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Department of Medicine, University of California, San Diego, La Jolla, California 92093-0931
We
performed bolus inhalations of 1-µm particles in four subjects on the
ground (1 G) and during parabolic flights both in microgravity (µG)
and in ~1.6 G. Boluses of ~70 ml were inhaled at different points
in an inspiration from residual volume to 1 liter above functional
residual capacity. The volume of air inhaled after the bolus [the
penetration volume (Vp)]
ranged from 200 to 1,500 ml. Aerosol concentration and flow rate were
continuously measured at the mouth. The deposition, dispersion, and
position of the bolus in the expired gas were calculated from these
data. For Vp 
400 ml, both
deposition and dispersion increased with Vp and were strongly gravity
dependent, with the greatest deposition and dispersion occurring for
the largest G level. At Vp = 800 ml, deposition and dispersion increased from 33.9% and 319 ml in µG
to 56.9% and 573 ml at ~1.6 G, respectively
(P < 0.05). At each G level, the
bolus was expired at a smaller volume than Vp, and this volume became smaller
with increasing Vp. Although dispersion was lower in µG than in 1 G and ~1.6 G, it still
increased steadily with increasing
Vp, showing that nongravitational
ventilatory inhomogeneity is partly responsible for dispersion in the
human lung.
gravity; aerosol bolus inhalation; convective mixing; ventilation
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