Emphysema, in Medicine, an unnatural distension of a part with air. Emphysema of the cellular texture is usually caused by a wound of the lungs or upper air-passages, from which air escapes during respiration into the cellular tissue. It may be confined to the immediate neighbourhood of the wound, or may extend all over the body. Emphysema is rarely produced otherwise than mechanically; but in gangrene and after death collections of fluid in a state of decomposition sometimes give out gases, which penetrate and distend the textures with which they are in contact.
Emphysema of the lungs is the name applied to two distinct conditions. (1) Interlobular or cellular emphysema, allied to the form described above in that it depends on a wound of the delicate lining-membrane, and that air occupies the interstices of the cellular tissue, is not common, and occurs only in childhood. (2) Vesicular emphysema consists in an unnatural distension of some of the natural air-cells or vesicles of the lungs, and is almost invariably present in those who have long suffered from chronic bronchitis or asthma, or have in any way been obliged to make excessive respiratory efforts—e.g. in the blowing of large wind-instruments. The walls of the affected vesicles become thinned, and may ultimately disappear between two or more in contact with each other, so that though the apparent size of the lung increases, the surface available for aeration of the blood is actually much diminished, and great shortness of breath results. The same process is common in the horse, and familiar under the name of 'broken wind.' The only treatment possible is that of the condition to which the emphysema is due; for the affected vesicles cannot be restored to their original condition.