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Sleep apnea sufferers may soon breathe easier

Worried, she elbowed him in the side. He roused just enough to inhale deeply, then fell back to sleep. She would do this three more times that night.

Aragon said her husband suffers from sleep apnea — a condition distinguished by infrequent breathing during deep sleep that, according to the National Sleep Foundation, afflicts more than 18 million American adults. Apart from extreme fatigue, sleep apnea can also cause heart disease.

The laboratory of UNM professor Dr. Nancy Kanagy may have found a way to treat the heart disease component. She was recently the first to identify, in an animal model, two main players in sleep apnea’s damaging cardiovascular effects — endothelins and hydrogen sulfide — which could provide promising treatment options, she said.

Endothelins and hydrogen sulfide have opposite roles within the body. Endothelins are potent vasoconstrictors – in other words, they narrows blood vessels, obstructing blood flow and leading to high blood pressure. Conversely, hydrogen sulfide opens blood vessels, a process known as vasodilation. Kanagy said she found that endothelins quickly increased in a model of sleep apnea, while hydrogen sulfide production was decreased — a recipe for high blood pressure.

Sleep apnea is typically caused by blockage of the airway in the area of the throat that connects the mouth and nose to the lungs. People with severe sleep apnea can have their breathing interrupted more than 30 times an hour, or every other minute, for two to 20 seconds at a time, Kanagy said.

As in Aragon’s story, sleep apnea is often discovered by an observer, such as a spouse, who notices that an individual is breathing irregularly. This is a concept with which Kanagy has first-hand experience, as she diagnosed her own husband after studying the disorder for her research, she said.

“If you’ve ever been around someone that has sleep apnea, you can hear that their airway is collapsing, which is the most frequent form of sleep apnea: obstructive sleep apnea. So when you go into REM sleep, you lose all muscle tone — muscle tone that is holding the upper airway open,” Kanagy said. “People with sleep apnea have a narrower airway than normal and often have other structural features of the airway making it susceptible to collapse when the muscle tone goes away during REM sleep.”

When the airway is no longer open the body continues trying to breathe, but oxygen cannot make its way into the lungs.

“When people quit breathing, their oxygen saturation levels are going to fall, and so levels can get as low as 70 percent instead of 95 percent,” Kanagy said. “That would be hypoxic (oxygen-deprived). At the same time that they quit breathing, they stop blowing off CO2, and so CO2 levels can go up a little bit.”

This combination of abnormally low oxygen levels and potentially elevated carbon dioxide triggers a response within the body that leads to high blood pressure, which can cause heart disease. In her animal model of sleep apnea, Kanagy said blood pressure was increased after only seven to 10 days.

Sleep apnea is typically treated by wearing a device called a CPAP, which increases air pressure in the throat and prevents it from closing. However, this involves wearing a mask over the nose and mouth, making it difficult for some patients to sleep. As a result, only about 40 percent of sleep apnea patients use their CPAP every day, Kanagy said.

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“They’ll use it until they get rested enough that they can go for a few days without it, and then they’ll quit using it,” Kanagy said. “Because (regular use of a CPAP) doesn’t happen, preventing cardiovascular disease in those non-compliant patients is very important. I think that an endothelin blocker and a hydrogen sulfide donor should be very effective treatments that could be used at low concentrations that don’t cause side effects.”

Endothelin blockers are available in pill form, while hydrogen sulfide is found naturally in many healthy foods such as kale, cabbage, broccoli and garlic, and may be responsible for many of their heart-healthy properties. Taken together, they could decrease the chance of heart disease.

Kanagy said that while her discovery could help reduce cardiovascular risks, the CPAP is still superior in treating the other health issues caused by sleep apnea, like the extreme fatigue that can make everyday tasks dangerous.

Much of this work was performed by Kanagy’s former graduate student Dr. Olan Jackson-Weaver.

“The project was fascinating work. We got to investigate this mysterious connection between sleep apnea and high blood pressure,” Jackson-Weaver said. “Although the work I did was only the first step in a long process that may someday lead to better treatment of sleep apnea patients, it was still very rewarding to know I was playing a part.”

Lauren Topper is a freelance reporter at the Daily Lobo. She can be contacted at news@dailylobo.com, or on Twitter @DailyLobo.

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