Post on 20-Jun-2015
description
TYPES OF HEARING AIDS
Terminology
Traditional Hearing
Aids
Air Conductio
n
Standard
Behind-the-ear (BTE)
Receiver-in-the-ear Receiver-in-
the-canal (RITE/RIC)
Custom
In-the-ear (ITE)
In-the-canal (ITC)
Completely-in-the-canal (CIC)Bone
Conduction
Headband
Eyeglass
Implantable hearing aids
Middle
Ear
Implant
s
Bone-
Anchore
d
Implant
s
Cochlear
Implant
s
Auditory
Brainste
m
Implant
s
Hearing aid styles
http://www.jefferson.edu/jmc/departments/otolaryngology/centers/balance_hearing/patient_services/hearing_loss.html
Hearing Aid Effect
Johnson et al 2005
HEARING AID COMPONENTS
Microphone
Digital Sound
Processor
Power Source
Receiver
Batteries
Batteries
Types Silver Oxide Mercury Zinc-Air
Long shelf-life Disposable
Sizes Smallest to
largest 10 yellow 312 brown 13 orange 675 blue
Zinc-Air batteries
Require air to work Battery compartment of
hearing aid must be permeable to air
Air activation pore may clog up
Affected by humidity Low humidity dries out the
electrolyte in the cell High humidity can flood the cell Teflon membrane in battery
helps moderate effect of humidity
A. separatorB. zinc powder anode and
electrolyteC. anode canD. insulator gasketE. cathode canF. air holeG. cathode catalyst/current
collectorH. air distribution layerI. semipermeable membrane
Batteries
Flat discharge rate
Capacity rating Capacity is in
Amperes/hour In general, larger
size batteries are designed for greater load.
Size
Capacity
Discharge
C/D
10 245 3000 Ω .08
312 215 1500 Ω .14
13 360 1500 Ω .24
675 320 620 Ω .52
Batteries
2320 cases of battery ingestion 1983 – 1990 952 were hearing
aid batteries (45%)
Of those cases, 312 (33%) were batteries removed from the hearing aid by the child
Litovitz & Schmitz, 1992
Batteries
Zinc-Air batteries are relatively benign
Of 418 cases of zinc-air ingestion, only 21 (5%) had negative outcomes Minor: nausea,
vomiting, fever Moderate: high
fever, bloody stools, dehydrationLitovitz & Schmitz, 1992
Batteries
If anyone ingests a battery, this is what you should do: Immediately call the 24-hour National Battery Ingestion
Hotline at 202-625-3333 (call collect if necessary), or call your poison center at 1-800-222-1222.
If readily available, provide the battery identification number, found on the package or from a matching battery.
In most cases, an x-ray must be obtained right away to be sure that the battery has gone through the esophagus into the stomach. (If the battery remains in the esophagus, it must be removed immediately. Most batteries move on to the stomach and can be allowed to pass by themselves.) Based on the age of the patient and size of the battery, the National Battery Ingestion Hotline specialists can help you determine if an immediate x-ray is required.
National Capital Poison Center
Batteries
Don't induce vomiting. Don't eat or drink until the x-ray shows the battery is beyond the esophagus.
Watch for fever, abdominal pain, vomiting, or blood in the stools. Report these symptoms immediately.
Check the stools until the battery has passed.
Your physician or the emergency room may call the National Button Battery Ingestion Hotline/National Capital Poison Center collect at 202-625-3333 for consultation about button batteries. Expert advice is available 24 hours a day, 7 days a week.
National Capital Poison Center
Microphones
Microphones
Converts acoustic energy to an electrical signal
Sound pressure waves enter front volume of microphone
Diaphragm oscillates Oscillating voltage
between diaphragm and backplate
Voltage amplified by field effect transistor (FET)
Diaphragm
Charged Electret Backplate
FET
Barometric relief hole
Damping screen
Types of Microphones
Omnidirectional mic Directional mic
Thompson, 2003
Directionality with a single directional microphone
Thompson, 2003
Directionality with a two omnidirectional microphone
Thompson, 2003
Directional sensitivity
Low frequencies lose sensitivity
Hearing aid must add gain to low frequency inputs to counteract reduced sensitivity
May make internal noise more audible
Broken microphone?
Listening check No feedback, no sound?
Check for debris in port, and clean out.
If applicable, turn hearing aid to t-coil and hold up to fluorescent light/CRT. Buzzing? Probably microphone. No buzzing? Probably receiver.
Receivers
Receivers
Signal Processors
Signal processorDigital
representation of microphone output
enters digital processor
Stuff
Digital representation of
modified signal sent to receiver
Digital signal processor
What is the stuff? Input assigned to channels (frequency
ranges) Analyzed for speech characteristics
Sound classification schemes Appropriate gain applied independently to
each channel per programmingScheme
Channels (Hz)
<500 500-1500
1500-3000
>3000
Speech
10 20 30 25
Music 15 20 20 20
Comfort
0 15 15 5
-1
0
1
250 500 1000 2000 4000 8000
-1
0
1
1.5 1.5 2.5
1
OTHER AIDS
Bone conduction hearing aids Intact cochlea Air conduction
hearing aids contraindicated Chronic drainage Microtia
Frequency (Hz)250 500 1000 2000 4000 8000
-10
Intensit
y (dB HL)
0
10
20
30
40
50
60
70
80
90
100
110
120
O O OO O O O
O
[[ [
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XX
X X XX
XX
CROS
Contralateral Routing of Signal Microphone on
one side Receiver on the
other No amplification Used for unilateral
loss One dead ear One normal ear
Frequency (Hz)250 500 1000 2000 4000 8000
-10
Intensit
y (dB HL)
0
10
20
30
40
50
60
70
80
90
100
110
120
O O OO O O O
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