What is noise-induced hearing loss? Introducing causes, symptoms, and preventive measures

What is noise-induced hearing loss? Introducing causes, symptoms, and preventive measures

  Point 

  • Noise-induced hearing loss is a disease that can be prevented if appropriate measures are taken.
  • It is important to detect noise-induced hearing loss early and take measures.
  • Possible triggers for early detection include noticing that you want to turn up the TV volume at night more than in the morning, or noticing symptoms of tinnitus.

 

What is hearing loss?

Hearing loss refers to difficulty in hearing sounds in ears. Common causes include threshold shift due to aging, diseases such as otitis media, acoustic trauma, and noise-induced hearing loss due to long-term noise exposure. This chapter explains noise-induced hearing loss.

 

What is noise-induced hearing loss?

Noise-induced hearing loss is a type of hearing loss caused by exposure to continuous noise levels greater than 85 dB for 8 hours a day for a long period of 5 to 15 years or more, and the organs of the ear are affected by the sound energy. Noise-induced hearing loss particularly affects workers who work in noisy environments for long periods of time. Noise-induced hearing loss remains one of the most common occupational diseases.

 

Specific symptoms of noise-induced hearing loss

Exposure to a loud noise damages hair cells, but they often recover. However, continuous noise exposure leads to gradual hearing loss and permanent damage (permanent threshold shift). In general age-related hearing loss, hearing loss occurs from high to low frequencies, but noise-induced hearing loss results in hearing loss localized to frequencies around 4000 Hz. According to Chen(2022), regarding the mechanism, mechanical theory, vascular theory, metabolic theory, and immunoinflammatory theory are considered. [Source number] Vibrations transmitted to the endolymph fluid in the cochlea block the supply of oxygen and nutrients to the capillaries. Noise vibrations also damage hair cells. The degree of damage varies depending on the exposure time and the height of the noise level.

 

Preventive measures for noise-induced hearing loss

In the early stages, symptoms such as temporary threshold shift and tinnitus may appear, but few people are aware of their hearing loss. Permanent threshold shift may occur with prolonged noise exposure. Although there is no effective treatment for noise-induced hearing loss, it is a preventable disease. Measures such as the use of hearing protection and reduction of noise exposure are recommended. Early detection is also important in taking measures to halt the progression of noise-induced hearing loss.

 

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＊Sound transmission path in the auditory system
Sound is collected through the pinna and reaches the tympanic membrane, and vibrations are transmitted to the cochlear in the inner ear via the ossicles in the middle ear. The cochlear is a spiral tube that converts mechanical vibrations from the auditory ossicles into signals used to transmit information within the nervous system. Hair cells line the basilar membrane within the cochlear. The vibrations transmitted to the endolymph fluid in the cochlear shake the basilar membrane, stimulating hair cells and producing electric potential changes that stimulate auditory nerve fibers and transmit them to the auditory cortex.

 　

＊Distribution of characteristic frequencies around the cochlear
When sound vibrations are transmitted to the endolymph fluid, the movement of the basilar membrane moves deeper in the form of a traveling wave, and the amplitude increases at a certain point. The position where this wave reaches its maximum amplitude is determined by the frequency, and has a distribution as shown in Figures 1 and 2. This results in damage to specific hair cells that correspond to frequencies with high sound energy in the frequency distribution of noise that enters the ear.
　diagram of frequency distribution of sound in the cochlea

 

<References>

Wada, T & Hara, A. (2015) "Latest knowledge of otorhinolaryngology that can be applied in the workplace -Noise-induced hearing loss ① History, medical and social background-" Industrial Medicine Journal, Vol. 38 No. 6, 77-82, in Japanese.

Chen, T. (2022). “The Role of Genetic Variants in the Susceptibility of Noise-Induced Hearing Loss.” Frontiers in Cellular Neuroscience, 16(7), 123-135.

 

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