Hypoxia
Hypoxia is a condition in which cells of the body are deprived of oxygen. Despite the varying reasons for hypoxia, depending on the location within the body, the consequence is the same: tissues cannot survive for long without oxygen. Prolonged oxygen deprivation proves fatal to cells. When the brain is involved, the consequence for a person is coma and death.
Cells acquire energy from oxygen and glucose. Most cells can survive for a short period using an anaerobic (lacking oxygen) metabolic process. But brain cells cannot. The damage to brain cells when hypoxia occurs is immediate. Blood carries a limited amount of reserve oxygen and brain cell death can occur within minutes of falling below normal oxygen levels.
There are several types of hypoxia. One of the more common is hypoxic hypoxia; the reduction of the amount of oxygen passing into the blood because of a reduced oxygen exchange (i.e., reduced lung capacity) or high altitudes. Reduction in lung capacity may be a result of lung damage, disease, or removal of portions of the lungs. Smokers are particularly susceptible to hypoxic hypoxia. People who change altitudes can adjust to the lower oxygen pressure as the blood produces more red blood cells carrying additional hemoglobin (the oxygen-carrying molecule in red blood cells).
Hypemic hypoxia occurs when the number of hemoglobin molecules or red blood cells is reduced. Either condition causes a reduction in the oxygen carrying capacity of the blood. Hypemic hypoxia can result from hemorrhage or anemia. It can also be induced by drugs, chemicals, or an increase in carbon monoxide (a condition experienced by smokers).
Stagnant hypoxia occurs as a result of poor blood circulation. Blood flow is reduced by prolonged sitting in one position, cold temperatures, or being exposed to g forces (the inertial force produced by acceleration or gravity). People who fly in aircraft frequently, sit in a chair for hours, or are sedentary may experience this type of hypoxia. It is important for the elderly or those whose movement is restricted to be sure they get enough oxygen to avoid this type of hypoxia.
Histotic hypoxia is the inability of the tissues to use oxygen. When organ tissues are involved, they appear blue in color and are called cyanotic. The blue color associated with cyanosis, especially noted around the lips, is due to the build-up of high levels of deoxygenated hemoglobin in capillaries. Drinking alcoholic beverages, poisoning by cyanide or carbon monoxide, and certain narcotics can impair gaseous exchange in the tissues, and lead to hypoxia. Prolonged hypoxia can lead to tissue damage or death.