Understanding Industrial Hearing Loss - Part 1

Sunday, July 6, 2003 | 0

The following article is part 1 of a 3 part series on occupational hearing loss by Dr. Stuart Gherini, a qualified medical examiner and expert in the field of otology. Part 1 provides a brief history on the condition and a comprehensive analysis on causes, specific types and costs associated with occupational hearing loss. Part 2 will include discussions on evaluating occupational hearing loss and long-term implications. Part 3 will provide an in-depth discussion on basic audiometric examinations and an overview on how to read an audiogram.

Mini-Monograph: Occupational Hearing Loss, Part I
Stuart Gherini, M.D.
Otology
A Brief Historical Perspective on Occupational Hearing Loss

Noisy jobs and hearing loss have long been known to go hand in hand. There are references in medical literature dating back to the sixteenth century describing hearing loss among blacksmiths, metal workers, and cannoneers (1). "Boiler maker's ears" was a term commonly used to describe the poor hearing of those working in boiler factories in the late 1800s and early 1900s. The existence of noise-induced hearing loss (NIHL) was widely known in occupational medical circles by about 1950. Hearing conservation programs began to appear in the military and industry in the 1950s and 1960s. Since the passage of the Occupational Safety and Health Act (OSHA) in 1971, more attention has been given to the problem of NIHL. In spite of OSHA 1971, it was not uncommon for some workers in the 1980s to be rebuked or suspended for using hearing protection.

Scope of the Problem

According to Sataloff, hearing loss due to occupational noise exposure is our most prevalent industrial disease (2). There are at least four million Americans with a NIHL severe enough for them to report hearing difficulties (3). There are some estimates that there are as many as 10 million U.S. production workers who now work - or have worked in - industrial locations with potentially hazardous noise levels.

The potential cost of treating each of these 10 million workers is staggering. If each of these 10 million workers were to develop a hearing loss severe enough to warrant the use of a hearing aid and was fitted with a single $1,000 hearing aid, the cost for a one-time fitting would be $10 billion.

Consider that excessive noise typically harms both ears and that most people with hearing loss do better with binaural (both ears) hearing aids, and this one-time cost is now $20 billion. If both ears were fitted with the newer programmable digital hearing aids (which can improve one's ability to follow speech in the presence of background noise and which retail for approximately $2,000 apiece) this one-time cost escalates to $40 billion.

Consider also that hearing aids have a useful life span of about three to five years. If all 10 million potentially affected workers were to be kept supplied with binaural state-of-the-art hearing aids, then approximately $40 billion could be spent every three to five years on hearing aids alone to remedy a completely preventable problem. In contrast to a $2,000 state-of-the-art programmable digital hearing aid, disposable foam rubber ear plugs (sufficient to protect most workers from most hazardous levels of noise) can he purchased in bulk for about a nickel a pair, quality ear muffs cost approximately $20, and custom-fit silicone ear plugs can be made for approximately $60 a pair.

That NIHL does not cost industry $10-40 billion every three to five years is partially due to hearing loss being a silent, painless disease, with an insidious onset. Often, a worker with an occupational NIHL is not aware that he has a hearing loss, or, if he is aware of the hearing loss, may not be aware that the hearing loss is at least partially due to years of on-the-job noise exposure. If the NIHL were to occur suddenly - as a fractured leg in a fall at work does - employees would complain bitterly about the work related hearing loss.

Types of Hearing Loss

Hearing loss is divided into three types: conductive, sensorineural, and mixed.

Conductive Hearing Loss

A problem which makes it difficult for sound to be conducted from the outer ear to the inner ear results in a "conductive" hearing loss. We have all experienced a conductive hearing loss. Placing one's fingers in the external auditory canals makes it difficult for sound waves to reach the eardrum and results in a temporary conductive hearing loss.

Common causes of conductive hearing loss include: excess cerumen (wax plugging the external auditory canal); scarring of the eardrum or around the ossicles from infection (thus restricting the motion of the drum and the ossicles); a hole in the drum reducing the eardrum's ability to capture sound; fluid in the middle ear space from a cold or allergy reducing the mobility of the eardrum and ossicles; and otosclerosis, a hereditary disorder in which a growth of bone occurs around the base of the stapes, restricting its motion. Head trauma can result in a conductive hearing loss by causing a dislocation of one or more of the ossicles, in essence, breaking the ossicular chain.

Sensorineural Hearing Loss

A problem in the inner ear or along the auditory nerve leading from the inner ear to the brain results in a sensorincoral or "nerve-type" of impairment. By far the most common anatomical finding in a sensorineural hearing loss is a loss of hair cells in the inner ear. Common causes of sensorineural hearing loss include: the natural aging process (the hair cells die off with age); noise exposure, blast injury, hereditary factors, metabolic factors (diabetes for example); prior or current infections, head trauma, and ototoxic medications (medications toxic to the inner ear); including some antibiotics and some forms of chemotherapy. A much less common cause of a sensorineural hearing loss is the presence of tumors along the auditory nerve between the inner ear and the brain.

Mixed Hearing Loss

When a person has both a conductive hearing loss and a sensorineural hearing loss, he has a "mixed" hearing loss. The most common cause of a mixed hearing loss is chronic infections in the middle ear, so called "chronic otitis media." This results in scarring of the eardrum, erosion of the ossicles, and damage to the inner ear. Other causes of a mixed hearing loss include hereditary disorders and severe head trauma. In medical-legal hearing loss evaluations, it is the physician's task to determine the type and severity of hearing loss, its cause or causes, and the best form of treatment.

References

(1) Sataloff, RT. Occupational hearing loss. New York: Mark Decker, 1987.
(2) ibid
(3) Dobie, R.A. Medical-legal evaluation of hearing loss. New York: Van Nostrand Reinhold, 1993.

Dr. Gherini is represented by MEDLink in the Sacramento, CA. area. Appointments can be made through MEDLink at: www.camedlink.com.

(c) 2001 MEDLink -- Reprinted by Permission. Additional articles may be read at www.camedlink.com . MEDLink affiliated QME physicians may be reached by e-mail at: camedlink@camedlink.com .