Greenebaum B, Sisken Betty F
Department of Physics, University of Wisconsin-Parkside, Kenosha, Wisconsin 53141, USA.
Bioelectromagnetics. 2007 Sep;28(6):488-92. doi: 10.1002/bem.20331.
We suggest an experimental comparison of two directions for applying the time-varying magnetic fields which have been found to speed spontaneous regeneration of injured peripheral nerves and in attempts to repair spinal cord injuries. Time-varying magnetic fields induce currents in a plane perpendicular to the magnetic field direction. The lower conductivity of the spinal cord's sheath (dura matter) or of the myelin sheath of peripheral nerves would seem to confine the induced electric fields and currents to the spinal cord or nerve itself. The proposed comparison could allow choosing between two possible modes of action of the fields: (1) Magnetically-induced electric fields or currents may be encouraging ion flow or otherwise helping enzyme, channel or other interactions at the cell membrane, as is thought to be the case in field stimulation of healing in bone. This mechanism should be independent of field direction. (2) Work in developing organisms and with fields applied to nerve cells in vitro has shown that neurite growth is guided parallel to both endogenous and external electric fields. This mechanism would be effective when induced electric fields are parallel, but not when they are perpendicular to the nerve. Any experimental test should seek to produce as close as possible to the same induced current intensity with both field directions. Possible confounding factors, as well as breakdowns in the assumptions of the simple model presented here, would have to be considered. This proposal was motivated by a recent report in which the authors listed a changed field direction as one of several possible reasons for an unsuccessful experiment.
我们建议对两种施加时变磁场的方向进行实验比较，这两种方向已被发现能加速受损外周神经的自发再生，并用于尝试修复脊髓损伤。时变磁场会在垂直于磁场方向的平面内感应出电流。脊髓鞘（硬脑膜）或外周神经髓鞘的较低电导率似乎会将感应电场和电流限制在脊髓或神经本身。所提议的比较可以在磁场的两种可能作用模式之间进行选择：（1）磁诱导电场或电流可能会促进离子流动，或以其他方式帮助细胞膜上的酶、通道或其他相互作用，就像在磁场刺激骨骼愈合中所认为的那样。这种机制应与磁场方向无关。（2）对发育中的生物体以及体外施加于神经细胞的磁场的研究表明，神经突的生长与内源性和外部电场平行。当感应电场平行时，这种机制将有效，但当它们垂直于神经时则无效。任何实验测试都应设法使两个磁场方向产生尽可能接近相同的感应电流强度。必须考虑可能的混杂因素以及这里提出的简单模型假设中的漏洞。这项提议是受最近一份报告的启发，在该报告中，作者将磁场方向改变列为实验失败的几个可能原因之一。
