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Prolonged exposure to inhaled micron-sized airborne particles is a known public health concern. These particles impact the health of staggering numbers of residents of polluted urban areas, as well as significant portions of the third world where it is still common to burn wood or charcoal indoors for cooking or heating. An understanding of the fate of inhaled particles in the lungs is useful for assessing their associated health risks, as well as improving the effectiveness of respiratory drug delivery techniques. The transport of microparticles is inseparable from behavior of the suspending airflow and this is studied using computational fluid dynamics techniques. The anatomy of the airways seems to have evolved to encourage turbulent airflow for functions such as mixing of flow to promote the warming and humidification of inhaled air, as well as for filtration. Large eddy simulation models are employed to capture turbulent flow in extremely complex patient-specific airway geometries. These collectively comprise the oral and nasal cavities, larynx, trachea, and the bronchial tree. The flow in anatomically-accurate rhesus macaque airways is also studied. Simulations are carried out for inspiratory flow rates corresponding to nominal Reynolds numbers in the hundreds to low-thousands yet somewhat surprisingly yield unsteady flows due to local geometric factors. A computed mean flow field is compared extensively with magnetic resonance velocimetry measurements carried out in the same computed-tomography--based lung geometry, showing good agreement. Microparticle deposition predictions are also verified. Focus is placed on the dynamics of the flow in the nasal airway, trachea, and bronchial tree. After becoming unsteady at constrictions in the upper airways, the flow is found to be chaotic, exhibiting fluctuations with broad-band spectra even at the most distal simulated airways in which the Reynolds numbers are as low as 300. The unsteadiness is attributed to the convection of turbulent structures produced in the upper airways as well as to local kinetic energy production throughout the bronchial tree.
The human nasal cavities, each with an effective length of only 10cm, feature a wide array of basic flow phenomena due to their complex geometries. Dependent on such airflow fields are the transport and deposition of micro- and nano- particles in the human nasal cavities, of interest to engineers, scientists, air-pollution regulators, and healthcare officials. By utilizing advanced CAD and reverse engineering skills, a realistic model of the human nasal cavity was constructed from MRI image data for 3-D computer simulations. Assuming laminar quasi-steady airflow, dilute micro- and nano-particle suspension flows and local deposition efficiencies were analyzed for 7.5
Traditional research methodologies in the human respiratory system have always been challenging due to their invasive nature. Recent advances in medical imaging and computational fluid dynamics (CFD) have accelerated this research. This book compiles and details recent advances in the modelling of the respiratory system for researchers, engineers, scientists, and health practitioners. It breaks down the complexities of this field and provides both students and scientists with an introduction and starting point to the physiology of the respiratory system, fluid dynamics and advanced CFD modeling tools. In addition to a brief introduction to the physics of the respiratory system and an overview of computational methods, the book contains best-practice guidelines for establishing high-quality computational models and simulations. Inspiration for new simulations can be gained through innovative case studies as well as hands-on practice using pre-made computational code. Last but not least, students and researchers are presented the latest biomedical research activities, and the computational visualizations will enhance their understanding of physiological functions of the respiratory system.
Keywords: CFD, drug delivery, airflow, particle deposition, nasal airway.
Currently serving as a resource for the National Center for Toxological Research in their work with the Gulf Coast oil spill, this book presents current research conducted primarily by the airforce on the toxic effects of JP-8 jet fuel on the pulmonary, immune, dermal, and nervous systems. In all, the book considers 13 toxicology studies
The aim of this work is to measure deposition patterns and efficiencies of aerosol particles within realistic, single-pathway physical models of the tracheobronchial airways of humans and experimental animals over a range of particle sizes for a variety of respiratory modes and rates. This will provide data needed to assess the dose to the bronchial epithelium from inhaled radon progeny. In prior grant years an empirical expression for diffusional deposition efficiency of particles in the upper airways was obtained based on experimental data collected in central airway casts. The work also provided new quantitative data of airflow distribution in a realistic central airway cast for two species for both steady and pulsatile inspiratory flow and for expiratory flow. Theoretical studies were then extended based on a developing flow model. We concluded that although the developing flow model is a better predictor of the data than assumption of parabolic flow, the predicted deposition is significantly lower than that predicted by our best fit equation. In the current year the experimental results were evaluated in terms of the parametric solution of the convective diffusion equation.
People may inhale 100 millions of particles each day, including toxic particulate matter as well as drug aerosols. Some of those deposited in the respiratory system can be either harmful or therapeutic to humans depending upon the particle material, deposition site, and local concentration. These transport and deposition phenomena as well as the resulting biomedical processes are greatly determined by the airflow field, particle properties, breathing pattern, and geometric airway characteristics. Realistic models of tracheobronchial and nasal⁄oral- tracheobronchial airways were built. Airflow and particle transport and deposition in these airway models were investigated in detail by mainly using the validated, in-house FORTRAN code CFPD (computational fluid-particle dynamics), which is a cell-centered, finite volume multi-block code. Both laminar and transitional-turbulent-laminar flows were considered for different transient and steady inhalation flow rates and inlet velocity profiles. The resulting effects of transients, upstream conditions and geometric characteristics, i.e., spatial angle and/or cartilaginous rings, are fully discussed. A new code based on the lattice-Boltzmann method (LBM) has been developed and validated to investigate airflow patterns and pressure changes in representative alveolar structures of the human respiratory zone. The new idea of targeted drug aerosol delivery technology was numerically tested for a more realistic human airway configuration and thereby addressing the problem of inter-subject variability. Specifically, controlled air-particle streams were studied using the oral and asymmetric tracheobronchial airway models. The results were compared with data obtained for a symmetric Weibel Type A tracheobronchial airway model.