Hearing Basics and Importance of Hearing
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Transcript of Hearing Basics and Importance of Hearing
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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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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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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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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