RVS flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Doppler equation

Relates Doppler shift frequency to blood velocity: f_d = (2·f₀·v·cosθ)/c, where c is tissue sound speed ≈1540 m/s and θ is the angle between beam and flow.

Nyquist limit

Half the pulse repetition frequency (PRF/2). Velocities exceeding it alias on pulsed-wave and color Doppler; raising PRF or lowering frequency reduces aliasing.

Resistive index

RI = (PSV − EDV)/PSV. It reflects distal vascular resistance; high-resistance beds approach 1.0, low-resistance beds (ICA, renal) are lower.

Pulsatility index

PI = (PSV − EDV)/TAMAX. It quantifies waveform pulsatility and is used to assess distal flow changes such as tardus-parvus.

Wall filter

A high-pass filter that removes low-frequency, high-amplitude signals from vessel wall motion. Set too high, it can eliminate slow flow signals.

Color Doppler variance

Color map that displays spectral broadening and turbulence, often as green or yellow added to the standard red/blue velocity map.

Bernoulli equation (simplified)

ΔP = 4v² estimates pressure gradient across a stenosis from peak velocity in m/s. It is used to grade stenosis severity hemodynamically.

Continuous-wave Doppler

Doppler mode with separate transmitting and receiving crystals. It has no Nyquist limit and no depth resolution, useful for high-velocity jets.

Aortic arch branches

Order from right to left: brachiocephalic trunk, left common carotid artery, and left subclavian artery. The brachiocephalic divides into right subclavian and right CCA.

Circle of Willis

Anastomotic ring at the brain base formed by anterior cerebral, anterior communicating, internal carotid, posterior communicating, posterior cerebral, and basilar arteries.

ICA vs ECA waveform

ICA is low resistance with continuous diastolic flow; ECA is high resistance with sharp upstroke and little diastolic flow. This helps identify each vessel.

Temporal tap maneuver

Tapping the superficial temporal artery produces artifact in the ECA spectrum and augments ECA flow, confirming ECA identity; the ICA is unaffected.

Lower extremity deep veins

Deep system includes common femoral, femoral, popliteal, posterior tibial, and peroneal veins, draining into the external iliac vein.

Calf muscle pump

Contraction of calf muscles compresses deep veins, driving blood cephalad through one-way valves. Immobility impairs this pump and promotes venous stasis.

Poiseuille law

Flow is proportional to ΔP·r⁴/(8ηL). Because of the fourth-power radius term, small lumen reductions cause large flow decreases.

Ankle-brachial index

ABI = ankle systolic pressure / brachial systolic pressure. Normal is 1.0–1.4; <0.9 indicates peripheral arterial disease; >1.4 suggests non-compressible vessels.

ICA stenosis velocity criteria

PSV >125 cm/s with ICA/CCA ratio >2.0 suggests ≥50% stenosis; PSV >230 cm/s with EDV >100 cm/s and ratio >4.0 suggests ≥70% stenosis.

Total ICA occlusion

Absent ICA flow, high-resistance or thumping CCA waveform, and often reversed ipsilateral ophthalmic artery flow indicate complete internal carotid occlusion.

Subclavian steal

Vertebral artery flow reversal or mid-systolic deceleration ipsilateral to subclavian stenosis or occlusion, often with arm-exertion symptoms.

DVT compression criterion

Non-compressibility of the vein is the primary ultrasound criterion for deep vein thrombosis; loss of phasic flow and echogenic thrombus support the diagnosis.

Acute versus chronic DVT

Acute thrombus is hypoechoic with a dilated vein; chronic thrombus is echogenic with a contracted vein, collaterals, and valve damage.

Carotid body tumor

A hypervascular mass splaying the ICA and ECA at the bifurcation. Biopsy is avoided because of significant bleeding risk.

Renal artery stenosis signs

Renal artery PSV >180–200 cm/s plus a tardus-parvus waveform distally (delayed upstroke, low RI) suggests hemodynamically significant stenosis.

Pseudoaneurysm features

A sac with color 'yin-yang' flow and a to-and-fro spectral waveform at its neck. Treatment includes compression or thrombin injection.

ALARA principle

Use the lowest output power and shortest exposure time that yields diagnostic information. Ultrasound is non-ionizing but has thermal and mechanical bioeffects.

Mechanical and thermal index

MI estimates cavitation risk and TI estimates heating. Both are displayed on systems and should be kept low, especially in sensitive exams.

Venous compression contraindication

Avoid forceful compression in suspected DVT with severe pain, recent surgery, or known thrombus because of embolization risk; use Doppler instead.

Acute arterial ischemia care

Compression stockings and limb elevation are contraindicated. Keep the limb dependent and warm, and expedite revascularization.

Universal precautions

Gloves for all vascular exams, eye protection when splash risk exists, and appropriate transducer disinfection between patients to prevent cross-contamination.

Patient positioning by exam

Supine for carotid and abdominal exams; reverse Trendelenburg or semi-Fowler for lower extremity venous filling; arms at sides for subclavian access.

Vasovagal response

Prolonged carotid sinus pressure can cause syncope. Stop the exam, lower the head, and monitor vital signs.

Pregnancy Doppler safety

Ultrasound is preferred over ionizing imaging. Limit Doppler to indicated exams and watch MI/TI, particularly in early gestation.