CAOHC Occupational Hearing Loss 2 — Questions and Answers
Question 1: What is the primary mechanism of noise-induced hearing loss at the cellular level?
- Destruction of cochlear hair cell stereocilia through mechanical damage and metabolic stress (Correct answer)
- Perforation of the tympanic membrane from loud sounds
- Dissolution of the ossicles in the middle ear
- Swelling of the auditory nerve from overstimulation
Correct answer: Destruction of cochlear hair cell stereocilia through mechanical damage and metabolic stress
Noise-induced hearing loss primarily results from damage to the stereocilia on the outer and inner hair cells of the cochlea.
Damage occurs through mechanical shearing, metabolic exhaustion, formation of reactive oxygen species, and disruption of blood supply. Since mammalian cochlear hair cells do not regenerate, this damage is permanent.
Question 2: What is the difference between temporary threshold shift and permanent threshold shift?
- TTS is a temporary hearing reduction that recovers after rest; PTS is irreversible hearing damage (Correct answer)
- TTS only affects one ear while PTS affects both
- TTS is caused by high-frequency noise and PTS by low-frequency noise
- There is no functional difference
Correct answer: TTS is a temporary hearing reduction that recovers after rest; PTS is irreversible hearing damage
A temporary threshold shift recovers after a period away from noise, while a permanent threshold shift represents irreversible damage.
TTS occurs when stereocilia become fatigued and less responsive. Recovery typically occurs within 14-16 hours. Repeated TTS episodes can lead to cumulative PTS as hair cells are progressively damaged beyond recovery.
Question 3: Which frequencies are typically affected first in noise-induced hearing loss?
- 3000 to 6000 Hz, with the characteristic notch at 4000 Hz (Correct answer)
- 250 to 500 Hz
- All frequencies equally
- Only frequencies above 8000 Hz
Correct answer: 3000 to 6000 Hz, with the characteristic notch at 4000 Hz
NIHL characteristically begins in the 3000-6000 Hz range, with the deepest notch typically at 4000 Hz.
The 4000 Hz vulnerability involves ear canal resonance amplifying 2000-4000 Hz, the basal turn receiving the most direct energy, and the acoustic reflex primarily attenuating low frequencies.
Question 4: How does noise-induced hearing loss differ from age-related hearing loss?
- Noise-induced shows a notch at 4000 Hz with recovery at 8000 Hz; presbycusis shows a gradual high-frequency slope without recovery (Correct answer)
- They produce identical audiometric patterns
- Presbycusis only affects low frequencies
- Noise-induced loss is always bilateral while presbycusis affects only one ear
Correct answer: Noise-induced shows a notch at 4000 Hz with recovery at 8000 Hz; presbycusis shows a gradual high-frequency slope without recovery
The key distinction is the notch pattern with 8000 Hz recovery versus gradual slope without recovery.
NIHL: bilateral, symmetrical, 4000 Hz notch with recovery, can occur at any age. Presbycusis: gradual high-frequency slope without recovery, progressive with age.
Question 5: What role does tinnitus play in occupational hearing loss?
- Tinnitus often accompanies NIHL and can be an early warning sign of cochlear damage (Correct answer)
- Tinnitus only occurs with conductive hearing loss
- Tinnitus has no relationship to noise exposure
- Tinnitus is always temporary
Correct answer: Tinnitus often accompanies NIHL and can be an early warning sign of cochlear damage
Tinnitus frequently accompanies NIHL and can serve as an early indicator, sometimes appearing before measurable threshold shifts.
Tinnitus affects approximately 50% of workers with NIHL. It can be temporary after acute exposure (a warning of TTS) or persistent with chronic exposure, causing sleep disruption and emotional distress.
Question 6: What is acoustic trauma and how does it differ from chronic noise-induced hearing loss?
- Acoustic trauma is sudden damage from a single intense event; chronic NIHL develops gradually from prolonged exposure (Correct answer)
- Acoustic trauma only affects one ear while chronic NIHL affects both
- They are the same condition at different stages
- Acoustic trauma causes low-frequency loss while chronic NIHL causes high-frequency loss
Correct answer: Acoustic trauma is sudden damage from a single intense event; chronic NIHL develops gradually from prolonged exposure
Acoustic trauma results from a single exposure to extremely intense sound causing immediate damage, while chronic NIHL develops over months or years.
Acoustic trauma occurs from impulse noise exceeding approximately 140 dB peak SPL. Chronic NIHL develops from repeated daily exposure above 85 dBA over years.
CAOHC Occupational Hearing Loss 2
What is the primary mechanism of noise-induced hearing loss at the cellular level?