This is the VOA Special English Health Report.

Scientists have discovered that stored blood loses a life-saving gas. This discovery may explain why a great number of people get sick after receiving stored blood.

In recent years, experts have wondered why patients who should survive sometimes

die after receiving a blood transfusion. The cause of death is often a heart attack or stroke.

Jonathan Stamler is a professor of medicine at Duke University in North Carolina. He and other researchers found that stored blood has very low levels of nitric oxide. Nitric oxide is a gas found in red blood cells. The gas helps to keep blood passages open so that oxygen in the cells can reach the heart and other organs.

Professor Stamler and his team found that nitric oxide in blood begins to break down as soon as the blood is collected. Their findings were reported in the Proceedings of the National Academy of Sciences.

Another team of Duke University scientists carried out a separate study. Professor Stamler says the second study found that the breakdown of nitric oxide begins within hours of blood collection.

He says the life-saving gas is partly lost after three hours. And about seventy percent of it is lost after just one day. As a result, he says, there is almost no time that stored blood has enough nitric oxide.

The researchers tested their findings on dogs. They found that low levels of nitric oxide reduced the flow of blood in the animals.

However, Professor Stamler says the scientists corrected the situation. They added nitric oxide to the stored blood given to the dogs. He says the extra nitric oxide repaired the ability of red blood cells to expand blood passages.

Professor Stamler says people who are in serious need of a blood transfusion should have one. But he says more studies are needed to show who would receive the most help from stored blood.

And that's the VOA Special English Health Report, written by SooJee Han. For more health news, along with transcripts and MP3 files of our reports, go to www.51VOA.com. And if you have a general question about health, click on the Contact Us link or write to special@voanews.com. We might answer your question in a future report, so please include your name and country. I'm Faith Lapidus.