David L. Swift

The coagulation of hydrosols by brownian motion and laminar shear flow

Abstract The coagulation of hydrosols was investigated theoretically and experimentally. A reduced form of the particle size distribution function, designated “self-preserving,” was found to satisfy Smoluchowskis equations of coagulation by Brownian motion and shear flow. Brownian motion coagulation experiments with two heterogeneous hydrosols showed that the distributions were self-preserving. The rate of coagulation for heterogeneous systems was found to be second order in total particle concentration, consistent with the self-preserving form of the distribution function. Coagulation experiments were carried out in a simple laminar shear field using a homogeneous Dow polystyrene latex dispersion. Smoluchowskis shear flow theory was confirmed for shear rates ranging from 1 to 80 sec. −1 The shear coagulation of a heterogeneous emulsion was studied at several shear rates, and the size distributions were self-preserving.

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.

Diffusional deposition of ultrafine aerosols in a human nasal cast

Abstract This report describes an experimental study of aerosol deposition in a human nasal cast. A clear polyester resin cast of the upper airways of a normal human adult was used. This life-sized model included nasal hairs, the nasal airways, oral cavity, nasopharynx, larynx and entrance to the trachea. For nasal air flow rates, the measured pressure drop in the cast was similar to the in vivo measurements reported in the literature. Thus, the cast appeared to be a good representation of the nasal airways of living humans. The total deposition was measured in the cast for monodisperse NaCl aerosols between 0.2 and 0.0046 μm at flow rates between 4 and 50 l min −1 of inspiratory flow. The deposition efficiency increased with decreasing particle size and flow rate, indicating that diffusion was the dominant mechanism for deposition. At 20 1 min −1 flow (comparable to that for normal breating at rest), inspiratory deposition efficiencies were 16 and 40% for 0.01 and 0.005 μm particles, respectively. A theoretical equation relating the deposition efficiency to the flow rate and diffusion coefficient was derived based on a turbulent diffusion process. The agreement achieved between the theoretical and measured deposition indicated that the turbulent diffusion was the dominant mechanism of deposition in the nasal cast. This information will be incorporated into future models of respiratory tract dosimetry.

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.

Deposition of ultrafine aerosols in the head airways during natural breathing and during simulated breath holding using replicate human upper airway casts

Natural breathing and simulated breath-holding techniques have been used to measure inspiratory and expiratory head deposition of inhaled particles in human subjects. Because the simulated breath-holding path, in which the aerosol is drawn through the nose and mouth, differs from the natural path where inhaled particles enter the nose and penetrate through the larynx and trachea, the present study was undertaken to compare the deposition of ultrafine aerosol between these two experimental methods. Two replicate human upper airway casts containing a nasal airway, an oral passage, and a laryngeal-tracheal section were used to measure the head deposition efficiencies of monodisperse silver or polystyrene latex particles. Particles whose thermodynamic diameters ranged from 3.6 to 150 nm were drawn through the casts at constant flow rates ranging from 4 to 30 L/min. For the inhalation study, test aerosols were drawn into the nasal airway and directed either through the laryngeal-tracheal section or through the...

Mechanisms of aerosol deposition in a nasal model

Abstract Total and regional aerosol deposition were investigated in a model of a normal human nasal airway. Contributions of fluid turbulence and particle inertia were evaluated using monodisperse aerosols. At fixed turbulent flow conditions, deposition percentage increased with particle size greater than 1 μm, suggesting that turbulent inertial deposition is a primary mechanism. With same size aerosol, deposition increased with increasing fluid turbulence but its contribution was less with larger size aerosol. Turbulent diffusion was the dominant transport mechanism for particles less than 1 μm, where deposition decreased with particle size. Two major deposition sites were visualized with radio-aerosol in the anterior region of the nasal airway. One is close to the ostium internum where turbulent eddies are well developed, and the other is the anterior region of the middle turbinate where direction of airflow changes from upward to horizontal.

Mouthpiece diameter affects deposition efficiency in cast models of the human oral airways.

We examined the effect of altering mouthpiece diameter to 1.5, 2.0, and 2.7 cm on the deposition efficiency of inertial size particles (2, 4, and 8 microm) in adult human oral-pharyngeal-laryngeal (OPL) airway cast models at various inspiratory flow rates (30, 60, 90, and 120 L/min). Deposition efficiency of 2-microm particles was unaffected by changes in mouthpiece diameter at all flow rates. Deposition of 4-microm particles decreased significantly with the 2.0- and 2.7-cm mouthpieces compared to the 1.5 cm mouthpiece at 60, 90, and 120 L/min (p < 0.01). Deposition of 4-microm particles was significantly reduced with the 2.7-cm mouthpiece compared to the 2.0-cm mouthpiece at 90 and 120 L/min (p < 0.05). Deposition efficiency of 8 microm particles decreased significantly with the 2.0- and 2.7-cm mouthpieces compared to the 1.5-cm mouthpiece at 60 L/min (p < 0.05), and with the 2.7-cm mouthpiece compared to the 1.5-cm mouthpiece at 120 L/min (p < 0.05). These results suggest that the effect of mouthpiece diameter varies with particle size, with 2- and 8-microm particles least affected. However, our findings may have important implications for improving the future design of mouthpieces of devices that deliver particles with 4-microm diameters and require inspiratory flow rates of > or = 60 L/min (i.e., DPIs) for adequate drug delivery.

THE MEASUREMENTS OF HUMAN INHALABILITY OF ULTRALARGE AEROSOLS IN CALM AIR USING MANNIKINS

An idea was first introduced during the 1970s that particles cannot produce adverse health effect unless they are inhaled into the human respiratory tract. Since then several studies have been carried out to investigate the inhalable fraction of ambient aerosols. However, the previous studies were confined to the conditions of external convective flow and particle aerodynamic diameter smaller than 100 μm. This paper reports the results from an inhalability study for particle aerodynamic diameter for a range of diameters which include diameters greater than 100 μm under a condition of no external convective flow. The concept of mass balance was used in this study to derive an equation for determining the ambient particle concentration from which inhalability was calculated. The results suggested that difference in ventilation demands between adults and children does not affect inhalability, however, the inhaled dose was significantly higher in adults than children because of higher ventilation demand of adults. In terms of the breathing mode, the inhalabilities of oronasal breathing for people at heavy exercise are much higher than those of nasal breathing which simulates breath at rest and moderate exercise. The inhalability curve derived from this study indicated that a cutoff diameter for zero inhalability exists, which should be considered in the future revision of ACGIH inhalable aerosols criteria.