Performing caloric testing (VNG)

Now we're getting ready to perform the caloric test. It's usually the last test that we do in the VNG test battery. I'm going to blow some air into my patient's ears. You can see that she's angled at 30 degrees. That's the proper angle to have her lateral canals in the right position to allow us to stimulate the ears properly.

This is a test for bilateral, peripheral vestibular lesions. And so we're going to be testing each of her ears individually.

Instructions to the patient before the test

Alright, so Tess, we're going to do that caloric test now. Okay. And so what's going to happen is I'm going to have this, what's called an irrigator, behind me, and it has an otoscope, like, what the doctor looks at in your ear with, right, but it's going to be blowing some air. It's kind of warm air.

So I want to bring that into your ear. It sounds kind of loud, but you'll eventually tune that out. And it's gonna feel a little bit warm, I'm gonna start blowing the air in there. I'm gonna have this cover on the goggles and your eyes are gonna be wide open. I might have to keep reminding you of that because sometimes it's hard to remember to keep your eyes open in the dark.

What will the patient feel?

And then I start blowing that air, which is gonna last 60 seconds. For the first 30 seconds, you're not gonna feel anything at all. You're just gonna hear that noise and you're gonna feel that warm air. After about 30 seconds, the fluids inside of your ear are gonna start to move because I've heated them up. And so you're gonna start to feel like you're turning over. That's completely normal. Don't worry about the motion, it's going to go away. Shortly after we stop the test, that'll go away.

Task to keep the patient busy

Okay, one other thing that we're going to do is, I'm going to give you a task. So I'm going to keep you busy after the test is done while I'm recording the data on your eye movements on the software.

So your task is going to be that you're going to name people's names that start with a certain letter of the alphabet. Okay, so I'm gonna call out, say, m, and you're gonna say, Michelle, Mary and Mike, and you're gonna try to name as many names as you can. If you run out of names, I'll throw another letter out. So you'll do that. Don't worry, there's no right or wrong answer. That's just a task to help keep you busy.

Fixate on light

And then one last thing is that after I've stopped the irrigator, and you're doing your naming, and I'm looking at your eyes, about 10 or 15 seconds into that process, a light is going to come on inside of the goggle. When you see that light come on, just look at it. Okay, and then you'll know when we're done with the test, because I'm gonna take the cover back off.

And then we're going to take a break for four or five minutes, and then we'll proceed to do the second irrigation.

Test procedure

Okay, so four all together, warm air, each ear, cool air, each ear and then we'll be done.

Okay. All right. Any questions? No, I'm good. All right, then I want to put the cover on and we're gonna get ready to start the test.

1. Warm irrigation in right ear

Here we go. So the irrigator is now running. It has reached its proper temperature of 48 degrees. It beeped, meaning I can go ahead and start the test. So here we go. Are you ready? All right.

First, get a really good look in your ear. I'm just gonna take the otoscope. Remember, you're gonna feel that air now and it's warm. All right, let me get a look in there. Okay, as soon as I can see your eardrum. Right there. I'm gonna go ahead and start the test now.

Now it's a little warm. Okay, yes. So nothing is happening. Yeah, you shouldn't feel anything other than the air. Okay, so now you might start to feel like you're turning towards me a little bit. Have you started to feel that? Okay, so you feel like you're turning towards me? Yes, that's a good normal thing. That's good responses. So we're gonna be able to deal with it. I'm here to help you. Okay, okay.

I only have a few more seconds left and then this irrigation is going to be done in five seconds. Okay, so don't close your eyes. Okay, remember we're going to leave our eyes open at this point. Now tell me what you feel like feel. Like you're turning towards me a little bit? Okay, so I'm gonna put my hand here so that you know I'm here.

I want you to name somebody's name for me that starts with the letter C as in Charlie. Okay, let's try the letter D as in David. And you're doing fine. And a few seconds, that response should start to slow down a little bit. Yes. 20 and then the fixation light should come on. There it is. So now I want you to just stare at that light for me.

I have 10 seconds left, you're doing really good. Okay, and now the fixation light went off. So you start to feel that little bit of that motion again. Okay. And one second left, and zero. Very good. I'm gonna take the cover off now and you're gonna take a break for five minutes. You did amazing. That was fantastic.

2. Warm irrigation in left ear

Okay, so there's the beep. That means our irrigator is ready to go. Tess has taken a 5+ minute break to let her ear cool to room temperature. So we are ready to go. Now we're going to do the second one on the test. So this time we're going to do the left ear with the warm irrigation. Oh, here we go. I'm just gonna get in here and get a good look. Perfect. Okay. still okay.

Feeling any rotation yet? Which way towards you? Right, very good. Okay. Looks like it's just starting. So it's not too bad yet, right now starting to get a little faster. Yes. Okay, very good. About 15 seconds left. So we're doing really well, hang in there. Down to five seconds. Remember to keep your eyes open. Okay, I'm going to take the irrigator out.

And let's start our task again. Let's start with the letter M for Michelle. Megan. Oh, that's very good. Let's try T. Thomas. Tina. Okay, you're good. Let's relax for a second. We're gonna now wait again for that fixation light to come on. So you still feel like you're spinning quite a lot. Yes. Okay, so let's give it some time to relax.

And any minute now, we should see the fixation light, there it is. So stare right at that light. When you're staring at the light, the response should feel like it gets a little slower for you. Because the fixation reduces that response a little bit. And now just a few more seconds, five more seconds. Hang in there. Now we've reached zero. Your second test is done.

And I on the software screen now have a mono-thermal warm screening threshold. So already at this point, I have an indication of what the overall result might be, which for you is 17%. And so far, so good. Looks like everything is working just the way that it should. So I'm going to take the cover off and we're gonna take another one of those 5+ minute breaks.

3. Cool irrigation in left ear

Okay, so now we're gonna start the cool irrigations. We finished both of the warm irrigations. The irrigator is cooling off, getting to its temperature of 24 degrees. So as soon as it beeps, we'll be ready to go. I'm going to put the cover on the goggles. Feeling okay? Great. We heard the beep in the background, so we are ready to go.

Right and get a good look in your ear, okay. So how are you feeling? Which way do you feel like you're turning this time? Away from you? That's correct. With the cool air you feel like you're turning in the opposite direction. Very good. All right, keep your eyes wide open for me.

That's a little more than halfway done. About 15 seconds more, down to the last five seconds. All right, so I'm gonna pull the irrigator out. Remember to keep your eyes wide open for me. And your letter is S for Sam. Sarah, Sophie, Simon. Okay, and try the letter T. Tom, Thomas, Tom, Tina. Okay, that's great. Let's rest a little bit, see if we can slow that response down. Still feel like you're turning the same amount or does it seem to be slowing down a little bit for you?

Okay, so in a few seconds, the light's gonna come on. There you go. Just take a stare at that light for me. That should make the response a little less when you're looking at the light. And now the light's gonna go off again. And then the response is gonna pick back up a little bit. Got about 10 more seconds. Hang in there. Keep your eyes nice and still. And perfect.

4. Cool irrigation in right ear

Alright, so now we got the irrigator running again, you've just finished your third break. So you had your third, five minute break. And I'm sure you're very happy. Now we're ready to do the very last one. Okay, so I'm gonna put the cover on again. This time I’m going into your right ear with some cold air.

We're on the last one. We want everything to be perfect. So remember, whatever you do, don't close your eyes. Keep your eyes nice and wide open. I come in here. Take a look right once I got a nice view of your eardrum, I'm gonna start the test.

All right. So nothing should be happening yet. Tell me when you start to feel that motion. Yes. Okay, which direction are you moving? Away from you. Okay, so to the left, which is correct. So that's good. We are halfway through, so there's another 25 seconds to go. You're doing good.

Does it feel about the same motion as you felt when we did the other ear? Yes, about equal that's good. Okay. So now we're down to the last 10 seconds. Here we go. I'm taking the irrigator out. Remember, don't close your eyes. Okay, let's start your tasking. Let's try the letter L. Luna, Lena, Lena. You know a lot of Ls. Let's try O. That's good. Let's take a rest.

Now we're gonna wait for that light to come on. Our last time should start to slow down that motion pretty soon. There we go, there's our light. Look right at the light. Hey, now the light's gonna go off. You're gonna feel a little bit of that motion again. Okay, just a few more seconds. So 3, 2, 1 and you are finished. And my software is now going to show me a final response, which looks very normal.

So you did a wonderful job. So good for you. Thank you.

Results interpretation

Okay, so we've completed the caloric test. We had a healthy, normal response on this patient.

So we can see that all four of the caloric tests were done. We have nice, strong nystagmus responses down here. We can see that the time is going this way. So at times zero, there was no response because it's taking a while for the irrigation to heat up the fluids. And then eventually we start to see these dots or this nystagmus building as we're heating the air and then it reaches a peak. That might be difficult to see. But it's a little dotted box there, that dotted box is the peak response.

And so we want to see what was the peak response for each of the four different irrigations and then we compare them together. And that gives us this calculation for unilateral weakness, which is the difference between the ears. And directional preponderance: were the beats to the right stronger than the beats to the left?

She got a value of 9% for unilateral weakness, so she's got a green checkmark, because that's well below the 25% cut off. And for directional preponderance, she got 9% left beating, which is again, well below the 30%. What is the total response? She has 70 degrees. If the total responses are too small, then the other calculations become inaccurate. We call that a bilateral weakness. But she has 70. That's great.

And then the only other thing that's important to look at on the screen is here you can see this yellow bar. That's the time period where the fixation light came on. So what should happen is you have less nystagmus when the light comes on. She looks at the light, which reduces the response quite a lot. So she's able to have what we call fixation suppression. So she's suppressing the response, which she did. And then when the light goes off, you can see the response starts to recover. So this is a beautiful test about as perfect as they come.

Example of a unilateral caloric weakness

So this is an example of a patient that has a unilateral caloric weakness, and we can see her irrigations. The right cool and the right warm responses are very small compared to her responses on the left side, where her responses were much larger. So we can see the nystagmus slow phases are very small, with both right cool and right warm significantly larger than left warm and left cool.

So her calculation shows a 55% unilateral weakness and a very small amount of directional preponderance. There's no error in the test. It's just a pure, right caloric weakness. And then just 31 degrees of overall nystagmus. So that's enough to really reliably analyze the test because you don't want to have too small a number of responses, because then the calculations suffer a little bit from the numbers being too close together.

But once you get past like 22 or 24, you can really rely on the results and she has 31. So this is just a nice example of a patient with a right unilateral caloric weakness.