hemodynamics why do waveforms look the way they do? · peripheral artery renal artery. interior of...
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Hemodynamics Why Do Waveforms
Look the Way They Do?
Laurence Needleman, MD
Sidney Kimmel Medical College of Thomas Jefferson University
Philadelphia, PA, USA
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No disclosures
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Doppler Spectrum
– Graphical representation of Doppler
– Makeup• Doppler frequency or
velocity - y axis• Time - x axis• Strength of signal -
gray scale–Number of
reflectors
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Characterization of Spectral Doppler“Describe, then diagnose”
– Site of signal • What is normal and
abnormal ?– Shape (edge, envelope)
of spectrum• Velocity of blood flow• Pulsatility
– Structure (contents) of spectrum
• Spectral broadening– Diagnosis
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The vascular network
http://www.cvphysiology.com/Blood%20Pressure/BP019.htm
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Aortic pressure stays high despite closing of aortic valve
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Lots of shapes in the pressure pulse Lots of squiggles in the Doppler
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Some principles• Pressure gradient drives flow
– Actually energy but generally the same• Waveform shape varies along arterial tree
– Pressure pulse takes time to go down arteries• Reflected waves occur at arterioles
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Why do parts of Doppler go backward?
• Normal– Reflected wave from arterioles reverse flow– Eddy currents
• Abnormal – Turbulence
• They don’t – Machine issue– Aliasing
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Diastolic Component
• Flow reversal–Created by
reflected waves from arteriolar branching
–More resistance ➟ stronger reverse component
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PulsatilityHigh “resistance” versus “low resistance”
Peripheral Artery Renal Artery
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AV Fistula
• Increased diastolic flow• Turbulence
–Color or spectral bruit• +/- Arterial pulsations on draining vein
Bruit
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Arteriovenous Fistula
• Usually traumatic, iatrogenic
• Low pulsatility waveform into AVF (bruit by color or spectrum)
• Arterialized vein (more variable, compare to other side if question)
Feeding Artery with Bruit
Draining arterialized vein
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Vein of Galen “Aneurysm”
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Characterization of Spectral Doppler“Describe, then diagnose”
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Pressure Waveforms• Pulse shape varies through the circulation• Note
– Femoral peak later, less diastolic pressure
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Which is the correct PSV? Left image or right image
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Weird Doppler from the bulb
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Flow separation
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Plaque
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Laminar flow:Parabolic vs. Plug flow
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Plug versus parabolic flow
Peripheral Artery Renal Artery
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Interior of the waveform• “Single“ velocity
– Pathological or physiological• Spectral broadening
– Pathological or physiological
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Single velocity Many velocities
Physiologic Plug flow (large straight vessels)
Parabolic flow (smaller vessels)
Curving vessels, vessel origins
Pathologic Jet inside a stenosis Post stenotic disturbed flow and turbulence
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Normal Spectral Broadening
• Blood flowing in one direction is laminar
• If many velocities are present, spectral broadening will be present
• Parabolic flow
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Abnormal Spectral Broadening• Spectral
broadening–Flow in many
directions and velocities
• Forward and reverse
• Ill defined edge• Shift of white to
baseline
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Stenosis
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Pre-stenosis Stenosis Post-stenosis
Total energy =Kinetic + potential
Total energy lower
Potential energy very decreased
Potential energydecreased
Kinetic energy very increased
Bournoulli and Stenosis
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Stenosis• Focal elevation of velocity in stenosis
– Jet is high velocity, laminar flow– Increased compared to prestenotic
segment– Velocity should drop off distal to stenosis
• (exceptions: long stenosis, near occlusive lesion)
– Measurement of velocity quantifies stenosis – Gray scale and color not quantitative, used
to locate stenosis
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PSV of ICA = 271 EDV of ICA = 73 IC/CC Ratio = 4.4
Pressure drops in stenosisVelocity goes up in a stenosis
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Jets are Laminar in a perfect world
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The highest velocity may not be laminar
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Increased Velocity in Stenosis
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Pre and In the stenosis
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Beyond the stenosis
• Change from small lumen to large lumen destabilizes flow– Jet spreads out
• High velocity also destabilizing– Frank breakdown of
regular flow disturbed flow (and evenually turbulence)
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Beyond the StenosisVelocity goes down, shape changes
• Disturbed flow distal to stenosis– Spectral broadening, loss of well defined
spectral edge, forward and reverse flow• Parvus tardus variable, further distal
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Turbulence
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3 parts to document stenosisThe “three musketeers”
1 Before stenosis2 Highest velocity in stenosis3 Disturbed flow and lower velocity beyond
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There are four musketeers
The fourth musketeer is:
1. Aramis2. Fourth guy3. D'Artagnan4. Porthos
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Parvus TardusFurther beyond a stenosis the shape changes and the post-stenotic flow
disturbances diminish or disappear
Delayed upstroke Diminished pulsatility
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Parvus tardus (tardus parvus)
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Parvus Tardus WaveformThe “fourth musketeer”
• Slow upstroke in systole
• Low systolic velocity (variable)
• Increased diastolic flow– Diminished
pulsatility
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Increased diastole is also seen after a stenosis
Multiphasic Peripheral Artery Monophasic Peripheral Artery
Normal, no stenosis Distal to stenosis
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Why high diastole after stenoses? Vasodilatation is not so important
• Pressure gradient throughout the cardiac cycle
• Weaker poststenotic antegrade pressure ➔– Weaker reflected retrograde pressure pulse– Forward flow is created by the absence of a strong
reflected wave
• Vasodilatation is a minor factor
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Monophasic StaccatoMonophasic ThumpProximal to stenosis
Monophasic Continuous
Distal to stenosis
Monophasic Signals are Abnormal in Peripheral Arteries
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Complicated signal simplified
• Multiphasic to monophasic Doppler
• Continuous signals in veins distal to obstruction– Could be DVT– Also extrinsic obstruction
(pelvic mass)
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Stenosis = filter
• A stenosis affects the blood flow beyond it in several ways– Pressure beyond the stenosis reduced– Complicated signals simplified– Propagation of blood flow slower
• Takes longer for the pulse to travel after a stenosis compared with an unobstructed artery
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Left = too little variation Right = too much variationDDX of loss of phasicity and/or asymmetry:Venous obstruction, scarring, extrinsic compression
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Hepatic vein web Normal at IVC, blunted before web
Case courtesy of Ron Wachsberg, M.D.
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Orchitis
Normal Testis Orchitis
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Nonspecificity of Neovascularity
Ovarian Cancer Benign Hemorrhagic Cyst
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High velocity without stenosisCollateralization
The brain is autoregulated to get flow. When one ICA is severely stenosed or occluded, the other
compensatesFlow = area x mean velocity,
Contralateral ICA size is unchanged, flow increases, velocity increases
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Antegrade and reflected pulse make waveform
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Without and with exercise
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from Frankel and associates, Purdue universityhttp://ristretto.ecn.purdue.edu/~sonusv/Frankel-webpage/ec_puls_l2pr.gif
Model of Pressure in a StenosisPressure Recovery
Pressure recovery
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Blood flow travels slower after a stenosis
Steal physiology in vertebrals– Also requires both vertebrals becoming basilar
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Notches
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Valve opens and closes versus QRST
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Systole is approximately 1/3 of cardiac cycle “Notches” occur before dicrotic notch
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AR
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Wave Intensity Analysis
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Oates: 180 ms or so for reverse wave to reach AV
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Summary• The final Doppler shape in the vessel you
insonate is created by many factors– The heart and all vessels before it– Local effects such as arteriolar resistance or
stenoses– Distal effects such as arteriovenous
connections, neovascularity and vasodilatation