Department of PM & R, Zablocki VA Medical Center, Mail Stop 117-D, 100 West National Avenue, Milwaukee, Wisconsin 53295, USA.
Muscle Nerve. 2010 Mar;41(3):318-23. doi: 10.1002/mus.21513.
Sensory nerve action potential (SNAP) amplitudes are frequently examined for evidence of axonal loss. Because digital nerves have parallel fibers, and parallel voltages do not add, SNAP amplitude may not accurately reflect axonal loss. In contrast, electrical power can be measured for digital nerves, and is additive. In this study we explore the ability of SNAP electrical power (SELP) to discriminate the increased number of axons in fingers with two median digital nerves versus fingers with only one median digital nerve. Antidromic SNAP amplitudes and SELPs were obtained for 15 fingers. Seventeen external resistors, R(ext), were sequentially connected from electrode to ground for SELP determination. The resulting bell-shaped power vs. R(ext) plot was regressed to the power transfer equation, which has a peak that defines SELP. SELPs of two-digital-nerve (median) fingers were 360-670 femtowatts (mean 525 fW). For one-digital-nerve fingers, SELP was 90-230 fW (mean 190 fW). Evaluation of one- vs. two-median-digital-nerve statistics showed the SNAP amplitude difference-of-means to be insignificant, whereas the SELP difference-of-means was 3.3 SD (P < 0.01). Using a criterion of 2 SDs, SNAP amplitude did not discriminate any one-median-digital-nerve fingers, whereas SELP discriminated all with no false positives. Because parallel voltages do not add, SNAP amplitudes may not reflect axonal loss. In contrast, electrical power is additive. We describe the SELP technique and demonstrate its ability to discriminate different numbers of axons as reflected by one digital nerve vs. two digital nerves.
感觉神经动作电位（SNAP）幅度常被用于检测轴突丢失的证据。由于指神经具有并行纤维，而并行电压不会相加，因此 SNAP 幅度可能无法准确反映轴突丢失。相比之下，可以测量指神经的电功率，而且是可累加的。在这项研究中，我们探讨了 SNAP 电功率（SELP）区分具有两根正中神经的手指与仅有一根正中神经的手指之间增加的轴突数量的能力。为 15 根手指获得了顺向 SNAP 幅度和 SELP。为了确定 SELP，我们依次将 17 个外部电阻器（R(ext)）从电极连接到地。得到的功率与 R(ext)的钟形关系图被回归到功率传递方程，该方程具有定义 SELP 的峰值。具有两根神经（正中神经）的手指的 SELP 为 360-670 飞瓦（平均 525 飞瓦）。对于一根神经的手指，SELP 为 90-230 飞瓦（平均 190 飞瓦）。对一根与两根正中神经手指的统计数据进行评估，发现 SNAP 幅度均值差异无统计学意义，而 SELP 均值差异为 3.3 个标准差（P<0.01）。使用 2 个标准差的标准，SNAP 幅度不能区分任何一根正中神经的手指，而 SELP 则可以区分所有手指，没有假阳性。由于并行电压不会相加，因此 SNAP 幅度可能无法反映轴突丢失。相比之下，电功率是可累加的。我们描述了 SELP 技术，并证明了它能够区分一根神经与两根神经所反映的不同数量的轴突。
