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The extent to which laryngeal-induced flow features penetrate into the upper tracheobronchial (TB) airways and their related impact on particle transport and deposition are not well understood. The objective of this study was to evaluate the effects of including the laryngeal jet on the behavior and fate of inhaled aerosols in an approximate model of the upper TB region. The upper TB model was based on a simplified numerical reproduction of a replica cast geometry used in previous in vitro deposition experiments that extended to the sixth respiratory generation along some paths. Simulations with and without an approximate larynx were performed. Particle sizes ranging from 2.5 nm to 12 mum were considered using a well-tested Lagrangian tracking model. The model larynx was observed to significantly affect flow dynamics, including a laryngeal jet skewed toward the right wall of the trachea and a significant reverse flow in the left region of the trachea. Inclusion of the laryngeal model increased the tracheal deposition of nano- and micrometer particles by factors ranging from 2 to 10 and significantly reduced deposition in the first three bronchi of the model. Considering localized conditions, inclusion of the laryngeal approximation decreased deposition at the main carina and produced a maximum in local surface deposition density in the lobar-to-segmental bifurcations (G2-G3) for both 40-nm and 4-microm aerosols. These findings corroborate previous experiments and highlight the need to include a laryngeal representation in future computational and in vitro models of the TB region.

Simulation of the dynamics and disposition of inhaled particles within human lungs is an invaluable tool in both the development of inhaled pharmacologic drugs and the risk assessment of environmental particulate matter (PM). The goal of the present focused study was to assess the utility of three-dimensional computational fluid dynamics (CFD) models in studying the local deposition patterns of PM in respiratory airways. CFD models were validated using data from published experimental studies in human lung casts. The ability of CFD to appropriately simulate trends in deposition patterns due to changing ventilatory conditions was specifically addressed. CFD simulations of airflow and particle motion were performed in a model of the trachea and main bronchi using Fluent Inc.'s FIDAP CFD software. Particle diameters of 8 microm were considered for input flow rates of 15 and 60 L/min. CFD was able to reproduce the observed spatial heterogeneities of deposition within the modeled bifurcations, and correctly predicted the "hot-spots" of particle deposition on carinal ridges. The CFD methods also predicted observed differences in deposition for high-versus-low flow rates. CFD models may provide an efficient means of studying the complex effects of airway geometry, particle characteristics, and ventilatory parameters on particle deposition and therefore aid in the design of human subject experiments.

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.

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.

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.

A computational fluid dynamics software package (FIDAP) has been employed to obtain three-dimensional flow data, which are used herein to calculate the trajectories of fluid particles. Our computations have demonstrated that the flow fields inside the larynx are very complex including eddies in the lumen and reverse motion along the surface. The effects of such flow fields will be to increase the residence times of entrained drug particles. Our computations have also demonstrated that the larynx has pronounced effects on the motion of air in the trachea.

Experimental deposition patterns of cigarette smoke in surrogate human airway systems are very heterogeneous. Particle deposits are enhanced at predictable, well-defined morphological regions; most specifically, carinal ridges within bifurcation zones and along posterior sections of tubular airways. The efficiency of the mucociliary transport mechanism in vivo is also reduced at airway branchings. The geometrical sites of preferential particle deposition and impaired clearance can be correlated with clinically observed anatomical sites exhibiting increased incidences of bronchogenic carcinomas. These locations are not compatible with current theoretical models simulating only the usual particle deposition processes of inertial impaction, sedimentation, and diffusion, while intending to account for particle hygroscopicity. Moreover, data from human subject exposures indicate that heretofore unknown factors affect the distribution of inhaled cigarette smoke. Herein, a new mathematical model is presented that explains cigarette smoke deposition patterns, including bifurcation "hot spots," in terms of composition and cumulative density. The behavior of mainstream cigarette smoke can be related to physicochemical parameters of its particulate and vapor-gas phases and is a result of two distinct effects: (1) particle cloud motion and (2) vapor-gas behavior. In lung airways, Effect 1 is the most prominent. The high particle number,ns approximately equal to 3 x 10(9) cm-3, and mass,rho s approximately equal to 10(-4) g cm-3, concentrations of smoke dictate that a bolus of it has kinetic properties of an entity (Effect 1 above), independent of the aerodynamic size characteristics of individual constituent particles. This motion may be exacerbated by the bulk movement (Effect 2 above) of the vapor-gas phase density of smoke.

The influence of hygroscopic growth within the human respiratory tract upon the deposition of H2SO4 aerosols is investigated using an analytical model. Particles are assumed to reach their equilibrium size and density upon entering the trachea from either the nasal or oral pharyngeal compartments. Calculated data are used to describe the equilibrium values for specified relative humidity conditions which simulate the atmosphere, inhalation exposure chambers, and the lung. Theoretical equations are used to calculate aerosol deposition efficiencies within conducting airways of the tracheobronchial tree. Hygroscopic growth is shown to affect both the total dose deposited and its regional distribution. For an inspiratory flow rate of 30 L min-1, the total deposition efficiency of H2SO4-and-H2O droplets, resulting from water condensation upon H2SO4 particles of initial geometric diameter D0, is greater than inspired nonhygroscopic particles of identical aerodynamic diameter when D0 greater than 0.1 mu m. The opposite is found when D0 less than 0.1 mu m. The effects of hygroscopic growth are explained in terms of the changing deposition efficiencies of the inertial impaction, sedimentation and diffusion mechanisms. Results imply that it is important that hygroscopic growth within the human respiratory tract be accounted for when assessing the potential health hazard of airborne particulate matter.

Experimental measurements of the growth of monodisperse dry NH4HSO4 aerosols by H2O vapor condensation have been reported in the literature. These data are incorporated into an aerosol deposition model to study the behavior of inhaled NH4HSO4 particles, which is of concern in relation to human health. The tracheobronchial tree is described by Weibel's model A morphology, and Landahl's formulas are used to compute particle deposition efficiencies. Enhanced losses in the trachea due to the action of the laryngeal jet are accounted for by using an empirical deposition efficiency equation. The effect of NH4HSO4 aerosol growth is quantitated by comparisons of total and intrabronchial deposition probabilities with those of a nonhygroscopic aerosol of equal aerodynamic size. Computations indicate that hygroscopic growth effects are a function of the size of the particles inhaled. Total deposition efficiencies of NH4HSO4-H2O droplet aerosols are greater than those of nonhygroscopic aerosols only if the former originate from dry NH4HSO4 particles exceeding a critical geometric diamter of 0.3 micrometer. Growth effects are explained in terms of the relative efficiencies of the dominant deposition mechanisms active in the lung.

A laboratory system has been developed in which the atmosphere and fluid dynamics of the upper tracheobronchial (TB) tree of the human are simulated. It is used to measure the hygroscopic growth rates of monodisperse NaCl and bronchodilator (Isuprel® hydrochloride with and without glycerine) aerosols. Dry particles are mixed with water vapour-laden air at the entrance to a growth chamber temperature controlled at 37°C with a relative humidity (RH) between 88 and 95%. Hygroscopic growth rates increased with degree of RH and magnitude of Reynolds number in the chamber. The growth data are incorporated into an aerosol deposition model to calculate the effect of hygroscopic growth upon the dose distribution of medicinal aerosols in the human TB network. The model uses some original deposition formulae to compute particle deposition efficiencies. Calculations show that the rate of water vapour absorption within TB airways is an important factor affecting the fate of particles used in aerosol therapy. © 1982 British Occupational Hygiene Society.