Auditory Hazard Units as an Index of Risk from Intense Sounds€¦ · Auditory Hazard Units as an...
Transcript of Auditory Hazard Units as an Index of Risk from Intense Sounds€¦ · Auditory Hazard Units as an...
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Auditory Hazard Units as an Index Auditory Hazard Units as an Index of Risk from Intense Soundsof Risk from Intense Sounds
G. Richard PriceUS Army Research Laboratory
and
AHAnalysis
Presented at the ThirdNational Occupational Research Agenda
(NORA) Hearing Loss Team Best Practice Workshop
Cincinnati, OhioMay 8, 2003
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The Impulse Noise ProblemThe Impulse Noise Problem
• A long history• Baffling data with traditional measures, e.g.
– If A-weighted energy is used:• 2000 - 3000 J/M2 measured under a muff found
acceptable for cannon impulses.• Implies that 2000+ rounds unprotected exposure from a
rifle would be safe• In fact, fewer than 10 rounds are hazardous
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Consider Peak Pressure and DurationConsider Peak Pressure and Duration
-6000
-4000
-2000
0
2000
4000
6000
8000
0 20 40 60 80 100 120
TIME IN MSEC
PRES
SUR
E IN
PA
SCA
LS
100 SAFE
6 HAZARDOUS
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Our approach to the problemOur approach to the problem• Try to understand the ear’s behavior at high level’s of
simulation,• Then devise a measure that was critically related.• The ear’s response is complex
– Several non-linearities– Simple graphic approach won’t work.
• A mathematical model of the ear created to deal with the complexity – the Auditory Hazard Assessment Algorithm for Human (AHAAH)
• A new unit of hazard produced:
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The Auditory Hazard Unit (AHU)The Auditory Hazard Unit (AHU)
• Defined within cochlea (site of damage) as:– Peak upward deflection of the basilar
membrane– In microns– Squared– Summed at a location
AHU = Sum (of peaks in microns2)• Is an output of AHAAH
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Insights Embodied in AHAAH Insights Embodied in AHAAH
• Primary site of damage is the organ of Corti. • Loss mechanism is mechanical at high SPLs
and becomes linear in time.• External and middle ears shape the flow of
energy:– A band-pass filter.– Middle ear muscles, when contracting,
attenuate by stiffening the middle ear.
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Basic Research Insights Embodied in Basic Research Insights Embodied in AHAAHAHAAH (continued)(continued)
– Annular ligament limits middle ear displacements - strongly peak clips at very high pressures.
• Mammalian ears are similar; hence fundamental loss processes will be as well.
• Accurate prediction is the goal:– Under-prediction results in hearing loss– Over-prediction results in unnecessary
restrictions and ineffective systems
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AHAA DevelopedAHAA Developed
Outer EarInner Ear
Middle Ear
area
Ue
Pe Lh RhCb
LdsCds
Rds
Eardrumconductive part
Ldm Cdc Rdc 1:Nt
Cm
Diffractionsoundfield
AirPlug
ConchaEarcanal
Li Ls Cal Ral LvCochleaIncus Stapes
Annularligament
VestibularVolume
Uc
Lo
RoRcPc
HelicotremaRoundwindow
Incudo-stapedal
joint
Malteo-Incudal
joint
Leverand area
ratio
Eardrumindependent
partBulla
Rmi
Cmi Cis
Ris Crw
Rdf
Ldf
2P P
Lpl
Rpl L1 L2 L3
A1 A2 A3
length
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Creation of AHAACreation of AHAA• Created first for the cat ear – allowed real ears to be
tested with damaging stimulation• Electrophysiological measures of hearing used• Wide range of conditions tested
– Primer impulses– M-16 rifle impulses– Airbags– SPLs from 135 to 172 dB peak– 1 to 50 impulses
• Predictions of AHAA compared with effects
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Prediction of Threshold ShiftPrediction of Threshold ShiftVALIDATION OF CAT EAR MODEL
y = 26.607Ln(x) - 140.08R2 = 0.8912
0
10
20
30
40
50
60
70
80
100 1000 10000AUDITORY DAMAGE UNITS
CTS
R = 0.94
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Correlation with hair cell lossCorrelation with hair cell loss
0
10
20
30
40
50
60
70
80
0.51248163264
FREQUENCY/PLACE
PTS
0102030405060708090
100
% IH
C L
OSS
PTSMODELIHC
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CTSCTS--PTS RelationshipPTS Relationship
RECOVERY AT 4.0 KHZ
-10
0
10
20
30
40
50
60
70
80
90
0 10 20 30 40 50 60 70 80 90
CTS
PTS
R= 0.76
SLOPE= 0.86
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For Cat Model:For Cat Model:
• Predicts:– CTS– PTS– Hair cell loss
• For wide range of stimuli• Model ready for transformation into human
form
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Creation of the Human VersionCreation of the Human Version
• Variables changed to human values• Adjusted to get conductive path correct• Stapes to basilar membrane transfer set to be similar
to cat in mid-range of sensitivity• Note: no hearing loss data used at this point (1997)• Expectation:
– Try to predict hearing loss data– Adjust as necessary
• In fact, no adjustment has been necessary
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Transfer function Transfer function –– FF to Ear Drum FF to Ear Drum
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Transfer function: ED to StapesTransfer function: ED to Stapes
MIDDLE EAR MUSCLES
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FF to Stapes, AFF to Stapes, A--WeightingWeighting
A-WEIGHTING
FF TO STAPES
MIDDLE EAR MUSCLES
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But does AHAAH predict hazard?But does AHAAH predict hazard?
• Compare AHUs from waveforms from human exposures with resulting changes in hearing
• Data sets available:– Albuquerque data– Small arms studies– Spark gap discharges– 120 mm mortar– Some clinical data
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The Albuquerque DataThe Albuquerque Data
• Large caliber fire simulated with explosive charges• 3 types of free field impulse
– At 7 levels (3 dB steps)– For 6,12, 25, 50 or 100 impulses– 178 dB to 194dB peak
• A reverberant impulse (at 7 levels, 1,2,3 rds)• 2 HPDs• In all, 53 conditions with 60 Ss per condition
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Hazard is predicted when:Hazard is predicted when:
• For AHAAH: >500 AHUs (sum during exposure)
• For A-weighted energy: >8.7 J/m2 (total during exposure)
• For MIL-STD 1474: Peak pressure/duration exceeds limits on chart
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How do we define How do we define ““successsuccess”” in a in a prediction ?prediction ?
• Hazard for an ear = >25dB TS at any frequency• To be 95% sure that 95%ile case has been reached,
for n= 60, must have 6 or more “failures”, i.e. >5 failures = hazardous condition
• Or, if failure is predicted, can’t say it was not hazardous if a least one failure occurs.
• For 2 to 5 cases, just can’t be 95% certain.• Rule(s) applied to predictions by MIL-Std 1474, A-
weighted energy and AHAAH.
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Evaluation DiagramEvaluation Diagram
OUTCOME SAFE HAZARDOUS
P
RED
ICTI
ON
H
AZAR
DO
US
SA
FE CORRECT RATING
CORRECT RATING
OVER-ESTIMATELESS EFFECTIVE WEAPONSMISSION ENDANGEREDEXCESS CASUALTIES
UNDER-ESTIMATEAUDITORY CASUALTIESPOORER COMMOMISSION ENDANGERED
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EVALUATION BY MIL STD-1474
OUTCOME SAFE HAZARDOUS
01 T1 T2F1 F2 F3G1 G2 G3R1 R2
O2 O3 O4 O5 O5 O7 O8 O9 OF OHT3 T4 T5 T6 T7 T8 T9 TF THF4 F5 F6 F7 F8 F9 FF FHG4 G5 G6 G7 G8 G9 GF R9GH R3 R4 R5 R6 R7 R8
P
RED
ICTI
ON
H
AZAR
DO
US
SA
FE
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EVALUATION BASED ON A-WEIGHTED ENERGY
OUTCOME SAFE HAZARDOUS
G1 G2 G3R1
O1 O2 O3 O4 O5 O6 O7 O8 O9 OF OFT1 T2 T3 T4 T5 T6 T7 T8 T9 TF THF1 F2 F3 F4 F5 F6 F7 F8 FF FH F9R2 R3 R4 R5 R6 R7 R8 R9G4 G5 G6 G7 G8 G9 GF GH
P
RED
ICTI
ON
HA
ZAR
DO
US
SAFE
ERRORS OFTEN > 20 DB
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EVALUATION BY AHAAH OUTCOME SAFE HAZARDOUS
O1 O2 O3 O4 O5 O6 O7 O8 T1 T2 T3 T4 T5 T6 T7 T8 F1 F2 F3 F4 F5 F6 F7 F8 G1 G2 G3 G4 G5 G6 G7 G8 G9 R1 R2 R3 R4 R5 R6 R7 R8 GF GH R9 O9 OF OH T9 TF TH F9 FF FH
P
RE
DIC
TIO
N
H
AZA
RD
OU
S
SA
FE
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Exposure to other impulsesExposure to other impulses
• Need good waveform for AHAAH analysis or A-weighted energy measure
• Data reported vary with study – AHAAH can calculate equivalent data for comparison
• Keep criterion of 25 dB threshold shift at any frequency as hazardous.
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Summary of AHAAH PredictionsSummary of AHAAH Predictions• 7.62mm, 50rds at 155dB - correct• 7.62mm, 25rds at 155dB - correct• 7.62mm, 25rds at 158dB - correct• FNC 6 rounds at 156dB - correct• FNC 5 rounds at 156dB - correct• G3 5 rounds at 159dB- correct• LAW 1 round - correct on 5 different exposures• Spark Gap impulses - correct on 4 predictions• AT4, 1 round, correct• 120 mm Mortar, 7 rounds, protected ears, correct
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In summaryIn summary
• AHAAH: 95% accuracy over all• MIL STD 1474: 38% accuracy (protected
ears)• A-weighted energy: 30% accuracy over all• AHAAH model works well
– All types of impulses– Protected ears– Unprotected ears
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Why does AHAAH work so well in Why does AHAAH work so well in comparison to other methods?comparison to other methods?
• At lower pressures, the normal transmission path dominates and the model reproduces it. (Similar to A-weighting).
• It accounts for middle ear muscle attenuation• Most important: at higher pressures, non-linear
middle ear correctly limits energy entering cochlea.• Given a non-linear middle ear, linear systems, if
correct at one pressure/frequency regime, must be wrong elsewhere.
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Functional issues: Accounting for Functional issues: Accounting for hearing protectionhearing protection
• Pressure waveforms measured under protector on a manikin at ear drum position or ear canal entrance can enter AHAAH at the right “place” and are properly evaluated.
• If a manikin is used, angular dependence of hazard is also correctly determined.
• Or effect of HPD can be calculated with digital filter or model – allows ‘de-rating’ to account for fit.
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Operational issues Operational issues –– How it worksHow it works
• Runs on a PC – short analysis time.• Uses WINDOWS conventions• Program includes tools for importing, editing,
analyzing and printing waveforms.• Operates on a digitized waveform.• Outputs hazard in AHUs and • Makes a movie of the action within the
cochlea (allows engineering insight)
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““OfficialOfficial”” Status of ModelStatus of Model
• Peer reviewed at request of U.S. Army Medical Research and Development Command by the American Institute of Biological Sciences
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AIBS Peer Review Affirmed: AIBS Peer Review Affirmed: “ The Panel recommends that free-field pressure traces should be input to the model ---------------- and that personnel be allowed to be exposed to combinations of noise that does not result in more than 500 ADUs per day. The Panel feels that it was satisfactorily demonstrated that this limitation would produce 95/95 protection –that is, there is 95% confidence that 95% of the population willexperience temporary threshold shift (TTS) that is less than 25 dB. The Panel feels that the process can be applied to all impulse noise conditions, including those whose pressure-time histories appear to be quite different from the ones collected in the Albuquerque study, and still provide the same protection. Finally, the Panel feels that this criterion will provide adequate protection against unacceptable auditory damage over the soldier’s occupational lifetime, as long as the devices are worn and properly fit.”
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““OfficialOfficial”” status of modelstatus of model• Successfully peer reviewed by AIBS• Used internationally by SAE as basis for evaluation of
noise of airbag deployment• Being proposed to Army’s Surgeon General by
USACHPPM as basis for impulse noise hazard rating (first ever!).
• In draft ANSI standard – (legacy of Dan Johnson) • Used by NOISH, SAIC, DEBAKOM• Will be available, with documentation, on ARL
website
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Thank you for your attention!Thank you for your attention!
Any questions? Any questions?