The term "barrel chest" describes a rounded, bulging chest that resembles the shape of a barrel. Barrel chest isn't a disease, but it may indicate an underlying condition.
Some people who have chronic obstructive pulmonary disease (COPD) — such as emphysema — develop a slight barrel chest in the later stages of the disease. It occurs because the lungs are chronically overinflated with air, so the rib cage stays partially expanded all the time. This makes breathing less efficient and aggravates shortness of breath.
Barrel chest can also relate to a rounding in the shape of the rib cage as some people age. The ribs may angle outward at the joints where they attach to the spine and become fixed in their most expanded position. The barrel shape of the rib cage may be more pronounced in older adults who also have an exaggerated, forward rounding of the back (kyphosis).
Generally, barrel chest itself isn't treated, but when the cause is severe emphysema or another disease, the underlying disease is treated.