Timing of Oxygen After a Stoke May Matter

Oct. 19 -- MONDAY, Oct. 19 (HealthDay News) -- Contradicting previous research, scientists have shown in animal studies that providing supplemental oxygen during an ischemic stroke can reduce brain damage.

But it's not a simple matter. Success in preventing brain damage, their new study says, depends on when 100 percent oxygen is given.

"The use of supplemental oxygen after blood flow is restored in the brain appears to actually cause harm by unleashing free radicals," Savita Khanna, an assistant professor of surgery at Ohio State University and principal investigator of the new study, said in a university news release. "The resulting tissue damage was worse than stroke-affected tissue that received no treatment at all."

The findings were scheduled to be presented Oct. 19 at the Society for Neuroscience annual meeting in Chicago.

According to the study authors, earlier research in people suggested that administration of oxygen actually could hurt those who'd had a stroke. But Khanna said it's crucial to consider the status of blood flow through the brain when someone is given oxygen.

The researchers looked at ischemic strokes, in which a blockage stops blood flow in the brain. In the other type of stroke, called hemorrhagic stroke, a blood vessel in the brain ruptures.

In the study, oxygen was given to five groups of rats that had induced strokes. Four groups were given normal oxygen or pressurized oxygen; some got it while blood flow was restricted, and others received it when blood flow was restored. One group of mice just breathed room air.

The researchers scanned the brains of the rats after two days to determine how much brain tissue was damaged. They found brain damage in the rats that were given supplemental oxygen while blood flow was blocked.

"Ultimately, the supplemental oxygen after blood flow is restored is more than the tissue can handle and is more than it needs," Cameron Rink, an assistant professor of surgery at Ohio State and a study co-investigator, said in the news release. "Why add oxygen on top of tissue that's already oxygenated? Supplemental oxygen during the blockage, on the other hand, is highly protective."