RVT Hemodynamics and Doppler Principles 2 — Questions and Answers
Question 1: Which hemodynamic principle states that flow rate equals the pressure gradient divided by resistance?
- Bernoulli's principle
- Poiseuille's law
- Ohm's law analogy for blood flow (Correct answer)
- Laplace's law
Correct answer: Ohm's law analogy for blood flow
The hydraulic analogy to Ohm's law describes blood flow (Q) as the pressure difference (ΔP) divided by vascular resistance (R).
Question 2: In a stenotic vessel, where is the highest flow velocity observed according to the continuity equation?
- Proximal to the stenosis
- At the site of maximum narrowing (Correct answer)
- Distal to the stenosis
- At the vessel wall
Correct answer: At the site of maximum narrowing
The continuity equation (A1V1 = A2V2) requires velocity to increase at the point of greatest cross-sectional area reduction.
Question 3: What does the resistivity index (RI) formula [(PSV - EDV) / PSV] primarily reflect?
- Cardiac output
- Downstream vascular resistance (Correct answer)
- Blood viscosity
- Vessel wall compliance
Correct answer: Downstream vascular resistance
The resistivity index quantifies the pulsatility of flow and correlates with peripheral vascular resistance distal to the sample site.
Question 4: A Doppler angle of 0° between the ultrasound beam and blood flow would result in:
- Zero Doppler shift
- Maximum Doppler shift (Correct answer)
- Aliasing artifact
- Mirror image artifact
Correct answer: Maximum Doppler shift
The cosine of 0° equals 1, making the Doppler equation yield maximum frequency shift when the beam is perfectly parallel to flow.
Question 5: Which waveform characteristic is most consistent with a high-resistance peripheral arterial system at rest?
- Monophasic forward flow throughout diastole
- Biphasic waveform with brief reverse flow
- Triphasic waveform with reverse flow component (Correct answer)
- Continuous low-velocity forward flow
Correct answer: Triphasic waveform with reverse flow component
Normal resting peripheral arteries (e.g., femoral) show triphasic waveforms with a brief reversal in early diastole reflecting high peripheral resistance.
Question 6: Turbulent flow is most likely to develop when the Reynolds number exceeds approximately:
- 200
- 500
- 2000 (Correct answer)
- 5000
Correct answer: 2000
Turbulent flow typically develops when the Reynolds number exceeds approximately 2000, indicating that inertial forces dominate viscous forces.
Question 7: During exercise, peripheral arterial waveforms typically change from triphasic to monophasic because:
- Heart rate decreases
- Peripheral resistance decreases due to vasodilation (Correct answer)
- Blood viscosity increases
- Cardiac output decreases
Correct answer: Peripheral resistance decreases due to vasodilation
Exercise-induced vasodilation in muscle beds reduces peripheral resistance, allowing continuous forward diastolic flow and a monophasic pattern.
RVT Hemodynamics and Doppler Principles 2
Which hemodynamic principle states that flow rate equals the pressure gradient divided by resistance?