Chapter 16 (page 78)

The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 16 (page 78)

Daniel and Irwin (l968) found that rhythmic duodenal electrical activity in dogs, recurring at a rate of l7 per minute, existed within one millimeter of rhythmic gastric electrical activity recurring at a rate of 4.3 to 5.1 per minute. There was a possibility of coupling between the gastric and duodenal electrical rhythms since the frequency of the two rhythms could indicate a 3:1 or 4:1 coupling. These authors did not agree with Bass et al (l961) that the stomach and duodenum were electrically insulated by an interposed electrically silent zone; such insulation could only be achieved by a continuous lipid membrane, and no such structure existed at the gastroduodenal junction.

Bortoff and Davis (l968) instituted in vivo animal studies to determine whether or not transmission of slow waves across the gastroduodenal junction occurred, to study the effect of myenteric denervation on slow wave transmission and to observe the effects of vagal and splanchnic nerve stimulation. Using suction electrodes applied to the serosal surface in cats, dogs, rhesus monkeys and baboons, it was shown that "antral" slow waves spread across the junction into the proximal duodenum, where they periodically augmented depolarizations of duodenal slow waves, thereby increasing the probability of duodenal spiking. After functional myenteric denervation the duodenal spread of antral slow waves continued, indicating that it was a myogenic process; this probably occurred via bundles of antral longitudinal muscle extending across the pylorus and interdigitating with duodenal longitudinal musculature. (Comment: Some longitudinal muscle fibres normally extend across the pylorus from the stomach to the duodenum as described in Chapter 3). However, the spread could be modulated neurologically; vagal stimulation increased both amplitude and duration of antral slow waves, augmenting depolarization on both sides of the junction and increasing spike activity. Thus duodenal spiking was temporally related to antral slow waves. Splanchnic stimulation had mixed effects, causing either excitation similar to that of vagal stimulation, or inhibition of antral slow waves. It appeared if the spread of antral slow waves into the proximal duodenum constituted the primary mechanism for co-ordination of the mechanical activity at the gastroduodenal junction.

Kwong et al (l970) studied the electrical activity of the gastric "antrum" up to 6.0 cm from the pylorus in 56 patients with upper gastrointestinal pathology, and in 12 patients with gall-stones acting as controls; at operation electrodes were implanted through the serosa and others attached to the mucosa by means of suction. The same frequency was recorded from the mucosal and serosal electrodes and the main components of the wave forms were the same. In the control patients the wave frequency was approximately 3 per minute, which was significantly less than the frequency in patients with gastric ulceration, duodenal ulceration and gastric carcinoma. The general pattern of the wave forms was the same in all groups, although areas replaced by tumor were electrically silent. It was concluded that while there were differences in frequency, no differences in the pattern of electrical activity appeared which might be of diagnostic significance in these conditions.

Duthie et al. (l97l) studied the pacesetter potential in the stomach and duodenum in patients undergoing cholecystectomy. Electrodes were implanted under the serosa in the gastric "antrum" and in the duodenum as far as the duodenal papilla, the indifferent electrode being placed on the skin of the abdomen. The frequency and amplitude of the electrical waves were measured, and where possible also the conduction times. In the antrum the frequency of the pacesetter potential was stable during recordings made at rest. The waveform was similar to that obtained from electrodes sucked on to the mucosa as found by Kwong et al. (l970), and the mean frequency of about 3.12 cycles per minute was also similar. Action potentials were seen only occasionally in the unstimulated stomach. In the duodenum, from 10 to 12cm distal to the pylorus, the frequency of the pacesetter potential was about 12 cycles per minute. In the proximal 4.0 to 5.0 cm of the duodenum, the predominant pattern consisted of 3 cycles/min as in the antrum, occasionally superimposed on 12 cycles/min. However, no direct relationship could be established between the frequency of the gastric (3 cycles/min) and duodenal (12 cycles/min) intrinsic activities. The conduction velocity of the electrical waves in the antrum between 4.0 and 1.5 cm from the pylorus was about 0.5 cm per second. Across the pyloric region it was approximately 2.0cm per second, i.e. about four times as fast.

Ingestion of water, citrate or oleate significantly slowed the frequency of the pacesetter potential in the "antrum"; the injection of morphine was followed by an increase in action potentials both in the antrum and the duodenum. Duthie et al (l97l) concluded that the 3 cycles/min rhythm of the antrum passed into the proximal duodenum, but they were not able to detect any relationship between this frequency and the intrinsic 12 cycles/min frequency of the remainder of the duodenum. The route of conduction from the stomach to the duodenum was probably via the longitudinal muscle fibres continuing from the antrum across the pylorus.

Sarna (l975) suggested that the inherent rhythmic myoelectrical activity of the stomach should be termed electrical control activity. When motor activity was present, the electrical control activity was accompanied by a second component with or without superimposed fast oscillating potential changes, for which he suggested the appellation electrical response activity.

El-Sharkawy et al. (l978) simultaneously recorded mechanical and intracellular electric activity from canine and human gastric musculature, and found regional differences in the electrical signal that caused contractions. Phasic contractions in the "terminal antrum" were initiated by spike potentials whereas phasic contractions in the corpus and orad antrum were regulated by the plateau potential.

Smout et al. (l980) called the first kind of electrical activity, i.e. the omnipresent periodic activity that is not indicative of contractile activity, the electrical control activity (ECA). Electrical response activity (ERA) only occurs in connection with phasic contractile activity, but is time-locked to ECA; it does not always consist of spikes. ERA may be absent, as in the motor quiescent phase of the interdigestive myoelectric complex.