NOCTURNAL EXPOSURE TO INTERMITTENT 60 HZ MAGNETIC-FIELDS ALTERS HUMANCARDIAC-RHYTHM

Heart rate variability (HRV) results from the action of neuronal and c ardiovascular reflexes, including those involved in the control of tem perature, blood pressure and respiration. Quantitative spectral analys es of alterations in HRV using the digital Fourier transform technique provide useful in vivo indicators of beat-to-beat variations in sympa thetic and parasympathetic nerve activity. Recently, decreases in HRV have been shown to have clinical value in the prediction of cardiovasc ular morbidity and mortality. While previous studies have shown that e xposure to power-frequency electric and magnetic fields alters mean he art rate, the studies reported here are the first to examine effects o f exposure on HRV. This report describes three double-blind studies in volving a total of 77 human volunteers. In the first two studies, noct urnal exposure to an intermittent, circularly polarized magnetic field at 200 mG significantly reduced HRV in the spectral band associated w ith temperature and blood pressure control mechanisms (P = 0.035 and P = 0.02), and increased variability in the spectral band associated wi th respiration (P = 0.06 and P = 0.008). In the third study the field was presented continuously rather than intermittently, and no signific ant effects on HRV were found. The changes seen as a function of inter mittent magnetic field exposure are similar, but not identical, to tho se reported as predictive of cardiovascular morbidity and mortality. F urthermore, the changes resemble those reported during stage II sleep. Further research will be required to determine whether exposure to ma gnetic fields alters stage II sleep and to define further the anatomic al structures where field-related interactions between magnetic fields and human physiology should be sought. (C) 1998 Wiley-Liss, Inc.