Sleep Apnea detection on the Apple Watch could have been much better with Blood Oxygen data.
Lauren Jeffries from Tom’s Guide talking about how reliable Apple Watch’s sleep apnea detection works:
To avoid the possibility of false positives, Apple decided to prioritise specificity over sensitivity. These terms mean:
Specificity: The percentage of those without moderate to severe sleep apnea who wouldn’t receive a notification
Sensitivity: The percentage of participants with moderate to severe sleep apnea who are correctly identified by the algorithm.
Apple recorded the notification performance as 66.6% for sensitivity and 95.9% for specificity. This means that there is potential for many cases of sleep apnea to remain undetected even when using the Apple Watch.
This is what concerns Dr Runge, who says, "The lack of accuracy is a significant issue. I don’t mind the idea that the Apple Watch will “over diagnose” sleep apnea. At least in that setting people will get formal evaluations. It is the under diagnosis that concerns me — people with sleep apnea may say to their partner 'see, I told you I didn’t have sleep apnea.'"
If you look at Apple’s study, sensitivity for severe sleep apnea had a sensitivity of 89.1%, while sensitivity for moderate sleep apnea was 43.4%, giving an average score of 66.3%. What that actually means is the Apple Watch is best at detecting severe sleep apnea 89% of the time. It is not that great at determining moderate sleep apnea at only 43%.
Apple would rather underdiagnose people than give false positives, which is still better than no diagnosis at all. They were able to get this far with just the accelerometer sensor:
The Sleep Apnea Notification Feature is a software-based medical device that analyzes Breathing Disturbance data collected nightly by the Apple Watch accelerometer sensor.
I wonder how much better the Apple Watch could have been at detecting Sleep Apnea if they included Blood Oxygen data, which is another key component in diagnosing sleep apnea. To perform another study at this scale would take years, but it wouldn’t surprise me if Apple’s sleep apnea detection gets better sensitivity with more crucial data points like blood oxygen levels once the battle with Masimo ends.