Stagnant Hypoxia
Stagnant means “not flowing,” and stagnant hypoxia, or ischemia, results when the oxygen-rich blood in the lungs is not moving, for one reason or another, to the tissues that need it.
An arm or leg “going to sleep” because the blood flow has accidentally been shut off is one form of stagnant hypoxia.
On a more serious note, this kind of hypoxia can also result from shock, the heart failing to pump blood effectively, or a constricted artery.
A rapid pull up from a steep dive causes a Grey Out due to excessive g-forces that occur during the recovery. This is due to the inability to move oxygen-rich blood to the brain. A Black Out is more pronounced.
Cold temperatures also can reduce circulation and decrease the blood supplied to extremities.
The illustrations with stagnant hypoxia are important but the underlying physiology is simpler.
