C.P. Yu

Total and regional deposition of inhaled aerosols in humans

Total and regional depositions of inhaled aerosols in the human respiratory tract have been calculated for a wide range of particle diameters, particle mass densities, mean flowrates and mean residence times. Good agreement is found with the recent experimental data of Heyder et al. (1975, 1980a) and Stahlhofen et al. (1980). The dependence of deposition upon particle characteristics and flow pattern is further discussed.

Inertial and interceptional deposition of spherical particles and fibers in a bifurcating airway

Abstract Based upon the concept of the stop distance and interception distance of a particle in the cross-section of the daughter tube, a method was developed to calculate the inertial and interceptional deposition of spherical particles and fibers in a bifurcating airway. Theoretical deposition results obtained from this method agree well with available experimental data. Effects of branching geometry and flow field on deposition efficiencies were evaluated and discussed.

Deposition of Cigarette Smoke Particles in the Human Respiratory Tract

Understanding tobacco related cancer etiology requires the knowledge of cigarette smoke particle (CSP) deposition. Measurements of CSP deposition are inconsistent with typical deposition data. A deposition model that accounts for hygroscopic growth, coagulation, particle charge, and cloud behavior of CSP has not yet been presented. Nor have smoking patterns been accounted for in either deposition measurements or computer models. The dosimetry of Benzo[a]pyrene (BaP), which would add critical information to the relationship between anatomic site preferences of tumors and their histology, is currently unknown. The deposition model presented in this study is the first to accurately account for the dynamic behavior of CSP. Using the model results, the effects of each dynamic behavior on deposition is examined along with the effect of smoking patterns. The dosimetry of BaP is also calculated. The results indicate that coagulation, hygroscopicity, and particle charge increase the total deposition by 16% over the stable charge-neutral case, which predicts 46%. Cloud behavior increases total deposition efficiency by 36% over the simple case. Increasing exhalation time increases the deposition fraction by 3.9%/s. BaP concentrations are found to be as large as 1.8E-4ng/cm2 for the cloud model and 2.4E-5 ng/cm2 for single particle behavior. Mass deposition occurs preferentially in the pulmonary region for all cases. However, significant increases in the tracheo-bronchial region are found if cloud behavior is considered. The model results indicate that cloud behavior,and not particle charge, coagulation, and hygroscopic growth, has a predominant effect on deposition. More data is required on cloud behavior in the airways to improve the accuracy of the model.

Precipitation of unipolarly charged particles in cylindrical and spherical vessels

Abstract An analysis is presented on the precipitation of unipolarly charged particles of uniform size in cylindrical and spherical vessels by their own space charge. When the particle number density is large the mechanism of deposition is due to mutual electrical repulsion and for small number density only image force is important. Expressions for the fractional deposition are obtained in both cases.

Deposition of fibers in the rat lung

Abstract The deposition and clearance of inhaled particles in the lungs of different mammals have been the subject of many investigations. Any analysis on the particle removal from the lung requires a knowledge of the initial deposition pattern of inhaled particles at different sites. In this study, a deposition model is employed in conjunction with the data of the airway geometry to calculate the deposition of fibers at various locations in the rat lung. In the process, the simultaneous effect of Brownian rotation and velocity shear on the fiber orientation is considered. The results show that although long fibers are effectively filtered by the airways in the head and tracheobronchial regions, a smaller fraction of those fibers can penetrate into the pulmonary region and deposit there. The calculated results compared favorably with the experimental data of Morgan et al. (Inhaled Particles IV. Pergamon Press, Oxford, 1977) and Hammad et al. (Ann. occup. Hyg.26, 179–187, 1982).

Deposition of charged particles from laminar flows in rectangular and cylindrical channels by image force

Abstract Precipitation of charged particles by their image force from laminar flows in rectangular and cylindrical channels is investigated theoretically. Calculations are based on the analysis of limiting trajectories of particles which enables the determination of the precipitation efficiency for channels of different dimensions. Results for cylindrical tubes are applicable to the deposition of charged particles in human lung airways.

Predicted deposition of diesel particles in young humans

This study utilized a mathematical model to predict the deposition patterns of inhaled diesel automobile exhaust particles in the respiratory tracts of young humans. A particle model was proposed to describe the physical characteristics and dynamic behavior of diesel particles, and this model was incorporated into the derivation of mathematical expressions for the airway deposition efficiency. An anatomical lung model for humans from birth to adulthood was formulated mathematically from available physiologic data and morphometric measurements. The growing lung model, together with the corresponding ventilation conditions, were then used to calculate the deposition of diesel particles in the lungs at any age up to maturity. We found that the deposition of diesel particles in young humans exhibited distribution patterns similar to those of adults. With the exception of alveolar deposition in very young children (below the age of 2 years), the predicted regional deposition fractions were always higher than in adults. For an equal duration of exposure, the surface minute dose in unciliated airways was predicted to change profoundly with age. The maximum calculated dose, which occurred at the age of 2 years, was approximately twice the adult value.

A clearance model of refractory ceramic fibers (RCF) in the rat lung including fiber dissolution and breakage

Abstract A new model has been developed to describe the clearance and retention of kaolin refractory ceramic fibers (RCF) in the rat lung. Fiber dissolution, breakage and differential clearance were considered in this model and their respective rates were determined from the available experimental data. It was shown that the new model offered a better interpretation of the observed fiber size distribution in the lung than our previous model (Yu et al. (1994a) Environ. Res. 65 , 243–253) in which none of these effects were considered.

Deposition modeling of refractory ceramic fibers in the rat lung

Abstract An earlier mathematical model (Asgharian and Yu, J. Aerosol Sci. 20, 355–366, 1989) has been modified to calculate the deposition of refractory ceramic fibers (RCF) in the rat lung. Using the anatomical whole lung model and lobar lung model proposed by Schum and Yeh ( Bull. Math. Biol. 42, 1–15, 1980), fractional deposition efficiency and size distribution of deposited fibers in various regions of the lung were determined. It was found that a large fraction of long and thick fibers deposited in the nasopharynx and the tracheobronchial tree by the mechanisms of impaction and interception, while the geometric mean diameter and length of the fibers deposited in the pulmonary region decreased considerably from their respective values in the aerosol state. The calculated size distribution in the pulmonary region of the accessory lobe was found in good agreement with the data obtained in recent exposure experiments.

Simultaneous diffusion and sedimentation of aerosols in channel flows

Abstract The problem of particle loss to the wall of a narrow rectangular channel through which an aerosol is passing is studied with simultaneous consideration of diffusion and sedimentation. Both slug flow and Poiseuille flow are considered. It is found that the relative importance of diffusion and sedimentation on the fractional penetration depends upon a parameter σ = hvg/D, where h is the half height of the channel, vg is the settling velocity of a particle and D is the Brownian diffusion coefficient. For σ 200, the loss is due to settling. The loss due to the combined mechanism in the range 0·1