Date of Award

Spring 1978

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Biomedical Engineering

First Advisor

Edward J. Zuperku

Second Advisor

Coon, Robert L.

Abstract

Differential nerve blocks have been widely used to study reflexes mediated through peripheral nerves in acute experimental preparations. Local anesthetics, pressure, asphyxia, and ischemia can all be used to achieve a selective block of nerve fibers. However, the order of conduction depression associated with local anesthetics is much debated, while pressure, asphyxia and ischemia produce irreversible blocks due to tissue damage. Other techniques such as cooling and the application of polarizing currents to the nerve, elicite reversible, differential blocks of conduction. Fibers are blocked in order of diameter with the largest fibers being blocked first. The nerve need not be sectioned and the block may be removed or reinstated at any time without tissue damage. It is not possible, however, to selectively block within the A-fiber group using cooling. A more selective block can be achieved with polarizing currents, and therefore, this method is preferred for initiating differential nerve blocks. It has been suggested that polarizing currents of sufficient strength to block myelinated A-fibers cause spontaneous discharge of nonmyelinated C-fibers. This asynchronous firing is thought to arise at the cathode of the bipolar blocking electrodes. The purpose of this research was to study the effects and effectiveness of anodal blockade on myelinated and nonmyelinated vagal afferent nerve fibers. In addition to the conventional bipolar blocking technique, a monopolar anodal block in which the anode is placed on the nerve and the cathode is placed on a subcutaneous needle electrode is also described.

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