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This paper presents measurements of the geometric shape, perimeter, and cross-sectional area of the human oral passage (from oral entrance to midtrachea) and relates them through dimensionless parameters to the depositional mass transfer of ultrafine particles. Studies were performed in two identical replicate oral passage models, one of which was cut orthogonal to the airflow direction into 3 mm elements for measurement, the other used intact for experimental measurements of ultrafine aerosol deposition. Dimensional data were combined with deposition measurements in two sections of the oral passage (the horizontal oral cavity and the vertical laryngeal-tracheal airway) to calculate the dimensionless mass transfer Sherwood number (Sh). Mass transfer theory suggests that Sh should be expressible as a function of the Reynolds number (Re) and the Schmidt number (Sc). For inhalation and exhalation through the oral cavity (O-C), an empirical relationship was obtained for flow rates from 7.5-30.0 1 min-1: Sh = 15.3 Re0.812 Sc-0.986 An empirical relationship was likewise obtained for the laryngeal-tracheal (L-T) region over the same range of flow rates: Sh = 25.9 Re0.861 Sc-1.37 These relationships were compared to heat transfer in the human upper airways through the well-known analogy between heat and mass transfer. The Reynolds number dependence for both the O-C and L-T relationships was in good agreement with that for heat transfer. The mass transfer coefficients were compared to extrathoracic uptake of gases and vapors and showed similar flow rate dependence. For gases and vapors that conform to the zero concentration boundary condition, the empirical relationships are applicable when diffusion coefficients are taken into consideration.

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 pm, 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-'. 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 deposition efficiency in the nasal airway was calculated taking into account particle losses in the mask, mouth tube, and transport lines. Our results were consistent with the turbulent diffusional deposition model previously established from studies using nasal airway casts. However, nasal deposition varied widely among the four subjects. From magnetic resonance imaging data of in vivo nasal airway dimensions for the subjects in this study, we calculated the mean cross-sectional area (A,), mean perimeter (pr), and total surface area (A,) of the individual nasal passages. The turbulent diffusional deposition model was extended to provide a relationship between deposition efficiency and nasal airway dimensions. Our results suggested that deposition can be correlated using the parameter of (~, /~, )~~~~(~r )~~~~.This information indicates a higher nasal deposition for a person with a smaller cross-sectional area, larger

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 a t 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 laryngealtracheal section or through the oral passage; these flow patterns were reversed for the exhalation study. Results indicated that the difference in ultrafine aerosol deposition was not statistically significant at the 95% confidence level between the nose-mouth and nosetrachea paths for inhalation ( p = 0.10) and exhalation ( p = 0.33). For the range of particle sizes and flow rates studied, this finding suggests that the simulated breath-holding method, where test aerosols are drawn through the nose and mouth, is appropriate for estimating the inspiratory and expiratory deposition efficiency of ultrafine particles in the nose-trachea path.

Nasal mucociliary clearance (NMC) is a biomarker of nasal mucosal function. Tobacco smokers have been shown to have abnormal NMC, but the acute effect of environmental tobacco smoke (ETS) on nonsmokers is unknown. This study evaluated acute tobacco smoke-induced alterations in NMC in 12 healthy adults. Subjects were studied on 2 days, separated by at least 1 week. Subjects underwent a 60-min controlled exposure at rest to air or sidestream tobacco smoke (SS) (15 ppm CO) in a controlled environmental chamber. One hour after the exposure, 99mTc-sulfur colloid was aerosolized throughout the nasal passage and counts were measured with a scintillation detector. Six out of 12 subjects showed more rapid clearance after smoke exposure than after air exposure, and 3/12 had rapid clearance on both days. However, substantial decreases in clearance occurred in 3/12 subjects, all of whom had a history of ETS rhinitis. In two subjects, more than 90% of the tracer remained 1 hr after tracer administration (2 hr after smoke exposure). Understanding the basis for biologic variability in the acute effect of tobacco smoke on NMC may advance our understanding of pathogenesis of chronic effects of ETS. Images Figure 1. Figure 2. Figure 3. Figure 4.

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 GI, 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 p m in diameter a t inspiratory and expiratory flow rates of 3, 7, and 16 L min-' (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 a t a given flow rate and particle size. At 16 L min -' , the inspiratory deposition efficiencies in Cast G were 33% and 6% for 0.008-and 0.03-pm particles, respectively. Nasal deposition of thoron progeny with a mean diameter of 0.0013 p m 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-') and flow rate (Q in L min-') 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 = 1exp( -~D'.'Q -0.'2s). 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 pm. This information will be useful in deriving future population-wide models of respiratory tract dosimetry.

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