Losing O2 isn't a huge deal as humans - it's the outsized effect of replacing O2 with CO2. O2 is 20% of the air, N2 is 78%.
CO2 lives in that last little bit and, given its miniscule contribution to composition, has a far outsized effect.
CO2 lives in that last little bit and, given its miniscule contribution to composition, has a far outsized effect.
The abstract basically says you can subtract the blood carbon monoxide level from the pulse oxymeter's reported blood oxygen level to find the actual blood oxygen level. (They were a bit more precise than that, but it was very nearly one-to-one.)
A pulse oxymeter measures oxygen levels indirectly. It works by checking the colour of your blood. I suppose that the colour of carbon-monoxide poisoned blood must be similar to that of oxygenated blood. Perhaps because carbon monoxide attaches to blood cells in a similar way to pure oxygen.
This is also the source of carbon monoxide toxicity, as it binds to CO tighter than O2.