In popliteal entrapment syndrome, foot flexion affects the systolic peak by:

• A. Increases by about four times
• B. Decreases by half
• C. No change
• D. Increases by ten times

Answer: (A)

Dynamic compression of the popliteal artery during foot flexion narrows the vessel, so the blood must speed up to maintain flow. In popliteal entrapment, provocative maneuvers like bending the knee and flexing the foot often squeeze the artery, causing a marked rise in peak systolic velocity across the compressed segment. This increase is typically substantial—in many cases about fourfold compared with resting measurements—reflecting how the reduced radius speeds up flow per the physics of blood movement. When the maneuver is released, the velocity tends to return toward baseline, which helps distinguish dynamic entrapment from fixed disease.