Too Much Oxygen Not Good

Dr. Kernie (seated) and Dr. Koch

Researchers demonstrate that too
much oxygen may actually inflict
additional harm; © UT Southwestern
Medical Center

Brain damage caused by oxygen deprivation, known as hypoxic-ischemic brain injury, can happen during birth trauma, near drowning and other crises. The researchers found that mice treated with less than a minute of 100 percent oxygen after a hypoxic-ischemic brain injury suffered far greater rates of brain-cell death and coordination problems similar to cerebral palsy than those allowed to recover with room air.

Most of the damage involved cells that create myelin, a fatty substance that insulates nerve cells and allows them to transmit electrical signals quickly and efficiently. Infants have much less myelin than adults; as myelin develops in children they become more coordinated. Areas of the brain with dense areas of myelin appear white, hence the term “white matter.”

“Patients with white-matter injuries develop defects that often result in cerebral palsy and motor deficits,” Doctor Steven Kernie, lead author of the study, said. Myelin comes from cells called glial cells, or glia, which reach out and wrap part of their fatty membranes around the extensions of nerve cells that pass electrical signals. The brain creates and renews its population of glial cells from a pool of immature cells that can develop into mature glia.

In their study, the researchers briefly deprived mice of oxygen, then gave them either 100 percent oxygen or room air, which contains about 21 percent oxygen, 78 percent nitrogen and 1 percent other gases. After 72 hours, mice given 100 percent oxygen fared worse than those given room air.

For example, they experienced a more disrupted pattern of myelination and developed a motor deficit that mimicked cerebral palsy. The population of immature glial cells also diminished, suggesting that the animals would have trouble replacing the myelin in the long term. Kernie said adding pure oxygen to the damaged brain increases a process called oxidative stress, caused by the formation of highly reactive molecules.; Source: UT Southwestern Medical Center