UBC Theses and Dissertations
Gastric electrical activity : the effects of vagal section and vagal stimulation Doran, Morton Lawrence
The current enthusiasm for vagotomy as treatment for peptic ulcer disease has been dampened by several problems, the most serious of which is recurrent ulceration. As this is due in most instances to incomplete vagal section, it is clear that the development of a reliable method to assess completeness of vagotomy during the course of surgery is an essential step toward reducing the 10-15% incidence of recurrent ulcer. The problem has been approached by studying some of the gastric effects of vagal stimulation during operation. These include changes in intragastric pressure, acid secretion, and electrical activity. The investigation as outlined in this thesis was aimed at developing a reliable, reproducible intraoperative method for assessing the completeness of vagotomy. The plan of the experiment was essentially twofolds: (i) to determine whether complete vagotomy would alter the gastric electrical activity in some reproducible manner such as would indicate that all vagal connectionshad been severed; (ii) to divide one vagus nerve at the level of the esophageal hiatus, assess the effect on electrical activity of stimulation of its distal or peripheral end, and then stimulate the central end with view to eliciting a response in the electrical activity via reflex pathways through the brainstem, vagal nuclei, and along the remaining intact efferent vagal fibres; these remaining fibres would then be divided, central stimulation of either vagal trunk repeated, and presumably the previously observed "characteristic" response of the gastric electrical activity would no longer be obtained, indicating complete division of all vagal fibres. Vago-vagal reflex responses to afferent vagal stimulation have been documented with respect to influence on both gastric tone and secretion. One may reasonably expect to be able to demonstrate the existence of a vago-vagal reflex pathway where by one might alter gastric electrical activity by central or reflex stimulation of the afferent vagal fibres. Gastric electrical activity has been recorded, and the effects of vagal section on this electrical activity have been assessed. The reduction in the frequency of the basic electrical rhythm (BER) observed following complete vagotomy, though of significance statistically, was found to be caused as well by other non-related factors, and was in any case of such a low order as to be of limited value in assessing any individual case. It could therefore not be considered indicative of complete vagal section. The disorganization of the BER observed following vagotomy was both temporary and inconsistent, and could not be interpreted as pathognomonic of complete vagotomy. The observations recorded during electrical stimulation of afferent vagal fibres have demonstrated the existence of a vago-vagal reflex pathway whereby gastric electrical and motor activity can be modified by afferent vagal stimulation. These effects are presumably conveyed via pathways through the central nervous system and along the intact efferent vagal fibres. The effects on gastric electrical activity are neither consistent nor reproducible, whereas the effects on gastric motor activity appear to be considerably more reliable. In the light of these observations, it would seem more appropriate to study the changes in the contractile force of gastrointestinal smooth muscle subsequent to afferent vagal stimulation in the search for a method to assess completeness of vagotomy during the course of surgery. The development of such a test will be a major factor in preventing this form of treatment from falling into disrepute because of a continued high rate of recurrent ulceration.
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