Physiological Testing of the Arteries- Basic Interpretation

Introduction to Physiologic Testing of Arteries

This morning's talk is on physiologic testing
of the arteries and providing a basic interpretation.
And this is probably one
of my favorite areas 'cause I've been doing this forever.
Hopefully I'll be able to give you some tips
that I've learned along the way
and also encourage you
to try physiologic testing if you haven't done so.

In terms of assessing the arterial system,
indirectly, of course we know we can do angiography,
but indirectly or non-invasive, I should say non-invasively,
we can do direct testing with duplex ultrasound,
which is great.
We all do that. We can see the vessels,
we'll talk more about it later on this session.
But we're gonna focus on right now the indirect methods
we can use to assess the arterial system.
And they really are the oldest techniques we've
had available to us.
Probably the measurement of ankle pressure by some format
is probably the oldest thing we've done to look
for vascular disease in the way of a specific test.

Measuring ankle pressure
and calculating an ankle brachial index are really a key
factor to looking for arterial disease.
We'll go over that. In addition to just getting
that single level pressure measurement,
then you can add in either segmental pressures, wave forms
that are derived from a continuous wave doppler
or waveforms that are obtained with plasmo graphic techniques.

The why, the reason, one
of the reasons why I like physiologic testing is it is
really very easy to perform.
And in just a few minutes you get an answer, yes or no.
Do you have arterial disease at rest?
Many people use physiologic testing
as a primary screening tool.
With that you it is qualitative to some degree.
You don't really get
to categorize a certain percent stenosis.
You'd rather you'll be able
to find out if somebody's got mild, moderate,
or severe disease.
Although this slide includes the word occluded,
the one problem is you can't really tell if something's
occluded versus severely stenotic.
And that is a fault of physiologic testing.

If we add in doing these tests over multiple levels,
whether it's PVR waveforms over multiple levels, CWA forms
or segmental pressures, we can then estimate as well,
not only the severity of the disease,
but the level of the disease, we can figure out inflow disease
or aortic iliac disease separate from femoral popliteal
disease and separate from tibial level disease.
So we can get a lot of good information. Alright.

Basics of Physiologic Testing: Pressures and Waveforms

Let's talk about some specifics.
If you're going to do physiologic testing, you have
to include the measurement
of systolic pressure at at least one level.
And by convention we always do the ankle level.
Now you can add more,
but we should always not only just limit it to
that pressure measurement, but we wanna include a waveform.
Many people just use the CW waveform,
which I'll talk about in a second.
Some people prefer pvs
and we can discuss that at the
conclusion of the talk if you want.

Continuous Wave (CW) Doppler Waveforms

CW wave forms are obtained
with the same doppler that we do.
Our pressure measurements, you've seen these,
they've gotten very nice in that
they actually do have a relatively broad beam.
So even if you're not exactly sure where the artery is,
you can usually, with very
subtle movements, find it quickly.
It's usually something between a five
and 10 megahertz crystal.
There's two crystals in there.
There's one that constantly sieves
and then there's a receiver.
So that's why it's continuous wave.
And because of that there's range ambiguity with this.
It's constantly sending, so it's not only going to stop
at x distance under the skin,
but it's gonna pick up any doppler shift the whole way down
until the signal attenuates.
So if you've got an artery overlying a vein,
you're gonna hear both signals.
Typically, we record our CWA forms usually
at five levels.
You can include both proximal and distal SFA,
but most folks do common fem SFA popliteal,
and then two recordings at the ankle, both the posterior tib
and dorsal pettus.

This is what we wanna see in terms of
a nice normal CW wave form.
It's multiphasic wave form. You can call it phasic as well.
There is some confusion
and maybe it's been talked about already,
but maybe we'll talk about it today.
When we get into spectral doppler
and ity of spectral doppler,
some people have a hard time
deciding what's monophasic versus biphasic,
but typically with CW wave forms, why it's easier to
delineate that ity is most equipment prints out on the
report this baseline.
And so really you're counting the number of components
that cross that baseline.
We have this systolic component here.
We have the reflected wave in early diastole
and then a third antegrade component in late
diastole in this patient.
In this example, there's actually a fourth component which
we sometimes can see anytime, almost,
you really can say this virtually all the time.
When you look at arterial waveforms,
you should see a nice sharp upstroke
and a relatively narrow systolic peak,
whether it's spectral doppler
or CW waveform that tells us we have a nice healthy system
and there's no drop in that pressure wave
as we've come down to wherever we've measured,
as we get disease, as blood flow has to go
through a stenotic area, we lose energy
or energy's converted to heat, primarily,
some inertial and viscous losses,
and then the waveform becomes more blunted and more rounded.
And we'll show examples in a second
as we get severe disease.
It's basically just a very monophasic pattern
where we just see flow in systole.

Now here's an example, we'll go through
with a little more detail.
This person actually did have segmental pressures done
as well as the CWA forms,
but we're going to do the pressures in a minute.
I want you just to be able to appreciate
and evaluate these wave forms.
As with any physiologic tests, we always include
bilateral brachial blood pressures.
So they're up here 151, 147, and here are our wave forms.
In this example, we only did four levels.
We did the femoral, the popliteal, the posterior tip,
and doused at the ankle.
And this looks very much like the example I just showed
of a very normal multiphasic pattern.
Again, the system indicates about
where a baseline should be evaluated
and we can see there's multiple components here.
We have the systolic peak, the reflected wave,
and we heard a little bit already about this too,
that reflected wave blood flows going down
a normal artery to the periphery.
Normally we have high resistance arterials,
slightly constricting, providing vasomotor tone.
So we go down, we kind of hit that slight constriction,
that sort of roadblock or stop cock with the arterials
and we get some flow reflected back.
That's in probably most of us now unless we're overheated.
Then we get into a low resistant system.
We'll talk about that. But normal arms, legs,
high resistance bed,
we always wanna see this reflected wave has to be there.
If it's a normal vessel,
then usually we will see a little bit
of an antegrade component in late diastole.
And pretty much this looks very normal all the way down.
There's a slight change in the overall amplitude.
We don't weigh as much on the amplitude as we do the shape,
but you can see when we look over here on the left side,
there's certainly a big difference.
We start right off at the thigh level
with a difference in the CW wave forms.
And what are we missing? Well, we're missing
that reflected wave.
So that tells us when we don't see that reflected wave,
we no longer have a normal high resistance bed.
We've got a low resistance bed. How do you get that?
Well, you get that if you run up a flight of stairs
or on a treadmill and you vasodilate
and you produce an exercise hyperemia.
But we also get that if we're ischemic
and we vasodilate in order to get more blood flow down.
So when we don't have that reflected wave, we know we've
no longer have that high resistance bed.
So we can see here that we have
lost that wave.
The shape has changed a little bit as well.
It's broader. That peak is more rounded.
So those are all signs that we've lost some energy
and as we come down the leg, we can see that
that signal dampens out further.
So without any numbers thrown into this picture,
you can clearly say there's inflow disease
to the left lower extremity.
It's not gonna be aortic iliac disease. Why?
Well, because the right femoral is normal.
If there was aortic disease of any degree,
that right femoral wouldn't be normal, but it is.
So we can rule out significant aortic disease.
So it's iliac or iliofemoral disease
or just simply inflow disease to the left lower extremity.
And chances are with the further dampening out of
that waveform distally,
there's additional distal disease present.

Now, this is a hard thing with physiologic testing
because if we start out bad at the top
and we have lower flow coming in,
we can't really fully assess
what the disease is below that level.
So this person could actually have some very severe
disease distal, but we can't figure that out
because it's already flow limited at the beginning.
I'm not a big fan of CW Doppler,
but it is a nice technique.
I don't like it because it is blind.
It does take a little bit
of attention from the user to do it correctly.
It is more operator dependent than PVR wave forms.
If you don't intonate the vessel correctly
and aren't using a correct angle,
you can make a good artery look relatively poor, easily.
And as I said, temperature will affect these wave forms.
If we vasodilate
and such, we also could be intonating right over a large
collateral vessel as well.

Segmental Pressures

Well, let's talk about segmental pressures.
This is something that most folks do
and add in on top of a waveform.
And this is just a setup showing how it's done.
When we do segmental pressures,
there are two camps out there.
There's one that uses four cuffs
and there's one that uses three cuffs.
And I'm not sure what each
of you do in your own labs if you're doing this,
but this is just showing, this is probably the standard.
We have a cuff around the ankle, one just
below the knee, one just above the knee,
and then one at the high thigh.
But sometimes, and you can appreciate here,
this person wasn't particularly short.
They were about 5'9", 5'10"
and there's not a lot of room on the thigh sometimes
to put two cuffs.
And sometimes the thigh is just not gonna work.
You don't wanna overlap the cuffs.
So many times people will choose
to use either just a single cuff, one of these narrow
or single cuffs and record one waveform over the thigh.
Or sometimes people will decide to use a contoured thigh cuff,
which actually fits most thighs really nicely.
They're usually about 17 centimeters.
We have wider cuff bladders for heavier legs
and this will actually better approximate the
actual thigh pressure.
This cuff here in particular
will overestimate the real thigh pressure
because it's too narrow with regard
to the width of the limb.
If you use a cuff,
the physicians in the room know this,
you learn this all in school,
if you don't use the right size cuff,
you won't get the right size pressure measurement.
If the cuff is too narrow,
your pressures are gonna be falsely high.
You can't get that bladder circumferentially
around the leg completely so
that you can apply good pressure
and get a proper blood pressure measurement.
So the numbers are elevated.
If the cuff is too wide, the pressures are falsely low.
And generally speaking, I use the rule of thumb,
it should be about 20% wider than the limb diameter.
That is the bladder, not the length.
The width of the cuff should be about 20% wider
and you can eyeball that quickly.
So it's important if you're gonna do these
to do them correctly, have some different size cuffs so
that you can correctly measure your ankle pressures.
Generally we include an arm pressure
'cause we normalize it back per patient
and we don't wanna see differences of greater than 20.
If it's less than 20, it's okay if it's greater than 20
in terms of any pressure.
But in this case with the brachial pressure, we have
to think maybe there's subclavian stenosis
or an innominate stenosis.
If it's on the right, we're going to use the higher
of the two pressures to calculate the ABI
in measuring the dorsalis pedis
and posterior tibial pressures,
they're not gonna be identical either.
They're usually close, usually within 15 or 20.
And usually they can be a little bit higher
and I'll show you some values in a minute,
but in some patients the pressure at the ankle can be 20
or 30% more than the pressure at the arm.

The big problem with measuring pressures is
medial calcification.
Even if your patient is not a diabetic,
certainly patients
with chronic renal disease get medial calcification,
you're not gonna be able to compress the arteries correctly.
You'll get falsely high pressures.
So you have to put this in the back
as you're doing in evaluating these patients.
The other common mistake for some folks new
to using a doppler is pushing too hard.
You don't wanna push in particularly if somebody's ischemic
and has lower pressure to begin with.
If this person is normal,
you can see they have still good hair on their legs and
they were just a normal model for the picture.
But if they were a disease patient
and had lower ankle pressures,
pushing this hard would impact what you measure for pressure
'cause you're gonna stop some of
that flow just pushing so hard.

Ankle Brachial Index (ABI) Interpretation

This is generally a good table to use for the ankle brachial index.
Now there's probably
at least three
or more commonly used scales out there.
And you can look through the literature
and find something that works for you.
Generally speaking,
a normal ankle brachial index is above 0.9.
I personally like to use greater than 0.95,
but this is from some published data
on an upper limit.
We used to say one was normal
and that's tweaked up a bit through the years
'cause that's what I just said about ankle pressure being higher than arm pressure somewhere
of 20-30%.
So an ABI generally is considered normal up
to about 1.3.
Beyond that, we know that
we probably have some calcification if we have to introduce
that much additional pressure.
Claudicant people with pain when they exercise usually have
ABIs that are above 0.5, but below our normal value,
and again, this is 0.9, I usually use 0.95,
but again, literature's out there, this is
something you can start with anyways.
When we start getting real more severe, moderate
to severe disease and we introduce symptoms such
as rest pain or tissue loss
or gangrene, then our ankle pressure
or ankle pressures go down.
Our ABIs are significantly diminished
and we're talking ABIs of less than 0.5
or less than 0.25 when we have the presence
of tissue loss and gangrene.
Again, generally if you have an ABI that's above 0.5,
most often you're dealing with a clot most often
that single vessel disease, whether it's SFA
or iliac as the pressure as we get a
further decrease in the ankle brachial index below 0.5,
that's often consistent with multi-level disease.
So there's some generalizations here,
but they actually work very well.

The reason why most folks like ankle brachial index is it's very stable and very reproducible
and we're normalizing it back to the systemic patient,
the systemic pressure of that patient.
But if you see a drop of greater than 15%
or 0.15 in the ABI visit to visit, then
that's an indicator that there's a problem
and you need to go to the next step.
Whatever that happens to be in your algorithm.
We do the ABI to identify disease,
then we do segmental pressures to try
to give us a level of disease.
And you can look through this slide,
but generally speaking
what it says is we want pressures within 20-20 millimeters
of mercury, either right to left or level to level.
So the thigh pressure, calf pressure,
ankle pressure should be ballpark within 20 or so.
If we get beyond that 20 millimeter range,
then we probably have some disease.
If it gets upward of 40 millimeters difference level
to level or side to side,
we probably have severe disease or occlusion.
Okay? So generally within 20 collaterals can impact
'cause it can bring enough flow through
and into back into the system.
And remember that both of these tests, both pressures
waveforms, PVR waveforms don't tell us really anatomy.
They tell us function.
And that's kind of what we wanna know, right?
We wanna make sure our patients can leave our offices
and walk out to their cars and not claudicate
or go through the mall and not claudicate
or sleep at night without rest pain.
We want that functional status.
If we know something's wrong by these tests of pressure
and function, then we can look for the anatomy with imaging
and or more invasive tests.

So here's the picture from before. Let's see how we did.
What did I say? The right was pretty normal
and the right is pretty normal.
All in all we have ankle pressures here.
Well, they're a little bit low but not too bad. Okay?
Our ankle brachial index is 0.8
and the major drop really happens down
along the tibial level.
Even though the waveform here is fairly well maintained,
you might make the case
that it's a little broader down here than it was
when we started up here.
So our ABIs are 0.8.
We also did toe pressures
and I'll come back to discussing those,
but it was 0.66, which
for most folks is slightly abnormal.
But on the left leg
where we clearly said there was inflow disease,
we were right because look, our pressure up here, 151,
our thigh pressure of 120.
So we've got greater than a 20 millimeter difference.
We've got an abnormality probably again in
that iliac system, but then we drop another 20
femoral popliteal.
So SFA disease probably thrown on top of that.
And then the pressures are kind of about the same.
And our ABI is about 0.5.
So we have added on that extra comfort level
to diagnosing based on these qualitative results.

Plethysmography (PVR Waveforms)

All right, plethysmography, in addition,
some folks will do plethysmography in addition
to segmental pressures and segmental waveforms with cw.
Some people will use plethysmography in place of cw.
I was with a very large group
of vascular surgeons for a number of years.
We never did CWA forms. They loved their pvs.
We did thousands of PVRs
and they got to interpreting those very well
and we're very comfortable with 'em.

There's basically,
plethysmography is just looking at variations in volume
and for us that volume change reflects blood flow changes.
There's a lot of different types of plethysmography.
What we use nowadays is mostly air plethysmography.
There's some antiquated things
that you might see in an old textbook.
We also use something called the PPG
or photo plethysmography photoelectric plethysmography,
which technically by the books is not really plethysmography
'cause we're not measuring volume change.
We're looking at changes in infrared detection of RBCs,
but the name has stuck and that's that PVS are old.
They were developed in the seventies by Dr.
Clem Darling II and Jeff Rains.
Jeff is a PhD still working in
I think he's in Miami and Dr.
Darling senior's passed on now, but they developed it.
And basically they came up with this device
where we put a cuff on
and we look for those volume changes
to produce a pressure change in the cuff and record it.

Here's the original format.
They tried to calibrate it so it would mimic a waveform
that we see on an arterial line.
We put cuffs on, we add air to the cuffs.
It gets up to about 65 millimeters of mercury, enough
to stop venous outflow.
So the only volume change going on under that cuff at
that time is due to arterial inflow.
And we'll record it over a few cycles.
And as what I said with pressures, we use the same cuffs.
You can do three cuff and four cuff method
and here's an example of a bounding normal.
Hopefully all of ours look this good bounding, normal
PVRs that were recorded.
High thigh above the knee, below the knee
and at the ankle along with segmental pressures.
Our ABIs are just over one on both sides.
And this is what we wanna see. A nice sharp up stroke.
Again, narrow peak with A PVR,
we're measuring a volume change.
So remember when I talked about that reflected wave
the blood going down, hitting the arterials
and bouncing back that bounce back that little bit of volume
that bounces back, it's this right here.
That's the reflected wave, that dichotic notch,
that little bit of volume coming back in under the cuff,
increasing the pressure.
And those are all textbook normal PVR amplitude.
The height can be impacted by a lot of things.
Obesity, edema, edema I think tend
to attenuate the signals.
Predominantly, it almost acts to muffle
that pressure wave coming through the tissue.
Amplitude is okay, but more important it's the contour.
The contour that waveform is gonna determine arterial status
and as I said, sharp up stroke narrow peak dicrotic notch.
Those are the key elements of A PVR.
As we get disease, it's gonna be similar to
what we talked about with CW waveform,
a more blunted rounding approach.
The dichotic notch,
that reflected wave we see in a high
resistance bed goes away.
And this is just a little cartoon here
or some examples of waveform normal down here.
We've lost that notch. It's broadened out.
It's not great but it's not bad.
It's not normal, but it's not bad.
So it's probably more mild disease.
Panel C is probably something with more moderate disease
and panel D is almost flat
and that's probably somebody with an occlusion or
or near occlusion.

I'm just gonna run through a couple of examples
'cause I could talk most of the morning
and we have other speakers to get up here.
So we'll go quickly through these.
This is an example of somebody with SFA disease.
This is pretty normal. Not much of a notch,
a tiny little bit of a bowing out here, but pretty normal
and our ankle pressures are maintained.
But on this side I think you can appreciate while there's a
little bit of a bowing out here
and these are symmetrical,
we see a drop off here when we get to the calf.
Now this is thigh calf ankle wave forms.
So that calf cuff is right here
and it's gonna sense what's going on above it.
So it's femoral popliteal disease,
most typically SFA disease.

This is a classic pattern we might see in a diabetic.
Perfectly normal PVS until you get down below the ankle.
And this fourth wave form here is actually recorded across the foot.
We use a small seven centimeter cuff
and cross over the forefoot
and we get a tracing at this metatarsal level.
And this trans metatarsal waveform is virtually flat.
So that's telling us even though
the way the flow in this particular patient is good all the
way down, it basically somewhere on the distal tibial end
of things, which is where we normally see
it in our diabetics.
We've got some severe disease.

You can do PVS in the upper extremity.
It won't talk too much about that same kind of thing.
We can put a cuff around the upper arm, forearm and wrist
and get these bounding normal waveforms.
They're gonna be of similar appearance.
When we see something like this, we know
that we probably have some disease.
'cause again, we start at the top
and there's asymmetry right here at the top.
So we know there's something going on
to the inflow of this left arm.
And if we look just a little closer,
not only are the waveform different,
the pressures are significantly different.
Textbook left subclavian artery stenosis.
Most of the time we do see it on the left.
You can see it on the right.

Exercise Testing

Take the last couple of minutes
and talk about exercise testing and also some PPGs.
It's great our patients come in,
they lie down on our exam tables, we do our tests,
they're normal, but as I said, can they get back walking out
to their car without claudicating?
So depending on the presenting symptoms,
in your own algorithms in your own lab,
you may wanna do exercise studies.
You can do it with pressures or pvs.
I have to say most folks do pressures
and they record it at the ankle level.
They'll walk a patient on a treadmill.
And they usually do this at somewhere
about two miles an hour at about a 10% grade.
But we often have to vary this patient
to patient based on their ability.
What we look at is not only to show a pressure drop
after exercise, but we look for that recovery time
because if they have relatively mild disease
or single vessel disease, they may drop their pressure
with exercise, but it will return a normal usually
within five minutes.
Persons with more severe disease, a multi-level disease,
it takes longer for their pressures to return to normal.
And why do we see the pressure drop? When we exercise?
We vasodilate, we open up those arterials,
we want more blood to the leg because we're exercising.
So we drop the resistance, okay?
And flow is changing pressure over resistance.
We drop the resistance,
but if we can't increase flow,
the math tells us the pressure has
to drop and that's what happens.
We drop resistance flow, can't compensate or increase.
So we see and measure that pressure drop.

As I said, you must use a treadmill.
I'm not gonna get into too much about coding,
but we can have some time for questions later.
93924.
That CPT code is specific to using a treadmill only.
And as I said, those are generally what we use
for our timing.
And we usually stop when the patient
can't walk any further as an alternate.
You can use toe ups
and do this several times with a person
who can't walk on a treadmill.

Here's a couple of quick examples on this.
Top panel was somebody who was treadmill
and they had to stop after about two minutes they had pain.
But if you can see their ABIs are still above 0.1,
their waveforms are still pretty normal.
This is probably somebody with neurogenic claudication
and we can tell those patients, right,
if you've ever taken care of 'em, they're the ones
that are gonna walk in kind of hunched.
And when they get on the treadmill,
they're gonna do everything they can to stay forward
and lean forward because as they lean forward,
they're opening up their lumbar spine decompressing things
so they can alleviate their pain.

The bottom panel is somebody a true positive study following exercise.
Not only are the PVS flattened out after exercise,
but we don't get any measurable pressure.
Much of the equipment nowadays has the ability for us
to sit there and keep recording pressure measurements
and do a timed recording
so we can look at our recovery times
and we can see does it come back
within four or five minutes?
Then it's probably not so bad. Does it take 10 minutes?
And this is a nice kind of output that you want to maybe use if you can when you're doing our exercise studies.

Photoplethysmography (PPG)

And I'm just gonna take another minute
or two quickly go through PPGs photo plethysmography.
As I said, this is an infrared sensor
and transmitter it sends in an infrared signal.
It picks up a reflection from the RBCs under the tissue.
Normally we wanna see, we can use that to measure pressure.
Normally we wanna see their toe pressures at least 70%
of our arm pressure.
So we can measure a toe brachial index.
Here's the little gadgets.
Sometimes you can use double stick tape.
Sometimes you have these little closed pin kind
of devices to put it on.
If we put the cuff below it, we'll get the PPG wave forms,
inflate the cuff and calculate our pressure.
We can do it on the digits.
This is primarily our first non-invasive test when we wanna rule
out digital ischemia.
And you can see in this patient they've got
some ulcerations here.
This is just an example again with our four cuff method,
but we've added in some PPG wave forms of the great toe
as well as pressures and they're pretty normal here.

Here is somebody pretty abnormal.
This gets to be hard diagnostically
because it's really pretty good here
and then really pretty bad down at the toes.
You wanna make sure that they're not cold,
particularly if you live in a cold environment.
Make sure your room temperature is good
in categorizing PPG waveforms.
It's very similar to what we do with the other waveforms.
Nice, normal, moderate disease, pretty severe disease.

One other thing to point out is this waveform here.
This people refer to this as a peaked pulse.
The group in Portland's probably
published the most about this.
It was formerly Dr. Porter's lab now Dr.
Mineta's lab. And that pulse,
that peaked pulse is very consistent with vasospasm.

The other thing we can do is an Allen's test.
If you happen to be involved in patients
who might be going to get a dialysis fistula
or use of a radial artery for bypass, for coronary bypass,
we can do an Allens test with the PPG
and see if somebody's radial or ulnar dominant.

Conclusion

Most of us who do this really like PVRs and pressures
or CWA forms
and pressures, they're quick, they are reliable reproducible
and they're very cost efficient.
Getting the
information from these indirect tests can certainly help us
in patient management.
And again, they provide us with an assessment
of global perfusion,
which can complement then the anatomic information we can
get from arterial imaging.
Thank you very much.