Sound practical
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Transcript of Sound practical
Tests of Hearing
Loud sounds and hearing loss
Intense sounds can cause
- hair cell death
- nerve fiber degeneration
Hearing testing is a means of evaluating an individual's overall hearing function.
What is Hearing Testing?
Hearing can be impaired due to lesions in the external ear canal, the middle ear, or the inner ear. The purpose of hearing testing is to evaluate hearing function and, if it is impaired, to attempt to localize the site of lesion.
• Nerve deafness – impairment of the cochlea or impairment of the auditory nerve
• Conduction Deafness – impairment of the physical structures that conduct the sound into the cochlea
Types of Deafness
destruction of the cochlear or the auditory
nerve
Nerve Deafness
the person becomes
permanently deaf
destruction of tympanum-ossicular
system
Conduction Deafness
sound can still be heard via bone (ossicular) conduction
Three different sized tuning forks. The higher pitched forks (such as the 512 Hz fork) are more appropriate for hearing testing.
Bedside Testing of Hearing
The single most common office test is a tuning fork test called the Rinne, named after Adolf Rinne, who described this test in 1855.
Rinne’s Test
In the Rinne test, a comparison is made between hearing elicited by placing the base of a tuning fork applied to the mastoid area (bone), and then after the sound is no longer appreciated, the vibrating top is placed one inch from the external ear canal (air).
Rinne’s Test
Normal Hears vibration in air after bone conduction is over
Conduction deafness of one
ear
Vibration in air is not heard after bone conduction is over
Partial nerve deaf- ness of one ear
Vibration in air is heard after bone conduction is over
Complete nerve deaf-ness of one
ear
Vibration is not heard on the affected side
Rinne’s Test
In the Weber test, a 512 Hz tuning fork is placed on the patient's forehead. If the sound lateralizes (is louder on one side than the other), the patient may have either an ipsilateral conductive hearing loss or a contralateral sensorineural hearing loss.
Weber’s Test
Normal Hears equally on both sides
Conduction deafness of one ear
Sound louder in the diseased ear
Partial nerve deaf- ness of one ear
Sound louder in the normal ear
Complete nerve deaf-ness of one
ear
Sound heard only in the normal ear
Weber’s Test
Audiometry
Audiometry is the term used to describe formal measurement of hearing. The measurement is usually performed using an "audiometer" by an "audiologist".
In audiometry, hearing is measured at frequencies varying from low pitches (250 Hz) to high pitches (8000 Hz).
Produces pure tones of different frequencies. Is used to determine the nature of hearing disabilities.
The audiometer is calibrated so that zero intensity level of sound at each frequency is the loudness that can barely be heard by the normal person (0 db).
Audiometer
Audiometry provides a more precise measurement of hearing. Air conduction is tested by having the subject wear earphones attached to the audiometer.
Audiometry
Audiometry
Pure tones of controlled intensity are delivered to one ear at a time. The subject is asked to raise a hand, press a button, or otherwise indicate when he/she hears a sound.
An attachment called a bone oscillator is placed against the bone behind each ear (mastoid bone) to test bone conduction.
Audiogram
Frequency
Hearing level(dbs)
normal-10
+10
100
The minimum intensity (volume) required to hear each tone is graphed, and the results are called an audiogram.
The hearing level is quantified relative to "normal" hearing in decibels (DB), with higher numbers of DB indicating worse hearing.
Audiometry
The DB score is not really percent loss, but neverthless 100 dB hearing loss is nearly equivalent to complete deafness for that particular frequency.
A score of 0 is normal. It is possible to have scores less than 0, which indicate better than average hearing.
Audiometry
Audiogram for a Patient with Normal Hearing
When there is a hearing loss, the next step is to try and determine whether the loss is caused by a sensory problem (sensorineural hearing loss) or a mechanical problem (conductive hearing loss).
Audiometry
This distinction is made by using a bone vibrator, which bypasses the mechanical parts of the middle ear.
If hearing is better using bone than air, this suggests a conductive hearing loss.
Audiometry
Audiogram
Conductive Hearing Loss
500 1000 2000 3000 4000 6000 80000
10
20
30
40
50
60
70
80
90
100
Left Ear Right Ear BC Left Ear
Frequency (Hz)
dB
Heari
ng L
evel
500 1000 2000 3000 4000 6000 80000
10
20
30
40
50
60
70
80
90
100
Left Ear Right Ear BC Left Ear
Frequency (Hz)
dB
Heari
ng
Level
Sensorineural Hearing Loss