Study type: Medical/biological study (experimental study)

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

By: Sait ML, Wood AW, Sadafi HA
Published in: Med Eng Phys 1999; 21 (5): 361-369
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Aim of study (acc. to author)

To study the effects of power frequency magnetic fields on heart rate and heart rate variability in groups of adult volunteers.

Background/further details

The study was carried out in two parts: a pilot study and a follow-up study. The aim of the pilot study was to provide an independent replication of the data of a previous study (Graham C, Cohen HD, Cook MR, Phelps JW, Gerkovich MM, Fotopoulos SS. A double-blind evaluation of 60 Hz field effects on human performance. In: Anderson LE et al, editor. Interaction of Biological Systems with Static and ELF Electric and Magnetic Fields. CONF-841041. Springfield (VA):NTIS, 1987:471-86). Graham et al. observed that exposure to occupational level of electromagnetic fields cause slowing of heart rate in laboratory experiments with human volunteers.
The follow-up study was designed to confirm the results of the pilot study and to investigate further possible interaction of short (a few minutes) magnetic field exposure on the spectral content of heart rate variability signal.
There were two data collection periods in which there was either an actual field applied followed bei a sham exposure, or these in the reverse order.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 50 Hz
Exposure duration: continuous for 100 or 150 s
Exposure 2: 50 Hz
Exposure duration: intermittent, 15 s on/15 s off for 100 or 150 s
Exposure 3: 50 Hz
Modulation type: pulsed
Exposure duration: continuous for 100 or 150 s
Exposure 4: 50 Hz
Modulation type: pulsed
Exposure duration: intermittent, 15 s on/15 s off for 100 or 150 s

Exposure 1

Main characteristics
Frequency 50 Hz
Type
Waveform
Polarization
  • circular
Exposure duration continuous for 100 or 150 s
Exposure setup
Exposure source
  • same setup as exposure 1
  • 2 sets of coils: open wooden rectangular frame 2x2x2m; 26, 11, 11, 26 turns (Merritt design)
Additional info One set of coils were directed in North-South direction and the others in East West.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 20 µT effective value measured - -
Additional parameter details

Gradient field was ± 9 mT/s.

Measurement and calculation details

Field levels were measured with EMDEX 2 meters. A FW Bell 4080 Triaxial meter was used for checking the field strengths on the spot. A small (0.1 m diameter) search coil connected to an oscilloscope for visual indication of the waveform.

Exposure 2

Main characteristics
Frequency 50 Hz
Type
Waveform
Polarization
  • circular
Exposure duration intermittent, 15 s on/15 s off for 100 or 150 s
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 20 µT effective value measured - -
Additional parameter details

Gradient field was ± 9 mT/s except for brief turn-on and turn off moments.

Exposure 3

Main characteristics
Frequency 50 Hz
Type
Waveform
  • rectangular
Polarization
  • circular
Exposure duration continuous for 100 or 150 s
Modulation
Modulation type pulsed
Rise time 1.6 ms
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 20 µT effective value measured - -
Additional parameter details

Gradient field was 23 mT/s.

Exposure 4

Main characteristics
Frequency 50 Hz
Type
Waveform
  • rectangular
Polarization
  • circular
Exposure duration intermittent, 15 s on/15 s off for 100 or 150 s
Modulation
Modulation type pulsed
Rise time 1.6 ms
Exposure setup
Exposure source
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 20 µT effective value measured - -
Additional parameter details

Gradient field was 23 mT/s except for brief turn-on and turn off moments.

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • before exposure
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

A small but significant slowing of heart rate was revealed 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 heart rate variability spectra in relation to continuous sinusoidal exposure revealed 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 findings indicate that short exposures to magnetic fields at occupational levels may influence heart rate control mechanisms.

Study character:

Study funded by

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