The tissues of the body have to have oxygen to live. When the supply of oxygen is inadequate the condition is called “anoxia.” The shortage of oxygen may be apparent in the circulating blood. The red cells of the blood may be inadequate in amount or in the red coloring matter necessary to carry oxygen. Anything that blocks the circulation will also block the oxygen supply. Sometimes the cells of the body are unable, because of changes, to take up the oxygen that reaches them.
Since all parts of the body must have oxygen, a shortage will affect all of them. However, some tissues of the body are much more dependent on oxygen than are others. Most sensitive of all are the tissues of the nervous system. Sudden lack of oxygen to the nervous system results in impairment of judgment, lack of co-ordination of movements, and a condition which, in general, resembles that of a person who is drunk. After the lack of oxygen has persisted the person becomes fatigued, drowsy, inattentive, and unable to respond to ordinary stimuli.
If lack of oxygen to the brain persists, death will result from inability to breathe.
A failure of sufficient oxygen to reach the liver and the muscles where foods are broken down to their ultimate condition for use by the body, results in acidosis and is therefore also incompatible with life. The body tries to meet the threat of anoxia by increasing the breathing rate, by increasing the number of red blood cells, and the amount of red coloring matter. The heart and the kidneys are likewise affected unfavorably if oxygen is not supplied to their cells. The increase in red blood cells and hemoglobin in response to anoxia may begin gradually and continue for weeks. At high altitudes the total increase may reach 40 per cent above the usual.