Overheating can significantly increase the chance of a newborn succumbing to Sudden Infant Death Syndrome, researchers at Dartmouth Medical School determined in a study presented to the American Physiological Society on April 18.
The researchers found that inhibiting breathing and increasing the temperature of newborn piglets by as little as four to five degrees Fahrenheit produced prolonged periods of unstable breathing.
SIDS accounts for 2,500 deaths in the United States each year, and affects roughly one in 2,000 infants. The incidence of the disease has declined dramatically in the last decade due to a campaign to convince parents to put their children to sleep lying on their backs. For reasons that are not entirely understood, this decreases the chance of SIDS.
SIDS occurs more often during winter months, when babies are wrapped up in blankets and then moved indoors, where they overheat.
In conducting the study, the researchers studied infant pigs, placing drops of distilled water directly on the piglets' larynxes. This procedure was meant to simulate mild regurgitation, a common occurrence in infants. The study compared pigs at room temperature to pigs that had been warmed by several degrees. The researchers observed that the 19 warmed pigs ceased breathing for longer periods of time than their unheated counterparts when water was placed on their larynxes.
Although infant pigs are analogous to human infants in many ways, the pigs used underwent an extensive preparation process that could have reduced the relevance the results of study to human infants, the researchers said. They plan to repeat the study with certain key changes, they said.
"We're going to repeat this injection of water into the larynx on intact pigs while they are both asleep and awake," Dr. Donald Barlett said.
Researchers performed a lobotomy on the thinking and sensing parts of the pigs' brains so that they wouldn't be forced to heavily anesthetize the animals. The repeated study by Barlett and his co-researchers will instead use electrodes to determine when the pigs fall asleep and then introduce an inhibitory stimulus to breathing.
Barlett said he became interested in the subject of SIDS about five years ago but did not begin work on this study until six months ago. Other recent research related to SIDS had focused on understanding the reflexes in the upper throat. Barlett and his colleagues began examine heat as a factor in SIDS cases after seeing a study published by Dr. Shosuke Haraguchi in 1983 which showed that anesthetized puppies needed smaller electrical shocks to close their larynxes as their body temperatures increased.
Other possible directions for future research include studying the pathways that could cause heat to impair breathing. The brain stem is the most likely culprit, according to Barlett.
The study, conducted by Barlett and coauthors Luxi Xia and James Leiter, was supported by a grant from the National Institute of Child Health and Human Development.
