Hemodynamics and Doppler Principles Flashcards

Which Doppler waveform pattern is characteristic of a low-resistance vascular bed, such as the internal carotid artery or renal artery?

Answer: Continuous forward flow throughout diastole with broad systolic peak

Organs with continuous metabolic demand (brain, kidneys) maintain low resistance, producing persistent forward diastolic flow on Doppler.

An increased pulsatility index (PI) proximal to a segment of arterial occlusion suggests:

Answer: Increased downstream resistance due to the obstruction

Proximal to an occlusion, high outflow resistance causes the waveform to become more pulsatile with reduced or absent diastolic flow.

The window beneath the systolic peak in a normal arterial spectral waveform is called the spectral window and reflects:

Answer: Laminar plug flow with a narrow velocity profile

A clear spectral window indicates organized laminar flow where most red blood cells travel at similar velocities near the vessel center.

When insonating at a Doppler angle of 60°, a measured velocity of 100 cm/s is obtained. If the true angle is actually 70°, the calculated velocity will be:

Answer: Higher than the true velocity

cos60° (0.50) > cos70° (0.34); using the smaller cosine (60°) to correct gives a higher velocity estimate than if the true 70° angle were used.

In the context of arteriovenous fistula (AVF) surveillance, which Doppler finding is most consistent with significant stenosis at the venous anastomosis?

Answer: Focal velocity elevation with post-stenotic turbulence and decreased access flow

Stenosis at the venous anastomosis causes a focal velocity increase and downstream turbulence while reducing overall access flow volume.

According to Bernoulli's principle, as blood accelerates through a stenosis, what happens to lateral pressure within the narrowed segment?

Answer: Lateral pressure decreases

Bernoulli's principle states that increased kinetic energy (velocity) is accompanied by decreased potential energy (pressure) in the stenosis.

Which of the following best describes the concept of 'critical stenosis' in arterial hemodynamics?

Answer: The degree of stenosis that begins to reduce resting blood flow

Critical stenosis is the threshold (typically ~50–75% diameter reduction) at which the pressure gradient across the lesion begins to reduce resting volumetric flow.