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C E Easterly

Publications and source records attributed to C E Easterly.

14 recordsLinked to original sources
PubMed2000

Creating a human phantom for the virtual human program.

A high-resolution human phantom--a computer representation of the human anatomy--is needed as part of the Virtual Human (VH) simulation environment being developed by Oak Ridge National Laboratory and collaborators. Within the VH environment, this 3D anatomical phantom is coupled with physiological models and data to investigate a wide range of human biological and physical responses to stimuli. This paper describes how the phantom was created using the Visible Human (male) image data from the U.S. National Library of Medicine. Initially, X-ray computed tomography (CT) as well as photographic images of the Visible Human (male) torso were segmented and classified with software developed using IDL. From these data, non-uniform, rational B-spline (NURBS) spatial models were fitted to represent the surfaces of discrete body structures such as bones and organs. This collection of NURBS models, referred to as the NURBS VH, defines the fundamental Virtual Human phantom. The NURBS VH is compatible with modeling and animation software, enabling dynamic manipulation of body structures and their associated visual representations. The organization of the structural data lends itself to existing and evolving Web and electronic communication standards, making it attractive for applications such as medical training. In addition, finite-element (FE) meshes were created from the NURBS VH for use in trauma simulation, electromagnetic field exposure modeling, dosimetry, and other applications requiring spatially-defined tissue properties. The ability to scale the NURBS VH to account for age and size and the ability to easily animate NURBS objects yield a very flexible human phantom for the VH simulation environment.

Anatomy, Cross-Sectional↗
PubMed1996

A RASH analysis of National Toxicology Program data: predictions for 30 compounds to be tested in rodent carcinogenesis experiments.

Relative potencies for 30 compounds scheduled for carcinogenic testing in the 2-year rodent bioassays were estimated based on comparisons with a wide variety of bioassay data for benzo[a]pyrene, nicotine, cisplatin, aflatoxin B1, and cyclophosphamide. Potential for oncogenic transformation of each of the compounds was estimated from short-term bioassays. Promoting strength was assigned on the basis of comparisons of the product of relative potency and test dose with the distribution of similar products obtained for 67 common compounds in the data-base of Gold et al. A potency class for promotion was assigned on the basis of whether the potency-adjusted test dosage was > 2 sigma below the mean, > 1 sigma below the mean, within +/- sigma of the mean, > sigma above the mean, or > 2 sigma above the mean, as determined from the 67 compounds. The underlying hypothesis is that a weak test dose may have a low probability of revealing a potential carcinogen, whereas a strong dose may have a high probability of producing false-positive results. Predictions are therefore directed at the central 68% of the log-normal frequency distribution according to the assumption that +/- sigma represents the ideal test dose.

Animals↗
PubMed1991

Ranking of carcinogenic potency using a relative potency approach.

Protocols for long-term carcinogen bioassays have become highly refined. The ability to interpret these bioassay results beyond the experimental setting, however, has not improved commensurately. As a consequence, society is still faced with the fact that data derived in these bioassays reflect highly specific experimental conditions which are vastly different from environmental exposures of the freely roaming, outbred human. The scientific community has responded with a "collective wisdom" approach by using expert committees to interpret bioassay evidence. This committee approach is believed to be successful in protecting human health, but the list of suspected carcinogens is growing faster than the expert committees can respond. We have developed a relative potency framework for ranking the hazards represented by potential human carcinogens. The results demonstrate a rank ordering of a variety of compounds which is independent of the reference compound used to standardize the information. The philosophic basis of the approach may facilitate expert risk assessment systems development because it: (1) complements and supports "expert committee" data selection; (2) has a simple set of rules and does not require mathematical modeling; (3) requires no special situation judgments; and (4) is suitable for use with electronic data bases.

Animals↗
PubMed1991

On the rodent bioassays currently being conducted on 44 chemicals: a RASH analysis to predict test results from the National Toxicology Program.

We use a method of relative potency comparisons to rank the potential strength of 44 compounds being tested in rodent carcinogenicity bioassays. All of our previous hazard evaluations have been for human conditions where great numbers of simultaneous and serial exposures may act in combination to produce a neoplasm comprised of 2(20) to 2(30) cells commonly expected to derive from a single precancerous cell. For human exposures, we have always assumed an initiated target tissue containing at least one transformed but subcarcinogenic cell per organ. Thus, for man we have focused on empirical correspondences that may help to index the monoclonal growth of a particular cell lineage during cancer expansion. In contrast to humans, initiation of target tissues in animals subjected to National Toxicity Program (NTP) bioassays may not be a given condition, because of extensive precautions taken to minimize exposures to contaminates in food, water and cage environments. For this evaluation, we used categorical assignments of 'unlikely', 'possible' and 'probable' carcinogens adapted from NTP tests. Our rank ordering, of compounds according to maximum doses tested in male mice and male rats, is coded accordingly to the three outcomes taken from the NTP tests, but the magnitude of potency depend completely upon our particular method of comparing toxicological data. We have attempted to demonstrate that a relative potency based analysis of a diversity of toxicological data may be useful for rank ordering potentially hazardous compounds to be tested by the NTP and for range-finding of their effective test doses to be administered during chronic test protocols.

Animals↗
PubMed1990

Formaldehyde in drinking water: comparative hazard evaluation and an approach to regulation.

Formaldehyde, a widely used industrial chemical to which humans are ubiquitously exposed, presented cause for concern when it was demonstrated to be carcinogenic in laboratory animals. Risk assessment protocols subsequently applied to formaldehyde are of questionable validity in light of the results of recent mechanistic investigations of biological responses to formaldehyde. Further, the hazard of ingested formaldehyde is not addressed in current assessment protocols. This paper addresses the potential human health risks accompanying low-level exposure to formaldehyde as a contaminant in drinking water. In this exposure scenario, noncarcinogenic risk from inhalation of formaldehyde from drinking water is evaluated through knowledge of the metabolism and biological effects of formaldehyde exposure. Noncarcinogenic risk from ingestion of formaldehyde in drinking water is evaluated from the perspective gained by comparison with dietary sources of formaldehyde. Carcinogenic risk to humans is evaluated in light of recent investigations into the mechanisms underlying biological responses to formaldehyde exposure. Finally, based on a comparison of ingestion of formaldehyde in drinking water with ingestion of naturally occurring formaldehyde in foods, a comparative hazard approach to formaldehyde regulation is offered as a supplement to the rigid evaluation protocols currently used.

Animals↗
PubMed1989

Statistical approach to combining the results of similar experiments, with application to the hematologic effects of extremely-low-frequency electric field exposures.

A large proportion of scientific effort in investigating the possible biological effects of exposure to extremely-low-frequency (ELF) fields consists of laboratory studies on experimental animals. Most experiments in which hematologic properties are measured show no statistically significant effect due to exposure. However, some studies show significant effects which, in general, are not clearly reproducible. A difficult question must then be addressed: Are these relatively few indications of ELF effects statistical artifacts due to the increased risk of a type I error in multiple studies, or is there a real biological effect that is undetected in most studies due to the relatively small sample sizes commonly used? A statistical approach for examining the accumulated results of multiple experiments which results in a single test for treatment effect is presented. The technique requires very mild assumptions, and is valid for experiments that vary widely in specific characteristics such as exposure level, duration, and laboratory. The method is applied to the results of a collection of hematologic and serum chemistry experiments, and the combined results indicate the existence of experimental effects on some end points.

Animals↗
PubMed1989

EMP simulators and public safety: an analysis.

Effects produced by electromagnetic fields from exoatmospheric nuclear detonations, known as electromagnetic pulses (EMPs) and devices, which simulate these EMPs are analyzed for their potential danger to human beings in contact with large energy collectors. Comparison is made with ANSI guidelines established for radio-frequency electromagnetic fields.

Accident Prevention↗
PubMed1989

Effects of noise and electromagnetic fields on reproductive outcomes.

Much public health research has been directed to studies of cancer risks due to chemical agents. Recently, increasing attention has been given to adverse reproductive outcomes as another, shorter-term biologic indicator of public health impact. Further, several low-level ubiquitous physical agents have been implicated recently as possibly affecting human health. These physical factors (noise and electromagnetic fields) represent difficult topics for research with epidemiologic study methods. This paper provides a brief review of the published data related to the risk of adverse reproductive outcomes and exposure to noise or electromagnetic fields. The discussion includes ideas for possible biologic mechanisms, considerations for exposure assessment, and suggestions for epidemiologic research.

Abortion, Spontaneous↗
PubMed1987

Electromagnetic fields and public health.

A review of the literature is provided for the topic of health-related research and power frequency electromagnetic fields. Minimal evidence for concern is present on the basis of animal and plant research. General observation would accord with the implication that there is no single and manifest health effect as the result of exposure to these fields. There are persistent indications, however, that these fields have biologic activity, and consequently, there may be a deleterious component to their action, possibly in the presence of other factors. Power frequency electromagnetic field exposures are essentially ubiquitous in modern society, and their implications in the larger perspective of public health are unclear at this time. Electromagnetic fields represent a methodological obstacle for epidemiologic studies and a quandary for risk assessment; there is need for more data.

Animals↗
PubMed1982

Cardiovascular risk from exposure to static magnetic fields.

The increasing potential for exposure to magnetic fields in science, industry and public sectors requires an assessment of the attendant potential biological consequences. At present, no model exists for such an assessment. Based on the physical principle of pressure loss when a conductive fluid moves through a magnetic field, a model of the cardiovascular system is used to estimate the potential increase in blood pressure in the presence of a magnetic field. This increased pressure, confined to the major arteries, along with epidemiological data, is used to provide the basis of a model which could be applied to make upper limit estimates of risk for blood pressure related health effects resulting from exposure to magnetic fields.

Environmental Exposure↗