Cervical VEMP - Modifications of the Assessment

Transcript

Amanda Goodhew: So we've seen a traditional cVEMP recording, and what I want to show you now is a couple of modifications.

First of all, if we have any middle ear pathology, or presence of wax in the ear canal, then air conduction may not be the best type of stimulation to use for our cVEMP.

We could alternatively use the bone conductor.

So I'm going to demonstrate how to do a cVEMP using bone conduction today.

We have our bone conductor here, this is the B81 bone conductor, which means we're actually able to run the cVEMP at 70 dB intensity level.

So the first thing we're going to do – the montage in terms of electrodes is all the same -- we're just going to pop the bone conductor behind the right ear first.

So very similar placement as we would in any case with the bone conductor: we want it on the mastoid prominence behind the ear there.

So that's nicely set up, and we're recording the, or presenting into the right ear.

So again, we're recording from the right SCM muscle.

So for this, we will get Leigh to turn his head towards the right – towards the left-hand side to engage and contract that right SCM muscle.

In the protocol, we do need to make a couple of changes.

So we just need to change our stimulus type to bone conduction, and we need to change our polarity to alternating in order to handle any stimulus artifact.

So we're going to select a level of 70, we're testing the right ear.

Again, we want the same amount of muscle contraction, the same action from our patient.

That's already looking good on the screen.

So I'll press start.

Once again, we would run for about a minimum of 100 sweeps, looking at that early portion, that pre-stimulus time base to see as flat a line as possible indicating that there's minimal noise in our system and in our recording.

So we're at 100 sweeps now, that's looking pretty good.

I am going to press stop there.

And once again, best practice in all evoked potentials is to run a repeat waveform: we can look for that repeatable morphology, repeatable latencies on the P1 and N1 peaks, and we can add them together to get the best overall averaged waveform.

So if you're okay to give us another contraction to the left there.

Again running at the same intensity level of 70.

We'll press start.

And again, we're looking for that pre-stimulus window, looking for repeatable morphology.

And we can see already that's coming through there, we've got very similar region of muscle contraction on the bar at the top of the screen, I can see that Leigh's giving us the same amount of muscle contraction as in the first recording.

So we can stop there.

And once again, we can go to our Edit tab and mark up the peak and trough.

So the P1 there, and N1 down at the bottom.

And on this side here P1 and N1.

And we can now move on to doing bone conduction on the left-hand side as well.

So now we want to run the bone conduction cVEMP test on the left ear.

So we need to take the bone conductor off, and we'll just place it behind the left ear there.

Again, making sure that we're not touching any wires.

I'm going to run this behind the head so that we're not crossing over with the electrode cables.

That looks like a good position there.

Fantastic.

So back into the software screen, we want to again select the same intensity level of 70.

We haven't changed any of the other parameters, just need to move over to the left-hand side.

We need Leigh to engage his left SCM muscle by looking towards the right.

So you ready to start?

Again, similar amount of muscle contraction on this side to the, the first side... ideally, that's what we're looking for.

We can encourage our patient with a little bit more, a little bit less, those sorts of instructions.

They can benefit from the EMG monitor on the screen as well.

Just going to let that one run a little bit longer because our pre-stimulus window is a little bit noisier than it was on the right-hand side.

So we'll use that minus 20 to 0 region.

And that's going to stop there.

That's fantastic.

Let's repeat that one more time.

Again, the repeat of the waveform gives us that double check that the morphology is truly repeatable.

And we can add these two waveforms together on each ear, if we need to, to reduce the amount of noise in the overall averaged waveform.

That's looking really good, particularly about minus 20 to 0 is much flatter on this one.

So I'm happy to stop the recording there.

If we go into our Edit tab, we can mark up the waveforms here on both of those.

And then we will add the two lefts together.

And we will add the two rights together.

So the top two waveforms are the ones that I would then mark up again and use to calculate the asymmetry ratio.

So let's put our P1 marker there, I just want to put a little bit higher actually there, and N1 down at the bottom.

So now we can set the two waveforms as partners to each other.

Set as VEMP partner there, and we can see that our asymmetry ratio is 0.07, which is fantastic.

I don't think we would necessarily need EMG scaling in this instance, but let's put it on and see.

That brings our asymmetry ratio down to 0.04, which is absolutely fantastic.

We've got no asymmetry between the two waveforms, between the right and the left side, in this case using bone conduction.

So the second modification I want to show you is where we have our patient in a slightly different position.

Some people, when we have them sitting upright and encourage them to turn their head to either side, cannot produce enough muscle contraction to give us a robust response.

So what we can do is have them lying down on a bed instead.

And in this position, we'd ask them to lift their head and then turn.

Typically, this will produce a much stronger muscle contraction.

So I'm going to ask Leigh to demonstrate this for us now.

If you could lift your head up and then turn towards me, we can see looking at the EMG monitor that we've actually got too much muscle contraction.

Now it's going to be difficult for him to reduce the amount of muscle contraction down.

So what I'm going to do is adjust the range on the EMG monitor instead.

So we can use these buttons here to increase or decrease the range.

So I'm going to increase it.

So again, Leigh if you could lift.

We'll just adjust that scale until he ends up back in between the two bars - that's in a really good place.

Okay, relax for me. Thank you.

So we know now that we've got the appropriate range for his muscle contraction.

And although this is different to the seated version, it's absolutely fine because what we want to see is the same muscle contraction on the left and the right.

So as long as we maintain this range for both sides that we test, it doesn't matter that it differs from one person to another.

So now to demonstrate this, we're going to run one recording in the right ear and one recording in the left ear.

So we'll start with the right-hand side.

Leigh, are you ready to lift your head up for us?

Go for it. Thank you, that's perfect.

This can be a more challenging task for the patient to do because they need to maintain this lifted position.

So really important that we check our patient history for any neck issues, any musculoskeletal issues, which might make this a contraindication.

But in this case, Leigh's managing really well.

We're at 100 sweeps.

I'm just going to alter the scale because we've got such a large recording, and I am going to let him stop there.

Thank you very much.