Apr 4, 2019


Tests of hearing, Audiological assessment, types and result interpretation

Clinical speech testing.
The patient is asked to repeat whispered words at different intensities (other ear is masked by Barany’s box).

Tuning fork tests

Audiological assessment (Audiometery)
This is the measurement of hearing by the use of a special apparatus (audiometer) for studying the degree of hearing at different intensities and different frequencies. The resultant data are recorded as an audiogram.
hearing_tests

Value:
  •  To detect the hearing threshold of the patient.
  •  Detect the type of hearing loss (conductive, sensorineural, or mixed).
  •  Detect the degree of hearing loss (mild, moderate, severe, or profound).
  •  Selection of a hearing aid if needed.

Types:

A- Pure tone audiometry: (PTA)

1- It is the measurement of the patient’s hearing threshold by using pure tones of a single frequency.
2- The test is done once with the ear phone to determine AC curve and once with a B.C. vibrator over the mastoid to determine B.C. curve. The hearing threshold is obtained at 8 frequencies (250, 500, 2000, 4000, 6000, 8000 HZ).

3- The hearing threshold is the minimum intensity of sound that the person can hear. Normally it varies from 0-20 dB at all frequencies.
4- The resultant two curves (A.C. curve and B.C. curve) are plotted on a graph (audiogram) and this will show the type of hearing loss.

Results:
1- Conductive hearing loss: elevated A.C. threshold, while B.C. threshold is normal (i.e. Air/bone gap).
2- Sensorineural hearing loss: Both A.C. and B.C. threshold are elevated .
3- Mixed hearing loss: Both A.C. and B.C. thresholds are elevated but with an air / bone gap (e.g. A.C. threshold is elevated more.
To determine the degree of hearing loss:
The average of A.C. threshold at 500, 1000, and 2000 HZ is obtained then the degree of hearing loss is obtained as follows:
  1.  Normal: 0 – 20 dB.
  2. Mild hearing loss: 20- 40 dB.
  3. Moderate hearing loss: 40 – 60 dB.
  4. Severe hearing loss: 60 – 80 dB.
  5. Profound hearing loss: more than 80 dB.




B- Speech audiometery

This is the hearing assessment using spoken words presented to the patient through earphones, and he is asked to repeat those words. It provides an idea about the ability to communicate:

Speech tests include:
1. Speech reception threshold (SRT)
It is the level (in dB) at which the patient can correctly repeat 50% of the presented speech material. It should match with the hearing threshold level obtained by PTA.

2. Speech discrimination
It is the percentage of the correctly repeated speech material by the patient to that presented to him. Scores of 90- 100% are normal. In SNHL it is poor than expected.
Values of speech audiometery:
-Confirms results of PTA. -Selection of a hearing aid.
-Detects malingerers. - Differentiates between cochlear and retrocochlear .

C- Impedence audiometry

(1) Tympanometry

This is the measurement of middle ear pressure, through measuring the mobility (compliance) of the T.M. :
1. Type A tympanogram: (normal)
2. Type As tympanogram: The pressure is normal but the compliance is reduced in cases of ossicular fixation as in otosclerosis.

3. Type A  tympanogram: (Hypermobile or flail)
The pressure is normal, but the compliance is increased above 1.75 mm H2O & it may exceed the limits of the machine. This occurs in ossicular disruption or dislocation.

4. Type B Tympanogram: (Flat curve) This occurs in secretory otitis media.
5. Type C Tympanogram: Normal compliance with negative pressure. This occurs in ET dysfunction.

N.B: Oscillating tympanogram occurs with glomus tumours.

(2) Acoustic reflex

Usually stapedius muscle contracts 70 – 90 dB above hearing threshold level.

D- Evoked response audiometery

This is recording of the action potentials anywhere in the auditory pathway from the cochlea up to the auditory cortex. They include:

1-Electocochleography. Diagnostic in Meniere’s disease.
2-Auditory brain stem response audiometry (ABR).
It records the electrical activity in the auditory pathway (from wave I to V.)
-Objective detection of hearing threshold level.
-Differentiates between cochlear and retrocochlear, a delay in latency of 0.4 m.sec. between the wave number V of both sides is suggestive of a retrochlear pathology (e.g. Acoustic neuroma).

3-Cortical evoked response.

E- Otoacoustic emission (OAES)

These are low intensity waves produced in the cochlear and recorded in the EAC. They are classified into:
1. Spontaneous OAES: recorded in the E.A.C. without provoking stimulus
2. Evoked OAES: recorded in response to a provoking stimulus (tones or clicks).
They are very sensitive to any cochlear abnormality and can detect and cochlear affection very early. It is used in hearing threshold detection especially in infants and children.

About Author

Tamer Mobarak, E.N.T resident at Qasr-Elainy teaching hospital, Cairo university.


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