摘要:

AbstractIf exposure to 60 Hz fields poses risks to public health, the relationship between exposure and risk may involve something other than the product of field strength and time. Such alternative possible relations, or “effects functions,” are of great interest to epidemiologists, engineers, risk analysts, and regulators. A structured survey and workshop were used to explore whether leading researchers in bioelectromagnetics share similar views about alternative possible effects functions. Substantial agreement was found about several effects functions in a few specific contexts such as calcium‐ion efflux and cell signaling, and biosynthesis pathways. No significant agreement emerged in many other contexts. No effects function possibilities were ruled out. Further effort of this sort was judged unlikely to yield greater consensus until more complete scientific understanding becomes available. However, a series of structured workshops on research planning and priority setting were judged to hold great potential for useful results. 1992 Wiley‐Li

ISSN:0197-8462    

DOI:10.1002/bem.2250130502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThirty‐two male rats were tested in two replicates of an experiment to determine whether body currents induced by 60‐Hz magnetic fields might lead to avoidance behavior comparable to that which results from exposure to strong 60‐Hz electric fields. The test apparatus was a two‐compartment Plexiglas® shuttlebox enclosed in a sound‐attenuating plywood chamber, which in turn was encompassed by two copper bus bars that, when energized, served as a source of 60‐Hz magnetic fields. Location of the rat, and traverse activity in the shuttlebox were monitored by nine infra‐red photo detectors equally spaced along the length of the apparatus. Rats were divided into 2 groups: 1 group of rats (n = 8 per group per replicate) was sham exposed while rats in the other group (n = 8 per group per replicate) were exposed to a 3.03 mT (30.3 G), 60‐Hz magnetic field whenever they traversed to or were located on the side (L or R) predetermined as the exposed side. To control artifact incident to side preference, the side exposed (L or R) was alternated over the exposed rats. Each rat was tested individually in a 1‐h session. A 2‐factor ANOVA (exposed vs. control, replicate 1 vs. replicate 2) failed to reveal any significant effects due to either factor or to an interaction between factors. These data demonstrate that rats do not avoid exposure to 60‐Hz magnetic fields at a flux density of 3.03 mT and further imply that the avoidance by rats of high level 60‐Hz electric fields is mediated by something other than the internal body currents induced by the exposu

ISSN:0197-8462    

DOI:10.1002/bem.2250130503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe assessed the merits of various point‐in‐time (“spot”) measurement protocols in case‐control studies based on an ordinal exposure scale. After classifying a number of houses on the basis of prolonged monitoring of the ambient, extremely low frequency (ELF) magnetic field, we determined the probability of misclassification for each “spot” measurement protocol. We calculated the effect of this misclassification on the relative risk estimates and on the Mantel test for trend. We found that classification based on a small group of point‐in‐time measurements allows an adequate estimate of the relative risk, although the statistical significance of the dose‐response gradient may be seriously underestimated. However, the use of automated ambient‐field monitors, which results in loss of information on spatial variability, can lead to similar consequences. Therefore, manually collected point‐in‐time measurements remain a viable option for exposure assessm

ISSN:0197-8462    

DOI:10.1002/bem.2250130504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractPrevious studies in our laboratory have established that pulsed microwaves at 2.45 GHz and 10 mW/cm2are associated with production of corneal endothelial lesions and with disruption of the blood‐aqueous barrier in the non‐human primate eye. In the study reported here we examined ocular damage in monkeys (M. mulattaandM. fascicularis) following topical treatment with one of two ophthalmic drugs (timolol maleate and pilocarpine) that preceded exposure to pulsed microwaves. Anesthetized monkeys were sham exposed or exposed to pulsed, 2.45 GHz microwaves (10 μs, 100 pps) at average power densities of 0.2, 1, 5, 10, or 15 mW/cm24 h a day for 3 consecutive days (respective SARs were 0.052, 0.26, 1.3, 2.6, and 3.9 W/kg). Immediately before microwave exposure, one or both eyes were treated topically with one drop of 0.5% timolol maleate or of 2% pilocarpine. Following administration of a drug, we observed a significant reduction in the power‐density threshold (from 10 to 1 mW/cm2) for induction of corneal endothelial lesions and for increased vascular permeability of the iris. Diagnostic procedures (in vivo specular microscopy and fluorescein iris angiography) were performed following each exposure protocol. In addition, increased vascular permeability was confirmed with horseradish peroxidase tracer techniques. Although we did not measure intraocular temperatures in experimental animals, the results suggest that a mechanism other than significant heating of the eye is involved. Our data indicate that pulsed microwaves at an average SAR of 0.26 W/kg, if administered after pretreatment with ophthalmic drugs, can produce significant ocular effects in the anesthetized primate. 1992 Wiley‐L

ISSN:0197-8462    

DOI:10.1002/bem.2250130505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractUsing a crossover experimental design, we evaluated our earlier findings that exposure to a 30 kV/m, 60 Hz electric field for 12 hours per day, 7 days per week for 6 weeks produced significant changes in the performance rates of social behaviors among young adult male baboons. In the crossover experiment, the former control group was exposed to a 30 kV/m, 60 Hz electric field for 3 weeks. Only an extremely small, incidental magnetic field was generated by the exposure apparatus. We found that electric‐field exposure again produced increases in the performance rates that index Passive Affinity, Tension, and Stereotypy. These findings, combined with results from our other electric‐field experiments, indicate that exposure to strong electric fields, in the absence of associated magnetic fields, consistently produces effects that are expressed as increases in rates of performance of social behaviors in young adult male baboons. 1992 Wiley‐Liss

ISSN:0197-8462    

DOI:10.1002/bem.2250130506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractA common mistake in biomagnetic experimentation is the assumption that Helmholtz coils provide uniform magnetic fields; this is true only for a limited volume at their center. Substantial improvements on this design have been made during the past 140 years with systems of three, four, and five coils. Numerical comparisons of the field uniformity generated by these designs are made here, along with a table of construction details and recommendations for their use in experiments in which large volumes of uniform intensity magnetic exposures are needed. Double‐wrapping, or systems of bifilar windings, can also help control for the non‐magnetic effects of the electric coils used in many experiments. In this design, each coil is wrapped in parallel with two separate, adjacent strands of copper wire, rather than the single strand used normally. If currents are flowing in antiparallel directions, the magnetic fields generated by each strand will cancel and yield virtually no external magnetic field, whereas parallel currents will yield an external field. Both cases will produce similar non‐magnetic effects of ohmic heating, and simple measures can reduce the small vibration and electric field differences. Control experiments can then be designed such that the only major difference between treated and untreated groups is the presence or absence of the magnetic field. Double‐wrapped coils also facilitate the use of truly double‐blind protocol, as the same apparatus can be used either for experimental or control groups. 1992 Wiley

ISSN:0197-8462    

DOI:10.1002/bem.2250130507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractA small, lightweight meter has been developed for magnetic‐field measurements, particularly those needed for exposure‐assessment purposes. This meter, known as the AMEX‐3D, continuously measures all three axes of magnetic‐flux density and electronically combines the data into a single estimate of cumulative exposure to the root‐mean‐square (rms) resultant flux density. The AMEX‐3D weighs about 120 g, measures 2.7 cm x 5.1 cm x 10.2 cm, and is battery powered. Two panel‐mounted jacks are provided for measuring battery voltage and for reading cumulative exposure data from the unit. The instrument has, within 3 dB, a flat response to magnetic flux densities at all frequencies in its 30–1,000 Hz bandwidth. A detailed analysis of error sources in the AMEX‐3D leads to an estimate of ±20% as the accuracy of the instrument over its dynamic range, which extends from 0.02 to 15 μT. The AMEX‐3D was tested in the field by asking electricutility distribution linemen to wear AMEX‐3D and EMDEX meters simultaneously while working. Agreement between the two measures of exposure was excell

ISSN:0197-8462    

DOI:10.1002/bem.2250130508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper analyzes data from a study conducted by the United States Office of Naval Research on the effects of pulsed magnetic fields on chick embryos. The experiment involved incubation of eggs under carefully controlled conditions in six different laboratories. The original analysis included inappropriate statistical methodology for analyzing the experimental results. Since the conclusions from this study rest so heavily on the results of statistical analyses, choosing the proper methodology is imperative. The major aim of this paper then is to introduce more appropriate analytic tools and illustrate their use in the present context. Qualitatively our results agree with those of the original analysis; our findings about interactions between effects, however, makes interpretation of these effects more subtle. We apply linear logistic modeling to counts of damaged embryos, using as covariates factors corresponding to exposure, laboratory, incubator, run, and measurements of background radiation. This facilitates estimation of the size of the effects. The effects of laboratory, incubator, and run are explored both as fixed and random effects. We find statistically significant exposure and laboratory effects, in accordance with the original study. However, we also find that the inter‐laboratory variation in exposure effect is at least as large as the exposure effect itself. The presence of such effects fundamentally alters the interpretation of the fitted model, as is graphically presented. 1992 Wiley‐Liss,

ISSN:0197-8462    

DOI:10.1002/bem.2250130509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractA simple, cost‐effective, and accurate technique to measure the whole‐body‐averaged specific absorption rate (SAR) in Sprague‐Dawley rat carcasses by a single‐gradient‐layer calorimeter is described. The results of SAR determinations showed a highly linear relation between the average power density of the incident field (1.25 GHz) and the normalized heat loading of the carcasses. 1992 Wile

ISSN:0197-8462    

DOI:10.1002/bem.2250130510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:0197-8462    

DOI:10.1002/bem.2250130511

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY