What does an ultrasonic Doppler flow detector measure?

• A. Respiration rate
• B. Red blood cell count
• C. Blood pressure
• D. Blood oxygenation

Answer: (C)

An ultrasonic Doppler flow detector works by emitting ultrasound and listening for the Doppler-shifted echoes from moving blood cells. The frequency shift you detect tells you how fast the blood is moving in that vessel (flow velocity). With the vessel’s cross-sectional area, you could estimate flow rate, but the device’s core measurement is velocity of flow, not counts of cells, respiration, or oxygen saturation. This flow is driven by the pressure difference across the vessel, so the measurement reflects the circulatory status tied to arterial pressure. Among the options, the one related to what the detector’s reading connects to is blood pressure, because arterial pressure is the driving force behind the flow the Doppler detects.