Peripheral Venous
The normal venous signature
A normal lower-extremity vein is spontaneous, phasic with respiration, augments with distal compression and release, non-pulsatile, and fully compressible under probe pressure. Loss of phasicity points to proximal obstruction; continuous non-phasic flow may indicate a proximal stenosis or collateral pathway.
Acute versus chronic thrombus
Acute deep vein thrombosis: the vein is distended, walls are thin, the lumen is hypoechoic or anechoic, it will not compress, and collaterals are absent. Chronic changes: small echogenic vein, partial compressibility, recanalization, prominent collaterals, damaged valves. Trap: partially recanalized chronic thrombus is often misread as acute. Vein caliber and echogenicity, not compression alone, are the discriminators.
Reflux testing
Test with the patient upright or in reverse Trendelenburg. Use Valsalva for the common femoral segment and manual or cuff compression more distally. Reflux is defined by duration of reversed flow: roughly above 0.5 s in deep veins and in the great and small saphenous veins, and above 0.35 s in perforating veins, though thresholds vary by laboratory protocol. Superficial reflux at the saphenofemoral junction above 0.5 s with a dilated great saphenous vein supports incompetence.
Worked example
Calf compression with release produces 1.2 s of retrograde popliteal flow. That exceeds the 0.5 s threshold, so the popliteal valve is incompetent. Note that the maneuver matters: reflux measured with the patient supine and no provocation is frequently underestimated.