Hemodynamics and Doppler Principles Flashcards

What is the primary cause of the 'to-and-fro' waveform pattern seen in a pseudoaneurysm neck on duplex ultrasound?

Answer: Bidirectional flow as blood enters during systole and exits during diastole

The neck of a pseudoaneurysm shows forward flow into the sac during systole and reverse flow back into the artery during diastole, creating the classic to-and-fro pattern.

A tardus-parvus waveform pattern distal to an arterial obstruction is characterized by:

Answer: Delayed, rounded systolic peak with reduced amplitude and loss of diastolic reversal

Tardus-parvus (slow-small) describes the damped, delayed waveform seen downstream from a hemodynamically significant stenosis or occlusion.

In renal artery duplex assessment, which indirect parameter best reflects significant proximal renal artery stenosis when direct visualization is limited?

Answer: Renal acceleration time and acceleration index

Acceleration time >70–100 ms and acceleration index <300 cm/s² in intrarenal segmental arteries are indirect indicators of significant proximal renal artery stenosis.

Which parameter is used to calculate volume flow rate (mL/min) when performing duplex assessment of a dialysis access?

Answer: Time-averaged mean velocity and vessel cross-sectional area

Volume flow = time-averaged mean velocity (TAMV) × cross-sectional area (πr²) × 60, providing flow in mL/min.

Harmonic imaging in vascular ultrasound primarily reduces which artifact?

Answer: Near-field clutter and side-lobe artifacts

Tissue harmonic imaging uses second-harmonic frequencies that are generated within tissue, reducing near-field clutter and side-lobe artifacts for improved image quality.

An arteriovenous fistula (AVF) feeding artery typically demonstrates which hemodynamic pattern compared to the contralateral normal artery?

Answer: Lower resistance with increased diastolic flow and elevated peak systolic velocity

The low-resistance shunt of an AVF draws continuous forward flow, causing high-volume, low-resistance flow in the feeding artery with elevated peak systolic and end-diastolic velocities.

When evaluating the vertebral arteries, complete subclavian steal physiology on the symptomatic side is confirmed when Doppler shows:

Answer: Complete reversal of flow direction throughout the entire cardiac cycle

Complete subclavian steal shows fully reversed (retrograde) vertebral artery flow throughout systole and diastole, supplying the ischemic arm via the posterior circulation.