![]() ![]() The equal-energy principle effectively states equal energy will cause equal damage (in any given individual), such that similar cochlear damage may result after exposure to a higher level of noise over a short period of time as would occur after exposure to a lower level of noise over a longer period of time. The energy level is a function of the sound pressure of noise (in decibels) and of the duration of exposure over time. The total amount of noise to which an individual is exposed can be expressed in terms of energy level. NIHL is a complex disease that results from the interaction of genetic and environmental factors, but is generally still dictated by the extent of biological damage caused by noise exposure. The objective of this review is to provide a comprehensive overview of NIHL including the fundamental and advanced pathophysiology, specific investigations, including detailed discussion on asymmetric NIHL, associated symptomatology, available interventions for prevention and treatment. Furthermore, the additional impact of noise-induced tinnitus and vestibular dysfunction is still not fully elucidated. The impact of hearing loss might be underestimated as recent studies have shown evidence for hidden hearing loss and synaptopathy-induced poor speech recognition. For many years, the maximum severity of NIHL was argued to be mild to moderate and symmetrical based on pure tone audiograms. Hearing loss was more prevalent among men than women, likely due to a disproportionate number of males in these occupations, and the risk of hearing loss increased with age.ĭespite its prevalence, there is still an ongoing debate about the consequence of the noise-induced damage. Within a group of one million noise-exposed workers, the highest risk occupations for hearing loss were identified to be those in mining, wood product manufacturing, construction of buildings, and real estate and rental leasing. However, among noise-exposed workers the prevalence is significantly higher at 23, 15 and 9%, respectively. In the United States among workers not exposed to noise, 7% have hearing loss, 5% have tinnitus, and 2% are afflicted with both hearing loss and tinnitus. Without doubt, chronic noise exposure and the resultant cochlear trauma cause hearing loss and tinnitus. Noise-induced hearing loss (NIHL) has long been recognized as an occupational disease, amongst copper workers from hammering on metal, blacksmiths in the 18 th century, and shipbuilders or “boilermakers” after the Industrial Revolution. The World Health Organization estimated that one-third of all cases of hearing loss can be attributed to noise exposure. It has been suggested that 12% or more of the global population is at risk for hearing loss from noise, which equates to well over 600 million people. This review provides a comprehensive update on the pathophysiology, investigations, prevalence of asymmetry, associated symptoms, and current strategies on the prevention and treatment of noise-induced hearing loss.Įxposure to excessive noise is the most common preventable cause of hearing loss. Currently, prevention and protection are the first lines of defence, although promising protective effects are emerging from multiple different pharmaceutical agents, such as steroids, antioxidants and neurotrophins. Deliberation of the prevalence, treatment and prevention of noise-induced hearing loss is important and timely. Furthermore, it is recently shown that acoustic trauma is associated with vestibular dysfunction, with associated dizziness that is not always measurable with current techniques. Recent epidemiology and animal studies have provided further insight into the pathophysiology, clinical findings, social and economic impacts of noise-induced hearing loss. Noise-induced damage to the cochlea is traditionally considered to be associated with symmetrical mild to moderate hearing loss with associated tinnitus however, there is a significant number of patients with asymmetrical thresholds and, depending on the exposure, severe to profound hearing loss as well. Noise-induced hearing loss is one of the most common forms of sensorineural hearing loss, is a major health problem, is largely preventable and is probably more widespread than revealed by conventional pure tone threshold testing. ![]()
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