Deposition of Ultrafine Aerosols in a Human Oral Cast

This paper reports experimental measurements of the total deposition of ultrafine aerosols in a human oral airway cast. A clear polyester resin cast of the upper airways of a normal human adult, including the nasal airways, oral cavity, tongue, nasopharynx, and larynx, was made from a postmortem solid cast. Measured pressure drop in the oral airway was slightly lower than in the nasal airway. The measured oral flow resistance was similar to the values reported for human volunteers breathing through the mouth at rest and for spontaneously opening of the mouth. Aerosol deposition data in the cast for monodisperse NaCl aerosols between 0.2 and 0.005 μm in diameter deposited in the cast were obtained for inspiratory and expiratory flow rates of 4, 20, and 40 L/min. Deposition efficiency increased with decreasing particle size and flow rate indicating that turbulent diffusion was the dominant mechanism for deposition. Higher deposition efficiency was observed for inspiratory flow in the oral airway than for expiratory flow. Oral deposition and nasal deposition for inspiratory flow were similar, but oral deposition was lower for expiratory flow. Deposition efficiency can be expressed as a function of the flow rate and diffusion coefficient of the particle.     

Particle Deposition in a Cast of Human Tracheobronchial Airways

Abstract

Regional particle deposition efficiency and deposition patterns were studied experimentally in a human airway replica made from an adult cadaver. The replica includes the oral cavity, pharynx, larynx, trachea, and four generations of bronchi. This study reports deposition results in the tracheobronchial (TB) region. Nine different sizes of monodispersed, polystyrene latex fluorescent particles in the size range of 0.93–30 μm were delivered into the lung cast with the flow rates of 15, 30, and 60 l min^{? 1}. Deposition in the TB region appeared to increase with the increasing flow rate and particle size. Comparison of deposition data obtained from physical casts showed agreement with results obtained from realistic airway replicas that included the larynx. Deposition data obtained from idealized airway models or replicas showed lower deposition efficiency. We also compared experimental data with theoretical models based on a simplified bend and bifurcation model. A deposition equation derived from these models was used in a lung dosimetry model for inhaled particles, and we demonstrated that there was general agreement with theoretical models. However, the agreement was not consistent over the large range of Stokes number. The deposition efficiency was found as a function of the Stokes number, bifurcation angle, and the diameters of parent and daughter tubes. An empirical model was developed for the particle deposition efficiency in the TB region based on the experimental data. This model, combined with the oral deposition model developed previously, can be used to predict the particle deposition for inertial effects with improved accuracy.     

Aerosol Deposition in the Extrathoracic Region

The extrathoracic region, including the nasal and oral passages, pharynx, and larynx, is the entrance to the human respiratory tract and the first line of defense against inhaled air pollutants. Estimates of regional deposition in the thoracic region are based on data obtained with human volunteers, and that data showed great variability in the magnitude of deposition under similar experimental conditions. In the past decade, studies with physical casts and computational fluid dynamic simulation have improved upon the understanding of deposition mechanisms and have shown some association of aerosol deposition with airway geometry. This information has been analyzed to improve deposition equations, which incorporate characteristic airway dimensions to address intersubject variability of deposition during nasal breathing. Deposition in the nasal and oral airways is dominated by the inertial mechanism for particles >0.5 w m and by the diffusion mechanism for particles <0.5 w m. Deposition data from adult and child nasal airway casts with detailed geometric data can be expressed as E n = 1 m exp( m 110 Stk), where the Stokes number is a function of the aerodynamic diameter ( d a ), flow rate ( Q ), and the characteristic nasal airway dimension, the minimum cross-sectional area ( A min ). In vivo data for each human volunteer follow the equation when the appropriate value of A min is used. For the diffusion deposition, in vivo deposition data for ultrafine particles and in vivo and cast data for radon progeny were used to derive the following deposition: E n = 1 m exp( m 0.355 S f 4.14 D 0.5 Q m 0.28 ), where S f is the normalized surface area in the turbinate region of the nasal airway, and D is the diffusion coefficient. The constant is not significantly different for inspiratory deposition than for expiratory deposition. By using the appropriate characteristic dimension, S f , one can predict the variability of in vivo nasal deposition fairly well. Similar equations for impaction and diffusion deposition were obtained for deposition during oral breathing. However, the equations did not include airway dimensions for intersubject variability, because the data set did not have airway dimension measurements. Further studies with characteristic airway dimensions for oral deposition are needed. These equations could be used in lung deposition models to improve estimates of extrathoracic deposition and intersubject variability.     

Deposition of Inhaled Ultrafine Aerosols in Replicas of Nasal Airways of Infants

Experimentally measured deposition of ultrafine particles, ranging from 13–100 nm in diameter, in nasal airway replicas of ten infants aged 3–18 months is presented. The replicas included the face, nostrils, and nasal airways including the upper trachea. A differential mobility analyzer (DMA) and a condensation particle counter (CPC) were used to quantify the nasal deposition by comparing the number of polydisperse sodium chloride particles, generated by evaporation from a Collison atomizer, at the inlet and outlet of the replicas. Particles were individually classified in size by DMA and subsequently were counted one size bin at a time by CPC upstream and downstream of each replica. Since in vivo data is not available for infants to compare to, we validated our experimental procedure instead by comparing deposition in nasal airway replicas of six adults with in vivo measurements reported in literature. In the infant replicas, tidal inhalation was simulated at two physiologically compatible flow rates and the effect of flow rate on deposition was found to be small. Deposition obtained at constant flow rates is lower than with tidal breathing, indicating the importance of unsteadiness, in contrast to similar data in adults where unsteadiness is known to be unimportant. An empirical equation, containing geometrical features of the nasal airways in the form of related non-dimensional dynamical parameters (Reynolds, Schmidt, and Womersley numbers), was best fitted to the infant data. This equation may be useful for a priori prediction of nasal deposition and intersubject variability during exposure of infants to ultrafine aerosols.     

Particle deposition in a hollow cast of the human tracheobronchial tree

The deposition of particles within the human airways was studied using a hollow silicone rubber cast of the larynx and tracheobronchial tree which extended to bronchi of approximately 0.2 cm dia. The cast was exposed to radioactively tagged, ferric oxide aerosols, having mass median aerodynamic diameters ranging from 2.5 to 8.1 μm. at three constant “inspiratory” flow rates. The detection system was designated for the determination of deposition within airways of all sizes and at various branch levels, and to allow selective measurements of the deposited activity within bifurcation and length regions of individual bronchi. Deposition efficiencies were determined and classified according to branch generation. Bifurcations were sites of preferential deposition over the range of particle sizes and flow rates used; bifurcation deposition generally peaked in generation 3.     

Microparticle Transport and Deposition in the Human Oral Airway: Toward the Smart Spacer

A key issue in pulmonary drug delivery is improving the medical delivery device for effective and targeted treatment. Spacers are clear plastic containers attached to inhalers aimed at delivering more drug particles to the respiratory tract. The spacer's one-way valve plays an important role in controlling and initializing the particles into the oral cavity. This article studied particle inhalation and deposition in an idealized oral airway geometry to better optimize the spacer one-way valve shape and design. Three steady flow rates were used 15, 30, and 60 l/min and a Lagrangian, one-way coupling particle tracking model with near-wall turbulence fluctuation correction was used to determine the deposition rates. For all three breathing rates, the velocity field in the midsagittal plane showed similar gross fluid dynamics characteristics, such as the separation and recirculation regions that occur after the larynx. The particle deposition rates compared reasonably well with available experiments. Most particles deposited at the larynx, where the airway has a decreasing cross-sectional area. For different particles sizes, most particles introduced at the lower region of the mouth show higher possibility to pass through upper airway and enter the trachea and lung airways. The particle deposition patterns in the airway were traced back to their initial inlet position at the oral inlet; and this information provides the background for a conceptual and optimized design of the spacer one-way valve.

Copyright 2015 American Association for Aerosol Research     

Micro-particle transport and deposition in a human oral airway model

Laminar-to-turbulent air flow for typical inhalation modes as well as micro-particle transport and wall deposition in a representative human oral airway model have been simulated using a commercial finite-volume code with user-enhanced programs. The computer model has been validated with experimental airflow and particle deposition data sets. For the first time, accurate local and segmentally averaged particle deposition fractions have been computed under transitional and turbulent flow conditions. Specifically, turbulence that occurs after the constriction in the oral airways for moderate and high-level breathing can enhance particle deposition in the trachea near the larynx, but it is more likely to affect the deposition of smaller particles, say, St<0.05. Particles released around the top/bottom zone of the inlet plane more easily deposit on the curved oral airway surface. Although more complicated geometric features of the oral airway may have a measurable effect on particle deposition, the present simulations with a relatively simple geometry exhibit the main features of laminar-transitional-turbulent particle suspension flows in actual human oral airways. Hence, the present model may serve as the “entryway” for simulating and analyzing airflow and particle deposition in the lung.     

A Charge Coupled Device System to Image Local Particle Deposition Patterns in a Model of a Human Nasal Airway

A new method was developed to measure local particle deposition patterns in a full-scale multisectional replica of a human nasal airway. Monodisperse dioctyl sebacate aerosol particles, labeled with the fluorescent dye Nile Red, were deposited in a human nasal airway model by drawing the aerosol through the replica at a constant airflow rate. Particle deposition patterns were then measured for each section of the model by using a charge coupled device to record particle fluorescence patterns. Customized imaging analysis software was used to extract the position and intensity of fluorescent sites. A resolution of 0.3 mm on fluorescent particle position was achieved. This method can be used to develop more efficient techniques for delivering medicinal drugs to the human body via inhalation and to understand better the mechanisms that control particle deposition in the geometrically complex nasal airways.     

CFD simulation of particle deposition in a reconstructed human oral extrathoracic airway for air and helium–oxygen mixtures

In order to compare the effects of using helium–oxygen and air in assisted breathing and inhalation therapies, flow and particle deposition results were obtained in a realistic model of human oral extrathoracic (ET) airways using computational fluid dynamics (CFD) and pressure loss measurements. As the main deposition mechanism for pharmaceutical aerosols in the ET is inertial impaction, the ET model was reconstructed from medical images to take into account the complexity of realistic morphological features. Calculations were performed with the CFD software Fluent^®, and pressure losses were measured on a cast based on a stereolithographic fabrication of the model. Results show that ET pressure loss and particle deposition are lower with helium–oxygen as compared to air. Moreover, further simulations were performed with various particle sizes and inspiratory flow rates, which indicate that particle deposition in the ET depends on both the Stokes and Reynolds number.     

Deposition of Ultrafine Particles in Human Tracheobronchial Airways of Adults and Children

Inhalation exposure to ultrafine particles, including radon progeny and other combustion aerosols, has been implicated in potential health risks of ambient and indoor environments. These particles deposit in the respiratory tract mainly by diffusion. The purpose of this study was to determine the deposition pattern of nanometer-sized particles in the human tracheobronchial (TB) airways of children and young adults. The deposition was determined for 1.75, 10, and 40 nm ²¹²Pb particles at flow rates corresponding to respiratory minute volumes at rest and during moderate exercise. The 1.75 nm particles were unattached clusters, whereas the 10 and 40 nm particles were silver particles with attached ²¹²Pb clusters. Replicate casts of the upper TB airways of 3, 16, and 23 year old humans were used, including the larynx, trachea, and bronchial airways down to generations 5-8. Deposition in each generation and total deposition were measured by counting the ²¹²Pb gamma photopeak in a NaI (Tl) detector. The effects of airway geometry, particle size, and flow rate on deposition efficiency were studied. The deposition of the 1.75 nm particle, corresponding to unattached indoor radon progeny, was substantially higher than that of the 10 and 40 nm particles. The dependence of particle deposition on the flow rate was relatively weak, and deposition efficiencies were only slightly higher at the lower flow rates. The deposition models for diffusion from parabolic flow underestimated aerosol deposition, whereas the diffusion deposition predicted for plug flow overestimated the TB deposition. The deposition models resulting from this study can be used for developing lung deposition models and in the risk assessment of radon progeny and ultrafine ambient particles.     

Deposition of Man-Made Fibers in a Human Nasal Airway

Many occupational lung diseases are associated with exposure to aerosolized fibers in the workplace. The nasal airway is a critical route for fiber aerosol to enter the human respiratory tract. The fiber deposition efficiency in the nasal airway could be used as an index to indicate the fraction of the inhaled fibers potentially transported to the lower airways. In this research, experiments of fiber deposition in the human nasal airway were conducted. Man-made carbon, glass, and titanium dioxide fibers in the inertia regime were used as the test fiber materials. The deposition studies were carried out by delivering aerosolized fibers into a human nasal airway replica at constant human inspiratory flow rates ranging from 15 l/min to 43.5 l/min. The deposition results were compared in detail between these fiber materials to study how the fiber characteristics affected the nasal airway deposition. The results showed that the deposition efficiency of the carbon fiber increases as the fiber impaction parameter increases. Many carbon fibers deposited in the anterior region of the nasal airway. In contrast, very few glass or titanium dioxide fibers deposited in the nasal airway, but relatively more of these two fibers deposited in the turbinate region. This result implies that, if a fiber in the inertia regime is inhaled during normal human breathing, the smaller the fiber, the more easily it could enter the human lower respiratory tract, possibly causing harm to the human respiratory tract.     

Deposition of Fiber in the Human Nasal Airway

Inhalation is the main route for aerosol entering the human body. Many occupational lung diseases are associated with exposure to fiber aerosol in the workplace. However, very few studies to date have been conducted for investigating fiber deposition in the human airway. As a result, there is a notable lack of information on the nature of the fiber deposition pattern in the human respiratory tract. With this in mind, this research consisted of a large number of experimental works to investigate the effects of fiber dimension on the deposition pattern for a human nasal airway. Carbon fibers with uniform diameter (3.66 μm) and polydispersed length were adopted as the test material. Deposition studies were conducted by delivering aerosolized carbon fibers into a nasal airway replica (encompassing the nasal airway regions from vestibule to nasopharynx) at constant inspiratory flow rates of 7.5, 15, 30, and 43.5 l/min. Fibers deposited in each nasal airway region were washed out and the length distribution was determined by microscopic measurement. The results showed that impaction is the dominant deposition mechanism. Most of the fibers with high inertia deposited in the anterior region of the nasal airway (vestibule and nasal valve). In contrast, fibers with low inertia were found to pass through the entire nasal airway easily and collected on the filter at the outlet. Comparing the deposition results between fibers and spherical particles, our data showed that the deposition efficiencies of fibers are significantly lower than that of spherical particles, which implies that the inhaled fibers could pass through the entire nasal airway comparatively easier than spherical particles. Thus, relatively more fibers would be able to enter the lower respiratory tract.     

Deposition of Ultrafine Aerosols and Thoron Progeny in Replicas of Nasal Airways of Young Children

The deposition efficiencies of ultrafine aerosols and thoron progeny were measured in youth nasal replicas. Clear polyester-resin casts of the upper airways of 1.5-yr-old (Cast G), 2.5-yr-old (Cast H), and 4-yr-old (Cast I) children were used. These casts were constructed from series of coronal magnetic resonance images of healthy children. The casts extended from the nostril tip to the junction of the nasopharynx and pharynx. These casts were similar in construction to those used in previous studies (Swift et al. 1992; Cheng et al. 1993). Total deposition was measured for monodisperse NaCl or Ag aerosols between 0.0046 and 0.20 (Jim in diameter at inspiratory and expiratory flow rates of 3, 7, and 16 L min^?1 (covering a near-normal range of breathing rates for children of different ages). Deposition efficiency decreased with increasing particle size and flow rate, indicating that diffusion was the main deposition mechanism. Deposition efficiency also decreased with increasing age at a given flow rate and particle size. At 16 L min^?1, the inspiratory deposition efficiencies in Cast G were 33% and 6% for 0.008- and 0.03-μm particles, respectively. Nasal deposition of thoron progeny with a mean diameter of 0.0013 μm was substantially higher (80%-93%) than those of the ultrafine aerosol particles, but still had a similar flow dependence. Both the aerosol and thoron progeny data were used to establish a theoretical equation relating deposition efficiency to the diffusion coefficient (D in cm² s^?1) and flow rate (Q in L min^?1) based on a turbulent diffusion process. Data from all casts can be expressed in a single equation previously developed from an adult nasal cast: E = 1 - exp(-aD ^0.5 Q ^?0.125). We further demonstrated that the effect of age, including changes to nasal airway size and breathing flow rate, on nasal deposition can be expressed in the parameter “a” of the fitted equation. Based on this information and information on minute volumes for different age groups, we predicted nasal deposition in age groups ranging from 1.5- to 20-yr-old at resting breathing rates. Our results showed that the nasal deposition increases with decreasing age for a given particle size between 0.001 to 0.2 μm. This information will be useful in deriving future population-wide models of respiratory tract dosimetry.     

Experiments on Particle Deposition in the Human Upper Respiratory System

ABSTRACT

In this study, the deposition of particles (0.3 μm to 2.5 μm in diameter) within a silicone rubber model of the human upper respiratory system was studied. The domain of the respiratory tract under investigation begins at the entrance (nostrils and mouth) and continues through to the second generation of the tracheobronchial airways (main bronchi). The particle deposition efficiency of the sample respiratory system was computed by measuring particle concentration at the inlet and outlet of the model. The regional deposition patterns of fluorescent particles (0.3 μm to 0.7 μm in diameter) was examined by measuring the fluorescent intensity with a fluorescence spectrophotometer. For simulated oral inhalation, the deposition efficiency of the oral cavity (0.9%-5.4%) is approximately the same as that of the oropharynx-trachea region (0.8%-4.8%). During simulated nasal inhalation, the deposition efficiency of the nasal region (20%-43.6%) is greater than the values of the nasopharynx-trachea region (2.8%-8.2%). The nasopharynx-trachea region exhibits a higher deposition efficiency than that of the oropharynx-trachea region. Deposition during the simultaneous oral and nasal inhalation is mostly affected by particle size. Flow rate through the model has less effect on deposition for particle diameter less than 1 μm. When particle diameter is greater than 1 μm deposition efficiencies are weakly and inversely related to the flow rate.     

In vitro deposition measurement of inhaled micrometer-sized particles in extrathoracic airways of children and adolescents during nose breathing

An in vitro study was conducted with the goal of developing empirical correlations to predict the deposition of particles with an aerodynamic diameter of 0.5–5.3 μm in nasal airways of children with ages 4–14 years. CT images of nasal airways of thirteen healthy subjects and one with congested nasal airways were used for fabricating the replicas by rapid prototyping. Replicas included nasal airways to the level of the upper trachea as well as the face. Four physiological breathing patterns (sinusoidal waves) of children were simulated by a pulmonary waveform generator. Using an Electrical Low Pressure Impactor (ELPI) we measured deposition of sunflower oil particles generated by a Collison atomizer. Moreover, using the same setup, particle deposition in five adult replicas fabricated using MRI images was measured for direct comparison with the child replicas and in vivo data available for adults. Deposition increased by increasing particle size and flow rate, indicating impaction as the dominant deposition mechanism. Existing correlations for adults were unable to reduce the scatter in the deposition data for children. A correlation was developed for prediction of deposition including the relevant non-dimensional numbers (Stokes and Reynolds numbers) that were calculated considering the dimensions of the airways. The corrected correlations should be useful for exposure estimation of children and for efficient pediatric drug delivery using face masks.     

Deposition of fiber in a human airway replica

Fiber is a notorious occupational hazard. Exposures to airborne asbestos fiber in the workplace increase the incidence of lung cancer for asbestos workers. Due to the lack of experimental data, the nature of fiber deposition in the human airway is unclear. In this study, a set of experiments were carried out to investigate the effect of fiber dimension and fiber inertia on the deposition pattern in the human airway replica. The deposition study was conducted by delivering aerosolized carbon fibers into the replica at constant inspiratory flow rates of 15–60 l/min. The results showed that impaction is the dominant deposition mechanism in this study. Most of the high-inertia fibers deposited in the oropharynx and the carina ridges of the bifurcations in tracheobronchial airways. A series of fiber deposition patterns were obtained and the deposition efficiencies were acquired for certain regions in the human airway replica.     

Aerosol Deposition in a Nasopharyngolaryngeal Replica of a 5-Year-Old Child

Particle deposition in a child's nasal cavity is much different than that in the nasal airway of an adult because of the differences in geometry and breathing patterns. However, most deposition studies have focused on adults, and only a limited number of studies have been reported in a child's nasal cavity. This study was conducted as an in vitro test and computational fluid dynamics (CFD) analysis of particle deposition in the nasal replica of a 5-year-old child; both total and regional depositions were evaluated. The geometry of the nasal replica was based on magnetic resonance images of the head of the child. The replica was made by a rapid-prototyping machine. Monodisperse oleic acid and polystyrene latex aerosols ranging in size between 1 and 20 μm were delivered into the replica at flow rates of 10 and 20 L/min. Results showed that the total deposition from the in vitro experiments and CFD predictions matched to a high degree. Good agreement was also obtained when results were compared to existing in vitro deposition data from children having comparable nasal geometries. For regional depositions, patterns between the replica and CFD data were similar in trend and magnitude for all four regions considered, although some regions deviated slightly. More tests in nasal replicas of different aged children will be carried out.

Copyright 2013 American Association for Aerosol Research     

Experimental measurements and computational modeling of aerosol deposition in the Carleton-Civic standardized human nasal cavity

Aerosol deposition in the novel, “Carleton-Civic” standardized geometry of the human nasal cavity was studied both numerically and experimentally. Inhalation flow rates varied from 30 to 90 L/min in the experiments, and aerosol droplets had diameters ranging from 1.71 to 9.14 μm (impaction parameters ranging from 123.3 to 2527.6 μm L/min). For the numerical simulations, both the RANS/EIM (Reynolds averaged Navier–Stokes equations for the gas phase and eddy-interaction random walk models for the particulate phase) and large eddy simulations were used. The mechanism of aerosol deposition in the standardized nasal cavity was dominated by inertial impaction. Deposition data from the standardized nasal cavity transected cited in vitro data based on individual subjects. The data also correlated very well with cited in vivo measurements but generally showed less aerosol deposition for a given value of the impaction parameter. Regional deposition characteristics within the nasal passages were also investigated both experimentally and numerically and new trends of regional deposition versus impaction parameter are discussed. These trends provide new insight into the general deposition behaviour of various sized aerosols within the human nasal cavity.     

Measurement of the Effect of Cartilaginous Rings on Particle Deposition in a Proximal Lung Bifurcation Model

Although cartilaginous rings are present in the trachea and main bronchi of actual human conducting airways, and despite previous authors' theoretical predictions that these effects are significant, little systematic experimental study has been conducted to quantify the effects of such localized morphological features on particle deposition. In the present study, the possible effects of cartilaginous rings upon particle deposition in an idealized airway model are investigated experimentally. The airway model includes the oral cavity, pharynx, larynx, trachea, and first three generations of bronchi. Gravimetry is used to determine the deposition of monodisperse aerosol particles with mass median diameters ranging between 2.9–6.3 µm for steady inhalation flow rates of 30 and 60 l/min. Particle deposition efficiency obtained from a model with cartilaginous rings present in the trachea is compared with that from a smooth-walled tracheo-bronchial model. Significantly enhanced deposition fraction in the trachea with cartilaginous rings present in the trachea is observed for all inhalation rates and particle sizes. The data also indicates that the disturbance of the airflow within the trachea by the presence of cartilaginous rings promotes deposition of particles through the entire trachea, but this influence does not propagate to bifurcations further downstream. The present work indicates that cartilaginous rings may be a critical element to be integrated into future modelling of airways due to their significant effect on inhaled aerosol deposition.     

Vaporizing Microdroplet Inhalation,Transport, and Deposition in a Human Upper Airway Model

Evaluation of injuries from inhalation exposure to toxic fuel requires detailed knowledge of inhaled aerosol transport and deposition in human airways. Focusing on highly toxic, easily volatized JP-8 fuel droplets, the three-dimensional airflow, temperature distributions, and fluid-particle thermodynamics, i.e., droplet motion as well as evaporation, are simulated and analyzed for laminar as well as locally turbulent flow conditions.

Specifically, using a commercial finite-volume software with user-supplied programs as a solver, the Euler-Lagrange approach for the fluid-particle thermodynamics is employed with: (1) a low Reynolds number k-ω model for laminar-to-turbulent airflow, and (2) a stochastic model for random fluctuations in the droplet trajectories with droplet evaporation. Presently, the respiratory system consists of two major segments of a simplified human cast replica, i.e., a representative oral airway from mouth to trachea (Generation 0) and a symmetric four-generation upper bronchial tree model (G0 to G3). Experimentally validated computational fluid-particle thermodynamics results show that evaporation of JP-8 fuel droplets is greatly affecting deposition in the human airway. Specifically, droplet deposition fractions due to vaporization decrease with increasing ambient temperatures and decreasing inspiratory flow rates. It is also demonstrated that assuming idealized velocity profiles and particle distributions in or after the trachea may greatly overpredict particle deposition efficiencies in the upper bronchial tree.