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GATE 2022 BM – Question 29

Sensors and Bioinstrumentation · Physiological Measurements · 1 mark · Multiple select

Which statements about pulse oximetry are correct?

  1. Arterial SpO₂ can be estimated noninvasively from transmitted light and the systolic pulsatile blood component
  2. An isosbestic wavelength gives equal absorbance for Hb and HbO₂
  3. SpO₂ can be determined using the absorbance ratio at 660 and 905 nm
  4. SpO₂ can be determined using the absorbance ratio at 850 and 950 nm

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Correct answer: (A) Arterial SpO₂ can be estimated noninvasively from transmitted light and the systolic pulsatile blood component; (B) An isosbestic wavelength gives equal absorbance for Hb and HbO₂; (C) SpO₂ can be determined using the absorbance ratio at 660 and 905 nm

Explanation

A identifies isolation of the arterial pulsatile component. B is the definition of an isosbestic wavelength. The source accepts red 660 nm combined with near-infrared 905 nm as its two-wavelength pair, C, with appropriate empirical calibration. Both wavelengths in D are on the near-infrared side and do not provide the intended red/infrared discrimination. A,B,C are the official selections; a practical oximeter uses calibrated pulsatile ratios, not an uncalibrated raw optical ratio.

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