Effect of Lung Airway Branching Pattern and Gas Composition on Particle Deposition. II. Experimental Studies in Human and Canine Lungs

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Abstract
The recovery of monodisperse inhaled particles from humans in vivo and from excised human and canine lungs was measured after a single breath for particles suspended in air and in mixtures of He or SF6 with O2. Comparisons were made using the unique particle sizes for which the intrinsic particle motions in air and each mixture were identical, so that differences in recovery could be associated with differences in convective flow. For the in vivo tests, only mixtures with 20% O2 were used, while for the excised lungs, mixtures with 10% O2 were also used. In humans in vivo and in excised human lungs, there was significantly greater deposition from He-O2 mixtures and less deposition from SF6-O2 mixtures, with no differences between the in vivo and the excised lung results for the 80-20 mixtures. For the canine lungs, there were no differences in deposition between air and any He or SF6 mixture. The interspecies differences are consistent with the hypothesis that particle exchange between tidal and residual lung gas is dependent on the distance into each airway that is needed to establish a stable flow profile. The more symmetrical branching of human lung airways causes the entry flow into daughter airways to be highly asymmetric, and flow profile rearrangement is greater than that in the monopodal canine lung.