Yung Sung Cheng

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...

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.

In vivo measurements of nasal airway dimensions and ultrafine aerosol deposition in the human nasal and oral airways

Understanding the filtration efficiency of the nasal and oral airways is essential for assessing doses of inhaled particles to the extrathoracic region as well as to the lung. This paper presents in vivo measurements of nasal airway dimensions and the extrathoracic deposition of ultrafine aerosols in 10 normal adult males. The nasal geometry of each subject was characterized using magnetic resonance imaging and acoustic rhinometry. The nasal and oral deposition efficiencies were measured for particles ranging from 4 to 150 run at constant flow rates of 167 and 333 cm3s−1. Results indicated that both nasal dimensions and particle deposition varied significantly among individuals. Inter-individual variability in particle deposition was correlated with the wide inter-individual variation of nasal dimensions measured by the total surface area, minimum cross-sectional area, and complexity of the airway shape. We concluded that the significant biological variability in extrathoracic filtration of ultrafine aerosols must be considered in developing population-wide dosimetry of inhaled particles.

Airflow and Deposition of Nano-Particles in a Human Nasal Cavity

A 3D computational model was developed to study the flow and the transport and deposition of nano-size particle in a realistic human nasal passage. The nasal cavity was constructed from a series of MRI images of coronal sections of a nose of a live human subject. For several breathing rates associated with low or moderate activities, the steady state flows in the nasal passage were simulated numerically. The airflow simulation results were compared with the available experimental data for the nasal passage. Despite the anatomical differences of the human subjects used in the experiments and computer model, the simulation results were in qualitative agreement with the experimental data. Deposition and transport of ultrafine particles (1 to 100 nm) in the nasal cavity for different breathing rates were also simulated using an Eulerian-Lagrangian approach. The simulation results for the nasal capture efficiency were found to be in reasonable agreement with the available experimental data for a number of human subjects given typical anatomical differences. The computational results for the nasal capture efficiency for nano-particles and various breathing rates in the laminar regime were found to correlate well with the ratio of particle diffusivity to the breathing rate especially for the particles smaller than 20 nm. Based on the simulated results, a semi-empirical equation for the capture efficiency of the nasal passage for nano-size particles was fitted in terms of Peclet number.

Characterization of marine aerosol for assessment of human exposure to brevetoxins.

Red tides in the Gulf of Mexico are commonly formed by the fish-killing dinoflagellate Karenia brevis, which produces nine potent polyether brevetoxins (PbTxs). Brevetoxins can be transferred from water to air in wind-powered white-capped waves. Inhalation exposure to marine aerosol containing brevetoxins causes respiratory symptoms. We describe detailed characterization of aerosols during an epidemiologic study of occupational exposure to Florida red tide aerosol in terms of its concentration, toxin profile, and particle size distribution. This information is essential in understanding its source, assessing exposure to people, and estimating dose of inhaled aerosols. Environmental sampling confirmed the presence of brevetoxins in water and air during a red tide exposure period (September 2001) and lack of significant toxin levels in the water and air during an unexposed period May 2002). Water samples collected during a red tide bloom in 2001 showed moderate-to-high concentrations of K. brevis cells and PbTxs. The daily mean PbTx concentration in water samples ranged from 8 to 28 μg/L from 7 to 11 September 2001; the daily mean PbTx concentration in air samples ranged from 1.3 to 27 ng/m3. The daily aerosol concentration on the beach can be related to PbTx concentration in water, wind speed, and wind direction. Personal samples confirmed human exposure to red tide aerosols. The particle size distribution showed a mean aerodynamic diameter in the size range of 6–12 μm, with deposits mainly in the upper airways. The deposition pattern correlated with the observed increase of upper airway symptoms in healthy lifeguards during the exposure periods.

Nasal Deposition of Ultrafine Particles in Human Volunteers and Its Relationship to Airway Geometry

ABSTRACT Very large and very small particles most often deposit in the nasal airways. Human volunteers have often been used in deposition studies using particles > 0.5 μm, whereas physical airway models have been used in studies of ultrafine particle deposition. Studies in airway models provide large data sets with which to evaluate the deposition mechanism, while in vivo deposition data are needed to validate results obtained with nasal models. Four adult male, nonsmoking, healthy human volunteers (ages 36–57 yr) participated in this study. Deposition was measured in each subject at constant flow rates of 4, 7.5, 10, and 20 L min −1. Monodisperse silver particles (5, 8, and 20 nm) and polystyrene latex particles (50 and 100 nm) were used. Each subject held his breath for 30–60 sec, during which time, the aerosol was drawn through the nasal airway and exhausted through a mouth tube. Aerosol concentrations in the intake and exhaust air were measured by an ultrafine condensation particle counter. The deposi...

Deposition of Thoron Progeny in Human Head Airways

Radon and thoron progeny are ultrafine particles in the size range of 1–200 nm, depending on whether or not they are attached to other aerosol particles. The diffusion coefficient of radon progeny is a critical parameter in determining its dynamics while airborne. Depending on their diffusion coefficient and the breathing pattern of the subject, ultrafine particles have been shown to deposit in the nasal or oral airways. Substantial deposition in the head airways reduces the amount of radioactivity that deposits in the tracheobronchial tree. Thus, for accurate dosimetric calculations, it is important to know the deposition fraction of radon progeny in the head airways. Several adult head airway models were used to study the radon progeny deposition in human nasal and oral airways. Radon-220 progeny (212Pb) were used in the study. The particle size as measured by a graded screen diffusion battery was between 1.2 and 1.7 nm, indicating that the particles were molecular clusters. Deposition was measured by c...

Inspiratory deposition of ultrafine particles in human nasal replicate cast

Abstract The deposition of particles in replicate cast models of the human nasal cavity has been measured in three different laboratories for a range of particle sizes from 0.6 to 200 nm. The results of these measurements on four different casts can be fit by a single equation of the form η=1 − exp [−bQ − 1 8 D 1 2 ], where η is the fraction of particles deposited in the nasal cavity, Q is the volumetric flow rate (1 min−1), D is the particle diffusion coefficient (cm2s−1), and b is found to be 12.65 ± 0.17. The measurements were conducted over a range of flow rates from 1.4 to 28.71 min−1 (501 min−1 for sizes from 4.6 to 200 nm) using radon and thoron decay product aerosols as well as larger ultrafine particles. These results thus represent a current best estimate of the diffusional deposition of ultrafine particles in the human nasal cavity.

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.

Recreational exposure to low concentrations of microcystins during an algal bloom in a small lake.

We measured microcystins in blood from people at risk for swallowing water or inhaling spray while swimming, water skiing, jet skiing, or boating during an algal bloom. We monitored water samples from a small lake as a Microcystis aeruginosa bloom developed. We recruited 97 people planning recreational activities in that lake and seven others who volunteered to recreate in a nearby bloom-free lake. We conducted our field study within a week of finding a 10-μg/L microcystin concentration. We analyzed water, air, and human blood samples for water quality, potential human pathogens, algal taxonomy, and microcystin concentrations. We interviewed study participants for demographic and current health symptom information. Water samples were assayed for potential respiratory viruses (adenoviruses and enteroviruses), but none were detected. We did find low concentrations of Escherichia coli, indicating fecal contamination. We found low levels of microcystins (2 μg/L to 5 μg/L) in the water and (<0.1 ng/m3) in the aerosol samples. Blood levels of microcystins for all participants were below the limit of detection (0.147μg/L). Given this low exposure level, study participants reported no symptom increases following recreational exposure to microcystins. This is the first study to report that water-based recreational activities can expose people to very low concentrations of aerosol-borne microcystins; we recently conducted another field study to assess exposures to higher concentrations of these algal toxins.