"AUDIOGRAMS MADE EASY" St George Hearing and Balance Clinic
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Pure-tone audiometry

– behavioral test measure used to determine hearing sensitivity

– test peripheral and central auditory systems

– Pure-tone thresholds (PTT’s) indicate:

• softest sound audible to an individual at least 50% of the time

• plotted on an audiogram

Audiogram

chart of hearing sensitivity

abscissa <=> frequency (range 250-8000 Hz)

                                  - represents most of speech spectrum

             - human ear can detect frequencies from 20-20,000 Hz

             - children can detect even higher frequencies

ordinate <=> intensity

Intensity: level of sound power measured in decibels;

                                             loudness is the perceptual correlate of intensity.

Hearing level (HL): measured in decibels

                                  (based on the standardised average of individuals with normal hearing                                     sensitivity)

Air Conduction

signal is transmitted through the outer, middle, and inner ear and then through the brain to the cortex.

may be performed using headphones, insert earphones, or sound fields.

Bone conduction

assesses sensitivity when the signal is transmitted through the bones of the skull to the cochlea and then through the auditory pathways of the brain.

bypasses the outer and middle ear.

Bone-conduction oscillator

– small oscillator is placed on mastoid.

– stimulates the bones of the skull, which in turn stimulates both cochleae

Masking

Masking presents a constant noise to the nontest ear to prevent crossover from the test ear.

The purpose of masking is to prevent the nontest ear from detecting the signal, so only the test ear can respond.

Speech Discrimination

ability to repeat correctly an open set of monosyllabic words at suprathreshold intensity.

Word lists are phonetically balanced (PB), ie: the speech sounds used occur with the same frequency as in the whole language.

• Hearing is measured with pure tones through headphones

• loudness of each tone is reduced until patient can just hear the tone.

Behavioral Observation Audiometry (BOA)
- infants < 7 months of age

                     - noisemaker testing

Visual Reinforcement Orientation Audiometry (VROA)

• children b/w 7 months & 3 years

• altering frequency and intensity of sounds,

                                           => child's ability to hear sounds across a range of freq’s

Play Audiometry

• children > 3 years of age.

• child listens to sounds and is taught to make a response every time a sound is heard.

Hearing Levels

10dB to 20dB = Normal range

21dB to 40 dB = Mild hearing loss

41 dB to 55 dB = Moderate hearing loss

56 dB to 70 dB = Moderately Severe hearing loss

71 dB to 90 dB = Severe hearing loss

over 90 dB = Profound hearing loss.

Conductive hearing loss     ("mechanical")

blockage or damage to outer +/- middle ear

– perforated tympanic membranes

– fluid in the middle ear system,

– scarring of tympanic membrane.

Sensorineural hearing loss   ("electrical")

damage or malfunction of the:

– sensory part (the cochlea) or

– neural part (the auditory nerve)

congenital or acquired

Mixed Hearing Loss

problem in both:

conductive pathway (outer or middle ear)

nerve pathway (inner ear or nerve)

– eg: CHL due to a middle-ear infection combined with a

                                                   SNHL due to damage associated with aging

Abbreviations

CNT - Could not test

DNT - Did not test

NR - No response

WNL - Within normal limits

AU - Both sides (ears)

AS - Left

AD - Right

BC - Bone conduction

AC - Air conduction

PTA - Pure-tone average

HL - Hearing level

Tympanometry

Measures compliance of middle ear

Normal (Type A)

Hypermobile TM (high peak – Ad)

Decreased TM mobility (shallow peak - As)

Flat (Type B) – OME or perforation

-’ve middle ear pressure (Type C)

Other tests

Oto-acoustic Emission Testing – OAE

measures function of outer hair cells in the cochlea

they respond to sound by producing a very soft sound of their own called oto-acoustic emission.

Brainstem Evoked Response Audiometry – BERA

                                          (or Auditory Brainstem Response – ABR)

provides information on electrical activity generated in response to sound stimulus along nerve pathway, brainstem, and cerebral cortex

< 6 months old (may be carried in natural sleep)

> 6 months old (under sedation in hospital)