When he gives lectures, Gordon Mitchell likes to quote a wise phrase from the famous film \The Karate Kid""-""No breath, no life.""
Mitchell, a UW-Madison professor of comparative biosciences, along with postdoctoral fellow Ryan Bavis, are trying to figure out why some people just stop breathing. Their research at the UW-Madison School of Veterinary Medicine could one day help prevent breathing disorders such as Sudden Infant Death Syndrome or adult disorders such as sleep apnea, which causes people to stop breathing for 10 or more seconds while asleep.
The two are focusing their research on the carotid body, a small round lump of tissue in the neck next to the carotid artery. It contains important chemoreceptors, which sense the amounts of oxygen and other chemicals in the blood.
""They're watchdogs over your breathing and sleeping,"" Mitchell said. ""But they don't always work as they're supposed to.""
Mitchell said that a decade ago, most scientists thought the function of the respiratory system was fixed from birth. Recent discoveries have questioned that thinking.
""It's something we had always wondered about,"" Mitchell said. ""What's become very apparent is that it's plastic. It's changeable.""
Using rats as models, Mitchell and Bavis are studying how the carotid body develops in infants and young children who are exposed to abnormal amounts of oxygen.
""If you expose rats to high oxygen levels during development, they're unable to respond to an acute oxygen deficiency as adults,"" Bavis said.
Their findings could have implications for infants in intensive care units, where some infants receive oxygen levels well above the natural level of 20 percent.
""Babies in the natal intensive care unit are exposed to high oxygen levels,"" Bavis said. ""It's not uncommon to see 30 percent oxygen.""
While breathing problems may have a childhood cause, it is possible to cure them in adults. When adult rats with underdeveloped carotid bodies are exposed to low oxygen levels, they can recover their breathing ability.
""It's kind of like using physical therapy,"" Mitchell said.
Alternate exposure to normal and low oxygen levels can ""exercise"" the carotid body, explained David Fuller, assistant scientist with the UW-Madison Department of Comparative Biosciences.
""We also tried a sustained low oxygen level,"" Fuller said. ""This affected the brain but not the carotid body.""
Mitchell said if the same low-oxygen treatment worked reliably on human patients, it would not require any complicated procedures.
""We could lower the oxygen coming through a mouthpiece,"" Mitchell said. ""It's actually fairly easy to do.""
Bavis said progress toward human treatments is naturally slow because of the differences in the species. ""Whatever we do to a rat isn't the same as what would happen to a human.""
Mitchell said testing on human infants, especially those with early childhood problems, isn't as easy.
""You would never set up an experiment where you exposed babies to too much oxygen,"" Mitchell said.
In the meantime, researchers will continue to model human responses in animals, and look at existing cases of breathing disorders to help find answers to these often-deadly health problems.
