What is the result of proximal compression during CW Doppler if the valves are competent?

When proximal compression is applied during continuous wave (CW) Doppler ultrasound, and the valves in the venous system are competent, the expected outcome is that flow signals should remain absent. This is due to the normal function of competent valves, which prevent retrograde flow (backward flow) in the veins.

In healthy venous systems, competent valves close during diastole, blocking any reverse flow that could occur when proximal compression is applied. As a result, when the compression is released, the flow should only be in the forward direction, and if the valves operate correctly, there will be no signal indicating the flow of blood back toward the site of compression.

Understanding this principle is crucial for interpreting Doppler signals in vascular studies, as it allows practitioners to determine the competency of venous valves effectively. If the valves were incompetent, then one might expect flow to be present or diminished when compression is applied, but in this case of competent valves, the absence of flow signals confirms the normal function of the valvular system.