If your Apple Watch alerts you to sleep apnea, here’s what it means and what to do next

By Brenda Goodman, CNN

(CNN) — Already multitool smart devices, Apple Watches added another buzzworthy feature last month: an app to detect sleep apnea.

Sleep apnea is a condition that causes a sleeper’s breathing to pause when the muscles of the throat relax too much and the airway collapses. It can contribute to loud snoring, which the sleeper may not even be aware of. Typically, a partner or roommate picks up on the problem first.

The condition has been linked to a host of health problems, primarily wear and tear on the cardiovascular system, including high blood pressure, stroke, heart attack, heart failure and heart rhythm problems such as atrial fibrillation. It’s also been tied to dementia and daytime sleepiness. And people with sleep apnea are more likely to be involved in traffic accidents, too.

Millions of people are thought to have this disrupted breathing condition but have not been diagnosed, and experts say the new app could be a valuable tool to point people to medical care. The sleep apnea notification is available on the latest Series 10 Apple Watches and some older models after a software update.

As with any kind of new technology, however, the sleep apnea feature has limitations and can have unintended consequences, including worse sleep if someone becomes too focused on the information or anxious about the results.

“We are seeing this phenomenon called orthosomnia. It’s people that get overly anxious about their sleep data and how they maximize and improve their sleep. And they go sometimes to extremes,” said Dr. Robson Capasso, the chief of sleep surgery at the Stanford University School of Medicine.

They may turn to risky supplements or extreme diets in pursuit of an ideal night’s rest.

New ways to track sleep don’t have to be source of stress, though.

“I feel that this is a great tool. It just needs to be implemented correctly,” Capasso said.

Erring on the side of caution

The Apple Watch’s new feature uses the device’s accelerometer, which measures movement, and Apple says it’s so sensitive it can detect even very slight movements of the wrist that correspond with breathing at night.

However, it’s an opt-in feature, so it must be turned on to start working.

In order to detect sleep apnea, the watch measures breathing disturbances during sleep over 30 days. If there are at least 10 sessions with breathing pauses, and at least five of these have abnormally high numbers of pauses, the watch sends a notification to the user.

How well does the feature work?

Apple tested it in almost 1,500 people, some who had normal breathing during sleep and others who had varying degrees of sleep apnea. Each wore the watch for at least 30 nights and also did at least two nights of a more conventional home sleep study with a monitor that recorded a host of factors including nasal pressure, blood oxygen, body position, breathing effort, pulse and leg movement.

Researchers used this home sleep study data to determine each person’s apnea-hypopnea index, the number of times per hour that breathing stops or is reduced. Researchers then compared how well the watch performed to the measures taken during the sleep study.

In general, Apple’s testing found that the watch picked up on any degree of sleep apnea about 66% of the time. It was more accurate at detecting severe bad sleep apnea, correctly alerting users about 89% of the time. It correctly alerted users to moderate breathing problems about 43% of the time.

Apple said it tweaked the watch’s algorithm to err on the side of not giving false positives that might scare users, and that seems to have worked. The new alert didn’t tell normal sleepers that they had sleep apnea 100% of the time.

So, if you get an alert, you can be fairly confident that the result is real and needs follow up with your primary care doctor or a sleep specialist. On the other hand, if you don’t get an alert, it doesn’t necessarily put you in the clear. You may still have sleep apnea, especially if you have other suggestive symptoms.

The company’s study hasn’t been peer-reviewed by outside experts or published in a medical journal. But the US Food and Drug Administration approved marketing of the sleep apnea feature on Apple Watches in mid-September.

There are other wearable devices that also promise to help people figure out whether they have sleep apnea, but the fact that this is an Apple entry into the market has gotten some attention.

“It has come up so many times in conversation,” said Dr. Jing Wang, clinical director of the Mount Sinai Integrative Sleep Center. “I have become more aware of it.”

The algorithm vs. a sleep doctor

Wang says the way the watch works is different from the steps she goes through to make a diagnosis. The watch is relying on wrist movements, but she starts with symptoms.

“Other than the watch saying this, or other than your tracker saying this, what else have you experienced?” Wang said.

Notably, the watch doesn’t ask about symptoms. It also doesn’t use the pulse oxygen feature, which has disappeared on some Apple watches because of an ongoing patent dispute.

Wang says typical things that tip her off to sleep apnea include loud snoring – although not everyone who snores has apnea – a partner who says they can’t sleep because of the noise or who has heard their bedmate stop sleeping at night, a patient who reports waking up choking or gasping, and someone who says they wake up tired or feel exhausted during the day. Morning headaches, high blood pressure and memory problems can also be in the mix, she says.

After this conversation, she would order a sleep study if she thinks it’s necessary. These can be done at home or in a sleep lab, which typically requires an overnight stay at a hospital or sleep center. Sleep studies record multiple variables including blood oxygen, respiratory rate, pauses in breathing and nighttime awakenings.

The Apple Watch has a few of these capabilities, but the company did not factor them into the sleep apnea feature. If it had, it might have been better able to detect mild and moderate cases of apnea, says Dr. Eric Topol, a cardiologist who is founder and director of the Scripps Translational Research Institute.

“When their watch had pulse oximetry in it – now lost – it would have provided useful data, at least in people not of color,” Topol wrote in an email. Studies have shown that wearable devices to detect oxygen, called pulse oximeters, are not as accurate in people with darker skin tones, leading to a push for better devices that are tested on more diverse populations.

“Unlike home tests or sleep labs, where oxygen saturation is continuously measured, the Apple watch algorithm relies on accelerometer measurements of movement, which would explain low sensitivity.”

It may not be such a bad thing that the watch is not so sensitive, Stanford’s Capasso said.

Even with full sleep studies, answers are not clear-cut. The main measure of a sleep study – the apnea-hypopnea index, or AHI – doesn’t always correlate with symptoms, he said. And not all cases of sleep apnea need to be treated.

How sleep apnea is treated

Capasso says that if a patient has many episodes of interrupted breathing and a bunch of drops in oxygen, he knows they need to be treated with a continuous positive airway pressure machine, or CPAP.

The machine is a “glorified air compressor” that delivers a steady stream of air through a mask to hold the airway open during sleep.

“There is plenty of evidence that these patients with frequent drops in oxygen, they have a closer correlation with clinical outcomes down the road, in particular cardiovascular outcomes,” he said.

If he has a patient with an AHI that puts them in the mild to moderate category and they’re also having daytime symptoms of sleepiness and brain fog, he might try also try CPAP.

Not everyone has success with these machines, though. Half of patients who are prescribed this therapy don’t use it the way they should, Capasso said.

For some people with mild apnea, the key to better rest may lie with other options, such as weight loss – which often cures the problem in people who are overweight or obese – and fixing poor sleep hygiene.

“A lot of time, fixing bed-related habits is enough,” he said.

In younger adults with sleep apnea who are not overweight, he might look at anatomical features, like the size of their jaws and tonsils, which can be a factor too.

In the end, he says, he considers a person’s age and the severity of their condition when deciding how aggressive to be with treatment.

Capasso thinks the Apple Watch alerts will be helpful for people who live alone or who don’t have easy access to sleep studies and specialists.

“This can be quite a good screening tool,” he said.

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