Science + Technology

UCLA Study Reveals Why Bad Things Happen Inside the Brain When We Inhale Pure Oxygen


It's a scenario straight out of "Grey's Anatomy"— aparamedic or doctor plops a mask over the face of a person struggling tobreathe and begins dispensing pure oxygen.

Yet growing research suggests that inhaling straight oxygencan actually harm the brain. For thefirst time, a new UCLA brain-imaging study reveals why. Published in the May 22edition of the journal Public Library of Science (PLoS)Medicine, the findings fly in the face of national guidelines for medicalpractice and recommend a new approach that adds carbon dioxide to the mix topreserve brain function in patients.

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

Harper's team used functional magnetic resonance imaging (fMRI) to capture detailed pictures of what occurs insidethe human brain during two different breathing scenarios. The technique detectssubtle increases in blood flow triggered by the activation of different partsof the brain, causing these regions to glow or light up on the color scan.

The researchers scanned the brains of 14 healthy children,ages 8 to 15, and monitored their breathing and heart rates as they inhaled 100percent oxygen through a mouthpiece for two minutes. After waiting eightminutes for the youngsters' breathing to return to normal, the team added 5percent carbon dioxide to the gas mixture and repeated the scan.

A comparison of the two scans revealed dramatic differences.

"When the children inhaled pure oxygen, their breathingquickened, resulting in the rapid exhalation of carbon dioxide from theirbodies," said study co-author Paul Macey, a UCLA associate researcher in neurobiology. "The drop in carbondioxide narrowed their blood vessels, preventing oxygen from reaching tissue inthe brain and heart."

That's when something surprising happened on the MRI scan. Threebrain structures suddenly lit up: the hippocampus, which helps control bloodpressure; the cingulate cortex, which regulates painperception and blood pressure; and the insula, whichmonitors physical and emotional stress.

All this activity awakened the hypothalamus, which regulatesheart rate and hormonal outflow. Activation of the hypothalamus triggered acascade of harmful reactions and released chemicals that can injure the brainand heart over time.

"Several brain areas responded to 100 percent oxygen bykicking the hypothalamus into overdrive," explained Harper. "The hypothalamusoverreacted by dumping a massive flood of hormones and neurotransmitters intothe bloodstream. These chemicals interfere with the heart's ability to pumpblood and deliver oxygen — the opposite effect you want when you're trying toresuscitate someone."

When the children inhaled the carbon dioxide–oxygen mix, thehypothalamus' hyperactivity vanished from the MRI scan.

"Adding carbon dioxide to the oxygen relaxed the bloodvessels, allowed oxygen to reach the heart and brain, calmed the hypothalamusand slowed the release of dangerous chemicals," Maceysaid.

"Pure oxygen kindles the match that fuels a forest fire ofharm to the body," Harper said. "But alittle whiff of carbon dioxide makes it all go away."

Based on their findings, the researchers strongly encouragehealth care providers to add carbon dioxide to oxygen dispensation, especiallywhen 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.

"When in doubt about a case, the current medical approach isto increase oxygen levels and wait to see if the patient improves," explainedHarper. "But no one has ever scannedpatients' brains to examine how they respond to oxygen therapy."

Earlier data on high oxygen's harmful effects have alreadyresulted in policy changes overseas. Instead of using straight oxygen, manyEuropean hospitals now resuscitate patients with room air, which contains amixture of nitrogen, oxygen and carbon dioxide, or with a blend of oxygen andcarbon dioxide.

Mary Woo, professor at the UCLA School of Nursing, was a co-authorof the study, which was supported by the National Institute of Child Health andDevelopment.



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