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What abnormalities can be detected using doppler on pedal pulses?

Discussion in 'General Issues and Discussion Forum' started by Paul_UK, Mar 15, 2013.

  1. Paul_UK

    Paul_UK Active Member


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    Hi everyone,

    I am looking for a list of conditions or abnormalities that can be detected using a doppler on the pulses of the foot and/or leg. If anyone also happens to have a sound clip of the condition/abnormality that would be great.

    All help most appreciated :eek:
     
  2. David Smith

    David Smith Well-Known Member

    This attachment 'Non invasive methods of arterial and venous assessment' might help.


    Dave
     

    Attached Files:

  3. Ros Kidd

    Ros Kidd Active Member

    I once put a doppler on a guy whose pulse rate was over 140b/m. He had undiagnosed atrial fibrillation he had a MET call and is alive today. All in a days work!
    Ros
     
  4. Mart

    Mart Well-Known Member

    Please explain why Doppler exam was more useful than simply palpating pulses?

    Dave's post was important because it implied need to understand underlying basic physics to arrive at proper interpretation of Doppler waveforms as opposed to using it simply as means to detect vessel occlusion from cuff compression; poor interpretation is potentially harmful because it may be misleading.

    Pitfalls using continuous pulse (hand held probes) vs duplex include

    1. integration of venous signal into arterial waveform (or sound)
    2. poor technique – probe must be oriented at approx 60 degs to plane of RBC flow for accurate arterial waveform interpretation, consider also that flow is at max at centre of vessel because of effect of fluid dynamics and will be turbulent (erratic) at site of stenosis.
    3. Use of wrong sized cuff measuring systolic pressure will create nonstandard value.
    4. Consider variance due to systematic error (check your technique)
    5. Ignoring confounding factor of vessel wall stiffness, this means that value of ABI in those with DM or other causes of vessel calcification is questionable and
    6. Realization that Doppler provides an index as opposed definitive impression based on direct visualization ie NIVT creates statistical probabilities not absolute indicators of vascular status

    Key points are

    Doppler examination of an artery distal to a stenosis will show characteristic changes in the velocity profile: the rate of rise is delayed, the amplitude decreased, and the transient flow reversal in early diastole is lost. In severe disease, the Doppler waveform flattens; in critical limb ischaemia it may be undetectable.

    Systolic blood pressure in the lower limbs cannot be measured reliably when the vessels are calcified and incompressible—for example, in patients with diabetes—as this can result in falsely high ankle pressures.

    An alternative approach - measurement of toe pressures is helpful because distal vessels are rarely stiffened to same degree. Normal toe systolic pressure ranges from 90-100 mm Hg and is 80-90% of brachial systolic pressure. A toe systolic pressure < 30 mm Hg indicates critical ischaemia.

    Exercise testing will assess the functional limitations of arterial stenoses and differentiate occlusive arterial disease from other causes of exercise induced lower limb symptoms—for example, neurogenic claudication secondary to spinal stenosis. A limited inflow of blood in a limb with occlusive arterial disease results in a fall in ankle systolic blood pressure during exercise induced peripheral vasodilatation.

    Cheers

    Martin
    Foot and Ankle Clinic
    1365 Grant Ave.
    Winnipeg Manitoba R3M 1Z8
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  5. Eve Croucher

    Eve Croucher Welcome New Poster

    Just happened to be reviewing posts, very good artical. Thanks Dave
     
  6. David Smith

    David Smith Well-Known Member

    Your welcome:welcome:

    Dave
     
  7. markjohconley

    markjohconley Well-Known Member

    Why is it that in "an artery distal to a stenosis ............. the transient flow reversal in early diastole is lost." I comprehend that the reverse flow is due to resistance within the arterioles.

    Another related query how important is the reverse flow for determining the risk status of a pt. Surely the shape (height and width) of the first phase (systole) is the only relevant phase that should be used?

    thanks, mark
     
  8. Mart

    Mart Well-Known Member

    Hi Mark

    My understanding is this:

    Ultrasound signals reflected off stationary surfaces retain the same frequency with which they were transmitted, the principle underlying Doppler ultrasonography is that the frequency of signals reflected from moving objects such as red blood cells (RBCs) shifts in proportion to the velocity of the target. The output from a continuous wave Doppler is usually presented as an audible signal, so that a sound is heard whenever there is movement of blood in the vessel being examined, and the frequency of the sound represents an averaging of the spectrum of velocities detected from reflected signal.

    Transient reverse flow is a function of elastic recoil from vessel walls as the the systolic phase progresses prior to diastole. For the vessel walls to apply a recoil they need to be stretched. To be stretched there needs to be sufficient pressure to stretch them.

    Arterial pressure at given location and time in lower limb is a primarily a function of force of ventricular contraction, internal vessel diameter (this controls resistance to flow from friction) and vessel volume (which will modulate according to sympathetic drive to vessel walls and arterovenous shunting).

    So arterial stenosis, which may be at multiple sites, will reduce flow and therefore pressure distal to occlusion. Note though that velocity will increase immediately proximal to and within the stenosis, this phenomena (bruits) is the result of the associated chaotic turbulent flow. If sum of occlusion is sufficient,there will be insufficient pressure to stretch the vessel walls distal to occlusion(s) and rebound reduced or absent. Also if compensatory dilation of extremity is present because of reflex ischaemia, there will be reduction or absence of reverse flow; this is why measuring post exercise effect on pressure indices and waveforms increases their sensitivity to detect occlusions.

    The slope of the waveform is an indicator of the rate of change in velocity - when there is occlusion the flow is reduced distally and the rate of change in RBC velocity reduces giving the characteristic "damped" waveform.

    Care needs to be taken in evaluating the waveform from continuous Doppler because it represents the frequency shift from averaging of all the sampled reflected signals which includes venous signal. So for example within the tarsal tunnel, in a patient with tortuous Venae comitantes, signal reflected from within veins will likely confound reliable interpretation of the waveform. Likewise the probe orientation to flow is typically assumed by equipment manufacturer to be 60 degs; waveform shape is partly a function of the angle of incident and reflected beam and therefore affected by probe angle . That is why duplex scanning is more reliable because you can accurately target the center of the arterial laminar flow excluding all other signals and measure incident angle and depth precisely to properly measure RBC velocity.

    So in answer to your second question; this will depend on quality of equipment and skill of operator to consider all the relevant factors to explain each individual set of data.

    I generally initially screen patients with hand held Doppler and regard monophasic signals as deserving further non-invasive vascular testing.

    Vital is that any NIVT metric needs to be considered in context of other signs and symptoms and is rarely an entirely reliable measure in isolation. As already discussed the sensitivity and specificity the various forms of NIVT are variable not only according to nature of the test and operator skill but the nature of each individuals physiology, that is why arteriography and to lesser extent duplex cartoonography remain gold standards.

    Hope that helps

    Cheers

    Martin

    Foot and Ankle Clinic
    1365 Grant Ave.
    Winnipeg Manitoba R3M 1Z8
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  9. markjohconley

    markjohconley Well-Known Member

    Thanks Mart, I didn't realise, "continuous Doppler ... represents the frequency shift from averaging of all the sampled reflected signals which includes venous signal", ... that's inconvenient, now know why duplex scanning is preferable, thanks;

    and so the lack of the transient reverse flow confirms what the dampened systole suggests?
    Mark
     
  10. Mart

    Mart Well-Known Member

    Not quite sure what you mean by last sentence . . loss of biphasic waveform could be explained by a number of things as mentioned. Try this; take your continuous Doppler probe and play around with its orientation relative to your tib post vessels - you will notice a wide variation in waveform being reported including a monophasic signal depending on the beam incidence and reflection angle, superimposed venous reflections and how close the beam is to centre of flow rather than edge where friction is higher and velocity slows. My understanding is that if you have no occlusions then irrespective of beam incidence the slope should remain steep not damped because the rate of change of flow will be normal, in other words occlusion and loss of peripheral resistance will increase the time to peak pressure. Don't forget that the absolute shape of any waveform will also depend on how machine is set up and the frequency of the probe used.


    Cheers

    Martin
     
  11. markjohconley

    markjohconley Well-Known Member

    'day Mart, i read that informative post as proximal occlusion results in BOTH damped systole phase and negative flow phase (of early diastole), mark
     
  12. markjohconley

    markjohconley Well-Known Member

    This part is a mystery to me, "and loss of peripheral resistance will increase the time to peak pressure"
     
  13. markjohconley

    markjohconley Well-Known Member

    see I thought peripheral resistance was the (or one of the) causes of the negative flow early diastolic phase not the systolic phase.

    why I keep at it is that I've been taught that on a audio only Doppler "monophasic bad , biphasic good" but does that hold, when attempting to categorise pts into a low risk v high risk category?
     
  14. Mart

    Mart Well-Known Member

    Did you try this?

    Here are 2 screen images of signal from my posterior tibial artery at tarsal tunnel.

    image 1 is optimized to centre of vessel with approx 60 degree incidence to flow vector - nice TP waveform

    vascular D 1.jpg


    image 2 - same vessel and equipment set up immediately after image 1 - wave form represents signal with a poorly positioned probe with beam angled perpendicular to flow and likely at margin of lumen where RBC velocity is reduced by increased fluid friction.


    vascular D 2.jpg


    This illustrates the potential to get poor information when doing qualitative doppler interpretation.

    When you talk about risk ......... what risk are you referring to?

    non-invasive vascular testing gives us a correlation to poor healing potential, probability of various grading of occlusion, and at extreme possibility of approaching critical ischaemia. All NIVT has limitations which are dependent on systematic error including equipment qulaity, features of patients limb, patient's physiology particularly presence of diabetes mellitus, skill of data acquisition and interpretation. To my knowledge there are no absolute correlations for any of NIVT approaches and the literature cites variations according to study methodology and populations sampled. NIVT must therefore be used in context of sum of clinical signs and NIVT interpretation NOT in isolation. Peripheral angiography remains gold standard to assess vessel patency with duplex sonography cartoonography as a useful safer alternative.

    hope that helps

    Cheers

    Martin

    Foot and Ankle Clinic
    1365 Grant Ave.
    Winnipeg Manitoba R3M 1Z8
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  15. markjohconley

    markjohconley Well-Known Member

    Thanks Mart,

    i work in a public outpatient clinic. Hopefully we decrease hospital admission rates by regularly treating those that are at greatest risk of foot complications if left to there own self-care. We use a neuro-vascular assessment tool to categorise pts into those of greater need, referred to as high risk, from all others, low-risk. The vascular assessment component includes the u/s doppler waveform. Unfortunately most dopplers are audio only (hand-held) and a judgement call has to be made. We have used the biphasic as a low-risk and monophasic as indicative of high-risk. This is what i query, is it possible to have a thin high first phase without a negative second early diastolic phase present?
     
  16. Mart

    Mart Well-Known Member

    Hi Mark

    I think that there would be low probability of someone with biphasic Doppler sounds having clinically significant occlusion and I can't think of how you might get an erroneous biphasic sound. Presence of a Monophasic sound would deserve further investigation especially if there were associated clinical signs of ischemia, Monophasic signal may occur simply as result of poor technique rather than clinically significant loss of reverse flow.

    If above is true then presence of Monophasic signal is likely sensitive but not specific as a screening tool. I am not sure if this idea has been properly validated and not sure how useful it is compared to ABPI or TBPI. I think this is an interesting question - last time I did a lit search on this I was unable to reach a conclusion. I was curious because the question seems a reasonable one. Perhaps I am missing something important?

    Someone please help out of they can substantiate an opinion on this.

    cheers Martin
     
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