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 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.     

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.     

Effectiveness of Direct Lagrangian Tracking Models for Simulating Nanoparticle Deposition in the Upper Airways

Direct Lagrangian particle tracking may provide an effective method for simulating the deposition of ultrafine aerosols in the upper respiratory airways that can account for finite inertia and slip correction effects. However, use of the Lagrangian approach for simulating ultrafine aerosols has been limited due to computational cost and numerical difficulties. The objective of this study is to evaluate the effectiveness of direct Lagrangian tracking methods for calculating ultrafine aerosol transport and deposition in flow fields consistent with the upper respiratory tract. Representative geometries that have been considered include a straight tubular flow field, a 90° tubular bend, and an idealized replica of the human oral airway. The Lagrangian particle tracking algorithms considered include the Fluent Brownian motion (BM) routine, a user-defined BM model, and a user-defined BM model in conjunction with a near-wall interpolation (NWI) algorithm. Lagrangian deposition results have been compared with a chemical species Eulerian model, which neglects particle inertia, and available experimental data. Results indicate that the Fluent BM routine incorrectly predicts the diffusion-driven deposition of ultrafine aerosols by up to one order of magnitude in all cases considered. For the tubular and 90° bend geometries, Lagrangian model results with a user-defined BM routine agreed well with the Eulerian model, available analytic correlations, and experimental deposition data. Considering the oral airway model, the best match to empirical deposition data over a range of particle sizes from 1 to 120 nm was provided by the Lagrangian model with user-defined BM and NWI routines. Therefore, a direct Lagrangian transport model with appropriate user-defined routines provides an effective approach to accurately predict the deposition of nanoparticles in the respiratory tract.     

Miniature Pipe Bundle Heat Exchanger for Thermophoretic Deposition of Ultrafine Soot Aerosol Particles at High Flow Velocities

The deposition of submicrometer soot aerosol particles in a miniature pipe bundle heat exchanger system has been investigated under conditions characteristic for combustion exhaust from diesel engines and oil or biomass burning processes. The system has been characterized for a wide range of aerosol inlet temperatures (390–510 K) and flow velocities (1–4 m s^?1), and particle deposition efficiencies up to 45% have been achieved over an effective deposition length of 27 cm. Thermophoresis was the dominant deposition mechanism, and its decoupling from isothermal deposition was consistent with the assumption of independently acting processes. The measured deposition efficiencies can be described by simple linear parameterizations based on an approximation formula for thermophoretic plate precipitators. The results of this study support the development of modified heat exchanger systems with enhanced capability for filterless removal of combustion aerosol particles.     

Inspiratory Deposition Efficiency of Ultrafine Particles in a Human Airway Bifurcation Model

The inspiratory deposition efficiency of ultrafine particles in a physiologically realistic bronchial airway bifurcation model, approximating the airway generation 3-4 juncture, was computed for different particle sizes, ranging from 1 to 500 nm, under three different flow conditions, representing resting to heavy exercise breathing conditions. For the smallest particle sizes, say between 1 and 10 nm, molecular diffusion is the primary deposition mechanism, as indicated by the inverse relationship with flow rate, except for the highest flow rate where the additional effect of convective diffusion has to be considered as well. For the larger particle sizes, say above 20 nm, the independence from particle size and dependence on flow rate suggests that convective diffusion plays the major role for ultrafine particle deposition in bifurcations. A semiempirical equation for the inspiratory deposition efficiency, m (D, Q), as a function of diffusion coefficient D and flow rate Q, due to the combined effect of molecular and convective diffusion was derived by fitting the numerical data. The very existence of a mixed term demonstrates that molecular and convective diffusion are not statistically independent from each other.     

Preparation of Ultrafine Zirconia Particles

Ultrafine ZrO₂ particles have been prepared via a new sol-gel process. This process involves the addition of excess C₂H₄O into the aqueous ZrOCl₂ solution and reacting the mixture at room temperature; a glassy ZrO(OH)₂ gel is formed moments later. An ultrafine ZrO₂ powder is obtained after the gel is dried and calcined; the powder is monoclinic. The average particle size is ∼12 nm, and its specific surface area is 55.1 m²/g. In addition, partially stabilized ZrO₂ can be prepared in the same manner, yielding a good result.     

Bipolar Charging of Ultrafine Aerosol Particles

The stationary bipolar charging characteristics of aerosol particles in the size range between 4.5 and 40 nm have been studied using a new technique whereby the particles neutralized by a ²⁴¹Am radioactive source are enlarged and directly observed in an electric field. The number ratio of charged particles to total particles obtained in this study was found to deviate from the charge distribution obtained from Boltzmann's law and to agree well with that calculated with the bipolar charging theory of Fuchs using his values for the ion properties. The ratio of positively charged to negatively charged particles was found to be approximately 0.35:0.65.

     

超微粒子的合成及其应用

本文综述了超微粒子的合成方法和应用。着重叙述了超微粒子在催化、生物、医学、记录材料、传感材料等方面的应用。     

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.     

Particle Deposition in a Cast of Human Oral Airways

Oral and nasal airways are entryways to the respiratory tract. Most people breathe through the nasal airway during rest or light exercise, then switch to oral/nasal breathing during heavy exercise or work. Resistance through the oral airways is much lower than through the nasal airways, so fewer aerosol particles are deposited in the oral airways. Aerosol drugs are usually delivered by inhalation to the lung via the oral route for that reason. Oral deposition data from humans are limited, and those available show great intersubject variability. The purpose of this study was to investigate the effects of particle size and breathing rate on the deposition pattern in a human oral airway cast with a defined geometry. The airway replica included the oral cavity, pharynx, larynx, trachea, and 3 generations of bronchi. The oral portion of the cast was molded from a dental impression of the oral cavity in a human volunteer, while the other airway portions of the cast were made from a cadaver. Nine different sizes of polystyrene latex fluorescent particles in the size range of 0.93-30 mu m were used in the study. Regional deposition was measured at a constant inspiratory flow rate of 15, 30, and 60 L min^-1. Deposition in the oral airway appeared to increase with an increasing flow rate and particle diameter. Deposition at the highest flow rate of 60 L min^-1 was close to 90% for particles >20 mu m. Particles> about 10 mu m deposited mainly in the oral cavity. Deposition efficiency has been found to be a unique function of the Stokes number, suggesting that impaction is the dominant deposition mecha nism. Oral deposition can be approximated by a theoretical deposition model of inertial impaction in a 180 degrees curved tube, assuming perfect mixing in a turbulent flow. Our model suggests that the minimum dimension near the larynx and the average cross-sectional area are important parameters for oral airway deposition; however, additional data from the oral airway replica are needed to ascertain whether these are indeed the critical dimensions. Information from the present study will add to our knowledge of the deposition mechanism, the correlation of particle deposition with airway geometry, and eventually the best way to deliver aerosol drugs.     

Condensational Growth May Contribute to the Enhanced Deposition of Cigarette Smoke Particles in the Upper Respiratory Tract

Previous experimental studies have shown that concentrated cigarette smoke particles (CSPs) deposit in the upper airways like much larger 6 to 7 μ m aerosols. Based on the frequent assumption that relative humidity (RH) in the lungs does not exceed approximately 99.5%, the hygroscopic growth of initially submicrometer CSPs is expected to be a relatively minor factor. However, the inhalation of mainstream smoke may result in humidity values ranging from sub-saturated through supersaturated conditions. The objective of this study is to evaluate the effect of condensation particle growth on the transport and deposition of CSPs in the upper respiratory tract under various RH and temperature conditions. To achieve this objective, a computational model of transport in the continuous phase surrounding a CSP was developed for a multicomponent aerosol consisting of water soluble and insoluble species. To evaluate the transport and deposition of dilute hygroscopic CSPs in the upper airways, a model of the human mouth-throat (MT) through approximately respiratory generation G6 was considered with four steady inhalation conditions. These inhalation conditions were representative of inhaled ambient cigarette smoke as well as warm and hot saturated smoke. Results indicate that RH conditions above 100% are possible in the upper respiratory tract during the inhalation of a warm or hot saturated airstream. For sub-saturated inhalation conditions, initial evaporation of the CSPs was observed followed by hygroscopic growth and diameter increases less than approximately 50%. In contrast, the inhalation of warm or hot saturated air resulted in significant particle growth in the MT and tracheobronchial regions. For the inhalation of warm saturated air 3°C above body temperature, initially 200 and 400 nm particles were observed to increase in size to above 3 μ m near the trachea inlet. The upper boundary inhalation condition of saturated 47°C air resulted in 7 to 8 μ m droplets entering the trachea. These results do not prove that the enhanced deposition of CSPs in the upper airways is only a result of condensational growth. However, this study does highlight condensational growth as a potentially significant mechanism in the deposition of smoke particles under saturated inhalation conditions.     

Aerosol Deposition Efficiencies and Upstream Release Positions for Different Inhalation Modes in an Upper Bronchial Airway Model

Accurate predictions of micron-particle deposition patterns and surface concentrations in lung airways are most desirable for researchers assessing health effects of toxic particles or those concerned with inhalation delivery of therapeutic aerosols. Focusing on a rigid, symmetric triple bifurcation lung airway model, i.e., Weibel's generations G3-G6, a user-enhanced and experimentally validated finite volume program has been employed to simulate the airflow and particle transport under transient laminar three-dimensional flow conditions. Specifically, the effects of 3 inhalation modes, i.e., resting and light and moderate activities, were analyzed for typical ranges of Stokes numbers (St h 0.2) and Reynolds numbers (0 h Re h 2100). The detailed results show particle deposition patterns and efficiencies in the triple bifurcation under cyclic as well as steady-state inhalation conditions. Cyclic inhalation generates higher local and segmentally-averaged deposition rates when compared to steady mean Reynolds number inhalation; however, matching Stokes and Reynolds numbers, i.e., the average between mean and peak values, were found to provide fully equivalent results for all inhalation modes and bifurcations. In addition, particle maps were developed that show the release positions of deposited aerosols.     

微细硫酸沙丁胺醇颗粒的制备

以沙丁胺醇和硫酸为反应物,在乙醇溶液中制备微细硫酸沙丁胺醇. 对影响产物粒径和产率的因素,如硫酸浓度、反应温度、搅拌转速和反应时间等进行了研究. 结果表明,当硫酸浓度为2.5 mol/L、反应温度为5oC、搅拌转速为900 r/min、反应时间为10 min时,可以得到短轴为800 nm左右、长径比为8~20、且短轴尺寸分布较窄的棒状硫酸沙丁胺醇微粒,产品收率为92.7%,纯度为98.5%. 经红外光谱、X射线衍射和紫外分光光度计分析测定证实,产物各项指标均符合中华人民共和国药典(2000年版二部)和英国药典(B. P., 1993)的要求.     

超支化聚酯改性超细氧化锌

采用富含—COOH基团的超支化聚酯(HBP)对超细氧化锌(μ-ZnO)进行表面改性,并对改性后的氧化锌的结构和特征进行了表征。结果表明：在氨水中得到了稳定期较长、清澈透明的μ-ZnO悬浮液,在n(—COOH)／n(μ-ZnO)为1／8时稳定期最长,超过72h;采用相同的方法,但溶剂为丙酮或乙酸丁酯时,稳定期只有0．5～1h;改性后的μ-ZnO在1575cm^-l处出现新的振动吸收,表面包覆了聚合物,团聚现象不明显,分散状态得到明显的改善。     

反应沉淀法制备阿奇霉素药物超微粉体

利用反应沉淀法进行了阿奇霉素微粉化的实验研究,考察了NaOH溶液浓度、搅拌速度、搅拌时间和反应温度等因素对产品粒度、形貌、分散性及收率的影响. 分别采用扫描电镜(SEM)、比表面分析仪、X射线衍射仪(XRD)和红外光谱仪(FT-IR)对产品进行了分析与表征,并对微粉化产品和原料药进行了溶出性能研究. 实验结果表明,利用此方法可以制备得到平均粒径约为413 nm的无定型阿奇霉素超微粉体,与原料药相比,微粉化的阿奇霉素粉体比表面积增加了约27倍,相应地,药物的溶出性能较原料药明显改善.     

超细羟基磷灰石颗粒的反相微乳液合成

采用AOT/异辛烷/Ca(H2PO4)2*H2O水溶液体系的微乳液与AOT/异辛烷/Ca(OH)2饱和溶液体系的微乳液反应,制备出了平均颗粒尺寸107nm,呈单分散的球形HAP超细颗粒.通过制备过程优化和AOT/异辛烷/Ca(H2PO4)2*H2O水溶液三元相图,确定了基本制备条件为AOT浓度0.1mol/dm3,正辛醇浓度0.1mol/dm3,增溶水量为w=9.采用该体系可改变HAP超细颗粒的生长习性,从而实现对HAP颗粒形貌的控制.     

超细硫酸钡颗粒的絮凝沉降研究

本文研究了影响超细硫酸钡沉降的各种因素 ,并对其进行了絮凝沉降实验。实验表明 ,无机絮凝剂和高分子絮凝剂均能起到加速粒子沉降目的 ;同时发现高分子絮凝剂的絮凝效果较好 ,其适宜用量为 0 3% ,搅拌时间为 8min ,其絮凝沉降速度可达未加絮凝剂的 8～ 9倍。并对其机理进行了初步的探讨     

Preparation of Ultrafine SiC Particles by Gas Evaporation

A new method for preparing ultrafine powder of SiC is proposed. A carbon rod is mounted vertically with a block of silicon at the bottom of the system. The apparatus is held in rarefied inert gas and heated by an electric current. The SiC produced by the heating then evaporates forming a smoke, the particles of which are β–SiC <100 nm in diam.     

Characterization of Submicrometer Aerosol Deposition in Extrathoracic Airways during Nasal Exhalation

Submicrometer and especially fine aerosols that enter the respiratory tract are largely exhaled. However, the deposition of these aerosols under expiratory conditions is not well characterized. In this study, expiratory deposition patterns of both ultrafine (<100 nm) and fine (100–1000 nm) respiratory aerosols were numerically modeled in a realistic nasal-laryngeal airway geometry. Particle sizes ranging from 1 through 1000 nm and exhalation flow rates from 4 through 45 L/min were considered. Under these conditions, turbulence only appeared significant in the laryngeal and pharyngeal regions, whereas the nasal passages were primarily in the laminar regime. Exhaled particles were simulated with both a continuous-phase drift flux velocity correction (DF-VC) model and a discrete Lagrangian tracking approach. For the deposition of ultrafine particles, both models provided a good match to existing experimental values, and simulation results corroborated an existing in vivo–based diffusion parameter (i.e., D ^0.5 Q ^?0.28). For fine particles, inertia-based deposition was found to have a greater dependence on the Reynolds number than on the Stokes number (i.e., St^0.1 _kRe^0.9), indicating that secondary flows may significantly influence aerosol deposition in the nasal-laryngeal geometry. A new correlation was proposed for deposition in the extrathoracic airways that is applicable for both ultrafine and fine aerosols over a broad range of nasal exhalation conditions. Results of this study indicate that physical realism of the airway model is crucial in determining particle behavior and fate and that the laryngeal and pharyngeal regions should be retained in future studies of expiratory deposition in the nasal region.