Cervical VEMP - Running the Test

This video demontrates a live recording of the cervical VEMP, and the identification of the biphasic response, and the marking of the waveform.

You can read the full transcript below.

Applying the transducers

Amanda Goodhew: So with my protocol set up, we're now ready to start the test.

There's one final step before we press start, and that is to get the insert earphones into the ears.

So I've positioned the insert cables behind Leigh, so that we're not crossing over with the electrode cables or the preamplifier, just to minimize any interference possibilities.

Now we're going to start with the left ear.

So we'll pop the insert earphone into the left ear first of all.

You can place both insert earphones in at the same time, but it is a little bit easier to communicate with your patient if you just do one ear at a time.

So I'm going to leave the right one out for now and just have the left one in.

Remember when you're putting insert earphones in, you want to give it a minute just for that foam to expand and fill up the ear canal before you do start your testing.

So we'll leave your right one out for now, EMG monitor we've got the left one in, which means we're testing the left ear, which means that we want to stimulate the or engage and contract the SCM muscle on the left side.

So in order to do that, I'm going to ask Leigh to turn his head towards the right.

And the benefit of him looking towards the right is that he can see the EMG monitor on the computer screen behind us.

Now, this is a visual indication for him as to how much muscle contraction is actually happening, how much muscle contraction he's producing.

We want him to be in between the two black bars; the blue is indicating that we're on the left side.

And when we see green, that means that he is in between those two bars, in between that sweet spot where we want him to be.

So I'll also encourage him, so if he does lose a bit of muscle contraction, I'll encourage him to give me a little bit more.

But this is a really useful visual indicator for him to make sure that he maintains the right amount of muscle contraction.

Are you ready to start testing?

Left ear

Fantastic. So if you turn your head towards the computer screen, and just lean into my hand a little bit.

So whilst we're running the test, I can encourage him, if I haven't got enough muscle contraction, to press against my hand, which can help to keep that muscle engaged.

But I can see we've got a good amount both on the screen and on the muscle there.

So I'm going to press Start now.

So now we can see our cVEMP is recording.

Typically we would run the test for a minimum of 100 sweeps.

And what we want to look at is the pre-stimulus window.

So the recording window in this protocol actually starts at minus 20.

We can look at the region between minus 20 and 0, and if we have a relatively flat line there, that's telling me that there's actually very little noise in the system.

I can see that is the case here.

So I'm going to stop testing now.

And in fact, I probably could have stopped testing a little bit earlier.

You can relax for me.

If we had a bit of noise in that pre-stimulus window, then what we could do is continue running for more sweeps, we could go up to about 200, potentially.

It's important to make sure that your patient can maintain that muscle contraction for that duration.

If they can't, you do have an alternative option, which is to run a repeat measurement.

So we're going to do that now.

If I can get you to engage your neck again, that's lovely.

It's always a good practice to repeat measurements when we're doing any form of evoked potentials recording.

It allows us to double check that morphology, make sure that what we've got is a genuinely repeatable response.

But also what we can do is add those two waveforms together.

If we do have some unwanted noise in our recordings, by adding them together that can help average out some of that extra noise.

So I'm going to stop that one there.

And we can see that we've got two really significantly large cVEMP responses on that left side.

The morphology, the latency is very repeatable, overlapping.

And actually in that minus 20 to 0 time base, we've got a relatively flat line in both of those waveforms.

So, it's all confidence that we've managed to record a really good quality waveform for this cVEMP test on the left ear.

Right ear

Now what we can do is move over to do two recordings in the right ear.

It is an option to alternate between the left and the right.

So you might do one on the left, one on the right, one on the left, one on the right.

This is useful in case there's any issues with the patient fatiguing.

So if they are not able to maintain that muscle contraction for long enough to get two good quality recordings on each side, one after the other, then by alternating it gives them a little bit of a break from one side to the other and helps to overcome any issues with fatigue.

So now we're going to take the insert earphone out of the left ear so that Leigh can continue to communicate with me, whilst we pop the right insert into the right ear and run the right cVEMP.

So I'm just going to pop the right insert earphone into Leigh's right ear.

We want to make sure again that we leave enough time for that foam to expand slightly to fill the ear canal before we start our test.

Once that's settled, we're ready to start the cVEMP on the right-hand side.

Remember, it's really important, we need to use the same stimulus type, the same intensity level.

So we're going to continue with our 500 Hz CE-Chirp at 97 dB.

What I'm going to do is start running the test but actually ask Leigh not to give us any muscle contraction to start with, so that I can show you how the EMG controlled stimulus works.

So I'm gonna press Start now.

And we can see that actually on our system, it says EMG is too low, no recording / stimulation.

And basically what is happening is that the system knows that Leigh hasn't given us enough muscle contraction, and so it's not going to start presenting the stimulus, and it's not going to start recording the response until we do get sufficient muscle contraction.

So if I could ask you to increase that head turn very slowly to the left so that we get the right muscle, we can see we've got a bit of red, so we're engaging.

Now we're into the green, that's fantastic, you're in the right spot, no more than that, we've gone a little bit too far.

So that's another thing that's really useful to see, if he gives us too much muscle contraction, then it will also stop recording.

So we won't record, we won't stimulate unless that muscle contraction is in between those two black bars, giving us the right amount.

Again, we can look at that minus 20 to 0 time base, we've got a really good flat line there.

We've got 140 sweeps.

So I'm going to stop that recording.

And you can relax for us.

Thank you very much.

And once again, we would run a repeat measurement on that right hand side, same level again.

So if I can ask you to engage your right SCM muscle by turning, that's fantastic.

And we are ready to run that repeat.

Now we do have a range of that EMG level because we have these two black bars.

And it's actually quite useful to try and make sure that they're not just within those two black bars, but both the right and the left were at a similar region.

So if your patient is delivering you the, the amount of muscle contraction that leads them to the right-hand side to the top end of that, that that bar, then if they do that on one side, it's nice to try and encourage them to achieve a similar amount of muscle contraction on the left-hand side, which Leigh has done really nicely for us.

So we can stop testing on the right side as well.

Once again, we've got a repeatable cVEMP morphology, latencies, the amplitudes do look very similar as well.

But to know exactly what we're looking at, we're going to mark up the waveforms, and then we can compare our left and right.

How to mark the waveforms

So now that we've got four recordings, two on each side, we're ready to mark up our waveforms.

If we go to the Edit tab, we can actually look at how much muscle contraction our patient delivered during each recording.

So at the top here, we're looking at this graph, which is the 'show EMG graph' option.

And it's showing us the amount of muscle contraction for the waveform that's highlighted.

So for this one on the right-hand side, we have a value of 68.

For the other one, on the right-hand side, we have a value of 101.

On the left, the values are slightly different.

We have 97 and 112.

And this is really important to look at because ideally, we want the same amount of muscle contraction on both sides, so that when we look at the symmetry or asymmetry value, it's not affected by an asymmetry in the amount of muscle contraction.

So the first thing we want to do is mark up the waveforms.

So we're going to place our P1 value here and our N1 on the negative peak.

I'll do that for all four.

Same on the right-hand side, P1 there and N1 at the bottom.

Waveform partners

And then we can set the left and right waveforms as partners.

So I am going to take the biggest difference so that I can show you what the Eclipse can do for us.

So the biggest difference in muscle contraction is between these two waveforms at the top here, this was 112, and this was 68.

So if I select -- I've selected the right one, if I right click on the left and click 'Set as VEMP partner', these two waveforms are now partnered together.

Applying EMG scaling

And what we want to do is take a look at this asymmetry value over here, which is 0.35, which is just on the edge of the normal range.

But what we haven't done at the moment is scale the waveforms according to the amount of muscle contraction that was present.

So what we can do is right click on the screen and select EMG scaling.

This has now altered the scale – the waveform slightly so that they are scaled according to the amount of muscle contraction that each side produced.

And we can see that that has actually brought our asymmetry down somewhat to well within the normal range.

So it's really important to apply that EMG scaling, particularly when you have got a difference in the muscle contraction from the left and the right-hand side, as we did in this case.

Using all waveforms

So in that example, I selected the two waveforms: the left and the right that had the biggest asymmetry in terms of muscle contraction, in order to show you the effect of EMG scaling.

However, in clinical practice, the best practice is to make use of all four waveforms that we have available to us.

So what I would like to do is add the two right waveforms together, and the two left waveforms together.

This way, we benefit from reducing the amount of noise in the overall average waveforms.

And we can then compare the left and right overall waveforms, to look at the asymmetry between those, making use of all of the recording that we've done during our test.

So I'm going to remove the EMG scaling.

And I'm going to unpartner these waveforms.

And now I'm going to add the two right waveforms together.

So the one at the top is the overall average waveform, and I'm going to do the same on the left-hand side.

So we're going to be using these top two waveforms for our interpretation.

Once again, we should mark up our P1 and N1 waves, and we'll do the same on the right-hand side here.

And now we can look at the amount of muscle contraction between these two.

On the right, we have 101. And on the left, we have 97.

So already, by combining the four waveforms, or combining the two on each side, we've got a much closer symmetry in terms of the amount of muscle contraction.

So I can set these as VEMP partners, and we can see that the asymmetry ratio is at 0.16, which is fantastic.

That's well within the normal range.

Because we've used all of the data that we have available, and we've got a close ratio in terms of the amount of muscle contraction, I'm not expecting to see a huge impact of applying EMG scaling.

However, it's always really good practice to make use of it so that we know we've scaled those curves in relation to the amount of muscle contraction.

So we'll apply EMG scaling, and we can see that we haven't got a huge impact of using that, as expected, because the amount of muscle contraction was similar in both of those overall averaged waveforms.

But these would be the final values that I would use for my clinical interpretation, using those top two overall averaged waveforms, benefiting from all of the testing that we've done today.