Noise induced hearing loss (NIHL) is caused by exposure to loud noises over time. It typically affects the higher frequencies and can be either temporary or permanent. The mechanisms of hearing involve sound being collected by the pinna and vibrations being transmitted through the ossicles to the cochlea, where hair cells convert it to electrical signals sent to the brain. Epidemiological studies show NIHL is very common occupationally and recreationally. Risk factors include occupational and recreational noise exposure as well as smoking. Pathology shows damage initially to outer hair cells. Clinical features are tinnitus, hearing loss, and normal exams. Diagnosis involves audiometry showing high frequency notches. Prevention focuses on limiting noise exposure and

1. NOISE INDUCED HEARING LOSS
(NIHL)
400LEVEL ATBU/ATBUTH

2. OUTLINE
• Introduction
• Overview of the mechanism of hearing
• Epidemiology
• Risk factors
• Types
• Pathology
• Clinical features
• Investigation and diagnosis
• Treatment
• Prevention
• Conclsuion

3. introduction
• Noise is defined as an aperiodic complex sound.
• The term noise induced hearing loss refers to the
reduction in auditory acuity associated with noise
exposure.
• Typical NIHL is of a sensorineural type. Involves
injury to the inner ear usually bilateral and
symmetrical. Affect the higher frequencies .
• The situation may be temporary threshold shift
(TTS) or permanent threshold shift (PTS). PTS may
occur following repeated TTS or a single episode
of noise exposure.

4. Overview of hearing mechanism
• A sound signal in the environment is collected by the
pinna, passes through external auditory canal and strikes
the tympanic membrane. Vibrations of the tympanic
membrane are transmitted to stapes footplate through a
chain of ossicles coupled to the tympanic membrane.
• Movements of stapes footplate cause pressure changes in
the labyrinthine fluids, which move the basilar membrane.
This stimulates the hair cells of the organ of Corti. It is these
hair
cells which act as transducers and convert the mechanical
energy into electrical impulses, which travel along the
auditory nerve.

5. Overview contd…
• Outer hair cells are primarily responsible for
responding to and amplifying lower-frequency
sounds, including those in the low- mid range
of audible spectrum.
• Inner hair cells are more specialized for
higher-frequency sounds, including those in
the mid to high frequency range. This division
of labor helps the auditory system efectively
cover the audible frequency range.

6. Epidemiology
• About 10% of world population work in
hazardous levels of noise.
• Worldwide, 16% of the disabling hearing loss in
adult is attributed to occupational noise, ranging
from 7 to 21% in the various subregions.
• NIHL is second most common form of acquired
hearing loss after age-related hearing loss, with
studies showing that people who are exposed to
noise levels higher than 85db suffered from NIHL.

7. Risk factors
• Occupational exposure such as factory
machinery, building sites, high impact tools
and military firearms
• Recreational exposure such as shooting, home
power tools, standing too close speakers at
concerts or night clubs and personal stereos,
• Smoking, DM, CVD, recreational drug use

11. Types
• NIHL can manifest in different ways and its effects
may vary based on factors such as the intensity
and duration noise exposure.
• There are two main types of NIHL
1. Temporary threshold shift: The hearing is
impaired immediately after exposure to noise
but recovers after an interval of few minutes to
few hours or even up to two weeks.
2. Permanent threshold shift: The hearing
impairment is permanent and does not recover
at all.

12. pathology
• Biological variability (inherited or genetic susceptibility) means that
individuals are not affected
equally by the same noise exposure. However,
with increasing noise levels above 90 dB(A), a
greater proportion of the exposed population
will exhibit pathological changes.
• Initially, noise exposure may lead to temporary
threshold shift (TTS), which is a recoverable
phenomenon. There are no obvious pathological changes in TTS and the
condition may be due to
metabolic ‘exhaustion’ of the hair cells of the
cochlea.
• It is thought that repeated episodes of
TTS may predispose patients to presbycusis at an
earlier age compared to those who have not had
such episode

13. Pathology contd…
• There is substantial experimental studies that shows a
change in cochlear blood flow associated with acoustic
stimulation.
• With increasing and repeated noise exposure,
there is permanent mechanical and metabolic
damage, initially to the outer hair cells (OHCs) of
row 1, and subsequently to the OHCs in rows 2 and
3 and the inner hair cells. Damage also occurs to
the supporting pillar cells and the stria vascularis.
The audiometric hearing loss tends to parallel the
loss of hair cells.

14. Clinical features
• The clinical features include the following:
• Tinnitus
• Otalgia
• Hyperacusis
• Dizziness
• Headache
• Sleep disturbances
• Poor concentration
• Otological examination will be normal

15. investigations
1. Pure tone audiometry (PTA)
classical audiometric pattern is of a high
frequencies loss with a notch appeared centred on 4 or
6kHz with some recovery at 8kHz. Significant audiometric
loss at frequencies below 2kHz is extremely uncommon
2. Typanometry is helpful to confirm normal middle ear
functioning
3. Audiometry brainstem response(ABR) records electrical
activity in response to auditory stimuli. Helps assess the
integrity of the auditory nerve and brainstem pathways.

18. Treatment
• If the hearing loss becomes more severe,
hearing aids may beneficial
• Tinnitus should be managed as a part of the
overall care package

19. prevention
• Once diagnosis is made, further noise
exposure should be kept away as far as
possible, if not possible, the use of ear
protection in the form of earplugs or earmuffs
or active noise reduction by electronic
machine

20. • In conclusion, NIHL is a prevalent and
preventable form of hearing impairment
resulting from exposure to loud sounds over
time. The diagnosis involves a multifaceted
approach, incorporating medical history,
audiometric testing and in some cases,
additional assessments.

21. Thank you

22. References
• PL Dhinghra & S Dhingra, Diseases of Ear, Nose
and Throat, Read Elsevier India private limited,
India, 6th edition.
• www.slideshare.com retrieved on 30/11/2023