高速率电刺激对豚鼠听神经兴奋性的影响

目的：评估高速率电刺激对豚鼠听神经兴奋性的影响。方法：切开受试豚鼠圆窗膜，标准电极插入鼓阶大约4mm，两个靠近蜗尖的电极作为刺激电极，切开圆窗用压碎的颞肌封住。随机选择一耳为刺激耳，另一耳则为对照耳，均安装上标准电极，刺激电极在整个测试过程中保持不动。在保持刺激强度处在临床正常水平[电刺激诱发听觉脑干电位(EABR)阈值上6dB]情况下，用200(n=14)、400(n=10)、1000(n=11)、2000(n=10)脉冲数／s(PPS)四种不同的电刺激速率急性刺激45只听力正常豚鼠鼓阶内电极2h，记录急性刺激前、后3h内EABR的阈值和Ⅰ波幅值，比较急性刺激前、后EABR的Ⅰ波幅值的变化。结果：急性刺激电流强度固定在临床正常水平(EABR阈上6dB)，急性刺激后EABR的Ⅰ波幅值同急性刺激前相比，采用200PPS刺激速率平均约升高20％；400PPS约升高9％；1000PPS约升高7％；2000PPS约升高30％。结论：在刺激电流强度为阈上6dB的情况下，人工耳蜗言语编码策略如果应用1000、2000PPS高速率电刺激不会导致听神经的兴奋性下降。此实验为临床上研制新的人工耳蜗采取高刺激速率语音信号处理方案提供了依据。

The effect of high-rate electrical stimulation on excitability of auditory nerve in Guinea pigs

OBJECTIVE: To assess the effect of high-rate electrical stimulation on excitability of the auditory nerve by recording the change of amplitude of the electrically evoked auditory brainstem responses (EABR). METHOD: After guinea pigs were in the anesthetic state, both bullae were exposed and the round window membranes incised. A standard electrode array was carefully inserted a distance of approximately 4 mm into the scala tympani of the both experimental cochlea and the control cochlea. The most apical electrodes were used as stimulating electrodes. The round window was then sealed with crushed temporal muscle. The electrode arrays were maintained in the same position throughout the experiment. While the stimulus intensities were kept constantly in the normal clinical level (6 dB above EABR threshold), four stimulus rates of 200 (n=14), 400 (n=10), 1000 (n=11), 2000 (n=10) pulses/s(PPS) were each delivered to bipolar electrodes in scala tympani of 45 guinea pigs for 2 h of acute electrical stimulation. Thresholds and wave I amplitudes of EABR were recorded for periods of 3 h following 2 h of acute stimulation. By comparing the pre-stimulus amplitudes of wave I in EABR with the post-stimulus ones(t test), the effect of high-rate electrical stimulation on excitability of the auditory nerve was assessed. RESULT: While the acute stimulus intensity was kept constantly in the normal clinical level (6 dB above EABR threshold), with comparison of pre-stimulus response with post-stimulus response of wave I, the latter increased by 20%, 30%, 9%, 7% at each of the four different stimulus rates of 200, 2000, 400, 1000 PPS. CONCLUSION: Within the 3 h post-stimulus monitoring period after 2 h acute stimulation, no reduction but increase in EABR amplitude was observed using stimulus intensity of 6 dB above EABR threshold at four stimulus rates (200, 400, 1000, 2000 PPS). Electrical stimulation presented at high rates of 1000 to approximately 2000 PPS with clinical intensity (6 dB above EABR threshold) did not result in the reduction of excitability of auditory nerve. These results supported to provide data for the envisaged introduction of a speech-processing strategy based on high stimulus rates.