Date of Award

8-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Electrical Engineering

Advisor

Burg, Timothy C

Committee Member

Kwartowitz , David M

Committee Member

Singh , Rajendra

Abstract

The vagus nerve is one of the most important nerves in the human body. It is associated with a plethora of functions one of them being acid secretion inside the stomach to aid in digestion. The cerebrum part of the brain initiates an action potential that is propagated along the vagus nerve to the parietal cells that secrete acid. In some cases, the cerebrum over stimulates the parietal cells leading to excess acid secretion, more than is needed for the digestion process. This excess acid leads to the formation of open sores along the stomach lining called gastric/peptic ulcers. In some cases, these gastric ulcers are curable by taking medicines. In other cases, medicines have little or no effect on these gastric ulcers and a surgical intervention, called a vagotomy is recommended to cure the gastric ulcers. Vagotomy is the surgical cutting of the vagus nerve branches that link the brain to the parietal cells that produce acid. Once a branch is cut, the signal from the cerebrum is blocked and acid production is reduced thereby reducing the formation of ulcers. Vagotomy surgery can be challenging to perform. The major hurdle facing surgeons is locating the vagus nerve branch responsible for excess acid secretion in a specific zone of the stomach. If the surgeons are unable to locate the correct branch or cut other nerve branches, it will not cure the gastric ulcer problem and the entire surgical exercise may need to be revised. Thus there is a need to develop a system that would help surgeons locate and identify the correct vagus nerve branch to cut during the vagotomy surgery. A system that artificially excites the vagus nerve and provides the surgeon feedback that the laparoscopic tool is near the vagus nerve branch of interest is proposed and designed. To facilitate the design process, an external electrical stimulation model of a human vagus nerve was developed using COMSOL Multiphysics simulation software. The nerve model is built in the simulation software using the approximate geometric and material properties of the human vagus nerve. The model recapitulates the salient feature that if an applied electric potential exceeds a threshold potential, it leads to the generation of an action potential that propagates through the length of the vagus nerve. The proposed vagus nerve tracer consists of a stimulation cuff to inject a trace signal into the vagus nerve and a receiver probe that can be placed near a nerve to detect the presence of the trace signal. The stimulation cuff is a set of copper electrodes that would be placed around the vagus nerve at a point above the stomach where the vagus nerve is clearly visible and accessible to the surgeons. The detector probe is designed as copper hook monopolar tip that could be affixed to a laparoscopic instrument. It can be placed around the vagus nerve branch without damaging it and can detect the action potential. An important third component is the square wave used as the trace signal. The developed system thus comprises the vagus nerve artificial electrical stimulation cuff, trace signal, and detector probe. Computer simulations have been performed to optimize the proposed design and to demonstrate its functionality and potential value to help surgeons overcome the complication of locating the correct branch of vagus nerve to cut during the vagotomy surgery.

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