Oura's Rem Sleep Tracking: How It Works

The Oura Ring is a sleep-tracking device that has gained popularity among fitness enthusiasts and celebrities since its debut in 2015. The ring uses infrared and red and green LED light beams to measure your respiratory rate, heart rate, heart-rate variability (HRV), blood oxygen levels, and body temperature. It also has an accelerometer to log your activity and movement.

The Oura Ring measures four separate stages of sleep: awake, REM, light, and deep. While the ring does not directly measure brain waves like medical devices, it uses a combination of movement, skin temperature, resting heart rate, HRV, and respiratory rate to determine which sleep stage your body is in.

The Oura Ring has been validated against polysomnography (PSG), the gold standard sleep laboratory test, with varying results. Some studies have found that the ring's sleep staging agreed with PSG about 65-79% of the time, while others have found that it underestimated or overestimated certain sleep stages.

Overall, the Oura Ring provides a wealth of data about sleep and health and can be a useful tool for improving sleep quality and understanding sleep physiology. However, it is important to note that the accuracy of the data may vary, and there are limitations to the ring's ability to detect certain sleep stages and movements.

The Oura ring uses infrared PPG to measure heart rate, respiration and heart rate variability

The Oura Ring measures directly from the arteries in your finger, rather than the surface capillaries in your wrist. This enables the ring to capture the signal as it leaves the heart, rather than on its return. This is one of the reasons why the Oura Ring is able to deliver research-quality data.

In addition to PPG, the Oura Ring also uses an accelerometer sensor to detect movement. This sensor is highly sensitive and can detect even subtle nighttime movements, such as twitching in a dream or turning over in bed.

The Oura Ring's sleep algorithm was tested and trained using machine learning and contains multiple components, including bedtime detection and sleep staging. The algorithm looks for patterns in the data to identify which sleep stage an individual is in.

It measures directly from arteries in the finger, capturing the signal as it leaves the heart

The Oura Ring is a sleep-tracking device that can be worn on the finger. It measures directly from the arteries in the finger, capturing the signal as it leaves the heart. This is in contrast to other wrist wearables that measure from surface capillaries, which results in a delayed signal.

The Oura Ring uses photoplethysmography (PPG) to measure heart rate, respiration, and heart rate variability at night. PPG refers to the infrared LED that measures these factors. The Oura Ring Gen3 samples PPG at 50Hz, meaning it completes 50 cycles per second.

The Oura Ring's PPG is infrared, which penetrates deeper than the greenlight PPG used in other wearables. It also leverages LEDs on either side of the finger, prioritising the clearest signal. This is in contrast to single-sided wrist wearables.

The Oura Ring's accelerometer sensor, which sits on the finger, enables highly sensitive activity detection for even subtle nighttime movements. This is more sensitive than the accelerometers used in wrist wearables.

Oura uses body temperature and activity patterns to determine if you're asleep or awake

The Oura Ring is a sleep-tracking device that is worn on the finger. It is designed to maximise sleep data quality and uses a combination of your body temperature and activity patterns to determine whether you are asleep or awake.

Oura is one of the only wearables that directly measures skin temperature. It can detect how your body temperature naturally drops as you fall asleep and rises again just before you wake up. Oura picks up on these patterns when you're headed to bed for the night or if you rest during the day.

The ring also has the advantage of a highly sensitive accelerometer to measure your movement. By being located on your finger, Oura can capture your subtlest movements and detect the differences between twitching in a dream, turning over in bed, and getting up for a nighttime trip to the bathroom.

However, it is important to note that the Oura Ring does not directly measure sleep stages, which are primarily correlated with brainwave patterns. Instead, it measures things like heartbeat, respiration, skin temperature, movement of your ring finger, and simple things like that. The software on your phone then analyses all of the data and correlates various sensor measurements and transitions with particular sleep stages.

It measures your movement and changes in your heart rate, respiration and temperature to identify sleep stages

The Oura Ring uses a combination of your body temperature and activity patterns to determine when you're asleep. It is one of the only wearables that directly measures skin temperature, detecting how your body temperature drops as you fall asleep and rises again when you wake up. It also has a highly sensitive accelerometer to measure your movement. This enables the ring to capture your subtlest movements, such as twitching in a dream, turning over in bed, or getting up to use the bathroom.

Once the Oura Ring has determined that you're asleep, it collects detailed data to generate sleep stage graphs called "hypnograms". At the end of the night, the ring takes all of your data and divides your sleep into 5-minute intervals. It then classifies your data into sleep stages—awake, light, deep, and REM—by looking for the most dominant sleep stage patterns in your data. The ring leverages your movement and changes in your heart rate, respiration, and temperature to identify the signatures of each sleep stage.

As you sleep, there are clear patterns that the Oura Ring analyzes for each sleep phase. When you fall asleep, your muscles relax and may jerk, your respiratory rate slows, your heart rate decreases, your body temperature drops, and your movement is suppressed. As you enter deep sleep, your heart rate and respiration become very stable, and your skin temperature is at its highest, indicating maximum vasodilation and a lower core body temperature. Your body becomes immobile to stop you from acting out your dreams. As you transition to REM sleep, your respiratory rate and heart rate increase.

The Oura ring is more comfortable and discreet to wear than most wristband wearable trackers

The Oura Ring is also designed to maximise sleep data quality. It uses infrared PPG (photoplethysmography) to measure heart rate, respiration and heart rate variability, and its accelerometer sensor, located on your finger, enables highly sensitive activity detection for even subtle nighttime movements. The ring measures directly from arteries in your finger, capturing the signal as it leaves the heart, rather than on a delay on the return. It also uses infrared PPG, which penetrates deeper than the greenlight PPG used in other wearables.

The Oura Ring is also one of the only wearables that directly measures skin temperature, detecting how your body temperature drops as you fall asleep and rises again when you wake. This, combined with its highly sensitive accelerometer, enables the Oura Ring to determine when you're asleep and what sleep stage you're in.

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