Deposition and dispersion of 1-μm aerosol boluses in the human lung:: effect of micro- and hypergravity

We performed bolus inhalations of 1-mu m particles in four subjects on the ground (1 G) and during parabolic flights both in microgravity (mu G) and in similar to 1.6 G. Boluses of similar to 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 (V-p)] ranged from 200 to 1,500 mi. 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 V-p greater than or equal to 400 ml, both deposition and dispersion increased with V-p and mere strongly gravity dependent, with the greatest deposition and dispersion occurring for the largest G level. At V-p = 800 ml, deposition and dispersion increased from 33.9% and 319 ml in mu G to 56.9% and 573 ml at similar to 1.6 G, respectively (P < 0.05). At each G level, the bolus was expired at a smaller volume than V-p, and this volume became smaller with increasing V-p. Although dispersion was lower in mu G than in 1 G and similar to 1.6 G, it still increased steadily with increasing V-p, showing that nongravitational ventilatory inhomogeneity is partly responsible for dispersion in the human lung.