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Biomedical subjects

K D Blehm

Publications and source records attributed to K D Blehm.

6 recordsLinked to original sources
PubMed1990

A predictive model for vapor concentration in a nose-only inhalation chamber.

A unique nose-only inhalation chamber was designed and constructed to deliver uniform concentrations of gas, vapor, and aerosol contaminants to mice. This research investigated the fluid dynamics of a vaporous contaminant in the vertical flow chamber. The vapor was introduced by allowing the liquid phase of the contaminant to evaporate freely into the chamber interior. A contaminant mass transfer model was developed to predict concentrations generated by the system. The mathematical model of the system used clean airflow, liquid surface area, thickness of the stagnant air layer covering the liquid, system pressure, contaminant diffusion coefficient, and contaminant vapor pressure to compute the vapor concentration delivered to exposure ports. The equation was verified by placing various containers of methyl isobutyl ketone in the chamber and determining with a photospectrometer the resulting equilibrium concentrations. Vapor pressure, diffusion coefficient, and system pressure were held constant while airflow, surface area, and stagnant air layer thickness were varied systematically within the chamber. The resulting empirical data points were compared to the curves predicted by the theoretical model. Empirical concentrations fell within 0 to 48% of the theoretical values, showing that the equation can be used to choose values for airflow, surface area, and stagnant air layer thickness that will result in chamber concentrations in close proximity to the target concentration. If an exact concentration is essential, parameters may be individually adjusted to converge on the target concentration.

Animals↗
PubMed1987

A predictive model for determining asbestos concentrations for fibers less than five micrometers in length.

The controversy of whether small asbestos fibers are biologically significant has not been resolved. The present standard method for evaluating asbestos fiber concentrations in workroom air excludes fibers less than 5 micron long even though it has been shown that small fiber concentrations dominate in a dust cloud. This research project was conducted to develop a mathematical model whereby one could predict small (less than 5 micron length) asbestos fiber concentration based on the fiber count concentration determined by phase contrast microscope analysis. Dry chrysotile asbestos was aerosolized into a chamber and sampled by membrane filtration. Segments from each filter were analyzed by both the NIOSH technique using phase contrast microscopy (PCM) and scanning electron microscopy (SEM) at 2000 X for fiber concentrations. A linear relationship was found to exist between the natural logarithm of the SEM-determined concentration and the natural logarithm of the PCM-determined concentration (r = 0.852). Using these data, a mathematical model was developed to predict SEM concentrations based on PCM counts. This model may have application in retrospective epidemiological studies for estimating small fiber exposure levels to determine if small fibers play a role in disease production. The greatest utility would be in those retrospective studies where the only exposure information available is based on PCM counts.

Air Pollutants↗
PubMed1986

Investigation of solid-phase ozonolysis reactions for use in a personal sampling method for ozone.

Three ozonolysis reactions were tested in the solid phase for reproducibility and quantitative yield of an aldehyde reaction product. The three starting olefins were t-stilbene, 4,4'-dimethoxystilbene and 1,2-di-(4-pyridyl) ethylene which, when reacted with ozone, gave benzaldehyde, p-anisaldehyde and pyridine-4-aldehyde, respectively. The starting olefins were coated on a variety of solid substrates, exposed to known ozone concentrations and then analyzed for the corresponding aldehyde with a gas chromatograph equipped with a flame-ionization detector. The best combination found for all three reactions was with the starting olefin coated on 30/60 mesh Florisil. Consistent yield was obtained for the methoxystilbene reaction within one batch of sorbent; very reproducible results were obtained within four replicate samples for the pyridyl ethylene reaction. No consistency was obtained, however, with any of the reactions between batches of sorbents and between different sets of samples. Several problems were identified which led to the inconsistent results. The t-stilbene and pyridyl ethylene sorbents oxidized over time while stored to form high aldehyde blanks. All three aldehydes, once formed on the sorbent, were volatilized off the sorbent bed as a result of airflow through the bed. Several different solid sorbents were tried unsuccessfully as traps for the purged aldehydes. Finally, lower flow rates resulted in the finding that significant amounts of the aldehydes also were being formed by oxygen in the air sample. Since oxygen was a strong positive interferent, these reactions were considered unacceptable as indicators of ozone.

Air Pollutants, Occupational↗
PubMed1986

Characterization of particleboard aerosol--size distribution and formaldehyde content.

Health hazards unique to particleboard include the generation of urea-formaldehyde resin bound in wood aerosol and release of formaldehyde gas that can be inhaled by the worker. A particleboard aerosol was generated by a sanding process and collected under laboratory conditions that determined the particle size distribution and formaldehyde content. Three side-by-side Marple 296 personal cascade impactors with midget impingers attached downstream collected particleboard aerosol and gaseous formaldehyde for ten sample runs. Gravimetric analysis quantified the collected aerosol mass, and chromotropic acid/spectrophotometric analytical methods were employed for formaldehyde content in particleboard aerosol and gaseous formaldehyde liberated from sanded particleboard. Significant variations (p less than .005) were observed for the particleboard mass and gaseous formaldehyde collected between sample runs. No significant differences (alpha = .05) were observed for the aerosol size distribution determined and formaldehyde content in particleboard aerosol per unit mass for sampling trials. The overall MMAD of particleboard aerosol was 8.26 microns AED with a sigma g of 2.01. A predictive model was derived for determining the expected formaldehyde content (microgram) by particleboard aerosol mass (mg) collected and particulate size (micron AED).

Aerosols↗
PubMedDate not supplied

The determination of ambient air quality within an environmental care unit.

Various chemicals found in the environment have been suspected of initiating or contributing to conditions such as asthma, dermatitis, irritability, headaches, cardiac arrhythmias, thrombophlebitis, and vasculitis. The increasing number and variety of chemicals present in the environment has led to the hypothesis that there may also be a corresponding increase in the number of people who are sensitive to these chemicals. Sensitive individuals may be continually exposed to chemical insults in their normal environment and may be experiencing a chronic reaction; however, an exposure-response relationship is difficult to establish. An Environmental Care Unit (ECU) provides an atmosphere that minimizes exposures to potential insults so patients symptoms of reaction to chemical insult may be relieved before challenge testing. Air quality required within an ECU to achieve this symptom remission is not known; therefore, this study was designed to document and compare concentrations of six criteria pollutants (sulfur dioxide, carbon monoxide, nitrogen dioxide, hydrocarbons, total suspended particular, and ozone) and formaldehyde within the ECU, the hospital outside the ECU, and the ambient atmosphere of the neighborhood around the hospital. Air movement studies indicated that the ECU was under positive pressure with respect to the rest of the hospital and had an air supply to air exhaust ratio of approximately two. Overall, no significant differences were found for any sampled pollutant at sites within the ECU or between ECU sites and the hospital proper. With an exception of ozone, significant differences among contaminant concentrations were noted between the atmosphere of the surrounding neighborhood and the hospital proper.(ABSTRACT TRUNCATED AT 250 WORDS)

Air Pollutants↗