Aerosol Bolus Dispersion and Recovery in a Human and Dog Airway Cast

In recent years methods in lung diagnostics have been developed using the aerosol bolus inhalation technique (Heyder et al., 1988; Anderson et al., 1989; Schulz et al., 1995; Blanchard 1996). A bolus is a small volume of aerosol sandwiched in particle-free air and inhaled into different volumetric regions of the lung. During inhalation and exhalation the original small bolus is dispersed over a larger volume. This dispersion is caused by convective mixing in the airways and by intrinsic particle motion. Because particles in the size range between 0.2 and about 1 um have low intrinsic motion, they can be used as tracers of the convective air transport in the lungs. The extent of broadening of the bolus measured in the exhaled air is a measure of the convective mixing during inhalation and exhalation, Blanchard (1996). The bolus inhalation technique can also be used to deliver aerosol into specific volumetric regions of the lungs. If a bolus is inhaled near the end of an inhalation, the aerosol particles cannot penetrate deep into the lungs and should be delivered preferentially to the tracheobronchial airways. In order to determine where the particles from an inhaled bolus are located within the lungs at end inhalation, dispersion and recovery studies were made in a dog and a human airway cast.