Satish Anjilvel

Inertial and Gravitational Deposition of Particles in a Square Cross Section Bifurcating Airway

Deposition of spherical particles in an airway bifurcation is studied numerically. Airway dimensions are based on the third airway generation of the Weibel symmetric lung model (1963). A square cross-sectional airway area is assumed, with parent and daughter tubes having different diameters. The flow field is solved by a finite element method for Reynolds numbers of 100 and 1000 with uniform and parabolic parent inlet velocities. The flow field is then used to calculate particle deposition in this geometry. Deposition by the mechanisms of impaction and sedimentation are incorporated. The results show that for particles larger than 10 μm, sedimentation losses are weakly dependent on the flow Reynolds number and the inlet condition, whereas impaction losses depend strongly on Reynolds number and inlet condition. Also, the calculated results gave good agreement with the predictive model of Pich (1972) for sedimentation losses in flows through parallel plates. For losses by impaction, the calculated results a...

Analysis of lobar differences in particle deposition in the human lung.

Lung diseases caused by the inhalation of various particulate pollutants have often been reported to occur at specific sites in the lung with some diseases preferentially occurring in one of the lobes. Models for the dosimetry of particulate matter in the lung, therefore, need to be developed at a level of resolution that allows for the study of lobar- and airway-specific patterns of deposition. Using an approach best described as a combination of asymmetric and symmetric approaches to modeling lung geometry, we calculated deposition of particulate matter (PM) ranging from ultrafine to coarse particles in each airway down to the level of the lobar bronchi. Further down the airway tree, we calculated deposition averaged over an airway generation in each lung lobe. We compared our results for regional and lobar deposition with various experimental data as well as with results from other models. The calculated results compared reasonably well with experimental data. Significant variations in deposition were observed among the lobar bronchi as well as among the five lobes. The differences among the lobes were accentuated as one examined generation-specific deposition. Deposition per unit surface area of each lobar bronchus was considerably elevated relative to that calculated for the whole lung. The relative distribution of aerosol deposited per unit surface area among the lobar bronchi was altered by breathing condition and aerosol size. Our observations suggest that a multiple-path model that incorporates the heterogeneous structure of airways in the lung is likely to reduce uncertainties in PM health risk assessments.

Inertial Deposition of Particles in the Human Upper Airway Bifurcations

ABSTRACT Particle deposition in symmetric bifurcating airways due to inertial impaction was studied numerically for inspiratory flows. Three-dimensional bifurcation models were constructed. The models had different parent and daughter diameters comparable to the airway generations 3–6 of the human lung. Bifurcation angles of the models were also varied (30®, 45®, and 60®). Airflow fields in the models were obtained by a finite–element method (FIDAP, Fluid Dynamics International, Evanston, IL) for different Reynolds numbers of 100, 265, 530, and 1060 under parabolic and uniform inlet velocity conditions. The calculated flow field data were used to simulate particle trajectory in the airways. Particle deposition efficiency was obtained using the limiting trajectory method. Inlet flow velocity profile, flow Reynolds number, and bifurcation angle were found to have substantial effects on particle deposition. Based on calculated deposition results, empirical equations were derived for particle deposition effic...

DOSIMETRIC ISSUES RELATING TO PARTICULATE TOXICITY

AbstractAn increasing number of epidemiological studies have reported excess mortality and morbidity thought to be associated with elevated levels of particulate matter air pollution. These studies call into question the adequacy of the current National Ambient Air Quality Standard for particulate matter in terms of being protective of human Jiects. The lack of data from the animal toxicology literature supportive of the types of effects seen in the epidemiology studies has raised issues of biological plausibility, adequacy of animal models, and relevance of endpoints measured in these models. We focused on various aspects of interspecies differences (rat vs. human) in the dosimetry of particles that may help explain the apparent lack of consistency between the toxicological and epidemiological findings. We ad Justed the predicted thoracic deposition fractions in rats for the probability of inhaling particles up to 10 μm in diameter. While deposition of particles on a mass per unit alveolar surface area i...

A Monte Carlo calculation of the deposition efficiency of inhaled particles in lower airways

Steady airflow and particle transport in a straight cylindrical tube and in a three-dimensional model of a bifurcating airway were calculated. The model domains were based on human lung data. For simplicity, airways in the bifurcating model were assumed to have a rectangular cross-section with hydraulic diameters similar to those of generations 16 and 17 of the Weibel model. Steady flow with a Reynolds number of unity within this domain was solved numerically by a finite element method using a commercial software package. Parabolic inlet conditions were assumed. Using the calculated flow profile, individual particle trajectories within the air stream were simulated by numerically solving the fundamental differential equations of particle motion. The simulation included the effects of diffusion and sedimentation. Deposition efficiencies by individual mechanisms and the total deposition efficiency were obtained using a Monte Carlo method. For parabolic flow in a straight tube, the results compared very well with existing formulas in the literature. For both geometries, the sum of the efficiencies due to individual mechanisms was greater than the numerical prediction of total efficiency. The total deposition efficiency, ηtotal, was accurately expressed in terms of the efficiencies of sedimentation, ηs, and diffusion, ηd, using the empirical formula ηtotal = (ηdp + ηsp)1/p. The best value of p depended on the particular geometry.

The Effect of Fiber Inertia on Its Orientation in a Shear Flow with Application to Lung Dosimetry

The effect of fiber inertia on its orientation in a flow field was studied. Expressions for fluid dynamic torque given by Jeffery (1923) were used in the Euler equations of motion to determine fiber orientation. Fiber orientation was found to depend on two nondimensional parameters; its aspect ratio and a nondimensional parameter related to the fluid viscosity, flow velocity gradient, and fiber mass density and diameter. Fiber orientation was calculated for different fiber diameters and was compared with that obtained by Jeffery (1923) for normal breathing in humans and rats. The inertial effects are significant when fiber diameter exceeds lμm.

Approximation of surfaces in quantitative 3-D reconstructions

In serial section reconstructions, a series of planar profiles are taken representing curves on the surface of the structure to be reconstructed. For a number of quantitative serial section methods, approximation of a surface is done by the formation of tiles between points of adjacent profiles. As generally proposed, finding this approximation has been difficult due to the inordinately large number of possible solutions resulting from different combinations of tiles between points. Current algorithms have either applied heuristic criteria to force the formation of only one solution, or have searched all acceptable combinations for one that minimizes some cost function. The algorithm presented has been developed to choose the tiling which minimizes the estimated error when the tile approximation of the surface is used in subsequent quantitative algorithms such as the calculation of surface area.<<ETX>>