Two-wavelength pulse oximetry uses which two light wavelengths?

Two-wavelength pulse oximetry uses which two light wavelengths?

• A. 660 nm and 940 nm
• B. 700 nm and 900 nm
• C. 660 nm and 780 nm
• D. 520 nm and 900 nm

Answer: (A)

Two-wavelength pulse oximetry relies on how oxyhemoglobin and deoxyhemoglobin absorb light differently at two specific wavelengths, so you can separate their contributions from the overall signal. The red wavelength at about 660 nm is where deoxyhemoglobin absorbs much more than oxyhemoglobin, giving a strong differential signal during the pulse. The infrared wavelength around 940 nm provides a second, independent contrast where the two forms also differ in absorption, helping to solve for the relative amounts of each form. By measuring the pulsatile (AC) change in absorption at both wavelengths and comparing it to the nonpulsatile background (DC), the instrument forms a ratio that cancels out factors like tissue thickness, light scatter, and baseline absorption. This ratio maps to the fraction of hemoglobin that is oxygenated, i.e., the oxygen saturation. That’s why the standard pair used is 660 nm and 940 nm.

Two-wavelength pulse oximetry relies on how oxyhemoglobin and deoxyhemoglobin absorb light differently at two specific wavelengths, so you can separate their contributions from the overall signal. The red wavelength at about 660 nm is where deoxyhemoglobin absorbs much more than oxyhemoglobin, giving a strong differential signal during the pulse. The infrared wavelength around 940 nm provides a second, independent contrast where the two forms also differ in absorption, helping to solve for the relative amounts of each form.

By measuring the pulsatile (AC) change in absorption at both wavelengths and comparing it to the nonpulsatile background (DC), the instrument forms a ratio that cancels out factors like tissue thickness, light scatter, and baseline absorption. This ratio maps to the fraction of hemoglobin that is oxygenated, i.e., the oxygen saturation. That’s why the standard pair used is 660 nm and 940 nm.