Vascular Chapter 5

What is Laminar flow and what does it look like on Spectral Doppler?

Definition: Smooth streamlined flow where blood layers move parallel to each other. (Fastest in center, slower at vessel walls)

Spectral Doppler: Clean spectral window with a narrow range of velocities.

What causes turbulent flow and what are its key ultrasound features?

Cause: Disorganized flow occurring immediately distal to a stenosis or sudden expansion.

Color Doppler: Mosaic Pattern (mixture of colors/direction)

Spectral Doppler: Spectral Broadening “filling in the spectral window)

Compare High Resistance Vs Low Resistance Wave forms

High Resistance: Sharp sysolic peak with minimal absent, or reversed dialostic flow. (resting extrmity arteries, ECA)

Low Resistance: Continous forward flow throughout diastole (organs requiring constant flow ICA, renal arteries)

What is Bernoullis Principle in vascular hemodynamics?

Principle: Total energy conserved: velocity and pressure are inversely related. (total energy = kinetic + pressure)

Key effect: Blood velocity increases through a stenosis while lateral pressure decreases.

According to Poiseuille’s Law, what single variable has the greatest effect on blood flow resistance?

Vessel Radius (r ) because radius is raised to the 4th power (r4) in Poiseullie’s equation, halving the vessel radius increases resistance by 16 times.

Define Triphasic arterial waveform

Normal resting peripheral arterial flow with 3 components, forward peak, early diastolic reversal, and late diastolic forward flow.

Define Biphasic arterial wave form

Mild diseases/aging or non resting state (forward peak + early diastolic reversal)

Define Monophasic arterial wave forms

Abnormal flow distal to a >50% stenosis (broad peak, delayed rise continuous forward diastolic flow)

What are the three primary mechanisms of venous return from the legs?

Calf Muscle Pump: Muscle contraction squeezes veins upward toward the heart

Venous Valves: Bicuspid valves prevent backward (reflux) flow.

Respiratory Changes: Diaphragmatic movement alters intra-abdominal pressure to propel blood

How does inspiration affect venous blood flow in the lower extremities?

Diaghragm moves down → intra-abdominal pressure increases → lower extremity venous return decreases or pauses.

What are 4 normal Doppler charactersistics of deep venous flow?

1. Spontaneity: Flow presents without squeezing

2. Respiratory Phasicity: flow changes with breathing

3. Augmentation: compression distal to the probe produces a velocity spike

4. Compressibility: Vein completely collapses with direct probe pressure.

What is venous Insuffiency and how is it diagnosed on doppler?

Definition: Failure of valves lading to retrograde pooling of blood

Diagnostic criteria: retrograde doppler flow lasting > 0.5 seconds in superficial veins or > 1.0 second in deep veins following distal squeeze or release.

Compare Ultrasound features of Acute DVT vs Chronic DVT

Acute DVT: Distended/enlarged vein, hypoechoic (dark) soft clot, poorly attached, non compressible.

Chronic DVT; small/contracted vein, hyperechoic (bright) fibrotic clot, firmly attached, presence of collateral vessels

What is Vichrow’s Triad and the 3 major factors predisposing to thrombus formation?

1. Stasis (sluggish flow)

2. Hypercoagulability (increased clotting immediately)

3. Endothelial (damage to vessel wall)