Adult breathing problems may have childhood cause

According to the National Institutes of Health, as many as 18 million Americans stop breathing for 10 seconds or more during the night. Sensors in the blood, known as carotid body chemoreceptors, react to the lack of oxygen by rousing the body to breathe. But what happens if the sensors stop working?

Professor Gordon Mitchell and Postdoctoral Fellow Ryan Bavis at the School of Veterinary Medicine believe defective carotid body chemoreceptors may help to unravel the mysteries of Sudden Infant Death Syndrome (SIDS) and sleep apnea.

They are exploring the relationship of abnormal oxygen levels to SIDS with Emeritus Professor Gerald Bisgard, and studying the long-term effects of exposure to slightly high or slightly low oxygen levels during early development.

Using rats as a model, they have seen that a slightly elevated oxygen level for several days or weeks during development – such as a baby might encounter in intensive care – leads to a reduced response to low oxygen.

“It’s like they’re blind to low oxygen,” says Mitchell. “The receptors don’t grow and develop naturally with increased oxygen levels. If you’re sleeping and stop breathing, receptors wake you up. If they don’t perform this role, you’re at risk.”

But Mitchell and Bavis say abnormal oxygen levels don’t affect adults in the same way.

“A baby’s brain is a work in progress. Likewise, your breathing is always changing, and if these changes happen early enough, then they become permanent,” Mitchell explains. “Older children and adults don’t change in the same way.”

He estimates that after age 5 in people and two weeks in rats, breathing patterns are fixed. But for rats and people exposed to abnormal oxygen, there is still hope. Rats that had spent most of their early development exposed to slightly elevated oxygen essentially recovered normal breathing responses after several days of repeated exposure to low oxygen.

“It’s a lot like exercising the nerves that control breathing,” Mitchell says.

The idea that early-life experiences affect adult breathing behavior, put forth by Mitchell, is less than 10 years old.

“People 10 years ago thought breathing was fixed, hard-wired from birth,” says Bavis. “It turns out that people have a considerable ability to adapt, which we call plasticity. But when this ability to learn goes awry due to environmental situations, it can lead to pathology.”

“Dr. Mitchell has moved the field of neural control of respiration in new directions,” says Bisgard. “The most significant contribution to new thinking largely involves his idea that the neural control of breathing is capable of plasticity.”