The initial pathologic descriptions of these airway alterations in emphysema highlighted the importance of two features: inflammation as a mechanism, and respiratory bronchioles
as the primary site of involvement.
In the low-dose miners, the interstitial compartments with the greatest amount of particulate material were the interlobular, intersegmental, and perivascular connective tissue; the alveolar and alveolar duct septa; the interstitium of respiratory bronchioles
; and the pleura.
The following histologic features were evaluated using a semiquantitative scale: macules, defined as collections of dust-laden macrophages in a size range of 0.1-0.6 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.
This paradigm suggested that any or all of the small cartilaginous airways and membranous or respiratory bronchioles
were structurally altered (remodeled in current COPD terminology) in cigarette smokers and that this remodeling induced turbulent flow and increased airway resistance despite the large cross-sectional area of the airways involved.
Like [O.sub.3] and PM, N[O.sub.2] injures the respiratory tract and has its greatest effect upon respiratory bronchioles
(Chauhan et al.
Removal of particles from the conducting airways (nose to respiratory bronchioles
) is carried out by "mucociliary clearance," helped by airway secretions.
A morphologic grading scheme for membranous and respiratory bronchioles
. Arch Pathol Lab Mod 109:163-165.
(9) However, studies based on lung cancer resection specimens have shown that fine fibrosis in the alveolar walls around respiratory bronchioles
is in fact very common in the lungs of cigarette smokers who have no clinical evidence of an ILD.
Cigarette smoking produces inflammatory changes in small airways, especially respiratory bronchioles
leading to dilatation and destruction of the small airways.
After the terminal bronchiole, the following seven generations of dichotomous divisions are called respiratory bronchioles
and serve the gas-exchanging parenchyma consisting of budding alveoli.
Cilia line the nose, paranasal sinuses, middle ear, Eustachian tube, bronchi as far as respiratory bronchioles
and tail of spermatozoa.
The main pathologic findings in respiratory bronchiolitis-associated interstitial lung disease are respiratory bronchiolitis, with lightly pigmented macrophages and mild inflammatory changes that are primarily centered on respiratory bronchioles
. Desquamative interstitial pneumonia is also associated with smoking in most cases.