An introduction to rotary chair testing
Rotary chair testing is one among many tests of vestibular function.
We've put this article together to give you a thorough idea of what it is, and how you can implement it in your vestibular test battery.
Contents (click on the links to jump straight to your point of interest):
What is rotary chair testing?
Rotary chair testing is a mid-frequency test of vestibular function, testing a range of different frequencies from 0.01 Hz to 0.64 Hz. Rotary chair (head) speed is compared to eye movement speed to assess the vestibulo-ocular reflex (VOR).
Patients are tested with their eyes open without fixation.
Thus, they are fitted with videonystagmography (VNG) goggles with the cover on or situated in a dark enclosure.
Mental alerting tasks are performed, and nystagmus is recorded and monitored.
Background on rotary chair testing
Rotary chair testing offers several benefits.
One of the primary benefits is its consistency in patients with bilateral weaknesses.
Compared to caloric testing, which is often considered as the gold standard for identifying unilateral losses, rotary chair testing is considered the gold standard for detection of bilateral vestibular losses.
Although, it is important to remember that the two tests are complementary in nature when assessing the patient’s vestibular system.
Before moving on, let’s further distinguish between rotary chair testing and caloric testing.
Simultaneous versus independent ear stimulation
Rotary chairs provide a means for assessing inner ear function.
In particular, the ability to assess the integrity of the vestibulo-ocular reflex (VOR) as well as the suppression of that reflex.
But due to the plane in which they rotate the patient, it is important to consider that rotary chair testing stimulates both ears at the same time versus independent with calorics.
Frequency range
Combining the two tests is very useful for looking at the entire frequency range of the vestibular system.
The frequency range is the range at which a patient can detect motion.
The caloric test only looks at the vestibular system at 0.003 Hz, while rotary chair testing adds 0.01 Hz all the way up to 0.64 Hz.
Rotary chair testing is better tolerated
Ice water calorics can be unpleasant for the patient, so rotary chair testing can be a better-tolerated assessment option for patients with a suspected bilateral loss.
3 common rotary chair tests
Three of the most common rotary chair tests are the sinusoidal harmonic acceleration (SHA) test, the vestibulo-ocular reflex (VOR) suppression test, and the velocity step test.
Let’s dive into them.
What is the SHA test?
In sinusoidal harmonic acceleration (SHA) testing, the patient is rotated several cycles in alternating directions and at many frequencies.
This is carried out without fixation using the cover on videonystagmography (VNG) goggles, or inside a dark enclosure.
At the slow frequencies, it is a lengthy procedure to complete a cycle.
Thus, most clinicians start at a mid-frequency, such as 0.08 Hz.
They then work up and down the frequency range from that point, completing as many frequencies as time permits.
The resulting data is filtered and signal-averaged to calculate gain, phase, and gain (a)symmetry.
What is the VOR suppression test?
The vestibulo-ocular reflex (VOR) suppression test is a brief test of the central neurological mechanism’s ability to suppress induced nystagmus.
The setup is like the sinusoidal harmonic acceleration (SHA) test, with the difference being that the patient is provided with a light on which to fixate their gaze position.
Under normal circumstances, the VOR can be suppressed when fixating on a target.
This is calculated by comparing the gain value in the VOR suppression test with the gain value in the SHA test.
If the gain diminishes by less than the normative value, this could show a central abnormality.
What is the velocity step test?
The velocity step test, also referred to as the step rotation test, consists of a rotation at constant velocity both clockwise and counterclockwise.
The acceleration will cause a burst of nystagmus, which will diminish as constant chair velocity is sustained.
When the rotary chair motion stops, the deceleration will cause another burst of nystagmus.
The test is performed once in each direction at two different speeds.
6 advantages of rotary chair testing
Rotary chair testing offers several advantages. The following six are not exhaustive but highlight some of the main advantages.
1. Monitoring peripheral vestibular function over time
As the vestibulo-ocular reflex (VOR) corrects from a vestibular insult, the phase abnormality and symmetry begin to recover.
Thus, rotary chair testing is a valuable diagnostic tool to track the function of the peripheral vestibular system over time.
2. Computer-controlled rotation
The rotation is very accurately controlled and is generally well-tolerated by patients.
The computer-controlled movements with rotary chairs cut any concerns of technique that are present in head impulse testing.
3. No contraindications
Contraindications such as neck trauma do not apply nor is goggle slippage an issue.
4. It's well-established
Rotary chair testing is well established in the literature and has a large base of normative data.
5. Ototoxicity monitoring
You can use rotary chairs to track ototoxic drug effects over time.
6. Pediatric testing
Children are compliant to testing in rotary chairs when compared to caloric irrigation.
3 tips for rotary chair testing
When conducting rotary chair evaluations, there are a few tips that can be helpful to promote the best possible patient responses and fewer technical errors.
Read on to get our top 3 tips.
1. Be sure the test environment is completely darkened
With a reclining rotary chair, such as Orion Reclining with VisualEyes™ 525, we rely on the goggles to provide the light-tight seal for a fixation-free evaluation.
This is because this type of rotary chair does not have a booth enclosure.
While the goggles can provide a good seal on most patients, there is always the possibility that there could be a small amount of light leaking in from time to time on certain patients.
For optimal patient VOR responses, we rely on a completely darkened test environment.
So, we recommend turning the room lights and TV off during the rotary chair part of the evaluation.
This will help to cut the risk of the patient fixating on any light leakage.
Also, a privacy screen cover for your computer screen will reduce any glare coming from the screen.
It will also decrease the likelihood of the patient seeing any light in the goggles during tests of rotation.
These same precautions will also be helpful with caloric testing.
2. Keep the patient's head in the correct orientation
Always remember to keep the patient’s head oriented in the correct direction during rotary chair evaluations.
For an optimal VOR gain response, you should position the patient’s head with a 30° tilt forward to place the lateral semicircular canals in a true horizontal orientation.
With the Orion Comprehensive and Auto-Traverse rotary chairs, you can do this by adjusting the head restraint system.
With the Orion Reclining rotary chair, you can do this by making sure that the chair is in the full upright position.
Then adjust the moveable headrest forward to place the patient’s head in the correct orientation.
Always use the Velcro straps on all versions of rotary chair that attach to the sides of the goggles.
These will lower the amount of head movement during your evaluations.
3. Keep a list of several tasking topics
Appropriate patient alerting tasks during rotary chair and caloric evaluations are valuable for promoting robust patient responses.
It is helpful to keep a list of several tasking topics in your exam room.
By doing so, you can pick from that list when necessary as not every patient will respond well to every tasking topic.
This becomes especially important when performing many frequencies of SHA testing when the evaluation can take several minutes.
Change topics often to keep the patient alert and ready.
For example, avoid tasks that are all related to numbers and counting.
Switch it up and keep the patient interested.
Not only does good tasking help to elicit better patient responses, but it also helps to keep the patient’s mind off the actual test procedure.
Rotary chair buyers guide
As mentioned above, Interacoustics offers the following rotary chairs:
- Orion Reclining
- Orion Comprehensive
- Orion Auto-Traverse
Let’s dive into each below.
Orion Reclining
This chair has been around for a few years and is rather different from the other two for the following reasons.
1. Limited space requirements
Orion Reclining is ideal for clinics that have limited space, as there is no booth enclosure.
The light-tight enclosure is accomplished by using VNG goggles.
It is important to bear in mind that patients below eight years of age may not be suited to the size of ordinary VNG goggles.
This can cause light leakage and unreliable results.
Patients from five to eight years of age can get away with testing in the reclining chair using the small face front mount goggle (Figure 1). Any younger and you will need to look towards the chairs in the next section.
Figure 1: Optional small face front mount goggle.
2. VNG test battery included
Orion Reclining includes the VNG test battery at no extra fee, which you will find with the advanced chairs below is an add-on option.
3. It can recline
Of course, one of the main points of this chair is that it can recline all the way down to a supine position.
This means you can perform the Dix-Hallpike maneuver and positional tests with the patient situated in the chair.
Orion Comprehensive
This chair has a six-foot booth enclosure (as does Orion Auto-Traverse).
Thus, the light tight environment is accomplished with that booth instead of with the goggles.
We still have the patient wearing goggles to record their eye movements through the exam.
But now we do not have to have the goggle cover on because the patient is already in a darkened environment.
Let’s dive further into some of Orion Comprehensive’s key benefits.
1. Pediatric assessment
This chair is ideal for any clinic that needs to do pediatric assessment.
It features the pediatric add-on option, which includes a car seat and in-booth camera (Figure 2), alongside the small face monocular goggle shown in Figure 1 above.
Figure 2: Orion Comprehensive with car seat and in-booth camera.
The small face goggle is for situations where the child cannot wear ordinary VNG goggles or electrodes.
The in-booth camera is handy for situations where the child keeps pulling off the electrodes. Then you at least get a view of what the patient’s eyes are doing.
2. Optional VNG test battery
By adding the VNG test battery, you get the following oculomotor tests:
A note on the optokinetic test is that the chair has a built-in optokinetic drum mounted to the roof of the enclosure. This enables a reflexive full-field optokinetic response.
Orion Auto-Traverse
This is the same chair as Orion Comprehensive upon visual inspection.
The subtle yet important difference between the two is that Orion Auto-Traverse can move off axis up to seven centimeters in each direction.
This allows for dynamic subjective visual vertical (SVV) testing, which can serve the following purposes:
- Clinical research
- Advanced assessment for traumatic brain injury (TBI)
- Vestibular rehabilitation
- Otolith testing
Dynamic SVV
Off-axis SVV testing allows us to position the center of rotation over the patient’s utricle instead of over the center axis.
This enables a more defined look at what is happening with each independent utricle.
With on-axis SVV testing you are assessing both utricles at the same time.
This does not provide as much insight, as we tend to see patients compensate very quickly for a utricular deficit. The on-axis evaluation sometimes fails to tease out this abnormality.
Electro-oculography
For pediatric facilities, or in patients that cannot tolerate goggles, you can add electro-oculography (EOG) to the Orion Comprehensive and Auto‑Traverse chairs.
The pre-amplifier is built into the back of the chair (Figure 3).
Figure 3: Built-in preamplifier.
The electrodes plug into the back of the chair and are then attached to the patient’s face (Figure 4).
Figure 4: Clinician attaching electrodes to the patient's face.
About Cammy Bahner, Au.D.
Cammy Bahner is the Director of Audiology-Balance Division for Interacoustics U.S. In her role, she provides clinical training, education, and support for a variety of products, with a primary emphasis in vestibular and electrophysiologic assessment. She provides clinical input for the development of vestibular products. She received her master’s degree from the University of Nebraska‑Lincoln in 1999 and her Au.D. from A.T. Still University, AZ School of Health Sciences in 2016. She has served as a guest speaker at state, national and international conventions and is a contributing author on published articles in hearing industry journals. Cammy is currently a member of AAA and ASHA.
