Hearing tests

Hearing, or auditory perception, is the ability to perceive sound by detecting vibrations and changes in the pressure of the surrounding medium through time through the ear . The transmission of sound waves can occur through air and called air conduction or through bone and called bone conduction.

Sound waves are collected by the external ear and funneled to the tympanic membrane to make it vibrate ,then vibrations are transmitted to the ossicles of the middle ear, this cause movement of the endolymph of the inner ear, which stimulates the hair cells (hearing receptors) , these cells send impulses to the brain through the cochlear nerve.

Types of hearing loss: 1-Conductive hearing loss: there is obstruction of external auditory canal or disease of middle ear. 2-Sensorineural hearing loss: disease affecting cochlea or cochlear nerve. 3-Mixed type

Objectives: To examine and compare air and bone conduction of the subject . instruments : Vibrating tuning fork (512 Hz).

Rinne's test Rinne`s test evaluates hearing loss by comparing air conduction to bone conduction. Base of vibrating tuning fork placed on mastoid process until subject no longer hears sound then the vibrating top is placed one inch from the auditory meatus, say to the patient, which is loudest?

In normal person, air conduction is greater than bone conduction (Rinne`s positive). In conductive hearing loss, bone conduction is greater than air conduction (Rinne`s negative) . In partial sensorineural hearing loss, air conduction is greater than bone conduction .

Weber's test It can detect unilateral conductive hearing loss (middle ear ) and unilateral sensorineural hearing loss (inner ear). The base of vibrating tuning fork is placed on the patient's forehead or the nasal root exactly in the midline.

Normally : Subject hears equally on both sides In conductive hearing loss (one ear) : The sound of the vibrating tuning fork is louder in diseased ear because masking effect of environmental noise is absent in diseased side. In sensorineural hearing loss (one ear): sound louder in normal ear .

Schwabach's test In this test we compare bone conduction of the patient with that of a normal subject . Normally: bone conduction is the same for examiner and patient In conductive hearing loss: bone conduction is better than examiner. In sensorineural hearing loss: bone conduction is less than examiner.

Audiometer Instrument to assess hearing in person with hearing problem. It measure the threshold of hearing (the lowest intensity of sound the patient can hear). Pure tones at various frequencies are generated ,and their levels are increased and decreased until threshold are found . Outputs may include earphone for air –conduction testing , a bone conduction vibrator for bone conduction testing.

Frequency : tone of sound measure in( Hz). Intensity : is loudness of sound measure in (dB).

Objectives of the test 1-Shows whether hearing is normal or not 2-If the hearing is abnormal ,it shows the severity of hearing loss 3-Also it shows type of hearing loss whether conductive or sensorineural or mixed type .

How to do the test In isolated room first we measure air conduction by using ear phones ,we deliver sounds for each frequency we change the intensity till we get the lowest intensity which the subject hear. The same is done for bone conduction .but we used bone vibrator instead of the ear phones. So the graphic representation between frequency and intensity called audiogram

Normal audiogram

Patient with conductive hearing loss

Patient with (high frequency )sensorineural hearing loss