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SYBP: Biologie und Physik

SYBP 3: POSTER

SYBP 3.10: Poster

Donnerstag, 30. März 2000, 15:00–18:00, D

The Electrical Stimulation of the Human Spinal Cord: A Computer Model Study — •Karen Minassian, Frank Rattay, and Harald Markum — Technische Universität, A-1040 Wien

A simplified model of the human spinal cord is developed from the “Visible Human Male” and patient data from X-ray and MRI pictures. The electric field of an implanted bipolar electrode was computed with the finite element program ANSYS. The voltage profiles along selected target neurons were used as input data for a cable model of myelinated nerve fibres. The ion channel dynamics in the active parts of the neural membrane was simulated using a mammalian nerve model. The order of excitation for 12 target neurons representing motoric and sensoric nerve fibres was evaluated for different medially and laterally positioned electrodes and mono- and biphasic pulses. Clinical applications of the electrical stimulation of the spinal cord with epidural electrodes cause a great variability in muscle responses including single twitches, constant tonus, suppression of spasms or generation of rhythmic activities. The shape of the electrodes and their positions relative to the excitable structures, the duration, intensity and polarity of the stimulus signal, and its repetition rate are the main elements that influence the large spectrum of those observed muscle activities which can be generated or affected by electrical stimulation. We simplify the situation to illuminate the relevant electrophysiological and biophysical relations in the epidural electrical stimulation of the lumbosacral cord. We test which nerve structures are excitable for different electrode positions and analyze the sequence of excitations with stepwise increase of the voltage of a stimulating dipole.