![](bg6.png)
Figure 10 shows the complete selectivity of axons
for PW > 9 ms. One can observe that only the
smaller parasympathetic fibers are active.
Figure 10: Activated axons for PW > 9 ms.
4 CONCLUSIONS
In this work design and testing of a multipolar cuff
electrode for peripheral nerve is presented. For that
purpose, a modeling workflow to study selectivity in
sacral nerve roots was implemented using ANSYS
Multiphysics, MATLAB and NEURON. Anatomical
studies were used to define a representative
distribution of fascicles in the sacral root. These
anatomical features were used to carry a study on the
effect of a multipolar cuff electrode on selective
stimulation of different fiber diameters. For pulse
widths higher than 9 ms, the selectivity is maximum
(most probably because of a “chronaxie effect”).
However to lower the need for electric power in the
electrical stimulation of sacral roots, further studies
have to be done in order to achieve selectivity for
lower pulse widths – e.g. increasing number of
electrode contacts, increasing number of rows of
electrodes in order to “reshape” the external
stimulation potential on each axon.
Modeling workflow showed to be effective for
the element size used in ANSYS. However, further
simulations are required for finer meshes in order to
study on effectiveness and stability of the workflow.
For that, a real anatomic mesh derived from a
histological cross section of the sacral roots will be
used.
ACKNOWLEDGEMENTS
This work was supported by the Portuguese
Foundation for Science and Technology
(SFRH/BD/62608/2009).
REFERENCES
Anon, 1996. Morphometric data of canine sacral nerve
roots with reference to electrical sacral root
stimulation. Neurourology Urodynamics, 15, pp.235–
248.
Brindley, G. S., 1977. An implant to empty the bladder or
close the urethra. Journal of Neurology, Neurosurgery,
and Psychiatry, 40, pp.358–369.
Choi, A., Cavanaugh, J. & Durand, D., 2001. Selectivity
of Multiple-Contact Nerve CuffElectrodes: A
Simulation Analysis. IEEE Transactions on
Biomedical Engineering, 48, pp.165–172.
Hauck, E. F. et al., 2009. Measurements and mapping of
282,420 nerve fibers in the S1-5 nerve roots. Journal
of neurosurgery. Spine, 11(3), pp.255–63. Available
at: http://thejns.org/doi/full/10.3171/
2009.3.SPINE17684 [Accessed November 2, 2011].
McIntyre, C., Richardson, A. & Grill, W., 2002. Modeling
the Excitability of Mammalian Nerve Fibers: Influence
of Afterpotentials on the Recovery Cycle. Journal
Neurophysiology, 87, pp.995–1006.
McIntyre, C. et al, 2002. No Title. Available at:
http://senselab.med.yale.edu/ModelDb/.
National Institute of Neurological Disorders and Stroke,
2012. Spinal Cord Injury: Hope Through Research.
Available at: http://www.ninds.nih.gov/disorders/sci/
detail_sci.htm [Accessed August 20, 2012].
Probst, M. et al., 1997. Neurostimulation for bladder
evacuation: is sacral root stimulation a substitute for
microstimulation? British Journal of Urology, 79,
pp.554–566.
Rijkhoff, N. et al., 1997. Selective Detrusor Activation by
Electrical Stimulation of the Human Sacral Nerve
Roots. Artificial Organs, 21, pp.223–226.
Rodrigues, F. et al., 2012. Flexible Multipolar Cuff
Microelectrode For FES Of Sacral Nerve Roots. In
Smart Machines – Neural Evolution. Banff, Canada:
IFESS .
Schiefer, A. et al., 2010. Selective stimulation of the
human femoral nerve with a flat interface nerve
electrode. Journal Neural Engineering, 7.
Social, H. and F. A. C., 2002. Towards concerted efforts
for treating and curing spinal cord injury. Available at:
http://assembly.coe.int/ASP/Doc/XrefViewHTML.asp
?FileID=17004&Language=EN [Accessed August 20,
2012].
ModelingWorkflowforStudyofFunctionalElectricalStimulationinPeripheralNerves
183