Vestibular testing is not only challenging for the patient, it is also difficult for the audiologist or student! A number of factors contribute to the challenging world of vestibular science. The anatomy and physiology is complex (brb– reviewing eye muscles). Each test evaluates a different part of the system and has its own measurement parameters (gain, phase, asymmetry, oh my!). Technical error(s) must be taken into account during each evaluation (yes, it was pointed at the eardrum. I think.). As does patient participation (how many times can I say open your eyes in an hour?? Here come the eye police!).
With all of these factors contributing to the stress of testing, we’ve compiled a list of tips and tricks to know before you enter this great frontier:
- Instructions are everything! While some vestibular tests are evaluating a natural reflex and others require the patient to perform a particular task (like lift their head), all vestibular tests require a certain level of participation from the patient. Instructions must be clear, concise, and consistent. Imagine that your patient has a significant hearing loss or speaks another language – what would be the most effective and efficient way to instruct your patient? “Follow the dot” is usually sufficient and ensures the patient knows what to do! You can always try incorporating tactile cues as well. Remember, simple is usually better.
- Frequency – it’s not what you think. As audiologists, we often think of Frequency (Hz) in terms of the physical properties of acoustic vibration. However, as you will see in the world of vestibular science, you will often see this term used to interpret results of tests.
- Frequency = cycles per second
- When you hear frequency being used in vestibular science (aside from VEMPs), it’s referring to the number of rotational oscillations.
- Velocity = speed in a given direction
- In this case, degrees per second. Therefore, peak velocity is important which we will touch on later!
- Get to know the VOR. The vestibulo-ocular reflex (VOR) is the eye’s ability to focus on and stabilize an image during head movement. However, we observe and measure the VOR in a number of ways during vestibular testing – for example, this reflex is present in the dark or with no visual fixation point (hello, calorics and rotary chair)! The VOR tells us that eyes move in an equal and opposite direction of head movement, making it a very predictable response to measure.
- The inner ear may not be the culprit. The purpose of a dizzy patient coming to audiology for vestibular testing is to determine if the inner ear is a part of or the origin of the patient’s dizziness. You should have a pretty good idea following case history (vertigo, imbalance, lightheadedness) and even an better idea following testing. However, the tricky thing about dizziness is that it may include the inner ear and it may not. It may also be a combination of inner ear and other stuff too. Vestibular testing is rarely black and white, so welcome to the gray! Hooray!
- You’re testing more than the vestibular system. In a conventional audiologic evaluation, we have a direct way to measure subjective perception of hearing. Currently in vestibular testing, we rely on the function of reflexes at a given point in time and reported symptoms to infer what is going on in the inner ear. That being said, it is very important to be aware of extraneous factors that can impact testing and interpretation. These factors can include anxiety, medication, alertness, central disorders, eye movement disorders and more!
- Frequency = cycles per second
Stimulus Input → extraneous central factors → output = Ear?
- It’s a task to task! Humans are smart. When we start feeling crummy, we either immediately identify what is making us feel that way and direct our attention to stop OR we distract our mind and suppress the feelings. Your brain will work to cease the feeling of dizziness! Tasking is essential to recording an accurate VOR response, especially when there is nothing for the brain to do but suppress! This is why we distract the brain by providing cognitive tasks during testing. Here are some examples of tasking prompts you can use with your patient: Name colors, animals in a zoo, animals on a farm, cities in your home state, types of cars, fruits, vegetables, etc. List for me girls/boys names beginning with the letter A (same with cities/states/places). Tell me about the last trip out of state you went on.
- During calorics, make sure you use a similar task for each ear. If one cognitive task is much harder or easier than the other, it may not be a fair comparison between ears.
- Not everyone needs to be tasked. Some people have a hard-enough time keeping their eyes open on. If they are utilizing their cognitive resources to keep their eyes open – that’s okay! Have a conversation and/or have them tell you a story.
- Be prepared to refer. Vestibular disorders require a significant amount of interdisciplinary interaction. As the diagnostic clinician on this multidisciplinary team, you must be aware of disorders and diseases that warrant an appropriate referral.
Next week, we’ll go over vestibular measures in detail and what anatomic mechanism is being stimulated and evaluated as well as the various measurement parameters to be aware of!
Daniel J. Romero, AuD is currently working on his PhD degree with an emphasis in vestibular science at James Madison University. He obtained his Doctor of Audiology degree from Northern Illinois University in 2018. His interests include vestibular assessment and management, vestibular perception, and auditory and vestibular evoked potentials.
Liz Marler, BA is a fourth year from Purdue University completing her externship at the Mayo Clinic in Phoenix, AZ. She is currently serving as the President of the SAA. Her interests include vestibular and electrophysiology.