(Bass drum) (Bass drum) (Bass drum) When sound travels through and enters the ear, it first reaches the external part of the ear called the pinna and continues down the external auditory canal to the tympanic membrane at the end.
This displacement of the air by sound causes the tympanic membrane to move and causes movement in the ossicles of the middle ear.
First, the malleus will be displaced then the incus, then the stapes.
The stapes attaches to the round window, the entrance of the inner ear structures, allowing sound energy to be transferred from the external ear, through the middle ear to the inner ear.
The inner ear is filled with fluid, so with movement of the ossicles, the resulting force on the round window causes the fluid in the inner ear to be displaced, creating vibratory patterns and displacement in the hearing organ, more commonly known as the cochlea.
The output from the cochlea travels through the vestibulocochlear nerve to the brain and higher auditory structures.
This is the basis of how sound information travels from the external environment, through our ear, onwards to the brain.
What many people are not aware of is this other organ that is part of the inner ear.
This is the called the vestibular system, and is a sensory organ that provides information on motion, equilibrium and spatial orientation.
More simply put; our vestibular system helps us maintain balance and posture.
Here is a closer view of the vestibular organs.
For reference purposes, here is our cochlea, and our vestibulocochlear nerve.
As you can tell by the name of the nerve, both the cochlea and the vestibular system share the same nerve to the brain.
So the vestibular system consists of three semicircular canals, which are stimulated by movement and orientation of the head, and are each responsible for movement in a different plane of motion.
First we have the anterior semicircular canal, then the posterior, and the horizontal semicircular canal.
Since we have a vestibular system on each side of our head, the canals work in pairs to detect motion and orientation.
For example, when shaking your head no, both the left and right horizontal semicircular canals are stimulated.
When you move your head forward towards the right shoulder, and backwards towards the left shoulder, the right anterior canal and the left posterior canal are stimulated.
When moving your head forwards to the left shoulder, and backwards to the right shoulder, the right posterior and left anterior canals are stimulated.
The various patterns of stimulation between the two ears help our brain understand movement and orientation of the head.
The two other organs of the vestibular system are referred to as otolith organs, and are responsible for detecting linear acceleration and changes in gravity.
These are called the saccule and utricle.
Damage to any of the vestibular organs, can produce symptoms directly related to vestibular dysfunction such as dizziness, vertigo, imbalance, nausea, motion intolerance, headaches.
But also hearing related concerns due to the close proximity of the organs, such as hearing loss, autophony, tinnitus, sound sensitivity, aural fullness.
But also issues related to other symptoms and brain function such as visual problems, oscillopsia and psychological disturbances such as depression and anxiety.
There are many tests that can be done to assess vestibular function, including videonystagmography, rotary chair, and computerized dynamic posturography.
This is the basis of VNG.
These are goggles are worn by the patient to measure and record eye movements while doing various tasks to assess how the vestibular system is functioning.
Eye movements are critical for vestibular testing because we are unable to directly measure and assess the vestibular system.
With stimulation of the vestibular organs, information travels through the vestibular-cochlear nerve, to the central vestibular neurons, and the extraocular motor neurons, which are connected to our eye muscles.
This stimulation produces predictable eye movements that can be measured in individuals with functioning vestibular systems and pick up when there is dysfunction if abnormal eye movements are produced.
The caloric test is part of the VNG battery and specifically tests the horizontal semicircular canals and the superior part of the vestibular nerve.
This test involves the person laying down with their head elevated 30 degrees to maximally stimulate the horizontal canals and introduce water or air of warm, then cool temperature into each ear separately while recording their eye movements Introducing a warm or cool temperature into the ear will cause the fluid of the inner ear to move at low frequencies and therefore cause movement of their eyes.
Depending on the resulting eye movements, this test provides information the excitability or weakness on that side of the vestibular system that is being stimulated.
Rotary chair testing involves recording a person’s eye movements using electrodes placed on their skin while they are sitting in a chair that moves in pre-determined speed and direction.
The purpose of rotary chair testing is to provide information of how the vestibular system functions at higher frequencies.
For the entirety of the test, the person is sitting in a pitch-black chamber while we are recording their eye movement relative to the speed and direction of the chair.
When this test is used in combination with VNG testing, we are able to obtain a well-rounded profile of how their vestibular system is functioning across a wide range of frequencies.
Unlike the other tests, computerized dynamic posturography is used to provide information on how a person is functioning functioning in their daily life with vestibular dysfunction by assessing their balance, center of gravity and stability in a variety of situations that simulate daily life while ensuring safety.
The overarching goal of this test is to be able to obtain information on how to continue with appropriate rehabilitation to manage balance, mobility and reduce the risk of falls and further disability.
This test assesses and manipulates three systems that are involved in maintaining balance: the somatosensory system, the visual system, and the vestibular system.
We can assess how well a person is able to use their vestibular system by creating an unstable surface, altering the somatosensory input, and creating unstable surroundings, affecting the visual input.
This test is extremely important in order to understand the debilitating effects vestibular system damage can have on a patient’s daily life.
Now that we have provided you with the basis of vestibular function and testing, it is important to know why we believe that vestibular audiology is an important field of our profession.
Firstly, fall prevention.
This affects not only the elderly but individuals of all ages.
Falls can be a result of dizziness or vertigo related to damage to the vestibular system, visual system or somatosensory system, which are all involved in maintaining balance.
Evidently, falls can lead to long-term issues such as injury, brain trauma, immobility, muscle weakness, isolation and loneliness.
Related to fall prevention is improvement of balance and stability.
As trained audiologists, we have access to the tools and expertise for accurate diagnoses that other health professionals do not.
Our rehabilitation plans are focused on our test results, and specific for the individual needs of the person depending on their location of damage and the resulting symptoms.
This is similar to stroke rehabilitation, as the stroke can affect our vestibular system and the input that it receives to maintain balance.
Vestibular testing and counselling also provide validation and concrete evidence of the issues patients can present with, providing reassurance that their symptoms and dysfunction is in fact real and warranted.
Finally, the most rewarding reason of why vestibular audiology is important is that we have the ability to help improve a person’s quality of life and mental health by helping them re-gain confidence in their movement and stability.
Dizziness and other associated symptoms can lead to extreme stress, anxiety and depression, therefore by helping a person with their vestibular issues, we can lessen the load on their mental health as well.
Due to the debilitating effects vestibular problems can have on daily functioning, we believe it is important to increase awareness to the public and also to other health professionals to promote the identification and management of vestibular systems through education.