The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 17 (page 81)

Chapter 17

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.

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