Why do people with emphysema sometimes have problems with fluid retention and ankle swelling?

Right heart strain: This is usually related to right heart strain from lung disease or from pulmonary hypertension (high pressure in the pulmonary vascular bed). Patients with advanced copd/emphysema develop increased pressure in their lungs which causes the right side of the heart to dilate/enlarge. This in turn causes fluid retention in the legs/ankles (known as edema).

Depends: Sometimes, people with emphysema had elevated pressure in the lungs due to the destruction of lung tissue. When this happens, it is harder to pump blood through the lungs, and it backs up in the legs and ankles. But, there are also other reasons why this would occur, including heart conditions and even side effects from medications. Definitely get checked out.

Right heart failure.: The right side of the heart pumps blood into the lungs to be oxygenated and for carbon dioxide removal. If the pulmonary vascular pressures are high, as sometimes happens with lung disease like copd, the right heart may not be able to effectively pump the blood into the lungs. This blood then is the reason for fluid retention, including ankle swelling.