In this paper, we report evidence that both carbonaceous and mineral dust are primarily distributed to the terminal and respiratory bronchioles and that there is anatomical remodeling within these same sites.
We also sampled parenchymal tissues and associated terminal and respiratory bronchioles were also sampled beyond the 12th airway generation of each airway path that was microdissected.
6 mm within the walls of respiratory bronchioles and adjacent alveoli; nodules, defined as fibrotic lesions up to 1 cm in size with round, irregular, or serpiginous borders and containing dust-laden macrophages; and interstitial fibrosis, defined as diffuse or irregular fibrosis of alveolar septa and/or alveolar ducts.
Small airways disease, subdivided into mineral dust-associated small airways disease (11) and smoking-related small airways disease (12,13), was identified, and exposure to cigarette smoke in the recent past was assessed on the basis of accumulation of characteristic smokers' macrophages within the respiratory bronchioles and adjacent alveoli (14,15).
To increase the power of this analysis, only cases with three or more complete sets of respiratory bronchioles consisting of contiguous first-, second-, and third-generation bronchioles were used.
Parenchymal tissues arising from the apico-posterior and apico-anterior regions were examined for membranous and respiratory bronchioles.
The results of the histologic and particle analysis of respiratory bronchioles by order of generation are given in Figure 6.
As a result of this sampling procedure, the importance of terminal and respiratory bronchioles as sites for particle retention and the association of particle retention with subtle but quantifiable changes in tissue remodeling have been clearly established.
Predominant pathological effects were also confined to the epithelial and interstitial tissue compartments of the respiratory bronchioles, forming the transitional zone between the conducting airways and gas-exchange regions of the lungs.
Analytical electron microscopic studies by Churg and colleagues (23) have revealed that the concentration of particles in respiratory bronchioles can be 25-100 times greater than the concentration of particles in the mainstem bronchus (23).
This region of the lung is anatomically distinct, as the respiratory bronchioles have some of the same properties of conducting airways as well as serving a gas-exchange function (25).