HIS 125 - The Audiologic Evaluation

THE AUDIOLOGIC EVALUATION

• Critics of clinical audiology assert

that audiometry can be

delegated to a minimally trained

technician, since these tests have

the appearance of being quite

simple to administer.


• The assumption that audiometry

can be administered by someone

with minimal understanding is a

failure to recognize the complexity

of the principles underlying

accurate audiometric assessment.


• Pure-tone audiometry has

developed from the basic

principles of the tuning fork tests.

• There are many problems inherent

in the use of tuning forks, and

results can be variable.


For example: Patients with

longstanding hearing loss have lost

the ability to localize sound and are

apt to provide tuning fork test results

that are inconsistent with their

hearing loss.


• However, the value of

understanding tuning fork tests

exist in modern audiometry. Every

audiometer used in diagnostic

testing has the capacity to

present tones by air conduction

and bone conduction.


• The comparison of air and bone

conduction results provides the

basis for determining if middle ear

dysfunction and conductive

hearing loss exists.


• The two tuning fork tests which are

most commonly used in

audiometry are:

1. The Weber test

2. The Rinne test


• The Weber test

When the tuning fork is placed at

the mid-line of the forehead and its

tone/sound localizes to the better

ear; this indicates that the opposite

ear has the greatest sensorineural

loss. (It determines the better cochlea)


• The Rinne test

This compares the loudness of the

tone/sound presented by first bone

then air conduction. A

sensorineural loss is determined if

the air conduction sound is heard

louder or longer than the bone

conduction. (a “positive Rinne”)


• The Rinne test

A “negative Rinne” result reveals

the presence of a conductive

hearing loss.


• Finding a THRESHOLD is defined as

the minimum effective sound

pressure that is capable of evoking an auditory sensation

which the patient/client will

respond to fifty percent of the time.


• The pure tone audiogram is obtained by establishing air-

conduction and bone-conduction

pure-tone thresholds at several

frequencies especially 500Hz,

1000Hz, 2000Hz, 3000Hz, 4000Hz.


• During air-conduction testing, the

entire auditory system is under

examination.

• Air conduction thresholds are

affected by influences from the

pinna, external and middle ear,

and cochlea.


• During bone –conduction testing

the middle ear is bypassed and

the result represents an estimation

of cochlear function of the ear.


• Bone Conduction Testing

The major problem, unique to the measurement of bone-conduction,

Is the lack of effective acoustic separation of the two cochlea.

Bone conduction activates both cochlea simultaneously and nearly equally.


• Bone Conduction Testing

Weber test results can provide information as to the first ear to test. Always perform bone-conduction on the ear which the Weber test lateralizes to.

Note: There is no need to mask when no air-bone gap is revealed.


• NOTE

• With today’s digital hearing

instruments, it is critical to also

measure the half octaves

displayed on the audiometer.

• Half octaves normally displayed

are 750Hz, 1.5K, 3K, 6K.


• NOTE

• When more that a twenty decibel

difference is found between

octaves (500Hz, 1000Hz, 2000Hz,

4000Hz, 8000Hz) it is also

recommended to measure that

half octave.


• There are three methods used to

by the tester to establish pure

tone thresholds. They are:

1. Ascending method

2. Descending method

3. Bracketing method


• You have learned the bracketing

method (five decibels up—ten decibels

down). It is a combination of the ascending and descending

method.

• We will continue to use this

method in our audiometric testing

procedure.


• Assessing Hearing Handicap and Disability

from Pure Tone Audiometry

1. Hearing handicap means the

disadvantage imposed by a hearing loss.

2. Hearing disability is the determination of

compensation for the hearing loss.

Let’s review Northern, chapter four, page #50.

(The hearing loss “label” based upon average hearing

loss level revealed from 500, 1K, 2K average results)


• Speech audiometry attempts to

measure two clinical quantities.

They are:

1. Speech Recognition Thresholds

(SRT)

2. Word Recognition Ability (WR)


• SPEECH RECEPTION THRESHOLD

This test uses thirty-six spondee

words (two-syllable words with

equal stress on both syllables).



Audiometers have been calibrated

so that there is close agreement

between the revealed pure tone

average and speech reception

threshold results—within five

decibels of each other.



When there is a large discrepancy

between the PTA and the SRT, this may be one of the first indications

of nonorganic hearing loss.

If the SRT is substantially better than

the PTA other tests may be

warranted.


• WORD RECOGNITION TESTING

These are administered at suprathreshold levels.

They consist of fifty word lists of words that are phonetically balanced (PB words).

This represents the frequency of occurrence of sounds in everyday English.



The variabilities introduced by live-

voice speech testing make that

approach unacceptable for diagnostic

testing.

The use of recorded speech stimuli

ensures that exactly the same stimulus

is presented on test-retest conditions.



Most WR word lists are administered

at thirty, forty or fifty sensation levels

(above threshold average)

When PB max tests are not used,

most WR word lists are presented at

the patient/client’s most

comfortable listening level (MCL).



PB max tests are used in diagnostic

evaluations to determine if a retro-

cochlear lesion may be present.

When the signal/loudness is

increased, the WR score will

become worse.



Also, when WR scores are grossly

poorer relative to the revealed

thresholds--such as a forty decibel

PTA hearing loss with WR scores less

than twenty-five percent; a retro-

cochlear problem may exist.



Generally, those with conductive

loss have excellent WR scores.

Those with cochlear hearing loss

have poorer WR scores which will

be also be consistent with a greater

degree of hearing loss.



When unusually poor WR results are

revealed relative to threshold

results, a neural lesion may be

present.


Routine audiometric tests do not

provide information about factors

affecting the central

hearing/auditory pathways.

Speech-in-noise tests are much

more revealing for identifying

Central Processing Disorders.

Technology

HIS 125 - The Audiologic Evaluation