Which wavelength combination correctly identifies deoxygenated and oxygenated hemoglobin in dual-wavelength sensing?

Which wavelength combination correctly identifies deoxygenated and oxygenated hemoglobin in dual-wavelength sensing?

• A. 660 nm = deoxy-Hgb, 940 nm = oxy-Hgb
• B. 660 nm = oxy-Hgb, 940 nm = deoxy-Hgb
• C. 700 nm = deoxy-Hgb, 900 nm = oxy-Hgb
• D. 700 nm = oxy-Hgb, 900 nm = deoxy-Hgb

Answer: (A)

Dual-wavelength sensing relies on the differing light-absorption spectra of oxyhemoglobin and deoxygenated hemoglobin. You want one wavelength where deoxy-Hgb absorbs more than oxy-Hgb and another where oxy-Hgb absorbs more than deoxy-Hgb. At 660 nm (red light), deoxy-Hgb has higher extinction than oxy-Hgb, so attenuation at this wavelength mainly reports the amount of deoxygenated blood. At 940 nm (near-infrared), oxy-Hgb absorbs more than deoxy-Hgb, so attenuation here increases with the amount of oxygenated blood. Using these two wavelengths together lets the device estimate the fraction of hemoglobin that is oxygenated versus deoxygenated. Other pairs don’t provide as clear a contrast between the two forms or swap which form dominates at each wavelength, making it harder to distinguish oxygenation levels reliably.

Dual-wavelength sensing relies on the differing light-absorption spectra of oxyhemoglobin and deoxygenated hemoglobin. You want one wavelength where deoxy-Hgb absorbs more than oxy-Hgb and another where oxy-Hgb absorbs more than deoxy-Hgb. At 660 nm (red light), deoxy-Hgb has higher extinction than oxy-Hgb, so attenuation at this wavelength mainly reports the amount of deoxygenated blood. At 940 nm (near-infrared), oxy-Hgb absorbs more than deoxy-Hgb, so attenuation here increases with the amount of oxygenated blood. Using these two wavelengths together lets the device estimate the fraction of hemoglobin that is oxygenated versus deoxygenated.

Other pairs don’t provide as clear a contrast between the two forms or swap which form dominates at each wavelength, making it harder to distinguish oxygenation levels reliably.