4 seconds (mean 3.6 ± 0.6 sec) and pyloric closure occurred at the midpoint of these contractions. The pylorus then opened as the terminal antrum relaxed and remained open until the next TAC started. Pyloric closure occurred with each terminal antral contraction and was not seen at any other time. During the few (2 percent) cyclical periods of motor activity in which terminal antral contractions did not occur, the pyloric "channel" (presumably the pyloric aperture) remained widely patent. The observations provided no evidence of independent pyloric function, i.e. independent function of the pyloric ring, in the post-prandial state in humans. Sixty-seven percent of the TACs were associated with contraction of the duodenal bulb. Ninety-four percent of duodenal bulb contractions occurred about 1 second after pyloric closure. The remaining 6 percent were ectopic, i.e. apparently unco-ordinated with TACs. Duodenal bulb contractions lasted approximately 5 seconds.

Discussion #

Real-time ultrasonic scanning plays an important role in the investigation of pyloric motility, pyloro-duodenal co-ordination and transpyloric fluid movement. Contractions of the pyloric region (designated pyloric "antrum" or "terminal antrum") closely resemble motility seen during radiological studies.

None of the authors quoted above related their findings to the specialized muscular anatomy of the pyloric sphincteric cylinder as described by Cunningham, Forssell and Torgersen (Chap. 3). However, it appears if the "terminal antrum" corresponds to the sphincteric cylinder. The finding that closure of the pyloric aperture occurs with each terminal antral contraction tallies with radiological observations that muscular closure of the aperture occurs during contraction of the sphincteric cylinder. According to ultrasonography the aperture closes as a gastric peristaltic wave reaches the midpoint of the terminal antrum, i.e. during terminal antral contraction (TAC). Radiologically it is seen that the aperture closes progressively during ongoing contraction of the cylinder. However, there is also an interplay between the right and left loops of the cylinder. If the left loop closes first, propulsion of contents into the duodenum occurs; if the right loop (surrounding the aperture) closes first, retropulsion from the cylinder (and not from the duodenum) into the more proximal part of the stomach occurs (Chap. 13). During maximal contraction of the cylinder both loops are tightly contracted and the aperture is closed.

In ultrasonography "forward flow" from stomach to duodenum, and "retrograde flow" from duodenum to stomach was described in association with TAC. The question arises whether true duodenogastric reflux was observed or whether retrograde movement of contents from the contracting sphincteric cylinder occurred.

With ultrasonography pyloro-duodenal co-ordination may be studied. This is hardly possible with conventional radiology; although it has been attemped by others, it has not been pursued in the present investigation. Ultrasonography has an advantage over radiology in that transpyloric flow of liquid contents may be quantified, using bran particles as sonic markers. Other advantages are that it is non-ionizing, non-invasive and non-traumatic.

Ultrasonography failed to identify independent action of the pyloric ring in the post- prandial state; this seems to confirm the view that the ring as such does not function as a sphincter.

References #

1. Bateman DN, Leeman S, Metreweli C, et al. A non-invasive technique for gastric motility measurement. Brit J Rad l977, 50, 526-527.
2. Bolondi L, Bortolotti M, Santi V, et al. Measurement of gastric emptying time by real-time ultrasonography. Gastroenterology l985, 89, 752-759.
3. Holt S, McDicken WN, Anderson T, et al. Dynamic imaging of the stomach by real-time ultrasound: a method for the study of gastric motility. Gut l980, 21, 597-601.
4. King PM, Adam RD, Pryde A, et al. Relationships of human antroduodenal motility and transpyloric fluid movement: non-invasive observations with real- time ultrasound. Gut l984, 25, 1384-1391.
5. King PM, Heading RC, Pryde A. Co-ordinated motor activity of the human gastroduodenal region. Dig Dis Sci l985, 30, 219-224, 24.