Role Play 2

a) how we know that many years of exposure to loud noise causes hearing impairment?
Sound-induced hearing loss is irreversible and the main form of treatment is prevention. Commonly, damage to sensory cells of the inner ear builds up over time. The hearing loss goes unnoticed at first and increases until it reaches a certain degree where it becomes obvious to the affected person. In rare cases, exposure to very loud sounds can lead to immediate damage.

exposure to loud sounds at a young age can make the ear more vulnerable to ageing. Over the years, there are small unnoticeable effects on the inner ear that only become evident many years later when the affected person develops hearing loss. Exposure to certain chemicals, smoking or lack of oxygen supply to the body also increase sound-induced hearing loss.
Exposure to loud sounds can produce some initial damage to the inner ear, for instance by causing inflammation. This triggers processes that cause cells to destroy themselves and results in further damage through the loss of sensory and nervous cells.

How do loud sounds affect the inner ear?
Extremely loud sounds such as those produced by bomb blasts can cause small cracks in various parts of the ear which can be seen with a simple microscope. However, in most cases, the damage to the inner ear occurs at cellular level and is thus less visible.

Sensory cells in the inner ear (hair cells of the cochlea) convert sounds into signals that can be interpreted by the brain and losing these cells causes permanent hearing loss. Different hair cells are receptive to different sound frequencies. The wider the loss, the larger the number of sound frequencies that are affected. For each frequency, the greater the number of lost cells, the larger the hearing impairment. Because of the shape and the characteristics of the human outer and middle ear, excessive exposure to loud sounds makes individuals less sensitive to high-pitched sounds at frequencies of 4 to 6 kHz.

Losing one type of sensory cells completely (outer hair cells) results in a hearing impairment of 50 to 70 dB and also makes affected individuals less capable of focusing on a particular frequency and therefore less able to understand speech in noisy environments.

Recent advances made using more powerful microscopes show that losing or damaging hair cells is not the only factor that harms hearing. Loud sounds can also harm other types of cells, such as nerve cells, in the organ of the inner ear that converts sound into electrical impulses (cochlea). However, the chain of events that leads to cell damage and to the resulting hearing loss is not well understood at present.

Short exposures to steady loud sounds can damage the cochlea but this damage is usually reversible and the effect on hearing loss is temporary. Repeated exposures to very loud sounds can cause irreversible damage; in that case the hearing loss is permanent.

The likelihood that exposure to a particular sound will result in temporary or permanent hearing loss depends not only on loudness and exposure time but also on how quickly sound levels increase. The body has a reflex to contract certain muscles in order to protect the ear from excessively loud sounds. Sudden, very loud sounds such as explosions occur too quickly for the body to activate this reflex and are therefore a lot more harmful to hearing than steady sounds, in particular at high frequencies.

The inner ear of some people is more vulnerable to damage than that of others. Several factors – some of which are genetic – play a role, such as smoking, high blood pressure, fat levels, age, gender, as well as other anatomical characteristics.

Average noise levels in certain working environments can reach up to about 90-125 dB. People also expose themselves to loud sounds in their leisure activities. Outside the workplace, a high risk of hearing impairment arises for instance from attending rock concerts and discos, from practicing noisy sports such as shooting, and from exposure to military noise. Children could be exposed to noisy toys such as trumpets (92 to 125 dB SPL), whistles (107 to 129 dB SPL) and toy weapons (113 to over 135 dB SPL).

Listening to music played at high volumes can be as dangerous to hearing as industrial noise. This applies not only to rock concerts or nightclubs but also to personal music players (and mobile phones with music playing function) which can generate sounds across a broad frequency range at high volumes without distortion.

In our daily lives we are also exposed to environmental noise from traffic, construction, aircraft or various noises in the neighbourhood. These noises do not reach levels that can damage hearing but can be very irritating and cause other harmful effects.

Excessive exposure to loud sounds is a major cause of hearing disorders worldwide and is the main avoidable cause of permanent hearing loss.

Among workers, noise-induced hearing loss is the most common irreversible occupational disease. Worldwide, 16% of the disabling hearing loss in adults is caused by exposure to noise at work, although this proportion varies in different parts of the world from 7% to 21%.

Sound-induced hearing loss affects an estimated 10 to 15 million people in the USA. In the UK, about 350 000 people aged 35 to 64 years have serious hearing difficulties, including tinnitus, caused by exposure to noise at work. In France, a survey carried out in 2003 indicates that 7 % of employed workers were exposed to excessive sound levels above 85 dB(A) for at least 20 hours a week . Most exposed workers belonged to industry agriculture or the building sector.
People working with vibrating tools, such as jackhammers, can develop hearing loss. The effect is worse if exposure to vibration and to loud sounds occurs at the same time. It is unclear whether body vibration causes any damage.

Go to this website http://www.abelard.org/hear/hear.php#how-loud
to find out the effects of specific decibels on our hearing


b) What happens to the ear when it is damaged by noise?
Exposure to harmful sounds causes damage to the hair cells as well as the auditory, or hearing, nerve. Impulse sound can result in immediate hearing loss that may be permanent. This kind of hearing loss may be accompanied by tinnitus—a ringing, buzzing, or roaring in the ears or head—which may subside over time. Hearing loss and tinnitus may be experienced in one or both ears, and tinnitus may continue constantly or occasionally throughout a lifetime.

Exposure to impulse and continuous noise may cause only a temporary hearing loss. If a person regains hearing, the temporary hearing loss is called a temporary threshold shift. The temporary threshold shift largely disappears 16 to 48 hours after exposure to loud noise. You can prevent NIHL from both impulse and continuous noise by regularly using hearing protectors such as earplugs or earmuffs.

Scientists believe that, depending on the type of noise, the pure force of vibrations from the noise can cause hearing loss. Recent studies also show that exposure to harmful noise levels triggers the formation of molecules inside the ear that damage hair cells and result in NIHL. These destructive molecules play an important role in hearing loss in children and adults who listen to loud noise for too long.

Sound-induced hearing damage is not limited to deafness or an inability to hear certain sounds, but also includes difficulties understanding speech in noisy environments, ringing in the ears (tinnitus) and hypersensitivity to loud sounds.

The initial damage caused by loud sounds is often small and causes slight hearing problems that disappear some time after the sound exposure, so these often go unnoticed.

With repeated exposure to loud sounds, hearing disturbances increase. By the time they are noticed, the damage has become permanent and almost always incurable.

Excessive exposure to loud sounds can not only damage the organ of the inner ear that converts sound into electrical impulses (cochlea) but also the part that contributes to balance and spatial orientation (vestibule). Balance involves the eye and the ear but also the neck muscles that keep the head stable. Hearing damage can therefore be assessed indirectly by creating a sound and measuring how the neck muscles react to it.

Temporary or permanent high-pitched ringing in the ear (tinnitus) induced by loud sounds can sometimes be the only indication of hearing damage in the early stage, which may then be accompanied by hearing loss with continued exposure. After exposure to very loud or sudden loud sounds, tinnitus appears rapidly and is often temporary. In opposition, when it results from continuous long-term sound exposure, tinnitus often only appears after several years but remains permanent.

One of the most common forms of hearing impairment is hearing loss, which is the inability of the affected individual to hear sounds below certain thresholds. This can be measured with standard hearing tests. Certain people with normal hearing thresholds can nonetheless have problems understanding speech due to difficulties in processing sounds.

Hearing problems linked to the outer or middle ear can usually be treated, while problems in the inner ear or the auditory nerve going from the ear to the brain are usually permanent.

Hearing impairment refers to the complete or partial loss of the ability to hear from one of both ears and can be graded as mild, moderate, severe or profound. When the hearing threshold in the better ear is at or below 25 dB, this will pose very little or no hearing problems. At the other extreme, threshold values in the better ear at or above 81 dB result in the listener being unable to hear and understand even a shouted voice.

Hearing impairment that is caused by a problem in the outer or middle ear can usually be treated. When the impairment is due to problems in the inner ear or the auditory nerve going from the ear to the brain, the hearing loss is usually permanent. Common causes of this type of hearing problem are ageing, excessive exposure to loud sounds and some drugs.

Hearing is usually tested by presenting sounds of different frequencies to the listener and measuring the lowest volume of the sound that the listener can detect. The threshold of hearing is set at 0 dB HL and levels between 0 and 20 are considered to be normal.

Any sign of a shift in this threshold, even within the normal range, could be a sign of impairment so it is important to assess any such change, particularly for children.

Hearing impairment may also arise in people with normal threshold levels of hearing but who cannot process the sound signals properly and therefore find it very difficult to understand speech. Other people have trouble focusing on particular sound frequencies; they cannot tune in to sounds of interest and are distracted by background noise.

The ability to understand speech depends on how loudly a person speaks and on hearing loss, and can be described by mathematical models. A normal-hearing person can understand the words in a sentence if about 30% of the information is present. Listeners can fail to understand speech if the volume of the sound is below the threshold value they can hear, or if there is a background noise that masks the sound signal.

In everyday situations, listeners are exposed to combinations of many different sounds. People with hearing loss at high frequencies have difficulties understanding speech in noisy environments such as a party where there are many different conversations taking place or in large rooms with a lot of echoes such as a church hall. For instance, if a normal-hearing person can communicate at a party at a distance of about one meter, a high-frequency hearing loss of about 40 dB makes it impossible to do so; the listener has to come closer to the speaker and reduce the distance to half a meter.

People with a more significant hearing loss at high frequencies will find it impossible to understand speech in noisy environments unless they get extremely close to the speaker, which may be socially unacceptable. Hearing aids can only partly compensate such loss. Therefore, high-frequency hearing loss, whether aided or not, will cause poorer speech understanding in a noisy environment.


c) How noise-induced hearing loss differs from conductive hearing loss?
Refer to Huey Ting's. Lazy to retype... =.='
Basically noise-induced hearing loss comes under sensorineural.

Conductive Hearing Loss
Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the tiny bones, or ossicles, of the middle ear. Conductive hearing loss usually involves a reduction in sound level, or the ability to hear faint sounds. This type of hearing loss can often be medically or surgically corrected.

Sensorineural hearing loss occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear (retrocochlear) to the brain. Sensorineural hearing loss cannot be medically or surgically corrected. It is a permanent loss.

Sensorineural hearing loss not only involves a reduction in sound level, or ability to hear faint sounds, but also affects speech understanding, or ability to hear clearly.

Sensorineural hearing loss can be caused by diseases, birth injury, drugs that are toxic to the auditory system, and genetic syndromes. Sensorineural hearing loss may also occur as a result of noise exposure, viruses, head trauma, aging, and tumors.

What is noise-induced hearing loss?

The sound pathwayEvery day, we experience sound in our environment, such as the sounds from television and radio, household appliances, and traffic. Normally, we hear these sounds at safe levels that do not affect our hearing. However, when we are exposed to harmful noise—sounds that are too loud or loud sounds that last a long time—sensitive structures in our inner ear can be damaged, causing noise-induced hearing loss (NIHL). These sensitive structures, called hair cells, are small sensory cells that convert sound energy into electrical signals that travel to the brain. Once damaged, our hair cells cannot grow back

What sounds cause NIHL?
NIHL can be caused by a one-time exposure to an intense “impulse” sound, such as an explosion, or by continuous exposure to loud sounds over an extended period of time, such as noise generated in a woodworking shop.