Smart watches have emerged in recent years as useful tools for, among other things, tracking health data and sleep in particular. Most smart watches on the market claim to be able to track sleep stages and quality of sleep, while others also track blood oxygen saturation which is used to detect likely sleep apnoea. But how accurate are these devices? Can your watch diagnose you with sleep apnoea and save you having to do a sleep study?
Diagnosing Sleep Apnoea
To make a formal diagnosis of sleep apnoea, you need to monitor several physiological factors overnight, including:
- Sleep stages (most accurately done with EEG electrodes on head)
- Cardiovascular system
- Oxygen saturation
- Body position
- Respiratory effort
Smartwatches cannot monitor all of these things which is why no watch on the market to date has been approved as a medical device for diagnosing sleep apnoea. It is possible that at some time in the future, a commercially sold smartwatch could be used as a medical device. There are level 4 home sleep test devices (not covered by Medicare), such as the ResMed One Test or WatchPAT, that are worn on the wrist or finger and can gather cardiovascular, motion and oxygen data and infer the rest using complex algorithms. These devices are most useful for detecting the most severe cases of sleep apnoea, which then requires a formal diagnosis using a level 1 hospital or level 2 home sleep study test.
No smartwatch is able to definitively diagnose sleep apnoea. The only way to truly diagnose sleep apnoea is with a level 1 or 2 sleep study, either in a hospital setting or with a home sleep study, such as provided by Home Sleep.
What Do Smart Watches Monitor?
Generally speaking, smartwatches monitor sleep based only on movement and heart rate, inbuilt algorithms then extrapolate information based on that data. It’s expected that when you are awake, you are moving around at least somewhat and your heart rate is slightly elevated compared to when you are asleep. When your smartwatch detects a sustained drop in heart rate and no motion, it records you as being asleep. They can infer, sometimes quite accurately, how deep a sleep you are in based on these basic ideas. When they can be fooled, however, is if you are relaxed and still wide awake, while lying down watching television, for instance. On the flip side, sleep apnoea causes you to frequently wake up, elevating your heart rate and causing you to move slightly can mislead the watch into thinking you are in a light sleep or awake when you might actually be in a deep sleep. A lot of watches will be able to monitor with some accuracy how many times you are waking up, which can be useful in screening for potential sleep apnea.
Some watches now also monitor blood oxygen saturation. This can be a very useful detection tool for severe sleep apnoea, but still not enough to diagnose the issue. If your watch shows oxygen desaturations overnight, this means you are very likely to have severe sleep apnoea and would be well advised to get a proper sleep study conducted as soon as possible. If your watch shows no oxygen desaturations, however, this does not mean you are necessarily in the clear. Many people with sleep apnoea are woken up frequently by their obstructed breathing, leading to excess stress on their bodies and tiredness during the day but don’t have the associated oxygen losses. The watches that monitor oxygen saturations also tend to have a low ‘sampling rate’. They can take a measurement every minute or every 5 minutes, which can lead to an underestimation of oxygen desaturation. They are also prone to giving incorrect low blood oxygen levels due to movement artifact. By contrast, the oxygen levels in a sleep study are sampled every second and the movement artifact is marked out based on manual inspection of the pulse signal.
When Should I Get a Sleep Study Done Based on Data from My Watch?
If your watch suggests that you are waking up more frequently than you realise, your heart rate is variable, you spend a long time in light sleep or awake when you feel like you’ve slept, or that your oxygen levels are dropping overnight, it’s a sign that you likely have sleep apnoea and would benefit from getting a proper sleep study conducted to confirm a diagnosis and point you towards the best treatment option for you. Here at Home Sleep, we have seen many patients reach out to us for a sleep study because of data from their smart watch suggesting likely sleep apnoea and we have been able to diagnose sleep apnoea and quickly get them onto the best treatment to make them feel their best again.
With or without a smart watch to give you sleep data, if you are excessively tired during the day, wake up with headaches, have poor concentration, have high blood pressure, are a known snorer, ever wake up choking or gasping and/or have been seen to stop breathing at night, it is a good idea to get a sleep study and find out if you are amongst the many millions of people who can easily get healthier sleep and feel better by simply treating their sleep apnoea.
What About Smart Phones?
There are apps available that monitor breathing patterns and snoring through sound and movement through the phone’s accelerometer that requires you to have your phone in the bed with you. These don’t look at heartrate or oximetry so are even less accurate than watches at measuring sleep stages, but through sound and movement can be useful indicators of likely sleep apnoea. If your sleep app suggests likely sleep apnoea, whether through loud snoring or if it’s detected you waking up frequently, it’s a good idea to follow up with a level 1 or 2 sleep study to get a definitive diagnosis.