COMPARISON OF CARDIAC AND 60 HZ MAGNETICALLY INDUCED ELECTRIC-FIELDS MEASURED IN ANESTHETIZED RATS

Extremely low frequency magnetic fields interact with an animal by ind ucing internal electric fields, which are in addition to the normal en dogenous fields present in living animals. Male rats weighing about 56 0 g each were anesthetized with ketamine and xylazine. Small incisions were made in the ventral body wall at the chest and upper abdomen to position a miniature probe for measuring internal electric fields. The calibration constant for the probe size was 5.7 mm, with a flat respo nse from at least 12 Hz to 20 kHz. A cardiac signal, similar to the no rmal electrocardiogram with a heart rate of about 250 bpm, was readily obtained at the chest. Upon analysis of its spectrum, the cardiac fie ld detected by the probe had a broad maximum at 32-95 Hz. When the rat s were exposed to a 1 mT, 60 Hz magnetic field, a spike appeared in th e spectrum at 60 Hz. The peak-to-peak magnitudes of electric fields as sociated with normal heart function were comparable to fields induced by a 1 mT magnetic field at 60 Hz for those positions measured on the body surface (where induced fields were maximal). Within the body, or in different directions relative to the applied field, the induced fie lds were reduced (reaching zero at the center of the animal). The card iac field increased near the heart, becoming much larger than the indu ced field. Thus, the cardiac electric field, together with the other e ndogenous fields, combine with induced electric fields and help to pro vide reference levels for the induced-field dosimetry of ELF magnetic field exposures of living animals. (C) 1997 Wiley-Liss, Inc.