Noise-induced Hearing Loss Flashcards
How is noise measured?
- Frequency or pitch of sound in Hertz
- Intensity of sound in decibels (decibel scale is logarithmic)
Tell me about the structure of the Ear?
- The Auricle (or Pinna) and Ear Canal constitute the outer ear, and act to funnel sound towards the Tympanic Membrane
- The Tympanic Membrane forms the beginning of the middle ear, which also comprises the malleus, incus and stapes bones. These small bones help to transmit vibrations generated by the sound towards the inner ear
- The Inner ear consists of the Cochlea (for hearing) and Vestibular System (for perception balance + acceleration)
The cochlea, dedicated to hearing; converting sound pressure patterns from the outer ear into electrochemical impulses which are passed on to the brain via the auditory nerve.
The vestibular system, dedicated to balance.
Tell me about the structure of the Cochlea?
- The inner ear has a snail-like structure called the Cochlea. If unrolled, the Cochlea would be approximately 33m long!
- Within the Scala Media of the Cochlea, is a structure called the Organ of Corti
- The Organ of Corti is filled with fluid and lined with mechanosensory hair cells
- Projecting from the top of hair cells are tiny finger-like projections called Stereocilia, which are arranged in a graduated fashion (shortest Stereocilia in the outer rows and longest in the centre)
- The Cochlea is Tonotopically organised, so different frequencies of sound waves interact with different locations on the structure
How does noise damage the ear?
- Exposure to loud noises is thought to damage the sensitive hair cells lining the Organ of Corti, located in the Cochlea
- Certain cells in the Cochlea seem to be more sensitive, so hearing loss generally affects certain frequencies. The basal part of the cochlea, which is concerned with hearing higher frequency sounds, is generally affected first
- If audiometry is performed there is generally reduction in auditory acuity in the 36 kHz range, often with a notch at 4 kHz
Clinical features of Noise-induced hearing loss
- Reduced auditory acuity
- Tinnitus
- Social isolation as hearing impairment worsens
- Can also reduce danger perception
Clues that noise may be a problem:
- Hearing ringing or humming in your ears when you leave work
- Having to shout to be heard by a co-worker who is within 2m
- Experiencing temporary hearing loss when leaving work
Which kind of workers are at risk of Noise-induced hearing loss?
- Construction workers
- Quarrying / mine workers
- Heavy machinery operators
- Airport / aviation workers
- Armed forces / security workers
- Entertainment industry (clubs/pubs/concert halls)
- Agriculture workers
- Orchestra / musicians
It is also important to ask about hobbies, which may expose the patient to loud sounds e.g. music, DIY, motor sport, shooting
Medical Risk Factors for Noise-induced hearing loss?
- Meningitis
- Meniere’s Disease
- Congenital infections (CMV, Rubella)
- Head injury
- Otitis Media
- Perforated Tympanic Membrane
- Family history of hearing impairment
- Ototoxic drugs e.g. aminoglycosides (such as Gentamicin), quinine, salicylates and furosemide
Health Surveillance for Noise-Induced hearing loss
- Pre-employment audiometry
- Annual testing in first 2 years of employment
- Three-yearly testing after the first 2 years
How to prevent Noise-Induced Hearing loss
Several measures can and should be taken in a hierarchical order:
1) Assessment of exposure
2) Switching to tools and equipment which generate a lower level of noise, through better design of machinery / equipment
3) Segregation from sound
4) Insulation from sound
5) Personal Protection (ear defenders, ear plugs) - can attentuate noise by 15 - 30dBA. Ear plugs should be the appropriate shape and inserted correctly. Note may cause irritation e.g. if dirty. Ear muffs fit over and around the outer ear, and should also be appropriately fitted
6) Surveillance with Audiometry
The ‘two metre rule’ is important - if an employee finds it difficult to communicate with a workmate at this distance due to noise, then the intensity of the noise is likely high enough to damage hearing.
What are some issues with hearing-protection?
- Reliance on personal protection, without adequate steps to reduce noise exposure at source
- Inappropriate protection (poor choice, poor fit, poorly maintained)
- Hearing protection not worn consistently
Tell me more about the decibel scale
Noise above 70 dB over a prolonged period of time may start to damage your hearing. Examples of occupational decibel levels:
- 40 Quiet Office, Library
- 50 Large Office
- 65-95 Power Lawn Mower
- 80 Manual Machine, Tools
- 90 Tractor
- 90-115 Subway
- 95 Electric drill
- 100 Factory Machinery
- 100 Woodworking Class
- 105 Snow Blower
- 110 Power Saw
- 110 Leaf Blower
- 120-125 Chainsaw, Hammer On Nail
- 120 Pneumatic Drills, Heavy Machine
- 120 Jet Plane at Ramp
- 120 Ambulance Siren
- 130 Jackhammer, Power Drill
- 130 Air Raid
- 130 Percussion Section at Symphony
- 140 Airplane Taking Off
- 150 Jet Engine Taking Off
- 150 Artillery Fire at 500 Feet
- 189 Rocket Launching from Pad
What occupational adjustments can be made for an employee with hearing impairment?
- Ask colleagues to speak clearly with sufficient volume and articulation during meetings etc
- Allow employee if they have not heard clearly
- Encourage colleagues to visibly speak in line of sight of impaired worked to allow lip reading)
- Using email / text in preference to telephone or speaking
- Consider transfer to a different role, where hearing impairment is less disadvantageous
- Recommend personal evacuation plan in the event of a fire or emergency, including buddying up with another worker / vibrating pager / flashing lights
