The feeling of discomfort usually causes a person to move the part affected, thus restoring blood to the muscles. When an arm or leg is pinned into one position for a long time artificially, however, damage, including gangrene , can occur. Another mild and easily remedied form of ischemia is familiar to anyone who has had leg cramps after heavy exertion with the leg muscles . An insufficient blood supply causes these cramps, which dissipate after a brief rest. Ischemia in the brain or heart is especially serious.
Brain tissue is particularly sensitive to blood supply.
The brain or any part of it dies if deprived of blood for only four or five minutes. Heart tissue also dies in a matter of minutes if deprived of blood. By contrast, the kidneys can go on functioning without adequate blood for an hour or more. A heart attack is perhaps the most serious condition that can be precipitated by ischemia of the heart . Also very serious is stroke from ischemia in part of the brain .