| Cardiac Autonomic Control Mechanisms in Power-Frequency Magnetic Fields: A Multistudy Analysis Charles Graham,1 Mary R. Cook,1 Antonio Sastre,1 Mary M. Gerkovich,1 and Robert Kavet2 1Midwest Research Institute, Kansas City, Missouri, USA
2EPRI, Palo Alto, California, USA Abstract
Heart rate variability (HRV) , a noninvasive indicator of autonomic control of cardiac activity, is predictive of long-term cardiac morbidity and mortality. Epidemiologic research suggests that occupational exposure to power-frequency magnetic fields may be associated with autonomically mediated cardiac mortality. Results from our laboratory studies of humans exposed to 60-Hz magnetic fields overnight, however, are inconsistent. HRV is altered in some studies but not others. To clarify this, the pooled data from seven studies involving 172 men were analyzed to test specific hypotheses concerning this inconsistency. After analysis, we excluded a) measurement drift or instability over time because HRV was stable under sham-exposed conditions across all studies ; b) inadequate statistical power or failure to maintain double-blind controls ; c) differences in field intensity (28.3 vs. 127.3 µT) or exposure pattern (intermittent versus continuous) as main effects ; or d) the inclusion of individuals sensitive to magnetic field exposure in some studies but not others. Four separate analytic techniques failed to identify a valid subpopulation of sensitive individuals. In some studies, however, hourly blood samples were collected using an indwelling venous catheter. HRV alterations occurred during intermittent exposure in these studies (p < 0.05) but not in similar studies without blood sampling. This result suggests a field interaction with modest arousal or disturbance. Because HRV is tightly coupled to electroencephalographic activity during sleep, these results are physiologically plausible and suggest that HRV alterations during exposure to magnetic fields may occur when accompanied by increases in physiologic arousal, stress, or sleep disturbance. Key words: EEG, EMF, heart rate variability, human, sleep, stress. Environ Health Perspect 108:737-742 (2000) . [Online 28 June 2000] http://ehpnet1.niehs.nih.gov/docs/2000/108p737-742graham/ abstract.html Address to correspondence to C. Graham, Midwest Research Institute, 425 Volker Boulevard, Kansas City, MO 64110 USA. Telephone: (816) 753-7600, ext 1161. Fax: (816) 753-7380. E-mail: cgraham@mriresearch.org We thank project staff members D.W. Riffle, S.J. Hoffman, J.L. Hackman, K.E. Kakolewski, and B.J. Peterson. Funding was provided by the EPRI (contract WO3349-13) , U.S. Department of Energy (subcontract 85X-SN602C) , and the National Institute of Environmental Health Sciences (grant ES 07053) . Received 22 December 1999 ; accepted 11 April 2000.
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