If we look for “sleep” in the mobile phone store, we will certainly find several apps that promise to monitor sleep. Many cell phones even come with sleep assessment functions from the factory. In addition, smartwatches (smart watches) almost always have some functionality related to sleep assessment. These tools together are called sleep monitors (or sleeptrackers). In general, these apps indicate the sleep time at night, as well as how much time has been spent in each sleep stage.
The appeal of these portable monitors is huge: First, because people are very interested in how they sleep at night. In addition, we must remember that polysomnography (the main exam in sleep medicine) is expensive and uncomfortable. Therefore, if we could replace polysomnography with a simple clock or app, we would make it much easier to assess the sleep pattern at night. These arguments are strong, but do portable sleep monitors really work?
One of the great challenges of sleep monitors is to be able to stage sleep, that is, to differentiate the sleep stages that happen during the night and report how much time we spend in each stage. In our night, we go through two major phases of sleep: Non-REM sleep and REM sleep.
REM sleep is one of the most famous stages of sleep as it is when most of our dreams happen. The acronym REM comes from the English term for rapid eye movement (Rapid Eye Movement), precisely because when we dream we move our eyes. This stage of sleep is very important for memory and cognition. People who have decreased REM sleep time can become more inattentive, have memory impairment and other problems related to cognition. This stage is more frequent at the end of the night and corresponds to about 25% of sleep time.
Non-REM sleep is more common in the first half of the night. It is divided into three parts: sleep N1, N2 and N3. Along these three parts our body becomes slower and slower. Our heart, our breathing and our brain gradually slow down. The stage where our functions are most reduced is stage N3, which is also called “slow wave sleep”. While REM sleep was important for brain function, non-REM sleep is very important for body function. It is in it, for example, that growth hormone is secreted. Stage N3 also takes up about 25% of our night.
Note that each stage of sleep plays an important and different role in our body. This is precisely why it is not enough for us to simply estimate sleep time; you need to know how much time passes in each stage of sleep. The Problem of Today's Sleep Monitors
Most of these sleep monitors use cell phone motion sensors and watches to estimate sleep. They are based on the premise that the less we move, the deeper our sleep. This premise is partially true. Based on this type of assessment, it is even possible to estimate the time when someone sleeps and wakes up. However, any analysis beyond that is uncertain. Simple motion analysis is unable to distinguish these stages adequately.
Some apps or devices separate sleep into “shallow sleep” and “deep sleep”. While this may sound interesting, it's a big technical problem. This “deep sleep” is usually quite imprecise, composed of an unclear mix between slow-wave sleep and REM sleep. As you cannot distinguish one from another, you do not know exactly what you are measuring. Other problems can also occur: many of these applications were never compared with the results of a polysomnography. So we run the risk of using information from apps that have never been properly tested and validated.
Still, it would be great to be able to identify sleep stages adequately and portable. As we've talked about before, this could lower sleep medicine costs, providing users with interesting information. In addition, tracking sleep at home can be a great way to check for sleep complaints, as well as monitor whether an insomnia treatment is working.
SleepUp is currently developing its own devices and technologies for sleep monitoring. However, we are aware of all these limitations, as well as a commitment not to launch anything without being sure that the results are reliable and validated. This is our way of respecting the sleep and trust of people who use our services! Keep an eye out for our social networks, as we'll soon have news!