A combined experimental and numerical study on upper airway dosimetry of inhaled nanoparticles from an electrical discharge machine shop

Backgrounds: Exposure to nanoparticles in the workplace is a health concern to occupational workers with increased risk of developing respiratory, cardiovascular, and neurological disorders. Based on animal inhalation study and human lung tumor risk extrapolation, current authoritative recommendations on exposure limits are either on total mass or number concentrations. Effects of particle size distribution and the implication to regional airway dosages are not elaborated. Methods: Real time production of particle concentration and size distribution in the range from 5.52 to 98.2 nm were recorded in a wire-cut electrical discharge machine shop (WEDM) during a typical working day. Under the realistic exposure condition, human inhalation simulations were performed in a physiologically realistic nasal and upper airway replica. The combined experimental and numerical study is the first to establish a realistic exposure condition, and under which, detailed dose metric studies can be performed. In addition to mass concentration guided exposure limit, inhalation risks to nano-pollutant were reexamined accounting for the actual particle size distribution and deposition statistics. Detailed dosimetries of the inhaled nano-pollutants in human nasal and upper airways with respect to particle number, mass and surface area were discussed, and empirical equations were developed. Results: An astonishing enhancement of human airway dosages were detected by current combined experimental and numerical study in the WEDM machine shop. Up to 33 folds in mass, 27 folds in surface area and 8 folds in number dosages were detected during working hours in comparison to the background dosimetry measured at midnight. The real time particle concentration measurement showed substantial emission of nano-pollutants by WEDM machining activity, and the combined experimental and numerical study provided extraordinary details on human inhalation dosimetry. It was found out that

CFD modelling of air flow and fine powder deposition in the respiratory tract

This project was to investigate and observe characteristics of micro particles suspended in the ambient air or pharmaceutical aerosols with respect to the mechanisms of deposition in human airways under different inspiratory conditions. Such determination includes pattern observations of inspiratory flow-field of the air, particle trajectory during inspiratory conditions and particle deposition. Computational fluid dynamic (CFD) was employed to simulate above problems, aiming to observe flow-field of the inspiratory air and characteristic of flow turbulence in the respiratory tract as well as particle behaviour in the respiratory tract regarding to the particle deposition. In order to do so, three different airway models were employed for the simulations: two realistic airway models introduced by Kitaoka and Weibel airways model. The motion of micro-sized particles between 1~20 μm were simulated under the steady state two inlet-inspiratory conditions – inhalation condition (60 L/min) and breathing condition (18 L/min); to evaluate deposition efficiency. Inertial impaction was dominantly caused high density deposition of particles in upper tracheobronchial region, particularly in regions where daughter airways bifurcate. Results also showed that the velocity in the first bifurcation of airway was higher than the inlet velocity. Back pressures were been observed in lower generations, and high pressures were been observed at every bifurcation regions. The increase of velocity was observed where the fluid directions rapidly changed. Turbulence kinetic energy was the least in main bronchus of respiratory tract and fluctuated from generation to generation. In Kitaoka’s generation 0-7 model, deposition fractions of 2 μm, 6 μm and 10 μm particles were 6.6%, 60.7% and 91.5% respectively under inhalation condition whereas deposition fractions of such particles were 2.9%, 9.0% and 44.9% under breathing condition. In Kitaoka’s generation 0-11 model, deposition fractions of 2 μm, 6 μm and 10 μm particles were 30.9%, 80.1% and 99.8% respectively under inhalation condition whereas deposition fractions of such particles were 16.2%, 24.4% and 62.6% under breathing condition. Furthermore in Weibel’s generation 3-6 model, deposition fractions of 2 μm, 6 μm and 10 μm particles were 9.7%, 38.3% and 97.4% respectively under inhalation condition whereas deposition fractions of such particles were 3.2%, 15.6% and 56.2% under breathing condition

Influence of human breathing modes on airborne cross infection risk

Producción CientíficaCFD simulation is an accurate and reliable method to predict the risk of airborne cross-infection in a room. This paper focuses on the validation of a 3-D transient CFD model used to predict personal exposure to airborne pathogens and infection risk in a displacement ventilated room. The model provides spatial and temporal solutions of the airflow pattern in the room (temperature, velocity and turbulence), as well as contaminant concentration in a room where two thermal manikins simulate two standing people, one of whom exhales a tracer gas N2O simulating airborne contaminants. Numerical results are validated with experimental data and the model shows a high accuracy when predicting the transient cases studied. Once the model is validated, the CFD model is used to simulate different airborne cross-infection risk scenarios. Four different combinations of the manikins’ breathing modes and four different separation distances between the two manikins are studied. The results show that exhaling through the nose or mouth disperses exhaled contaminants in a completely different way and also means that exhaled contaminants are received differently. For short separation distances between breathing sources the interaction between breaths is a key factor in the airborne cross-infection for all the breathing mode combinations studied. However, for long distances the general airflow conditions in the room prove to be more important.Spanish Ministry of Economy and Competiveness to the National R&D project TRACER with references DPI2014-55357-C2-1-R and DPI2014-55357-C2-2-R. This project is cofinanced by the European Regional Development Fund (ERDF)

Modeling of Airflow Characteristics and Particle Deposition in Human Upper Respiratory Tract Using CFD Simulations

The objectives are to analyze the mechanisms of airflow and particle transport in the extrathoracic airways. Understanding these features in greater detail not only helps in the treatment of diseases related to the respiratory tract but also aims to reduce the amount of animal testing. For the evaluation, computational fluid dynamic (CFD) simulations were utilized. ANSYS was used as a leading software to perform a simulation of different inspiratory flow rates. In this work, Large Eddy Simulations (LES) is engaged due to its real-world performance. The geometry of the upper airways is obtained from CT scans, to preserve the topological data of the upper airways. Furthermore, the deposition of inhaled particles of varying diameters 1-10 m was examined, helping us better understand the therapeutic effects of inhaled particles. Two types of inhalations simulations were carried out. First, inhalation through the nose, simulating the inhalation with a nebulizer with airflow rates of 15 l/min and 30 l/min. Second, through mouth simulating inhalation with a dry-powder inhaler with a flow rate of 90 l/min. Simulated results show that most of the particles deposit at the entrance of the nasal or oral cavity. When flow rates of 15 and 30 l/min were compared, it can be seen the higher initial velocity is, the particles of large diameter (6-10 m) are stuck in the nasal cavity and do not appear in the laryngeal region, whereas with low velocity the more particles of 6-10 m can be found in this region. The maximum number of particles leaving the trachea was observed with a flow rate of 15 l/min, accounting for 26 %. As opposed to 90 l/min where only 13 % left the upper respiratory tract. Also, typical pressure drop can be observed in pressure contours describing the larynx region. This was most significant for a flow rate of 90 l/min where the pressure from the oropharynx to subglottis dropped by 490 Pa.The objectives are to analyze the mechanisms of airflow and particle transport in the extrathoracic airways. Understanding these features in greater detail not only helps in the treatment of diseases related to the respiratory tract but also aims to reduce the amount of animal testing. For the evaluation, computational fluid dynamic (CFD) simulations were utilized. ANSYS was used as a leading software to perform a simulation of different inspiratory flow rates. In this work, Large Eddy Simulations (LES) is engaged due to its real-world performance. The geometry of the upper airways is obtained from CT scans, to preserve the topological data of the upper airways. Furthermore, the deposition of inhaled particles of varying diameters 1-10 m was examined, helping us better understand the therapeutic effects of inhaled particles. Two types of inhalations simulations were carried out. First, inhalation through the nose, simulating the inhalation with a nebulizer with airflow rates of 15 l/min and 30 l/min. Second, through mouth simulating inhalation with a dry-powder inhaler with a flow rate of 90 l/min. Simulated results show that most of the particles deposit at the entrance of the nasal or oral cavity. When flow rates of 15 and 30 l/min were compared, it can be seen the higher initial velocity is, the particles of large diameter (6-10 m) are stuck in the nasal cavity and do not appear in the laryngeal region, whereas with low velocity the more particles of 6-10 m can be found in this region. The maximum number of particles leaving the trachea was observed with a flow rate of 15 l/min, accounting for 26 %. As opposed to 90 l/min where only 13 % left the upper respiratory tract. Also, typical pressure drop can be observed in pressure contours describing the larynx region. This was most significant for a flow rate of 90 l/min where the pressure from the oropharynx to subglottis dropped by 490 Pa.

Numerical studies of fluid-particle dynamics in human respiratory system

 This thesis investigates particle inhalation and its deposition in the human respiratory system for therapeutic and toxicology studies. Computational Fluid Dynamics (CFD) techniques including the Lagrangian approach to simulate gas-particle flows based on the domain airflow are used. The Lagrangian approach is used as it tracks each individual particle and determines its fate (e.g deposition location, or escape from computational domain). This has advantages over a Eulerian approach for respiratory inhalation flows as the volume fraction of the second phase can be neglected and a disperse phase for one-way coupling can be used. However, the very first step is to simulate and detail airflow structures. For the external airflow structures, the heat released from the human body has a significant effect on the airflow micro-environment around it in an indoor environment, which suggests that the transport and inhalation characteristics of aerosol particulates may also be affected since they are entrained by the air and their movement is dependent on the airflow field. Emphasis was put on the effect of human body heat on particle tracks. It was found that body heat causes a significant rising airflow on the downstream side of the body, which transports particles from a lower level into the breathing zone. The importance of body heat decreases with increasing indoor wind speed. Since the rising airflow exists only on the downstream side of an occupant, the occupant-wind orientation plays an important role in particle inhalation. The effect of body heat has to be taken into account when an occupant had his or her back to the wind, and the effect of body heat could be neglected when the occupant is facing the wind. A CFD model that integrates the three aspects of contaminant exposure by including the external room, human occupant with realistic facial features, and the internal nasal-trachea airway is presented. The results from the simulations visualize the flow patterns at different contaminant concentrations. As the particles are inhaled, they are transported through the respiratory airways, where some are deposited onto surrounding mucus walls while others may navigate through the complex geometry and even reach the lung airways, causing deleterious health effects. The studies in this thesis demonstrated that the transport and deposition of micron sized particles are dominated by its inertial property while submicron and nano sized particles are influenced by diffusion mechanisms. Studies based on an isolated model of the human nasal cavity or tracheobronchial airway tree rely on idealised inlet boundary condition imposed at the nostril or where, were a blunt, parabolic or uniform profile is applied. It is apparent that an integrated model made up of: i) room and ventilation, ii) aspiration efficiency, iii) and particle deposition efficiencies in the respiratory airway is needed. This leads to a more complete and holistic set of results, which can greatly contribute towards new knowledge in identifying preventative measures for health risk exposure assessment. With regards to the internal airflow structures and particle inhalation, ultrafine particle deposition sites in the human nasal cavity regions often omit the paranasal sinus regions. Because of the highly diffusive nature of nanoparticles, it is conjectured that deposition by diffusion may occur in the paranasal sinuses, which may affect the residual deposition fraction that leaves the nasal cavity. Thus a nasal-sinus model was created for analysis. In general there was little flow passing through the paranasal sinuses. However, flow patterns revealed that some streamlines reached the upper nasal cavity near the olfactory regions. These flow paths promote particle deposition in the sphenoid and ethmoid sinuses. Some differences were discovered in the deposition fractions and patterns for 5 and 10nm particles between the nasal-sinus and the nasal cavity models. This difference is amplified when the flow rate is decreased and at a flow rate of 4L/min the maximum difference was 17%. It is suggested that future evaluations of nanoparticle deposition should consider some deposition occurring in the paranasal sinuses especially if flow rates are of concern. Inhaled particles with pharmacological agents (e.g. histamine, methacholine) are introduced into the nasal cavity for targeted delivery. Effective nasal drug delivery is highly dependent on the delivery of the drug from the nasal spray device. Atomization of liquid spray occurs through the internal atomizer that can produce many forms of spray patterns and two of these, hollow-cone and full-cone sprays, are evaluated in this study to determine which spray pattern produced greater deposition in the middle regions of the nasal cavity. Past studies of spray particle deposition have ignored the device within the nasal cavity. Experimental measurements from a Particle Droplet Image Analyzer (PDIA) were taken in order to gain confidence to validate the initial particle conditions for the computational models.. Subsequent airflow patterns and its effects on particle deposition, with and without a spray device, are compared. Contours and streamlines of the flow field revealed that the presence of a spray device in the nasal vestibule produced higher levels of disturbed flow, which helped the dispersion of the sprayed particles. Particle deposition was found to be high in the anterior regions of the nasal cavity due to its inertia. Evaluation of the two spray types found that hollow spray cones produced more deposition in the middle regions of the nasal cavity