Transcript OCCUPATIONAL HEARING LOSS

ABNORMAL
NORMAL
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OCCUPATIONAL
HEARING LOSS
BY: MORTEZA DAVOODI M.D.
INTRODUCTION
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Despite widespread institution of hearing
conservation programs in noisy industries,
NIHL is currently one of the most common
occupational diseases.
Although NIHL is permanent, irreversible, and
prevalent, it is preventable.
In addition to the major problem of NIHL, the
ear is susceptible to other environmental factors.
Safe noise exposure
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It is impossible to establish to any clear-cut distinction
between “safe” and “unsafe” noise exposure.
Because of the normal variation in susceptibility
between individuals, it is not possible scientifically to
set a realistic standard for exposure to noise that will
protect everyone who is exposed.
Generally, limits are set with the intention of protecting
90% or more of an exposed population.
How hearing maybe impaired
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Infection of the ear
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Infection of external ear
Chronic infection of the middle ear
Obstruction or injury by physical agents
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Impacted cerumen
Foreign bodies
Trauma to the ear (Slag burns)
A sudden, intense pressure wave
Prolonged noise exposure
Barotrauma (aerotitis)
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Middle ear damage due to rapid changes in altitude
Radiation induced damage
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Radiation to head and neck
How hearing maybe impaired
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Toxic agents
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Quinine and its derivatives
Organic solvents, heavy metals, CO, NSAIDS, cisplatin,
furosemide, Tobacco (nicotine) and aspirine (salicylates) are
possible causes in hypersusceptible patients.
Antibiotics :
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streptomycin, neomycin, kanamycin, paromomycin, rifampin,
aminoglycosides , vancomycin,
symmetrical progressive high frequency SNHL
Diseases :
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Meningitis, tumors, mumps, measles, scarlet fever, diphtheria,
respiratory infections
Differential diagnosis of SNHL
(Nonoccupational Hearing Loss)
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Presbycusis
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Hereditary hearing impairment (HHI):
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Gradual symmetrical progressive high frequency SNHL
Is distinguished by a family history and early age at onset.
e.g; otosclerosis (Can be conductive, mixed, or SNHL)
Metabolic disorders
DM, Thyroid dysfunction, renal failure, autoimmune
disease, hyper-lipidemia and hyper-cholesterolemia
 SNHL that is bi-lateral, progressive, and high frequency
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Differential diagnosis of SNHL
(Nonoccupational Hearing Loss)
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Sudden SNHL
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Sudden onset usually within 1 or 2 hours in the absence of precipitating
factors
Almost always unilateral
Can be exhibited at low frequencies, flat or high frequencies hearing loss.
The degree of HL can be from mild to severe .
Infectious origin:
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Bacteria or virus infections including meningitis and encephalitis.
HL can be unilateral, but is usually bilateral.
Mumps may cause a rather severe, most typically unilateral SNHL
Differential diagnosis of SNHL
(Nonoccupational Hearing Loss)
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CNS disease:
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Cerebellopontine angle tumors especially
acoustic neuroma maybe present progressive
SNHL that is unilateral.
MS : sudden unilateral hearing loss that
typically recovers to some degree.
Menieres disease
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Fluctuating low frequency or flat unilateral
SNHL, fullness or pressure in the affected
ear, tinnitus and episodic disabling vertigo
Exteraauditory effects of noise
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Alterations in blood pressure
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Adverse influences on existing illnesses
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Due to release of adrenocortical hormones and
sympathomimetic mediators
Hyperlipoproteinemia and diabetes
Pregnancy and noise:
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It is unclear what effect exposure to noise during pregnancy
may have on the unborn child, in terms of increased rate of
miscarriage, low birth-weight, or prematurity.
CLINICAL EVALUATION OF
HEARING LOSS
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Detailed work and health history
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Age
Family history
Ototoxic chemicals and drugs
Presence of tinnitus
Noise exposure (occupational and non occup.)
Hearing loss onset, progression, fluctuation and symmetry.
the use of hearing protection devices
Radiation to the head and neck
Head injury
CNS infections
Complete otologic examination,
Audiologic examination
Importance of the history
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A careful evaluation of the workers medical,
occupational, and family history is probably the
most important step in the diagnostic procedure.
The following factors regarding past and
present occupations should be evaluated
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Job titles
Type of work performed
Duration of each type of activity
Dates of employment for each job activity
Condition of PPE used and frequency and
duration of periods of use
Nature of noise exposure include frequency,
intensity and average duration
Estimation of noise exposure
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It is estimated that workers in an 85 dB environment
will have to speak loudly,
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While those in 85-90 dB will have to shout to
communicate at arm length.
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As the surrounding noise reaches 95 db ,
communications only occurs with shouting, even if the
workers stand next to each other.
NOISE INDUCED HEARING LOSS
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Acoustic trauma
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SNHL
CHL
Mixed
Tinnitus
Can more severe than NIHL, especially in the low and middle
frequencies.
Disequilibrium
In addition to immediate hearing loss, affected individuals may also
complain of vertigo, tinnitus and pain.
The injury may be unilateral or bilateral, depending upon the direction of
blast.
SNHL from acoustic trauma may exhibit some recovery from initial
levels; patient need to be followed for 4 to 6 month.
Temporary threshold shift (TTS)
Permanent threshold shift (PTS)
Chronic NIHL
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Defining Characteristics
Audiometric test rooms
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TABLE D-1 - MAXIMUM ALLOWABLE OCTAVE-BAND SOUND
PRESSURE LEVELS FOR AUDIOMETRIC TEST ROOMS
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Octave-band center
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frequency (Hz)...............
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500 1000 2000 4000 8000
Sound pressure level (dB) ... 40
40
47
57
62
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Factors Affecting NIHL
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Noise Intensity or Sound Pressure
Frequency or Pitch
Length of Daily Exposure
Duration of Exposure in Years
Individual Susceptibility
Other Factors (disease, genetics, lifestyle, age,
etc.)
NOISE INDUCED HEARING LOSS
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Clinical presentation of NIHL:
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Irreversible and usually bilaterally
symmetric SNHL,
High frequency hearing loss in the
region around 4000 Hz, with recovery
at higher frequencies.
Often accompanied by high frequency
ringing tinnitus.
Persons with NIHL typically complain
of being able to hear but not
understand speech.
Scale of Hearing Impairment
Threshold (dB HL) Degrees of Impairment
-10 – 25
26 – 40
41 – 55
56 – 70
71 – 90
> 90
Within normal limits
Mild HL
Moderate HL
Moderate to severe HL
Severe HL
Profound HL
There are a number of indicators that will
suggest the need for careful consideration of
causes other than noise
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CHL
MIXED hearing loss
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Inconsistent responses during different tests
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Indicates that exposure to noise is not the only cause
Indicates the possibility of malingering or functional loss
If SRT is 15dB or more than the average of the pure
tone levels at 500, 1000, and 2000 Hz, a psychogenic
loss or malingering should be suspected.
A pronounced loss in one ear
Noise Exposures
Source
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dBA
Whisper
20
Refrigerator
40
Conversation
60
Average TV
74
Blender
80
No exposure to
continuous, intermittent,
or impact noise of a peak
C-weighted level of 140
dB shall occur.
Source
Walkman
dBA
90
Woodworking
93-120
Gun Shot
130-140
Riding Motorcycle
90
Snow Mobile
120
Rock Concert
140
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No exposure shall exceed a
time weighted average of
115 dBA for continuous
noise.
Asymmetric hearing loss
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Greater noise exposure in one ear
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Most indoor factory environment, are highly reverberant
so that one ear rarely receives significantly more noise
than the other.
Non occupational noise sources (Hunters).
 Menieres disease
 Sudden idiopathic SNHL
 Acoustic neuromas
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Audiometric surveillance for NIHL
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The OSHA hearing conservation program mandates audiometric
surveillance of workers who are exposed to noise levels equal to
or exceeding 85 db on an 8h TWA. (when beginning work and
then annually).
This routine audiometric testing can be performed by an
audiometric technician who has completed the necessary
education and training requirements.
For the base line audiogram, the individual should not have been
exposed to loud noise for at least 16h prior to testing, to avoid
TTS.
Subsequent surveillance tests do not require noise free interval.
OSHA regulations require testing at the frequencies of 500,
1000, 2000, 3000, 4000, 6000 and 8000 Hz.
Audiometric surveillance for NIHL
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The results of the periodic audiogram should be
compared to the base line. If the employees test shows
a shift from base line in excess of 10 db for the average
hearing level at 2000, 3000, and 4000 Hz in either ear
(STS) a retest may be performed within 30 days. If the
shift persists, the employee must be informed in writing
within 21 days, fitted with hearing protectors if not
already using them, refitted and counseled if already
using protectors, and referred for a clinical audiologic
evaluation and/or otologic evaluation if appropriate.
Calculations and Application of Age
Corrections to Audiograms
(This appendix is non-mandatory )
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In determining whether a standard threshold shift (STS)
has occurred, allowance may be made for the
contribution of aging to the change in hearing level by
adjusting the most recent audiogram. If the employer
chooses to adjust the audiogram, the employer shall
follow the procedure described below. This procedure
and the age correction tables were developed by the
National Institute for Occupational Safety and Health
in a criteria document.
Calculations and Application of Age
Corrections to Audiograms
(This appendix is non-mandatory )
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I. Determine from Tables F–1 or F–2 the age correction values
for the employee by:
 A. Finding the age at which the most recent audiogram was
taken and recording the corresponding values of age
corrections at 1000 Hz through 6000 Hz;
 B. Finding the age at which the baseline audiogram was taken
and recording the corresponding values of age corrections at
1000 Hz through 6000 Hz.
II. Subtract the values found in step (I)(B) from the value found
in step (I)(A).
III. The differences calculated in step (II) represented that
portion of the change in hearing that may be due to aging.
Example: Employee is a 32-year-old male. The audiometric history for his
right ear is shown in decibels below.
Table F–1—Age Correction Values in Decibels for Males
Table F–1—Age Correction Values in Decibels for Males
Go to Table F–1 and find the age correction values (in dB) for 4000 Hz at age
27 and age 32.
CRITERIA FOR REFERAL OF INDIVIDUALS
TO AN OTOLARYNGOLOGIST
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Baseline audiogram
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Periodic audiograms
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Average hearing levels at 500, 1000, 2000, and 3000 Hz
greater than 25 db in either ear.
Difference in average hearing level between the better and
poorer ears of more than 15db at 500, 1000, and 2000 Hz, or
more than 30 db at 3000, 4000, and 6000 Hz.
Change for the worse in average hearing level in either ear
compared to the base line audiogram of more than 15db at
500, 1000, and 2000, or more than 20db at 3000, 4000, and
6000 Hz.
Audiometric findings are inconsistent
CRITERIA FOR REFERAL OF INDIVIDUALS
TO AN OTOLARYNGOLOGIST
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Ear pain
Drainage
Dizziness
Severe persistent tinnitus
Fluctuating or rapidly progressive hearing loss
Presence of accumulated cerumen or other
foreign materials within the ear canal.
PREVENTION
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A hearing conservation program has consisted of at least
seven identifiable elements:
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Monitoring hearing hazards
Engineering and administrative controls
Audiometric evaluation
Personal hearing protective devices
Education and motivation
Record keeping
Program evaluation
“By showing the worker his personal record of hearing
sensitivity, the nurse or physician has a most effective device
for the promotion of hearing protection.”
HEARING PROTECTIVE DEVICES
(HPDs)
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What is the best hearing protector?
The answer is:
“the best protector is the one properly fitted and the
one you wear.”
HEARING PROTECTIVE DEVICES
(HPDs)
HEARING PROTECTIVE DEVICES
(HPDs)
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Earplugs
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Custom molded
Provide satisfactory attenuation if properly fitted.
 Require cleaning and maintenance
 Offer few advantages over the less expensive foam plugs.
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Expandable foam plug
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Are usually quite comfortable to wear and they also can
provide high noise attenuation values.
Proper Use of Hearing Protection
Earplugs must be properly inserted
source: http://www.cdc.gov/niosh/mining/topics/hearingloss/earplug.htm
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1. Roll the earplug up into a small, thin "snake" with your fingers. You
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2. Pull the top of your ear up and back with your opposite hand to
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3. Hold the earplug in with your finger. Count to 20 or 30 out loud
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Check the fit when you're all done. Most of the foam body of the
can use one or both hands.
straighten out your ear canal. The rolled-up earplug should slide right in.
while waiting for the plug to expand and fill the ear canal. Your voice will
sound muffled when the plug has made a good seal.
earplug should be within the ear canal. Try cupping your hands tightly over
your ears. If sounds are much more muffled with your hands in place, the
earplug may not be sealing properly. Take the earplug out and try again.
Illustrations and Photo courtesy of NIOSH
HEARING PROTECTIVE DEVICES
(HPDs)
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Earmuffs
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The cup material should be rigid and of large volume so as to
provide the best low frequency attenuation levels.
Since earmuffs do not require insertion into the ear canal,
they are more hygienic and less likely to cause external ear
canal infections.
They are easier to remove and replace in conditions of
intermittent noise exposure.
The singular disadvantage to these devices is that they are
cumbersome and bulky.
In conditions of extremely high noise, it may be necessary to wear
both earplugs and earmuffs together.
Noise reduction ratings
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NRRs are based on laboratory attenuation data
and achieved under ideal conditions.
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Actual noise reduction achieved under field
conditions using any HPDs will be much lower
than the assigned NRR.
Noise reduction ratings
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Weighting Scale Adjustment:
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If workplace noise levels are determined using the “C” scale
(dBC) on the monitoring instrumentation, the assigned NRR
may be subtracted directly from the actual measured TWA
noise levels
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If workplace noise levels are determined using the “A” scale
(dBA) on the monitoring instrumentation, the assigned NRR
must be reduced by 7db before being subtracted from the
actual measured TWA noise levels
Noise reduction ratings
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50% Derating:
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In order to more accurately predict the NRR of
HPDs during actual use, a 50% derating of the
assigned NRR (after weighting scale adjustment)
should be applied to determined its “relative
performance”.
OSHA does not require the 50% derating.
Derate by Type
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Derate the hearing protector attenuation by type
using the following requirements:
A. Subtract 7 dB from the published Noise
Reduction Rating (NRR).
 B. Reduce the resulting amount by:
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1. 20% for earmuffs,
 2. 40% for form-able earplugs, or
 3. 60% for all other earplugs.
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Noise reduction ratings
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Combining HPDs:
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Under such circumstances, OSHA advises its
inspectors that 5 dB are to be added after the
weighting scale adjustment is applied to the device
with the higher NRR .
Tinnitus
Diagnostic Approach to Tinnitus
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Tinnitus is common, affecting up to 10 percent of the
U.S. general population.
It is most prevalent between 40 and 70 years of age, has
a roughly equal prevalence in men and women, and
occasionally can occur in children.
The severity of tinnitus varies from an occasional
awareness of a noise (e.g., ringing, hissing, buzzing,
roaring, clicking, or rough sounds) in one or both ears,
to an unbearable sound that drives some persons to
contemplate suicide.
Diagnostic Approach to Tinnitus
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Epidemiologic data reveal that approximately one fourth of persons with
tinnitus are discomforted by it, whereas the remaining three fourths
experience the condition without significant symptoms.
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Subjective tinnitus, which is more common, is heard only by the patient.
Objective tinnitus can be heard through a stethoscope placed over head
and neck structures near the patient's ear.
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In general, pulsatile tinnitus, unilateral tinnitus, and tinnitus associated
with other unilateral otologic symptoms represent potentially more
serious underlying disease than bilateral tinnitus.
Causes of Tinnitus
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SUBJECTIVE TINNITUS
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Otologic disorders are the most common cause of subjective
tinnitus. Most cases of tinnitus result from the same
conditions that cause hearing loss.
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Both CHL & SNHL
OBJECTIVE TINNITUS
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Objective tinnitus is rare. Patients with objective tinnitus
typically have a vascular abnormality, neurologic disease, or
eustachian tube dysfunction.
Patients experience worsening of symptoms at night and
usually do not have other otologic complaints.
Tinnitus and Significant Medical History
Where to Get More Information
http://www.cdc.gov/niosh/topics/noise/defaul
t.html. National Institute for Occupational
Safety.
 http://www.osha.gov/.Occupational Safety and
Health Administration.
 http://www.bgsu.edu/offices/envhs/ppe/docu
ments/ppeprogram.pdf. Bowling Green State
University. Personal Protective Equipment.
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