Brain frequency magnetic fields alter cardiac autonomic control mechanisms

Objective: Heart rate variability (HRV) is a noninvasive indicator of sympa thetic and vagal cardiovascular control known to be tightly correlated with sleep stages. Recent studies indicate that HRV in humans is altered by noc turnal exposure to power-frequency (60 Hz) magnetic fields. Given the centr al origin of autonomic cardiac control, we determined if field exposure in the beta(1) EEG/MEG frequency range was a more effective stimulus for HRV a lteration than 60 Hz fields, and explored the mechanisms involved. Methods: Healthy young men were exposed (n = 9) overnight to an intermitten t magnetic field (16 Hz, 28.3 microTesla, muT), or sham exposed (n = 9), un der blind test conditions in a laboratory exposure facility. Results: Field exposure was associated (P < 0.05) with reduced power in the low band of the HRV frequency spectrum, and with decreases in mean heart r ate. Analysis of the timing of the R waves surrounding each on-off transiti on of the intermittent field revealed no evidence for a direct effect on th e cardiac pacemaker. Conclusions: Magnetic field exposure in the EEG/MEG beta(1) frequency range alters HRV via a CNS effect. Phase-resetting experiments rule out a direct effect on the cardiac pacemaker. Biophysical calculations of the intensity of the electric fields induced in brain versus heart under the present exp osure conditions are also consistent with and support a central rather than a peripheral site of action. (C) 2000 Elsevier Science Ireland Ltd. All ri ghts reserved.