How the Apple Watch detects sleep apnea

In order to receive certification from a government agency such as the FDA, manufacturers must submit devices for their studies that prove that their products do not cause harm and that they are effective. Apple has now released one such study to detect sleep apnea on the Apple Watch.

On the one hand, the manufacturer points out in the study that the new algorithm on the Apple Watch (from Series 9) detects so-called sleep interruptions, which can indicate the risk of sleep apnea. Basically, the Apple Watch does not use the blood oxygen sensor for this, but rather the watch’s acceleration sensor. The reason for this is probably the legal dispute with the medical company Masimo in the USA.

Apple promises that the Apple Watch’s accelerometer not only registers general body movement, but also micro-vibrations when breathing. Using an algorithm, the device can determine whether breathing stops or is disturbed during sleep. However, the Apple Watch only sends a warning if it has registered a sleep interruption on at least 10 of the 30 nights.

A total of 4,702 participants took part in the design stage of Apple’s study, and 1,499 in the validation stage. Apple says it has trimmed the algorithm to avoid “false positives,” and the specificity is accordingly high – 95.9 percent. The sensitivity is significantly lower and is 66.6 percent.

Explanation of the numbers

One Specificity of 95.5 percent means that a negative test actually means the absence of disease in 95.9 percent of cases. A sensitivity of 66.6 percent means that in 66.6 percent of cases there is actually a disease if the test is positive.

How to interpret the results of the Apple Watch study

The fact that the Apple Watch monitors the body for sleep apnea while you sleep is a good thing. Some studies estimate that sleep apnea occurs in 10 percent of the adult population worldwide. At the same time, the condition is often asymptomatic, especially in the mild and moderate stages; up to 80 percent of those affected are unaware of it. Sleep apnea is one of the risk factors for serious illnesses such as high blood pressure, heart attacks or strokes. At the same time, sleep apnea can be easily and reliably alleviated.

If you receive an alert from your Apple Watch that you may have sleep apnea, there is no need to panic, as in a third of cases it could be a false alarm (see box above). We would recommend that you discuss the Apple Watch results with your GP and have them recheck if necessary.

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