59 minutes ago at 02:46 pm
https://rk.md/2020/apple-watch-6-does-not-measure-blood-oxygen/Yes, I made this point here in another thread yesterday. 'Blood Oxygen Levels' does not equate to 'Pulse Oximetry'.But even my colleague there simplifies it somewhat...
You can be hypoxic even if your pulse oximetry is normal and your Hb levels are normal.How?If a large proportion of your Hb is in a form that can't carry oxygen (eg. from carbon monoxide poisoning). However, if you ran a sample of the same blood through a laboratory *co-oximeter* it would show that your true saturations are in fact low.
Pulse oximeters measure functional oxygen saturation, ie. what percentage of Hb that can carry oxygen (ie functional Hb), is carrying oxygen. Even hospital pulse oximeters are limited in this way.
Laboratory co-oximeters measure fractional saturation, ie. what percentage of all Hb is carrying oxygen.In short, if your Hb is normal (ie. you're not anaemic) and there is no chance there is a lot of abnormal Hb floating around (Met-Hb, Carboxy-Hb) then pulse oximetry is a good indicator of 'oxygen levels'.None of this really matters to the user, but they really should rename 'Blood Oxygen Levels' to 'Pulse Oximetry'. It's correctly named in the 'Health' app.
If you were significantly anaemic you'd also have an abnormally increased heart rate so perhaps the Watch might pick up on that? I just feel sorry for all my US friends that have to pay lots of money to see a General Practitioner. We pay almost nothing here in Australia (but we do pay - happily - more tax for that benefit).