Oxygen-carrying capacity of the blood is reduced. Moreover, the sickled cells do not flow freely but tend to clump together and clog the blood vessels, particularly the narrow capillaries . These blockages further hinder the delivery of oxygen and produce harmful areas of dead tissue in body organs. The heart must work too hard to compensate for the anemic blood it is pumping. The heart rate is rapid and palpitating, and the heart itself may become overenlarged and susceptible to failure.
Hypoxia is both a cause and effect of sickling and becomes part of a vicious cycle.
It can be triggered by a temporary reduction of oxygen in one localized area of the body through infection, stress, or even exertion. As the red blood cells in that area sickle, they produce shortages of oxygen elsewhere in the bloodstream and further sickling. Not only do the sickled cells break down faster than they can be replaced, they sometimes decay more quickly than their resulting waste products can be disposed of by the liver . These wastes then build up in the bloodstream, causing a yellowish discoloration of the skin , the mucous membranes, and the whites of the eyes. The liver itself may be enlarged and tender, and dead tissue may cause it to be permanently damaged.