利用单电极不对称双向脉冲电刺激实现有髓神经传导阻断的仿真研究

基于McNeal的神经电缆模塑,以有限长度的有髓神经纤维F-H模型为研究对象,探讨采用单电极不对称双向脉冲刺激实现有髓神经传导阻断的规律.仿真结果表明,当刺激脉冲的频率高于9kHz时,不对称双向脉冲可实现不同直径(2～20μm)神经纤维的完全阻断,并且阻断电流的强度随刺激频率的升高而增大.粗纤维具有更低的阻断阈值.刺激电极一神经纤维距离增大时,神经纤维实现完全阻断所需电流强度随之增大.仿真温度从20℃升高到37℃时,神经纤维的阻断阈值降低.研究结果将为相关的动物实验和功能电刺激的临床应用提供更多的信息.     

不同刺激模式对神经传导阻断影响的仿真研究

目的为减少长期电刺激导致的神经疲劳,提高治疗效率,本研究比较多种刺激模式在神经传导阻断中的阻断阈值,为动物实验选择最好的刺激模式。方法以有限长单根有髓神经为研究对象,采用有髓神经纤维Frankenhaeuser-Huxley(F-H)模型进行仿真,比较双向对称方波、正弦波、双向对称方波簇的阻断阈值以及叠加不同信噪比的双向对称方波阻断阈值。结果在刺激频率范围内,对称方波的阻断波形低于正弦波和方波簇的刺激阻断阈值。对于叠加噪声的对称方波,叠加-50 d B的高斯白噪声能够降低方波的阻断阈值。结论方波的阻断阈值低于正弦波和方波簇。在相同的条件下,叠加高斯白噪声对方波阻断阈值的影响明显,尤其是叠加-50 d B的噪声。     

用高频双向脉冲电刺激实现有髓神经传导阻断的仿真研究

探讨由高频双向脉冲电刺激实现神经传导阻断的可能性.采用McNeal的神经电缆模型,利用单电极高频双向脉冲刺激对基于Frankenhaeuser-Huxley(FH)方程的有髓神经纤维,仿真研究传导阻断的阈值及机制.结果显示,当刺激脉冲频率高于10kHz时,不同直径(5～20μm)的神经纤维可以完全被阻断.在神经纤维的传导阻断中,刺激电流的频率越高,所需的刺激强度越高.粗纤维具有低的传导阻断阈值.对于由高频双向脉冲引起的神经纤维传导阻断,其阻断的机制主要取决于钾离子通道的开放.研究结果为相关动物实验及功能神经电刺激的临床应用提供更多信息.     

低频电刺激对脊髓损伤后膀胱过度活动抑制的仿真研究

目的 探讨低频脉冲（0～10Hz）刺激时,不同刺激波形对脊髓损伤后逼尿肌反射亢进诱发的膀胱过度活动症的结果,以寻求抑制膀胱过度活动的最优刺激波形.方法 首先根据McNeal的神经纤维电缆模型,基于Frankenhaeuser-Huxley （FH） 方程建立有髓神经纤维的膜外点电极刺激的仿真系统,评价低频电刺激中的四种波形,即正向脉冲、负向脉冲、双向对称脉冲、双向不对称脉冲的效果.通过电刺激脊髓损伤犬的阴部神经实验,验证仿真条件下最优刺激波形的临床效果.结果 仿真实验表明双向不对称脉冲的抑制效果最佳;动物实验表明以3V、0.1ms的正向脉冲为起始脉冲,结合1V、0.3ms的负向脉冲的双向不对称波形的抑制效果为最优.结论 低频脉冲刺激脊髓损伤犬阴部神经时,正向脉冲在前的双向不对称脉冲的刺激波形仿真效果最佳,并适用于临床实验,能够有效抑制膀胱过度活动,保护神经避免电化学损伤.     

双向脉冲可实现的神经纤维选择性兴奋

背景：研究证明利用电刺激外周神经纤维可恢复一些因失去中枢神经控制的肌肉的功能。 目的：验证双电极1 mm较近距离下双向方波脉冲实现神经选择性兴奋的正确性,并基于此实现神经的选择性兴奋。 方法：成年Wistar大鼠8只,麻醉后暴露大鼠坐骨神经,将电极小心放于坐骨神经干,建立神经选择性刺激模型。实验用电极为自制Cuff双极性电极,刺激器采用的是Grass S88刺激器和AWG2005任意波形信号发生器。采取双电极双向刺激方式,两个电极之间距离为1 mm,刺激波形选用脉宽为0.2 ms的对称双向脉冲,其输出脉冲的幅度、脉宽和延时均可调。调节刺激强度,研究双电极双向刺激下神经兴奋性的规律,以此实现神经的选择性兴奋,并利用“碰撞法”原理验证利用双电极双向刺激方法实现神经选择性兴奋的可行性。 结果与结论：实验过程中神经动作电位的变化将经P511放大器放大后接入示波器显示,双电极刺激波形为脉宽为0.2 ms的对称双向脉冲。随着刺激幅度的增大,实现神经的选择性兴奋。说明用距离很近(1 mm)的双电极双向对称脉冲的方法实现了神经的选择性兴奋,并利用“碰撞法”原理证实了此种方法的有效性和可行性。     

用双向脉冲作选择性神经刺激的研究

双向脉冲选择性刺激是避免神经纤维电化学损伤、使肌肉平稳收缩、降低疲劳的有效电刺激模式。本文提出了单电极、双电极和三电极三种双向刺激模式,利用计算机模型仿真有效地实现了选择性刺激,并且利用蟾蜍的离体坐骨神经干在动物实验上验证了这几种方法的可行性。这些方法可望推进神经电刺激向临床应用迈进的步伐     

高频双向电刺激下无髓神经模型传导阻断的仿真研究

目的神经纤维异常兴奋会造成许多功能障碍疾病,因此,研究无髓神经纤维受到电刺激时动作电位的传播规律及传导阻断情况有重要的科研意义和临床价值。方法本文基于Hodgkin-Huxley模型,在高频双向电刺激下研究无髓神经纤维的阻断阈和阻断机制,并提出一种电刺激结束后轴突恢复初始状态的时间测量方法。结果电刺激下直径大的神经纤维先被阻断,直径小的神经纤维后被阻断,并随着刺激频率的增加,阻断阈在12~16 k Hz时达到峰值。阻断电极处钠离子和钾离子通道的持续开放造成神经纤维的传导阻断。电刺激结束后,神经纤维恢复初始状态的时间随着频率的增加而增加。结论本研究揭示了无髓神经纤维的阻断机制以及电刺激结束后神经纤维恢复初始状态的时间与电刺激频率的关系,这些结果将为相关动物实验和功能电刺激的临床应用提供更多的信息。     

神经纤维双向选择性刺激方法仿真研究

双向选择性刺激是避免神经纤维电化学损伤、使肌肉平稳收缩、降低疲劳的有效电刺激模式。利用计算机模型仿真，提出了单电极、双电极和三电极三种双向刺激模式，有效地实现了选择性刺激，推进了神经电刺激向临床应用迈进的步伐。     

采用准梯形电流脉冲得到脊髓小运动神经元的选择激活特性

我们已找到了一种在同一神经干内只激活较小神经纤维而避免激活大神经纤维的电激活法。该方法出自这样一个事实:对小的神经纤维来说,冲动潜在性在大的神经纤维里能被比较小的膜超极化作用所阻断。在我们的神经刺激系统中,通过一根三极根套电极的Q电流脉冲由膜的超极化作用能导致不同的冲动潜在性阻断。Q     

外部电场作用下的视神经纤维兴奋性的仿真研究

基于刺入式电极的视神经视觉假体,为盲人的视觉修复提供了新的可能性。为了对该视神经假体的电刺激策略和微电极设计提供理论支持,基于真实的电极结构,在COMSOL软件中建立刺入式微电极的外部电场仿真模型,并将其与利用NEURNO软件实现的神经纤维双层电缆模型结合,系统地研究电极与视神经纤维的相对位置、电刺激脉冲宽度以及电极几何结构的改变对视神经纤维兴奋阈值的影响。不同电极位置、刺激脉宽刺激下阈值变化规律的仿真结果,与以往报道的动物实验和仿真实验结果相符,证明了所建模型的有效性。 根据仿真结果,对刺入式视神经假体中刺激脉宽的选择和电极几何结构的设计,建议如下：窄脉宽刺激有利于降低能量消耗;电极锥度的设计要在满足电极力学特性及易于植入视神经的基础上,尽可能地减小,以降低纤维兴奋的阈值;电极的暴露面积越小,纤维兴奋所需的电流阈值越低,但电荷密度阈值越高;较低的电流阈值有利于减少能量消耗,但过高的电荷密度阈值却容易造成组织损伤,因此电极暴露面积的设计需要在耗能与安全性之间进行综合考虑。电极绝缘层厚度的改变对视神经纤维的兴奋阈值没有明显的影响,但从电极插入的难易考虑,应尽可能减小绝缘层厚度。以上结果对人体其他部位神经纤维的电刺激同样具有参考价值     

The relative efficacy of monopolar vs. bipolar electrodes in stimulation-produced analgesia

Summary Focal brain stimulation (FBS) of the periaqueductal gray (PAG) produces reliable anti-nociception. The use of different electrode configurations alters the distribution of excitation as well as the locus of cells being stimulated, making it difficult to compare results across laboratories. This study compared the analgesic properties of bipolar electrodes delivering biphasic current and monopolar electrodes delivering either a biphasic or a monophasic current to the ventral PAG. Naloxone reversibility of the analgesia was also tested. Results indicate that biphasic current with either monopolar or bipolar electrodes is more likely to elicit analgesia than monophasic current using monopolar electrodes. Naloxone reversed the analgesia produced by the monopolar/monophasic model, but only attenuated the monopolar/biphasic FBS and did not affect the analgesia produced by the bipolar/biphasic configuration. Biphasic current delivered through bipolar electrodes results in the sequential activation of different cell populations. Use of bipolar electrodes may widen the distribution of excitation beyond that of either monopolar configuration. Thus, a wider neural field of excitation may cause a bleedover of the field of stimulation into two systems (one opiate and one nonopiate).     

The relative efficacy of monopolar vs. bipolar electrodes in stimulation-produced analgesia

Focal brain stimulation (FBS) of the periaqueductal gray (PAG) produces reliable antinociception. The use of different electrode configurations alters the distribution of excitation as well as the locus of cells being stimulated, making it difficult to compare results across laboratories. This study compared the analgesic properties of bipolar electrodes delivering biphasic current and monopolar electrodes delivering either a biphasic or a monophasic current to the ventral PAG. Naloxone reversibility of the analgesia was also tested. Results indicate that biphasic current with either monopolar or bipolar electrodes is more likely to elicit analgesia than monophasic current using monopolar electrodes. Naloxone reversed the analgesia produced by the monopolar/monophasic model, but only attenuated the monopolar/biphasic FBS and did not affect the analgesia produced by the bipolar/biphasic configuration. Biphasic current delivered through bipolar electrodes results in the sequential activation of different cell populations. Use of bipolar electrodes may widen the distribution of excitation beyond that of either monopolar configuration. Thus, a wider neural field of excitation may cause a bleedover of the field of stimulation into two systems (one opiate and one nonopiate).     

刺入式电极刺激视神经的仿真研究

目的 刺入式电极激活视神经纤维是发展视神经假体的新思路.以MATLAB为平台建立仿真系统来研究其作用机制,并通过改变刺激参数来探讨刺激效果.方法 首先建立视神经的容积导体模型和视神经纤维模型,然后计算在刺入式电极刺激下不同深度纤维的兴奋阈值,并用激活函数和组织激活区来表征外加刺激的作用效果；随后改变纤维的直径、刺激脉冲脉宽来探讨不同参数对刺激效果的影响.结果 兴奋阈值随着电极-纤维距离的增加增大,此时视神经内能同时被激活的纤维数量增多；增大纤维直径,同一深度纤维兴奋阈值会减小,电极-纤维距离越大,阈值减小程度也越大；增加单相矩形波脉宽,兴奋阈值减小,脉宽大于0.5 ms时,同一深度纤维兴奋阈值几乎不再随脉宽增加而变化.结论 刺入式电极可以实现对视神经的有效刺激,不同的刺激参数能产生不同的激活效应.所得结论对实验具有一定的指导意义.     

Preliminary observations with a technique for measuring current spread in the rat brain

Intracranial spread of current from monopolar and bipolar electrode configurations was evaluated by using a motor effect of VII nerve stimulation. A tripolar electrode was lowered through the medulla toward the nerve in 1 mm steps; the currents necessary to produce threshold levels of sustained vibrissae vibration with monopolar and bipolar combinations of tips were determined at each step. Bipolar stimulation had a steep gradient and its effects were largely confined to a region within 2 mm of the minimum threshold point. Monopolar stimulation had a broader gradient and spread further. This technique appears promising for quantitative evaluation of ICS characteristics.     

Development of a Tri-polar Concentric Ring Electrode for Acquiring Accurate Laplacian Body Surface Potentials

Potentials recorded on the body surface from the heart are of a spatial and temporal function. The 12-lead electrocardiogram (ECG) provides a useful means of global temporal assessment; however, it yields limited spatial information due to the smoothing effect caused by the volume conductor. In an attempt to circumvent the smoothing problem, researchers have used the five-point method (FPM) to numerically estimate the analytical solution of the Laplacian with an array of monopolar electrodes. Researchers have also developed a bipolar concentric ring electrode system to estimate the analytical Laplacian, and others have used a quasi-bipolar electrode configuration. In a search to find an electrode configuration with a close approximation to the analytical Laplacian, development of a tri-polar concentric ring electrode based on the nine-point method (NPM) was conducted. A comparison of the NPM, FPM, and discrete form of the quasi-bipolar configuration was performed over a 400 × 400 mesh with 1/400 spacing by computer modeling. Different properties of bipolar, quasi-bipolar and tri-polar concentric ring electrodes were evaluated and compared, and verified with tank experiments. One-way analysis of variance (ANOVA) with post hoc t-test and Bonferroni corrections were performed to compare the performance of the various methods and electrode configurations. It was found that the tri-polar electrode has significantly improved accuracy and local sensitivity. This paper also discusses the development of an active sensor using the tri-polar electrode configuration. A 1-cm active Laplacian tri-polar sensor based on the NPM was tested and deemed feasible for acquiring Laplacian cardiac surface potentials.     

Properties of implanted electrodes for functional electrical stimulation

Implanted wire electrodes are increasingly being used for the functional electrical stimulation of muscles in partially paralysed patients, yet many of their basic characteristics are poorly understood. In this study we investigated the selectivity, recruitment characteristics and range of control of several types of electrode in triceps surae and plantaris muscles of anaesthetized cats. We found that nerve cuffs are more efficient and selective (i.e., cause less stimulus spread to surrounding muscles) than intramuscular electrodes. Bipolar intramuscular stimulation was more efficient and selective than monopolar stimulation, but only if the nerve entry point was between the electrodes. Monopolar electrodes are efficient and selective if located close to the nerve entry point, but their performance declines with distance from it. Nonetheless, for a variety of reasons monopolar stimulation provides the best compromise in many current applications. Short duration pulses offer the best efficiency (least charge per pulse to elicit force) but high peak currents, increasing the risk of electrode corrosion and tissue damage. Electrode size has little effect on recruitment and should therefore be maximised because this minimises current density.     

Recruitment properties of monopolar and bipolar epimysial electrodes

Muscle force was studied as a function of stimulus parameters, epimysial electrode position relative to nerve supply, and muscle length to provide insight into the properties of motor prostheses that employ epimysial electrodes. The results of the acute experiments indicated that the dependence of recruitment (force versus stimulus amplitude) on muscle length was minimal for a monopolar electrode positioned close to nerve entrance or 5 mm proximal to the motor point. The selectivity of stimulation (minimal activation of adjacent muscles) was best, and the recruitment rate the highest, for an electrode placed close to the nerve entrance. A bipolar pair of electrodes placed on the superficial surface of the muscle opposite to the nerve entrance gave better selectivity than the monopolar electrode at the low end of the recruitment range, and poorer selectivity at the high end. This electrode configuration required greater stimulus currents and exhibited a lower recruitment gain than was obtained for a monopolar electrode in the same position. Examination of tissue surrounding the electrode 30 days after implantation showed that the fibrous tissue encapsulating the electrode had been incorporated into the fascial layer. Slightly larger dependence on muscle length and lower selectivity of stimulation were measured after encapsulation than were measured in the acute experiments. Supported by the NIH-NINCDS Neural Prostheses Program, contract number N01-NS-0-2330 and the Swiss National Science Foundation, grant number 82.722.0.79.     

Selective stimulation of intrapulpal nerve of rat lower incisor using a bipolar electrode method

The purpose of this study is to determine how reliable the stimulus condition is for selective stimulation of rat lower incisor tooth pulp using a bipolar electrode. In the rat lower incisor, two components were distinguished in the compound action potential, recorded from the inferior alveolar nerve, whose conduction velocities were both in the Aδ-range when only the intrapulpal nerve was stimulated. On increasing the stimulus intensity, the fast component of the compound action potential, which disappeared after local anesthesia was applied to the periodontal tissue, began to reappear, indicating that current spread occurred outside the pulp. The most adequate stimulus conditions for selective intrapulpal nerve stimulation were: (1) interpolar distance of the bipolar electrode: 2 mm, (2) depth of the insertion of the electrode: 20 mm from the tip of the incisor, (3) stimulus pulse duration: 0.1 msec. Under these conditions, rectangular constant current pulses with the intensity of about 50 to 550 μA excited only the intrapulpal nerve. These results suggest that the rat lower incisor may be usefully employed for physiological or behavioral studies of nociceptive mechanisms.