Deposition of inhaled monodisperse aerosols in small rodents

Aerosols of five different sizes varying from about 0.05 micron to 3 micron in aerodynamic equivalent diameter were prepared from spherical aluminosilicate particles (p=2.2 g/cm3) labelled with 169Yb. Fifty hamsters and fifty rats were exposed, while anaesthetized, to these monodisperse aerosols under controlled laboratory conditions to determine quantitatively deposition in the respiratory airways with respect to particle size and volume of air inhaled. Ten animals of each species were exposed to each of the particle sizes. Five animals were exposed simultaneously for 20 min in an inhalation exposure apparatus which provided automatic recordings of respiratory rates and volumes using individual whole-body plethymographs; three were sacrificed immediately after exposure and the remaining two after 20 h had elapsed for radioanalysis of selected tissues to determine deposition quantities and organ distribution. Detailed results are given for the observed deposition fractions for the different aerosols in the various parts of the respiratory tract. The lowest fractional total deposition occurred for particles between 0.5 micron and 1 micron in aerodynamic equivalent diameter. Relative deposition among the various lung lobes showed remarkable consistency with respect to particle size. Based upon the results of morphometric measurements of replica casts of lungs of the two species, interpretations are made relating the observed deposition phenomena to tracheobronchial anatomy.