Pure oxygen = brain damage

Pic: At left, yellow outlines multiple brain areas activated by 100 percent oxygen. These regions trigger hyperactivity in the hypothalamus, which reacts by flooding the body with stress hormones and neurotransmitters. At right, adding 5 percent carbon dioxide to the inhaled oxygen calms the hypothalamus and slows the release of harmful chemicals. (Credit: UCLA/Harper lab)

Though our brains and bodies need oxygen to survive, pure oxygen can cause brain damage.

"For decades, the medical community has championed 100 percent oxygen as the gold standard for resuscitation. But no one has reported what happens inside our brains when we inhale pure oxygen," explained Ronald Harper, distinguished professor of neurobiology at the David Geffen School of Medicine at UCLA. "What we discovered adds to a compelling body of evidence for modifying a widely practiced standard of care in the United States."

Thanks to fMRI, they observed the following:

"When the children inhaled pure oxygen, their breathing quickened, resulting in the rapid exhalation of carbon dioxide from their bodies," said coauthor Paul Macey, associate researcher in neurobiology. "The drop in carbon dioxide narrowed their blood vessels, preventing oxygen from reaching tissue in the brain and heart."
That's when something surprising happened on the MRI scan.
Three brain structures suddenly lit up: the hippocampus, which helps control blood pressure; the cingulate cortex, which regulates pain perception and blood pressure; and the insula, which monitors physical and emotional stress.
All this activity awakened the hypothalamus, which regulates heart rate and hormonal outflow. Activation of the hypothalamus triggered a cascade of harmful reactions and released chemicals that can injure the brain and heart.

http://www.sciencedaily.com/releases/2007/05/070521213022.htm