In emphysema, the walls of the air sacs (alveolar septae) are destroyed. Consequently, the individual air spaces (alveoli) become larger but irregular and decreased in number. These larger spaces are less efficient than normal sized alveoli for gas exchange. Thus, emphysema impairs diffusion of oxygen and carbon dioxide (gas exchange). The more extensive the emphysema, the poorer the gas exchange becomes. Also, in emphysema, the capillaries are destroyed with the rest of the alveolar wall. As a result, emphysema also disrupts the normal blood supply
Emphysema usually starts in the upper lobes of the lung and is more severe in the upper lobes for complex reasons. That is, the abnormal (enlarged and irregular) air sacs (alveoli) are more prominent in the upper lobes. (The blood vessels in the lungs should not be mistaken for the abnormal air sacs.)
In someone with severe emphysema, the entire chest actually can enlarge. What probably happens is that the patient's extra (compensatory) efforts to suck in as much air as possible (to increase ventilation) contribute to enlarging the lungs and the chest. Thus, a person with severe emphysema often develops what has been described as a barrel-chest.
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