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

Abstract

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.