ID Number		2718
Study Type		Human / Provocation
Model		Cardiac, neurophysiological and melatonin studies in humans exposed to magnetic fields.
Details		AUTHORS' ABSTRACT: Graham et al. 2000 (IEEE #6811): Clinical and epidemiological studies attest that alterations in heart rate variability (HRV) are predictive of specific types of cardiovascular morbidity and mortality in otherwise healthy persons. Recent reports also suggest that changes in HRV may be associated with exposure to intermittent magnetic fields (60 Hz, 28.3 microT) in the laboratory and that mortality is increased in cardiac disease categories related to altered HRV for utility workers whose jobs involve longer exposure to elevated magnetic fields. This study combined three approaches to learn more about the specific exposure circumstances under which changes in HRV occur. First, cardiac autonomic control, as indexed by HRV spectral analysis measures, was measured in 24 men during exposure to a much higher intensity field than any previously examined (resultant flux density = 127.3 microT [1273 milliGauss, mG]). Second, HRV measures from the same individual were compared across three relevant test conditions: intermittent and continuous field exposure and during a no-exposure, control condition. Third, electrocardiographic data were analyzed to determine if the precise timing of when the magnetic field switched on or off in relation to the cardiac cycle results in phase-resetting of the human cardiac rhythm. HRV measures were not altered by either field exposure condition compared to the control condition, and no evidence for a phase-resetting mechanism was found. Further research is needed to resolve the differences between the present and the earlier laboratory-based studies of HRV and to determine if cardiac rhythm disturbances are associated with exposure to the more complex magnetic fields found in the man-made environment. AUTHORS' ABSTRACT: Graham et al. 2000 (IEEE #6812): In previous research, intermittent exposure to sinusoidal 60 Hz magnetic fields at a resultant flux density of 28.3 microT was found to alter heart rate variability (HRV) in men during night sleep. When the 24 men in the present study were exposed under similar conditions, HRV was not altered. The previous studies included the hourly collection of blood samples via an indwelling venous catheter, while the present study did not. This may account for the observed differences in results. Further research is needed to determine if field exposure interacts with physiological arousal mechanisms to alter autonomic nervous system control over cardiac rhythms. AUTHORS' ABSTRACT: Graham et al. 2000 (IEEE #6846): Heart rate vaiability (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 magetic fields overnigt,. however, are inconsistent. HRV is altered in some studies but not other. To carify this, the pooled data from seven studies involving 172 men were analyzed to test specific hypotheses concerning this inconsistency. After analysis, we exduded 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 mantain double-blind controls; c) differences in field intensity (283 vs. 127.3 pT) or exposure pattern (intermittent versus continuous) as main efhcts; or 4) the indusion 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 work EEG, EMF, heart rate variability, human, sleep, stress. AUTHORS' ABSTRACT: Sastre et al. 1998 (IEEE #6847): Heart rate variability (HRV) results from the action of neuronal and cardiovascular reflexes, including those involved in the control of temperature, blood pressure and respiration. Quantitative spectral analyses of alterations in HRV using the digital Fourier transform technique provide useful in vivo indicators of beat-to-beat variations in sympathetic and parasympathetic nerve activity. Recently, decreases in HRV have been shown to have clinical value in the prediction of cardiovascular morbidity and mortality. While previous studies have shown that exposure to power-frequency electric and magnetic fields alters mean heart rate, the studies reported here are the first to examine effects of exposure on HRV. This report describes three double-blind studies involving a total of 77 human volunteers. In the first two studies, nocturnal exposure to an intermittent, circularly polarized magnetic field at 200 mG significantly reduced HRV in the spectral band associated with temperature and blood pressure control mechanisms (P  0.035 and P  0.02), and increased variability in the spectral band associated with respiration (P  0.06 and P  0.008). In the third study the field was presented continuously rather than intermittently, and no significant effects on HRV were found. The changes seen as a function of intermittent magnetic field exposure are similar, but not identical, to those reported as predictive of cardiovascular morbidity and mortality. Furthermore, the changes resemble those reported during stage II sleep. Further research will be required to determine whether exposure to magnetic fields alters stage II sleep and to define further the anatomical structures where fieldrelated interactions between magnetic fields and human physiology should be sought.
Findings		Effects
Status		Completed With Publication
Principal Investigator		Midwest Research Institute, Kansas City, MO, USA
Funding Agency		DOE, USA
Country		UNITED STATES
References		Graham, C et al. Bioelectromagnetics., (2000) 21:413-421 Graham, C et al. Bioelectromagnetics., (2000) 21:480-482 Graham, C et al. J Pineal Res., (1998) 24:230-238 Graham, C et al. Environmental Health Perspectives, (2000) 108:737-742 Sastre, A et al. Bioelectromagnetics., (1998) 19:98-106 Graham, C et al. International journal of psychophysiology. , (1999) 33:169-175 Graham, C et al. Environmental health perspectives., (2001) 109:501-507 Graham, C et al. Journal of pineal research., (2000) 28:1-8 Graham, C et al. Journal of pineal research., (2001) 31:109-113
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