Definition
Emphysema is a pathologic condition of the
lung which is characterized by permanent expansion of airspaces
distal to the terminal bronchiole. The walls of the airspaces are destroyed but without
fibrosis (scarring).
Pathology
Although the definition of emphysema describes the basic pathology, this disease can be
further divided into four subgroups based on the part
of the respiratory acinus (lobule) which is damaged and the location of these damaged
lobules within the lung. (Refer to Figures 15-8 and
15-9 in your textbook).
- Centriacinar: The respiratory bronchiole (proximal and central part of the
acinus) is expanded. The distal acinus or alveoli are unchanged. Occurs more commonly in
the upper lobes.
- Panacinar: The entire respiratory acinus, from respiratory bronchiole
to alveoli, is expanded. Occurs more commonly in the lower lobes, especially basal
segments, and anterior margins of the lungs.
- Distal acinar (paraseptal): The distal respiratory acinus,
including alveolar duct and alveoli, is expanded. Occurs primarily adjacent to the pleura
and connective tissue septa, especially in the upper lobes.
- Irregular:( Paracicatritial ) The respiratory acinus is
irregularly expanded. This form of emphysema is frequently associated with a scar (healed
inflammation).
Pathogenesis
- Emphysema is associated with heavy cigarette smoking. But how
does smoke damage the respiratory acinus?
- Protease - antiprotease theory: The walls of
acinus are destroyed when there is an imbalance between proteases and anti-proteases in
the lung. Protease is an enzyme like elastase, which can digest connective tissue
elements. Proteases are found throughout the body, especially in neutrophils and
macrophages. To counterbalance the destructive effects of proteases, nature provides
inhibitors such as alpha-antitrypsin.
- Smoking increases the level of lung proteases while impairing the action of
anti-proteases. Patients with panacinar emphysema may lack alpha-antitrypsin.
Pathophysiology
Progressive dyspnea, over inflated lungs, barrel chest, hyperresonance, and distant breath
sounds.
