A source of experimental underestimation of aerosol bolus deposition

We examined the measurement error in inhaled and exhaled aerosol concentrat ion resulting from the bolus delivery system when small volumes of monodisp erse aerosols are inspired to different lung depths. A laser photometer tha t illuminated similar to 75% of the breathing path cross section recorded l ow inhaled bolus half-widths (42 ml) and negative deposition values for sha llow bolus inhalation when the inhalation path of a 60-ml aerosol was strai ght and unobstructed. We attributed these results to incomplete mixing of t he inhaled aerosol bolus over the breathing path cross section, on the basi s of simultaneous recordings of the photometer with a particle-counter samp ling from either the center or the edge of the breathing path. Inserting a 90 degrees bend into the inhaled bolus path increased the photometer measur ement of inhaled bolus half-width to 57 mi and yielded positive deposition values. Dispersion, which is predominantly affected by exhaled bolus half-w idth, was not significantly altered by the 90 degrees bend. We conclude tha t aerosol bolus-delivery systems should ensure adequate mixing of the inhal ed bolus to avoid error in measurement of bolus deposition.