视网膜上假体电刺激脉冲参数的优化

Parameters Optimization of Electrical Stimulation Pulse for Epiretinal Prostheses

目的目前视网膜上假体的常用刺激波形是双相不对称矩形脉冲,而脉冲参数是影响刺激响应的主要因素之一。本文目的是寻找视网膜上假体的最佳脉冲参数组合。方法视神经节细胞用房室模型模拟,膜特性采用Fohlmeister-Colman-Miller(FCM)模型。双相不对称矩形脉冲的参数包含阴极相幅值,阴极相持续时间,阴极相与阳极相幅值比和相间间隔。胞外理想点电极刺激视神经节细胞的仿真期间,寻找产生动作电位(AP)的最佳脉冲参数组合。刺激有效性采用刺激阈值,阴极相传递电荷量和能量消耗来比较。结果阴极相持续时间为1 ms,阴极相与阳极相幅值比为1和相间间隔为0.1 ms时有最低刺激阈值。阴极相持续时间为0.1 ms,阴极相与阳极相幅值比为1和相间间隔为0.2 ms时获得最低阴极相传递电荷量。最低能量消耗在阴极相持续时间0.9 ms,阴极相与阳极相幅值比10和相间间隔0.6 ms。结论在最低刺激阈值,最低阴极相传递电荷量和最低能量消耗时,双相不对称矩形脉冲参数组合不同。这些为视网膜上假体选择合适的脉冲参数组合提供一个有意义的参考。

Objective The stimulus waveform for the epiretinal prostheses is usually the biphasic asymmetric rectangular pulse at present,and the parameter of the pulse is one of the major factors that have an effect on the stimulation response. In this paper the optimal combination of parameters of the pulse for epiretinal prostheses was studied. Methods The ganglion cell was simulated by the compartment model and its membrane property was modeled by the Fohlmeister-Colman-Miller（ FCM） model. The parameters of a biphasic asymmetric rectangular pulse consisted of the cathodic phase amplitude,the cathodic phase duration,the amplitude ratio of cathodic phase to anodic phase and the gap between the phases. During the simulation of extracellular electrical stimulation of the retinal ganglion cell with the ideal point electrode,the minimum cathodic phase amplitude of the pulse which could make the cell to generate an action potential（ AP） was searched. The stimulus threshold,the quantity of charge delivered by cathodic phase and the energy consumption at the stimulus threshold were used as the criterion of stimulus effectiveness. Results The minimum stimulus threshold was obtained at the cathodic duration of 1 ms,the amplitude ratio of cathodic phase to anodic phase of 1 and interphase gap of 0. 1 ms. The parameters of the pulse which had the minimum quantity of charge transferred by cathodic phase were the cathodic phase duration of 0. 1ms,the amplitude ratio of 1 and interphase gap of 0. 2ms. The lowest energy consumption was acquired at cathodic phase duration of 0. 9 ms,the amplitude ratio of10 and the interphase gap of 0. 6 ms. Conclusions The parameters of the biphasic asymmetric rectangular pulse are different at the minimum stimulus threshold,the minimum quantity of charge delivered by cathodic phase and the lowest energy consumption at the stimulus threshold. These provide a meaningful reference for choosing the appropriate combination of the pulse parameters for epiretinal prostheses.