In Doppler ultrasound, high resistance distal to the insonation is most consistent with what upstream condition?

• A. Upstream blockage
• B. Downstream obstruction
• C. Normal flow
• D. Increased venous return

Answer: (A)

High resistance downstream is produced when flow into the distal vascular bed is impeded by something upstream. If a blockage sits proximal to the Doppler sample site, the driving pressure entering the downstream vessels is reduced, so the distal arteries tend to show a high-resistance waveform: a prominent systolic peak with diminished or absent diastolic flow. This pattern reflects the impedance imposed by the upstream obstruction. If the obstruction were downstream, the waveform proximal to it would show different changes (such as a damped or tardus‑parvus pattern), not a distal high-resistance signal. Normal flow would preserve diastolic flow, and increased venous return affects venous, not arterial, Doppler patterns.