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Biomedical subjects

T B Wenzl

Publications and source records attributed to T B Wenzl.

10 recordsLinked to original sources
PubMed2000

Use of accelerometers as an ergonomic assessment method for arm acceleration-a large-scale field trial.

Ergonomists need easy-to-use, quantitative job evaluation methods to assess risk factors for upper extremity work-related musculoskeletal disorders in field-based epidemiology studies. One device that may provide an objective measure of exposure to arm acceleration is a wrist-worn accelerometer or activity monitor. A field trial was conducted to evaluate the performance of a single-axis accelerometer using an industrial population (n=158) known to have diverse upper limb motion characteristics. The second phase of the field trial involved an examination of the relationship between more traditional observation-based ergonomic exposure measures and the monitor output among a group of assembly-line production employees (n=48) performing work tasks with highly stereotypic upper limb motion patterns. As expected, the linear acceleration data obtained from the activity monitor showed statistically significant differences between three occupational groups known observationally to have different upper limb motion requirements. Among the assembly-line production employees who performed different short-cycle assembly work tasks, statistically significant differences were also observed. Several observation-based ergonomic exposure measures were found to explain differences in the acceleration measure among the production employees who performed different jobs: hand and arm motion speed, use of the hand as a hammer, and, negatively, resisting forearm rotation from the torque of a power tool. The activity monitors were found to be easy to use and non-intrusive, and to be able to distinguish arm acceleration among groups with diverse upper limb motion characteristics as well as between different assembly job tasks where arm monitors were performed repeatedly at a fixed rate.

Acceleration↗
PubMed1997

Estimating magnetic field exposures of rail maintenance workers.

A measurement survey was undertaken to estimate exposures to 25 hertz (Hz) magnetic fields of maintenance workers on electrified rail lines near Philadelphia, Pa. Because of the mix of frequencies expected, a strategy was developed using new instrument to capture magnetic field waveforms, which were then analyzed by fast Fourier transform for their frequency components. This instrument could only take spot measurements, so a personal monitor repeatedly measured magnetic fields in the ranges of 40-100 Hz. To power trains in the mid-Atlantic region, electrical current flows from the overhead catenary to the locomotive and returns through the rails in a loop up to 10 miles long. This flowing current was the primary source of the magnetic field exposures when a train was near the maintenance work site being measured. A total of 93 spot measurements was taken at five locations. Peak magnetic flux densities ranged from 34 to 185 milligauss (mG) near a transformer, while medians at the five locations ranged from 6.5 to 40 mG. Time-weighted average personal exposures were estimated by combining spot measurements at occupied locations, with estimates of how much time was spent at each location. These averages were estimated to lie between 3.0 and 18 mG, depending on the location of how often trains passed the work site. Comparisons between the spot measurements in the 40-100 Hz frequency range and summarises from the personal dosimeter showed reasonably good agreement. Further characterization of personal exposures in this region may be justified, since on-train workers and passengers may be more highly exposed.

Bias↗
PubMed1996

Occupational exposure to 60-hertz magnetic fields and risk of breast cancer in women.

We used data from a large population-based case-control study to test the hypothesis that women whose "usual occupation" entailed exposure to higher than background 60-Hz magnetic fields had a higher risk of breast cancer than women without such exposure. Breast cancer cases were identified from four statewide tumor registries, and controls were randomly selected from lists of licensed drivers and Medicare beneficiaries. Information on usual occupation and breast cancer risk factors was obtained by telephone interview. We calculated adjusted odds ratios from logistic regression models for women holding occupations with potential for low, medium, or high magnetic field exposure, compared with background exposure. There was a modest increase in risk for women with potential for high exposure [odds ratio (OR) = 1.43; 95% confidence interval (CI) = 0.99-2.09], and no increase for women with potential for medium (OR = 1.09; 95% CI = 0.83-1.42) or low (OR = 1.02; 95% CI = 0.91-1.15) exposure The risk among premenopausal women in the highest-exposure category was higher (OR = 1.98; 95% CI = 1.04-3.78) than for postmenopausal women (OR = 1.33; 95% CI = 0.82-2.17).

Breast Neoplasms↗
PubMed1995

Comparisons between magnetic field exposure indices in an automobile transmission plant.

Personal monitoring of extremely low frequency magnetic fields was conducted at a large automatic transmission plant for a case-control study of primary brain cancer. Current workers were selected to represent the jobs most commonly held by study subjects. Several exposure indices, corresponding to different plausible biological mechanisms, were computed for each of 81 workers who wore the monitoring instrument for one-half shift. Average exposures covered a range from 0.16 to 46 mG; median exposure was 1.3 mG. Nonparametric correlations were estimated to learn whether all of these indices rise and fall together. Results were mixed, in that indices sensitive to high values showed correlations above 0.7, but other correlations were between 0.4 and 0.6. Different indices may thus identify different groups as "highly" exposed. The authors also tested whether indices based on the fraction of time spent above hypothesized thresholds were accurately predicted by a lognormal model. For 47% of the workers, the observed indices significantly exceeded those predicted by such a model, suggesting that lognormality is not a good model for distributions of individuals' short-term exposures.

Automobiles↗
PubMedDate not supplied

Assessment of magnetic field exposures for a mortality study at a uranium enrichment plant.

A survey of workplace exposures to 60-Hz magnetic fields was carried out at a large uranium enrichment facility to assign exposures for an updated mortality study. Stratified random selection was used to choose workers for measurement in all jobs and areas, to determine whether consistent distinctions could be made between job groups based on average magnetic field exposures. A total of 252 workdays was measured with a personal monitor, and individual average magnetic field exposures ranged from 0.20 to 82.6 mG. A priori job groups showed significant differences between geometric mean exposures, which ranged from 0.80 to 3.51 mG. Most of these groups showed widely ranging exposures, so they were subdivided based on location and job title to improve the precision of the exposure assignments for the mortality study. These final assignments were made up of 26 groups having arithmetic means ranging from 0.43 to 24.9 mG, with most groups defined by location in addition to job title. In general, electrical maintenance workers did not have elevated magnetic field exposures (> 3 mG), but the exposures of the electricians in switchyard (substation) jobs were elevated. Available employment records did not allow most electricians to be distinguished based on location, so they were assigned exposures based on their plantwide average (above 7 mG). An estimated 9% of the work time of this cohort was spent at daily average exposures above 3 mG, despite the very large electric power consumption at this plant.

Analysis of Variance↗
PubMedDate not supplied

Magnetic field exposures in an automobile transmission plant.

Inconsistent findings from recent mortality studies of workers exposed to magnetic fields have led to calls for more detailed understanding of exposure distributions and metrics in various industries. The authors undertook personal monitoring at an automobile transmission plant to (a) learn if magnetic field exposure differences were present, (b) make assignments for a brain cancer study, and (c) compare two exposure indices. A wide range of average exposures occurred (i.e., 0.016-4.6 microtesla). Within-day variability was also large, and it reached 4 orders of magnitude for some workers. Unexpectedly, demagnetizers were found among the strong sources that contributed to elevated exposures. The authors used conventional summary measures to assign job groups to exposure categories, and they used a new index of exposure irregularity to make alternative assignments. These new assignments appeared to differ from the original ones with respect to work time in each exposure group (i.e., 54% of the work time fell into different exposure categories).

Analysis of Variance↗
PubMedDate not supplied

Leukemia mortality among radiation-exposed workers.

The qualitative leukemogenicity of ionizing radiation was firmly established by studies of medical workers and patients exposed to high radiation levels in the mid-1900s. Quantitative relationships were evaluated through extensive studies of atomic bomb survivors and patients who received therapeutic radiation, for whom the duration of exposure was brief. Although many studies have been conducted of nuclear workers and others exposed occupationally, uncertainty remains about quantitative aspects of the leukemia-radiation exposure relation for low dose-rate, fractionated exposures. Some studies have shown dose-related increases in leukemia risks for certain nuclear workers in the U.S. and Europe, although these findings are inconsistent across populations. Despite limitations in low-dose epidemiology, well-designed studies among nuclear workers should inform some controversial aspects of the relation between ionizing radiation exposure and leukemia risk.

Epidemiologic Methods↗