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Biomedical subjects

I Nair

Publications and source records attributed to I Nair.

13 recordsLinked to original sources
PubMed1995

Distinguishability of the video display terminal (VDT) as a source of magnetic field exposure.

Magnetic field strength or its surrogate has been used as the measurement of exposure in all studies involving field exposure. Video display terminals (VDTs) are considered a minor source on this scale because its field strengths lie in the low range of magnetic fields. Several experiments show, however, that field strength may not be the only relevant variable in determining exposure. This paper explores the use of a method based on "effects functions" to determine the extent to which the VDT can be distinguished from other sources. It is shown that VDT exposure may be of consequence if exposure depends on certain types of time variation of the field. Because of the incompleteness of science in this area, this is a demonstration of a method rather than an actual demonstration of VDT as a significant source of exposure.

Computer Simulation↗
PubMed1995

A method for assessing alternative effects functions that uses simulation with EMDEX data.

A method for evaluating a variety of alternative biologically plausible effects functions through the use of simulation studies conducted on personal-monitor exposure data is described. Using magnetic field time series collected with EMDEX instruments, we demonstrate how the method can be used to explore 1) how the outputs from various effects functions simulations compare to the results obtained by assuming that effects are proportional to time average field strength; 2) how the results of epidemiological studies might be used to assess the relative likelihood that each of the alternative effects functions describes biological reality; and 3) how the results might be used to assess possible health risks. Although the available data are sufficient to demonstrate the general method, they are not yet sufficient to support actual discrimination among possible alternatives. The arguments on the use of the method are for illustrative purposes only.

Computer Simulation↗
PubMed1995

A method for evaluating transmission line magnetic field mitigation strategies that incorporates biological uncertainty.

A method to determine how much reduction in public exposure to power frequency magnetic fields can be obtained for different levels of investment is presented. Which if any "effects function" best describes the relationship between field exposure and biological effect is uncertain at this time. Also, in a particular context such as construction of new transmission lines there are a variety of different technologies which might be used to reduce exposure. We describe and demonstrate a method by which exposure reduction supply curves (i.e., the cost of purchasing different amounts of exposure reduction given various mitigation options) can be estimated parametrically for different exposure conditions and effects functions, and we display illustrative results.

Cost-Benefit Analysis↗
PubMed1992

Alternative functional relationships between ELF field exposure and possible health effects: report on an expert workshop.

If 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 signalling, 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.

Animals↗
PubMed1990

Lay understanding of low-frequency electric and magnetic fields.

People do not start with a blank slate when they hear risk-communication messages. All such messages are processed through existing knowledge structures and understanding. Hence, to design effective and reliable risk-communication materials one must understand the state of people's knowledge--correct and incorrect--about an issue. We developed a simple "mental model" of what people minimally need to know to make informed decisions about field-related issues. Then we performed studies to explore how and to what extent respondents of various groups understood physical properties of 60-Hz electric and magnetic fields. Actual knowledge of respondents was then compared with the predicates of the model. Electrical engineering juniors and semi-technical employees of utilities displayed a good command of most of the concepts in the simple model, but little awareness of the limits to their knowledge. Lay respondents correctly knew only a few of the simplest elements of the model, but they displayed a much greater awareness of the limits to their knowledge. Both lay and semi-technical respondents were found to share several misconceptions. On average, they correctly rank-ordered some common field-exposure conditions by field strength, but they could not differentiate between electric and magnetic fields and could not differentiate among field strengths associated with different appliances. Most respondents dramatically underestimated the range of actual field strengths. Many respondents understood that field strength decreases with distance from a source, but they underestimated the rate of decrease. In contrast to X-rays and microwaves, which respondents appeared to think about in rather similar terms, 60-Hz fields were not thought of as being highly similar to any other agent, although the closest parallels were found with ultrasound. Changes in mood, thought, and behavior, and the existence of an "electrical aura," were all seen as plausible results of exposure to a 60-Hz field. Although lay respondents displayed a variety of incomplete and confusing ideas, most of these ideas probably do not pose significant obstacles to the learning of a correct, simple, mental model.

Communication Barriers↗
PubMed1990

Viability of Mycobacterium leprae inside macrophages from different strains of mice and possible genetic control.

Peritoneal macrophages from Swiss white mice in vitro tolerated Mycobacterium leprae and allowed metabolism of the bacteria leading to release of bacteria-specific antigenic protein. This was associated with the maintenance of viability of the bacilli inside the cells. Macrophages from C57BL mice reduced viability of M. leprae after phagocytosis, and this was associated with the production of superoxide. Blockage of superoxide production resulted in maintaining viability of the cells of these mouse strains. Associated with loss of viability of the bacilli is the absence of the production of antigenic protein in the lysate. Interestingly, the maintenance of viability or loss of viability and the factors controlling such viability in the macrophages of Swiss white and C57BL mice, respectively, appeared to be genetically controlled.

Animals↗
PubMed1990

Antigenic protein from Mycobacterium leprae released in macrophages in vitro as indicator of viability of bacteria.

Peritoneal macrophages from randombred, Swiss white mice, when cultured and infected with Mycobacterium leprae for 24 hours, are able to show the presence of antigen(s) with binding affinity to antibodies present in the sera of bacteriologically positive, lepromatous leprosy patients. Such antibodies are not seen in sera from normal and healthy persons, tuberculoid leprosy patients, or long-term-treated, bacteriologically negative, lepromatous leprosy patients. The production of the antigen(s) is blocked by the anti-M leprae drug rifampin. Other mycobacteria when incubated with macrophages from mice show very little antigens in the lysate but the antigens have an equal affinity for antibodies in sera from both normal individuals and lepromatous patients. Only the lysates from macrophages exposed to live M. leprae could discriminate and could exhibit differential binding to sera from leprosy patients compared to sera from normal individuals. This antigen(s) does not have any binding ability to the monoclonal antibodies available to the antigens of M. leprae identified at present and shown to be specific to M. leprae. This indicates a separate identity of this product which has potential for further exploitation in exploring host-pathogen interactions related specifically to the leprosy infection and the tolerance of M. leprae inside cells.

Animals↗
PubMed1985

Powerline frequency electric and magnetic fields: a pilot study of risk perception.

The perception of the potential risk arising from human exposure to 50/60 Hz electric and magnetic fields was studied with a quasi-random sample of 116 well-educated, opinion leaders using the risk perception framework previously developed by Slovic, Fischhoff, and Lichtenstein. These individuals rated exposure to fields from transmission lines and electric blankets on a variety of scales that have been found useful in characterizing people's risk attitudes and perceptions. These judgments allowed us to conjecture about the likely desire for regulation of these potential hazards and the likely response to a publicized problem (e.g., an accident or ominous research finding) involving these two sources of exposure. Various forms of detailed information about 50/60 Hz fields were supplied to respondents. The provision of information produced modest, but statistically significant, changes in perceptions in the direction of greater concern about the risks. In response to questions of public policy, participants desired modest regulatory control of field exposure from transmission lines and little or no control of field exposure from appliances like electric blankets.

Electric Injuries↗