By Dr Sheikh Mohd Saleem
Occupational hearing loss (OHL) is hearing loss that occurs as a result of occupational hazards, such as excessive workplace noise and ototoxic chemicals. Noise is considered to be a major risk factor for noise-induced hearing loss among workers but it’s not the only risk factor that can result in a work place related hearing loss. Hearing loss usually affect adults and older persons and the causes behind it may be legion. More commonly we believe that workers working in industries only have risk of occupational exposure and they are immune to non-occupational exposures. Evidence suggests that some illnesses and their management can affect the way in which the ear responds to potentially damaging noise. When we talk about Industrial workers, we must take occupational noise exposure later into consideration but there might be other aspects of the workplace that may affect the ears and must be considered first. Workplace accidents like trauma over the head leading to skull fracture, direct blow to the external ear, blast injury or barometric trauma may affect the middle or inner ear. Furthermore, the normal ageing process in workers may, in some cases pose a continuous risk and makes these workers more vulnerable to accidents because of their slowed reaction time, poor vision, balance or mobility. It is essential to maintain a high quality safety and general wellbeing of workers at the work place so as to minimize the risk of accidents among them.
Occupational hearing loss is a prevalent occupational concern in various work place environments worldwide. Hearing loss caused by occupational exposures has been recognized for decades and preventative measures have also been used for almost as long. Hearing impairment entirely due to ageing process is not as common as generally thought. Older people with hearing loss when evaluated properly will reveal that 15-20% among them have no known cause of the hearing loss. Preventive measures are possible only among those with known etiology. It may also be possible to prevent some of the hearing loss that is age related. That means, occupational factors may be the only reason behind individuals hearing impairment and preventive measures should be maintained to prevent the loss.
Another factor is the synergism between drugs, antibiotics like gentamycin, streptomycin, tobramycin, loop diuretics like furosemide and chemotherapy agents like cisplatin, carboplatin and vincristine are known ototoxic agents. Researchers have demonstrated that there is a slight synergism affect between high doses of amino glycosides, a class of antibiotics and loud noise. The researcher further argues that if the workers are ill enough to be on high doses of antibiotics, they are unlikely to be at work. Research evidence show that exposures to noise level what is currently recommended safe for an individual can be damaging if the worker is exposed to these ototoxic agents.
Other recent articles on the etiology of hearing impairment in old adults have highlighted the importance of other easily screened for and potentially preventable causes of hearing impairment. Scientists have found a significant relationship between hypertension and hearing loss. Especially rise is systolic blood pressure among older individuals have been found to be amongst one of the important causes behind hearing loss. Rise in blood viscosity and mitochondrial disorders have also been found to the causes behind hearing loss.
Prevention: A lesser known fact is that the hearing loss caused due to occupational exposure is 100% preventable. Currently, the interventions to prevent it involve many components. Occupational noise exposure and recreational noise exposure is a bunch of educational tool included in standard noise exposure reduction technique and have been used to reduce hearing loss among industrial workers. Despite legislations, it’s not always possible to persuade industrial workers to use the personal protective equipment (PPE). This technique has been shown to improve user rates in military personnel’s. Engineering solutions like designing of quieter machinery and use of simple devices like ear plugs and earmuffs when used correctly can reduce exposure to noise to safer levels to achieve the potential attenuation.
Other potential means of preventing hearing loss due to noise exposure and ageing has been a major concern of scientists over the last decade and many fruitful results have been achieved. Excessive noise stimulates glutamate, an excitatory neurotransmitter in the inner hair calls. The excess of glutamate causes damage to the primary auditory dendrites. A glutamate antagonist, kynurate has shown promising results in preventing hearing loss among guinea pigs. Another neurotransmitter, Nitric oxide has also been implicated to have a role in causing cell death in the inner ear causing hearing loss. Scientists are of the view that blocking the synthesis of Nitric oxide in the inner ear can prevent this kind of hearing loss. How can one forget the role of free radical in hearing loss? On exposure to highly intense forms of noise, free radicals are generated and are converted to highly destructive hydroxyl radicals in the inner ear causing hearing loss. Antioxidants have been implicated to prevent such hearing loss and are currently in use. Moreover, magnesium supplementation have been shown to protect against impact noise as noise exposure causes increased consumption of energy in the inner ear resulting in depletion of magnesium and calcium stores.
However, the main stay of treatment for hearing loss among occupational workers is preventive rather than curative. This will require man power training for prevention, early identification and management of hearing loss. Capacity building of the health sector right from the primary care level to the tertiary care level in respect of audiology infrastructure. Early detection and management of hearing impaired cases and their rehabilitation at all levels of health care. Most importantly regular screening of occupational workers for hearing loss as per standard protocols to save them from long term morbidity. Most importantly, strict implementations of legislative laws governing occupational noise exposures at the workplace are the need of an hour. Policy makers and Government should take necessary steps and actions to implement legislative laws governing noise exposures at the work place with spirit and those industries not following the laws should be fined accordingly. By this we can rightly fit into the WHO’s current theme on World Hearing Day Theme which states that “Don’t let hearing loss limit you…hearing for life”.
(The writer is associated with Department of Community Medicine, Government Medical College, Srinagar. He can be reached at: Email: [email protected])