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How does SleepRate measure sleep?

First of all, how does one measure sleep? The gold standard is polysomnography, or PSG for short. When patients are referred to a sleep laboratory, it is very likely that their sleep will be measured using PSG. Poly is Latin for many, and in polysomnography many aspects of body functioning are monitored including brain waves, eye movements, heart rhythm, muscle activation, breathing effort, and airflow. All in all, the patient usually sleeps with at least 22 wires attached to various parts of their body.

What is done with all of that information? A registered technician examines the recording and uses established criteria to classify each 30-second “epoch” as wake, light sleep, deep sleep, or REM. Some epochs involve a transition between one phase of sleep and another, and are hard to distinguish. Even so, any two experienced raters will likely agree on somewhere between 76-80% of the epochs.

How does SleepRate measure sleep? SleepRate uses a patented algorithm that classifies wake and sleep stages using heart rate variability. This technique was developed through sleep research spanning 20 years. This technique takes advantage of the fact that heart rhythm provides a window into the activity of our autonomic nervous system, that part of the nervous system in charge of all the vital involuntary functions of our body including breathing, muscle tone, and digestion, as well as heart rate. This system has two complementary branches: one that increases the heart beat and is in charge of the fight-or-flight reaction, which prepares the body for alert action, and another that promotes a slow-down, the rest-and-digest response, which prepares the body for relaxation and recovery. The balance between these two branches changes from wake to sleep and between different stages of sleep. For example, our fight-or-flight reaction for alert action quiets down the most when we are in deep sleep, and at the same time the recovery response is taking over. Intriguingly, insomnia is thought to involve 24-hour hyperarousal, or continuous over-activation of the fight-or-flight system, which makes it difficult to obtain adequate and refreshing sleep. 

How does SleepRate differ from other sleep trackers? There are several sleep trackers that use actigraphy, or body movements, to estimate sleep timing and duration. Actigraphy is often measured with sensors embedded in a watch or bracelet, or even your iPhone. Indeed, any tracker that involves placing your iPhone on your bed to measure sleep is using actigraphy. With actigraphy, the basic assumption is that if you are moving more, you are awake, and if you are moving less, you are asleep. This technique is not as accurate as PSG, but works reasonably well in healthy individuals. With individuals suffering from insomnia, however, these devices are significantly less accurate. This makes sense if you consider that individuals with insomnia may lie awake with their bodies relatively still but their mind racing! A sleep tracker using actigraphy will likely classify these periods as sleep although the person is actually all too awake. In sum, accelerometers overestimate total sleep time, and are even less accurate when measuring the sleep of individuals suffering from insomnia.

SleepRate uses heart rate variability to assess sleep. This method is more accurate than actigraphy, and has the added benefit of being able to detect increases in hyperarousal, which is associated with chronic insomnia. This means that with ongoing monitoring, an upcoming period of insomnia could be prevented before it even starts. It turns out that several major consumer sleep trackers are beginning to use heart rate. It should be noted, however, that none of these consumer sleep trackers have been validated against PSG measures, and even sleep scientists are not sure whether they are accurate.

I can’t sleep, I suffer from insomnia, should I have a PSG? In short, probably not, but talk to your doctor to be sure. PSG provides a highly detailed snapshot of a single night of sleep, and is used to diagnose sleep apnea and other abnormalities experienced while asleep. For example, if you or your partner notice that you are gasping for air during sleep, a PSG may be used to test for sleep apnea. Insomnia, on the other hand has a fluctuating course, where sleep quality fluctuates greatly from night to night depending on stress and other factors. Also, individuals suffering from insomnia sometimes find they sleep better in the laboratory than they do at home. For both reasons, PSG data involving a single night of sleep is not used as a means of diagnosing insomnia. Instead, insomnia is diagnosed with a clinical interview.

I can’t sleep, I suffer from insomnia, should I measure my sleep with SleepRate? SleepRate is a valuable tool in helping detect difficulty falling asleep or staying asleep, as is often seen in patients who suffer with insomnia. Importantly, SleepRate is sensitive enough to show you changes over time as your sleep improves, as well as ongoing monitoring to prevent you from entering another period of insomnia. SleepRate will also customize a sleep improvement program for you, based on your sleep data, so that you can ensure you are getting healthy, refreshing sleep.

Who can benefit from SleepRate? Anyone who is curious to know more about their sleep. Each morning SleepRate will give you a sleep report detailing how much you slept, as well as the percentage of time spent in the various sleep stages. This report indicates if you snored, as well as the percentage of the night that you snored. Any loud sounds in the night are recorded for you to listen to and SleepRate will let you know whether or not they disrupted your sleep. Further, an optional sleep improvement service creates treatment plans tailored to each individual; these provide cognitive and behavioral strategies shown to be effective for reducing hyperarousal and improving sleep by numerous, independent scientific studies. In sum, SleepRate can provide insight into your sleep patterns as well as how to improve them.

Adrienne is a SleepRate research scientist and customer advocate.

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