Effect of Magnetotherapy on Evoked High Frequency Short Duration Electromyogram a Preliminary Report

The effect of a pulsing electromagnetic field (PEMF) on the change of evoked electromyograms of the hypothenar muscles was investigated in patients exhibiting cardiopulmonary failure. The ulnar nerve was stimulated at the wrist by supramaximal square-wave current p ulses (0.2 msec) at 200 Hz delivered by a constant-current nerve stimulator. The patient was then exposed to a PEMF (5 mT, 10 Hz, for 20 min) and the electromyogram was repeated. The change of evoked compound muscle action potential (CMAP) was measured and expressed as a percent a mplitude reduction between the initial and subsequent CMAPs of the electromyogram. A control group of 30 patients showed a 20% change. Changes of 60% or more were observed in patients exhibiting cardiopulmonary failure. Improvement in the change (54.3 f 11.7% to 38.1 13.2%) was found in 7 patients after the a pplication of PEMF. In 4 cases no significant change (74.5 f 11.1% to 73.2 10.8%) occurred, and in 3 cases worsening (70.6 f 6.6% to 83.6 4.1%) of the change was seen f ollowing the magnetotherapy. In this preliminary s tudy, t he PEMF was found to affect the bioelectric function of motor-unit membranes. Further s tudy is needed since in 21% of our measurements worsening in the change of the evoked electromyogram was measured.