Richard Michael Schreck

Effect of the laryngeal jet on particle deposition in the human trachea and upper bronchial airways

Abstract Preferential sites of particle deposition within the human respiratory system are known to correlate with primary cancer sites, and are therefore important in the etiology of neoplastic respiratory diseases. In this study, we characterized the intrabronchial and intratracheal patterns of deposition in a hollow cast of a human larynx-tracheobronchial tree, and examined the effects of airflow and turbulence on particle deposition by performing airflow measurements in the hollow cast and an “ideal” airway bifurcation model. Experimental results revealed a deposition “hot spot” for particles greater than 2 μm in mass median aerodynamic diameter in the trachea at 2 cm below the larynx. The enhancement of deposition in the trachea was studied by making comparative airflow and detailed morphometry measurements in a hollow lung cast and in an “ideal” model. The larynx had a significant effect on the local flow field in the trachea of the hollow cast and this effect extended to and beyond the tracheal bifurcation. This accounted for some of the difference in flow field at the bifurcation between the cast and an “ideal” model. Additional differences were related to the different shapes of the transitional regions near the bifurcation.

Experimental Measurements of the Independent Effects of Dilution Ratio and Filter Temperature on Diesel Exhaust Particulate Samples

A dilution mini-tunnel is described that collects diesel exhaust particulate samples with independent control of dilution ratio and sample filter temperature. The small dilution system requires no pumps or blowers and offers much flexibility in controlling the dilution process. Experiments were conducted with the dilution system to establish individual effects of filter temperature and dilution ratio on particulate samples collected by filtration from the exhaust of an automotive diesel engine. Exhaust particulate aerosol was generated with a single-cylinder test engine operating at constant load and speed. Increasing filter temperature from 35-100 degrees C while maintaining a constant 10.8:1 dilution ratio decreased particulate mass by about 13%. Increasing the dilution ratio from 5:1 to 100:1 at a constant filter temperature of 52 degrees C decreased particulate mass by about 26%. These changes were attributed to variations in the soluble portion of the particulate sample. Supplemental information is appended on dilution system development, residence time and filter material effects on particulate mass, and dilution ratio calculation.

Fluid dynamics in airway bifurcations: I. Primary flows.

The subject of fluid dynamics within human airways is of great importance for the risk assessment of air pollutants (inhalation toxicology) and the targeted delivery of inhaled pharmacologic drugs (aerosol therapy). As cited herein, experimental investigations of flow patterns have been performed on airway models and casts by a number of investigators. We have simulated flow patterns in human lung bifurcations and compared the results with the experimental data of Schreck (1972). The theoretical analyses were performed using a third-party software package, FIDAP, on the Cray T90 supercomputer. This effort is part of a systematic investigation where the effects of inlet conditions, Reynolds numbers, and dimensions and orientations of airways were addressed. This article focuses on primary flows using convective motion and isovelocity contour formats to describe fluid dynamics; subsequent articles in this issue consider secondary currents (Part II) and localized conditions (Part III). The agreement between calculated and measured results, for laminar flows with either parabolic or blunt inlet conditions to the bifurcations, was very good. To our knowledge, this work is the first to present such detailed comparisons of theoretical and experimental flow patterns in airway bifurcations. The agreement suggests that the methodologies can be employed to study factors affecting airflow patterns and particle behavior in human lungs.The subject of fluid dynamics within human airways is of great importance for the risk assessment of air pollutants (inhalation toxicology) and the targeted delivery of inhaled pharmacologic drugs (aerosol therapy). As cited herein, experimental investigations of flow patterns have been performed on airway models and casts by a number of investigators. We have simulated flow patterns in human lung bifurcations and compared the results with the experimental data of Schreck (1972). The theoretical analyses were performed using a third-party software package, FIDAP, on the Cray T90 supercomputer. This effort is part of a systematic investigation where the effects of inlet conditions, Reynolds numbers, and dimensions and orientations of airways were addressed. This article focuses on primary flows using convective motion and isovelocity contour formats to describe fluid dynamics; subsequent articles in this issue consider secondary currents (Part II) and localized conditions (Part III). The agreement between calculated and measured results, for laminar flows with either parabolic or blunt inlet conditions to the bifurcations, was very good. To our knowledge, this work is the first to present such detailed comparisons of theoretical and experimental flow patterns in airway bifurcations. The agreement suggests that the methodologies can be employed to study factors affecting airflow patterns and particle behavior in human lungs.

FLUID DYNAMICS IN AIRWAY BIFURCATIONS: II. Secondary Currents

As the second component of a systematic investigation on flows in bifurcations reported in this journal, this work focused on secondary currents. The first article addressed primary flows and the third discusses localized conditions (both in this issue). Secondary flow patterns were studied in two lung bifurcation models (Schreck, 1972) using FIDAP with the Cray T90 supercomputer. The currents were examined at different prescribed distances distal to the carina. Effects of inlet conditions, Reynolds numbers, and diameter ratios and orientations of airways were addressed. The secondary currents caused by the presence of the carina and inclination of the daughter tubes exhibited symmetric, multivortex patterns. The intensities of the secondary currents became stronger for larger Reynolds numbers and larger angles of bifurcation.As the second component of a systematic investigation on flows in bifurcations reported in this journal, this work focused on secondary currents. The first article addressed primary flows and the third discusses localized conditions (both in this issue). Secondary flow patterns were studied in two lung bifurcation models (Schreck, 1972) using FIDAP with the Cray T90 supercomputer. The currents were examined at different prescribed distances distal to the carina. Effects of inlet conditions, Reynolds numbers, and diameter ratios and orientations of airways were addressed. The secondary currents caused by the presence of the carina and inclination of the daughter tubes exhibited symmetric, multivortex patterns. The intensities of the secondary currents became stronger for larger Reynolds numbers and larger angles of bifurcation.

Fluid Dynamics in Airway Bifurcations: III. Localized Flow Conditions

Localized flow conditions (e.g., backflows) in transition regions between parent and daughter airways of bifurcations were investigated using a computational fluid dynamics software code (FIDAP) with a Cray T90 supercomputer. The configurations of the bifurcations were based on Schrecks (1972) laboratory models. The flow intensities and spatial regions of reversed motion were simulated for different conditions. The effects of inlet velocity profiles, Reynolds numbers, and dimensions and orientations of airways were addressed. The computational results showed that backflow was increased for parabolic inlet conditions, larger Reynolds numbers, and larger daughter-to-parent diameter ratios. This article is the third in a systematic series addressed in this issue; the first addressed primary velocity patterns and the second discussed secondary currents.Localized flow conditions (e.g., backflows) in transition regions between parent and daughter airways of bifurcations were investigated using a computational fluid dynamics software code (FIDAP) with a Cray T90 supercomputer. The configurations of the bifurcations were based on Schreck s (1972) laboratory models. The flow intensities and spatial regions of reversed motion were simulated for different conditions. The effects of inlet velocity profiles, Reynolds numbers, and dimensions and orientations of airways were addressed. The computational results showed that backflow was increased for parabolic inlet conditions, larger Reynolds numbers, and larger daughter-to-parent diameter ratios. This article is the third in a systematic series addressed in this issue; the first addressed primary velocity patterns and the second discussed secondary currents.

High-Solids Paint Overspray Aerosols in a Spray Painting Booth: Particle Size Analysis and Scrubber Efficiency

Particle size distributions of high-solids acrylic-enamel paint overspray aerosols were determined isokinetically in a downdraft spray painting booth in which a 7-stage cascade impactor was used. Three different industrial paint atomizers were used in this study, and the paint aerosols were characterized before and after a paint booth scrubber. The mass median aerodynamic diameter (MMAD) of a metallic basecoat and an acrylic clearcoat paint aerosol from air-atomized spray guns ranged from 4-12 µm and was dependent on atomization pressure. The clearcoat paint aerosols also were generated from rotary atomizers and had MMADs, which ranged from 20-35 µm depending on rotational speed. When the paint booth was operated under controlled conditions simulating those in a plant, the collection efficiency of paint overspray aerosols by a paint scrubber was found to be size dependent and decreased sharply for particles smaller than 2 µm to as low as 64% for clearcoat paint particles of 0.6 µm. Based on the performanc...

Breath monitoring of inhalation and dermal methanol exposure

Abstract A fundamental assumption of monitoring breath for a toxicant is that the concentration of the toxicant in breath is proportional to the concentration in blood. The present study was designed, in part, to assess the conditions under which measurement of methanol in breath would be useful for estimating the blood concentration of methanol following inhalation or dermal exposures to methanol. Paid volunteer subjects underwent controlled inhalation exposure to methanol vapor at various concentrations for 8 hours, or dermal exposures (without inhalation exposure) to methanol for varying periods of time. Blood and end-expiratory air were analyzed for methanol from samples obtained prior to exposures, and at various times during and after exposures. The results demonstrate that blood and breath concentrations of methanol are disproportional for varying periods of time during and following cessation of methanol exposure, depending on the route of exposure (dermal versus inhalation). In settings where the...

Biomedical applications of tunable diode laser spectrometry: Correlation between breath carbon monoxide and low level blood carboxyhemoglobin saturation

Tunable diode laser spectrometry was used to measure breath carbon monoxide (CO) concentrations in nonsmoking subjects. Corresponding blood carboxyhemoglobin (COHb) saturations between physiological levels and levels after 1 and 8 hours exposure to 9 ppm CO, the maximum permissible concentration in the air under federal regulations, were also determined. A good linear correlation between breath CO and blood COHb saturation for low levels representing ambient conditions was established, with a correlation coefficient better than 0.999 for the means and 0.945 for the individual data points. Similar studies on the other compounds of concern are also possible using tunable diode laser spectrometry, requiring only a breath sample and with no sample preparation. This technique will facilitate fast, noninvasive environmental health effect and biomedical studies.

Carboxyhemoglobin Levels in Humans: Effects of Altitude

AbstractThese studies were conducted to determine the effects of altitude on endogenous blood carboxyhemoglobin (COHb) concentrations and on COHb concentrations produced by breathing carbon monoxide (CO). COHb concentrations were determined at sea level (SL) and at altitude (HA) in human volunteers breathing ambient air (group I) or 9 ppm CO for 1 hr (group II). Breath CO measurements were also made in both groups. The first measurements were made at College Station, Texas (elevation 330 ft) and the second at Hoosier Pass, Colorado (elevation 11,540 ft) after 20 hr at altitude. Blood drawn from the finger was immediately frozen for COHb and hemoglobin analysis in Lubbock, Texas. Alveolar air samples, collected in aluminized Mylar bags, were analyzed for CO in Warren, Michigan. In group 1 subjects, COHb levels increased significantly (p <.05) from 0.790% and 0.795%, respectively, in males and females at SL to 0.947% and 0.945% at HA. The overall increase for both groups was approximately 20%. In group 2 su...

Evaluation of Methanol and Formate in Urine as Biological Exposure Indices of Methanol Exposure

Abstract Biological monitoring of exposure to industrial chemicals commonly involves laboratory analyses of a toxicant or metabolites in urine. The American Conference of Governmental Industrial Hygienists has recommended biological exposure indices for methanol exposure based on methanol and formate in urine. The present study was designed primarily to evaluate methanol in urine and other potential biological determinants of methanol exposure. Volunteer subjects underwent controlled exposure to methanol vapor at different concentrations for approximately 8 hours to simulate a standard work shift. Urine was collected immediately prior to exposure sessions, during exposures, and immediately following cessation of exposures. Samples were analyzed for methanol, formate, specific gravity (SpGr), and creatinine. The following biological determinants were examined: total methanol excreted during the shift; mean concentration of methanol excreted during the shift (uncorrected, and corrected for SpGr and creatini...