Plethysmography measures which of the following?

• A. Blood pressure
• B. Volume changes
• C. Oxygen saturation
• D. Flow velocity

Answer: (B)

Plethysmography measures changes in volume within a limb or organ over time, reflecting how blood volume rises and falls with each heartbeat and with venous outflow. This makes it the best choice because it directly tracks volume changes rather than a static pressure reading, oxygen content, or flow speed. Blood pressure is a pressure measurement; oxygen saturation is the proportion of hemoglobin carrying oxygen; flow velocity is the speed of blood flow. Plethysmography uses sensors (air, infrared light, or electrical impedance) to detect limb volume changes, producing a waveform that represents volume variation rather than pressure, oxygenation, or velocity.