Regional Alveolar Deposition Patterns of Inhaled Particles are Dependent upon Airway Branching Patterns.

Results from recent studies indicate that anatomical regional differences in inhaled asbestos fibre burdens are inversely related to the pathlengths of intrapulmonary airways of rats, i.e. increased numbers of fibres were retained in cranial regions containing the shortest pathlengths from the main bronchus while fewer fibres were retained in caudal regions at the base of the same lobe. It was not established, however, whether the increased fibre retention was due to enhanced deposition or reduced clearance of inhaled fibres. Thus, the present study was undertaken to test the hypothesis that enhanced particle deposition occurs at cranial regions with the shortest pathlengths. Male Long- Evans rats were exposed to aerosols of carbonyl iron (CI) particles for 1 or 6 h at a concentration of 107 mg m−3. Immediately following exposures, exposed rats were vascularly-fixed for particle deposition studies. Subsequently, the left lobes of all rats were microdissected along the long axes for a minimum of five airway generations; the tissue blocks were then dried and further dissected to the level of the broncho-alveolar junctions. Particle deposition was quantified by scanning electron microscopy. Our data indicated that increased numbers of particles deposited in cranial regions (P <0.05 compared to caudal or costolateral), and this correlated with enhanced alveolar macrophage chemotactic responses. Our results suggest that airway pathlengths influence regional deposition patterns for inhaled particulate materials. [ABSTRACT FROM PUBLISHER]