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Biomedical subjects

D Covert

Publications and source records attributed to D Covert.

6 recordsLinked to original sources
PubMed1997

High-resolution maps of regional ventilation utilizing inhaled fluorescent microspheres.

The regional deposition of an inhaled aerosol of 1.0-micron diameter fluorescent microspheres (FMS) was used to produce high-resolution maps of regional ventilation. Five anesthetized, prone, mechanically ventilated pigs received two 10-min inhalations of pairs of different FMS labels, accompanied by intravenous injection of 15.0-micron radioactive microspheres. The lungs were air dried and cut into 1.9-cm3 pieces, with notation of the spatial coordinates for each piece. After measurement of radioactive energy peaks, the tissue samples were soaked in 2-ethoxyethyl acetate, and fluorescent emission peaks were recorded for the wavelengths specific to each fluorescence label. The correlation of fluorescence activity between simultaneously administered inhaled FMS ranged from 0.98 to 0.99. The mean coefficient of variation for ventilation for all 10 trials (47.9 +/- 8.1%) was similar to that for perfusion (46.2 +/- 6.3%). No physiologically significant gravitational gradient of ventilation or perfusion was present in the prone animals. The strongest predictor of the magnitude of regional ventilation among all animals was regional perfusion (r = 0.77 +/- 0.13).

Administration, Inhalation↗
PubMed1988

Physical, morphological, and chemical studies of dusts derived from the machining of composite-epoxy materials.

This work (in three parts) inquires into whether respirable dusts derived from the machining of six composite-epoxy materials (e.g., aircraft industry) may pose a health risk to the operators. Dust samples representative of a variety of composites and structural components were aerodynamically sized and fractionated. Bulk and fractionated samples were examined by light and electron microscopy and analyzed chemically by thermogravimetry (TGA), gas chromatography (GC) and mass spectrometry (MS). Relative fractions of respirable to total mass of bulk samples were less than 3%; aerodynamic diameters of fractionated particles ranged from 0.8 to 2.0 microns. By microscopy, bulk particles ranged from 7 to 11 microns in diameter, with mean aspect ratios from 4 to 8:1. Mean diameter of fractionated particles was 2.7 microns. By TGA, weight losses were negligible below 250 degrees C and variable but elevated at temperatures up to 860 degrees C. In assays of vapors released at 250 degrees C, GC/MS indicated a variety of compounds in different amounts for each sample. We conclude that under the present machining protocols, dusts at the tool face contained few particles of respirable size with no evidence of splitting of fibers longitudinally and were of a low volatilizable chemical content. Overall, composites were judged to be well cured and thermally stable.

Chemical Phenomena↗
PubMed1984

Biological availability of lead in a paint aerosol. 1. Physical and chemical characterization of a lead paint aerosol.

This study was conducted to determine the physical and chemical characteristics of an aerosol of lead-based paint, generated in an industrial spray operation, that might influence the biological availability of lead present in inhaled aerosols. Paint aerosols were collected, and mass-size distribution was determined using a portable cascade impactor under actual occupational conditions. Approx. 2% of the particulate mass collected was in the respirable range (less than 10 micron mean aerodynamic diameter), although the maximum airborne concentration of lead was found to be 2-3 mg/m3. The lead concentration in a dried aerosol was very resistant to chemical digestion. Analysis by X-ray diffraction, atomic absorption spectroscopy and inductively coupled plasma emission spectroscopy showed approx. 11% lead by dry weight, although the wet weight concentration of lead reported by the manufacturer was 12.8%.

Aerosols↗
PubMed1980

The chemical neutralization of inhaled sulfuric acid aerosol.

We hypothesize that gaseous ammonia (NH3) released into respiratory airways can neutralize inhaled acidic particles and alter or mitigate their toxicity. To test this hypothesis, we have examined the relationship between respiratory NH3 and the chemical neutralization of inhaled sulfuric acid (H2SO4) aerosol in the surgically isolated upper airways of anesthetized dogs. With air entering via the mouth, the NH3 concentration measured at the larynx, ranged between 30 and 225 parts per billion (ppb). The extent of neutralization at this point ranged from 8%-70% (n = 16) for the 0.5-micrometer particles and 7%-22% (n = 16) for the 1.0-micrometer particles. With air entering via the nose, the laryngeal NH3 concentrations ranged between 50 and 220 ppb. Neutralization values were between 15%-65% (n = 8) for 0.5-micrometer particles, and between 16%-18% (n = 3) for 1.0-micrometers particles. For both routes of entry, the extent of neutralization was correlated with the laryngeal NH3 concentration. We conclude that the chemistry of acidic particles is significantly altered by respiratory NH3 during inhalation. The extent of neutralization is related to both the NH3 concentration in the airway and the size of the particle entering the airway. The extent of neutralization per ppb of laryngeal NH3 is related to the route of entry, being greater for the mouth than the nose.

Aerosols↗
PubMed1972

Relationships of temperature and sodium chloride concentration to the survival of Vibrio parahaemolyticus in broth and fish homogenate.

The interaction of temperature and NaCl concentration in affecting the survival of three strains of Vibrio parahaemolyticus was studied in Trypticase soy broth and fish homogenate. Cells of V. parahaemolyticus suspended in Trypticase soy broth without NaCl were quite unstable and readily killed. The presence of NaCl appeared to be protective to the cells at 48 +/- 1 C, with the optimal concentration strain-dependent for the 3 to 12% range tested. Temperatures of 5 +/- 1, -5 +/- 1, and -18 +/- 1 C reduced the number of viable organisms per milliliter regardless of the NaCl concentration. In the presence of NaCl, viable cells, in numbers ranging up to 580 per ml, were still detected at the end of 30 days of storage. Similar results were obtained for cells suspended in fish homogenate, except that fish homogenate itself was protective as compared with Trypticase soy broth. This protection was significantly lower than that provided by NaCl in any amount tested.

Bacteriological Techniques↗