Analyzing Sleep with Wearables

Studying Sleep: Wearables or PSG?

Although polysomnography is still considered the gold standard for measuring characteristics of sleep, wearables are proving to be a feasible alternative largely due to their lower cost, reasonable accuracy, and ability to measure sleep in the wild.

What is polysomnography?

Polysomnography (PSG) is a sleep test conducted through a variety of sensors attached to the body. It measures a person’s brain waves, heart rate, breathing, muscle tone, blood oxygen levels, and body and eye movements during sleep. These tests are often done for diagnostic purposes in a hospital or sleep clinic under the supervision of a sleep technologist. 

However, PSG is time-consuming, onerous, and costly. As sensors keep improving, more researchers are now looking to wearable sleep trackers to facilitate sleep research. Wearables can allow researchers to measure sleep onset, wake time, total sleep duration, and time spent in each of the sleep stages. 

The benefits of wearables for measuring sleep

Although wearables are not as accurate as PSG, they are considerably less expensive and the data can be collected for longer stretches of time on account of their comfort and ease of use.  

As you can imagine, it might be difficult for a participant to sleep normally in a clinical setting with cumbersome electrodes stuck to their body. Wearables provide the dual comfort of being in one’s own bed while using an unobtrusive device. Wearing a smartwatch in their own home for weeks (as long as they remember to charge it regularly), can potentially allow for more insight into participants' overall sleep patterns than just one or two nights in a lab can offer.

‍

Sleep interventions

Since they can be worn for longer periods of time in a natural environment, wearables are particularly useful for measuring the effectiveness of interventions on sleep. In a study conducted with breast cancer survivors, researchers used wearable technology to examine the effects of activity intervention on sleep quality. They concluded that wearable technology can increase physical activity and improve sleep for breast cancer survivors.

How wearable devices measure sleep

First, it should be noted that sleep metrics vary by brand. Sleep results from Garmin compared to Fitbit or Apple will look slightly different because they each have their proprietary algorithms to analyze sleep data. That said, most modern wrist-worn wearables monitor sleep by measuring heart rate and movement data from an accelerometer. 

Monitoring body movements through an accelerometer helps determine how much time was likely spent awake versus asleep. Looking at heart rate and the changes throughout the night can approximate the amount of time you spent in each sleep cycle. Some wearable devices may also collect respiration rate data or even use heart rate variability to estimate sleep stages. For example, the Advanced Sleep Monitoring feature on some Garmin smartwatches analyzes the user’s HRV, respiratory rate, heart rate, body movement, and bedtime to give a sleep score.

How accurate are wearable sleep trackers?

Wearables have a reasonable degree of accuracy and have been found to be adequate lower-cost alternatives to measuring sleep variables such as sleep onset and total sleep time in healthy individuals. In fact, a systematic review  of current literature showed that wearables-based sleep monitoring is acceptable in a wide range of clinical applications. 

A key limitation of wearables that only use accelerometer data is mistaking being awake and motionless for sleep. This can be a problem for those who wake multiple times throughout the night or who have insomnia and lie still in bed while awake. Therefore, a watch with optical PPG sensors to measure heart rate is recommended for more accuracy. According to one sleep study, a wearable device using actigraphy and optical heart rate sensors, such as the Garmin vívosmart 4, can estimate sleep stages with nearly 70% accuracy.  

‍

Overall, wearables can provide exciting new opportunities for monitoring sleep in healthy populations. See how Labfront can be used in your next sleep study!  

‍