Now, it’s time for you to think about some auditory tests. There are two tests that can be performed
to determine how intact the auditory pathway is. One is the Rinne test. The other test for you
to remember is the Weber test. First, I want you to understand the Rinne test as an auditory test.
Here, a tuning fork is going to be used to assess bone conduction and air conduction of sound.
First, a tuning fork would be placed at the mastoid process. This will help you evaluate bone
conduction as a practicing clinician. From here, the tuning fork would be placed near the external
acoustic meatus or the ear canal to evaluate the conduction of audition through the air. If this is normal,
air conduction time will be twice as long as bone conduction time.
When the sound is produced through a tuning fork in a normal ear,
it travels through air causing the tympanic membrane to vibrate, and ossicles to move.
This is the conductive component and cochlear fluid to displace.
This is the sensory neural component, in a normal ear the period of tuning forks kept near the ear
will be longer than the time period of where the tuning fork is kept next to the mastoid,
that means even after the perception of sound through air seizes,
the bone will be able to conduct the sound making the patient to still perceive the sound,
since solid matter conduct sound better than gas.
However, in a conductive hearing loss,
the time period for bone conduction is longer than ear conduction since the patient has conductive hearing loss,
the conductive component will not be able to transmit the sound wave effectively, causing the patient to hear it for a lesser time period,
thus, sensory component predominates where the patient can hear through the bone conduction for a longer period,
and effectively when the tuning fork is placed on the bone,
in sensory neural hearing loss, time period is longer through air conduction than bone conduction
since the tympanic membrane and ossicles are functioning.
However, if someone has conduction hearing loss, again this is conduction hearing loss,
bone conduction will be greater or equal to air conduction.
If the loss is attributable to damage to the neural pathway and this would be sensorineural loss and if this is the case,
air conduction is going to be greater than bone conduction but less than twice as long.
Your normal would be twice as long if you have sensorineural loss.
Air conduction is still going to be greater than bone conduction but it'll be less than twice as long.
The Weber test is another auditory test that can be performed. Here, the tuning fork,
once it’s vibrating will be placed on the top of the middle skull. You'll ask the patient where is the sound coming from.
If everything is working normally, the patient will respond that they can hear in both ears.
If there’s some pathology at play such as conduction hearing loss, if it’s unilateral, the vibration will be louder in the affected ear.
So if there’s conduction hearing loss in the left ear,
the vibration will be louder in the left ear because that’s the one that’s affected.
If there’s unilateral sensorineural loss, the vibration is going to be louder in the normal ear because of the impairment in the affected ear.
This table on auditory tests allows you to make sense of the Weber test versus the Rinne test, normal versus abnormal.
So if we take a look here, normal evaluation in the Rinne test
which shows that air conduction is greater than bone conduction bilaterally. This should be about twice as long.
In the Weber test, the individual should be able to hear and localize the sound in both ears.
With conductive hearing loss, the Rinne test will demonstrate that bone conduction
is going to be greater than air conduction in the affected ear,
whereas air conduction will be greater than bone conduction in the unaffected ear.
With the Weber test, conductive hearing loss will be characterized by the lateralization to the affected ear.
Then lastly, with sensorineural hearing loss with the Rinne test,
air conduction is going to be greater than bone conduction in both ears.
Then the Weber test will demonstrate lateralization to the unaffected ear away from the affected ear.