Hearing Loss Types & Causes

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The Causes andConsequences of Hearing Loss

byJAMES C. SAUNDERS, Ph.D.

Department ofOtorhinolaryngology: Head andNeck Surgery

November 19, 2010


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Assessing Hearing

1. Subjective The Audiogram

Other Behavioral Tests

2. Objective - Auditory Brainstem Response

Otoacoustic Emissions


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The Audibility Curve


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Types of Hearing Loss

1. Conductive -- Blockage of Sound Conducting Path From

Source to Cochlea.

-- 120 Million Cases/year

-- 30 - 40 dB Hearing Loss

-- Treatable and Reversible


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Pinna or Concha

About 25 mm

The Outer Ear

Pathology

Blockage of the

Ear Canal

Artesia of the Canal,

Pinna Malformation,Ear Wax in Canal,

Bugs in the Canal!!


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The Middle Ear

DISORDERS

Ear-Drum Perforation,

Ossicle disarticulation,Otosclerosis, Otitus Media,

Colesteatoma, Poor

Eustachian Tube function,

Perilymphatic Fistula,


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0

10

20

30

40

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90

100

500 1000 2000 3000 4000 6000 8000

Frequency (Hz)

dB

H

earingL

evel

Left Ear Right Ear BC Left Ear

DiagnosingDiagnosing

Conductive Hearing LossConductive Hearing Loss

Bone Conduction

Threshold

Air Conduction

Threshold

The Air-Bone

Gap Reveals the

ConductiveLoss


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Types of Hearing Loss

2. Sensorineural -- Damage to Inner Ear or Central AuditoryPathway

-- Hair Cell Loss

-- Auditory Nerve Loss

-- Vascular Damage

-- Incurable, Leads to

Permanent Hearing Loss


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0

10

20

30

40

50

60

70

80

90

100

500 1000 2000 3000 4000 6000 8000

Frequency (Hz)

d

B

H

earingLevel

Left Ear Right Ear BC Left Ear

DiagnosingDiagnosing

Sensorineural Hearing LossSensorineural Hearing Loss

Note:

There is no

Air-Bone

Gap Thus

There is No

Conductive

Component to

The Hearing Loss


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-- 30 35 Million Americans Suffer

Measurable Sensorineural Hearing

Loss

-- 1.4 Million are Completely Deaf

-- 1 in 1000 Babies are Born with Severe

Hearing Loss, 50% of which are

Due to Genetic Factors

-- 14 Million Americans Suffer from Tinnitus

-- 1 in 3 Americans over 65 Have Age

Related Hearing Loss CalledPresbycusis (1 in 2 Over 75)


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Sources of Sensorineural Hearing Loss

-- Bacterial, Viral, Vascular Damage

-- Genetic Origins: e.g., Presbycusis

-- Ototoxic Drug ExposureGentamycine, Cisplatin, etc.

-- Overstimulation (Exposure toIntense Sound

Recreational

Occupational


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AUDIOGRAM

PRESBYCUSIS


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SOURCES OF LOUD SOUND

AND HEARING LOSS


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MEMBRANOUS LABYRINTH


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IHC AND OHC SENSORY HAIR BUNDLES


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Basilar Membrane Movement Creates a

Shearing Force that Bends theStereocilia of the Hair Cells


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2 microns

Cell Body of Hair Cell

Sensory Hair Bundle of Hair Cell

Water Jet

Isolated Single

Hair Cell

A

B

C


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Sustained Loud Sound Exposure

can Cause Injury by:

1. Mechanical Injury and Destruction to the Hair Bundle

and Organ of Corti

2. Metabolic Fatigue leading to Hair Cell Death


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Stereocilia filaments

Normal Exposed

Actin FilamentsCross-Bridged

By Fimbrin

Excessive Sound

Causes

DepolymerizationOf the Actin-Fimbrin

Paracrystal Array


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Floppy

Collapsed

Splayed

Fused


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GATING SPRING HYPOTHESIS OF HAIR CELL TRANSDUCTION

Tip Link


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Control

Exposed

Tip-Links can Repair

Themselves!!


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Note: Major Outer Hair Cell Loss and Some Inner Hair Cell Loss

Sustained Exposure can Metabolically Fatigue the Hair cells and

This Results in Their Death


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LOSS OF 8th NERVE FIBERS AFTER HAIR CELL LOSS


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ASYMPTOTIC THRESHOLD SHIFT

A window into the dynamics of hearing loss and recovery


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Octave Band Noise


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Relation between hair cell loss and Permanent Hearing Loss


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Consequences of Hearing Loss

Loss of Communication

Psychological and Social IsolationQuality of Life

Danger in Failure to Detect Distance Stimulation

What Can be Done?Hearing Aid

Other Assisted Listening Devices

Lip Reading Training

Cochlear Implant

Documents

Hearing Loss Types & Causes