Which plethysmography method uses backscattered infrared light to detect blood volume changes?

Which plethysmography method uses backscattered infrared light to detect blood volume changes?

• A. Photoplethysmography
• B. Volume plethysmography
• C. tcPO2
• D. Impedance plethysmography

Answer: (A)

Photoplethysmography detects changes in blood volume by using light. When infrared light is shined into tissue, the amount of light that is absorbed versus reflected changes with the pulsatile blood volume in the microvasculature. In backscattered (reflection) photoplethysmography, the sensor reads the light that bounces back from the tissue; during systole, the arterial blood volume increases, more light is absorbed, and the detected signal changes in a characteristic pulsatile pattern. This optical approach is what allows pulse waveform and heart-rate information to be obtained from a fingertip, earlobe, or wearable sensor. Impedance plethysmography, by contrast, relies on electrical impedance changes to infer blood volume, not light; volume plethysmography measures limb volume changes with cuffs or other non-optical methods; tcPO2 measures tissue oxygen tension rather than pulsatile blood volume.

Photoplethysmography detects changes in blood volume by using light. When infrared light is shined into tissue, the amount of light that is absorbed versus reflected changes with the pulsatile blood volume in the microvasculature. In backscattered (reflection) photoplethysmography, the sensor reads the light that bounces back from the tissue; during systole, the arterial blood volume increases, more light is absorbed, and the detected signal changes in a characteristic pulsatile pattern. This optical approach is what allows pulse waveform and heart-rate information to be obtained from a fingertip, earlobe, or wearable sensor.

Impedance plethysmography, by contrast, relies on electrical impedance changes to infer blood volume, not light; volume plethysmography measures limb volume changes with cuffs or other non-optical methods; tcPO2 measures tissue oxygen tension rather than pulsatile blood volume.