Date of Award


Degree Name

MS in Biomedical Engineering


Biomedical and General Engineering


Rober Szlavik


An estimated 0.5% of world’s population has been diagnosed with epilepsy. Of these patients 20-30% will be unable to achieve seizure control with anti-epileptic drugs. Vagus nerve stimulation (VNS) may be an appropriate treatment option for some patients with pharmaceutically refractory, partial-onset seizures.

VNS therapy uses a helical electrode to interface between the implantable pulse generator and the vagus nerve. While there have been several studies related to the mechanical and electrical safety of such electrodes, little work has been done toward understanding the effectiveness of the helical electrode in nerve stimulation. A better understanding of the voltage field and nerve fiber activation patterns produced by a helical electrode is necessary in order to evaluate its effectiveness and suggest design improvements.

This thesis is primarily focused on investigating the effect on nerve fiber activation of changing the circumferential coverage of the platinum conductor. Finite Element Analysis and a nerve fiber model were used to evaluate several electrode designs.

The circumferential coverage caused significant changes to nerve fiber activation. Coverage greater than 330°-360° was found to be inversely related to fiber activation. It was also noted that neurons located near the electrode ends, or near where the ends cross when coverage is greater than 360° were more difficult to activate. The phenomenon is discussed at length and several electrode design improvements were suggested based on these findings