Who doesn’t love data, especially their own? With that in mind, I’ve owned several activity trackers over the years, including at least two Fitbits, and I often check on my iPhone to see how far I’ve walked or how many steps I’ve 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’re included on many of the newer activity trackers and smartwatches, but the design and breakdown of daily sleep, activity and alertness counts 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 useful 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 can show findings that warrant further medical refinement,” Neubauer said. “It’s impressive that these devices estimate sleep as well as they do, but there’s a problem with how they divide sleep stages that can make people believe their sleep is worse than it actually 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 has been reorganized into N1, N2 and N3 (combining the older stages 3 and 4, representing “deep sleep” or “slow wave sleep”) and REM sleep. We usually spend more time in N2 than the other phases. However, the device companies often categorize their sleep estimates as “light sleep,” “deep sleep,” or “REM.” With “light sleep,” they lump N1 and N2 sleep together, and that’s misleading, Neubauer said. “It’s understandable that people often think there’s something wrong when their tracker reports they’re spending a lot of time in light sleep, when in fact their sleep may be completely normal.”
Validity of sleep tracker
A study by de Zambotti 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 of total sleep but underestimates the time spent in N3 stage sleep by about 20 minutes while overestimates the time spent in REM sleep by 17 minutes. They concluded that the ring has potential to be clinically useful, but that further studies and validation are needed.
A larger study of the latest, third-generation Oura tracker, conducted by Altini and Kinnunen at Oura Health, found that the added sensors with the new-generation ring led to improved accuracy, but they noted that the study with a healthy population was done. and may 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 . Reid said: “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.”
Clinical uses for sleep trackers
More accurate information can be reassuring for patients. Goes added, “For example, one use could be to help patients limit or wean off long-term hypnotics with a more benign intervention that includes passive monitoring like that in the Oura ring. Some patients are unduly concerned that they are not in state is not. to sleep, and sleep monitoring data may be helpful in reducing some of these concerns so that patients can focus on safer interventions, such as cognitive behavioral therapy for insomnia.” Reid believes that wearable trackers have potential utility in monitoring sleep in patients with insomnia. “In insomnia, sleep state misperception is common. They are hyper-arousal, and they perceive themselves to be awake when in fact they are asleep.”
Goes mentioned another use for sleep trackers in clinical settings. “In our inpatient units, the nurses open the door every hour to check on patients to monitor and document whether they are sleeping. If they check in and the patient is not moving, they will ask the patient to raise their hand, which of course isn’t going to help someone get back to sleep.” Wearable devices can provide data on sleep without the risk of waking patients every hour throughout the night.
Not medical devices
However, Neubauer emphasized that current sleep trackers are not medical devices, saying: “They may measure the same parameters that are measured with medical devices, for example pulse oximetry or sleep conditions, but there is still no simple answer to the question of whether the devices provide reliable data for clinical decision-making.”
Neubauer is skeptical about the accuracy of some of the measures the device provides. “I wouldn’t use the information from a consumer device to rule out obstructive sleep apnea based on good oxygen saturation numbers. So much depends on history — snoring, wheezing awakenings, reports from bedmates and daytime sleepiness. These devices don’t measure respiratory exertion or nasal airflow as sleep studies do. But large drops in oxygen saturation from a consumer device certainly warrant attention for further evaluation.” Neubauer also noted that the parameters on sleep trackers do not distinguish between central or obstructive sleep apnea, and that insurers will not pay for continuous positive airway pressure to treat sleep apnea without a sleep study.
I enjoy looking at the data, even knowing it’s not entirely accurate. As future versions of these multisensor devices become more specific and sensitive, I predict that they will play a role in the diagnosis and treatment of sleep disorders, and we may find more clinical uses for these devices. For now, I’m off to get more exercise, at the suggestion of my tracker!