Bioelectric properties of frog sciatic nerves during exposure to stationary magnetic fields

Abstract

The bioelectric properties of frog sciatic nerves have been measured during exposure to homogeneous, stationary magnetic fields. The action potential amplitude, conduction velocity, absolute refractory period and relative refractory period were found to be unaffected by a continuous 4-h exposure to perpendicular or parallel 2.0 T (1 T equal 10(4) G) magnetic fields. These parameters also remained unchanged during a 1-h post-exposure period. The conduction velocity was similarly found to be unchanged when the field was applied continuously for 17 h. Exposure of sciatic nerves to a 1.0-T field led to no alteration in the threshold for neural excitation. The absence of magnetic field effects on nerve electrical activity observed in the present experiments contrasts with the positive findings reported previously by other investigators. These discrepancies may be attributable to an inadequate control of ambient temperature in the earlier studies.

MRI does not change fetal cardiotocographic parameters

“…These low potentials are electromotive force (EMF) potentials induced by blood flow in the magnetic field and they can lead to T-wave changes in ECGs (Budinger, 1981). Tenforde et al (1983) demonstrated reversible T-wave alterations without any other clinical changes in macaque monkeys in magnetic fields of up to 1·5 T. Clinically, the magnitude of EMF potentials depends on the volume of blood flow, which in man is normally not sufficient to induce an EMF potential in static fields of less than 2 T. Gaffey and Tenforde (1983) in a study on frog sciatic nerves showed no change in action potential amplitude, absolute refractory period, or in conduction velocity, when using exposures of 4 h at 2 T field. Such effects could, in theory, reduce fetal movement or basal heart-rate frequency.…”

Influence of static magnetic fields on pain perception and sympathetic nerve activity in humans

“…For example, several studies have reported that exposing nerves to 1.2-to 2.0-T static magnetic fields did not alter nerve conduction velocity, membrane potentials, transmembrane currents, action potential amplitudes, and refractory periods (9,28,29). Moreover, in humans exposure to either 1.0-T or 0.045-T static magnetic fields did not alter nerve conduction velocities (34,36).…”

The wonders of magnetism

“…During the decade from 1976 to 1986, my colleagues at LBNL, along with numerous collaborators, studied the possible effects of exposure to large static magnetic fields on the functions of many major organ and tissue systems. In addition to the studies on the cardiovascular system described above, it was found that exposure to fields with flux densities up to 2 T have no measurable effects on nerve bioelectric activity [Gaffey and Tenforde, 1983], animal behavior [Davis et al, 1984], vision [Tenforde, 1992], immune system competence [Tenforde and Shifrine, 1984], thermoregulatory capacity [Tenforde, 1986b], and physiological regulation and circadian rhythms [Tenforde, 1984;Tenforde et al, 1987]. As in the cardiovascular studies on animals exposed to strong magnetic fields, many of the experiments on animal physiology and behavior required the design and fabrication of customized, nonmagnetic transducers and other specialized equipment.…”