Maccabee P J, Amassian V E, Cracco R Q, Cadwell J A
Department of Neurology, State University of New York Health Science Center, Brooklyn 11203.
Electroencephalogr Clin Neurophysiol. 1988 Dec;70(6):524-33. doi: 10.1016/0013-4694(88)90150-2.
We compared conventional electrical and magnetic coil (MC) stimulation of distal median nerve in 10 normal subjects and 1 patient. Orthogonal (90 degrees to volar forearm)-longitudinal (the plane of the MC aligned with the long axis of nerve or wire), tilted (to 45 degrees) longitudinal, and tangential edge orientations elicited maximal or near maximal compound motor axon potentials (CMAPs) without simultaneous co-activation of ulnar nerve. Transverse and symmetrical tangential orientations were inefficient. A simulation study of an ideal volume conductor confirmed these findings by predicting that the maximum current density was near the outer edge of the MC and not at the center where the magnetic flux intensity is maximal. An orthogonal-longitudinal MC induces a current in the adjacent volume conductor (for example elbow or wrist), which flows in the same circular direction as in the MC. This differs from a tangentially orientated MC which classically elicits current flow in the volume conductor opposite in circular direction to that in the MC. Amplitude and latency of the CMAP were both altered, but not identically, by changing the intensity of MC and cathodal stimuli. Rotating an orthogonal-longitudinal MC through 180 degrees, thus reversing the direction of current flow, elicited single fiber muscle action potentials whose peak latencies differed at most by 100 microseconds. Thus, the (virtual) cathode and anode are significantly closer (i.e., 5-6 mm) with MC than with electrical stimulation where they are at least 20 mm apart. A disadvantage of MC stimulation is the imprecision in defining exactly where the distally propagating nerve impulse originates. In different subjects, using maximum output and orthogonal or tilted (to 45 degrees) longitudinal orientations, the calculated site of excitation in the median nerve varied 2-15 mm distal to the midpoint of the contacting edge of the MC. This limits the usefulness of the MC in its current configuration for determining distal motor latencies. Future advances in MC design may overcome these difficulties.
我们比较了10名正常受试者和1名患者的正中神经远端的传统电刺激和磁线圈（MC）刺激。正交（与掌侧前臂成90度）-纵向（MC平面与神经或导线长轴对齐）、倾斜（至45度）纵向和切向边缘方向可引出最大或接近最大的复合运动轴突电位（CMAP），而不会同时激活尺神经。横向和对称切向方向效率较低。对理想容积导体的模拟研究证实了这些发现，预测最大电流密度靠近MC的外边缘，而不是磁通强度最大的中心。正交-纵向MC在相邻容积导体（如肘部或腕部）中感应出电流，该电流与MC中的电流沿相同的圆周方向流动。这与切向取向的MC不同，后者经典地在容积导体中引起与MC中电流方向相反的圆周电流。通过改变MC和阴极刺激的强度，CMAP的幅度和潜伏期都会改变，但并非完全相同。将正交-纵向MC旋转180度，从而反转电流方向，可引出单纤维肌肉动作电位，其峰值潜伏期最多相差100微秒。因此，与电刺激相比，MC的（虚拟）阴极和阳极距离明显更近（即5-6毫米），电刺激中它们至少相距20毫米。MC刺激的一个缺点是在精确确定远端传播的神经冲动起源位置方面不够精确。在不同受试者中，使用最大输出和正交或倾斜（至45度）纵向取向，正中神经中计算出的兴奋位点在MC接触边缘中点远端2-15毫米处变化。这限制了当前配置的MC在确定远端运动潜伏期方面的实用性。MC设计的未来进展可能会克服这些困难。
