A study of heart rate and heart rate variability in human subjects exposed to occupational levels of 50 Hz circularly polarised magnetic fields.

The effects of power-frequency magnetic fields on heart rate and heart rate variability (HRV) were studied in groups of adult volunteers. Exposure consisted of 28 microT (280 mG) at 50 Hz (circularly polarized) for 100 or 150 seconds either following or prior to a similar period of sham-exposure. A small but significant slowing of heart rate of the order of 2% was observed in two separate studies in which the fields were generated by continuous sinusoidal currents. Magnetic fields generated by square-wave currents or by currents turned alternatively on and off at 15 second intervals during the exposure period produced inconsistent effects on heart rate. Analysis of the HRV spectra in relation to continuous sinusoidal exposure showed a consistent reduction in the ratio of power in the Low Band (0.02-0.15 Hz) to the High Band (0.16-1.0 Hz). This reduction in ratio was significant for experiments in which respiration was controlled at 0.2 Hz (12 breaths/minute) where the order was actual exposure followed by sham exposure (On-->Off). The spectral power in the Low Band was significantly reduced for both orders, but the High Band power was significantly raised only for the On-->Off order. Although there are some inconsistencies, these data indicate that short exposures to magnetic fields at occupational levels may influence heart rate control mechanisms.