How do pulse oximeters guess the oxygen level in your blood?
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They measure the intensity of certain colors of light that go through your tissue.
The protein hemoglobin in your red blood cells carries oxygen to all parts of your body. If you shine a light through the hemoglobin, its shadow (transmitted light) will be different depending on if it carries oxygen (oxygenated) or if it does not (deoxygenated). To be more specific, deoxygenated blood absorbs more red light than oxygenated blood. For near-infrared light (NIR), the reverse happens, oxygenated blood absorbs more NIR light than deoxygenated.
By measuring the differences in these transmitted colors shining through your tissue during your normal blood flow pulses with a red- and NIR-colored LED, it’s possible to determine the percentage of oxygenated blood vs. deoxygenated blood.
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