Hypoxia is a reduction in oxygen supply to one or more areas
of the body. Total absence of oxygen is called anoxia. Cells
throughout the body depend on oxygen to survive; when the
oxygen supply is reduced, cells begin to starve and eventually
The brain, which is the body's single largest
consumer of oxygen. Although the brain represents only about
2% of the body's weight, it utilizes about 20% of the body's
oxygen. As a result, the brain is especially sensitive to
hypoxia. After about 4 to 6 minutes without oxygen, large
numbers of brain cells begin to die. Prolonged hypoxia (e.g.
suffocation) results in death.
Shorter intervals of hypoxia may result
in lesser degrees of brain damage. The effects of hypoxia
are especially severe in the hippocampus.
Individuals who survive an hypoxic episode often sustain hippocampal
damage and anterograde
Ischaemic hypoxia is caused by a circulatory
problem. Normally, oxygen is carried throughout the body via
the bloodstream. When the flow of blood is reduced or blocked,
cells which depend on that bloodflow are deprived of oxygen
(and other nutrients). Ischaemic hypoxia can be caused by
a variety of conditions including cardiac arrest, stroke
or aneurysm, and
Anemic hypoxia occurs when oxygen levels
in the blood fall below normal levels. In this case, bloodflow
continues to reach its target areas, but does not bring the
needed oxygen with it. Anemic hypoxia can be caused by conditions
including carbon monoxide poisoning, respiratory failure or
obstruction (e.g. choking or near-suffocation), sleep
apnea, or anesthesia overdose.
Further Reading: "Arrested
by Catherine E. Myers. Copyright © 2006 Memory Loss and the Brain