Simulation Of Epidural Spinal Cord Stimulation In Rats

Epidural spinal cord stimulation(ESCS) is mainly used to treat the nervous system disease by implanting electrode in the epidural space of the spinal cord, and then adopts a certain stimulation pulse width to activate the related nerve fibers. Related studies have shown that ESCS has obvious curative effect on the inhibition of the chronic and intractable pain and the recovery of motor function after spinal cord injury. But the basic neural mechanism of the therapy and the design of the stimulus parameter have to be decided by the study of the animal experiment and the certain of the computer simulation. Based on the study of the rat spinal cord anatomy and the Nissl's staining picture, the thesis built the three-dimensional geometry model. The conductivity of the spinal cord's tissue and the boundary condition of the model were set using COMSOL Multiphysics. The electric potential distribution of the spinal nerve fiber was solved. Based on the basic principles of the neural electrophysiology, the double cable model was established using NEURON. The excitation threshold of the nerve fibers after importing the electric potential distribution of the spinal nerve fibers in the rat was calculated.The distribution of the electric field under the mono-polar stimulation in rat's spinal cord was simulated using infinite element method in the thesis. The change of excitation thresholds of the dorsal root fibers and ventral root fibers within different segment, and the different depth of dorsal column fibers under different stimulus parameters were verified.The impact of the fiber location and the stimulation pulse width on the excitation threshold of nerve fibers was analyzed. The influence of electrode polarity and the segment of spinal cord on the conduction of action potential in nerve fibers was studied. The simulation results showed that the dorsal root fiber under the electrode had the lowest excitation threshold with the value of 0.41 V. The excitation threshold of the dorsal column in the superficial layers of spinal cord was 0.47 V. The ventral root fiber's excitation threshold was 0.78 V. Theexcitation threshold of dorsal column fibers decreased with the increase of stimulation pulse width. The difference among the excitation threshold of dorsal column fibers with different depth gradually reduced. But the excitation threshold of the dorsal column fibers reduced slowly with the increase of the pulse width. The position of the electrode which output stimulus pulse had obvious effect on the starting position of the action potential conduction.The appropriate pulse width pulse was conducive to the deep dorsal column fibers excited.The activation regions of the spinal cord tissue was increased with the reasonable pulse width. The ability to raise the deep nerve fiber was enhanced using the suitable pulse width.The simulation results can be a reasonable choice of stimulus parameters of clinical and animal experiments. The guidance in improving the target performance of the electrode array can be also provided.