Go with the flow (hemodynamics)
3 main forces controlling blood flow
Cardiac function, pressure gradient, gravity/hydrostatic pressure
Percentage of total blood volume contained in the veins
About 2/3rds
the main purpose of a lower extremity venous ultrasound
R/O or assess DVT
three factors of Virchow’s Triad
Stasis, hypercoagulability, vessel injury
A common symptom of an acute DVT
Limb swelling, calf pain, tenderness, shortness of breath if PE
According to Poiseuille's Law, this factor has the biggest impact on flow
What is vessel radius (to the 4th power)
the role of venous valves
Maintain unidirectional flow
the patient position for scanning the femoral vein
Supine, hip externally rotated, knee slightly flexed
most common site of thrombus formation in the calf
Soleal sinuses
reverse Trendelenburg affect on LE scanning
Helps veins fill for easier visualization
Bernoulli principle in simple terms
Velocity ^ = pressure v ; total energy remains constant if no losses
Calf muscle contraction affects venous blood flow by....
Propels blood toward the heart, reduces venous pressure
primary technique to assess for DVT during scanning
Transverse compression every 2–3 cm
percentage of pulmonary emboli originate from the lower extremities
About 90%
the risk of untreated PE
~30% mortality rate
Volume flow rate formula
Q=A x V (area x mean velocity)
Inspiration's affect on venous return in the legs
Decreases flow (increased abdominal pressure)
the normal appearance of a vein on ultrasound with compression
Vein lumen is echo-free and walls coapt fully
two sonographic features of chronic thrombus
Echogenic, striated or web like, contracted vein, collateral formation, thickened walls, recanalization, calcifications
consistent scanning protocol is critical for LE venous ultrasound because it
Ensures accuracy and reduces operator dependence errors... compressions are vital to complete prior to augments
Describe transmural pressure
Difference between intravascular and interstitial pressure, determining vein shape
Why does edema occur in venous disease?
Increased venous pressure disrupts fluid absorption into lymphatics, fluid enters tissues
Name one provocative maneuver used to evaluate venous flow
Calf augmentation, Valsalva maneuver, distal compression
The condition that involves compression of the left common iliac vein by the right iliac artery.
May-Thurner Syndrome
two differences between acute and chronic thrombus
Acute = hypoechoic, dilated vein, poorly attached; Chronic = echogenic, contracted vein, collaterals, calcification