| Summary: | 碩士 === 國立成功大學 === 醫學工程研究所碩博士班 === 90 === Electrical stimulation techniques have been applied in restoration of certain dysfunctions in central nerve system lesion patients. Conventional neural stimulation method recruits the muscle nerves in a reverse order of physiologic manner, i.e., can not recruit small diameter nerve fibers without recruiting large diameter ones. However, high frequency blocking technique is a feasible method for achieving selective stimulation and blocking nerve fibers. The aim of the study is to establish an experiment system and animal model for high frequency blocking investigation.
In this study, we selected New Zealand white rabbit for acute animal study. A nerve cuff electrode with five rings was mounted on right side of sciatic nerve, and delivered two channels of stimulus current to nerve cuff at proximal site (for driving stimulus) and distal site (for blocking stimulus) for high frequency blocking investigation. Furthermore, a torque measurement system was established for assessing the stimulation or blocking performance in this study. We first find out suitable stimulation parameters for driving stimulus to activate all motoneuron fibers in nerve trunk and to produce smooth and tetanic muscle contraction. Three different blocking waveforms including monophasic, symmetric biphasic, and asymmetric biphasic waveforms, were tested to compare the blocking effects and to search for suitable blocking parameters. Finally, a muscle fatigue experiment was performed to verify whether high frequency blocking can selective stimulation and blocking varied sizes of nerve fibers.
From the animal studies, we found that at a stimulation frequency above 60 Hz smooth muscle contraction with small variation less 10 % of maximal torque can be achieved. After obtaining the isometric recruitment curves for each experiment, blocking stimulus with biphasic asymmetric waveform at varied blocking current amplitude shows better blocking effect. The maximal manipulation range can be above 90 % of maximal torque output. In muscle fatigue test, our results proved that high frequency blocking technique could achieve selective stimulation of smaller nerve fibers and blocking larger fibers. The development of high frequency blocking technique is not only a basis for developing the neural prostheses for bladder control and spasticity suppression, but also is a novel tool for neuromuscular control studies.
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