Hearing Basics and Importance of Hearing

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ANATOMY OF THE EAR

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ACOUSTIC REFLEX

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Arterial Supply of Inner Ear

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Outer & Inner Hair Cells

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Auditory Pathway

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The Auditory Cortex

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Speech Banana

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Normal: -10 to 25 dB Mild: 26 to 40 dB Moderate: 41 to 55 dB Moderately-Severe: 56 to 70 dB Severe: 71 to 90 dB Profound: > 90 dB

Picture Adapted from: Bess, F.H., Humes, L.E., Audiology: The fundamentals, 2003.

Degree of Hearing Loss

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Common Audiogram Configurations

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Type of Hearing Loss

Sensorineural (SNHL) No air-bone gaps ≥15 dB gap between AC and BC thresholds

Conductive (CHL) ≥15dB air-bone gap

Consistent with middle ear pathology

Maximum conductive component is 60dB

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CONDUCTIVE HEARING LOSS

ossicular discontinuity with intact TM - 50 to 60 dB

ossicular discontinuity with perforated TM - 30 to 50 dB

TM perforation - 10 to 30 dB

otosclerosis - less than 50 dB

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Degree, Type, Location Examples: Mild to severe sloping SNHL No location implies that loss affects all frequecies

Severe high frequency SNHL Moderate to mild rising low frequency CHL

Describing Results

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Interpretation

Not Audible

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RESONANCE FREQUENCY

frequency at which a mass vibrates with the LEAST amount of external force

VALUES:

External Auditory Canal 3000 Hz

Middle Ear 800 to 5000 Hz (mostly 1 to 2K)

Tympanic Membrane 800 to 1600 Hz

Osssicular Chain 500 to 2000 Hz

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MASKING REQUIREMENT

air conduction when test tone is 40 to 60 dB louder than bone thresholds of nontest ear

bone conduction when there is any difference between air conduction and bone conduction thresholds

masking dilemma occurs when there is bilateral 50 dB air-b0ne gaps and requires special audiometric techniques

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TYMPANOGRAM

A graphic representation of ear compliance in relation to static pressure changes20

Normative Tympanometric Values

EAR CANAL VOLUME (cm3)

COMPLIANCE (ml)

MEAN 0.5 0.7

90% RANGE 0.4 to 1.0 0.2 to 0.9

EAR CANAL VOLUME (cm3)

COMPLIANCE (ml)

MEAN 1.1 0.8

90% RANGE 0.6 to 1.5 0.3 to 1.4

Children Ages 3-5 years Adults

Peak Pressure is typically WNL in the range of -150 to +25 daPA Compliance refers to mobility of tympanic membrane

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TYMPANOMETRY

TYPE A - Normal

A. TYPE AS - "shallow" (otosclerosis, tympanosclerosis)

B. TYPE AD - "deep" (ossicular discontinuity)

TYPE B - "flat" (middle ear effusion, TM perforation)

TYPE C - negative pressure (Eustachian tube dysfunction)

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Type A

⦿ Hypermobile ! Aging ! Atrophic scars ! Healed perforation ! Ossicular discontinuity

Type A Type As Type Ad

⦿ Hypomobility ! Otosclerosis

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Type B

ECV = 7.0

Type B

ECV = 1.0

Type B

ECV = 0.2

Type B

⦿ Flat ! Perforated TM ! Patent PE tube

⦿ Flat ! Middle ear fluid

! Serous Otitis ! Blocked PE tube

⦿ Flat ! Impacted cerumen

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Type C

Type C⦿ Negative pressure

! Eustachian Tube dysfunction

! Developing otitis media

! TM retraction

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