[How Pulse Oximeters Work]
Pulse oximetry is based on the principle that https://abs.twimg.com/emoji/v2/... draggable="false" alt="1️⃣" title="Tastenkappe Ziffer 1" aria-label="Emoji: Tastenkappe Ziffer 1"> O2Hb (oxyhemoglobin) and https://abs.twimg.com/emoji/v2/... draggable="false" alt="2️⃣" title="Tastenkappe Ziffer 2" aria-label="Emoji: Tastenkappe Ziffer 2"> HHb (deoxyhemoglobin) differentially absorb red and near-infrared (IR) light. Both have differences in absorbance at red (660 nm) and near-IR (940 nm) in the light spectrum

Oxyhemoglobin absorbs greater amounts of IR light and lower amounts of red light than the deoxy form HHb:
https://abs.twimg.com/emoji/v2/... draggable="false" alt="⛔" title="Nicht betreten" aria-label="Emoji: Nicht betreten">Well-oxygenated blood with its higher concentrations of O2Hb appears bright red
https://abs.twimg.com/emoji/v2/... draggable="false" alt="⛔" title="Nicht betreten" aria-label="Emoji: Nicht betreten">HHb absorbs more red light and appears less red

By exploiting the differences in light absorption between oxyhemoglobin and deoxyhemoglobin forms, pulse oximeters emit two wavelengths of light, red at 660 nm and near-IR at 940 nm from a pair of small light-emitting diodes located in one arm of the finger probe.

Light that is transmitted through the finger is then detected by a photodiode on the opposite side of the probe (relative amount of red and IR light absorbed) are used by the device to calculate for the the proportion of Hb bound to oxygen https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Pfeil nach rechts" aria-label="Emoji: Pfeil nach rechts">https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Pfeil nach rechts" aria-label="Emoji: Pfeil nach rechts">https://abs.twimg.com/emoji/v2/... draggable="false" alt="➡️" title="Pfeil nach rechts" aria-label="Emoji: Pfeil nach rechts"> oxygen saturation readings