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AUDITORY BRAINSTEM RESPONSE AUDITORY BRAINSTEM RESPONSE

AUDITORY BRAINSTEM RESPONSE - PowerPoint Presentation

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AUDITORY BRAINSTEM RESPONSE - PPT Presentation

ABR DRSHHASHEMI 1 2 Auditory Assessment Subjective tests Pure Tone Audiometry Speech Audiometry Objective tests Acoustic Immittance Auditory Brainstem Responses ABR Electrocochleography ID: 217676

hearing abr brainstem auditory abr hearing auditory brainstem loss wave response normal latency frequency cochlear sensory iii click threshold latencies profound sever

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Slide1

AUDITORY BRAINSTEM RESPONSE (ABR)

DR.S.H.HASHEMI

1Slide2

2Auditory Assessment

Subjective tests:

Pure Tone

Audiometry

Speech

Audiometry

Objective tests:

Acoustic

Immittance

Auditory Brainstem Responses (ABR)

Electrocochleography

(

ECochG

)

Otoacoustic

Emissions (OAE)

Auditory Steady-State Response (ASSR)Slide3

What is an auditory evoked potential ?

Electrical activity of the auditory system that occurs in response to an acoustic stimulus, which can be recorded by

surface electrodes.

3Slide4

Short latency response (

< 10 ms )

Middle latency response ( 10-100 ms )

Long latency response (

> 100 ms

)

4Slide5

Introduction

What is an ABR? The Auditory Brainstem Response is the representation of electrical activity

generated by the eighth cranial nerve

and

brainstem

in response to auditory stimulation.

Jewett &

williston ( 1971)

BSER (Brainstem Evoked Response)

BAER (Brainstem Auditory Evoked

Responce

)

BAEP (Brainstem Auditory Evoked potential)

5

ABR assesses the

integrity

of the

peripheral auditory system

and

auditory brainstem pathway.Slide6

Introduction . . .

It’s a set of seven

positive waves recorded during the first

10

msec

after a click stimuli. They are labeled as I – VII.

Waves labeled with

Roman

numerals

6Slide7

PHYSIOLOGY

ABR typically uses a click stimulus that generates a response from the hair cells of the cochlea, the signal travels along the

auditory pathway from the cochlear nuclear complex to the inferior

colliculus

in midbrain generates wave I to wave V.

7Slide8

Origin of each wave

Wave

Origin

I

Distal cochlear nerve

II

Proximal cochlear nerve

III

Cochlear nucleus

IV

Superior

olivary

complex

V

Lateral

lemniscus

VI

Inferior

colliculus

VII

Medial

geniculate

body

8Slide9

9

I

II

III

IV

V

VI

VIISlide10

10

Auditory cortex

Inferior colliculi

Medial geniculate bodies

VII

VISlide11

11Slide12

12Slide13

Electrode placement

Cz (at vertex) (recording electrode)Ipsilateral ear lobule or mastoid process (reference electrode)

Contra lateral ear lobule (act as a ground)

13Slide14

14Slide15

Normal values

ABR should be done at around 80dB

1000Hz – 4000Hz

Latencies are the key measure

Peaks I, III, and

V

most useful

Calculate the peak –

interpeak latencies for the ABR waves

Find out the

interpeak

latencies of

I–III

,

III–V

,

I–V

Disorders will produce delays

Wave

Latency

I

1.5 m.sec

II

2.5 m.sec

III

3.5 m.sec

IV

4.5 m.sec

V

5.5 m.sec

VI

6.5 m.sec15Slide16

LatencyAmplitude

Morphology

Interpretation

16Slide17

Interpretation . . .

Wave I : delayed or absent may indicate

cochlear lesion.

Wave

V

: delayed or absent may indicate

upper brainstem lesion.

I – III

inter-peak latency: prolongation may indicate lower brainstem lesion.

III – V

inter-peak latency: prolongation may indicate

upper

brainstem lesion.

I – V

inter-peak latency: prolongation may indicate

whole

brainstem lesion

. 17Slide18

Applications

Auditory threshold testing

Identifying the hearing loss

Differential diagnosis

Classification of type of deafness (conductive or

sensorineural

)

Neonatal hearing screening

Identification of

retrochoclear

pathology

Neurosurgical

interoperative

monitoring

18Slide19

Disadvantages

Not normally possible for awake children

SkillTime consuming

Not frequency specificity

Not sensitive to hearing loss

< 1000 Hz

or

> 4000 Hz

Cannot provide information about entire audiogram

ABR recorded just at

90dB

( cannot differentiate between

sever

and

profound

hearing loss )

19Slide20

Factors affecting the ABR

Factors that not affecting

AwakeSleep

Sleep stages

Level of arousal

Degree of attention paid to the eliciting stimulus

Factors that affecting

Age

Gender

Females

have slightly shorter wave

III

and

V

latencies than males.

Pharmacological agents

No affect

sedatives, general anesthetics, neuromuscular blocking agents Affect

→ phenytoin,

lidocaine

,

alcohol

Body temperature

↓ Body temperature → ↑ latencies

20Slide21

Limitation

ABR assesses the integrity of the

peripheral auditory system

and

auditory brainstem pathway

, before sound is received by the cortex.

ABR will

not be sensitive

to lesions above the midbrain level.

[Example:

Central deafness

(bilateral temporal lobe lesions),sever to profound pure tone hearing loss but ABR is normal ]

21

ABR is generated

subcortically

, it

does not

truly measure hearing. Slide22

Auditory threshold testing

Click : 1000 Hz – 4000 Hz

Beginning at a

80dB

and continuing down to lower levels until wave

V

is

no larger seen ( 20 dB)

.It is good practice to obtain two waveform at each stimulus level.

In normals

and

conductive HL

click threshold will be

~10-20 dB

higher than the best audiometric threshold.

In

Sensory HL

click threshold will be

~ 5 dB

higher than the best audiometric threshold.Because maximum output for click is limited to ~ 90-100 dB

one will not be able to differentiate between sever

and

profound losses.

The most common cause of

absence

of ABR waves is

sever to profound hearing loss

.

22Slide23

23Slide24

Latency-intensity function ( LIF )

24Slide25

25

The

relation

between LIF and hearing loss is quite

complex

(due to the myriad of possible audiometric contours). Slide26

Normal 26Slide27

Normal27Slide28

Identifying the hearing loss28Slide29

Conductive HL

Latency-intensity function ( LIF ) slope

→ NL

The latency of wave

V

at each intensity → prolonged

Shifted to the

right

29Slide30

Conductive HL30Slide31

Sensory hearing loss

Wave V latencies show NO or

LESS prolongation compared with conductive HL.

LIF lies close to normal curve

31Slide32

Sloping sensory hearing loss

Slope of the LIF is typically steeper than normal.

The region of the cochlea

where the response is initiated (

high-frequency fibers

in the

basal region

are stimulated and longer when

lower frequency fibers toward the apical region are stimulated ).32Slide33

Low frequency sensory (cochlear) hearing loss with normal ABR

33Slide34

Sever high frequency sensory (cochlear)hearing loss with normal ABR

34Slide35

Mild-to-moderate, high frequency sensory (cochlear) hearing loss with normal ABR

35Slide36

Mild-to-moderate , high frequency neural (retrochochlear) hearing loss

36Slide37

Severe-to-profound hearing loss with absent ABR

37Slide38

Neonatal hearing screening

Several clinical trials have shown ABR testing as an effective screening tool in the evaluation of hearing in newborns.

sensitivity of 100%

and

specificity of 96-98%

Can be recorded as early as

28wks

gestational age.

38Slide39

Neonatal hearing screening . . .

Wave I amplitude

is larger

than in adults

(Recording electrode is closer to the cochlea due to the smaller head size of infants.)

The

latencies

of the ABR waveform components are

longer than adults

(Decreased throughout the maturation of the cochlea and brainstem.)

Should correct by

18-24 months

of age.

39Slide40

Intraoperative monitoring

IN SURGERY :

ABR is useful in the prevention of

neurotologic

dysfunction and the preservation of postoperative hearing loss.

For many patients with

tumors of CN VIII

or

the cerebellopontine

angle, hearing may be diminished or completely lost postoperatively, even when the auditory nerve has been preserved anatomically.

40Slide41

Identification of retrochoclear pathology

ABR is considered an effective

screening tool in the evaluation of suspected

retrocochlear

pathology such as an

acoustic

neuroma

or vestibular schwannoma.

41Slide42

42Slide43

43Slide44

44Slide45

Acoustic neuroma

45Slide46

Likely abnormal in:

Multiple Sclerosis and other demyelinating

processes

Hyperbilirubinemia

at levels requiring exchange transfusion

46