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Emphysema |
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The term Emphysema is also used to describe
other forms of dilated air space.
Generalized emphysema is characterized by dilatation of air spaces and
destruction of alveolar
walls without scarring.
Emphysema can be defined as 'a permanent dilatation of any part of the
respiratory acinus (air spaces distal to
the terminal bronchiole), with destruction of tissue in the absence of
scarring'.
In practical terms, there is loss of elastic recoil in lungs as respiratory
tissue is destroyed and the area
available for gas exchange is reduced. Individuals with severe emphysema have
reduced oxygen uptake despite increase
in ventilation. Although they manage to maintain blood oxygenation by a rapid
respiratory rate, they feel breathless
on the slightest exertion and become hypoxic (type 1 respiratory failure). In
pure emphysema, cyanosis,
hypercapnia and cor pulmonale develop only late in the disease,after progressive
decline in respiratory function.
There are two main forms of generalized emphysema, defined by the location of
damage in the respiratory acinus.
Centriacinar emphysema (centrilobular emphysema)} is the most common form and is
associated with cigarette smoking.
chronic bronchitis and inflammation of distal airways It is probable that
chronic bronchiolitis
seen in early cigarette smokers progresses to this form of emphysema.
It is most often seen in the upper lobes.
It is likely that the pathogenesis of this type of emphysema is related to
secretion
of extracellular proteases by local inflammatory cells.
Cigarette smoke may also inhibit the effect of protease inhibitor a-1
antitrypsin,
thereby potentiating tissue destruction.
Panacinar emphysema involves the whole respiratory acinus and is commonly
associated with smoking.
As with centriacinar emphysema, its pathogenesis is related to excessive
activity of
extracellular proteases secreted by inflammatory cells. Individuals with
congenital deficiency
in a-1 antitrypsin also develop this pattern of emphysema at an early age.
Generalized emphysema.
The normal lung acinus distal to the terminal bronchiole consists of respiratory
bronchioles,
alveolar ducts and terminal acini.
In centriacinar emphysema, there is dilatation of the respiratory bronchioles at
the centre of the acinus.
This is seen in a very high power macroscopic photograph.
In panacinar emphysema there is dilatation of the terminal alveoli and alveolar
ducts,
which later affects respiratory bronchioles, thereby affecting the whole acinus.
Macroscopically lungs are voluminous and, on cut surface, show large dilated air
spaces. More than one
pattern may exist in the same lung. |
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