Blood-blockage link to cot deaths

Two studies, in Europe and America, could shed more light on why infants who lie on their stomachs are more likely to die of sudden infant death syndrome.

One shows that lying prone can twist a baby's neck so far that the arteries leading to the head become blocked. The other study found that nerve cells near brain arteries might not work properly.

Both support the view that babies should be put to sleep on their backs.

Sudden infant death syndrome (Sids), also known as cot death or crib death, is a catch-all term to describe inexplicable infant deaths. In the United States more than 2000 babies die of Sids each year.

The number used to be higher. After findings in 1992 that babies who slept on their bellies were at greater risk of Sids, the American Academy of Paediatrics started a campaign to promote back sleeping.

Experts say the campaign resulted in a 40 per cent drop in Sids deaths. Similar publicity in Europe had the same effect.

Sids is also more likely in the babies of mothers who smoke, babies put down in overheated rooms and babies who are wrapped in blankets.

A defect in liver enzymes is blamed in 5 per cent of cases, and some research also points to a defect in the brain stem where breathing is controlled.

Dr Stefan Puig and colleagues at the University of Vienna in Austria looked at 12 babies, six who died of Sids, four who died of trauma such as a car crash and two who died of heart disease.

They twisted their heads the way a baby does when it sleeps.

"If you have a baby, you know that they are much more flexible than adults," Dr Puig said.

Ultrasound was used to test the flow of blood in their neck arteries.

"We found that 71 per cent of the children diagnosed with Sids and 29 per cent of the other infants had narrowed vertebral arteries when they were put on their stomachs and their necks were rotated to the left or right," he said.

"When the neck was rotated and extended, half of both groups had compressed arteries. This study suggests that narrowing of the vertebral artery could be a factor in Sids."

A second study, done at Yale University, found that neurons thought to be important in Sids were near some of the largest arteries supplying the brain.

Dr George Richerson and colleagues said the neurons produced serotonin, an important message-carrying chemical. Earlier research had showed that brain cells that hold serotonin were strongly stimulated by carbon dioxide - suggesting that serotonin helped signal the brain that the gas was present.

"When someone falls asleep with their face in a pillow, carbon dioxide levels rise," Dr Richerson said.

"The normal response is to wake up slightly, turn the head and breathe harder. There is evidence that some infants that die of Sids lack this normal protective response."

If the neurons meant to detect dangerously high levels of carbon dioxide did not work, perhaps the baby suffocated instead of waking up and moving, he said.

Last month, Australian doctors reported that babies who died of Sids had high levels in their blood of a toxin associated with E coli bacteria.

Other researchers reported that babies who were exposed to second-hand smoke had a higher risk of crib death.

- REUTERS

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