Weiland J D, Anderson D J
Wilmer Eye Institute, Johns Hopkins University, Baltimore, MD 21287, USA.
IEEE Trans Biomed Eng. 2000 Jul;47(7):911-8. doi: 10.1109/10.846685.
Experiments were conducted to assess the effect of chronic stimulation on the electrical properties of the electrode-tissue system, as measured using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Silicon, micromachined probes with multiple iridium oxide stimulating electrodes (400-1600 micron 2) were implanted in guinea pig cortex. A 10-17 day post-operative recovery period was followed by five days of monopolar stimulation, two hours/electrode each day using biphasic, constant current stimulation (5-100 microA, 100 microseconds/phase). EIS and CV data were taken before and after stimulation. The post-stimulation impedance [at mid-range frequencies (100 Hz-100 kHz)] consistently and significantly decreased relative to prestimulation levels. Impedance magnitude increased permanently at low frequencies (< 100 Hz), correlating to a change in the charge storage capacity (the area under a cyclic voltammagram). Impedance magnitude significantly increased during the recovery period, though this increase could be mostly reversed by applying small currents. A mathematical model of the electrode-tissue system impedance was used to analyze in vivo behavior. The data and modeling results shows that applying charge to the electrode can consistently reduce the impedance of the electrode-tissue system. Analysis of explanted probes suggests that the interaction between the tissue and electrode is dependent on whether chronic pulses were applied. It is hypothesized that the interface between the tissue and metal is altered by current pulsing, resulting in a temporary impedance shift.
进行了实验以评估慢性刺激对电极 - 组织系统电学特性的影响，该影响通过电化学阻抗谱（EIS）和循环伏安法（CV）进行测量。将带有多个氧化铱刺激电极（400 - 1600平方微米）的微加工硅探针植入豚鼠皮层。术后10 - 17天的恢复期后，进行为期五天的单极刺激，每天每个电极刺激两小时，采用双相恒流刺激（5 - 100微安，每相100微秒）。在刺激前后采集EIS和CV数据。相对于刺激前水平，刺激后的阻抗[在中频范围（100赫兹 - 100千赫兹）]持续且显著降低。在低频（<100赫兹）时，阻抗幅值永久性增加，这与电荷存储容量的变化（循环伏安图下的面积）相关。在恢复期，阻抗幅值显著增加，不过通过施加小电流，这种增加大多可以逆转。使用电极 - 组织系统阻抗的数学模型来分析体内行为。数据和建模结果表明，向电极施加电荷可以持续降低电极 - 组织系统的阻抗。对取出的探针进行分析表明，组织与电极之间的相互作用取决于是否施加了慢性脉冲。据推测，电流脉冲会改变组织与金属之间的界面，从而导致暂时的阻抗变化。
