Bronchiole Inflammatory scarring/obliteration Tobacco smoke, air pollutants,
miscellaneous
Cough, dyspnea
*A feature of chronic bronchitis (see text).
Of these, only the first two cause clinically significant airflow obstruction ( Fig. 15-5 ). Centriacinar emphysema is far more common than the panacinar form, constituting more than 95%
of cases. Clinical management does not rely on precise anatomic diagnosis and classification, which, however, do provide important clues to pathogenesis.
Centriacinar (Centrilobular) Emphysema.
The distinctive feature of this type of emphysema is the pattern of involvement of the lobules; the central or proximal parts of the acini, formed by respiratory bronchioles, are affected,
whereas distal alveoli are spared ( Fig. 15-6B ). Thus, both emphysematous and normal airspaces exist within the same acinus and lobule. The lesions are more common and usually more
severe in the
Figure 15-5 A, Diagram of normal structures within the acinus, the fundamental unit of the lung. A terminal bronchiole (not shown) is immediately proximal to the respiratory bronchiole.
B, Centriacinar emphysema with dilation that initially affects the respiratory bronchioles. C, Panacinar emphysema with initial distention of the peripheral structures (i.e., the alveolus and
alveolar duct); the disease later extends to affect the respiratory bronchioles.
Figure 15-6 A, Centriacinar emphysema. Central areas show marked emphysematous damage (E), surrounded by relatively spared alveolar spaces. B, Panacinar emphysema involving the
entire pulmonary architecture.
Figure 15-7Pathogenesis of emphysema. The protease-antiprotease imbalance and oxidant-antioxidant imbalance are additive in their effects and contribute to tissue damage. a1 -
antitrypsin (a1 -AT) deficiency can be either congenital or "functional" as a result of oxidative inactivation. See text for details. IL-8, interleukin 8; LTB4 , leukotriene B4 ; TNF, tumor
necrosis factor.
TABLE 15-4-- Emphysema and Chronic Bronchitis
Predominant Bronchitis Predominant Emphysema
Age (yr) 40–45 50–75
Dyspnea Mild; late Severe; early
Cough Early; copious sputum Late; scanty sputum
Infections Common Occasional
Respiratory insufficiency Repeated Terminal
Cor pulmonale Common Rare; terminal
Airway resistance Increased Normal or slightly increased
Elastic recoil Normal Low
Chest radiograph Prominent vessels; large heart Hyperinflation; small heart