Apple Watch: How the sleep apnea feature works

With watchOS 11, Apple is launching a new sleep apnea detection feature on the Apple Watch Ultra 2 and the Apple Watch Series 9 and 10 that can determine whether you may be suffering from sleep apnea. The Apple Watch Series 10 will be available from Friday; watchOS 11 is already available for download. Apple has now revealed details of how the new feature works.

Experts are particularly interested in the sensor that Apple uses to detect signs of sleep apnea. As Apple has now announced, the watch's acceleration sensor is used to detect breathing disorders during sleep. The blood oxygen sensor is not used for this feature.

The detection feature must be approved by the authorities before it can be released on the market. For this purpose, Apple has commissioned a clinical validation, the results of which the company has now published. This documentation describes exactly how the sleep apnea detection function works:

Apple Watch tracks movement using triaxial accelerometers that capture both coarse and fine movements, including those associated with breathing. Apple has developed an algorithm that uses the accelerometer time series data to classify breathing disturbances that occur during sleep tracking, which are temporary interruptions in the breathing pattern. Figure 1 shows the relationship between Apple Watch accelerometer data (X, Y, and Z) and traditional methods of detecting breathing disturbances, including abdominal belts and airflow meters.

The Sleep Apnea Notification feature consists of two components: a nightly measurement of Breathing Disorders and a notification sent to the user when Breathing Disorders scores are elevated over a 30-day period, indicating signs of possible moderate to severe sleep apnea. Note that neither component is intended or approved for use by individuals who have already been diagnosed with sleep apnea. Breathing Disorders is not the same as the AHI.

Using this feature for the first time requires a short onboarding process and enabling sleep tracking on Apple Watch. Once enabled, breathing disorder scores can be viewed in the Health app. Tracking breathing disorder helps users understand their sleep and the behaviors or lifestyle factors that may affect their breathing disorder scores. The notification feature alerts users who are at risk for moderate to severe sleep apnea. An example of breathing disorder data viewed in the iPhone Health app is shown in Figure 2. In this example, the majority of nights were classified as non-elevated, so the time period shown is summarized as non-elevated.

If you are interested in the full documentation, you can find it here.

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