Oxygen saturation measured with a pulse oximeter on the finger or ear lobe is supposed to be 95%-100%. However, the fingers and ear lobes are pretty peripheral areas — why is the oxygen saturation this high if oxygen is being consumed by cells between the heart and the tip of the finger/earlobe/etc?
I could see oxygen saturation being 95-100% coming directly out of the heart, as it has just been oxygenated by the lungs, but why is it still this high all the way in the peripheral areas of the finger tips? Wouldn’t oxygen be consumed by the cells between the heart and finger tips making it lower?
In: Biology
No. Oxygen only leaves the blood in capillaries. Pulse oximeters, as the name suggests, measure the oxygen saturation in the pulsatile component of the blood i.e. that in the arteries/arterioles, not the capillaries or the veins.
The arterial/arteriolar blood will not have gone through any capillaries yet, so no oxygen has been extracted.
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