Faculty Bibliography

A cast of human tracheobronchial airways, which is complete to airways less than 0.1 cm in diameter, was employed for experimental studies of gas convective transport by high-frequency ventilation (HFV). The cast was ventilated with gases of different kinematic viscosity (He, air, and SF6) and tidal volumes of 10-60 mL. The convective transport through the cast was followed by labeling the tidal volume with 0.5-micron aerosol particles. Such particles undergo little diffusion and have a short relaxation time and, therefore, can serve as tracers of stream flow. The time of arrival of particles transported to isolated peripheral segments of the cast during HFV was measured with an optical particle counter at various oscillatory tidal volumes and frequencies. Distally directed particle transport was found to be substantial in He and air, but weak in SF6. The extent of transport increased with increasing tidal volume. These results provide evidence for a distally directed axial flow during quasi-steady-state tidal breathing of lung airways over a wide range of frequency. This superimposed distal flow along the axial core is consistent with (1) the demonstrated efficacy of O2-CO2 exchange during HFV, and (2) concentrations of particles deposited on bifurcations of alveolar ducts as observed during normal breathing in small animal inhalation studies

A study was undertaken to investigate the mass size dispersion of particles classified according to their electrical mobilities. This is of primary concern in experiments that measure a concentration dependent property of the classified particles. Initially, the mass size distribution of particles produced by the 3-jet Collison, 6-jet Collison, and Misty-Ox nebulizers was measured. A 0-2 stage impactor was placed after the nebulizers and the size mass distribution was measured again. The polydisperse particle stream was then used to generate 'size classified' aerosol and the mass size distribution of the equal mobility particles was calculated and measured. It was found that without an impactor in line, the aerosol stream contained a significant mass fraction of multiply charged particles. When an impactor was inserted directly after the nebulizers, the multiply charged particles were effectively removed and the particles were nearly monodisperse