doi:10.1016/S0021-8502(02)00187-8 
Copyright © 2003 Elsevier Science Ltd All rights reserved.
Effect of gravitational sedimentation on simulated aerosol dispersion in the human acinus
Chantal Darquenne
, a, 
and G.Kim Priska
aDepartment of Medicine, Physiology/NASA Laboratory 0931, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0931, USA
Received 12 July 2002;
accepted 12 November 2002.
Available online 28 February 2003.
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Abstract
We studied the effect of gravitational sedimentation on the dispersion of 0.5 and 1 μm-diameter particle boluses within a two-dimensional symmetric six-generation model of the human acinus. Boluses were introduced at the beginning of a 2-s inspiration immediately followed by a 4-s expiration, in normal gravity (1G) and in the absence of gravity (0G). The flow corresponded to a flow rate at the mouth of 500 ml/s. In 0G, simulated dispersion (Hsim) was 16 ml for both particle sizes. In 1G, Hsim was 71 and 242 ml for 0.5 and 1 μm-diameter particles, respectively, showing the effect of gravitational sedimentation. The difference between experimental data (J. Appl. Physiol. 86 (1999) 1402) and simulations was independent of particle size. This suggests that the residual dispersion was independent of the intrinsic properties of the particles and was more likely due to other mechanisms such as ventilation inhomogeneities, cardiogenic oscillations and alveolar wall motion.
Keywords: Computational fluid dynamics; Aerosol bolus; Human lung
Fig. 1. Symmetric six-generation structure of alveolated ducts representative of the respiratory zone of the human lung. The ducts are made of a central lumen fully surrounded by alveoli. See text for details.
Fig. 2. Expired aerosol tracings for different orientations α of the structure as a function of expiration time (lower axis) or exhaled volume at the mouth (upper axis). — α=0, 
α=+45 (downward), - - - - α=−90 (upward). (A) 0.5 μm-diameter particles and (B) 1 μm-diameter particles.
Fig. 3. Total exhaled bolus as a function of expiration time (lower axis) or exhaled volume at the mouth (upper axis) for 0.5 (dashed line) and 1 μm-diameter particles (solid line). The computed average half-width is also shown in the figure for both particle sizes. (A) 1G and (B) 0G.
Fig. 4. Experimental dispersion (Hexp) in the alveolar zone of the lung. Data are shown for 0.5 (•) and 1 μm-diameter (■) particles in 1G. Hexp was calculated as the increase in H from a lung depth of 500 to 1500 ml, which corresponds to the lung volume probed by the aerosol bolus in our simulations. Experimental data are from Darquenne et al. (1999). See text for details.
Fig. 5. Trajectories of 1 μm-diameter particles in a single smooth-walled bifurcation model in normal gravity calculated for illustrative purposes. Simulations were performed for a 2-s inspiration immediately followed by a 2-s expiration. Trajectories are shown for particles with three different initial radial locations. The positions of each particle at the end of inspiration (1i,2i,3i) and the end of expiration (1e,2e,3e) are shown in the figure. See text for details.
Table 1.
Computed (Hsim) and experimental (Hexp) dispersion of an aerosol bolus
ΔH(=Hexp−Hsim), difference between experimental observations and simulations; G, gravity; dp, particle diameter.
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