Li Xiaoyan, Jahanmiri-Nezhad Faezeh, Rymer William Zev, Zhou Ping
IEEE Trans Inf Technol Biomed. 2012 Nov;16(6):1143-9. doi: 10.1109/TITB.2012.2193410. Epub 2012 Apr 4.
The objective of this study was to assess whether there is evidence of motor unit loss in muscles paralyzed by spinal cord injury (SCI), using a measurement called motor unit number index (MUNIX). The MUNIX technique was applied in SCI (n=12) and neurologically intact (n=12) subjects. The maximum M waves and voluntary surface electromyography (EMG) signals at different muscle contraction levels were recorded from the first dorsal interosseous (FDI) muscle in each subject. The MUNIX values were estimated using a mathematical model describing the relation between the surface EMG signal and the ideal motor unit number count derived from the M wave and surface EMG measurements. We recorded a significant decrease in both maximum M wave amplitude and in estimated MUNIX values in paralyzed FDI muscles, as compared with neurologically intact muscles. Across all subjects, the maximum M wave amplitude was 8.3 ± 4.4 mV for the paralyzed muscles and 14.4 ± 2.0 mV for the neurologically intact muscles (p<0.0001). These measurements, when combined with voluntary EMG recordings, resulted in a mean MUNIX value of 112 ± 71 for the paralyzed muscles, much lower than the mean MUNIX value of 228 ± 49 for the neurologically intact muscles (p<0.00001). A motor unit size index was also calculated, using the maximum M wave recording and the MUNIX values. We found that paralyzed muscles showed a mean motor unit size index value of 80.7 ± 17.7 ìV, significantly higher than the mean value of 64.9 ± 10.1 ìV obtained from neurologically intact muscles (p<0.001). The MUNIX method used in this study offers several practical benefits compared with the traditional motor unit number estimation technique because it is noninvasive, induces minimal discomfort due to electrical nerve stimulation, and can be performed quickly. The findings from this study help understand the complicated determinants of SCI induced muscle weakness and provide further evidence of motoneuron degeneration after a spinal injury.
本研究的目的是使用一种称为运动单位数量指数（MUNIX）的测量方法，评估脊髓损伤（SCI）导致麻痹的肌肉中是否存在运动单位丢失的证据。MUNIX技术应用于SCI患者（n = 12）和神经功能正常的受试者（n = 12）。记录了每个受试者第一背侧骨间肌（FDI）在不同肌肉收缩水平下的最大M波和自愿表面肌电图（EMG）信号。使用一个数学模型来估计MUNIX值，该模型描述了表面EMG信号与从M波和表面EMG测量中得出的理想运动单位数量计数之间的关系。与神经功能正常的肌肉相比，我们记录到麻痹的FDI肌肉的最大M波幅度和估计的MUNIX值均显著降低。在所有受试者中，麻痹肌肉的最大M波幅度为8.3±4.4 mV，神经功能正常的肌肉为14.4±2.0 mV（p<0.0001）。这些测量结果与自愿EMG记录相结合，得出麻痹肌肉的平均MUNIX值为112±71，远低于神经功能正常肌肉的平均MUNIX值228±49（p<0.00001）。还使用最大M波记录和MUNIX值计算了运动单位大小指数。我们发现，麻痹肌肉的平均运动单位大小指数值为80.7±17.7μV，显著高于神经功能正常肌肉的平均值64.9±10.1μV（p<0.001）。与传统的运动单位数量估计技术相比，本研究中使用的MUNIX方法具有几个实际优点，因为它是非侵入性的，由电神经刺激引起的不适最小，并且可以快速进行。本研究的结果有助于理解SCI导致肌肉无力的复杂决定因素，并为脊髓损伤后运动神经元变性提供进一步的证据。
