Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, TCC-810, Boston, MA 02215, United States.
Clin Neurophysiol. 2010 Jun;121(6):882-6. doi: 10.1016/j.clinph.2010.01.017. Epub 2010 Feb 11.
Applied electrical current flows preferentially along rather than across muscle fibers, a characteristic called anisotropy. In this study, we investigate the alteration in muscle anisotropy after denervation.
Eight adult male rats underwent sciatic nerve crush and the gastrocnemius was harvested from 1 to 2.5 weeks later. Muscle from 12 additional healthy rats was also obtained. Multifrequency electrical impedance measurements were made on the tissue and its conductivity and relative permittivity (i.e., its polarizability) calculated. Anisotropy of the tissue was determined by calculating conductivity and permittivity differences, subtracting transverse from longitudinal values. Muscle fiber and blood vessel quantification were also performed.
The mean conductivity difference for sciatic crush animals was higher (p<0.05) than for the healthy animals across the frequency spectrum, due to a greater increase in longitudinal conductivity than in transverse conductivity. For example, at 10 kHz, the conductivity difference was 0.15S/m for healthy animals and 0.29 S/m for post-crush animals. Relative permittivity difference values, however, were similar between groups. There was a strong correlation of conductivity anisotropy to muscle fiber size but not to blood vessel area.
Anisotropy of muscle conductivity increases markedly after subacute denervation injury.
This alteration in anisotropy has direct relevance to the clinical application of electrical impedance myography. We also speculate that it may impact other forms of diagnostic testing, including needle electromyography and magnetic resonance imaging.
电流优先沿肌纤维流动而不是穿过肌纤维，这种特性称为各向异性。本研究旨在探讨失神经后肌肉各向异性的变化。
8 只成年雄性大鼠接受坐骨神经挤压，2.5 周后采集比目鱼肌。还从 12 只健康大鼠中获得肌肉。对组织进行多频电阻抗测量，并计算其电导率和相对介电常数（即极化率）。通过计算电导率和介电常数的差异来确定组织的各向异性，从纵向值中减去横向值。还进行了肌纤维和血管定量。
由于纵向电导率的增加大于横向电导率的增加，挤压动物的平均电导率差在整个频谱上均高于健康动物（p<0.05）。例如，在 10 kHz 时，健康动物的电导率差为 0.15 S/m，挤压后动物的电导率差为 0.29 S/m。然而，各组之间的相对介电常数差值相似。电导率各向异性与肌纤维大小有很强的相关性，但与血管面积无关。
亚急性失神经损伤后肌肉电导率的各向异性显著增加。
这种各向异性的改变与电阻抗肌图的临床应用直接相关。我们还推测，它可能会影响其他形式的诊断测试，包括针电极肌电图和磁共振成像。
