Comparison of clearance of particles inhaled with bolus and extremely slowinhalation techniques

Ten healthy nonsmokers inhaled 6-mu m (aerodynamic diameter) Teflon particl es labelled with In-111 twice, once with the shallow bolus technique (volum etric diameter 76 +/- 20 mL ([+/- SD]) and once with the extremely slow inh alation technique (0.05 L/s). The radioactivity in the lungs was measured a t 1 and 24 hours as well as at 1, 2, and 3 weeks after both inhalations. Th e 24-hour lung retention as a percentage of lung deposition was significant ly lower for the bolus inhalation, 46% +/- 9% (+/- SD) than for the extreme ly slow inhalation, 56% +/- 11%. The retention after 21 days as a percentag e of the 24-hour retention was 55% +/- 9% for the shallow bolus Inhalation and 56% +/- 10% for the extremely slow inhalation. Also within the subjects , clearance was similar for the 2 modes of inhalation. Deposition of partic les inhaled with the 2 modes of inhalation was calculated with 2 models, on e bring based on Monte Carlo particle transport together with an asymmetric lung model. Deposition predicted with this model agreed well with the expe rimental data under the assumption that there are large retained fractions only in small ciliated airways (bronchioli) and not in large ones. For the bolus inhalation, the model predicted 43% to 50% deposition in the bronchia l (BB) region of initial lung deposition, 33% to 38% in the bronchiolar (bb ) region, and 16% to 22% in the alveolar region. For the extremely slow inh alation, the model predicted 31% to 34% deposition in the BB region, 45% to 47% in the bb region, and 21% to 22% in the alveolar region. In addition, it predicted about the same ratio between bb and alveolar depositions for t he 2 modes of inhalation. Thus, both the experimental and theoretical data indicate that the shallow bolus particles to a considerable extent reach bo th the bb and the alveolar regions and that they do that at about the same extent as the particles inhaled extremely slow. This conclusion is concerni ng the experimental data based on the assumption that there are no large re tained fractions in the BB region. Another interpretation of the similar cl earance the two modes of inhalation in that there are large retained fracti ons in both the BB and the bb regions and that individual characteristics o f clearance of these fractions are of importance rather than the site of de position.