Transcript Noise-induced Hearing Loss

Effects of noise on hearing and
“Noise-induced hearing loss”
Peter R Thorne
Section of Audiology, Department of Physiology and
Centre for Brain Research
Introduction
Purpose:
• to look at what we know about the incidence
and prevalence of “Noise-induced Hearing
Loss” in NZ
• what factors influence hearing loss from noise
Noise and Hearing
• Noise exposure causes injury to the inner ear
and temporary and permanent hearing loss:
clinically latter is NIHL or Noise-induced
hearing loss
• Has always been assumed that Temporary
effects are precursors to Permanent damage.
This is being challenged, including our own
research, suggesting some temporary loss is
the ear adapting to noise.
Noise and Hearing
• Main factor defining severity and rate of progression
of injury and loss of hearing is the sound energy;
defined by the intensity (loudness) and duration of
the sound exposure.
New Zealand Exposure Limits to produce permanent loss
(and other jurisdictions too)
Time-Weighted Average
=100% Dose
Recommended exposure
limit
85 dBA
8 hours
88 dBA
4 hours
91 dBA
2 hours
94 dBA
1 hour
97 dBA
30 minutes
100 dBA
15 minutes
103 dBA
7.5 minutes
106 dBA
3.25 minutes
…..3 dB exchange rate
What do these levels mean?
The audiogram is key quantitative index of the noise injury with greater
loss at 4kHz. Extent of loss correlated to intensity and duration
deepens
Study of
weaving factory
workers, (Burns
1963)
broadens
Noise-induced Hearing Loss
7
Influence of Duration and Intensity
For given intensity hearing loss
plateau after ~10yrs exposure
8
Increasing evidence that TTS is not totally reversible.
TTS in young mice (16wks) recovers but suprathreshold
changes in ABR suggest neural injury. Cochlea show loss
of synapses and nerve fibres
(Kujawa and Liberman, J Neurosci , 29:14077–14085 , 2009)
• These data suggest that some injury with
TTS may not recover although thresholds
do
• Indicate that noise injury has profound
suprathreshold functional changes
• Indicates that thresholds (audiogram) may
not be sensitive index of noise-induced
functional change
Noise a predominant occupational hazard
• Noisy industries
major cause of
hearing loss
Noise levels in NZ Industries
Note the large range of exposure levels
12
1.
Estimates of Incidence and Prevalence of
NIHL
• International estimates are 10-30% of hearing loss
prevalence is due to noise exposure
• WHO data suggest 16% of hearing loss is due to
noise
• No previous epidemiological data for NZ. NIHL
epidemiology difficult to do.
Modelling Estimates of Prevalence and Incidence
• Using Global Burden of Disease model for occupational NIHL
(WHO, Concha-Barrientos et al., 2004)
• Proportion of working population in economic sectors
exposed to noise (>85dBA) estimated from international and
NZ data;
• Relative risk of occupational noise-induced hearing loss
above background (age) estimated from ISO1999-1990;
• NZ data obtained from field measurements of noise
levels in different industries and personal dosimetry
• International data obtained from NIOSH (1998), WHO
(2004) and Prince et al., (1997)
Modelling Estimates of Prevalence and Incidence
• Modelled prevalence and incidence calculated (DISMOD II
software) using NZ hearing loss prevalence data (eg
Greville, 2005) and census data (NZ Statistics retrospective
and prospective estimates);
• Estimated for 2006 as anchor year (last census) and
backward and forward (1986-2030)
• Using international data and NZ data provides a range of
estimates
• Important that these are seen as estimates only
Estimated number of
new cases of NIHL
(>25dBHL 0.5-4kHz) in
the workforce has
increased since 1986,
but incidence (rate) has
decreased.
Estimated number of
new cases of NIHL
(>25dBHL 0.5-4kHz) in
the workforce has
increased since 1986,
but incidence (rate) has
decreased.
This we assume to be
due to decline in
workforce in noisy
industries
Comparison of prevalence estimates with International
(WHO) and NZ data
Measure
WHO Data
N
%
NZ Data
N
%
Prevalence
Hearing
Impaired
Population
%
NIHL only,
Workforce
29242 1.47
42497
2.14
Some NIHL
Workforce
42309 2.13
47026
2.37
NIHL only,
Population
62169 1.54
69613
1.73
15.4-17.3
Some NIHL
Population
90699 2.25 104088 2.58
22.5-25.8
*Assuming a prevalence of hearing loss in NZ of 10% (Greville, 2005)
Comparison of prevalence estimates with International
(WHO) and NZ data
Measure
WHO Data
N
%
NZ Data
N
%
Prevalence
Hearing
Impaired
Population
%
NIHL only,
Workforce
29242 1.47
42497
2.14
Some NIHL
Workforce
42309 2.13
47026
2.37
NIHL only,
Population
62169 1.54
69613
1.73
15.4-17.3
Some NIHL
Population
90699 2.25 104088 2.58
22.5-25.8
*Assuming a prevalence of hearing loss in NZ of 10% (Greville, 2005)
Comparison of prevalence estimates with International
(WHO) and NZ data
Measure
WHO Data
N
%
NZ Data
N
%
Prevalence
Hearing
Impaired
Population
%
NIHL only,
Workforce
29242 1.47
42497
2.14
Some NIHL
Workforce
42309 2.13
47026
2.37
NIHL only,
Population
62169 1.54
69613
1.73
15.4-17.3
Some NIHL
Population
90699 2.25 104088 2.58
22.5-25.8
*Assuming a prevalence of hearing loss in NZ of 10% (Greville, 2005)
Comparison of prevalence estimates with International
(WHO) and NZ data
Measure
WHO Data
N
%
NZ Data
N
%
Prevalence
Hearing
Impaired
Population
%
NIHL only,
Workforce
29242 1.47
42497
2.14
Some NIHL
Workforce
42309 2.13
47026
2.37
NIHL only,
Population
62169 1.54
69613
1.73
15.4-17.3
Some NIHL
Population
90699 2.25 104088 2.58
22.5-25.8
*Assuming a prevalence of hearing loss in NZ of 10% (Greville, 2005)
Estimates of prevalence of NIHL by
occupation/industry
Total Number of NIHL Cases by Industry (Male 25dbHL+)
Services
Finance
4%
2%
Trans
4%
Education Unemployed
1%
0%
NEI
3%
Ag
11%
Mining
3%
Trade
7%
Mfg
29%
Constr
36%
Elec
0%
Estimates show similarity to level of hearing loss in different industries
2.
Variation in Individual Susceptibility to Noise
• Very clear that individuals show different sensitivities
to the same noise exposure, indicating that there are
other factors which define the response to noise.
Factors Affecting Risk of NIHL
Genetic differences (Gates et al., 2000, Rosenhall et al.,
2003)
Solvents and ototoxic drugs/compounds, smoking
(eg. Uchida et al., 2005; Wild et al., 2005)
Sex/gender
Age?
Exposure variances
= Large variation in susceptibility
Factors Affecting Risk of NIHL in Humans
250
Frequency (Hz)
500 1000 2000 4000 6000 8000
-10
Hearing Level (dBHL)
0
10
Normal
20
10 percentile
30
40
50
50 percentile
90 percentile
60
70
80
90
65 year old males exposed > 10 years
ISO 1999-1990 10 yr exposure at
100dBLAeq
Conclusions and Implications
• Prevalence of occupational NIHL in NZ is around 1.52.4% of workforce and 1.5-2.6% of the population (1525% of the hearing impaired population)
• Estimate around 1800 new cases each year
• Effects of noise on the ear affected by many factors.
Genetic and environmental influences significant
• Thresholds (Audiogram) may be insensitive to injury
and do not tell the full story