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Biomedical subjects

Thomas W Armstrong

Publications and source records attributed to Thomas W Armstrong.

4 recordsLinked to original sources
PubMed2005

Chronic exposure to benzene results in a unique form of dysplasia.

Hematotoxicity following chronic benzene exposure has been recognized for over a century, although the mechanism remains unknown. We describe a novel form of bone marrow dysplasia in 23 workers exposed to high concentrations of benzene. Distinguishing features of benzene-induced dysplasia include: marked dyserythropoiesis, eosinophilic dysplasia and abnormal cytoplasmic granulation of neutrophilic precursors. Hematophagocytosis, stromal degeneration and bone marrow hypoplasia are also seen. Severe bone marrow dysplasia is frequently accompanied by clonal T cell expansion and alterations in T lymphocyte subsets. No clonal cytogenetic abnormalities were observed. These results suggest that autoimmune-mediated bone marrow injury is an early or predisposing event in the pathogenesis of benzene-induced persistent hematopoietic disease.

Adult↗
PubMed2005

Occupational exposure limits: an approach and calculation aid for extended work schedule adjustments.

Past reviews of occupational exposure limit (OEL) adjustments have covered both decision logic and calculation methods to derive factors to assure protection of workers on extended (also known as unusual) work shifts. The approaches reviewed included several Haber's rule based methods, several variants of single compartment toxicokinetic (TK) models, and physiologically based pharmacokinetic modeling. These models calculate OEL adjustment factors based on the work shift and the uptake and elimination of the toxicant. A key parameter of the TK models is the biologic half-life of the toxicant, but reliable data for the half-life are not available for all substances of concern. A spreadsheet is presented that implements TK calculations, with one of the presented TK calculation alternatives not dependent on half-life data. This half-life data independent approach is suggested as a viable option for situations when the toxicant's half-life is unknown or uncertain.

Environmental Pollutants↗
PubMedDate not supplied

Using a spreadsheet to compute contaminant exposure concentrations given a variable emission rate.

Two key elements of mathematical exposure models are the contaminant's emission rate and pattern of dispersion in room air. Assuming that the mass emission rate is constant and room air is perfectly mixed affords relative mathematical simplicity. However, treating a highly variable emission rate as constant underestimates peak exposure intensity, which may be toxicologically important, and assuming a well-mixed condition underestimates exposure intensity near the source. In the past decade multizone models and turbulent diffusion models have been used to account for spatial variability in airborne concentrations, and variable emission rate functions have been described for different processes. Due to the greater complexity of these models, closed-form equations for concentration as a function of time may not be available. This article presents a numerical method that combines a variable contaminant emission rate function with the three dispersion constructs most commonly used by industrial hygienists-the well-mixed room, the near field/far field, and hemispherical turbulent eddy diffusion. The article describes how the numerical method is implemented by a computer spreadsheet program, and illustrates the method using a sinusoidal contaminant emission rate function.

Air Pollution, Indoor↗