audiometry

Audiometry Concepts

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Pure Tone Audiometry

Sound has 2 components:

• Frequency (pitch) cf. wavelength

Hz / kHz

• Intensity (loudness) cf. amplitude

dB

Decible scales

Human Speech level

• Speech Freq= 300- 3500 Hz• vowels have most of their energy lower than

1000 Hz. • Speech is mixture of pure tones• Frequency- testes PTA= 250- 8000Hz

audiometry

• Subjective methods1. PTA2. STH /SA• Objective methods1. OAE2. ABR3. ECOG4. Acoustic reflex

Hearing Classification

PTA• used to identify hearing threshold levels

determination of the degree, type and hearing loss• AC done1. know pt is deaf or Normal2. Know the degree of impairment- BC done3. To know the type of deafness4. To know the inner ear statusA-B gap = average of all frequencies Usually BC curve is higher than AC

PTA

• Pure tone- tone of particular single frequnecy• Single frequency used because– Easy to generate,measure and calibrate

• Noise= tone of mixed frequency• test frequency range= 125- 8000hz• Pure tone avearge= Avg of hearing threholds of

500, 1000 and 2000 hz• X-axis- octave of frequency, Yaxis- intencity in dB

Patterns of hearing loss

Masking

• Done to prevent hearing from the Non test ear while testing the deaf ear

• Due to cross over of sound from test ear to non test ear by bony vibration

• cross hearing suspected best to do masking to the non-test ear.

1. Types- complex, pink,white,speech noise

• IA= 40-80 dB IA= 0-10dB• i/D- cross hearing suspected1. Mask AC :threshold (test- non test) ear => 40 dB2. Mask BC: A-B gap of test ear >10dB

NORMAL

• Speech fequency is 300 – 3000 hz• Consonants and vowel make up words and

speech• AC= 2*BC• Normal Air bone gap (A-B) - absent or minimal.

• Vowel information is more cocncentrated in lower Freq • Consonants centered at higher frequencies

Basic AlgorithmHow to READ ?

BC

N AbN

AC A-B Gap

SNHL MIXED

<20 dB

CHLNORMAL

>20dB<20dB

>20 dB

>20 dB

STEP 1

STEP 2

Cochlear• Recruitment ++• Tone decay less 0-20dB• SDS- 50 to 70% max• Menieres, presbycusis

Retrocochlear• Absent• Tone decay more than 20dB• Very poor-• VIII and cerebellopontine angle

• Differntiated by suprathreshold tests- differntial liamen, SISI, ABLB test, tone decay tests

• Recruitment- nonlinear growth or abnormal growth of loudness, hallmark of cochlear disease

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BOILER’S NOTCH

Up sloping- LFHL

1. Can hear consonants but not vowels2. often can still understand human speech well.3. Fluid ME, Meniere’s and Otosclerosis

Downsloping-HFHL

1. Can hear vowels but not consonants2. difficulty talking in groups3. Unable to hear when background noise is present4. NIHL,Ototoxicity,presbycusis, genetic, schwanoma, mobile induced

ABLB

Speech audiometry

• SRT• How much can I hear words correctly.• Lowest hearing level at which 50% of a list of

SPONDEE words are correctly identified.• 2 sylabble with equal stress, baseball,

eardrum, arm chair• Difference between PTA and SRT should not

exceed 12dB- malingering.

• SDS• I can hear but cannot understand words clearly• the percentage of correctly idientifed words from

a list of phonetically balanced words.• Monosyllable- man,van,tan,can• Normal-100%, CHL-= 100%, SNHL-reduced• inference=- HA not useful < 50%

tympanogram

Tympanogram/ impedance audiolmetry

Stapedial reflex

ABR

BERA

OAE

Emissions from the outer hair cellls of cochlea

OAE

• 2 types- Transient and DP OAE• Used for neonnatal screening• Provides integrity of cochlea• identify in early cochlear damage

ECOG

• Integrity of cochlea and VIII nerve• Cochlea is transducer, electrical activity in response

to sound stimulus is recorded• 3 parameters1. Cochlear Microphonics2. Action Potential - AP3. Summation Potential- SPUsed in Meneire’s disease. SP/AP=>0.4 (N--SP/AP=0.4)Used in measuring hearing threshold.

WHAT U SHOULD KNOW

• Causes of CHL, SNHL• Algorithm of audiometry.• identify the PTA- patterns• Identify- Impedence audiometry pattern