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USC Viterbi researchers shed light on sleep apnea

While often overlooked in children, sleep apnea is now understood to have broad lasting effects on childhood development, from stunted growth, to behavioral problems, to obesity through adulthood. According to the American Sleep Apnea Association, the condition affects 1 percent to 4 percent of children, and it may be on the rise as childhood obesity rates increase. Thanks to a grant from the National Institutes of Health, three USC professors were recently charged with studying the condition’s effect on children.

USC Viterbi’s Krishna Nayak, professor of electrical engineering, and Michael Khoo, professor of biomedical engineering, and Dr. Sally L. Davidson Ward, chief of pediatric pulmonology and sleep medicine at Children’s Hospital Los Angeles and associate professor of medicine at the Keck School of Medicine at USC, are developing techniques for understanding how this disease affects all people differently. Such knowledge may help doctors identify treatments tailored to patients’ specific needs.

While nearly everyone has heard of sleep apnea, most people don’t realize just how much variation can exist from person to person. “The NIH study we ran sought to unravel the reasons as to why this diversity in sleep-related breathing behavior occurs,” Khoo said.

First, the researchers are using new, dynamic imaging techniques to see which part of a person’s airway is most prone to collapse. “It used to be assumed that the narrowest point of an airway would naturally be the most likely to collapse,” Nayak said. “We now know that this isn’t always the case.”

For some patients, the problem is a structural one. For others, it may be soft airways that are prone to collapse. Some struggle with the way that their brain controls airway muscle tone while sleeping. Obesity is a major cause of the disease as well, as more weight on the chest and throat can constrict airways during sleep.

Another factor could be related to differences in how wakefulness and sleep affect each person’s breathing. Because breathing and airway muscle tone are controlled by the brain in response to changes in blood oxygen and carbon dioxide levels and changes in the sleep-wake state, the researchers have also looked at how sleep apnea affects these responses.

This isn’t the team’s first work in the field. Three years ago, the group began using MRI machines in a novel way to observe the breathing patterns of patients with sleep apnea. The result: real-time videos of patients breathing while asleep, where doctors could see exactly how the airway was opening and closing, thereby pinpointing the locations and types of collapse.

“I’ve been a sleep medicine physician my whole career,” Ward said, “and I’d never seen [a collapse] happen. I was able to view the MRIs, and that was pretty amazing.”

Since the project began, the team has come a long way. From scanning patients’ breathing in real-time to seeing how airways and brain activity varies on a case-by-case basis. Although their research was initially focused on sleep apnea in children, they are now applying these same techniques to study adults, too. Three years on, they’re getting closer to understanding the diverse causes of the disease.

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