**4.3.5 Overinflation**

Air space distention with or without alveolar rupture and is often reversible. "Simple air space enlargement" in which there is no destruction or loss of orderly appearance of the lung acinus, occurs in the contralateral lung following pneumonectomy(Compensatory overinflation or emphysema). Air spaces, particularly alveolar ducts, enlarge with advancing age, resulting in what has been termed "senile emphysema". Obstructive overinflation results from partial obstruction of a bronchus or bronchiole, when it becomes more difficult for air to leave the alveoli than to enter; there is a gradual accumulation of air distal to the obstruction, the so-called bypass, ball valve, or check valve type of obstruction. These conditions are listed in Table 1.


Table 1. Conditions with overinflation mimicking Emphysema
