Occupational hearing loss

Occupational hearing loss - occupational hearing loss - develops as a result of the intensive influence of working conditions (excessive noise of more than 80 decibels, vibration, intoxication, etc.). In the majority of cases (about 80-85%) we are talking about sensorineural chronic hearing loss. This problem is considered to be particularly widespread and requires increased attention from the medical and occupational health and safety systems.

Epidemiology

Occupational hearing loss is an urgent problem in many industries. The number of workers who are regularly exposed to high noise levels amounts to tens of millions of people annually. As a result, noise-induced occupational hearing loss is the leading occupational disorder among representatives of various occupations.

Over the last decades, morbidity rates have shown a tendency to increase - almost twofold. Among direct occupational pathologies provoked by physical factors (noise, vibration, radiation, etc.), the rates of development of noise-induced hearing loss range from 49 to 59% (according to the statistics of different years of the last two decades).

According to some reports, one in three patients with occupational hearing loss worked in conditions that did not meet sanitary and hygienic standards.

The main industries whose workers are most likely to suffer from occupational hearing loss are:

• mining;
• production and transportation of gas, electricity, water;
• transportation;
• industrial processing.

Among the representatives of the most "noisy" professions the leading ones are:

• miners, drillers;
• drivers of locomotives and freight trains, sinkers;
• blacksmiths, locksmiths;
• garment workers;
• quarry machinists, drivers of agricultural machinery;
• pilots;
• Military (participants in active combat operations).

In most cases, occupational hearing loss occurs over one or two decades of intense noise or toxic exposure. Most often the pathology makes itself known at the age of over 40 years. Moderate hearing loss is found in about 40-45% of cases, and significant hearing loss in almost 30% of cases.

More than half of patients with a primary diagnosis of occupational hearing loss become unfit for work and are assigned a disability group due to occupational pathologies of the auditory organs. Since people far from retirement age become disabled, this issue is important not only in medical but also in socio-economic terms.

Causes of the professional hearing loss

Every day people are exposed to a mass of sounds, ranging from light and barely perceptible to noisy and deafening. Many industries and even cities are categorized as environments with excessive noise exposure. The professional activities of millions of people are associated with increased noise levels.

Noise levels from 65-75 decibels increase the risks of cardiovascular disorders. However, the hearing organs are primarily affected by noise. Among all known occupational pathologies, hearing problems account for about ⅓. The problem is especially common among workers in mining, oil and refining industries, as well as metallurgists, construction workers and so on. The risks increase if noise exposure is combined with vibration or toxic exposure. [1]

If working conditions are poor, occupational health and safety standards are not met, and noise levels exceed permissible levels, workers will gradually develop hearing loss. This process can be accelerated by such factors:

• concomitant pathologies of the cardiovascular, nervous, immune system;
• psycho-emotional stressors;
• intoxication;
• bad habits (smoking, alcohol consumption);
• chronic fatigue.

Occupational hearing loss has a negative impact on the patient's quality of life. There is anxiety, frequent mood swings, and decreased stress resistance. Depressive states, cardiovascular and nervous system diseases often develop.

Risk factors

Occupational hearing loss does not develop in all people working in potentially hearing-damaging environments. There is information that cardiovascular pathologies to some extent contribute to the development of sensorineural hearing loss: the pathogenesis includes hemodynamic disorders. In this regard, experts point to the existence of interrelation of the above disorders, as well as the need to determine the primary and secondary nature of their development, as it depends on the direction of therapeutic measures. The dominant vascular factor contributing to the development of hearing loss against the background of occupational hazards is arterial hypertension.

The second place among the associated factors belongs to osteochondrosis of the cervical spine. The frequency of its detection varies in the range of 12-39%, it is detected most often in miners and workers in the engineering industry.

Other common co-morbidities diagnosed concurrently with occupational hearing loss:

• dyscirculatory encephalopathy;
• atherosclerosis of the cerebral vessels;
• ischemic heart disease and arrhythmias;
• type 2 diabetes.

Occupational hearing loss is about 1.5-2 times more frequent in persons with the above-mentioned somatic diseases. In addition, there is a positive correlation between the degree of hearing loss and the presence of cardiovascular disorders. [2]

Pathogenesis

There is evidence that noise, being an acoustic stimulus, provokes disorders of the peripheral part of the auditory analyzer, which leads to the development of occupational hearing loss of sensorineural type. In addition, noise can be attributed to factors that have increased bioactivity and lead to a chain of non-specific changes in various organs and systems.

It is scientifically proved that prolonged influence of noise and vibration stimuli causes exhaustion of adaptive capabilities of the organism, leads to formation of cardiological and cerebrovascular complications, worsens working capacity and hinders socialization of a person.

With prolonged exposure of the auditory organs to noise, the hair cells of the cochlea die. The receptor apparatus of the cochlea is a branch of the auditory analyzer involved in the transmission of sound vibrations to the nerve fibers of the inner ear. As the disorder progresses, the number of hairs decreases, the quality of sound reproduction suffers, and hearing loss develops.

Doctors have several theories regarding the mechanisms of occupational hearing loss due to prolonged noise exposure.

According to the adaptation-trophic version, excessive noise leads to exhaustion and degenerative changes in the peripheral receptor section of the auditory analyzer located in the membranous labyrinth of the cochlea. As a result, the transformation of the sound signal into a nerve impulse is blocked.

According to the vascular version, a strong noise results in a stress response of the body, causing a cascading vascular spasm. The secondary disorders in the inner ear caused by the spasm, in turn, provoke degenerative changes.

Specialists note that the type of sound exposure matters in terms of the rate of increase of pathological phenomena. For example, repetitive powerful sounds are more dangerous than monotonous continuous noises, and high-frequency sound is more harmful than low-frequency sound.

Symptoms of the professional hearing loss

Special criteria have been developed for assessing hearing function by means of an audiogram, and at the same time doctors perform other examinations. As for the patients themselves, they should know that the hearing of high-frequency sounds is first of all impaired, followed by the deterioration of mid-frequency and low-frequency hearing. The symptoms develop in stages:

1. The initial period may last a few months or a few years (not more than 5 years). The person begins to feel tinnitus, sometimes mild pain, and by the time the working day is over, severe fatigue, both physical and mental, is noticeable. After some time there is noise adaptation of the hearing organs, although during the audiogram is registered exceeding the threshold of sensitivity to high frequencies. Such changes are gradually compensated for, but the hearing organ itself undergoes some irreversible processes: individual hair cells that transform auditory vibrations into nerve impulses die.
2. The stage of the first clinical pause follows: it lasts for 3-8 years of staying in noisy conditions. The person can perceive spoken speech quite well in all conditions, whispers can be heard from about 3 meters away. Discomfort and pain in the ears disappear, the auditory function normalizes, and the feeling of fatigue after a working day is somewhat reduced. However, irreversible changes in the auditory organs naturally remain.
3. In the third stage, occupational hearing loss builds up. The duration of this period is from five to 12 years (subject to further work in noisy conditions). A person can still distinguish conversation from a distance of up to 10 meters, and whispered speech - from 2 meters. There may be an increase in blood pressure and irritability.
4. The fourth stage represents a second clinical remission, which consists of a repeated sham stabilization of the condition that is invariably followed by a final terminal stage.
5. The final stage occurs as the completion of the process of formation of occupational hearing loss. The person perceives loud sounds only from a distance of about 4 meters, conversation - from one and a half meters, and whispered speech - only directly next to the ear. Speech comprehension and identification of sounds is intensely affected. The tinnitus becomes strong and constant, the vestibular apparatus is disturbed.

First signs

Too loud sounds for a long time have a negative impact not only on the hearing organs, but also on the body as a whole: even before the onset of professional hearing loss, a person may notice disturbances in the nervous and cardiovascular systems. Thus, vasospasm is noted, blood pressure increases, myocardial infarction, ischemic heart disease, gastric ulcer and 12-peritoneal ulcer, sometimes - strokes can develop. Therefore, occupational hearing loss is not the only possible complication of constant high noise exposure. [3]

Associated diseases often mask the onset of hearing loss, but it is not uncommon for hearing loss to manifest with asthenic autonomic and neurotic processes that need to be addressed:

• on the part of the nervous system - inattention, impaired memory performance, increased fatigue and irritability;
• cardiovascular system - increase in blood pressure, changes in heart rate, peripheral vascular spasms, arrhythmias;
• respiratory organs - changes in the frequency and depth of respiratory acts;
• sensory organs - deterioration of twilight vision, dizziness, vestibular disorders;
• gastrointestinal tract - deterioration of intestinal motility, decreased gastric secretory activity, vascular spasms, trophic disorders;
• from the auditory organs - development of occupational hearing loss.

Stages

The International Classification of Hearing Impairment considers these degrees of occupational hearing loss:

• Normal: the person retains the ability to perceive sounds of all frequencies from 0 to 25 decibels, there are no problems with communication.
• Mild, or Grade I: only sounds above 26-40 decibels are perceived, and there are problems hearing distant and quiet speech.
• Medium, or II degree: sounds exceeding 41-55 decibels are perceived, dialog becomes somewhat problematic.
• Moderately severe, or III degree: speech exceeding 56-70 decibels in volume is perceived, there are difficulties with collective and telephone communication.
• Severe, or IV degree: a person is able to hear speech exceeding 71-90 decibels in volume, only shouting is available for understanding, telephone communication is impossible.
• Profound hearing impairment, deafness: perceived sounds of at least 91 decibels.

Forms

Occupational hearing loss can be caused by various reasons, and as a result, there are different types of pathology:

• Conductive hearing loss is caused by obstacles in the path of sound vibrations. This type of disorder is well succumbed to conservative, less often - surgical, treatment. Examples of causes of conductive pathology: otosclerosis, earwax, otitis media.
• Neurosensory (other name - sensorineural) hearing loss - is caused by improper conversion of mechanical waves into electrical impulses. Caused by disorders of the cochlea or inner ear. Occupational sensorineural hearing loss is most common because it is caused by prolonged acoustic trauma. The disorder is difficult to treat and often requires hearing aids.
• Mixed type of hearing loss - combines the above two forms of pathology.

Depending on the acuteness of the pathological process, there are different types of hearing loss:

• sudden (hearing deteriorates within a few hours);
• acute (hearing deteriorates over 1-3 days and lasts up to 4 weeks);
• subacute (worsening persists for 4-12 weeks);
• chronic (persistent) occupational hearing loss (the hearing problem is long-lasting, exceeding 3 months).

In addition, hearing loss can be unilateral or bilateral (symmetrical or asymmetrical).

Complications and consequences

At the initial stage, occupational hearing loss is of little concern to the person. As a rule, the first signs are detected, first of all, by people close to the person.

Hearing impaired patients begin to perceive information poorly and have difficulty interpreting it: this adaptation becomes more and more difficult with age.

Making an ordinary phone call or watching television becomes a challenge. Most people with an occupational hearing loss feel isolated, lonely and experience a general decrease in quality of life. There are problems with concentration, anxiety, fear, bad moods and lower self-esteem. People become dependent on their loved ones, they lose self-confidence, their opportunities are sharply limited.

The most common physical complications include constant fatigue, chronic fatigue, head and muscle pain, dizziness and high blood pressure due to constant stress. Sleep and appetite are disturbed, and digestive tract disorders may occur, again due to prolonged stress exposure.

Adults often suffer from psychopathies, neuroses caused by limited communication and lack of socialization. All of these consequences significantly complicate the subsequent treatment or correction of occupational hearing loss. The most unfavorable complication in the absence of treatment is complete deafness.

Diagnostics of the professional hearing loss

The earlier occupational hearing loss is detected, the better the chances of successful correction and restoration of hearing function.

Diagnosis begins with the collection of anamnesis. The doctor asks questions about the place of work and conditions, about the period of stay in a noisy environment. It is desirable that the specialist also familiarizes himself with the cards of occupational examinations or medical examinations, obtain information about the general condition of the patient.

Next, the doctor conducts an examination of the ENT organs, prescribes additional tests. When initially detecting a hearing problem, doctors use basic diagnostic methods that allow them to determine the possible cause of the pathology:

• tympanometry (measuring the sound impact on the membrane with a special probe);
• otoscopy (determination of air and bone conduction with the help of a tuning fork);
• electrocochleography (electrical stimulation of the auditory nerve to identify the causes of hearing loss);
• Schwabach test (comparative assessment of bone conduction);
• audiogram (using a special device called an audiometer).

If necessary, ancillary instrumental diagnostics such as computed tomography of the temporal bones and magnetic resonance imaging of the brain, cerebral vessels and inner ear are also used.

Laboratory tests of blood and urine are nonspecific, the doctor usually prescribes them as part of a general clinical examination - in particular, to detect the inflammatory process in the body.

Differential diagnosis

Occupational hearing loss should be distinguished from hearing impairment caused by taking ototoxic drugs. Most often, these are diuretics, salicylates, aminoglycosides, chemotherapy drugs. The use of several ototoxic drugs at the same time is especially dangerous.

In addition, an autoimmune origin of the problem must be ruled out. In patients with autoimmune hearing loss, there is a sudden onset of increasing bilateral sensorineural hearing loss, impaired speech identification, possible dizziness and vestibular disorders. Such pathology builds up over several months, at the same time background autoimmune diseases may make themselves known. In most such cases, the clinical picture improves with prednisolone treatment, and a positive response to hormone therapy is considered the most indicative diagnostic method. An alternative to long-term prednisolone therapy is treatment with Methotrexate.

In unilateral hearing loss, these conditions should be ruled out:

• Meniere's disease;
• Idiopathic unilateral sensorineural hearing loss (usually due to viral infection or vascular stroke);
• VIII cranial nerve tumor.

Treatment of the professional hearing loss

Electrophonophoresis, electrical stimulation of the inner ear, acupuncture and electroacupuncture are used at the initial stages of professional hearing loss. Such procedures often help to reduce tinnitus, eliminate dizziness, improve sleep, and increase the general tone of the body.

Medication is more effective in the early stages of pathology. Therapy with drugs that improve blood circulation and conduction of nerve impulses, normalizing blood pressure can be successfully applied. With neuropsychiatric disorders, psychotropic drugs are used. The patient is injected with anti-inflammatory and anti-edematous drugs, drugs that help improve microcirculation, as well as antioxidants and antihypoxants. After the course of injections is completed, they switch to tablet vasoactive agents, nootropics.

In combination, treatment is prescribed to help inhibit the pathological process of hearing loss. If necessary, an external hearing aid or cochlear implant is fitted. In addition to common behind-the-ear hearing devices, virtually invisible in-the-ear and intracanalicular mini-apparatuses are often used, which are placed in close proximity to the eardrum. Binaural hearing aids, in which devices are placed in both the left and right ears, are most recommended.

Physiotherapy methods are widely used: acupuncture, laser acupuncture, oxygen therapy. Ultraphonophoresis, electrophoresis, magnetotherapy are prescribed only to those patients who do not have hypertension, glaucoma, cardiovascular diseases.

Medications such as these may be prescribed:

• Piracetam, Nootropil (nootropic drugs).
• Gammalon, Aminalon (agents based on gamma-aminobutyric acid).
• Antihypoxants, ATP.
• Trental, Nicotinic acid, Cavinton (drugs to optimize microcirculation).
• B-group vitamins.

However, the most important condition for treatment is the cessation of noise exposure that exceeds the maximum permissible values. The patient is advised to change occupation.

Prevention

The main measures for the prevention of occupational hearing loss are as follows:

• introduction of quality modern silent production technologies;
• effective noise reduction;
• full and competent provision of hearing organ personal protective equipment to at-risk workers;
• adherence to the principles of professional selection;
• timely and regular rehabilitation of representatives of vulnerable professions in medical and prophylactic institutions.

Early detection and correction of organ-functional disorders of the hearing organs, examination of the whole organism, application of etiological, symptomatic and pathogenetic therapy, implementation of measures to preserve health and maximize longevity of labor life are recommended.

In general, preventive measures can be primary and secondary. Primary include:

• organizing and controlling compliance with working conditions, ensuring soundproofing standards, introducing noise reduction mechanisms, and rehabilitating workers in potentially hazardous occupations;
• Improvement of production equipment, introduction of protective equipment (headphones, helmets, earplugs), use of various sound-isolating techniques, possible exclusion of excessively noisy episodes from the work process;
• informing employees about work standards and personal protective equipment, conducting regular preventive examinations, and psychological support.

Secondary prevention consists of a set of medical, social, sanitary, hygienic, psychological and other measures aimed at the earliest possible detection of occupational hearing loss, to prevent further progression and disability (loss of working capacity).

If a person works in an environment with excessive noise exposure, preventive measures are extremely important: one should not wait until the first signs of hearing impairment appear. It is necessary to think about possible consequences in advance and use all available protection against sound overload:

• use special noise-canceling headphones, earplugs;
• observe the work and rest regime;
• periodically switch noise modes, organize "minutes of silence".

It is important to report any violations of working conditions to your employer and, if necessary, to change jobs.

Forecast

Hearing impairment in working-age people leads to a loss of occupational fitness: people have to leave their jobs, re-train and learn a new specialty.

In complex and neglected cases, professional hearing loss can lead to a reduced quality of life and problems in self-care. Forced loss of work often causes depression and increases the risk of dementia. Most patients are distressed by their condition, their quality of communication deteriorates significantly, and they become isolated from others. Some of them develop stress-associated psychotic symptoms. The hearing impaired person becomes suspicious and may experience hallucinations.

Meanwhile, early diagnosis allows to start rehabilitation measures in time to install a cochlear implant or perform reconstructive surgery.

Occupational hearing loss can be diagnosed at both old and young ages. Refusal of treatment almost always leads to a worsening of the condition: the patient loses the ability to work, other unfavorable consequences develop.