Question

Which of the following statements related to the operating principle of pulse oximetry are CORRECT?

• A. Pulse oximeter can non-invasively determine arterial oxygen saturation (SpO$_2$) by analyzing the light transmitted through the skin during the systolic phase of the blood flow through the tissue
• B. In a pulse oximeter, isosbestic wavelength is the wavelength at which Hb and HbO$_2$ have same optical absorbance
• C. Pulse oximeter can accurately determine the SpO$_2$ of blood by computing the ratio of absorbances at 660 nm and 905 nm wavelengths
• D. Pulse oximeter can accurately determine the SpO$_2$ of blood by computing the ratio of absorbances at 850 nm and 950 nm wavelengths

Hint:

Pulse oximeters rely on the different absorption spectra of oxyhemoglobin and deoxyhemoglobin at red and infrared wavelengths.

Answer 1

The Correct Option is A, B, C

(A) Pulse oximeters use transmitted light during systole to measure arterial oxygen saturation, so this statement is true.
(B) An isosbestic point is indeed a wavelength where Hb and HbO$_2$ absorb light equally — correct.
(C) Standard pulse oximeters use red (660 nm) and IR (905–940 nm), so this statement is correct.
(D) The pair 850–950 nm is not used for SpO$_2$ measurement — incorrect.