Transcript Introduction to Audiometry.

Principles of Audiologic
Evaluation
SPA 5304
Audiology As a Profession
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Huh?
History
Mission
Whom do we work with?
The Au.D.
• Detection and Prevention of ____________
• Audiologic ____________________
• Audiologic ____________________
• Referral to:
• Across the ______________
• With patients from various _______________
and _________________ _________________.
Scope of Practice
• Range of _____________________
• Where do you get these?
• Specializations?
Client? Patient? What do I call you?
Does that affect what I think of you?
How do I treat you?
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With R-E-S-P-E-C-T
With Positive Regard
With Congruence
With Empathy
First Impressions...
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Ambassadors of First Impressions?
Eye Contact
Handshake
Honorifics
Small Talk?
Purpose of Visit
Interview:
• Open/Closed Questions
• Neutral/Leading Questions
• Feedback:
– Honest? Hostile? Judging?
– Probing? Reassuring? Understanding?
– Silent? Nonverbal?
• How we ask and how we respond sets up
expectations on the part of the pt.
Your Social Style:
Are you a
• Driver?
• Analytic?
• Amiable?
• Expressive?
Some Basics
Sound, acoustically:
vibratory motion of molecules
propagated in a medium from a
vibrating sound source.
IMPEDANCE
• The opposition to vibration, or
• What, other than motion, happens to your
applied force?
• That is what do you have to overcome?
Impedance has 3 components:
• Resistance: Energy lost to heat through friction
• Mass Reactance: Energy taken to overcome
inertia
• Stiffness Reactance: Energy taken to overcome
restoring force
Impedance and Frequency:
• Resistance is generally the same across frequency
• Reactance Components change with frequency
Reactance and Frequency:
• Mass reactance is greater at high frequencies
--it’s harder to get massive objects to vibrate
quickly
• Stiffness reactance is greater at low frequencies
--it’s harder to get stiff objects to vibrate slowly
Resonant Freq.
Mass and Stiffness Reactance
1.2
Reactance
1
0.8
0.6
Xm
Xs
0.4
0.2
0
100
500
1000
Frequency
4000
At Resonant Frequency
• Mass and Stiffness Reactance Cancel
• Only opposition to vibration is Resistance
• In Forced Vibration, you get the most
vibratory amplitude for amount of force
applied
Threshold?
• Absolute Threshold -- lowest value of stimulus
which can be detected
• Difference Threshold -- smallest detectable
change in a stimulus
The Auditory Response Area
Decibels Sound Pressure Level
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dB SPL = 20 log (Pm/Pref)
Reference Press. = 20 micropascals
So,
0 dB SPL = level of a sound with 20
μPa of pressure
Decibels Hearing Level (dB HL)
• Referenced to average human
thresholds in SPL
Which depends on:
• Frequency, and
• Transducer
SPL to HL Conversions
Corresponds to
height of curve
DECIBELS A, B, and C scales
Critical Bands: Fletcher
A Basic View of Hearing & Hearing
Loss
• The Hearing Pathway can be divided into two
major divisions:
– CONDUCTIVE
– SENSORINEURAL
• Outer & Middle Ear = Conductive Mechanism
• Inner Ear &Aud Nerv. Sys = Sensorineural Mech.
Two Routes to Stimulate Hearing
• AIR CONDUCTION: Uses both
conductive and sensorineural mechanisms
• BONE CONDUCTION: “Bypasses”
conductive mechanism to stimulate
sensorineural mechanism directly.
Hearing Loss, A.C. and B.C.
• Sensorineural Pathway is disordered:
– HL is seen in both AC and BC
• Conductive Pathway is disordered:
– HL only via ?
Bone Conduction-the Magic and
the Myth
MAGIC!
• A bone conducted signal reaches both
cochleae equally
• No matter where you place it!
Myth
• Bone Conduction doesn’t use conductive
mechanism
• The truth is it actually does depend on the
outer and middle ear to some extent.
Tuning fork tests often use
A.C. and B.C.
• E.G., the Rinne, in which you compare
hearing by AC to that by BC.
• What should happen:
• If there is a sensorineural hearing loss?
• If there is a conductive loss?
Tuning Fork Test #2:The Weber
• Via BC at midline.
• Can you hear this? If so, where?
• Louder in RE?//Equal?//Louder in
LE?
• What should happen?
T.F. Test # 3: The Bing
• Comparing BC with the ear open/occluded
• Any difference in loudness?
• Yes ___________________________
• No_____________________________
Introduction to Audiometry.
• Threshold is ARBITRARY:
• Lindner study: people can percieve
qualities of sounds they cannot
"hear."
Components of an Audiometer
1. BASIC:
Oscillator
Amplifier
Attenuator
Gate
Transducer
Generates tones
Increases Level
Controls Level
Turns tone on/off
Earphone/Speaker/
Bone Vibrator
Level Control
Switch
Frequency Control
Instructions:
• Identify listening task
– Listening for tones (mostly very soft)
– Starting in which ear**
• Identify response:
– Onset
– Offset
• Encourage guessing
• Ask if any questions
Modified Hughson-Westlake
• Ascending Procedure
• Adaptive
• Raising level in 5 dB steps
– With each failure to respond
• Reducing level in 10 dB steps
– With each response to the signal
THRESHOLD
the lowest level at which responses
occur in at least half
of a series of ascending trials with a
minimum of three responses
required at a single level.
THE AUDIOMETRIC
FREQUENCIES
• The octaves from 250 to 8000 Hz. Why?
• Speech perception.
• Inter-octaves (750, 1500, 3000, 6000 Hz)
– required when thresholds at the adjacent octaves
differ by 20 dB or more
• Above 8000 Hz = “Ultra-audiometric”
– Used in tracking ototoxicity
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Severity of Hearing Impairment
Hearing Level (dB HL)
Classification
-10 to 15
Normal
16 to 25
Slight
26 to 40
Mild
41 to 55
Moderate
56 to 70
Moderately Severe
71 to 90
Severe
> 90
Profound
Audiometric Configuration
Flat
< 5 dB avg. diff/octave
Gradually Sloping
6 to 10 dB/octave
Sharply Sloping
11-15 dB/octave
Precipitously Sloping
> 16 dB/octave
Rising
Better hrg in high freqs
Trough
> 20 dB poorer in mid
freqs.
Sharply poorer hrg at one
freq.
Notch