Numerical Modeling of Deposition of Inhaled Particles in Central Human Airways (original) (raw)
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Aerosol Science and Technology, 2000
An area identi® ed as having a high priority by the National Research ( ) Council NRC 1998 relating to health effects of exposure to urban particulate matter is the investigation of particle deposition patterns in potentially-susceptible subpopulations. A key task for risk assessment is development and re® nement of mathematical models that predict local deposition patterns of inhaled particles in ( ) airways. Recently, computational¯uid dynamic modeling CFD h as provided the ability to predict local air¯ows and particle deposition patterns in various structures of the human respiratory tract. Although CFD results generally agree with available data from human studies, there is a need for experimental particle deposition investigations that provide more detailed comparisons with computed local patterns of particle deposition. Idealized 3-generation hollow tracheobronchial models based on the Weibel symmetric morphometry for airway lengths ( ) and diameters generations 3± 5 were constructed with physiologically-realistic ( bifurcations. Monodisperse¯uorescent polystyrene latex particles 1 and 10 m m ) aerodyn amic diameter were deposited in these models at a steady inspiratory¯ow ( ) of 7.5 L r r r r r min equivalent to heavy exertion with a tracheal¯ow of 60 L r r r r r min . The models were opened and the locations of deposited particles were mapped usinḡ uorescence microscopy. The particle deposition predictions using CFD for 10 m m particles correlated well with those found experimentally. CFD predictions were not available for the 1 m m diameter case, but the experimental results for such particles are presented.
In the present investigation, detailed two-phase flow modeling of airflow, transport and deposition of micro-particles (1–10 mm) in a realistic tracheobronchial airway geometry based on CT scan images under various breathing conditions (i.e. 10–60 l/min) was considered. Lagrangian particle tracking has been used to investigate the particle deposition patterns in a model comprising mouth up to generation G6 of tracheobronchial airways. The results demonstrated that during all breathing patterns, the maximum velocity change occurred in the narrow throat region (Larynx). Due to implementing a realistic geometry for simulations, many irregularities and bending deflections exist in the airways model. Thereby, at higher inhalation rates, these areas are prone to vortical effects which tend to entrap the inhaled particles. According to the results, deposition fraction has a direct relationship with particle aerodynamic diameter (for d p ¼1–10 mm). Enhancing inhalation flow rate and particle size will largely increase the inertial force and consequently, more particle deposition is evident suggesting that inertial impaction is the dominant deposition mechanism in tracheobronchial airways.
univ-ubs.fr
A CT based simplified upper human airway model was created by preserving all critical geometrical features. The fluid flow at breathing flow rates of 30 L/min and 60 L/min are numerically studied employing RANS and LES methodology. The deposition efficiency and the deposition patterns for the particle diameters 2, 4, 6, 8 and 10 µm are presented. In this paper special emphasis is given to the identification of possible hot spots of particle accumulation. Such spots might be responsible for the development of cancerous lesions. For smaller particle size (2µm and 4µm) RANS shows accumulations of particles (or hot spots) at epiglottis and just above glottis while LES shows negligible amount of particle accumulation. For bigger sized paticles (8µm and 10µm) the locations of the hot spots remain essentially the same in mouth and pharynx regions. The only difference between RANS and LES is that, RANS predicts a hot spot at the mouth roof while LES doesn't.
Journal of Aerosol Science, 2007
Investigation of the effect of sidewall and carinal tumours, airway constrictions and airway blockage on the inspiratory airflow and particle deposition in the large central human airways was the primary objective of this study. A computational fluid and particle dynamics model was implemented, validated and applied in order to simulate the air and particle transport and to quantify the aerosol deposition in double airway bifurcation models. Our investigations revealed that surface abnormalities and tubular constrictions can significantly alter the airstreams and the related local aerosol deposition distributions. Sidewall tumours have lead to an enhanced deposition of large particles and caused lower deposition efficiency values of nano-particles compared to the deposition efficiency in healthy airways. Central tumours multiplied the deposition efficiency of large particles but hardly affected the deposition efficiency of nano-particles. Airway blockage caused a significant redistribution of particle deposition sites. The deposition efficiency of the inhaled aerosols in constricted airways was much higher than the same deposition efficiency in healthy airways. Current results might help in the understanding of the adverse health effects of the inhaled air-pollutants in patients with lung disease and might be integrated into future aerosol therapy protocols.
It is recognised that knowledge of air flow characteristics in the tracheo-bronchial tree was essential to the understanding of airway resistance, intrapulmonary gas mixing, and deposition of airborne particles. Numerical and mathematical methods had previously been used extensively to obtain particle deposition patterns inside a single airway and various regions of the human lung for a range of physiological conditions. However, detailed analysis of particle deposition, in asymmetrical human upper airways, under transient conditions, had not been uncovered in published literature at the time this research commenced. In this research study, a commercial CFD package, called "CFX Workbench 11" was deployed to analyze flow fields, transient flow and particle deposition. This research work was an extension to earlier research published in 2008 by the authors here. The airway geometry applied in this current research was created by closely following the values published by another researcher (Horsfield), where the transient flows for three different breathing cycles were used as the input boundary conditions. The findings of the modelling presented herein indicated that the release position did not vary significantly at different time steps or with changes in particle size, but it did vary significantly with breathing patterns. Moreover, the rate of particle deposition at the wall was found to increase with the rising of the branching angles.
Micro Particles Transport and Deposition in Realistic Geometry of Human Upper Airways
2012
The realistic geometry of human upper airways from the mouth to the end of the trachea was reconstructed by implementing the CT-Scan images of a male subject. A computational simulation was developed for analyzing the airflow in the airways. To capture the anisotropy of the inhaled airflow in the upper airways, the Reynolds stress transport turbulence model was used in these simulations. The inhalation rates of 15, 30 and 60 l/min which represented the resting, normal and active conditions of human, respectively were underlined. The transport and deposition of micro particles in the realistic model of human upper airways were studied. The transport of micro particles was analyzed using the Lagrangian particle trajectory approach. Since the mass fraction of inhaled particles was very small, one-way coupling assumption was used. That is, the airflow carries the particles, but particles do not affect the airflow condition. The predicted deposition fractions of the particles of different sizes in the upper airways were compared with the available experimental data to find good agreements. Comparison of the results of the deposition fraction obtained from the realistic model with the earlier simulations of the idealized geometry of the airways showed certain differences especially in regional depositions. Therefore, it was concluded that the realistic geometry must be used for more accurate evaluation of micro particle deposition rates especially for local and regional depositions.
2019
In the present study, the realistic model of the human trachea with five generations that are obtained from computerized tomography scan images is considered. Due to the complexity of lung geometry, many researchers have used simple models. Therefore in the present study realistic model with all geometrical details are considered. The airflow behavior, particle transport and deposition in various conditions such as steady flow, transient flow, light breathing and heavy breathing condition for various micro-particles diameters are investigated. Governing equations are solved and obtained results show that the flow patterns in the realistic model are much more complicated than those of symmetrical models. Also, the particle deposition pattern in the realistic condition is very different from that of the symmetrical model and the details of the trachea are very important and affect the deposition fractions in the small airways. Also, results show that the turbulent effect should be cou...
Flow and particle deposition using an integrated CFD model of the respiratory system
2011
In the present study a theoretical investigation on flow, particle motion, and deposition in the respiratory system is reported. An integrated computational model of the respiratory system is developed comprised of nine sequential computational blocks corresponding to the nasal cavity, the pharyngo-trachea, and a series of branches of the pulmonary system. Airflow during steady-state inhalation inside the human respiratory system was determined using computational fluid dynamics (CFD) for inlet velocities, v in = 1-20 m/s, corresponding to inhalation flow rates of 9 to 180 L/min, and particle deposition was examined in detail for particle sizes, D=1-20μm. Local deposition efficiencies as well as spatial distribution of deposited particles were found to be strongly dependent on the particle size and volumetric flow rate.
Flow and Particle Deposition Patterns in a Realistic Human Double Bifurcation Airway Model
Inhalation Toxicology, 2007
Velocity profiles, local deposition efficiencies (DE) and deposition patterns of aerosol particles in the first three generations (i.e. double bifurcations) of an airway model have been simulated numerically, in which the airway model was constructed from CT scan data of real human tracheobronchial airways. Three steady inhalation conditions and a range of micron-particle sizes were simulated. The results indicate that the local DE in the first bifurcation increase with a rise in the Stokes number (St). DE in the second bifurcations (both left and right) is dropped dramatically after St increased to 0.17. Also, the second bifurcation in the right side was found to show a much higher (almost double) DE than the left side. This may be due to the fact that the left main bronchus is longer and has greater angulation than the right main bronchus. The present simulation proved that the current technique developed would be useful in clinical study.