Particle transport through a hollow canine airway cast by high-frequency oscillatory ventilation

High-frequency oscillatory ventilation (HFV) of the mammalian respiratory tract can maintain good respiratory ventilation, even with tidal volumes less than half of the anatomic dead space. A steady bidirectional drift is established in airways when the frequency is greater than 2 Hz, resulting in quasi-steady axial streams in the airways. Convective transport from the trachea to peripheral airways takes place in the central core of the bifurcating network of the bronchial tree. It takes place in the opposite direction in the annular regions near the airway walls. In this study, aerosol particle transport was measured in a hollow cast of a canine tracheobronchial tree that extended from the trachea to terminal bronchioles. The 0.5 micron particles, placed in the upper trachea as a bolus, were transported rapidly to the terminal airways of the cast by HFV with tidal volumes of less than one third the volume of the cast. Carrier gases of different kinematic viscosity were used to investigate the fluid dynamics of the transport. Particle transport during HFV was fastest in a gas of high kinematic viscosity (helium), and slowest in a gas of low kinematic viscosity (sulfur hexafluoride). The results are consistent with the application of lubrication theory, improve our understanding of convective processes involved in HFV, and provide new insights into particle penetration in the airways and other aspects of respiratory ventilation.