About the data: We used the family income data from the 2013 American Community Survey. This counts only families, which the government defines as households with two or more people related by birth, marriage or adoption. The graph focuses on families living in the country's 30 most populous cities.
The higher pressure causes swelling in the legs and feet. Congestive heart failure, a condition in which the heart can no longer pump efficiently, causes fluid buildup in the lungs and other parts of the body. Swelling is often most visible in the feet and ankles. Pregnancy can cause edema in the legs as the uterus puts pressure on the vena cava, a major blood vessel that returns blood to the heart from the legs. Fluid retention during pregnancy also can be caused by a more serious condition called preeclampsia.
Muscle activity in the legs helps propel blood and lymphatic fluid upward and out of the legs. Prolonged standing or sitting may cause a buildup of fluid within the lower legs due to gravity and diminished propulsive action of the leg muscles. Extended sitting during air, train or automobile travel may cause significant bilateral ankle edema.