Brain and Mind Centre, The University of Sydney, Sydney, Australia.
MRC Centre for Neuromuscular Diseases, National Hospital for Neurology and Neurosurgery, Queen Square, London, UK; Institute of Neurology, University College London, Queen Square, London, UK.
J Neurosci Methods. 2018 Mar 15;298:45-53. doi: 10.1016/j.jneumeth.2018.02.003. Epub 2018 Feb 11.
Excitability studies on normal and diseased human axons in vivo have been greatly enhanced by fast non-invasive threshold-tracking techniques, using surface stimulation and recording. Although sensory axons are often more affected in disease, most studies to date have focussed on motor axons, because of technical difficulties in resolving pathologically small nerve volleys in the presence of noise and stimulus artefact.
This paper describes techniques for tracking low-amplitude compound action potentials, using a battery-powered, isolated preamplifier of simple construction with high common mode rejection (>125 dB [balanced inputs]) and low noise (<0.4 μV referred to inputs [shorted]).
We demonstrate the preamplifier's capability by tracking targets as small as 2 μV for a full range of excitability measurements without the usual distortion due to residual stimulus artefact and without the need for clamping, additional filtering or ensemble averaging.
In practice, threshold-tracking studies have been unable to study sensory axons when the maximal compound sensory action potential was less than about 15 μV. The techniques and amplifier in the present study allow measurements to be made from nerve with maximal responses less than half that size, and we present three recordings in patients with pathologically small nerve action potentials ≤7 μV.
Based on measurements of stimulus artefact distortion, noise and the performance in experiments, we conclude that the techniques described here will facilitate the study of diseased axons for which the sensory potentials have high thresholds and may be only a few microvolts in amplitude.
通过快速非侵入性的阈值跟踪技术，使用表面刺激和记录，极大地增强了对正常和患病人类轴突的兴奋性研究。尽管感觉轴突在疾病中通常受到更大的影响，但迄今为止的大多数研究都集中在运动轴突上，因为在存在噪声和刺激伪影的情况下，解析病理性小神经冲动的技术难度较大。
本文介绍了使用电池供电、结构简单的隔离前置放大器跟踪低幅度复合动作电位的技术，该前置放大器具有高共模抑制比（>125dB[平衡输入]）和低噪声（<0.4μV 参考输入[短路]）。
我们通过跟踪小至 2μV 的目标来证明前置放大器的能力，无需通常由于残留刺激伪影引起的失真，也无需箝位、额外滤波或集合平均，即可进行全范围的兴奋性测量。
实际上，当最大复合感觉动作电位小于约 15μV 时，阈值跟踪研究就无法研究感觉轴突。本研究中的技术和放大器允许从最大反应小于该尺寸一半的神经进行测量，我们在三个患有病理性小神经动作电位≤7μV 的患者中进行了记录。
基于对刺激伪影失真、噪声和实验性能的测量，我们得出结论，这里描述的技术将有助于研究感觉阈值高且幅度可能只有几个微伏的患病轴突。
