Industrial audiology Flashcards
Effect of noise on the auditory system, diagnosis of noise-induced hearing loss, non-auditory effects of noise, legislation and medico-legal aspects of NIHL
What is the definition of noise?
-Unwanted sound
-Wanted sound e.g. music
What are the four types of noise?
- Steady-state noise- Continuous noise that does not vary by more than 5 dB over time, either gradually or rapidly e.g. workers operating machinery that runs constantly
- Fluctuating noise- Continuous that does vary by more than 5 dB over time, gradually or rapidly e.g. workers who move around within their work environment
- Intermittent noise- Non- hazardous noise mixed with hazardous noise e.g. workers using hand tools, turning equipment on and off
- Impulse noise- Contains rapid pressure transients, consists of single bursts with duration <1s and peak levels 15 dB higher than the background noise e.g. gunfire
What are the three measurements of noise?
- dB SPL- sound intensity
- dBA- takes into account intensity and how the human ear/ auditory system responds
- dBC- specifies peak or implace noise levels e.g. gunfire
Which measurement of noise is best correlated with the relative risk of noise induced hearing loss?
dBA because it takes into account the respose of the auditory system in addition to the sound intensity itself
What are the different noise injuries that exposure to loud sounds can cause?
-Temporary threshold shift
-Permanent threshold shift
-Tinnitus
-Hyperacusis
-Abnormal pitch perception
Who is specifically vulnerable to abnormal pitch perception following noise exposure?
Musicians
What are the factors influencing someone’s vulnerability to cochlear hearing loss as a response to noise exposure?
- Sound level of the exposure
- Duration of the exposure
- Spectrum of sound
What is the primary site of lesion of noise-induced cochlear hearing loss?
The death of the outer hair cells
Does noise-induced hearing loss occur rapidly or gradually?
-Generally noise-induced hearing loss happens following long-term exposure to moderately intense noise
-However it develops insidiously- therefore challenges with communication and changes in music perception are often not obvious until the degree of hearing loss is quite significant
Which area of the audiogram will likely be affected by a noise-induced hearing loss
-Typically effects region around 4 kHz initially
-Further exposure extends loss at lower and higher frequencies
-Hearing loss of 60 dB HL or greater
-Damage to IHCs and auditory nerve fibres
Aside from hearing loss, what problem is often experienced by people with noise-induced hearing loss?
Tinnitus
Why is a notch at 4 kHz specifically observed in noise-induced hearing loss?
-The frequency of maximum cochlear damage is 0.5 to 1 octave above the frequency of maximum stimulation
-Resonance amplifies sound by 15-25 dB a the resonant frequency
-Resonance in the ear canal/ pinna produces enhancement of frequencies around 2-4 kHz
Which end of the cochlea is the most vulnerable to noise?
-The basal end which is associated with high-frequency sounds
-This is because there is less blood perfusion/ oxygenation in the basal end of the cochlea compared to the apex
What is temporary threshold shift (TTS)?
-Experienced directly after noise exposure
-Hearing may be dulled and may experience tinnitus
-Recovery usually 16-48 hours post-exposure
What is a permanent threshold shift (PTS)?
-Gradual loss of hearing, combined with age
-Currently incurable
What is the relationship between TTS and PTS?
-TTS is not a predictor of PTS thus someone who demonstrates a large TTS following noise exposure is no more susceptible to permanent hearing loss later
-If a sound exposure is sufficient to cause a TTS then it is sufficient to cause a PTS
What are the characteristics of noise-induced hearing loss (NIHL)?
-Always sensorineural hearing loss
-Often bilateral and symmetrical
-Does not produce a profound loss
-Once the noise exposure stops the hearing does not continue to deteriorate
-Rate of loss decreases as thresholds increase
-Most severe at 4 kHz
-Maximum loss is seen after 10-15 years after exposure
-Continuous noise more damaging than intermittent noise
When is noise-induced hearing loss not bilateral and symmetrical?
In the case of gunfire where the gun is one side or only one side is being protected
At what sound level does hearing damage begin?
85 dB
With ever ____ dB increase in the noise level, the duration of permissible exposure becomes ____
-3 dB
-Half
What are some non-auditory effects of noise?
-Hypertension
-Heart disease
-Annoyance
-Sleep disturbance
-Stress
What is the procedure for hearing tests administered for the purpose of meeting the requirements of the Health and Safety Executive for those exposed to noise at work?
-Air conduction testing without masking
-Testing starts with the better ear and at 1000 Hz
-Then test 2000 Hz, 3000 Hz, 4000 Hz, 6000 Hz, 8000 Hz and 500 Hz
-Retest at 1000 Hz- if retest value is no more than 5 dB different from the original take the more sensitive threshold as the final value
