Audiological Evaluation

Audiology is the branch of science dealing with normal and abnormal aspects of hearing. The scope of audiology includes clinical audiology, rehabilitative audiology, which includes also prescription, trial and fitting of hearing aids.

Sound is the form of physical energy dealt with by auditory system. Sound in nature is found in different forms . It may be a simple sound as pure tones, or it may be a complex sound as noise and speech.

Physical characteristics of sound:

1- Frequency: sounds may be harsh in pitch as the sound of a drum, these are low frequency sounds. High frequency sounds are like violin. The unit of measurement of frequency is called Hertz (Hz). The audible frequency range is between 20 Hz to 20.000 Hz.

2- Intensity: referred to the amount of loudness of sound. Low intensity sounds, are soft while high intensity sounds are loud. The unit of measurement is called decibel (dB).

Pure Tone Audiometry

It is a procedure by which the hearing threshold of an individual is determined using pure tone at different frequencies as a stimulus both by air and bone conduction

Speech Audiometry

It involves presenting speech stimuli to the subject in order to assess the communicative ability of the individual.

Immittancemetry

It includes a battery of tests that evaluate middle ear integrity:

Types of tympanograms:

According to the amplitude of the tympanogram and the middle ear pressure, it is classified into:

1. Type "A" tympanogram: (normal curve):

2- Type "As" tympanogram: (stiffness curve):

The middle ear pressure is normal but the amplitude is reduced. It occurs in cases of ossicular fixation as otosclerosis.

3- Type “AD" tympanogram:

The middle ear pressure is normal but the amplitude is increased. This occurs in ossicular disruption or dislocation and monomeric drum (healed perforation).

4-Type "B" tympanogram (flat curve):

It indicates no middle ear pressure. This occurs in secretary otitis media.

5-Type "C" tympanogram:

Middle ear pressure is negative. This occurs in Eustachian tube dysfunction or resolving middle ear effusion.

• Acoustic reflex refers to the reflexive contraction of middle ear muscles resulting from sound stimulation.

• It is present in normal ears and some cases of sensorineural hearing loss and absent in conductive hearing loss.

• It is a protective reflex against high intensity sounds.

Category: ENT Notes