CAQ-CVTS flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Doppler equation
- Frequency shift equals twice the transmitted frequency times velocity times cosine of the Doppler angle, divided by tissue sound speed of about 1540 m/s. The factor two accounts for the round trip.
- Nyquist limit
- Half the pulse repetition frequency; Doppler shifts above this value alias. Correct by raising PRF, lowering frequency, increasing the angle toward 60 degrees, or switching to continuous wave.
- Resistive index
- Peak systolic velocity minus end-diastolic velocity, divided by peak systolic velocity. Values above roughly 0.70 to 0.75 in native renal arteries suggest increased downstream resistance.
- Pulsatility index
- Peak systolic velocity minus end-diastolic velocity, divided by time-averaged mean velocity. It reflects the pulsatility of the waveform across the cardiac cycle.
- Spectral broadening
- Widening of the Doppler spectrum indicating a range of velocities within the sample volume. It occurs with turbulence, sampling across a stenosis, or an oversized sample gate.
- Wall filter function
- Removes low-frequency, high-amplitude signals from vessel wall motion. Setting it too high can erase genuine low-velocity flow in a nearly occluded vessel.
- Aliasing correction options
- Raise the pulse repetition frequency, lower the transmit frequency, increase the Doppler angle toward 60 degrees, shift the baseline, or use continuous wave Doppler to eliminate the Nyquist limit.
- ICA stenosis velocity criteria
- Seventy percent or greater stenosis is suggested by internal carotid peak systolic velocity above 230 to 250 cm/s, end-diastolic velocity above 100 cm/s, and ICA to CCA ratio above 3.2 to 4.0.
- Tardus-parvus waveform
- A damped waveform with a delayed, rounded systolic upstroke and low peak velocity. In the carotid or renal circulation it suggests severe upstream stenosis or near occlusion.
- Ophthalmic artery reversal
- Reversed ophthalmic artery flow suggests severe ipsilateral internal carotid disease with collateral supply from the external carotid. Confirm with indirect testing only when clinically safe.
- Vertebral artery steal
- Retrograde vertebral flow, often with a high-resistance or biphasic signal, suggests subclavian stenosis proximal to the vertebral origin. Arm exercise may provoke symptoms and flow reversal.
- Transcranial vasospasm velocity
- Middle cerebral artery mean velocities above 120 cm/s suggest vasospasm in the appropriate clinical setting, such as after subarachnoid hemorrhage. Compare with the contralateral side and trend over time.
- Ankle-brachial index
- Highest ankle systolic pressure divided by highest brachial systolic pressure. Normal is 1.00 to 1.40; 0.90 or below is abnormal, and above 1.40 suggests non-compressible calcified vessels.
- Segmental pressure gradient
- A drop of more than 20 to 30 mmHg between adjacent cuff levels localizes disease to the segment at or above the higher-pressure cuff. Document cuff order and limb position.
- Toe-brachial index
- Toe systolic pressure divided by brachial systolic pressure. Normal is above 0.70; it is preferred in diabetics and dialysis patients because toe vessels are less often calcified.
- Pulse volume recording damping
- Loss of the dicrotic notch and a rounded, widened waveform distal to a stenosis. Progressive damping across segments indicates more severe proximal occlusive disease.
- Post-exercise ankle pressure
- A fall of more than 20 mmHg after treadmill exercise, or failure to recover within about five minutes, supports hemodynamically significant peripheral arterial disease when resting values are borderline.
- Venous reflux thresholds
- Reversed flow longer than 0.5 seconds in the common femoral and femoral veins, and longer than 1.0 second in the popliteal and calf veins, defines reflux. Study the patient standing.
- Acute DVT appearance
- A hypoechoic, non-compressible vein with expanded caliber, absent spontaneous flow, and continuous or absent respiratory phasicity. Compression is the primary diagnostic maneuver.
- Chronic DVT appearance
- An echogenic, narrowed, or recanalized vein with thickened walls, collateral channels, and partial compressibility. Distinguish from acute thrombus because management differs.
- Venous phasicity
- Normal lower extremity venous flow varies with respiration. Loss of phasicity or failure to augment with distal compression suggests obstruction or valve failure.
- Renal artery stenosis velocity
- Peak systolic velocity above 180 to 200 cm/s with post-stenotic turbulence suggests stenosis. A renal-aortic ratio above 3.5 supports the diagnosis.
- Renal parvus-tardus
- A damped intrarenal waveform with prolonged acceleration time above 0.07 seconds suggests upstream stenosis or reduced parenchymal perfusion. Compare with the contralateral kidney.
- Abdominal aortic aneurysm size
- An infrarenal aortic diameter of 3.0 cm or more defines an aneurysm. Measure outer wall to outer wall in both anteroposterior and transverse planes.
- Hepatic artery resistive index
- Normal post-transplant hepatic artery resistive index is roughly 0.55 to 0.80. A very low value can reflect stenosis or an arterioportal fistula.
- Portal vein flow direction
- Normal portal flow is hepatopetal at about 15 to 30 cm/s. Reversed or biphasic flow suggests portal hypertension, a shunt, or outflow obstruction.
- Fistula flow volume
- Brachial artery flow volume equals time-averaged mean velocity times cross-sectional area times 60. A mature arteriovenous fistula typically carries more than 500 to 600 mL/min.
- Access stenosis velocity ratio
- A peak systolic velocity ratio above 2 to 1 across a narrowing, with greater than 50 percent diameter reduction, supports access stenosis. Compare with the adjacent normal segment.
- Preoperative vein diameter
- A venous diameter of about 2.0 to 2.5 mm with tourniquet, and arterial diameter of about 2.0 mm, supports creation of a usable autogenous fistula.
- Access steal syndrome
- Reversed flow in the artery distal to the anastomosis with hand ischemia suggests steal. Document flow direction in the distal radial or ulnar artery and correlate with symptoms.
- Mechanical and thermal index
- The mechanical index estimates cavitation risk and should stay below 1.9; the thermal index estimates heating and should be kept at or below 1 where practical.
- ALARA in Doppler
- Exposure depends on output power, dwell time, and frame rate. Doppler modes expose tissue to higher intensities than B-mode, so minimize power and scanning time consistent with diagnostic need.