Absence of arterial signal with low diastolic component in the segment proximal to the area indicates what?

• A. Aneurysm
• B. Occlusion
• C. Normal flow
• D. Vasospasm

Answer: (B)

Understanding Doppler signals here hinges on how downstream blockage affects flow patterns upstream. When there’s an area of occlusion downstream, the arterial segment before it loses forward flow because the pathway to the distal bed is blocked. That’s why you can see the absence of signal. The still-present but reduced diastolic component indicates that whatever flow remains to the proximal segment is coming in with higher resistance from the downstream blockage, so diastolic velocity is diminished. This combination—no detectable forward flow with a diminished end-diastolic portion—points to an occlusive process. If the issue were vasospasm, you’d expect the waveform to be damped but not completely absent, and if it were an aneurysm, you’d expect abnormal flow patterns or turbulence rather than a total loss of signal. Normal flow would show a clear systolic upstroke and a robust diastolic component.