XIX Sympozjum Srodowiskowe PTZE - materialy.pdf
XIX Sympozjum Srodowiskowe PTZE - materialy.pdf
XIX Sympozjum Srodowiskowe PTZE - materialy.pdf
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Introduction<br />
<strong>XIX</strong> <strong>Sympozjum</strong> <strong>PTZE</strong>, Worliny 2009<br />
NUMERICAL PROTOTYPING<br />
OF VAGUS NERVE STIMULATOR<br />
Jacek Starzyński, Robert Szmurło, Stanisław Wincenciak,<br />
Bartosz Sawicki, Przemysław Płonecki<br />
Warsaw University of Technology<br />
The authors aim was to analyze the feasibility of a magnetic stimulation device for vagus<br />
nerve. Due the costs of medical experiments, a numerical simulator was chosen as the primarily<br />
tool for such study.<br />
Numerical model allows fast prototype verification and even optimal design of the best possible<br />
construction.<br />
The design goal and the field model<br />
To formulate the optimum criteria the authors of the paper have evaluated several models of<br />
neural tissue activation. The activation of peripheral nerves can be described by the following<br />
nonlinear cable equation:<br />
2<br />
dV ⎛ d V ⎞<br />
m<br />
m dEz<br />
( t)<br />
Cm<br />
+ Iion<br />
− G ⎜ ⎟<br />
a = −G<br />
2<br />
a<br />
dt ⎜ dz ⎟<br />
,<br />
⎝ ⎠ dz<br />
where Iion is the nonlinear component of ionic currents (simulated with Hodgkin-Huxley<br />
membrane model adapted to vagus nerve), G a is the internodal axoplasmic conductance, C m<br />
is the transmebrane nodal capacitance and Ez (t)<br />
is the electric field component along the<br />
nerve.<br />
The threshold value necessary to stimulate a human, myelinated, peripheral nerve was proposed<br />
as fT=6820 V/m 2 . It was used as a goal for the optimal design problems presented here.<br />
Thanks to small conductivity of human tissue (less than 0.33 S/m for considered frequency<br />
range) the model can neglect displacement currents and magnetic field due to eddy currents<br />
induced in the human body. With these simplifications the electric field induced in tissue can<br />
be described with combination of electric scalar potential and with magnetic vector potential.<br />
Such model is simple to implement and optimal in terms of numerical costs. Finite element<br />
model is restricted to the head only. The external field expressed with the magnetic vector<br />
potential is calculated with help of Biot-Savart law.<br />
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