In order to measure SpO2 you require a red & infrared LED array - not green & infrared. <snip>
A pulse oximeter needs a red & infrared LED due to the unique characteristics of the difference between the absorption spectra of oxygenated haemoglobin & deoxygenated haemoglobin at very specific light frequencies - which just happen to be red (660nm) & infrared (940nm).
Unless the old hardware has a dormant red LED which I’m pretty sure it doesn’t, this will require new hardware.
Disclosure: I’m an Anaesthesiologist.
I worked on developing SpO2 a long time ago, this is a great description. Unless the current watches somehow have more LEDs tucked away, this will require another transmitter/sensor pair - so, a new watch.
The location of the sensors is also tricky. This would be reflective and not transmissive. Most SpO2 is done at the fingertip, where you can easily shine both wavelengths through the fingertip (transmissive) and also capture the pulsatile waveform.
Top of the wrist? That'll be interesting - it will have to be reflective, and that's harder to work with. But Apple has resources - money, time, no doubt some smart hires as well.
Also worked on home-based sleep apnea kits, also a long time ago. The union of SpO2, pulse rate and accelerometer readings (maybe even snore detection) - all on the wrist? That would be game-changing. Undiagnosed sleep apnea is very common - getting people aware that they have signs of it would be quite a win.
No, not a diagnosis. No, not treatment. But there are likely millions out there that would benefit from some level of detection - probably quite a few more than the already-accepted Afib detection.
FDA will of course be involved, as well as their counterparts in other countries. Do you allow actual SpO2 readings to be displayed? Or do you only allow something less than readings?
Fun times. But detecting sleep apnea would be entirely in line with Apple's direction of using technology to help people in real & direct ways.