Sleep Apps: Detecting Rem Sleep, How Does It Work?

Sleep apps are a popular way to track sleep and improve sleep quality. These apps can be used as a standalone or in conjunction with wearables. They use the phone's built-in accelerometer, microphone, and speaker to collect data about the user's sleep. This data includes movement, heart rate, respiration rate, and environmental factors such as light and temperature. The app then uses algorithms and statistical analysis to determine the different stages of sleep, including REM sleep, and provide insights to the user about their sleep quality and duration. While these apps can be useful for tracking sleep patterns and making suggestions for improvement, they have limitations and should not be solely relied upon for diagnosing sleep disorders.

Heart rate and respiration

Sleep apps can track your heart rate and respiration while you sleep, which can give you greater insight into your overall health. For example, the Apple Watch Series 9 can break your sleep down into four stages based on the heart rate sensor and the accelerometer. Newer models can also measure blood oxygen and temperature. The Apple Health app can be used to set up sleep goals and create a customised sleep schedule. The app can also be used to view your sleep history, including your heart rate and respiratory rate in relation to your time spent asleep.

The Oura Ring 4 is another example of a sleep tracker that monitors your heart rate, temperature trends, and blood oxygen levels. The data is translated into three scores: Sleep Score, Activity Score, and Readiness Score. The Whoop 4.0 is a similar device that monitors your heart rate, respiratory rate, blood oxygen levels, and skin temperature.

The Muse S Headband Sleep Tracker is a wearable device that measures brain activity, movement, heart rate, and breathing. The Withings Sleep Tracking Mat is a non-wearable device that can be placed under your mattress to detect heart rate, breathing, and movement.

Environmental factors

• Light and temperature: Some sleep trackers record environmental factors such as the amount of light or temperature in the bedroom. These factors can influence sleep quality and quantity. For example, a warmer temperature may cause more frequent waking throughout the night.
• Noise: Some sleep trackers use a microphone to capture noise from the room or the user's body. This can include snoring, which is an indicator of sleep quality and potential sleep disorders such as sleep apnea.
• Heart rate and respiration: While not strictly environmental factors, heart rate and respiration rates are considered important parameters of physiological data. They vary significantly during sleep and are closely related to each sleep stage, as the autonomic nervous system influences both. Respiration, in particular, is considered the most important parameter as it clearly indicates sleep disorders such as snoring and sleep apnea.
• Lifestyle factors: Some trackers prompt users to input information about activities that can affect sleep, such as caffeine consumption, meal times, and stress levels. By tracking these factors, users can identify patterns and make adjustments to improve their sleep.

Actigraphy

The actigraph is an integrated electronic device that generally embeds a real-time clock or timer to start/stop the recording at specific times and to record accumulated values for a specific time frame. It also has a non-volatile memory to store the resulting values and an interface, usually USB, serial, or low-power wireless, to program the timer and download the data from memory.

Tracking sleep cycles

Sleep tracking is a relatively new area of technology that tech companies are still experimenting with. There are several ways to track your sleep, from wearable devices to phone apps.

Sleep tracking devices and apps can help you determine how often you wake up at night and whether you are entering the deep sleep stages your body needs. They can also help you identify patterns in your sleep habits. For example, you might find that you feel more sluggish sleeping from 10 pm to 6 am, but more energetic if you sleep from 11 pm to 7 am.

Most sleep trackers measure sleep quantity and quality using accelerometers, which are small motion detectors. Accelerometers measure how much you move while you sleep. This data is then analysed using an algorithm to estimate sleep time and quality. However, accelerometers cannot accurately measure sleep stages because there is little difference in movement between the different stages.

Some sleep trackers estimate REM sleep in addition to deep and light sleep by measuring heart rate. Heart rate and respiration rates are known to vary during sleep and are closely related to each sleep stage since the autonomic nervous system significantly affects both. Respiration is considered the most important parameter of physiological data because it clearly indicates sleep disorders such as snoring and sleep apnea.

Some sleep trackers also use a microphone to capture noise from the room or your body. For example, if you are moving frequently and not sleeping well, some trackers will note that. A microphone can also measure your respiration, detecting snoring, sleep apnea, and how often you wake up during the night. Some trackers with thermometers can measure the temperature of your room and may show that you wake up frequently when it is too warm.

If you are looking for a wearable-free option, there are several phone apps that can track your sleep. For example, Sleep as Android works with or without connected wearables. It uses your phone's built-in accelerometer to assess how restful your sleep is, then runs algorithms and statistical analysis to split your sleep up into deep and light periods. Every morning, you can see how many hours of sleep you got, plus a score indicating how well you slept.

Pillow is another app that can work with an Apple Watch or just an iPhone placed on the bed. It analyses your movements through the night to record how long you've been sleeping and splits your sleep into three categories: light, deep, and REM. It also has a smart alarm feature that uses your movements to find the best time to wake you up.

SleepScore can work from your bedside table or your mattress, using readings from your phone's microphone and speaker to judge how well you're sleeping. The tracking is detailed, covering how long it takes you to fall asleep, and the time spent in light, deep, and REM sleep. The app also asks you to set goals, such as falling asleep more quickly or having more energy in the mornings, and provides suggestions on how to improve your sleep.

Sleep Cycle Alarm Clock gives you at-a-glance information about your sleeping habits, including periods of wakefulness and light and deep sleep, which you can measure over time. It also has a smart alarm clock feature that will wake you up when your body is in a lighter period of sleep.

While these apps can be useful for tracking your sleep, they have their limitations. For example, if you sleep with a partner or a pet, this can mess up the data. Additionally, these apps cannot directly track REM sleep, which is the cycle with the highest amount of brain activity.

Limitations of sleep apps

Sleep apps have become increasingly popular due to their accessibility and ease of use. However, they do come with certain limitations and concerns.

Firstly, there are data privacy concerns with many sleep apps. While these apps collect highly sensitive information, such as sleep habits, their privacy policies often state that user data may be shared with business and marketing partners for research and analysis purposes. This data can be used for targeted advertising, with marketing companies sending online advertisements based on user data. For example, if a user's sleep data suggests frequent sexual intercourse, they may receive multiple advertisements for contraceptives. Furthermore, online hackers have been able to access unencrypted audio files of users' sleep sounds, and malicious apps with read storage permission can send these recordings to external servers.

Secondly, few sleep apps are supported by rigorous empirical evidence or clinical input. A review of sleep apps in the Google Play Store found that only 32.9% demonstrated empirical evidence for their claims, and only 15.8% were developed with clinician input. Additionally, a systematic review of sleep apps that detect sleep parameters showed that only 3 out of 73 apps had undergone validation studies using polysomnography, the gold standard for sleep studies. These validation studies demonstrated a weak correlation between polysomnography and the sleep apps, including the detection of sleep stages.

Thirdly, sleep apps may increase engagement with healthcare professionals, which could place additional strain on already overburdened sleep services. This is compounded by the fact that some sleep apps produce many false positives, and clinicians would need additional time and training to analyze the data provided by these apps, as there are no standardized methods for presenting sleep app data.

Lastly, sleep apps should not be considered a replacement for medical advice or a clinical sleep study. While they can provide insights into sleep patterns and help identify variables that contribute to better sleep, they are not a substitute for professional medical care.

In conclusion, while sleep apps offer convenience and accessibility, users should be aware of the limitations and concerns associated with them, including data privacy issues, lack of empirical evidence, potential strain on healthcare services, and the need for professional medical advice.

Frequently asked questions