The Physiological Determinants of Aerosol Bolus Dispersion in Healthy Subjects

An impulse-response method was utilized for studying the dispersion of an 0.5 μm aerosol bolus in the respiratory tract of 11 male and 12 female healthy non-smoking subjects. The increase in bolus volume variance (σv^2) between inspiration and expiration was used as an index of dispersion. The effects of bolus penetration (Vi), bolus volume (Vboi), lung inflation, and gender on σv^2 were investigated. The Vi was varied in 250 ml increments over a subject's tidal volume (Vt) . Procedures were repeated for the Vboi of 75, 150, and 300 ml in two Vt (1.0 and 1.5 L in females, 1.0 and 2.0 L in males). For the experimental conditions, diffusion of the bolus was negligible due to the low intrinsic motion of 0.5 μm particles. σv^2 was found to increase in an exponential manner with Vi over the range of experimental data (250 < Vi < 1750 ml) . The only significant factors were Vi and Vboi (p<0.001 for both). The effects of gender, Vt, and all interactions were not significant. A volume shift in the mean of the expired bolus toward the periphery was observed for all subjects. This shift decreased with increasing Vi and was significant for all levels of Vi (p