Static magnetic field influence on human nerve function.

In an attempt to understand the possible neural mechanism mediating the effects of a static magnetic field (SMF), nerve conduction velocity (NCV) and excitability index (EI), measured as the ratio of the amplitude of the submaximally evoked compound muscle action potential during or after magnetic exposure to that before exposure from the same intensity of stimulation of the motor nerve, were studied on ten normal volunteers (aged 17 to 39), when the nerve was exposed to an SMF of 1 tesla (T) for 15 seconds. NCV and EI were measured before, during (5, 10, and 15 sec) and three minutes after magnetic exposure. Both NCV and EI were measured on median nerve in all ten subjects, the peroneal nerve in seven subjects, while the ulnar nerve was measured for only EI in eight subjects. There was no significant change in NCV over the segment exposed to the magnetic field. However, EI was significantly increased during the magnetic exposure in all three nerves. The effects were observed as early as five seconds after exposure and disappeared by three minutes after exposure. It is concluded that the excitability of the motor nerve is increased when it is exposed to an SMF with a density of 1T.