CVT Vascular Technology & Hemodynamics 3 — Questions and Answers
Question 1: In Poiseuille's law, if the radius of a vessel is halved, the resistance to flow will:
- Double
- Quadruple
- Increase 8-fold
- Increase 16-fold (Correct answer)
Correct answer: Increase 16-fold
Poiseuille's law states resistance is inversely proportional to the fourth power of the radius, so halving the radius increases resistance 16-fold (2^4 = 16).
Question 2: A patient with an abdominal aortic aneurysm (AAA) has swirling color Doppler flow within the sac. This turbulent flow pattern is caused by:
- High-velocity jet through a stenosis
- Flow separation and recirculation within the dilated segment (Correct answer)
- Retrograde flow due to aortic regurgitation
- Arteriovenous fistula formation
Correct answer: Flow separation and recirculation within the dilated segment
Aneurysmal dilation disrupts laminar flow, causing flow separation at the dilated walls and recirculation eddies visible as swirling color Doppler patterns.
Question 3: Which finding on mesenteric duplex ultrasound suggests significant celiac artery stenosis?
- Peak systolic velocity less than 100 cm/s
- Peak systolic velocity greater than 200 cm/s with post-stenotic turbulence (Correct answer)
- Absent end-diastolic flow in the fasting state
- Reversed flow direction in the superior mesenteric artery
Correct answer: Peak systolic velocity greater than 200 cm/s with post-stenotic turbulence
A celiac artery PSV greater than 200 cm/s with post-stenotic turbulence is the threshold for hemodynamically significant stenosis on mesenteric duplex.
Question 4: The normal spectral waveform of the superior mesenteric artery (SMA) in the fasting state is best described as:
- Low-resistance with continuous forward diastolic flow
- High-resistance with absent or reversed diastolic flow (Correct answer)
- Biphasic with a small reversed component
- Monophasic with slow systolic upstroke
Correct answer: High-resistance with absent or reversed diastolic flow
The fasting SMA has a high-resistance waveform with absent or minimal diastolic flow because the intestinal vascular bed is constricted when not digesting.
Question 5: Which color Doppler aliasing pattern indicates the presence of a high-velocity stenotic jet?
- Uniform blue color throughout the vessel
- Mosaic pattern of mixed colors with brightness at the stenosis (Correct answer)
- Absence of color signal in the vessel lumen
- Color reversal from red to blue at the vessel bifurcation
Correct answer: Mosaic pattern of mixed colors with brightness at the stenosis
A mosaic color pattern with a bright core at the stenosis indicates aliasing and flow disturbance caused by a high-velocity jet exceeding the Nyquist limit.
Question 6: Which venous Doppler finding is consistent with right heart failure or elevated central venous pressure?
- Augmented flow with distal compression
- Continuous non-phasic venous flow pattern
- Pulsatile hepatic vein waveform with prominent retrograde flow (Correct answer)
- Absence of venous flow during Valsalva
Correct answer: Pulsatile hepatic vein waveform with prominent retrograde flow
Elevated right heart pressure transmits pulsatility into the hepatic veins, producing exaggerated pulsatile waveforms with prominent retrograde (S-wave reversal) components.
Question 7: When performing a toe-brachial index (TBI), a value below which threshold indicates significant digital ischemia?
- 0.9
- 0.7
- 0.6 (Correct answer)
- 0.4
Correct answer: 0.6
A TBI below 0.6 is considered abnormal and indicates significant digital ischemia; below 0.15 suggests critical ischemia at the digital level.
CVT Vascular Technology & Hemodynamics 3
In Poiseuille's law, if the radius of a vessel is halved, the resistance to flow will: