The distribution of inhaled particles in aerosol measurements of pulmonaryairspace size

When the deposition of aerosol boluses is used to estimate mean pulmonary a irspace size, an implicit assumption is made that the inhaled particles are distributed uniformly among normal and diseased lung regions. This assumpt ion was examined in a series of dogs in which emphysema was experimentally induced by exposure to papain. After the experimental disease had developed for several weeks, boluses of fluorescent particles were inhaled, using a breathing pattern similar to that used for aerosol measurements of airspace size. The lungs were then excised and 18-20 tissue blocks were obtained fr om each lung. A section from each tissue block was analyzed to determine th e mean liner intercept (Lm), which was considered as an index of lung injur y. In the same sections, the density of particles was determined by countin g particles in a number of microscopic fields and dividing the particle cou nt by the number of fields sampled, Correlation analysis generally revealed a negative correlation of particle density with Lm, indicating fewer parti cles being delivered to diseased regions. One lung, however, showed a posit ive correlation between particle density and Lm. Correction for the fractio nal deposition of aerosol in the lung: regions weakened but did not reverse the relationship between particle density and Lm. A model calculation of t he effect of the observed nonuniform distribution of aerosol on the determi nation of airspace size found a negligible effect of uneven ventilation on mean airspace size determination in this experimental preparation.