0:01

So let's talk about how to read spectral Doppler waveforms.

0:03

And most of the pathology that you're going to see is going to come down to

0:06

understanding a handful of these waveform features.

0:09

If you understand how these things work in one area, you're going to understand how

0:12

they work in almost every part of the body, which is very helpful.

0:16

So there's different components of the waveform.

0:18

So, the things that you're going to want to know are the PSV, or peak systolic

0:22

velocity, the EDV, or end-diastolic velocity, the portions of the waveform which

0:27

represent systole, diastole, and then what we call the spectral window.

0:31

The spectral window itself is important.

0:33

That is the clear space under the waveform.

0:36

When it's nice and clean, it indicates really orderly flow or laminar flow.

0:41

As the flow becomes turbulent, you have more areas that are represented of

0:45

different velocities, and so you get what we call spectral broadening.

0:48

I'll talk a little about that in a second.

0:50

But the areas that we talked about here with the PSV is the top peak systolic

0:54

velocity, so that highest velocity during systole.

0:57

The end-diastolic velocity, that happens at the very end of diastole.

1:01

So that'll typically be the lowest velocity that you see.

1:05

And so you're going to look at these to build your waveform and what you look at.

1:09

You'll see a thing here that we'll talk about in a second called resistive index,

1:13

and how that is calculated is the peak systolic minus end-diastolic velocity over

1:17

peak systolic velocity. And so this is reflective of downstream resistance.

1:22

So it essentially tells us how that vascular bed sees the blood after it's leaving

1:27

and how resistant the tissue is that it's trying to perfuse.

1:32

Normally, you'd like to see this in most organs at around 0.5 to 0.7.

1:37

We have a classification pattern of what we look at for arterial waveforms.

1:42

We can classify those as high, intermediate, and low resistance.

1:45

As I mentioned, this is going to reflect the tissue that's being perfused.

1:48

Organs like brain, liver, kidney, et cetera, they're going to need constant blood

1:52

flow, so they have low resistance waveforms.

1:55

You don't want to resist blood from going into there.

1:57

Things like skeletal muscle, for instance, where you rely on that contractile

2:01

system, you are going to have a high resistance waveform, and then you can have

2:05

things in the middle. So we'll start with high resistance, and so one of the

2:10

typical ways that we see this are in the peripheral vessels, but we also see this

2:13

in other structures like the external carotid artery, where you are perfusing a lot

2:18

of those muscles in the face, for instance.

2:21

They will have relatively high systolic peaks with very little diastolic flow, and

2:26

some even have no diastolic flow, or you'll see flow reversal in diastole.

2:31

So that is a typical interpretation of what these look like.

2:34

This is your triphasic waveform in a popliteal artery.

2:38

You can see a big bump in systole. Early diastole, you start to get that flow

2:42

reversal, and then as things go on, you return to more forward flow.

2:47

And then there's a gap here where we essentially have, during that relaxation

2:50

period, we don't have any additional forward flow.

2:52

Sometimes, like in the external carotid artery, you will have a little bit of

2:55

forward flow at all times. So that can be just a remnant of the tissue that's there

3:00

and what the upstream velocities look like.

3:04

There are also intermediate resistance, and so one of the classic examples for this

3:07

is the common carotid artery, because since that is supplying both a

3:11

high-resistance circulation like the ECA that we just talked about, or the

3:15

low-resistance circulation like the ICA or internal carotid artery like we'll talk

3:19

about next slide, it's going to result in this intermediate waveform.

3:22

So you have a nice pretty sharp peak systolic velocity, but you have more diastolic

3:28

flow than you would typically have in your typical high-resistance waveforms.

3:33

So here is our low-resistance waveform.

3:35

So again, the ICA is a common example of this.

3:37

But renal arteries, vertebral arteries, hepatic arteries are all areas that will

3:42

fall under this as well. They are going to have that consistent forward flow

3:46

through diastole because the tissue requires constant perfusion.

3:49

There's no benefit to the body to not perfuse the brain at some point through the

3:52

cardiac cycle. So hemodynamics is the key of why we do all this, and most of this

3:58

pathology is ultimately going to alter the flow.

4:01

And so this is based on a physics principle of when a vessel narrows, the velocity

4:05

needs to increase to maintain that same degree of flow, and that forms the basis of

4:09

essentially every kind of stenosis criteria that we use.

4:13

Distal to that stenosis, you will see some turbulence develop.

4:17

So I mentioned spectral broadening earlier when we were talking about the spectral

4:20

window. This is an example of that.

4:22

You can see compared to that more clear spectral window that we had previously

4:26

here, you see that whole area fill in.

4:28

And that's showing you that in this person's internal carotid artery, you have more

4:34

different velocities of blood flow that are showing up all at the same time as the

4:39

flow is trying to go through that channel.

4:42

This is another example of what that stenosis can look like and how the changes

4:46

look pre and post that stenosis. So before the level of stenosis, you may have some

4:52

increased downstream resistance, obviously, because of that tighter spot, and that

4:56

can potentially reduce the diastolic flow.

4:59

Once you get into that site of stenosis where you see this area of increased color,

5:03

the velocity accelerates, and then distal, we start to get more of a turbulent flow

5:07

beyond that point. Further downstream, we see an additional change when there is a

5:11

flow restriction known as a tardus parvus waveform.

5:14

And so this is tardus is delayed, parvus is small.

5:18

Essentially, this is a waveform where you have a delayed upstroke.

5:21

So instead of your normal waveform where you have a nice sharp upstroke, you see a

5:25

much slower and lower increase in that systolic velocity.

5:29

Sometimes you'll see some rounding of this peak, and then we have less difference

5:33

between the end-diastolic velocity and the peak systolic velocity.

5:37

So here you can see we have a much bigger difference between the peak and the

5:40

valley. So when you have a tardus parvus waveform, this is one of the strongest

5:45

signs that you are distal to a stenosis.

5:48

So that's one of the things that you're going to want to look for because you need

5:51

to put all the pictures together.