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Fitness trackers: Useful in sleep medicine?


 

Who doesn’t love data, especially their own? With that thought in mind, over the years I have owned several activity trackers, including at least two Fitbits, and I frequently check my iPhone to see how far I’ve walked or how many steps I have taken. My most recent acquisition is an Oura (smart ring, third generation), which includes my first sleep tracker.

Sleep trackers are not unique to the Oura Ring; they are included on many of the newer activity trackers and smart watches, but the design and breakdown of daily sleep, activity, and readiness scores are hallmarks of Oura Rings.

The ring generates data for different phases of sleep, movements, oxygen saturation, disturbances in breathing, heart rate, and heart rate variability. I began to wonder how useful this information would be clinically and whether it might be helpful in either the diagnosis or treatment of sleep disorders.

David Neubauer, MD, is a psychiatrist at the Johns Hopkins Sleep Disorders Center. “Sleep tracking devices are more than just toys but less than medical devices. They do have clinical utility and might show findings that warrant further medical workup,” Dr. Neubauer said. “It is impressive that these devices estimate sleep as well as they do, but there is a problem with how they divide sleep stages that can lead people to believe their sleep is worse than it really is.”

For more than 50 years, he explained, sleep researchers and clinicians have categorized sleep as non–rapid eye movement (NREM) sleep stages 1-4 and REM sleep. More recently, sleep was reorganized to N1, N2, and N3 (which combines the older stages 3 and 4, representing “deep sleep” or “slow wave sleep”) and REM sleep. We normally spend more time in N2 than the other stages. However, the device companies often categorize their sleep estimates as “light sleep,” “deep sleep,” or “REM.” With “light sleep,” they are lumping together N1 and N2 sleep, and this is misleading, said Dr. Neubauer. “Understandably, people often think that there is something wrong if their tracker reports they are spending a lot of time in light sleep, when actually their sleep may be entirely normal.”

Sleep tracker validity

A study by Massimiliano de Zambotti, PhD, and colleagues, “The Sleep of the Ring: Comparison of the ŌURA Sleep Tracker Against Polysomnography”, looked at sleep patterns of 41 adolescents and young adults and concluded that the second-generation tracker was accurate in terms of total sleep but underestimated time spent in N3 stage sleep by approximately 20 minutes while overestimating time spent in REM sleep by 17 minutes. They concluded that the ring had potential to be clinically useful but that further studies and validation were needed.

A larger study of the newest, third-generation Oura tracker, conducted by Altini and Kinnunen at Oura Health, found that the added sensors with the newer-generation ring led to improved accuracy, but they noted that the study was done with a healthy population and might not generalize to clinical populations.

Fernando Goes, MD, and Matthew Reid, PhD, both at Johns Hopkins, are working on a multicenter study using the Oura Ring and the mindLAMP app to look at the impact of sleep on mood in people with mood disorders as well as healthy controls. Dr. Reid said that “validation of sleep stages takes a hit when the ring is used in people with insomnia. We find it useful for total sleep time, but when you look at sleep architecture, the concordance is only 60%. And oxygen saturation measures are less accurate in people with dark skin.”

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