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HOUSTON, Nov. 21 - If toddlers with sleep apnea slept less on their backs their quality of sleep and associated symptoms might improve.

So it appeared from a retrospective study of 60 children under age three that found a direct association between the time children sleep on their back and respiratory disturbances. Symptoms can extend to daytime breathing through the mouth, excessive daytime sleepiness, and behavioral problems, including hyperactivity.

The findings suggest simply repositioning the child during sleep could help alleviate breathing disruptions, Kevin D. Pereira, M.D., a pediatric otolaryngologist at the University of Texas Health Science Center here and colleagues reported in the November issue of Archives of Otolaryngology, Head & Neck Surgery.

During supine sleep the mean respiratory disturbance index-a measurement of sleep disruptions- was 8.5, but then it dropped to 4.9 when children slept on their sides or stomachs, the investigators found.

What's more, when children spent 50% of their sleeping time on their backs, the mean respiratory disturbance index increased from 5.6 to 8.5, Dr. Pereira and colleagues said. When supine sleep accounted for 75% of total sleep time, the respiratory disturbance index went even higher to 10.5.

These findings apply to toddlers but not to infants, the researchers said. Their study included few infants and the authors did not focus specifically on this age groups' breathing, they said.

"Therefore, we cannot comment on the relevance of our findings to the practice of putting infants to sleep on their backs to avoid sudden infant death syndrome," Dr. Pereira and his team wrote. Since 1992, the American Academy of Pediatrics has recommended that infants be placed on their backs, not their stomachs, to reduce the risk of SIDS.

Pediatric obstructive sleep apnea affects 500,000 children a year in the U.S. and is primarily caused by enlarged tonsils and adenoids, Dr. Pereira said. To determine whether there was any relationship between body position and disruptive sleep, the children underwent polysomnography testing between December 2001 and December 2003. They later underwent adenotonsillectomy between December 2000 and November 2003.

The investigators collected data on the child's age, sex, total sleep time, time spent in supine sleep, time spent in rapid eye movement sleep, the frequency of respiratory disruptions in both supine and non-supine positions, and lowest oxygen saturation.

Their analysis showed that as supine sleep decreased, so did the respiratory disturbance index. This finding contradicted earlier research involving children who were ages 10 and younger, which found respiratory disruptions were reduced when patients slept on their backs. It's possible, Dr. Pereira and his colleagues said, that "toddlers have sleep characteristics that are different from those of older children."

Pediatric obstructive sleep apnea syndrome peaks between the ages of two and five, the researchers said, and is prevalent in 2% of this age group. In addition to snoring, the most common symptoms of obstructive sleep apnea syndrome include paradoxical chest motion, cyanosis and poor quality of sleep, and even nocturnal urinating.

When these symptoms are due to enlarged tonsils and adenoids, "most of them are reversed by adenotonsillectomy," the authors said.

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