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【medical-news】婴儿瘁死的新奇理论
婴儿瘁死的新奇理论
Provocative new theory on sudden infant death
By Andrea Pitzer, Special for USA TODAY
Breath stops, and the baby turns blue. The pulse slows. Blood pressure drops. The infant is in crisis.
Using a simulation baby ("Sim Baby") to train medical teams to handle just such scenarios, from meningitis to cardiac arrest, pediatric anesthesiologist Daniel Rubens of Children's Hospital and Regional Medical Center in Seattle has long been thinking about infants and sudden death.
During more than 10 years of putting real children to sleep for surgery, Rubens has often considered the mystery most feared by the parents of newborns: sudden infant death syndrome (SIDS).
"I'm a parent myself. I work with babies. (SIDS) is the most disastrous thing that can happen," he says. "Here we are in 2007, but when it comes to understanding why SIDS happens, I don't think we've moved very much at all."
A relative newcomer to SIDS research, British-born Rubens, 44, is making a name for himself with a controversial theory about what causes infants to die in their sleep.
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Rubens' study, published in July in the journal Early Human Development, suggests that SIDS results from an injury to the inner ear and the brain caused by a high-pressure surge of blood from the placenta during delivery. In the months since, as Rubens works to advance his research, the theory has been met with scorn, hopefulness and curiosity from other experts and parent groups.
Working without funding, Rubens and his colleagues studied an archive of newborn hearing tests, comparing those given to babies who later died of SIDS with the testing of similar children who survived. They found that the babies who later died had lower hearing levels in the right ear.
Rubens believes the finding indicates that delicate vestibular hairs in the right inner ear were damaged during birth. He suggests that the hairs, known for their role in maintaining balance, are actually responsible for transmitting information that regulates breathing.
In SIDS infants, when environmental factors interfere with normal breathing, Rubens says, the signal to breathe when the body's carbon dioxide levels increase comes through weakly, if at all. If carbon dioxide levels climb high enough and oxygen levels drop low enough, it can start a death spiral.
If he is correct, he may have solved a mystery that has eluded scientists for generations. But even Rubens acknowledges that some view his work with skepticism.
When colleagues learned that he was looking to the ear for answers, Ruben says, "My impression is that they thought I was nuts."
SIDS kills more than 2,000 infants in the USA each year. According to the National Center for Health Statistics, it is the leading cause of infant deaths.
The National Institutes of Health spends $76 million a year on SIDS research. Since a public-health campaign in the early 1990s to focus on prevention of risk factors, such as putting the baby to sleep on his or her stomach and exposure to secondhand smoke, SIDS deaths have dropped more than 50%, according to the American Academy of Pediatrics.
Idea fits with other observations
Laura Reno, spokeswoman for First Candle, a non-profit SIDS and stillbirth advocacy group, says that if researchers identify the cause, it will give parents "a little more closure and an understanding that maybe something really was wrong with their baby."
Rubens says his theory is compatible with researchers' earlier observations about SIDS:
•Babies die in the first year but not the first three weeks of life. At birth, the baby has an autopilot left over from the fetal state to spur breathing that will remove carbon dioxide. The crossover to adult breathing around 4 weeks of age opens a window of danger.
•SIDS happens during sleep, when breathing and heart rates slow and carbon dioxide increases.
•Overbundling raises body temperature and increases metabolism, using more oxygen when there already isn't enough and creating more carbon dioxide.
•Placing the baby on his or her stomach keeps the chest from expanding, which brings in less oxygen from the lungs.
•Brain-stem abnormalities found in SIDS babies at autopsy may represent additional damage from the placental surge of blood.
Pediatric cardiologist Warren Guntheroth of the University of Washington in Seattle dismisses Rubens' theory as "not biologically plausible."
SIDS researcher and pathologist J. Bruce Beckwith says he doubts that such an injury would allow the infant to live for a month or more, as SIDS babies generally do.
"But that still leaves his data out there, needing to be explained," Beckwith says. He couldn't recall a SIDS study in which a theorized abnormality showed up more consistently in the infants studied.
Still 'a lot to prove'
Rubens is still coordinating Sim Baby's visits to Seattle area medical facilities while he begins the painstaking work of testing his theory. One project focuses on the effects of inner ear damage on breathing in baby mice, and another is in the initial phases, developing mathematical models of high pressure injury and turbulence in blood vessels.
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作者:admin@医学,生命科学 2011-07-14 17:12
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