Estimation of fibrous aerosol deposition in upper bronchi based on experimental data with model bifurcation

Lagrangian tracking of fibres in a channel flow

Tracking of fibres in a fluid flow is much more complicated than tracking of spherical particles. In fibre motion, the orientation of fibre against the flow direction plays a very important role. In addition to the standard equation of motion, additional equations for orientation and angular velocity must be solved during the tracking of fibres. A mathematical model describing fibre motion is introduced in this work. Capabilities of this model are demonstrated through simulations of fibre transportation by air in a channel flow. The importance of the terms in the equation of angular velocity are discussed.

Insulation fiber deposition in the airways of men and rats. A review of experimental and computational studies

The typical insulation rock, slag and glass wool fibers are high volume materials. Current exposure levels in industry (generally ≤ 1 fiber/cm³ with a median diameter ∼1 μm and length ≥10 μm) are not considered carcinogenic or causing other types of severe lung effects. However, epidemiological studies are not informative on effects in humans at fiber levels >1 fiber/cm³. Effects may be inferred from valid rat studies, conducted with rat respirable fibers (diameter ≤ 1.5 μm). Therefore, we estimate delivery and deposition in human and rat airways of the industrial fibers. The deposition fractions in humans head regions by nasal (∼0.20) and by mouth breathing (≤0.08) are lower than in rats (0.50). The delivered dose into the lungs per unit lung surface area during a 1-day exposure at a similar air concentration is estimated to be about two times higher in humans than in rats. The deposition fractions in human lungs by nasal (∼0.20) and by mouth breathing (∼0.40) are higher than in rats (∼0.04). The human lung deposition may be up to three times by nasal breathing and up to six times higher by oral breathing than in rats, qualifying assessment factor setting for deposition.

Computational Analysis of Non-Spherical Particle Transport and Deposition in Shear Flow With Application to Lung Aerosol Dynamics—A Review

All naturally occurring and most man-made solid particles are nonspherical. Examples include air-pollutants in the nano- to micro-meter range as well as blood constituents, drug particles, and industrial fluid-particle streams. Focusing on the modeling and simulation of inhaled aerosols, theories for both spherical and nonspherical particles are reviewed to analyze the contrasting transport and deposition phenomena of spheres and equivalent spheres versus ellipsoids and fibers.

A theoretical approach to the deposition and clearance of fibers with variable size in the human respiratory tract

In the study presented here, a mathematical approach for the deposition and clearance of rigid and chemically stable fibers in the human respiratory tract (HRT) is described in detail. For the simulation of fiber transport and deposition in lung airways an advanced concept of the aerodynamic diameter is applied to a stochastic lung model with individual particle trajectories computed according to a random walk algorithm. Interception of fibrous material at airway bifurcations is considered by implementation of correction factors obtained from previously published numerical approaches to fiber deposition in short bronchial sequences. Fiber clearance is simulated on the basis of a multicompartment model, within which separate clearance scenarios are assumed for the alveolar, bronchiolar, and bronchial lung region and evacuation of fibrous material commonly takes place via the airway and extrathoracic path to the gastrointestinal tract (GIT) or via the transepithelial path to the lymph nodes and blood vessels. Deposition of fibrous particles in the HRT is controlled by the fiber aspect ratio beta in as much as particles with diameters <0.1 microm deposit less effectively with increasing beta, while larger particles exhibit a positive correlation between their deposition efficiencies and beta. A change from sitting to light-work breathing conditions causes only insignificant modifications of total fiber deposition in the HRT, whereas alveolar and, above all, tubular deposition of fibrous particles with a diameter >or=0.1 microm are affected remarkably. For these particles enhancement of the inhalative flow rate results in an increase of the extrathoracic and bronchial deposition fractions. Concerning the clearance of fibers from the HRT, 24-h retention is noticeably influenced by beta and, not less important, by the preferential deposition sites of the simulated particles. The significance of beta with respect to particle size may be regarded as similar to that determined for the deposition scenarios, while breathing conditions do not have a valuable effect on clearance.

Simulation of Fiber Deposition in Bronchial Airways

Penetration probabilities of inhaled man-made mineral fibers to reach central human airways were computed by a stochastic lung deposition model for different flow rates and equivalent diameters. Results indicate that even thick and long fibers can penetrate into the central airways at low flow rates. Deposition efficiencies and localized deposition patterns were then computed for man-made fibers with variable lengths in a three-dimensional physiologically realistic bifurcation model of the central human airways by computational fluid dynamics (CFD) techniques for characteristic breathing patterns. The results obtained for inspiratory flow conditions indicate that deposition efficiencies were highest for parallel orientation of the fibers, increasing with rising flow rate, branching angle, and fiber length at all orientations. Furthermore, deposition patterns were highly inhomogeneous and their localized distributions showed hot spots in the vicinity of the carinal ridge and at the inner sides of the daughter airways. Comparisons with other theoretical results demonstrate that the equivalent diameter concept, if including interception, presents a reasonable approximation for the parameter ranges employed in the present study.

A computer program for the simulation of fiber deposition in the human respiratory tract

As inhaled fibers may lead to a variety of lung diseases, detailed information on their deposition in the human respiratory tract is an indispensable requirement in medical science. In the work presented here, a Visual Basic((R)) computer program, termed FIBROS, is described which enables the simulation of fibrous particle deposition in both the extrathoracic region and different parts of the lung itself, including the results of published numerical studies on inertial/interceptional as well as diffusional and gravitational deposition. The input window of FIBROS includes the selection of specific breathing conditions by variation of the tidal volume and breathing cycle. Furthermore, the user is able to determine fiber properties such as diameter, aspect ratio, specific weight, and fiber orientation with respect to the air stream in the upper and lower airways of the lungs. Besides the offer of various deposition formulae for each region of the respiratory tract, thereby also allowing a distinction between mouth and nose breathing, the user may select between different morphometric datasets of the lung and respective airway scaling procedures. Analysis routines of FIBROS include the estimation of regional deposition fractions, thereby distinguishing between extrathoracic, bronchial, and acinar compartments, and a calculation of generation-by-generation deposition probabilities within tubular and alveolar structures. Preliminary results presented here should demonstrate the effects on fiber deposition due to variations of the breathing behaviour and the particle properties.

Inertial deposition effects: a study of aerosol mechanics in the trachea using laser Doppler velocimetry and fluorescent dye

This study characterizes the axial velocity and axial turbulence intensity patterns noted in the tracheal portion of a cadaver-based throat model at two different steady flow rates (18.1 and 41.1 LPM.) This characterization was performed using Phase Doppler Interferometry (Laser Doppler Velocimetry). Deposition, as assessed qualitatively using fluorescent dye, is related to the position of the laryngeal jet within the trachea. The position of the jet is dependent on the downstream conditions of the model. It is proposed therefore that lung/airway conditions may have important effects on aerosol deposition within the throat. There is no correspondence noted between regions of high axial turbulence intensity and deposition.