Fitness tracker: Useful in sleep medicine?

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 regularly check my iPhone to see how far I’ve walked or how many steps I’ve taken. My latest purchase is an Oura (smart ring, third generation) which includes my first sleep tracker.

Sleep trackers aren’t unique to the Oura Ring; They’re found in many of the newer activity trackers and smartwatches, but the design and breakdown of daily sleep, activity, and readiness metrics are hallmarks of Oura Rings.

The ring generates data for different sleep phases, movements, oxygen saturation, respiratory disorders, heart rate and heart rate variability. I began to wonder how useful this information would be clinically and if it could be helpful in diagnosing or treating 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 have clinical utility and could show results that warrant further medical workup,” said Neubauer. “It’s impressive that these devices are as good at estimating sleep as they are, but there’s a problem with sleep staging that can lead people to believe their sleep is worse than it really is.”

He explained that sleep researchers and clinicians have classified sleep into stages 1-4 of non-rapid eye movement (NREM) and REM sleep for more than 50 years. More recently, sleep has been restructured into N1, N2, and N3 (combining the older stages 3 and 4 and representing “deep sleep” or “slow wave sleep”) and REM sleep. We usually spend more time in N2 than on the other stages. However, device manufacturers 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. “Understandably, people often think something is wrong when their tracker reports that they’re spending a lot of time lightly sleeping when their sleep can actually be quite normal.”

Validity of the sleep tracker

A study by de Zambotti and colleagues, “The Sleep of the Ring: Comparison of the ŌURA Sleep Tracker Against Polysomnography,” examined the sleep patterns of 41 adolescents and young adults and concluded that the second-generation tracker compared to the Accurately total sleep, however, time spent in N3 sleep stage was underestimated by about 20 minutes, while time spent in REM sleep was overestimated by 17 minutes. They concluded that the ring has the potential to be clinically useful, but that further study and validation is needed.

A larger study of the latest third-generation Oura tracker, conducted by Altini and Kinnunen at Oura Health, found that the additional sensors with the newer-generation ring resulted in improved accuracy, but they found that the study with was performed in a healthy population and may not generalize to clinical populations.

Fernando Goes, MD, and Matthew Reid, PhD, both at Johns Hopkins, are collaborating on a multi-center study using the Oura Ring and the mindLAMP app to examine the effects of sleep on mood in people with mood disorders as well as healthy controls. Reid said: “Validating sleep stages is a blow 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 agreement is only 60%. And oxygen saturation measurements are less accurate in people with dark skin.”

Clinical Applications for Sleep Trackers

More accurate information could prove reassuring to patients. Goes added: “One application could be, for example, to help patients limit or discontinue long-term hypnotics with a more benign intervention that involves passive monitoring like that in the Oura ring.” Some patients are overly concerned about not being able to sleep, and sleep monitoring data can be helpful in allaying some of those concerns so patients can focus on safer interventions, such as cognitive behavioral therapy for insomnia.” Reid believes wearable trackers can help may be useful in monitoring sleep in patients with insomnia.”A misperception of sleep state is common in insomniacs. They are hyper-aroused and perceive they are awake when in fact they are asleep.”

Goes mentioned another use for sleep trackers in clinical settings. “In our inpatient units, nurses open the door every hour to check on patients to monitor and document if they are sleeping. If they look in and the patient doesn’t move, they ask the patient to raise their hand, which of course doesn’t help anyone get back to sleep.” Wearable devices could provide sleep data without the risk of waking patients up every hour throughout the night.

No medical devices

However, Neubauer emphasized that current sleep trackers are not medical devices: “Although they measure the same parameters that are measured with medical devices, for example pulse oximetry or sleep states, there is still no simple answer to the question of whether this is the case and the devices provide it reliable data for clinical decision making.”

Neubauer is skeptical about the accuracy of some of the measurements the device offers. “I would not use consumer device information to rule out obstructive sleep apnea based on good oxygen saturation levels. So much depends on history – snoring, waking up wheezing, reports from bed partners, and daytime sleepiness. These devices do not measure respiratory effort or nasal airflow like sleep studies do. But a sharp drop in oxygen saturation from a consumer device certainly warrants attention for further evaluation.” Neubauer also noted that the parameters on sleep trackers do not differentiate between central or obstructive sleep apnea, and that insurers do not pay for continuous positive airway pressure to diagnose sleep apnea without a sleep study to treat.

I like looking at the data, even though I know it’s not entirely accurate. As future versions of these multi-sensor devices become more specific and sensitive, I predict they will play a role in the diagnosis and treatment of sleep disorders, and we may find more clinical applications for these devices. For now, on the advice of my tracker, I’m heading out to exercise more!