Pure Oxygen Can Damage the Brain

Researchers at the University of California, Los Angeles (UCLA; USA) used functional magnetic resonance imaging (fMRI) to capture detailed imagesof what occurs inside the human brain during two different breathing scenarios. The researchers scanned the brains of 14 healthy children, ages 8 to 15, and monitored their breathing and heart rates as they inhaled 100% oxygen through a mouthpiece for two minutes. After waiting eight minutes for the youngsters' breathing to return to normal, the team added 5% carbon dioxide to the gas mixture and repeated the scan. A comparison of the two scans revealed dramatic differences.

"Several brain areas responded to 100% oxygen by kicking the hypothalamus into overdrive,” explained lead author Ronald Harper, a professor of neurobiology at the David Geffen School of Medicine at UCLA. "The hypothalamus overreacted by dumping a massive flood of hormones and neurotransmitters into the bloodstream. These chemicals interfere with the heart's ability to pump blood and deliver oxygen--the opposite effect you want when you're trying to resuscitate someone.”

However, when the children inhaled the carbon dioxide-oxygen mix, the hypothalamus' hyperactivity vanished from the MRI scan. The researchers concluded that adding carbon dioxide to the oxygen relaxed the blood vessels, allowed oxygen to reach the heart and brain, calmed the hypothalamus, and slowed the release of the dangerous chemicals. The study was published in the May 22, 2007, edition of the journal Public Library of Science (PLoS) Medicine.

Based on their findings, the researchers strongly encourage health care providers to add carbon dioxide to oxygen dispensation, especially when resuscitating infants or administering oxygen for more than a few minutes. The new direction could hold particular implications for patients of stroke, heart attack, carbon monoxide poisoning, and any long-term oxygen therapy.


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