This presentation will focus on reviewing various tools that an audiologists can use to assess vestibular function. So the purpose of vestibular assessment is the determination of whether an individual's performance falls within the normal range. For formal vestibular testing, we're using calibrated stimuli and we're measuring responses objectively. Patient variables can impact the validity of the test results including medications. Some medications suppress the vestibular response. Fatigue, whether somebody is to attend to the task and whether somebody is able to follow instructions. There are also examiner variables that can affect the validity of the results. Most importantly, controlling the patient variables as well as repeating tests as needed when the performance may be impacted by some patient variables. The clinical history is probably the very most important part of a vestibular assessment. It's important to distinguish between symptoms that might be vestibular in nature versus other dizziness kinds of symptoms that are typically non-vestibular. Children often have a hard time talking about what they are feeling and describing it accurately. They might not even have the language to describe what they're sensing. So using targeted questions can be helpful. Some examples would be, when did it start? How does it feel? Sometimes providing prompts for them about options. Does anything make it better or worse? How many times has it happened? How long does it last? When it occurs, do you have anything else like a headache? What other medical problems do you have? There are some potential limitations to the battery of tests that I'm going to talk about. First of all, not all facilities have access to all tests. With children, tests must be modified sometimes given the attention and abilities and tolerance. It's important to realize that the audiologist may only get limited data. So the strategy for testing needs to be developed based on what the question is that's trying to be asked. Then the results of testing need to be analyzed using data based on norms for the patient's age. This is a list of the possible formal assessment tools. Electronystagmography or Videonystagmography, Rotational Testing, static balanced testing or Posturagraphy, Video Head Impulse Testing which is also referred to as vHIT, vestibular-evoked myogenic potentials or VEMPs, and there are two types: a Cervical VEMP and an Ocular VEMP. For ENG and VNG testing, eye movements are recorded on the horizontal and vertical planes. The distinction between the two is that for ENG, electrodes are utilized to record eye movements. For VNG, we are using infra-red video cameras to record eye movements. It's possible to either record movements from one eye, so monocular or more typically we prefer to be able to see the movements of both eyes, which is binocular recording. A typical battery for ENG or VNG includes recording and measurement of spontaneous eye movements, positional and positioning tests and calorics. Calorics testing is the only test in the battery that allows for assessment of individual ear function. All the other tests involve really stimulating both ears at the same time. So caloric testing uses a non physiologic thermal stimulus which can be air or water. The temperature of the stimulus is slightly above or slightly below body temperature. The goal is to induce endolymph flow in the horizontal semicircular canal. There are typically four irrigations including one warm irrigation and one cool irrigation in each ear. These are presented in alternate fashion. The dependent measures for caloric testing include, total eye speed, directional preponderance, which means the difference between right beating versus left beating nystagmus and unilateral weakness. So a difference in outcome for the right ear versus left ear. Caloric testing can be modified for children including using monothermal calorics. So if there's no difference between the warm response for the right ear and left ear, then cool irrigations are not necessary. It's also possible to decrease the flow time of the stimulus and to adjust the stimulus temperature to be closer to body temperature, which would be less toxic. Modifications done must be documented of course and they must be consistent across all trials. When doing serial testing, so for example if you're monitoring function for a patient who's exposed to aminoglycoside antibiotics, it's important for the stimulus parameters to be the same across all sessions. For rotational testing, eye movements are recorded and measured. There's a chair that is placed in a surround that is dark and again we're using infra-red camera technology most typically. The patient is seated in a chair that's attached to a motor that's capable of delivering calibrated stimuli. There really are two kinds of tests, sinusoidal which involves rocking the patient from side to side, and the other one is rotating the patient at a constant velocity in one direction at a time. For rotary chair, both ears are stimulated simultaneously and the assumption is that the chair is controlling the head movement. There are two protocols that are utilized. Sinusoidal rotational testing which I mentioned before, is rocking the patient from side to side and we do that in a variety of speeds that are much closer to the head movement when a patient is ambulating. In the dependent measures for sinusoidal testing are phase, which is a timing relationship between the head and the eyes, gain, which is the amplitude of the response, and symmetry, which is the difference between rightward versus leftward movements. Rotational step testing uses a constant velocity acceleration, and there really are four steps. So acceleration to the right and then rapid deceleration, and acceleration to the left and then rapid deceleration. The dependent measures really are peak eye velocity and the time constant, which is the time it takes for the response to decrease from peak to two thirds down. Again, there are modifications that are possible for rotary chair testing. For sinusoidal testing, we can do fewer speeds, so using alternating octaves. For step testing, we can use a lower peak velocity. For example, 100 degrees per second versus 240 degrees per second. There are really four methods of recording eye movements. We can use electrodes, we also can use a video camera that's attached to a chair. There are pediatric monocular goggles and then there are the typical binocular goggles, which you can put a plate on to make the vision denied if the child is claustrophobic. These photos illustrate two of the methods that I mentioned. On the left-hand picture, the patient is wearing the monocular video goggles with the camera on the left eye and plate causing vision denied on the right eye. On the right-hand picture, that child is seated in a booster seat with the camera being attached to a pole. So in that case, we're not able to measure eye movements but we are able to video record them to make gross determinations of responsivity for rightward or leftward rotations. The gold standard test for evaluating static balance is a test called Computerized Dynamic Posturography. In that test, we're able to assess the patient's ability to use vision, the vestibular system and proprioception. They're age adjusted norms, down to three years of age. What's being measured is anterior and posterior sway and sheer. The conditions are systematically modified to evaluate loss of access to accurate sensory stimuli. vHIT is used to record eye movements following head perturbations on three planes; horizontal plane, the right anterior left posterior plane, and the left anterior right posterior plane. The goggles that are used are very small and light weight and they have an infra-red camera and an accelerometer attached to them. For this test, the dependent measures are eye moment gain relative to head movement, as well as the recording of covert and overt saccades. Vestibular evoked myogenic potential testing is focused on assessing otolith function. The cervical VEMP provides information about saccule and inferior vestibular nerve whereas the oVEMP provides information about utricular and superior vestibular function. These tests can be recorded on very young children and their child-friendly protocols that exist. So in summary, formal vestibular testing includes a battery of tests approach. Each test result contributes valuable information. Also consideration of symptoms and the clinical history is important and interpretation of findings. Protocols can be modified for children and answering the question posed is the desired outcome. Thank you for your attention.
